PIASy-mediated repression of the Ets-1 is independent of its sumoylation

EHF suppresses cancer progression by inhibiting ETS1-mediated ZEB expression

ETS homologous factor (EHF) belongs to the epithelium-specific subfamily of the E26 transformation-specific (ETS) transcription factor family. Currently, little is known about EHF’s function in cancer. We previously reported that ETS1 induces expression of the ZEB family proteins ZEB1/δEF1 and ZEB2/SIP1, which are key regulators of the epithelial–mesenchymal transition (EMT), by activating the ZEB1 promoters. We have found that EHF gene produces two transcript variants, namely a long form variant that includes exon 1 (EHF-LF) and a short form variant that excludes exon 1 (EHF-SF). Only EHF-SF abrogates ETS1-mediated activation of the ZEB1 promoter by promoting degradation of ETS1 proteins, thereby inhibiting the EMT phenotypes of cancer cells. Most importantly, we identified a novel point mutation within the conserved ETS domain of EHF, and found that EHF mutations abolish its original function while causing the EHF protein to act as a potential dominant negative, thereby enhancing metastasis in vivo. Therefore, we suggest that EHF acts as an anti-EMT factor by inhibiting the expression of ZEBs, and that EHF mutations exacerbate cancer progression.

Homeoprotein Msx1-PIASy Interaction Inhibits Angiogenesis

Previously, we demonstrated that the homeoprotein Msx1 interaction with p53 inhibited tumor growth by inducing apoptosis. However, Msx1 can exert its tumor suppressive effect through the inhibition of angiogenesis since growth of the tumor relies on sufficient blood supply from the existing vessels to provide oxygen and nutrients for tumor growth. We hypothesized that the inhibition of tumor growth by Msx1 might be due to the inhibition of angiogenesis. Here, we explored the role of Msx1 in angiogenesis. Overexpression of Msx1 in HUVECs inhibited angiogenesis, and silencing of Msx1 by siRNA abrogated its anti-angiogenic effects. Furthermore, forced expression of Msx1 in mouse muscle tissue inhibited vessel sprouting, and application of an Ad-Msx1-transfected conditioned medium onto the chicken chorioallantoic membrane (CAM) led to a significant inhibition of new vessel formation. To explore the underlying mechanism of Msx1-mediated angiogenesis, yeast two-hybrid screening was performed, and we identified PIASy (protein inhibitor of activated STAT Y) as a novel Msx1-interacting protein. We mapped the homeodomain of Msx1 and the C-terminal domain of PIASy as respective interacting domains. Consistent with its anti-angiogenic function, overexpression of Msx1 suppressed the reporter activity of VEGF. Interestingly, PIASy stabilized Msx1 protein, whereas deletion of the Msx1-interacting domain in PIASy abrogated the inhibition of tube formation and the stabilization of Msx1 protein. Our findings suggest the functional importance of PIASy-Msx1 interaction in Msx1-mediated angiogenesis inhibition.

TDP2 negatively regulates axon regeneration by inducing SUMOylation of an Ets transcription factor

In Caenorhabditis elegans, the JNK MAP kinase (MAPK) pathway is important for axon regeneration. The JNK pathway is activated by a signaling cascade consisting of the growth factor SVH-1 and its receptor tyrosine kinase SVH-2. Expression of the svh-2 gene is induced by axonal injury in a process involving the transcription factors ETS-4 and CEBP-1. Here, we find that svh-14/mxl-1, a gene encoding a Max-like transcription factor, is required for activation of svh-2 expression in response to axonal injury. We show that MXL-1 binds to and inhibits the function of TDPT-1, a C. elegans homolog of mammalian tyrosyl-DNA phosphodiesterase 2 [TDP2; also called Ets1-associated protein II (EAPII)]. Deletion of tdpt-1 suppresses the mxl-1 defect, but not the ets-4 defect, in axon regeneration. TDPT-1 induces SUMOylation of ETS-4, which inhibits ETS-4 transcriptional activity, and MXL-1 counteracts this effect. Thus, TDPT-1 interacts with two different transcription factors in axon regeneration.

