kDa Form Research Articles

Impairment of Neuronal Glutamate Uptake and Modulation of the Glutamate Transporter GLT-1 Induced by Retinal Ischemia

Excitotoxicity has been implicated in the retinal neuronal loss in several ocular pathologies including glaucoma. Dysfunction of Excitatory Amino Acid Transporters is often a key component of the cascade leading to excitotoxic cell death. In the retina, glutamate transport is mainly operated by the glial glutamate transporter GLAST and the neuronal transporter GLT-1. In this study we evaluated the expression of GLAST and GLT-1 in a rat model of acute glaucoma based on the transient increase of intraocular pressure (IOP) and characterized by high glutamate levels during the reperfusion that follows the ischemic event associated with raised IOP. No changes were reported in GLAST expression while, at neuronal level, a reduction of glutamate uptake and of transporter reversal-mediated glutamate release was observed in isolated retinal synaptosomes. This was accompanied by modulation of GLT-1 expression leading to the reduction of the canonical 65 kDa form and upregulation of a GLT-1-related 38 kDa protein. These results support a role for neuronal transporters in glutamate accumulation observed in the retina following an ischemic event and suggest the presence of a GLT-1 neuronal new alternative splice variant, induced in response to the detrimental stimulus.

Identification of Serpin Determinants of Specificity and Selectivity for Furin Inhibition through Studies of α1PDX (α1-Protease Inhibitor Portland)-Serpin B8 and Furin Active-site Loop Chimeras

α1-Protease inhibitor Portland (α1PDX) is an engineered serpin family inhibitor of the proprotein convertase (PC), furin, that exhibits high specificity but limited selectivity for inhibiting furin over other PC family proteases. Here, we characterize serpin B8, a natural inhibitor of furin, together with α1PDX-serpin B8 and furin-PC chimeras to identify determinants of serpin specificity and selectivity for furin inhibition. Replacing reactive center loop (RCL) sequences of α1PDX with those of serpin B8 demonstrated that both the P4-P1 RXXR recognition sequence as well as the P1'-P5' sequence are critical determinants of serpin specificity for furin. Alignments of PC catalytic domains revealed four variable active-site loops whose role in furin reactivity with serpin B8 was tested by engineering furin-PC loop chimeras. The furin(298-300) loop but not the other loops differentially affected furin reactivity with serpin B8 and α1PDX in a manner that depended on the serpin RCL-primed sequence. Modeling of the serpin B8-furin Michaelis complex identified serpin exosites in strand 3C close to the 298-300 loop whose substitution in α1PDX differentially affected furin reactivity depending on the furin loop and serpin RCL-primed sequences. These studies demonstrate that RCL-primed residues, strand 3C exosites, and the furin(298-300) loop are critical determinants of serpin reactivity with furin, which may be exploited in the design of specific and selective α1PDX inhibitors of PCs.

HtrA1 in human urothelial bladder cancer: A secreted protein and a potential novel biomarker

Our aim was to analyze the expression of the serine protease HtrA1 in human bladder tissue and urine in order to point out its possible association with the presence of urothelial bladder cancer. Bladder tissue and urine specimens from cancer patients with different tumor grades and stages (n = 68) and from individuals with cystitis (n = 16) were collected along with biopsy specimens and urine from healthy individuals (n = 68). For the first time, we demonstrated by immunohistochemistry that HtrA1 protein is produced by bladder urothelium in both physiological and inflammatory conditions, whereas it is not detectable in urothelial cancer cells regardless of tumor grade and stage. A different HtrA1 expression between normal-looking and neoplastic bladder tissue, despite similar HtrA1 mRNA levels, was also found by western blotting, which disclosed the presence of two forms of HtrA1, a native form of ∼50 kDa and an autocatalytic form of ∼38 kDa. Our investigations documented the presence of the two forms of HtrA1 also in urine. The ∼38 kDa form was significantly down-regulated in neoplastic tissue, whereas significantly higher amounts of both HtrA1 forms were found in urine from cancer patients compared with both healthy subjects and patients with cystitis. Our findings suggest that HtrA1 is a downexpressed molecule since an early stage of bladder urothelial carcinoma development and that urinary HtrA1 protein may be considered, if successfully validated, as an early and highly sensitive and specific biomarker for this neoplasia (the sensitivity and specificity of HtrA1 are 92.65% and 95.59%, respectively).

