Protein Family Of Transcription Factors Research Articles

Genomic Analisys of Notch Mutations in a Case of Alagille Syndrome with Acute Lymphoblastic Leukemia

Alagille syndrome (ALGS), or arteriohepatic dysplasia, is a congenital multisystem disease due to Notch signalling pathway mutations, most commonly affecting JAGGED-1 (ALGS type 1), and more rarely NOTCH-2 (ALGS type 2), leading to hepatic, lung, renal and ocular dysfunction (chronic cholestasis, peripheral pulmonary artery stenosis, dysplastic kidneys pigmentary retinopathy), and skeletal abnormalies (minor vertebral segmentation, characteristic facies, posterior embryotoxon/anterior segment defects). ALGS is an autosomal dominant disease, but it is characterized also by variable penetrance and clinical expression and somatic/germline mosaicism.A 20-year-old man with ALGS was admitted to the University Hospital of Verona because of pancytopenia. Following analyses led to the diagnosis of Philadelphia chromosome/bcr-abl-negative, CD10-positive, B-lineage acute lymphoblastic leukemia (common B-ALL).In order to identify the genetic components involved in this complex phenotype, we sequenced the exome of a bone marrow sample collected from the patient. By genome interpretation with Knome pipeline applied to the reference genome UCSC hg19, we found missense variants both in NOTCH-2 (E38K) and JAGGED-1 (P871R) genes that are mainly involved in the syndrome, although their effect on protein function was predicted not to be deleterious. However, we detected putative damaging mutations in genes such as PAX5 (R38H) and NOTCH-1 (K1821N), which might be strongly related to the observed disease. In fact, PAX5 is a member of PAX protein family of transcription factors implicated into regulation of early development that binds NOTCH-2 and likely altering its functionality. On the other hand, NOTCH-1 is involved in cell growth and proliferation and thus the predicted alteration of function of the corresponding protein may have an important role in neoplastic transformation. DisclosuresMartinelli:Novartis: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; Pfizer: Consultancy; ARIAD: Consultancy.

The yeast forkhead HCM1 controls life span independent of calorie restriction.

Regulation of life span by members of the forkhead transcription factor family of proteins is one of the most highly investigated pathways in the field of aging. Nevertheless, despite the existence of forkhead family homologues in yeast, our knowledge of these proteins' role in yeast longevity is limited. Here, we show that yeast Hcm1p forkhead is the closest homologue of the worm PHA-4 forkhead, which regulates Caenorhabditis elegans life span. Overexpressing the yeast forkhead HCM1 or its deficiency resulted in a significant extension or reduction in yeast replicative life span, respectively. HCM1 regulates stress resistance, significantly increases the mRNA levels of several stress response genes including the catalase enzymes CTA1 and CTT1, and positively regulates life span independently of calorie restriction. Thus, HCM1 is a key regulator of life span, through a mechanism independent of calorie restriction.

Biophysical properties of intrinsically disordered p130Cas substrate domain--implication in mechanosensing.

Mechanical stretch-induced tyrosine phosphorylation in the proline-rich 306-residue substrate domain (CasSD) of p130Cas (or BCAR1) has eluded an experimentally validated structural understanding. Cellular p130Cas tyrosine phosphorylation is shown to function in areas without internal actomyosin contractility, sensing force at the leading edge of cell migration. Circular dichroism shows CasSD is intrinsically disordered with dominant polyproline type II conformations. Strongly conserved in placental mammals, the proline-rich sequence exhibits a pseudo-repeat unit with variation hotspots 2–9 residues before substrate tyrosine residues. Atomic-force microscopy pulling experiments show CasSD requires minimal extension force and exhibits infrequent, random regions of weak stability. Proteolysis, light scattering and ultracentrifugation results show that a monomeric intrinsically disordered form persists for CasSD in solution with an expanded hydrodynamic radius. All-atom 3D conformer sampling with the TraDES package yields ensembles in agreement with experiment when coil-biased sampling is used, matching the experimental radius of gyration. Increasing β-sampling propensities increases the number of prolate conformers. Combining the results, we conclude that CasSD has no stable compact structure and is unlikely to efficiently autoinhibit phosphorylation. Taking into consideration the structural propensity of CasSD and the fact that it is known to bind to LIM domains, we propose a model of how CasSD and LIM domain family of transcription factor proteins may function together to regulate phosphorylation of CasSD and effect machanosensing.