The significance of SUMOylation of angiogenic factors in cancer progression

Angiogenesis is the process of endothelial cell migration and proliferation induced by angiogenic factors, which is essential for the development of tumors. In recent years, studies have reported that SUMOylation acts on tumor angiogenesis by targeting angiogenic factors as one of post-translational modifications of proteins. Anti-angiogenic therapy is a new treatment method for tumor treatment following radiotherapy and chemotherapy, and it inhibits tumor growth by blocking tumor blood vessels. Therefore, SUMOylation may become a potential target for anti-angiogenesis therapy. This article focuses on the effect of SUMOylation on vascular growth factors, important signaling pathways proteins, and the migration and function of endothelial cells, in order to provide a new research idea for the anti-angiogenic therapy of tumors.

The E3 SUMO ligase PIASγ is a novel interaction partner regulating the activity of diabetes associated hepatocyte nuclear factor-1α

The transcription factor hepatocyte nuclear factor-1α (HNF-1A) is involved in normal pancreas development and function. Rare variants in the HNF1A gene can cause monogenic diabetes, while common variants confer type 2 diabetes risk. The precise mechanisms for regulation of HNF-1A, including the role and function of post-translational modifications, are still largely unknown. Here, we present the first evidence for HNF-1A being a substrate of SUMOylation in cellulo and identify two lysine (K) residues (K205 and K273) as SUMOylation sites. Overexpression of protein inhibitor of activated STAT (PIASγ) represses the transcriptional activity of HNF-1A and is dependent on simultaneous HNF-1A SUMOylation at K205 and K273. Moreover, PIASγ is a novel HNF-1A interaction partner whose expression leads to translocation of HNF-1A to the nuclear periphery. Thus, our findings support that the E3 SUMO ligase PIASγ regulates HNF-1A SUMOylation with functional implications, representing new targets for drug development and precision medicine in diabetes.

Transcription Factor ETS-1 and Reactive Oxygen Species: Role in Vascular and Renal Injury

The E26 avian erythroblastosis virus transcription factor-1 (ETS-1) is a member of the ETS family and regulates the expression of a variety of genes including growth factors, chemokines and adhesion molecules. Although ETS-1 was discovered as an oncogene, several lines of research show that it is up-regulated by angiotensin II (Ang II) both in the vasculature and the glomerulus. While reactive oxygen species (ROS) are required for Ang II-induced ETS-1 expression, ETS-1 also regulates the expression of p47phox, which is one of the subunits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and a major source of ROS in the kidney and vasculature. Thus, there appears to be a positive feedback between ETS-1 and ROS. ETS-1 is also upregulated in the kidneys of rats with salt-sensitive hypertension and plays a major role in the development of end-organ injury in this animal model. Activation of the renin angiotensin system is required for the increased ETS-1 expression in these rats, and blockade of ETS-1 or haplodeficiency reduces the severity of kidney injury in these rats. In summary, ETS-1 plays a major role in the development of vascular and renal injury and is a potential target for the development of novel therapeutic strategies to ameliorate end-organ injury in hypertension.

PIASγ controls stability and facilitates SUMO-2 conjugation to CoREST family of transcriptional co-repressors

CoREST family of transcriptional co-repressors regulates gene expression and cell fate determination during development. CoREST co-repressors recruit with different affinity the histone demethylase LSD1 (KDM1A) and the deacetylases HDAC1/2 to repress with variable strength the expression of target genes. CoREST protein levels are differentially regulated during cell fate determination and in mature tissues. However, regulatory mechanisms of CoREST co-repressors at the protein level have not been studied. Here, we report that CoREST (CoREST1, RCOR1) and its homologs CoREST2 (RCOR2) and CoREST3 (RCOR3) interact with PIASγ (protein inhibitor of activated STAT), a SUMO (small ubiquitin-like modifier)-E3-ligase. PIASγ increases the stability of CoREST proteins and facilitates their SUMOylation by SUMO-2. Interestingly, the SUMO-conjugating enzyme, Ubc9 also facilitates the SUMOylation of CoREST proteins. However, it does not change their protein levels. Specificity was shown using the null enzymatic form of PIASγ (PIASγ-C342A) and the SUMO protease SENP-1, which reversed SUMOylation and the increment of CoREST protein levels induced by PIASγ. The major SUMO acceptor lysines are different and are localized in nonconserved sequences among CoREST proteins. SUMOylation-deficient CoREST1 and CoREST3 mutants maintain a similar interaction profile with LSD1 and HDAC1/2, and consequently maintain similar repressor capacity compared with wild-type counterparts. In conclusion, CoREST co-repressors form protein complexes with PIASγ, which acts both as SUMO E3-ligase and as a protein stabilizer for CoREST proteins. This novel regulation of CoREST by PIASγ interaction and SUMOylation may serve to control cell fate determination during development.