Interleukin-1β stimulates early myogenesis of mouse C2C12 myoblasts: the impact on myogenic regulatory factors, extracellular matrix components, IGF binding proteins and protein kinases

The purpose of the study was to examine the mechanisms important for early myogenesis in mouse C2C12 myogenic cells exposed to interleukin-1beta. Cyclin A and cyclin B1 were increased by interleukin-1beta (1 ng/ml), but the level of cyclin D1 and total DNA content was unaffected. Fusion index and the rate of protein synthesis was increased in the presence of IL-1beta, but these effects were limited to 3-day-treatment. IL-1beta increased the level of MyoD, myogenin and MHC on the 3rd day of differentiation, without altering the content of the active form of myostatin, as well as it augmented the level of fibronectin, integrin beta1 and full length 100 kDa form of ADAM12. IL-1beta caused a decrease in IGFBP-4 and IGFBP-6 levels and a marked increase in IGFBP-5. The phosphorylation of PKB and ERK1/2 and the cellular content of p38 were elevated by IL-1beta. We conclude that the myogenic effect of IL-1beta was limited to the onset of myoblast fusion and was associated with: i) increase in the level of myogenic transcription factors i.e. MyoD and myogenin expression, ii) modification of extracellular matrix assembly and signaling, manifested by an increase in fibronectin, integrin-beta1 and ADAM12 content, iii) drop in IGFBP-4 and IGFBP-6, and an increase in IGFBP-5, that could alter the local IGF-1 bioavailability, and iv) increase in phosphorylation of PKB and ERK1/2, and the expression of p38 kinase, leading to activation of intracellular pathways essential for myogenic differentiation.

A 43-kDa TDP-43 Species Is Present in Aggregates Associated with Frontotemporal Lobar Degeneration

The transactive response DNA-binding protein (TDP-43) is a major component of the abnormal intracellular inclusions that occur in two common neurodegenerative diseases of humans: (1) a subtype of frontotemporal lobar degeneration and (2) amyotrophic lateral sclerosis. Genetics, experiments in cultured cells and animals, and analogy with other neurodegenerative diseases indicate that the process of TDP-43 aggregation is fundamental to the pathogenesis of these 2 diseases, but the process by which this aggregation occurs is not understood. Biochemical fractionation has revealed truncated, phosphorylated and ubiquitinated forms of TDP-43 in a detergent-insoluble fraction from diseased CNS tissue, while these forms are absent from controls. However, a large amount of the normally predominant 43-kDa form of TDP-43 is present in the detergent-insoluble fraction even from control brains, so it has not been possible to determine if this form of TDP-43 is part of pathological aggregates in frontotemporal lobe degeneration. We used semi-denaturing detergent-agarose gel electrophoresis to isolate high molecular weight aggregates containing TDP-43 that are present in the cerebral cortex of individuals with frontotemporal lobar degeneration but not that of controls. These aggregates include the same covalently modified forms of TDP-43 seen in detergent-insoluble extracts. In addition, aggregates include a 43-kDa TDP-43 species. This aggregated 43-kDa form of TDP-43 is absent or present only at low levels in controls. The presence of 43-kDa TDP-43 in aggregates raises the possibility that covalent modification is not a primary step in the pathogenic aggregation of TDP-43 associated with frontotemporal lobar degeneration and amyotrophic lateral sclerosis.

Combination of prenatal immune challenge and restraint stress affects prepulse inhibition and dopaminergic/GABAergic markers

Gestational immune challenge with the viral-like antigen poly I:C is a well-established neurodevelopmental model of schizophrenia. However, exposure to inflammation during early life may sensitize the developing brain to secondary insults and enhance the central nervous system vulnerability. To gain a better understanding of the pathophysiology of schizophrenia, we thus developed a two-hit animal model based on prenatal poly I:C immune challenge followed by restraint stress in juvenile mice. C57BL/6 gestational mice were intraperitoneally injected with poly I:C or saline at gestational day 12. Pups were then submitted or not, to restraint stress for 2h, for three consecutive days, from postnatal days 33 to 35. Prepulse inhibition (PPI) of acoustic startle response is commonly used to assess sensorimotor gating, a neural process severely disrupted in patients with schizophrenia. Our results revealed that the combination of prenatal immune challenge with poly I:C followed by a restraint stress period was able to induce a PPI disruption in 36-day-old pups, as opposed to each insult applied separately. PPI deficits were accompanied by dopaminergic and GABAergic abnormalities in the prefrontal cortex and striatum. Indeed, measurements of cortical and striatal dopamine D2 receptor (D2R) mRNA and protein levels revealed that the combination of gestational exposure to poly I:C and postnatal restraint stress induced an increase in D2R protein and mRNA levels. Likewise, the combination of both insults reduced the mRNA and protein expression levels of the 67 kDa form of glutamic acid decarboxylase (GAD67), in those two brain regions. To our knowledge, this two-hit animal model is the first in vivo model reporting PPI deficits at pubertal age. This two-hit animal model may also help in studying innovative therapies dedicated to the treatment of schizophrenia, especially in its early phase.

