Mutant cDNA Research Articles

A Novel TWIST2-ID2 Axis That Modulates The Growth and Imatinib Sensitivity Of CML CD34+ Cells

TWIST is a basic helix-loop-helix transcription factor that specifies Drosophila mesoderm development. In mammals there are 2 members, TWIST1 and TWIST2. TWIST2 is a regulator of osteoblasts and muscle development and plays a critical role in the epithelial-mesenchymal transition process, as well as in cancer initiation and metastasis. Twist2-deficient mice develop a myeloproliferative disease. These findings led us to query a potential role of TWIST2 in normal and leukemic (CML) human hematopoietic cells.RT-PCR and immuno-fluorescence analysis of CD34+ bone marrow (BM) cells obtained from healthy donors demonstrated their expression of TWIST2 transcripts and protein. Lentiviral vector-mediated knockdown of TWIST2 with 2 independent shRNA sequences enhanced the erythroid and granulopoietic colony-forming activity of transduced normal BM cells ∼2-fold compared with control transduced cells (n=3, p<0.05). Interestingly, ChIP studies showed that TWIST2 can bind directly to the DNA promoter for ID2 in CD34-enriched BM cells and knockdown of TWIST2 reduced ID2 expression by 50%.In lin-CD34+ cells from 14 chronic myeloid leukemia (CML) patients, we found both TWIST2 and ID2 transcripts to be 5 and 6 fold lower than those from 6 healthy BM donors (p<0.05), with similar findings for TWIST2 and ID2 protein in the same cells. BCR-ABL1-transduced Baf/3 cells also showed a reduction in Twist2 expression. Conversely, TWIST2 expression became elevated when K562 cells were treated with Imatinib mesylate (IM). We then generated a lentiviral vector encoding TWIST2 which proved capable of inhibiting the growth of K562 and MEG-01 cells as well as CFC production from CML CD34+ cells (n=11, p<0.05). Overexpression of TWIST2 in MEG-01 cells also reduced their tumorigenic ability in subcutaneously injected nude mice (0/8 for TWIST2 group, 7/8 for control group). In addition, increased TWIST2 sensitized the IM response of K562 cells and IM-resistant CD34+ cells from CML patients (2 in chronic phase and 2 in blast crisis). Correspondingly, knockdown of TWIST2 in K562 cells enhanced their cloning efficiency by 15% and made them IM-resistant.To obtain further insight into these biological effects of TWIST2, we generated several TWIST2 mutant cDNAs, including ones with a N-terminal truncation (ΔN), a C-terminal truncation (ΔC), a F86P dimerization mutant and a b- DNA binding mutant. Analysis of the effects of these mutants when overexpressed in CML cells and cell lines showed TWIST2 dimer formation was critical for the effects obtained with wild-type TWIST2, whereas the DNA binding domain could modulate these effects but was not essential, and the N-terminal and C-terminal domains were dispensable. We also found that overexpression of TWIST2 enhanced ID2 expression in CML CD34+ cells (n=3), as well as K562 and MEG-01 cells, and ChIP analyses confirmed the binding of TWIST2 to ID2 promoter DNA from K562 and MEG-01 cells. Using ID2 promoter-driven luciferase reporter and a mutant derivative (with only the E-box sequence altered), we found that TWIST2 could activate the wild-type promoter but not the mutated one in both K562 and MEG-01 cells. Finally, we co-transduced CML cells from 3 patients with TWIST2 and shRNA against ID2 and found that this reversed the suppressed production of CFC obtained with TWIST2 alone. Similarly in K562 cells this treatment partially restored their growth rate and IM resistance.Taken together, we report a novel TWIST2-ID2 regulatory axis in normal hematopoietic progenitor cells, which can also modulate the growth and IM response of CML progenitor cells. These findings provide a baseline for the future development of more effective therapy of CML. Disclosures:No relevant conflicts of interest to declare.

Identification Of BCL11A Structure-Function Domains For Fetal Hemoglobin Silencing