SUMOylation of the KRAB zinc-finger transcription factor PARIS/ZNF746 regulates its transcriptional activity

Parkin-interacting substrate (PARIS), a member of the family of Krüppel-associated box (KRAB)-containing zinc-finger transcription factors, is a substrate of the ubiquitin E3 ligase parkin. PARIS represses the expression of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), although the underlying mechanisms remain largely unknown. In the present study, we demonstrate that PARIS can be SUMOylated, and its SUMOylation plays a role in the repression of PGC-1a promoter activity. Protein inhibitor of activated STAT y (PIASy) was identified as an interacting protein of PARIS and shown to enhance its SUMOylation. PIASy repressed PGC-1a promoter activity, and this effect was attenuated by PARIS in a manner dependent on its SUMOylation status. Co-expression of SUMO-1 with PIASy completely repressed PGC-1a promoter activity independently of PARIS expression. PARIS-mediated PGC-1a promoter repression depended on the activity of histone deacetylases (HDAC), whereas PIASy repressed the PGC-1a promoter in an HDAC-independent manner. Taken together, these results suggest that PARIS and PIASy modulate PGC-1a gene transcription through distinct molecular mechanisms.

The role of the transcription factor Ets1 in carcinoma

Ets1 belongs to the large family of the ETS domain family of transcription factors and is involved in cancer progression. In most carcinomas, Ets1 expression is linked to poor survival. In breast cancer, Ets1 is primarily expressed in the triple-negative subtype, which is associated with unfavorable prognosis. Ets1 contributes to the acquisition of cancer cell invasiveness, to EMT (epithelial-to-mesenchymal transition), to the development of drug resistance and neo-angiogenesis. The aim of this review is to summarize the current knowledge on the functions of Ets1 in carcinoma progression and on the mechanisms that regulate Ets1 activity in cancer.

Ets-1 as an early response gene against hypoxia-induced apoptosis in pancreatic β-cells

Hypoxia complicates islet isolation for transplantation and may contribute to pancreatic β-cell failure in type 2 diabetes. Pancreatic β-cells are susceptible to hypoxia-induced apoptosis. Severe hypoxic conditions during the immediate post-transplantation period are a main non-immune factor leading to β-cell death and islet graft failure. In this study, we identified the transcription factor Ets-1 (v-ets erythroblastosis virus E26 oncogene homolog 1) as an early response gene against hypoxia-induced apoptosis in pancreatic β-cells. Hypoxia regulates Ets-1 at multiple levels according to the degree of β-cell oxygen deprivation. Moderate hypoxia promotes Ets-1 gene transcription, whereas severe hypoxia promotes its transactivation activity, as well as its ubiquitin-proteasome mediated degradation. This degradation causes a relative insufficiency of Ets-1 activity, and limits the transactivation effect of Ets-1 on downstream hypoxic-inducible genes and its anti-apoptotic function. Overexpression of ectopic Ets-1 in MIN6 and INS-1 cells protects them from severe hypoxia-induced apoptosis in a mitochondria-dependent manner, confirming that a sufficient amount of Ets-1 activity is critical for protection of pancreatic β-cells against hypoxic injury. Targeting Ets-1 expression may be a useful strategy for islet graft protection during the immediate post-transplantation period.

The transcription factor ETS1 in lymphomas: friend or foe?