The Activating Transcription Factor 3 Protein Suppresses the Oncogenic Function of Mutant p53 Proteins

Mutant p53 proteins (mutp53) often acquire oncogenic activities, conferring drug resistance and/or promoting cancer cell migration and invasion. Although it has been well established that such a gain of function is mainly achieved through interaction with transcriptional regulators, thereby modulating cancer-associated gene expression, how the mutp53 function is regulated remains elusive. Here we report that activating transcription factor 3 (ATF3) bound common mutp53 (e.g. R175H and R273H) and, subsequently, suppressed their oncogenic activities. ATF3 repressed mutp53-induced NFKB2 expression and sensitized R175H-expressing cancer cells to cisplatin and etoposide treatments. Moreover, ATF3 appeared to suppress R175H- and R273H-mediated cancer cell migration and invasion as a consequence of preventing the transcription factor p63 from inactivation by mutp53. Accordingly, ATF3 promoted the expression of the metastasis suppressor SHARP1 in mutp53-expressing cells. An ATF3 mutant devoid of the mutp53-binding domain failed to disrupt the mutp53-p63 binding and, thus, lost the activity to suppress mutp53-mediated migration, suggesting that ATF3 binds to mutp53 to suppress its oncogenic function. In line with these results, we found that down-regulation of ATF3 expression correlated with lymph node metastasis in TP53-mutated human lung cancer. We conclude that ATF3 can suppress mutp53 oncogenic function, thereby contributing to tumor suppression in TP53-mutated cancer.

Momilactone B induces apoptosis and G1 arrest of the cell cycle in human monocytic leukemia U937 cells through downregulation of pRB phosphorylation and induction of the cyclin-dependent kinase inhibitor p21Waf1/Cip1

Momilactone B, a terpenoid phytoalexin present in rice bran, has been shown to exhibit several biological activities. The present study was conducted using cultured human leukemia U937 cells to elucidate the possible mechanisms by which momilactone B exerts its anticancer activity, which to date has remained poorly understood. Momilactone B treatment of U937 cells resulted in a dose-dependent inhibition of cell growth and induced apoptotic cell death as detected by chromatin condensation, DNA fragmentation, the cleavage of poly(ADP-ribose) polymerase and Annexin V-FITC staining. Flow cytometric analysis revealed that momilactone B resulted in G1 arrest in cell cycle progression, which was associated with the dephosphorylation of retinoblastoma protein (pRB) and enhanced binding of pRB with the E2F transcription factor family proteins. Treatment with momilactone B also increased the expression of cyclin-dependent kinase (Cdk) inhibitor p21Waf1/Cip1 in a p53-independent manner, without any noticeable changes in G1 cyclins and cyclin-dependent kinases (Cdks), except a slight decrease in cyclin E. Moreover, in vitro kinase assay indicated that momilactone B significantly decreased Cdk4- and Cdk6-associated kinase activities through a notably increased binding of p21 to Cdk4 and Cdk6. Our results demonstrated that momilactone B caused G1 cell cycle arrest and apoptosis in U937 cells through the induction of p21 expression, inhibition of Cdk/cyclin-associated kinase activities, and reduced phosphorylation of pRB, which may be related to anticancer activity.

Activating transcription factor 3 (ATF3) in the human adrenal cortex: its possible involvement in aldosterone biosynthesis.