Reactivation of fetal hemoglobin (HbF, α2γ2) expression in adults ameliorates the clinical symptoms in patients with the major β-hemoglobin disorders, sickle cell disease (SCD) and β-thalassemias. The zinc-finger protein BCL11A is a major modulator of hemoglobin switching and HbF silencing. BCL11A was initially identified by genome-wide association studies (GWAS) as a new HbF-associated gene. Down-regulation of BCL11A in primary human erythroid cells induces HbF expression. Knockout of BCL11A in mice impairs HbF silencing in adult erythroid cells. Most importantly, inactivation of BCL11A alone in humanized SCD mice corrects the hematologic and pathologic defects through high-level HbF induction. These studies established BCL11A as a genetically and functionally validated transcriptional regulator of HbF switching and silencing.In human and mouse erythroid cells, BCL11A is expressed as several isoforms, yet their individual roles in globin gene expression remain unexplored. Furthermore, the functional domains within the BCL11A protein responsible for its activity in HbF repression are largely unknown. To further understand the mechanistic roles of BCL11A in globin expression, we established a functional assay based on a BCL11A-null erythroid cell line generated by transcription activator-like effector nucleases (TALENs)-mediated deletion of an obligate erythroid-specific enhancer of BCL11A in murine erythroleukemia (MEL) cells. In the BCL11A-null cells, the expression of β-like embryonic globin genes is markedly induced (>200-fold), consistent with the role of BCL11A in repression of murine embryonic globin genes. To examine the activity of known BCL11A isoforms in HbF silencing, we expressed various BCL11A isoforms in these engineered BCL11A-null cells. Ectopic expression of full-length BCL11A-XL isoform, but not the alternatively spliced, C-terminally truncated L isoform, restored the full repression of β-like embryonic globins in BCL11A-null cells. Since XL and L differ only by 91 amino acids containing three tandem C2H2-type zinc finger motifs, these results indicate that the C-terminal zinc finger motifs are indispensable for BCL11A-mediated transcriptional repression.To systemically define BCL11A functional domains for globin gene repression, we next generated a panel of BCL11A mutant cDNAs, including deletion of the N-terminal NuRD-interacting motif and one or more C2H2-type zinc finger domains. Analysis of various BCL11A mutants in the functional rescue assay identified several functional domains, including the N-terminal NuRD-interacting motif and five out of the six C2H2 zinc fingers, that are required for BCL11A-mediated repression. These findings provide the foundation for further molecular analysis of BCL11A functional domains in globin gene repression. BCL11A is known to interact with several transcriptional co-repressor complexes including Mi-2β/NuRD/HDAC1/HDAC2, LSD1/CoREST and SWI/SNF complexes, occupy discrete regions within the human β-globin cluster, and promote long-range chromosomal interactions. Our results suggest that BCL11A functional domains may be involved in protein-protein interactions, protein homo-/heterodimerization, and/or chromatin/DNA association that are required for its activity in HbF silencing.In summary, we demonstrate that several functional domains on BCL11A protein are indispensable for its transcriptional activity in HbF silencing. Further focused studies of BCL11A structure-function domains in HbF silencing not only will advance our understanding of the molecular mechanisms by which BCL11A controls the clinically important fetal-to-adult globin switch, but may identify novel cellular targets for therapeutic HbF induction in β-hemoglobinopathies. Disclosures:No relevant conflicts of interest to declare.

Disruption of N-linked glycosylation promotes proteasomal degradation of the human ATP-binding cassette transporter ABCA3

The lipid transport protein, ABCA3, expressed in alveolar type 2 (AT2) cells, is critical for surfactant homeostasis. The first luminal loop of ABCA3 contains three putative N-linked glycosylation sites at residues 53, 124, and 140. A common cotranslational modification, N-linked glycosylation, is critical for the proper expression of glycoproteins by enhancing folding, trafficking, and stability through augmentation of the endoplasmic reticulum (ER) folding cycle. To understand its role in ABCA3 biosynthesis, we utilized EGFP-tagged fusion constructs with either wild-type or mutant ABCA3 cDNAs that contained glutamine for asparagine substitutions at the putative glycosylation motifs. In A549 cells, inhibition of glycosylation by tunicamycin increased the electrophoretic mobility (Mr) and reduced the expression level of wild-type ABCA3 in a dose-dependent manner. Fluorescence imaging of transiently transfected A549 or primary human AT2 cells showed that although single motif mutants exhibited a vesicular distribution pattern similar to wild-type ABCA3, mutation of N124 and N140 residues resulted in a shift toward an ER-predominant distribution. By immunoblotting, the N53 mutation exhibited no effect on either the Mr or ABCA3 expression level. In contrast, substitutions at N124 or N140, as well a N124/N140 double mutation, resulted in increased electrophoretic mobility indicative of a glycosylation deficiency accompanied by reduced overall expression levels. Diminished steady-state levels of glycan-deficient ABCA3 isoforms were rescued by treatment with the proteasome inhibitor MG132. These results suggest that cotranslational N-linked glycosylation at N124 and N140 is critical for ABCA3 stability, and its disruption results in protein destabilization and proteasomal degradation.