Abstract 490: Clinical improvement of symptomatic advancing chronic lymphocytic leukemia following mifepristone therapy despite normal serum levels of the immunomodulatory protein the progesterone induced blocking factor (PIBF).

Abstract Recently a sensitive ELISA assay been created to detect serum levels of the immunomodulatory protein, the PIBF. One of the 34 kDa forms of PIBF increases markedly after exposure to progesterone (P) and inhibits natural killer (NK) cytolytic activity by stabilizing perforin granules and causes of shift from thymic helper (TH)1 to TH2 dominance thus diminishing the activity of the cellular immune system. The 34 kDa form is secreted by gamma/delta T cells and is considered a vital step in preventing immune destruction of the fetal semi-allograft. Evaluation of mRNA for PIBF and PIBF protein found that 29 of 29 human leukemia cell lines over-expressed mRNA for PIBF but only 3 of the lines expressed the PIBF protein. Adding P to the culture up-regulated PIBF protein expression whereas adding the P receptor antagonist mifepristone caused down-regulation of PIBF expression. Mifepristone treatment has been demonstrated to show significant palliative effects on a wide variety of murine and human cancers many of which are not known to be P receptor positive. The hypothesized mechanism is that these tumors either secrete PIBF or direct secretion by gamma/delta T cells in the tumor microenvironment and thus inhibit NK cell cytolytic activity. The inhibition is abrogated by inhibiting P receptors and thus a local form of P secretion by the tumor is hypothesized. The objective of this study was to determine if mifepristone will only help inhibit cancer growth in those individuals who have an increased PIBF level present in their serum. An 81 year old woman with chronic lymphocytic leukemia (CLL) started more rapid advancement and became very symptomatic. She refused chemotherapy when she almost had a lethal complication to oral chlorambucil. She requested mifepristone. Her serum PIBF level of 34.9 ng/mL was in the same range as controls without cancer. However within a month of taking 200mg daily of mifepristone orally she showed a dramatic improvement in her CLL with her white blood cell count dropping from 28,000 to 8,000. Her platelet count increased from 40,000 to 240,000 and 2 lung nodules thought to represent possible primary lung cancer (but possibly nodules from her CLL) completely disappeared on repeat CT scan. Also her energy markedly improved and her persistent cough stopped. The serum PIBF did not decrease with mifepristone therapy - 48.3 ng/mL one month later. These data demonstrated that failure to see a marked increase in serum PIBF in a patient with cancer does not predict failure to respond to mifepristone. Though mifepristone has ameliorated murine leukemia in AKR mice this is the first case report of this drug improving human leukemia. The 34-36 kDa PIBF found in cytoplasm of cancer cells may either not be secreted in the serum or may be immunologically different from serum PIBF found after P exposure. Citation Format: Jerome H. Check, Ann DiAntonio, Diane Check, Alex Jaffe, Rachael Cohen, Mojirayo Sarumi, Maya Srivastava. Clinical improvement of symptomatic advancing chronic lymphocytic leukemia following mifepristone therapy despite normal serum levels of the immunomodulatory protein the progesterone induced blocking factor (PIBF). [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 490. doi:10.1158/1538-7445.AM2013-490

FNDC5/Irisin Is Not Only a Myokine but Also an Adipokine

Exercise provides clear beneficial effects for the prevention of numerous diseases. However, many of the molecular events responsible for the curative and protective role of exercise remain elusive. The recent discovery of FNDC5/irisin protein that is liberated by muscle tissue in response to exercise might be an important finding with regard to this unsolved mechanism. The most striking aspect of this myokine is its alleged capacity to drive brown-fat development of white fat and thermogenesis. However, the nature and secretion form of this new protein is controversial. The present study reveals that rat skeletal muscle secretes a 25 kDa form of FNDC5, while the 12 kDa/irisin theoretical peptide was not detected. More importantly, this study is the first to reveal that white adipose tissue (WAT) also secretes FNDC5; hence, it may also behave as an adipokine. Our data using rat adipose tissue explants secretomes proves that visceral adipose tissue (VAT), and especially subcutaneous adipose tissue (SAT), express and secrete FNDC5. We also show that short-term periods of endurance exercise training induced FNDC5 secretion by SAT and VAT. Moreover, we observed that WAT significantly reduced FNDC5 secretion in fasting animals. Interestingly, WAT of obese animals over-secreted this hormone, which might suggest a type of resistance. Because 72% of circulating FNDC5/irisin was previously attributed to muscle secretion, our findings suggest a muscle-adipose tissue crosstalk through a regulatory feedback mechanism.