The activating transcription factor 3 (ATF3) is a member of the cAMP-responsive element-binding (CREB) protein family of transcription factors. ATF3 is expressed in H295R human adrenocortical carcinoma cells and considered a rapid-responder gene to angiotensin-II stimulation. However, the functions of ATF3 in human adrenocortical tissues have remained unknown. In this study, we analyzed the localization and possible regulatory mechanisms of ATF3 in human adrenocortical cells and tissues. The expression levels of ATF3 mRNA were analyzed in 66 aldosterone-producing adenomas (APA) and 14 cortisol-producing adenomas (CPA) using real-time RT-PCR. To localize the ATF3 protein, we performed immunohistochemical analysis in 20 non-pathological adrenal glands, 9 adrenal glands with idiopathic hyperaldosteronism (IHA), 20 APA, and 5 CPA using a mouse monoclonal antibody against human ATF3. We showed that ATF3 mRNA levels were higher in APA compared to CPA (P = 0.0053). ATF3 was immunolocalized to the zona glomerulosa of non-pathological adrenal glands and adrenal glands with IHA, and diffusely detected in the tumor cells of APA and CPA. Subsequently, H295R cells were treated for 6 h with each inhibitor of Src kinase (SRC), PKC, JAK2, and calcium-dependent calmodulin kinase-II (CaMKII) in the presence or absence of angiotensin-II. The expression levels of ATF3 mRNA were increased by angiotensin-II (about 3.5-fold induction), but the magnitude of the induction was significantly decreased in the presence of an inhibitor for SRC (PP2) or CaMKII (KN93). These results suggest that ATF3 is a downstream target of SRC and CaMKII signaling, and may be involved in adrenocortical aldosterone synthesis.

ER stress-inducible ATF3 suppresses BMP2-induced ALP expression and activation in MC3T3-E1 cells

Endoplasmic reticulum (ER) stress suppresses osteoblast differentiation. Activating transcription factor (ATF) 3, a member of the ATF/cAMP response element-binding protein family of transcription factors, is induced by various stimuli including cytokines, hormones, DNA damage, and ER stress. However, the role of ATF3 in osteoblast differentiation has not been elucidated. Treatment with tunicamycin (TM), an ER stress inducer, increased ATF3 expression in the preosteoblast cell line, MC3T3-E1. Overexpression of ATF3 inhibited bone morphogenetic protein 2-stimulated expression and activation of alkaline phosphatase (ALP), an osteogenic marker. In addition, suppression of ALP expression by TM treatment was rescued by silencing of ATF3 using shRNA. Taken together, these data indicate that ATF3 is a novel negative regulator of osteoblast differentiation by specifically suppressing ALP gene expression in preosteoblasts.

Genomic Analysis Of Notch Mutations In a Case Of Alagille Syndrome With Acute Lymphoblastic Leukemia

Alagille syndrome (ALGS), or arteriohepatic dysplasia, is a congenital multisystem disease due to Notch signalling pathway mutations, most commonly affecting JAG1 (ALGS type 1), and more rarely NOTCH2 (ALGS type 2), leading to hepatic, lung, renal and ocular dysfunction (chronic cholestasis, peripheral pulmonary artery stenosis, dysplastic kidneys pigmentary retinopathy), and skeletal abnormalies (minor vertebral segmentation, characteristic facies, posterior embryotoxon/anterior segment defects). ALGS is an autosomal dominant disease, but it is characterized also by variable penetrance and clinical expression and somatic/germline mosaicism.A 20-year-old man with ALGS was admitted to the University Hospital of Verona because of pancytopenia. Following analyses led to the diagnosis of Philadelphia chromosome/bcr-abl-negative, CD10-positive, B-lineage acute lymphoblastic leukemia (common B-ALL).In order to identify the genetic components involved in this complex phenotype, we sequenced the exome of a bone marrow sample collected from the patient. By genome interpretation with Knome pipeline applied to the reference genome UCSC hg19, we found missense variants both in NOTCH2 (E38K) and JAG1 (P871R) genes that are mainly involved in the syndrome, although their effect on protein function was predicted not to be deleterious. However, we detected putative damaging mutations in genes such as PAX5 (R38H) and NOTCH1 (K1821N) which might be strongly related to the observed disease. In fact, PAX5 is a member of PAX protein family of transcription factors implicated into regulation of early development, that binds NOTCH2 and likely altering its functionality. On the other hand, NOTCH1 is involved in cell growth and proliferation and thus the predicted alteration of function of the corresponding protein may have an important role in neoplastic transformation. Disclosures:No relevant conflicts of interest to declare.