Mutations in MAP3K1 tilt the balance from SOX9/FGF9 to WNT/β-catenin signaling

In-frame missense and splicing mutations (resulting in a 2 amino acid insertion or a 34 amino acid deletion) dispersed through the MAP3K1 gene tilt the balance from the male to female sex-determining pathway, resulting in 46,XY disorder of sex development. These MAP3K1 mutations mediate this balance by enhancing WNT/β-catenin/FOXL2 expression and β-catenin activity and by reducing SOX9/FGF9/FGFR2/SRY expression. These effects are mediated at multiple levels involving MAP3K1 interaction with protein co-factors and phosphorylation of downstream targets. In transformed B-lymphoblastoid cell lines and NT2/D1 cells transfected with wild-type or mutant MAP3K1 cDNAs under control of the constitutive CMV promoter, these mutations increased binding of RHOA, MAP3K4, FRAT1 and AXIN1 and increased phosphorylation of p38 and ERK1/2. Overexpressing RHOA or reducing expression of MAP3K4 in NT2/D1 cells produced phenocopies of the MAP3K1 mutations. Using siRNA knockdown of RHOA or overexpressing MAP3K4 in NT2/D1 cells produced anti-phenocopies. Interestingly, the effects of the MAP3K1 mutations were rescued by co-transfection with wild-type MAP3K4. Although MAP3K1 is not usually required for testis determination, mutations in this gene can disrupt normal development through the gains of function demonstrated in this study.

N-Acetyl-L-Cysteine Prevents Stress-Induced Desmin Aggregation in Cellular Models of Desminopathy

Mutations within the human desmin gene are responsible for a subcategory of myofibrillar myopathies called desminopathies. However, a single inherited mutation can produce different phenotypes within a family, suggesting that environmental factors influence disease states. Although several mouse models have been used to investigate organ-specific desminopathies, a more general mechanistic perspective is required to advance our knowledge toward patient treatment. To improve our understanding of disease pathology, we have developed cellular models to observe desmin behaviour in early stages of disease pathology, e.g., upon formation of cytoplasmic desmin aggregates, within an isogenic background. We cloned the wildtype and three mutant desmin cDNAs using a Tet-On Advanced® expression system in C2C12 cells. Mutations were selected based on positioning within desmin and capacity to form aggregates in transient experiments, as follows: DesS46Y (head domain; low aggregation), DesD399Y (central rod domain; high aggregation), and DesS460I (tail domain; moderate aggregation). Introduction of these proteins into a C2C12 background permitted us to compare between desmin variants as well as to determine the role of external stress on aggregation. Three different types of stress, likely encountered during muscle activity, were introduced to the cell models—thermal (heat shock), redox-associated (H2O2 and cadmium chloride), and mechanical (stretching) stresses—after which aggregation was measured. Cells containing variant DesD399Y were more sensitive to stress, leading to marked cytoplasmic perinuclear aggregations. We then evaluated the capacity of biochemical compounds to prevent this aggregation, applying dexamethasone (an inducer of heat shock proteins), fisetin or N-acetyl-L-cysteine (antioxidants) before stress induction. Interestingly, N-acetyl-L-cysteine pre-treatment prevented DesD399Y aggregation during most stress. N-acetyl-L-cysteine has recently been described as a promising antioxidant in myopathies linked to selenoprotein N or ryanodin receptor defects. Our findings indicate that this drug warrants further study in animal models to speed its potential development as a therapy for DesD399Y-linked desminopathies.

Variations of the UNC13D Gene in Patients with Autoimmune Lymphoproliferative Syndrome

Autoimmune lymphoproliferative syndrome (ALPS) is caused by genetic defects decreasing Fas function and is characterized by lymphadenopathy/splenomegaly and expansion of CD4/CD8 double-negative T cells. This latter expansion is absent in the ALPS variant named Dianzani Autoimmune/lymphoproliferative Disease (DALD). In addition to the causative mutations, the genetic background influences ALPS and DALD development. We previously suggested a disease-modifying role for the perforin gene involved in familial hemophagocytic lymphohistiocytosis (FHL). The UNC13D gene codes for Munc13-4, which is involved in perforin secretion and FHL development, and thus, another candidate for a disease-modifying role in ALPS and DALD. In this work, we sequenced UNC13D in 21 ALPS and 20 DALD patients and compared these results with sequences obtained from 61 healthy subjects and 38 multiple sclerosis (MS) patients. We detected four rare missense variations in three heterozygous ALPS patients carrying p.Cys112Ser, p.Val781Ile, and a haplotype comprising both p.Ile848Leu and p.Ala995Pro. Transfection of the mutant cDNAs into HMC-1 cells showed that they decreased granule exocytosis, compared to the wild-type construct. An additional rare missense variation, p.Pro271Ser, was detected in a healthy subject, but this variation did not decrease Munc13-4 function. These data suggest that rare loss-of-function variations of UND13D are risk factors for ALPS development.

THU0099 Adenovirus-Mediated IGFBP-3 Gene Transfer Induces Apoptosis and Suppresses Inflammation and Bone Destruction in Rheumatoid Arthritis

BackgroundInsulin-like growth factor binding protein-3 (IGFBP-3) is known to interfere NF-κB signaling pathway and effectively promotes apoptosis in tumor cells by a variety of mechanisms.ObjectivesDue to the pivotal roles of...