Purification and biochemical analysis of catalytically active human cdc25C dual specificity phosphatase

We describe a reliable and efficient method for the purification of catalytically active and mutant inactive full-length forms of the human dual specificity phosphatase cdc25C from bacteria. The protocol involves isolating insoluble cdc25C protein in inclusion bodies, solubilization in guanidine HCL, and renaturation through rapid dilution into low salt buffer. After binding renatured proteins to an ion exchange resin, cdc25C elutes in two peaks at 350 and 450 mM NaCl. Analysis by gel exclusion chromatography and enzymatic assays reveals the highest phosphatase activity is associated with the 350 mM NaCl with little or no activity present in the 450 mM peak. Furthermore, active cdc25C has a native molecular mass of 220 kDa consistent with a potential tetrameric complex of the 55-kDa cdc25C protein. Assaying phosphatase activity against artificial substrates pNPP and 3-OMFP reveals a 220 kDa form of the phosphatase is active in a non-phosphorylated state. The protein effectively activates cdk1/cyclin B prokinase complexes in vitro in the absence of cdk1 kinase activity in an orthovanadate sensitive manner but is inactivated by A-kinase phosphorylation. In vitro phosphorylation of purified cdc25C by cdk1/cyclin B1, cdk2/cyclin A2 and cdk2/cyclin E shows that distinct TP/SP mitotic phosphorylation sites on cdc25C are differentially phosphorylated by these 3 cdk/cyclin complexes associated with different levels of cdc25C activation. Finally, we show that endogenous native cdc25C from human cells is present in high molecular weight complexes with other proteins and resolves mostly above 200-kDa. These data show that untagged cdc25C can be purified with a simple protocol as an active dual specificity phosphatase with a native molecular mass consistent with a homo-tetrameric configuration.

Biogenesis and Proteolytic Processing of Lysosomal DNase II

Deoxyribonuclease II (DNase II) is a key enzyme in the phagocytic digestion of DNA from apoptotic nuclei. To understand the molecular properties of DNase II, particularly the processing, we prepared a polyclonal antibody against carboxyl-terminal sequences of mouse DNase II. In the present study, partial purification of DNase II using Con A Sepharose enabled the detection of endogenous DNase II by Western blotting. It was interesting that two forms of endogenous DNase II were detected – a 30 kDa form and a 23 kDa form. Neither of those forms carried the expected molecular weight of 45 kDa. Subcellular fractionation showed that the 23 kDa and 30 kDa proteins were localized in lysosomes. The processing of DNase II in vivo was also greatly altered in the liver of mice lacking cathepsin L. DNase II that was extracellularly secreted from cells overexpressing DNase II was detected as a pro-form, which was activated under acidic conditions. These results indicate that DNase II is processed and activated in lysosomes, while cathepsin L is involved in the processing of the enzyme.

Secretion of SerpinB2 from endothelial cells activated with inflammatory stimuli

Due to the lack of an N-terminal signal peptide, SerpinB2 (plasminogen activator inhibitor type 2) accumulates in cells and only a small percentage of it is secreted. The extracellular concentration of SerpinB2 significantly increases during inflammation. In the present study we investigated the mechanism with which SerpinB2 can be secreted from endothelial cells activated with LPS. We evaluated the intracellular distribution of SerpinB2 by double immunogold labeling followed by a high resolution electron microscopy analysis. We found that SerpinB2 gathers in the vesicular structures and in the endothelial cell periphery. These vesicles stained positive for the trans-Golgi network marker TGN46, which is consistent with their formation by the endoplasmatic reticulum (ER) and Golgi-dependent pathways. SerpinB2 was delivered to the plasma membrane, apparently together with TGN46 in the same vesicles, which after fusion with the membranes released cargo. Secretion of SerpinB2 was partially inhibited by brefeldin A. The secreted SerpinB2 was predominantly in its nonglycosylated 43kDa form as evaluated by Western immunoblotting. Our data suggest that increased expression of SerpinB2 by an inflammatory stimulus is sufficient to generate structures that resemble secretory vesicles. These vesicles may represent the mechanism by which high local concentrations of SerpinB2 are released at inflammation sites from endothelial cells.