Expression patterns and regulation of SlCRF3 and SlCRF5 in response to cytokinin and abiotic stresses in tomato (Solanum lycopersicum)

Cytokinin is an influential hormone involved in numerous aspects of plant growth and development. A group of transcription factors–cytokinin response factors (CRFs) has been included as a side branch to cytokinin signaling pathway which also constitute a subset of the AP2/ERF family of transcription factor proteins. This study examined the expression patterns of two transcription factor genes SlCRF3 and SlCRF5 in tomato (Solanum lycopersicum) to determine their regulation in response to cytokinin and a variety of abiotic stress conditions. Analyses conducted during different developmental stages by RT-PCR or GUS reporter gene expression revealed that these genes are differentially expressed in vegetative and reproductive organs. qRT-PCR experiments were also performed to study regulation by the hormone cytokinin and abiotic stress conditions such as flooding, drought, osmotic, oxidative, and temperature. These showed that SlCRF3 and SlCRF5 have different patterns of regulation in leaf, stem, and roots with SlCRF5 showing greater induction in leaf or root tissue compared to SlCRF3 in most cases. Additionally, knockdown analysis for SlCRF5 revealed defects across development including leaf morphology, primary root growth, and lateral root formation. Together, these findings indicate that SlCRF3 and SlCRF5 are potential regulators of tomato developmental processes associated with cytokinin or abiotic stresses.

Neu-p11 reduces clock/apelin expression in insulin-resistant mouse adipocyte model

It is generally accepted that a major risk factor of type 2 diabetes mellitus (T2DM) is insulin resistance and is often associated with obesity [1]. Apelin (expressed in adipose tissue) appears as a beneficial adipokine with anti-diabetic and antiobesity properties [2]. Clock is a large and complex gene encoding a novel member of the basic helix-loop-helix/ Per-ARNT-Sim protein family of transcription factors. Circadian clocks can regulate metabolic homeostasis and clock disruption leads to obesity and the metabolic syndrome [3]. Melatonin (Mel) is an integral part of the homeostatic mechanism in the body. It is best known as a regulator of seasonal and circadian rhythms, with high expression level during the night and low level during the day. Interestingly, insulin levels are also adapted to day/night changes through Mel-dependent synchronization. Mel may influence diabetes and be associated with metabolic disturbances by regulating insulin secretion [4]. Luzindole is the non-specific Mel receptor antagonist that can block some functions of Mel [5]. Although Mel has a wide range of biological effects, studies have found that once it gets into human body, its metabolism can be very fast, with a half-life of 20–30 min. Therefore, apparent effects cannot be achieved from direct administration of this medicine. Besides, the extraction and synthesis of Mel are relatively difficult, and some side effects may arise if its dose is too high. Neu-P11 is a new type of non-selective agonist of Mel [6]. It has the following characteristics: it can be synthesized relatively easily in vitro; its effective time can be longer with fewer side effects; it can substitute Mel to interact with its receptors, and sequentially play a wide range of biological roles. The aim of the present study was to explore the mechanism of the Mel and its receptor agonist Neu-P11 and the change of clock/apelin in insulin-resistant 3T3-L1 adipocytes. To examine the changes of clock and apelin expression levels resulted from Neu-P11 treatment, insulin-resistant 3T3-L1 adipocytes were used in this study. Neu-P11 was provided by Neurim Pharmaceuticals Ltd. (Habarzel, Israel). A 5-mM stock solution was prepared by dissolving Neu-P11 in dimethylsulfoxide. 3T3-L1 pre-adipocytes were purchased from Institute of Basic Medicine, Chinese Academy of Medical Sciences (Beijing, China). Cells were differentiated in adipogenic cocktail by 3-isobutyl-1-methylxanthine (Sigma, St Louis, USA), dexamethasone, and insulin, and identified by oil red O staining. Insulin-resistant 3T3-L1 adipocytes were induced in Dulbecco’s modified Eagle’s medium (Gibco, Gaithersburg, USA) with high glucose/ high insulin for 24 h. Glucose consumption was detected by enzymatic method to evaluate the model [7,8].