Acidosis-mediated regulation of the NHE1 isoform of the Na+/H+exchanger in renal cells

The mammalian Na⁺/H⁺ exchanger isoform 1 (NHE1) is a ubiquitous plasma membrane protein that regulates intracellular pH by removing a proton in exchange for extracellular sodium. Renal tissues are subject to metabolic and respiratory acidosis, and acidosis has been shown to acutely activate NHE1 activity in other cell types. We examined if NHE1 is activated by acute acidosis in HEK293 and Madin-Darby canine kidney (MDCK) cells. Acute sustained intracellular acidosis (SIA) activated NHE1 in both cell types. We expressed wild-type and mutant NHE1 cDNAs in MDCK cells. All the cDNAs had a L163F/G174S mutation, which conferred a 100-fold resistance to EMD87580, an NHE1-specific inhibitor. We assayed exogenous NHE1 activity while inhibiting endogenous activity with EMD87580 and while inhibiting the NHE3 isoform of the Na⁺/H⁺ exchanger using the isoform-specific inhibitor S3226. We examined the activation and phosphorylation of the wild-type and mutant NHE1 proteins in response to SIA. In MDCK cells we demonstrated that the amino acids Ser⁷⁷¹, Ser⁷⁷⁶, Thr⁷⁷⁹, and Ser⁷⁸⁵ are important for NHE1 phosphorylation and activation after acute SIA. SIA activated ERK-dependent pathways in MDCK cells, and this was blocked by treatment with the MEK inhibitor U0126. Treatment with U0126 also blocked activation of NHE1 by SIA. These results suggest that acute acidosis activates NHE1 in mammalian kidney cells and that in MDCK cells this activation occurs through an ERK-dependent pathway affecting phosphorylation of a distinct set of amino acids in the cytosolic regulatory tail of NHE1.

Mutations in BICD2, which Encodes a Golgin and Important Motor Adaptor, Cause Congenital Autosomal-Dominant Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a heterogeneous group of neuromuscular disorders caused by degeneration of lower motor neurons. Although functional loss of SMN1 is associated with autosomal-recessive childhood SMA, the genetic cause for most families affected by dominantly inherited SMA is unknown. Here, we identified pathogenic variants in bicaudal D homolog 2 (Drosophila) (BICD2) in three families afflicted with autosomal-dominant SMA. Affected individuals displayed congenital slowly progressive muscle weakness mainly of the lower limbs and congenital contractures. In a large Dutch family, linkage analysis identified a 9q22.3 locus in which exome sequencing uncovered c.320C>T (p.Ser107Leu) in BICD2. Sequencing of 23 additional families affected by dominant SMA led to the identification of pathogenic variants in one family from Canada (c.2108C>T [p.Thr703Met]) and one from the Netherlands (c.563A>C [p.Asn188Thr]). BICD2 is a golgin and motor-adaptor protein involved in Golgi dynamics and vesicular and mRNA transport. Transient transfection of HeLa cells with all three mutant BICD2 cDNAs caused massive Golgi fragmentation. This observation was even more prominent in primary fibroblasts from an individual harboring c.2108C>T (p.Thr703Met) (affecting the C-terminal coiled-coil domain) and slightly less evident in individuals with c.563A>C (p.Asn188Thr) (affecting the N-terminal coiled-coil domain). Furthermore, BICD2 levels were reduced in affected individuals and trapped within the fragmented Golgi. Previous studies have shown that Drosophila mutant BicD causes reduced larvae locomotion by impaired clathrin-mediated synaptic endocytosis in neuromuscular junctions. These data emphasize the relevance of BICD2 in synaptic-vesicle recycling and support the conclusion that BICD2 mutations cause congenital slowly progressive dominant SMA.

Auxiliary KChIP4a Suppresses A-type K+ Current through Endoplasmic Reticulum (ER) Retention and Promoting Closed-state Inactivation of Kv4 Channels

In the brain and heart, auxiliary Kv channel-interacting proteins (KChIPs) co-assemble with pore-forming Kv4 α-subunits to form a native K(+) channel complex and regulate the expression and gating properties of Kv4 currents. Among the KChIP1-4 members, KChIP4a exhibits a unique N terminus that is known to suppress Kv4 function, but the underlying mechanism of Kv4 inhibition remains unknown. Using a combination of confocal imaging, surface biotinylation, and electrophysiological recordings, we identified a novel endoplasmic reticulum (ER) retention motif, consisting of six hydrophobic and aliphatic residues, 12-17 (LIVIVL), within the KChIP4a N-terminal KID, that functions to reduce surface expression of Kv4-KChIP complexes. This ER retention capacity is transferable and depends on its flanking location. In addition, adjacent to the ER retention motif, the residues 19-21 (VKL motif) directly promote closed-state inactivation of Kv4.3, thus leading to an inhibition of channel current. Taken together, our findings demonstrate that KChIP4a suppresses A-type Kv4 current via ER retention and enhancement of Kv4 closed-state inactivation.