Apoptotic cells selectively uptake minor glycoforms of vitronectin from serum

Apoptosis profoundly alters the carbohydrate layer coating the membrane of eukaryotic cells. Previously we showed that apoptotic cells became reactive with the α2,6-sialyl-specific lectin from Sambucus nigra agglutinin (SNA), regardless of their histological origin and the nature of the apoptotic stimulus. Here we reveal the basis of the phenomenon by showing that in apoptotic cancer cell lines SNA reactivity was mainly associated with a 67 kDa glycoprotein which we identified by MALDI-TOF/TOF and immunoblot analysis as bovine vitronectin (bVN). bVN was neither present in non-apoptotic cells, nor in cells induced to apoptosis in serum-free medium, indicating that its uptake from the cell culture serum occurred only during apoptosis. The bVN molecules associated with apoptotic cancer cell lines represented minor isoforms, lacking the carboxyterminal sequence and paradoxically containing a few α2,6-linked sialic acid residues. Despite their poor α2,6-sialylation, these bVN molecules were sufficient to turn apoptotic cells to SNA reactivity, which is a late apoptotic event occurring in cells positive to both annexin-V and propidium iodide. Unlike in cancer cell lines, the major bVN form taken up by apoptotic neutrophils and mononuclear cells was a 80 kDa form. In apoptotic SW948 cells we also detected the α2,6-sialylated forms of the stress-70 mitochondrial precursor (mortalin) and of tubulin-β2C. These data indicate that the acquisition of vitronectin isoforms from the environment is a general, although cell specific phenomenon, potentially playing an important role in post-apoptotic events and that the α2,6-sialylation of intracellular proteins is a new kind of posttranslational modification associated with apoptosis.

Molecular Expression and Characterization of Erythroid-Specific 5-Aminolevulinate Synthase Gain-of-Function Mutations Causing X-Linked Protoporphyria

X-linked protoporphyria (XLP) (MIM 300752) is a recently recognized erythropoietic porphyria due to gain-of-function mutations in the erythroid-specific aminolevulinate synthase gene (ALAS2). Previously, two exon 11 small deletions, c.1699_1670ΔAT (ΔAT) and c.1706_1709ΔAGTG (ΔAGTG), that prematurely truncated or elongated the ALAS2 polypeptide, were reported to increase enzymatic activity 20- to 40-fold, causing the erythroid accumulation of protoporphyrins, cutaneous photosensitivity and liver disease. The mutant ΔAT and ΔAGTG ALAS2 enzymes, two novel mutations, c.1734ΔG (ΔG) and c.1642C>T (p.Q548X), and an engineered deletion c.1670-1671TC>GA p.F557X were expressed, and their purified enzymes were characterized. Wild-type and ΔAGTG enzymes exhibited similar amounts of 54- and 52-kDa polypeptides on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), whereas the ΔAT and p.F557X had only 52-kDa polypeptides. Compared to the purified wild-type enzyme, ΔAT, ΔAGTG and Q548X enzymes had increased specific activities that were only 1.8-, 3.1- and 1.6-fold, respectively. Interestingly, binding studies demonstrated that the increased activity Q548X enzyme did not bind to succinyl-CoA synthetase. The elongated ΔG enzyme had wild-type specific activity, kinetics and thermostability; twice the wild-type purification yield (56 versus 25%); and was primarily a 54-kDa form, suggesting greater stability in vivo. On the basis of studies of mutant enzymes, the maximal gain-of function region spanned 57 amino acids between 533 and 580. Thus, these ALAS2 gain-of-function mutations increased the specific activity (ΔAT, ΔAGTG and p.Q548X) or stability (ΔG) of the enzyme, thereby leading to the increased erythroid protoporphyrin accumulation causing XLP.

Processing of the glycosomal matrix-protein import receptor PEX5 of Trypanosoma brucei

Glycolysis in kinetoplastid protists such as Trypanosoma brucei is compartmentalized in peroxisome-like organelles called glycosomes. Glycosomal matrix-protein import involves a cytosolic receptor, PEX5, which recognizes the peroxisomal-targeting signal type 1 (PTS1) present at the C-terminus of the majority of matrix proteins. PEX5 appears generally susceptible to in vitro proteolytic processing. On western blots of T. brucei, two PEX5 forms are detected with apparent Mr of 100kDa and 72kDa. 5′-RACE-PCR showed that TbPEX5 is encoded by a unique transcript that can be translated into a protein of maximally 72kDa. However, recombinant PEX5 migrates aberrantly in SDS–PAGE with an apparent Mr of 100kDa, similarly as observed for the native peroxin. In vitro protease susceptibility analysis of native and 35S-labelled PEX5 showed truncation of the 100kDa form at the N-terminal side by unknown parasite proteases, giving rise to the 72kDa form which remains functional for PTS1 binding. The relevance of these observations is discussed.

Phenethyl Isothiocyanate (PEITC) Regulates Autophagy in Chronic Lymphocytic Leukemia.