Mechanism and Regulation of Mycobactin Fatty Acyl-AMP Ligase FadD33

Mycobacterial siderophores are critical components for bacterial virulence in the host. Pathogenic mycobacteria synthesize iron chelating siderophores named mycobactin and carboxymycobactin to extract intracellular macrophage iron. The two siderophores differ in structure only by a lipophilic aliphatic chain attached on the ε-amino group of the lysine mycobactin core, which is transferred by MbtK. Prior to acyl chain transfer, the lipophilic chain requires activation by a specific fatty acyl-AMP ligase FadD33 (also known as MbtM) and is then loaded onto phosphopantetheinylated acyl carrier protein (holo-MbtL) to form covalently acylated MbtL. We demonstrate that FadD33 prefers long chain saturated lipids and initial velocity studies showed that FadD33 proceeds via a Bi Uni Uni Bi ping-pong mechanism. Inhibition experiments suggest that, during the first half-reaction (adenylation), fatty acid binds first to the free enzyme, followed by ATP and the release of pyrophosphate to form the adenylate intermediate. During the second half-reaction (ligation), holo-MbtL binds to the enzyme followed by the release of products AMP and acylated MbtL. In addition, we characterized a post-translational regulation mechanism of FadD33 by the mycobacterial protein lysine acetyltransferase in a cAMP-dependent manner. FadD33 acetylation leads to enzyme inhibition, which can be reversed by the NAD(+)-dependent deacetylase, MSMEG_5175 (DAc1). To the best of our knowledge, this is the first time that bacterial siderophore synthesis has been shown to be regulated via post-translational protein acetylation.

Conjugated linoleic acid-induced milk fat depression in lactating ewes is accompanied by reduced expression of mammary genes involved in lipid synthesis

Conjugated linoleic acids (CLA) are produced during rumen biohydrogenation and exert a range of biological effects. The trans-10,cis-12 CLA isomer is a potent inhibitor of milk fat synthesis in lactating dairy cows and some aspects of the mechanism have been established. Conjugated linoleic acid-induced milk fat depression has also been observed in small ruminants and our objective was to examine the molecular mechanism in lactating ewes. Multiparous lactating ewes were fed a basal ration (0.55:0.45 concentrate-to-forage ratio; dry matter basis) and randomly allocated to 2 dietary CLA levels (n=8 ewes/treatment). Treatments were zero CLA (control) or 15g/d of lipid-encapsulated CLA supplement containing cis-9,trans-11 and trans-10,cis-12 CLA isomers in equal proportions. Treatments were fed for 10wk and the CLA supplement provided 1.5g of trans-10,cis-12/d. No treatment effects were observed on milk yield or milk composition for protein or lactose at wk 10 of the study. In contrast, CLA treatment significantly decreased both milk fat percentage and milk fat yield (g/d) by about 23%. The de novo synthesized fatty acids (FA; <C16) were significantly decreased in proportion (15%) and daily yield (27%), and the proportion of preformed FA (>C16) was increased (10%) for the CLA treatment. In agreement with the reduced de novo FA synthesis, mRNA abundance of acetyl-coenzyme A carboxylase α, FA synthase, stearoyl-CoA desaturase 1, and glycerol-3-phosphate acyltransferase 6 decreased by 25 to 40% in the CLA-treated group. Conjugated linoleic acid treatment did not significantly reduce the mRNA abundance of enzymes involved in NADPH production, but the mRNA abundance for sterol regulatory element-binding factor 1 and insulin-induced gene 1, genes involved in regulation of transcription of lipogenic enzymes, was decreased by almost 30 and 55%, respectively, with CLA treatment. Furthermore, mRNA abundance of lipoprotein lipase decreased by almost 40% due to CLA treatment. In conclusion, the mechanism for CLA-induced milk fat depression in lactating ewes involved the sterol regulatory element-binding protein transcription factor family and a coordinated downregulation in transcript abundance for lipogenic enzymes involved in mammary lipid synthesis.