Abstract 543: A loss of function Cbl-c mutation in a murine breast cancer model.

Abstract Receptor Tyrosine Kinase (RTK) signaling is essential for normal biological processes and inappropriate RTK activity can result in malignant transformation. Cbl proteins are a family of RING finger ubiquitin ligases that negatively regulate a variety of RTKs, including EGFR, MET, RET and components of the TCR pathway and disruption of this negative regulation can lead to tumor initiation and progression. Recent studies have identified a growing number of Cbl mutations associated with human myeloid neoplasias and epithelial tumors. Cbl-c is the most recently identified human Cbl protein and is expressed exclusively in epithelial cells. Recently, a novel Cbl-c cDNA has been isolated from a ductal carcinoma which developed in a C3(1)SV40Tag mouse, a murine model of breast cancer driven by Large T antigen. This mutant cDNA encodes a Cbl-c protein which lacks the catalytic domain of Cbl-c, thereby resembling known Cbl family mutations associated with myeoloid neoplasias. Genomic analysis of both parental and transgenic lines shows no evidence of germline mutation indicating that this mutation is likely somatic and may contribute to malignant transformation in this animal model. In overexpression studies, this mutant Cbl-c protein fails to mediate ubiquitination and degradation of activated EGFR and acts as a dominant negative protein, preventing ubiquitination of the EGFR by wild type Cbl proteins. The mutant Cbl-c protein also enhances transformation of NIH 3T3 cells by SV40 Large T antigen and through subsequent analysis of transforming capacity and signal pathway regulation, we are assessing interacting partners of Cbl-c and the potential role of this mutation in tumorigenesis. This mutant Cbl-c protein is the first functional evidence for the involvement of Cbl-c in transformation. Citation Format: Stephen C. Kales, Philip E. Ryan, Marion Nau, Jeffrey E. Green, Stanley Lipkowitz. A loss of function Cbl-c mutation in a murine breast cancer model. [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 543. doi:10.1158/1538-7445.AM2013-543

Hypomorphic Mutations in PGAP2, Encoding a GPI-Anchor-Remodeling Protein, Cause Autosomal-Recessive Intellectual Disability

PGAP2 encodes a protein involved in remodeling the glycosylphosphatidylinositol (GPI) anchor in the Golgi apparatus. After synthesis in the endoplasmic reticulum (ER), GPI anchors are transferred to the proteins and are remodeled while transported through the Golgi to the cell membrane. Germline mutations in six genes (PIGA, PIGL, PIGM, PIGV, PIGN, and PIGO) in the ER-located part of the GPI-anchor-biosynthesis pathway have been reported, and all are associated with phenotypes extending from malformation and lethality to severe intellectual disability, epilepsy, minor dysmorphisms, and elevated alkaline phosphatase (ALP). We performed autozygosity mapping and ultra-deep sequencing followed by stringent filtering and identified two homozygous PGAP2 alterations, p.Tyr99Cys and p.Arg177Pro, in seven offspring with nonspecific autosomal-recessive intellectual disability from two consanguineous families. Rescue experiments with the altered proteins in PGAP2-deficient Chinese hamster ovary cell lines showed less expression of cell-surface GPI-anchored proteins DAF and CD59 than of the wild-type protein, substantiating the pathogenicity of the identified alterations. Furthermore, we observed a full rescue when we used strong promoters before the mutant cDNAs, suggesting a hypomorphic effect of the mutations. We report on alterations in the Golgi-located part of the GPI-anchor-biosynthesis pathway and extend the phenotypic spectrum of the GPI-anchor deficiencies to isolated intellectual disability with elevated ALP. GPI-anchor deficiencies can be interpreted within the concept of a disease family, and we propose that the severity of the phenotype is dependent on the location of the altered protein in the biosynthesis chain.

Ahsg-fetuin blocks the metabolic arm of insulin action through its interaction with the 95-kD β-subunit of the insulin receptor

We previously have shown that Ahsg, a liver glycoprotein, inhibits insulin receptor (InsR) tyrosine kinase (TK) activity and the ERK1/2 mitogenic signaling arm of insulin signaling. Here we show that Ahsg blocks insulin-stimulated GLUT4 translocation and Akt activation in intact cells (mouse myoblasts). Furthermore, Ahsg inhibits InsR autophosphorylation of highly-purified insulin holoreceptors in a cell-free, ATP-dependent system, with an IC50 within the range of single-chain Ahsg concentrations in human serum. Binding of 125I-insulin to living cells overexpressing the InsR shows a dissociation constant (KD) of 250pM, unaltered in the presence of 300 nM Ahsg. A mutant InsR cDNA encoding the signal peptide, the β-subunit and the furin processing site, but deleting the α-subunit, was stably expressed in HEK293 cells. Treatment with peroxovanadate, but not insulin, dramatically increased the 95 kD β-subunit tyrosine phosphoryation. The level of tyrosine phosphorylation of the 95-kD β-subunit can be driven down sharply by treatment of living HEK293 transfectant cells with physiological doses of Ahsg. Treatment of myogenic cells with Ahsg blunts insulin-stimulated InsR autophosphorylation and AKT phosphorylation. Taken together, we show that Ahsg antagonizes the metabolic functions initiated by InsR activation without interference in insulin binding. The experiments suggest a direct interaction of Ahsg with the InsR ectodomain β-subunit in a mode that does not significantly alter the high-affinity binding of insulin to the holoreceptor's two complementing α-subunits.