AbstractAbstract 2906Chronic Lymphocytic leukemia (CLL) is currently incurable using conventional therapies. CLL cells can evade killing by various therapeutic strategies. However the precise mechanisms are currently unknown. Autophagy is regulated by a complex system of proteins, and is used by both normal and malignant cells as a protective mechanism against cellular stress induced by starvation, hypoxia, reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress. In malignant cells autophagy was shown to promote tumorigenesis and/or resistance to chemotherapy. Therefore we hypothesized that autophagy may play a role in CLL biology.Autophagy can also promote cell death when stress signals are elevated above a particular threshold for a prolonged period of time. In this study we investigated the basal expression levels of autophagy specific genes and the effect of autophagy specific inhibitors (Bafilomycin, 3-methyladenine and hydroxychloroquine) and inducers (Phenethyl isothiocyanate) on CLL survival. Phenethyl isothiocyanate (PEITC) is about to enter clinical trials for CLL (NCT00968461).We have investigated induction of components of the autophagic pathway following treatment of CLL cells in vitro with a range of chemical inhibitors. Immunoblotting was carried out to investigate components of the autophagy pathway using phosphorylation state-specific and pan-reactive antibodies. Bafilomycin (BAF), 3-methyladenine (3-MA) and hydroxychloroquine (HCQ) toxicity towards CLL samples were evaluated by Annexin V/PI staining, MTT assay and immunoblotting for cleavage of the caspase 3 substrate poly(ADP ribose) polymerase (PARP) from its 116KDa to its 85KDa form. PEITC was used at concentrations between 2.5 and 25μM to investigate its effect on signaling. Autophagy was quantitated by immunoblotting of LC3-I and LC3-II. Lipidation of LC3 from LC3-I to LC3-II is a surrogate marker of autophagy and is essential for autophagasome formation. Immunoblotting was also performed for ATG3, ATG5 and ATG7, key components of the autophagy pathway. Monodansylcadaverine (MDC) was used with immunofluorescence and FACS analysis to investigate increases in autophagasome formation. Transmission electron microscopy (TEM) was used to confirm double membrane bound autophagosomes. Co-immunoprecipitation was used to evaluate if Beclin-1 was sequestered by Bcl-2 preventing autophagy. Its release from Bcl-2 enables Beclin-1 to interact with other autophagy specific proteins and initiates autophagasome formation.LC3-I was lipidated to LC3-II (p=0.019) and ATG3 (p=0.021) was upregulated to a greater extent in CLL samples compared with normal B-cell controls at basal levels. This suggested that autophagy was active to a greater extent in CLL samples compared with normal individuals. In addition Beclin was dissociated from Bcl-2 in CLL samples indicating that autophagy was active. Autophagy appears to be a pro-survival mechanism in untreated CLL cells as inhibiting basal levels of autophagy with autophagy inhibitors BAF (50–200nM), 3-MA (5–10mM) and hydroxychlorquine (5–10μM) resulted in CLL apoptosis as shown by MTT, Annexin V/PI analysis and PARP cleavage.Interestingly augmenting autophagy was also capable of inducing apoptosis in CLL samples. Treatment with PEITC caused an increase in punctate staining using MDC which is suggestive of autophagosome formation. We went on to determine that PEITC further induced LC3-II lipidation using immunoblotting and showed a substantial increase in overall LC3 protein expression. PEITC also induced the expression of ATG3, a key protein in the autophagy pathway. We then evaluated autophagosome formation using TEM (Figure 1). Our data showed greater numbers of autophagosomes in the PEITC treated samples compared to the untreated controls.Therefore autophagy in CLL sits on a knife-edge, such that perturbations that either increase pro- death or decrease pro-survival autophagy signals can result in CLL cell death, depending on the duration and intensity of the signal. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Clusterin Expression and Localization Are Affected by Rituximab and Doxorubicin Treatment in Non-Hodgkin Lymphoma Cells and B Lymphocytes