WRINKLED Transcription Factors Orchestrate Tissue-Specific Regulation of Fatty Acid Biosynthesis in Arabidopsis

Acyl lipids are essential constituents of all cells, but acyl chain requirements vary greatly and depend on the cell type considered. This implies a tight regulation of fatty acid production so that supply fits demand. Isolation of the Arabidopsis thaliana WRINKLED1 (WRI1) transcription factor established the importance of transcriptional regulation for modulating the rate of acyl chain production. Here, we report the isolation of two additional regulators of the fatty acid biosynthetic pathway, WRI3 and WRI4, which are closely related to WRI1 and belong to the APETALA2-ethylene-responsive element binding protein family of transcription factors. These three WRIs define a family of regulators capable of triggering sustained rates of acyl chain synthesis. However, expression patterns of the three WRIs differ markedly. Whereas only WRI1 activates fatty acid biosynthesis in seeds for triacylglycerol production, the three WRIs are required in floral tissues to provide acyl chains for cutin biosynthesis and prevent adherence of these developing organs and subsequent semisterility. The targets of these WRIs encode enzymes providing precursors (acyl chain and glycerol backbones) for various lipid biosynthetic pathways, but not the subsequent lipid-assembling enzymes. These results provide insights into the developmental regulation of fatty acid production in plants.

Changes in mRNA Stability Associated with Cold Stress in Arabidopsis Cells

Control of mRNA half-life is a powerful strategy to adjust individual mRNA levels to various stress conditions, because the mRNA degradation rate controls not only the steady-state mRNA level but also the transition speed of mRNA levels. Here, we analyzed mRNA half-life changes in response to cold stress in Arabidopsis cells using genome-wide analysis, in which mRNA half-life measurements and transcriptome analysis were combined. Half-lives of average transcripts were determined to be elongated under cold conditions. Taking this general shift into account, we identified more than a thousand transcripts that were classified as relatively stabilized or relatively destabilized. The relatively stabilized class was predominantly observed in functional categories that included various regulators involved in transcriptional, post-transcriptional and post-translational processes. On the other hand, the relatively destabilized class was enriched in categories related to stress and hormonal response proteins, supporting the idea that rapid decay of mRNA is advantageous for swift responses to stress. In addition, pentatricopeptide repeat, cyclin-like F-box and Myb transcription factor protein families were significantly over-represented in the relatively destabilized class. The global analysis presented here demonstrates not only the importance of mRNA turnover control in the cold stress response but also several structural characteristics that might be important in the control of mRNA stability.

Roles of VWRPY motif‐mediated gene repression by Runx proteins during T‐cell development

Runx transcription factor family proteins have essential roles during T-cell development by either activating or repressing target genes. For instance, lineage- and stage-specific expression of Cd4 and ThPOK is controlled by a transcriptional silencer embedded in each locus, whose activity requires bindings of Runx complexes. The evolutionarily conserved VWRPY penta-peptide sequences in Runx proteins have been shown to be responsible for repressive function as a platform to recruit Groucho/TLE transcriptional corepressors. However, it remains elusive whether requirement for the VWRPY motif differs among Runx target genes. By examining mice lacking VWRPY motifs in both Runx1 and Runx3 proteins, here, we show a full and partial derepression of Cd4 and ThPOK in CD8-linegae T cells, respectively. Thus, whereas Cd4 silencing completely depends on the VWRPY motif, both VWRPY-dependent and -independent mechanisms operate to repress ThPOK gene. These results indicate that Runx proteins utilize different modes to repress expression of different target genes.

NF-κB p65 phosphorylated at serine-536 is an independent prognostic factor in Swedish colorectal cancer patients

The NF-κB transcription factor protein family has diverse cellular and biological functions, and posttranslational modification is important to regulate these functions. An important site of phosphorylation of NF-κB p65 subunit is at serine-536 (phospho-Ser536-p65), and this phosphorylation is involved in regulation of transcriptional activity, nuclear localization, and protein stability. In this study, we investigated expression of phospho-Ser536-p65 in colorectal cancers and its relationships with clinicopathological factors. The expression of phospho-Ser536-p65 was examined by immunohistochemistry in 203 primary colorectal cancers, 156 normal mucosa specimens, and 18 metastases in the lymph nodes. The expression of phospho-Ser536-p65 increased from normal mucosa to primary tumor (p < 0.0001). Further, the increased expression of phospho-Ser536-p65 in the cytoplasm of the primary tumors correlated with worse survival of the patients independently of gender, age, tumor location, stage, and differentiation (p = 0.04; hazard ratio, 1.89; 95% CI 1.03-3.47). The NF-κB p65 subunit phosphorylated at serine-536 is an independent prognostic factor in colorectal cancer patients.