Assessment of Mitochondrial Functions and Cell Viability in Renal Cells Overexpressing Protein Kinase C Isozymes

The protein kinase C (PKC) family of isozymes is involved in numerous physiological and pathological processes. Our recent data demonstrate that PKC regulates mitochondrial function and cellular energy status. Numerous reports demonstrated that the activation of PKC-a and PKC-ε improves mitochondrial function in the ischemic heart and mediates cardioprotection. In contrast, we have demonstrated that PKC-α and PKC-ε are involved in nephrotoxicant-induced mitochondrial dysfunction and cell death in kidney cells. Therefore, the goal of this study was to develop an in vitro model of renal cells maintaining active mitochondrial functions in which PKC isozymes could be selectively activated or inhibited to determine their role in regulation of oxidative phosphorylation and cell survival. Primary cultures of renal proximal tubular cells (RPTC) were cultured in improved conditions resulting in mitochondrial respiration and activity of mitochondrial enzymes similar to those in RPTC in vivo. Because traditional transfection techniques (Lipofectamine, electroporation) are inefficient in primary cultures and have adverse effects on mitochondrial function, PKC-ε mutant cDNAs were delivered to RPTC through adenoviral vectors. This approach results in transfection of over 90% cultured RPTC. Here, we present methods for assessing the role of PKC-ε in: 1. regulation of mitochondrial morphology and functions associated with ATP synthesis, and 2. survival of RPTC in primary culture. PKC-ε is activated by overexpressing the constitutively active PKC-ε mutant. PKC-ε is inhibited by overexpressing the inactive mutant of PKC-ε. Mitochondrial function is assessed by examining respiration, integrity of the respiratory chain, activities of respiratory complexes and F0F1-ATPase, ATP production rate, and ATP content. Respiration is assessed in digitonin-permeabilized RPTC as state 3 (maximum respiration in the presence of excess substrates and ADP) and uncoupled respirations. Integrity of the respiratory chain is assessed by measuring activities of all four complexes of the respiratory chain in isolated mitochondria. Capacity of oxidative phosphorylation is evaluated by measuring the mitochondrial membrane potential, ATP production rate, and activity of F0F1-ATPase. Energy status of RPTC is assessed by determining the intracellular ATP content. Mitochondrial morphology in live cells is visualized using MitoTracker Red 580, a fluorescent dye that specifically accumulates in mitochondria, and live monolayers are examined under a fluorescent microscope. RPTC viability is assessed using annexin V/propidium iodide staining followed by flow cytometry to determine apoptosis and oncosis. These methods allow for a selective activation/inhibition of individual PKC isozymes to assess their role in cellular functions in a variety of physiological and pathological conditions that can be reproduced in in vitro.

Clk/STY (cdc2-Like Kinase 1) and Akt Regulate Alternative Splicing and Adipogenesis in 3T3-L1 Pre-Adipocytes

The development of adipocytes from their progenitor cells requires the action of growth factors signaling to transcription factors to induce the expression of adipogenic proteins leading to the accumulation of lipid droplets, induction of glucose transport, and secretion of adipokines signaling metabolic events throughout the body. Murine 3T3-L1 pre-adipocytes sequentially express all the proteins necessary to become mature adipocytes throughout an 8–10 day process initiated by a cocktail of hormones. We examined the role of Clk/STY or Clk1, a cdc2-like kinase, in adipogenesis since it is known to be regulated by Akt, a pivotal kinase in development. Inhibition of Clk1 by a specific inhibitor, TG003, blocked alternative splicing of PKCβII and expression of PPARγ1 and PPARγ2. SiRNA depletion of Clk1 resulted in early expression of PKCβII and sustained PKCβI expression. Since Clk1 is a preferred Akt substrate, required for phosphorylation of splicing factors, mutation of Clk1 Akt phosphorylation sites was undertaken. Akt sites on Clk1 are in the serine/arginine-rich domain and not the kinase domain. Mutation of single and multiple sites resulted in dysregulation of PKCβII, PKCβI, and PPARγ1&2 expression. Additionally, adipogenesis was blocked as assessed by Oil Red O staining, adiponectin, and Glut1 and 4 expression. Immunofluorescence microscopy revealed that Clk1 triple mutant cDNA, transfected into pre-adipocytes, resulted in excluding SRp40 (SFSR6) from co-localizing to the nucleus with PFS, a perispeckle specific protein. This study demonstrates the role of Akt and Clk1 kinases in the early differentiation of 3T3-L1 cells to adipocytes.