AbstractAbstract 1318 Introduction.Diffuse large B-cell lymphoma (DLBCL) is the most frequently aggressive Non-Hodgkin’s lymphoma (NHL). DLBCL first line therapy consists of R-CHOP regimen, which combines classical chemotherapeutical drugs and corticosteroids with Rituximab. Rituximab is a chimeric anti-CD20 monoclonal antibody which targets the CD20 surface antigen expressed on both normal and malignant B cells. Rituximab triggers antibody- and complement-dependent cytotoxicity, growth inhibition and apoptosis. Rituximab inhibits the expression of the anti-apoptotic proteins Bcl-2/Bcl-XL, down-modulating different survival pathways. Clusterin (CLU) is an ubiquitary protein involved in many physiological and pathological processes such as apoptosis and cancer. CLU has different transcriptional isoforms, which share exons from 2 to 9 but have a unique exon 1 and at least two protein forms: The cytoplasmatic precursor of about 60 kDa is secreted outside the cell after post-traslational modifications (sCLU), whereas a truncated protein (50–55 kDa) is produced only in particular conditions and localizes in the nucleus (nCLU). CLU expression is disregulated in almost all cancers and its role has been deeply investigated in solid tumors. Only limited information is currently available about its function in lymphomas. Methods.Toledo, a DLBCL-derived cell line and normal B lymphocytes were chosen as experimental models. B lymphocytes were purified and immuno-magnetically sorted from peripheral blood of 4 healthy volunteers. Toledo and B lymphocytes were treated with 10 or 100 μg/ml Rituximab or doxorubicin (from 0.05 to 1 μM) for 48 hours. Phenotype analysis was performed by flow cytometry; cell viability was assessed by Trypan blue exclusion; apoptosis was evaluated by Annexin V/propidium iodide. CLU expression and localization were evaluated by real time PCR, Western Blot (WB) and immunocytochemistry (ICC). Primers for the real time PCR were design in order to distinguish the unique exon 1 of each CLU transcriptional isoforms or exons common to all variants (CLU3-4). Results.Rituximab treatment doesn’t significantly inhibit Toledo proliferation and does not induce apoptosis despite the fact that these cells are CD20+. This suggests that Toledo are resistant to Rituximab. As expected, doxorubicin causes a marked growth inhibition by necrosis and apoptosis. Toledo cells have a very low basal level of the 60 kDa CLU protein form. Both Rituximab and doxorubicin up-regulate the 60 kDa form with 1 μM doxorubicin causing the most dramatic increase. The analysis of transcriptional isoforms by real-time PCR shows that CLU mRNA is almost undetectable in Toledo. CLU transcriptional variant 2 (CLU2) and regions common to all CLU transcripts (CLU3-4) are significantly up-regulated only after 1 μM doxorubicin but not after Rituximab. Fluorescence microscopy clearly shows a cytoplasmic localization of CLU under normal growth conditions. Interestingly, the treatment with both Rituximab and doxorubicin causes the appearance of a nuclear staining. This fact might be consistent with the onset of a process of cell death. 10 and 100 μg/ml Rituximab inhibits B lymphocytes cell survival in a dose-dependent manner (39.7% and 44% respectively after 48 hours). Interestingly, B lymphocytes clearly express high basal levels of the 60 kDa CLU and produce an additional form of about 55 kDa only after Rituximab but not after doxorubicin. Furthermore Rituximab-treated B lymphocytes display a Bcl-2 protein decrease while Toledo cells show high expression of Bcl-2 that doesn’t seem to change in response to Rituximab. Conclusions.Toledo are resistant to Rituximab up to 100 μg/ml and express very low levels of CLU under normal growth conditions. 60 kDa CLU is partially up-regulated and Bcl-2 expression is not significantly affected by Rituximab treatment. Doxorubicin strongly up-regulates the 60 kDa CLU isoform. At the transcriptional level CLU2 shows the same expression profile of the 60 kDa protein form. On the contrary, Rituximab changes the CLU profile of responsive B lymphocytes in that leads to the appearance of a 55 kDa form that is not visible after doxorubicin treatment. Rituximab also causes a reduction in the expression of the antiapoptotic protein Bcl-2. The biological role of CLU during the response of peripheral B lymphocytes to Rituximab treatment is yet to be determined and is currently being investigated. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Effects of endoplasmic reticulum stressors on maturation and signaling of hemizygous and heterozygous wild-type and mutant forms of KIT

Gain of function mutations of KIT are frequent in some human tumors, and are sensible to tyrosine kinase inhibitors. In most tumors, oncogenic mutations are heterozygous, however most in vitro data of KIT activation have been obtained with hemizygous mutation. This study aimed to investigate the maturation and activation of wild-type (WT) and mutant (M) forms of KIT in hemizygous and heterozygous conditions. WT and two types of exon 11 deletions M forms of human KIT were expressed in NIH3T3 cell lines. Membrane expression of KIT was quantified by flow cytometry. Quantification of glycosylated forms of KIT and phosphorylated forms of AKT and ERK were performed by western blot. Simultaneous activation of WT KIT and treatment with endoplasmic reticulum (ER) inhibitors, tunicamycin or brefeldin A induced a complete inhibition of membrane expression of the 145 kDa form of KIT. By contrast activation or ER inhibitors alone, only partly inhibited this form. ER inhibitors also inhibited KIT activation-dependent phosphorylation of AKT and ERK1/2. Brefeldin A induced a complete down regulation of the 145 kDa form in hemizygous M, and induced an intra-cellular accumulation of the 125 kDa form in WT but not in hemizygous M. Heterozygous cells had glycosylation and response to ER inhibitors patterns more similar to WT than to hemizygous M. Phosphorylated AKT was reduced in hemizygous cells in comparison to WT KIT cells and heterozygous cells, and in the presence of brefeldin A in all cell lines. Effects of ER inhibitors are significantly different in hemizygous and heterozygous mutants. Differences in intra-cellular trafficking of KIT forms result in differences in downstream signaling pathways, and activation of PI3K/AKT pathway appears to be tied to the presence of the mature 145 kDa form of KIT at the membrane surface.