MKL2 Functions in the Absence of MKL1 to Promote Megakaryocyte Maturation

Abstract 2336 Background:The transcriptional cofactors, MKL1 and MKL2, are members of the myocardin related factor family, which bind and activate the transcription factor Serum Response Factor (SRF) (Cen et al J Cell Biochem, 2004). Megakaryocytes, large, highly polyploid myeloid cells give rise to platelets, which promote blood clotting in response to tissue damage. The Krause lab has reported a significant decrease in Mk ploidy with a 50% decrease in mature platelets in Mkl1 knockout (KO) mice, indicating that MKL1 may contribute to megakaryocyte maturation (Cheng et al Blood, 2009). The phenotype of the Mk specific (PF4-Cre) Srf conditional KO (SRF PF4-cKO) further supports the importance for the MKL1/SRF pathway in Mk differentiation (Halene et al Blood, 2010); although similar to the Mkl1 KO mouse, the Srf PF4-cKO mouse has a more severe phenotype with a 90% decrease in platelet counts suggesting the presence of compensatory proteins or redundant pathways in Mkl1 KO mice. Objective:This study addresses the hypothesis that MKL2 is critical for normal megakaryocytopoiesis particularly in the absence of MKL1. Methods and Results:Using bone marrow (BM) transplantation, we determined that the Mkl1 KO phenotype (decreased megakaryocyte ploidy and decreased platelets) is cell autonomous. Lethally irradiated WT recipients of Mkl1 KO BM cells had a 50% decrease in platelet count, as well as significantly decreased ploidy indicated by the percentage of Mk with 2N (60% and 40% in the recipients of Mkl1 KO vs WT BM, respectively, p<0.0001). Transduction of Mkl1 KO donor BM cells with retrovirus encoding MKL1 cDNA rescued the ploidy phenotype. Although the Mkl1 KO mice are thrombocytopenic, their bleeding times are not significantly increased. In vitro studies show that MKL2 and MKL1 activate the same promoters in luciferase assays and have similar subcellular localization patterns, suggesting redundancy.To assess MKL2’s compensatory function in Mkl1 KO mice, we crossed Mkl2F/F mice with PF4-Cre mice to induce Mkl2 deletion in the Mk compartment (Mkl2 PF4-cKO). The Mkl2 PF4-cKO mice were mated onto the Mkl1 KO background to create double KO (DKO) megakaryocytes. The megakaryocyte ploidy and platelet counts (decreased by 90%) of DKO mice are more severe than the Mkl1 KO and comparable to the Srf PF4-Cre cKO mice In addition, bleeding times were significantly increased compared to WT and Mkl1 KO mice (p<0.0001). Electron microscopy and immunofluorescence of DKO megakaryocytes and platelets indicate abnormal cytoskeletal and membrane organization with decreased granule complexity. These morphological changes are consistent with abnormal in vitro platelet activation in response to ADP or thrombin. Conclusions:Our investigation reveals that both MKL1 and MKL2 are important for megakaryocyte differentiation, and that MKL2 mitigates the phenotype of MKL1 deficient megakaryocytes. The Mkl1 KO/Mkl2 PF4-cKO (DKO) mice phenocopy the Srf PF4-cKO mice suggesting that SRF activity in megakaryocyte differentiation is dependent on the myocardin related transcription factor family of proteins. Disclosures:No relevant conflicts of interest to declare.