Conopeptide ρ-TIA Defines a New Allosteric Site on the Extracellular Surface of the α1B-Adrenoceptor

The G protein-coupled receptor (GPCR) superfamily is an important drug target that includes over 1000 membrane receptors that functionally couple extracellular stimuli to intracellular effectors. Despite the potential of extracellular surface (ECS) residues in GPCRs to interact with subtype-specific allosteric modulators, few ECS pharmacophores for class A receptors have been identified. Using the turkey β(1)-adrenergic receptor crystal structure, we modeled the α(1B)-adrenoceptor (α(1B)-AR) to help identify the allosteric site for ρ-conopeptide TIA, an inverse agonist at this receptor. Combining mutational radioligand binding and inositol 1-phosphate signaling studies, together with molecular docking simulations using a refined NMR structure of ρ-TIA, we identified 14 residues on the ECS of the α(1B)-AR that influenced ρ-TIA binding. Double mutant cycle analysis and docking confirmed that ρ-TIA binding was dominated by a salt bridge and cation-π between Arg-4-ρ-TIA and Asp-327 and Phe-330, respectively, and a T-stacking-π interaction between Trp-3-ρ-TIA and Phe-330. Water-bridging hydrogen bonds between Asn-2-ρ-TIA and Val-197, Trp-3-ρ-TIA and Ser-318, and the positively charged N terminus and Glu-186, were also identified. These interactions reveal that peptide binding to the ECS on transmembrane helix 6 (TMH6) and TMH7 at the base of extracellular loop 3 (ECL3) is sufficient to allosterically inhibit agonist signaling at a GPCR. The ligand-accessible ECS residues identified provide the first view of an allosteric inhibitor pharmacophore for α(1)-adrenoceptors and mechanistic insight and a new set of structural constraints for the design of allosteric antagonists at related GPCRs.

Molecular mechanisms of antithrombin deficiency caused by novel double heterozygous mutations

To explore the molecular mechanisms of antithrombin (AT) deficiency caused by novel double heterozygous mutations. Wild-type and mutant AT cDNA expression plasmids (ATwt, AT-c.134G > A, AT-c.342T > G, AT-c.134G > A and AT-c.342T > G) were transfected into HEK293T cells. Western blot was used to detect the AT:Ag in cell lysates. Homology was used to reestablish 3-D spatial structure of AT. Laser confocal assay was utilized to analyze the distribution of AT in endoplasmic reticulum (ER). Compared to the wild-types, the AT expression of HEK293T cells sharply increased when they were transfected by AT-c.342T > G or AT-c.134G > A and c.342T > G. Homology modeling showed that the mutation (AT-c.342T > G) caused a decreased distance between Arg and surrounding bases as Arg's side chain was significantly longer than Ser's. The mutation of 13th base pair decreases the distance between AT and heparin. Laser confocal assay showed that the AT protein concreted in HEK293T cells when they were transfected by mutant plasmids (AT-c.134G > A and c.342T > G) and aggregated in ER. The main molecular mechanism of AT deficiency in this pedigree is the disturbed AT secretion as a result of the mutation of AT-c.342T > G.

Nicotinic Receptor Transduction Zone: Invariant Arginine Couples to Multiple Electron-Rich Residues

Gating of the muscle-type acetylcholine receptor (AChR) channel depends on communication between the ACh-binding site and the remote ion channel. A key region for this communication is located within the structural transition zone between the ligand-binding and pore domains. Here, stemming from β-strand 10 of the binding domain, the invariant αArg209 lodges within the hydrophobic interior of the subunit and is essential for rapid and efficient channel gating. Previous charge-reversal experiments showed that the contribution of αArg209 to channel gating depends strongly on αGlu45, also within this region. Here we determine whether the contribution of αArg209 to channel gating depends on additional anionic or electron-rich residues in this region. Also, to reconcile diverging findings in the literature, we compare the dependence of αArg209 on αGlu45 in AChRs from different species, and compare the full agonist ACh with the weak agonist choline. Our findings reveal that the contribution of αArg209 to channel gating depends on additional nearby electron-rich residues, consistent with both electrostatic and steric contributions. Furthermore, αArg209 and αGlu45 show a strong interdependence in both human and mouse AChRs, whereas the functional consequences of the mutation αE45R depend on the agonist. The emerging picture shows a multifaceted network of interdependent residues that are required for communication between the ligand-binding and pore domains.