Expression of different forms of transglutaminases by immature cells of Helianthus tuberosus sprout apices

Immature cells of etiolated apices of sprouts growing from Helianthus tuberosus (H. t.) tubers showed Ca(2+)-dependent transglutaminase (TG, EC 2.3.2.13) activity on fibronectin (more efficiently) and dimethylcasein as substrates. Three main TG bands of about 85, 75 and 58 kDa were isolated from the 100,000×g apices supernatant through a DEAE-cellulose column at increasing NaCl concentrations and immuno-identified by anti-TG K and anti-rat prostate gland TG antibodies. These three fractions had catalytic activity as catalyzed polyamine conjugation to N-benzyloxycarbonyl-L-γ-glutaminyl-L-leucine (Z-L-Gln-L-Leu) and the corresponding glutamyl-derivatives were identified. The amino acid composition of these TG proteins was compared with those of several sequenced TGs of different origin. The composition of the two larger bands presented great similarities with annotated TGs; in particular, the 75 kDa form was very similar to mammalian inactive EPB42. The 58 kDa form shared a low similarity with other TGs, including a maize sequence of similar molecular mass, which, however, did not present the catalytic triad in the position of all annotated TGs. A 3D model of the H. t. TGs was built adopting TG2 as template. These novel plant TGs are hypothesized to be constitutive and discussed in relation to their possible roles in immature cells. These data suggest that in plants, multiple TG forms are active in the same organ and that plant and animal enzymes probably are very close not only for their catalytic activity but also structurally.

An oocyte-specific astacin family protease, alveolin, is released from cortical granules to trigger egg envelope hardening during fertilization in medaka (Oryzias latipes)

It has long been hypothesized that in fishes the contents of cortical granules are involved in the hardening of egg envelope following fertilization. We previously purified the egg envelope hardening initiation factor from the exudates released from activated medaka (Oryzias latipes) eggs and tentatively termed this protein alveolin. Alveolin is a member of the astacin metalloprotease family and was proposed to be a protease which hydrolyzes ZPB at one restricted position to allow starting cross-linking with ZPC. Here, we investigated the complete pathway from biosynthesis and accumulation to secretion of alveolin. A single alveolin transcript was detected only in ovarian preparations, confirming the specific expression of alveolin in the ovary. In situ hybridization indicated that the alveolin mRNA is already expressed in the very early previtellogenic oocytes. However, immunocytochemical studies revealed that the appearance of alveolin protein was delayed until the beginning of the vitellogenic stage. The cortical granules isolated from unfertilized eggs contained a high molecular weight form of glycosylated alveolin with a 50kDa relative molecular mass. Hypotonic treatment burst isolated granules in vitro and transformed alveolin to a 21.5kDa form, which is the same size as that of natural alveolin released from eggs upon fertilization. This transformation was inhibited in the presence of leupeptin and 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF), suggesting that a serine protease is involved in alveolin activation upon fertilization. Furthermore, the phylogenetic relationship of alveolin with other vertebrate astacin family members was analyzed. The result shows that alveolin and its teleostean homologs make a new group which is separate from either the hatching enzyme, meprin and BMP1/tolloid groups.

The Neuroendocrine Protein 7B2 Is Intrinsically Disordered

The small neuroendocrine protein 7B2 has been shown to be required for the productive maturation of proprotein convertase 2 (proPC2) to an active enzyme form; this action is accomplished via its ability to block aggregation of proPC2 into nonactivatable forms. Recent data show that 7B2 can also act as a postfolding chaperone to block the aggregation of a number of other proteins, for example, α-synuclein. To gain insight into the mechanism of action of 7B2 in blocking protein aggregation, we performed structural studies of this protein using gel filtration chromatography, intrinsic tryptophan fluorescence, 1-anilino-8-naphthalenesulfonate (ANS) binding, circular dichroism (CD), and nuclear magnetic resonance (NMR) spectroscopy. Gel filtration studies indicated that 7B2 exists as an extended monomer, eluting at a molecular mass higher than that expected for a globular protein of similar size. However, chemical cross-linking showed that 7B2 exhibits concentration-dependent oligomerization. CD experiments showed that both full-length 27 kDa 7B2 and the C-terminally truncated 21 kDa form lack appreciable secondary structure, although the longer protein exhibited more structural content than the latter, as demonstrated by intrinsic and ANS fluorescence studies. NMR spectra confirmed the lack of structure in native 7B2, but a disorder-to-order transition was observed upon incubation with one of its client proteins, α-synuclein. We conclude that 7B2 is a natively disordered protein whose function as an antiaggregant chaperone is likely facilitated by its lack of appreciable secondary structure and tendency to form oligomers.