ETS1 is a member of the ETS family of transcription factors, which contains many cancer genes. ETS1 gene is mapped at 11q24.3, a chromosomal region that is often the site of genomic rearrangements in hematological cancers. ETS1 is expressed in a variety of cells, including B and T lymphocytes. ETS1 is important in various biological processes such as development, differentiation, proliferation, apoptosis, migration and tissue remodeling. It acts as an oncogene controlling invasive and angiogenic behavior of malignant cells in multiple human cancers. In particular, ETS1 deregulation has been reported in diffuse large B-cell lymphoma, in Burkitt lymphoma and in Hodgkin lymphoma. Here, we summarize the function of ETS1 in normal cells, with a particular emphasis on lymphocytes, and its possible role as an oncogene or tumor suppressor gene in the different mature B cell lymphomas.

Transcription factor Ets1, but not the closely related factor Ets2, inhibits antibody-secreting cell differentiation

B cell differentiation into antibody-secreting cells (ASCs) is a tightly regulated process under the control of multiple transcription factors. One such transcription factor, Ets1, blocks the transition of B cells to ASCs via two separate activities: (i) stimulating the expression of target genes that promote B cell identity and (ii) interfering with the functional activity of the transcription factor Blimp1. Ets1 is a member of a multigene family, several members of which are expressed within the B cell lineage, including the closely related protein Ets2. In this report, we demonstrate that Ets1, but not Ets2, can block ASC formation despite the fact that Ets1 and Ets2 bind to apparently identical DNA sequence motifs and are thought to regulate overlapping sets of target genes. The DNA binding domain of Ets1 is required, but not sufficient by itself, to block ASC formation. In addition, less conserved regions within the N terminus of Ets1 play an important role in inhibiting B cell differentiation. Differences between the N termini of Ets1 and Ets2, rather than differences in the DNA binding domains, determine whether the proteins are capable of blocking ASC formation or not.

Protein inhibitors of activated STAT (Pias1 and Piasy) differentially regulate pituitary homeobox 2 (PITX2) transcriptional activity

Protein inhibitors of activated STAT (Pias) proteins can act independent of sumoylation to modulate the activity of transcription factors and Pias proteins interacting with transcription factors can either activate or repress their activity. Pias proteins are expressed in many tissues and cells during development and we asked if Pias proteins regulated the pituitary homeobox 2 (PITX2) homeodomain protein, which modulates developmental gene expression. Piasy and Pias1 proteins are expressed during craniofacial/tooth development and directly interact and differentially regulate PITX2 transcriptional activity. Piasy and Pias1 are co-expressed in craniofacial tissues with PITX2. Yeast two-hybrid, co-immunoprecipitation and pulldown experiments demonstrate Piasy and Pias1 interactions with the PITX2 protein. Piasy interacts with the PITX2 C-terminal tail to attenuate its transcriptional activity. In contrast, Pias1 interacts with the PITX2 C-terminal tail to increase PITX2 transcriptional activity. The E3 ligase activity associated with the RING domain in Piasy is not required for the attenuation of PITX2 activity, however, the RING domain of Pias1 is required for enhanced PITX2 transcriptional activity. Bimolecular fluorescence complementation assays reveal PITX2 interactions with Piasy and Pias1 in the nucleus. Piasy represses the synergistic activation of PITX2 with interacting co-factors and Piasy represses Pias1 activation of PITX2 transcriptional activity. In contrast, Pias1 did not affect the synergistic interaction of PITX2 with transcriptional co-factors. Last, we demonstrate that Pias proteins form a complex with PITX2 and Lef-1, and PITX2 and β-catenin. Lef-1, β-catenin, and Pias interactions with PITX2 provide new molecular mechanisms for the regulation of PITX2 transcriptional activity and the activity of Pias proteins.

PIASγ enhanced SUMO-2 modification of Nurr1 activation-function-1 domain limits Nurr1 transcriptional synergy