Abstract P1-05-06: A novel mutation in the tyrosine kinase domain of ErbB2: molecular and proteomic investigation of its role in breast cancer invasion

Abstract Introduction: A landmark genomic study revealed 17 somatic coding mutations in a lobular metastatic breast tumor, none of which were present in the patient's primary tumor. Among these was a novel mutation in the tyrosine kinase domain of ErbB2, a gene often amplified in breast cancer. Other mutations in this domain have been shown to stimulate transformation, growth and invasion in breast cancer cells. We hypothesize that an accumulation of mutations in the primary tumor over time preceded the development of an invasive clone, which allowed it to metastasise. Therefore, we investigated the specific effects of ErbB2 on cellular signalling and invasion, in conjunction with proteomic analyses to show its effects on global protein expression. Methods: Wild-type and mutant ErbB2 cDNAs were cloned into V180 pLP 3X FLAG-tagged expression vectors. T47D breast cancer cells were transfected with one of these constructs. Protein was detected by immunoblotting with an anti-ErbB2 antibody. Membranes were then immunoblotted with an anti-phospho-ERK1/2 antibody. Transfected cells were seeded onto Matrigel; cells that migrated through the matrix were stained and counted after 48h. To identify global proteomic changes caused by mutant ErbB2, T47D cells transfected with mutant/wild-type ErbB2 or vector control, were differentially labeled by growing them in medium containing various lysine/arginine isotopes (known as stable isotope labeling of amino acids in cell culture; SILAC). Protein lysates were mixed and subjected to LC-MS/MS mass spectrometry. Proteomic changes were analysed using MaxQuant and DAVID software. Results: Overexpression of the wild-type or mutant ErbB2 genes produced protein expression in T47D, a non-invasive breast cancer cell line, confirmed by western blotting. To measure signalling downstream of ErbB2, we measured levels of the MAP kinase phospho-ERK1/2. Increased phosphorylation of ERK1/2 was demonstrated in cells expressing mutated ErbB2, compared with cells transfected with wild-type. This indicates increased activation of mutant ErbB2, demonstrating distinct phenotypic effects between wild-type and mutant ErbB2 in breast cancer cells. To analyze whether increased activation was accompanied by enhanced invasive properties, invasion assays were performed using Matrigel. A greater number of cells (1.5-fold increase) expressing mutant ErbB2 migrated across this matrix compared with wild-type-expressing cells. Global proteomic analysis of T47D cells overexpressing wild-type or mutant ErbB2 yielded 1,357 total proteins, of which 543 could be quantified. Two subsets of proteins were identified, whose levels were either increased or decreased, in the mutant versus wild-type-transfected lysates (compared to control ratios). Proteins elevated in the mutant-expressing cells included candidates involved in cell migration, inhibition of apoptosis and promotion of cellular survival. Proteins showing reduced expression were involved in pathways including adhesion and DNA damage response. Conclusion: This previously undescribed mutation in the tyrosine kinase domain of ErbB2 differentially effects downstream signalling pathways and may play a role in invasion of breast cancer cells. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-05-06.

Ribavirin-Resistant Mutants of Human Enterovirus 71 Express a High Replication Fidelity Phenotype during Growth in Cell Culture

It has been shown in animal models that ribavirin-resistant poliovirus with a G64S mutation in its 3D polymerase has high replication fidelity coupled with attenuated virulence. Here, we describe the effects of mutagenesis in the human enterovirus 71 (HEV71) 3D polymerase on ribavirin resistance and replication fidelity. Seven substitutions were introduced at amino acid position 3D-G64 of a HEV71 full-length infectious cDNA clone (26M). Viable clone-derived virus populations were rescued from the G64N, G64R, and G64T mutant cDNA clones. The clone-derived G64R and G64T mutant virus populations were resistant to growth inhibition in the presence of 1,600 μM ribavirin, whereas the growth of parental 26M and the G64N mutant viruses were inhibited in the presence of 800 μM ribavirin. Nucleotide sequencing of the 2C and 3D coding regions revealed that the rate of random mutagenesis after 13 passages in the presence of 400 μM ribavirin was nearly 10 times higher in the 26M genome than in the mutant G64R virus genome. Furthermore, random mutations acquired in the 2C coding regions of 26M and G64N conferred resistance to growth inhibition in the presence of 0.5 mM guanidine, whereas the G64R and G64T mutant virus populations remained susceptible to growth inhibition by 0.5 mM guanidine. Interestingly, a S264L mutation identified in the 3D coding region of 26M after ribavirin selection was also associated with both ribavirin-resistant and high replication fidelity phenotypes. These findings are consistent with the hypothesis that the 3D-G64R, 3D-G64T, and 3D-S264L mutations confer resistance upon HEV71 to the antiviral mutagen ribavirin, coupled with a high replication fidelity phenotype during growth in cell culture.