The auxin responsive AP2/ERF transcription factor CROWN ROOTLESS5 is involved in crown root initiation in rice through the induction of OsRR1, a type‐A response regulator of cytokinin signaling

Cytokinin is known to have negative effects on de novo auxin-induced root formation. However, the regulatory mechanisms of root initiation by both cytokinin and auxin are poorly understood. In this study, we characterized a rice mutant, termed crown rootless5 (crl5), which produced fewer crown roots and displayed impaired initiation of crown root primordia. The expression of CRL5, which encodes a member of the large AP2/ERF transcription factor family protein, was observed in the stem region where crown root initiation occurs. Exogenous auxin treatment induced CRL5 expression without de novo protein biosynthesis, which also required the degradation of AUX/IAA proteins. A putative auxin response element in the CRL5 promoter region specifically interacted with a rice ARF, demonstrating that CRL5 may be a direct target of an ARF, similar to CRL1/ADVENTITIOUS ROOTLESS1 (ARL1) that also regulates crown root initiation. A crl1 crl5 double mutant displayed an additive phenotype, indicating that these two genes function in different genetic pathways for crown root initiation. In addition, ProACT:CRL5/WT showed a cytokinin-resistant phenotype for crown root initiation, and also up-regulated the expression of two negative regulators of cytokinin signaling, OsRR1 and OsRR2, which were downregulated in crl5. Transgenic plants that over-expressed OsRR1 under the control of the CRL5 promoter in a crl5 mutant background produced a higher number of crown roots than the crl5 plant. Taken together, these results indicate that auxin-induced CRL5 promotes crown root initiation through repression of cytokinin signaling by positively regulating type-A RR, OsRR1.

CTF/NF1 transcription factors act as potent genetic insulators for integrating gene transfer vectors

Gene transfer-based therapeutic approaches have greatly benefited from the ability of some viral vectors to efficiently integrate within the cell genome and ensure persistent transmission of newly acquired transgenes to the target cell progeny. However, integration of provirus has been associated with epigenetic repercussions that may influence the expression of both the transgene and cellular genes close to vector integration loci. The exploitation of genetic insulator elements may overcome both issues through their ability to act as barriers that limit transgene silencing and/or as enhancer-blockers preventing the activation of endogenous genes by the vector enhancer. We established quantitative plasmid-based assay systems to screen enhancer-blocker and barrier genetic elements. Short synthetic insulators that bind to nuclear factor-I protein family transcription factors were identified to exert both enhancer-blocker and barrier functions, and were compared to binding sites for the insulator protein CTCF (CCCTC-binding factor). Gamma-retroviral vectors enclosing these insulator elements were produced at titers similar to their non-insulated counterparts and proved to be less genotoxic in an in vitro immortalization assay, yielding lower activation of Evi1 oncogene expression and reduced clonal expansion of bone marrow cells.

Targeting activating transcription factor 3 by Galectin-9 induces apoptosis and overcomes various types of treatment resistance in chronic myelogenous leukemia.

Tyrosine kinase inhibitors (TKI) against Bcr-Abl are the first-line therapeutics for chronic myelogenous leukemia (CML). However, the resistance to Bcr-Abl TKIs is induced in leukemic cells not only by loss of sensitivity to TKIs through Bcr-Abl-related molecular mechanisms but also by loss of addiction to Bcr-Abl TK activity by acquiring Bcr-Abl-unrelated additional oncogenic mutations. Therefore, the identification of an additional therapeutic target has been anticipated for achievement of a complete cure and to overcome resistance to treatment. We here showed that modified human Galectin-9 (hGal9), a lectin that show specific affinity for beta-galactosides, inhibits the proliferation of five CML-derived cell lines by inducing apoptosis at their IC(50)s from 17.5 to 164.9 nmol/L. Our study revealed that activating transcription factor 3 (ATF3), a member of the ATF/cAMP-responsive element binding protein family transcription factors, is the critical mediator for cell killing by hGal9, and that Noxa is one of the downstream effector molecules of ATF3. Bim, on the other hand, the BH3-only protein essential for apoptosis by Bcr-Abl TKIs, was not associated with hGal9-induced cell death. ATF3-mediated cell death by hGal9 was not hampered by the absence of p53, the presence of mutant Abl(T315I), or by P-glycoprotein overexpression. In addition, hGal9 showed the additive growth-inhibitory effect with imatinib on CML cell lines. Collectively, hGal9 is a candidate agent that may overcome various kinds of resistance to treatment for CML and may suggest that ATF3 may be a new target molecule for the development of new treatment modalities that can overcome resistance to currently available chemotherapeutics.