Nurr1 (NR4A2) is a transcription factor that belongs to the orphan NR4A group of the nuclear receptor superfamily. Nurr1 plays key roles in the origin and maintenance of midbrain dopamine neurons, and peripheral inflammatory processes. PIASγ, a SUMO-E3 ligase, represses Nurr1 transcriptional activity. We report that Nurr1 is SUMOylated by SUMO-2 in the lysine 91 located in the transcriptional activation function 1 domain of Nurr1. Nurr1 SUMOylation by SUMO-2 is markedly facilitated by overexpressing wild type PIASγ, but not by a mutant form of PIASγ lacking its first LXXLL motif (PIASγmut1). This PIASγmut1 is also unable to interact with Nurr1 and to repress Nurr1 transcriptional activity. Interestingly, the mutant PIASγC342A that lacks SUMO ligase activity is still able to significantly repress Nurr1-dependent transcriptional activity, but not to enhance Nurr1 SUMOylation. A SUMOylation-deficient Nurr1 mutant displays higher transcriptional activity than the wild type Nurr1 only in promoters harboring more than one Nurr1 response element. Furthermore, lysine 91, the major target of Nurr1 SUMOylation is contained in a canonical synergy control motif, indicating that SUMO-2 posttranslational modification of Nurr1 regulates its transcriptional synergy in complex promoters. In conclusion, PIASγ can exert two types of negative regulations over Nurr1. On one hand, PIASγ limits Nurr1 transactivation in complex promoters by SUMOylating its lysine 91. On the other hand, PIASγ fully represses Nurr1 transactivation through a direct interaction, independently of its E3-ligase activity.

Review of Ets1 structure, function, and roles in immunity

The Ets1 transcription factor is a member of the Ets gene family and is highly conserved throughout evolution. Ets1 is known to regulate a number of important biological processes in normal cells and in tumors. In particular, Ets1 has been associated with regulation of immune cell function and with an aggressive behavior in tumors that express it at high levels. Here we review and summarize the general features of Ets1 and describe its roles in immunity and autoimmunity, with a focus on its roles in B lymphocytes. We also review evidence that suggests that Ets1 may play a role in malignant transformation of hematopoietic malignancies including B cell malignancies.

Protein inhibitor of activated STAT, PIASy regulates α-smooth muscle actin expression by interacting with E12 in mesangial cells

Phenotypic transformation of mesangial cells (MCs) is implicated in the development of glomerular disease; however, the mechanisms underlying their altered genetic program is still unclear. α-smooth muscle actin (α-SMA) is known to be a crucial marker for phenotypic transformation of MCs. Recently, E-boxes and the class I basic helix-loop-helix proteins, such as E12 have been shown to regulateα-SMA expression. Therefore, we tried to identify a novel E12 binding protein in MCs and to examine its role in glomerulonephritis. We found that PIASy, one of the protein inhibitors of activated STAT family protein, interacted with E12 by yeast two-hybrid screens and coimmunopreciptation assays. Overexpression of E12 significantly enhanced theα-SMA promoter activity, and the increase was blocked by co-transfection of PIASy, but not by a PIASy RING mutant. In vivo sumoylation assays revealed that PIASy was a SUMO E3 ligase for E12. Furthermore, transforming growth factor-β (TGF-β) treatment induced expression of both PIASy and E12, consistent with α-SMA expression. Moreover, reduced expression of PIASy protein by siRNA specific for PIASy resulted in increased TGF-β-mediated α-SMA expression. In vivo, PIASy and E12 were dramatically upregulated along with α-SMA and TGF-β in the proliferative phase of Thy1 glomerulonephritis. Furthermore, an association between PIASy and E12 proteins was observed at day 6 by IP-western blotting, but not at day 0. These results suggest that TGF-β up-regulates PIASy expression in MCs to down-regulateα-SMA gene transcription by the interaction with E12.

Characterizing the N- and C-terminal Small ubiquitin-like modifier (SUMO)-interacting motifs of the scaffold protein DAXX

DAXX is a scaffold protein with diverse roles that often depend upon binding SUMO via its N- and/or C-terminal SUMO-interacting motifs (SIM-N and SIM-C). Using NMR spectroscopy, we characterized the in vitro binding properties of peptide models of SIM-N and SIM-C to SUMO-1 and SUMO-2. In each case, binding was mediated by hydrophobic and electrostatic interactions and weakened with increasing ionic strength. Neither isolated SIM showed any significant paralog specificity, and the measured μM range K(D) values of SIM-N toward both SUMO-1 and SUMO-2 were ∼4-fold lower than those of SIM-C. Furthermore, SIM-N bound SUMO-1 predominantly in a parallel orientation, whereas SIM-C interconverted between parallel and antiparallel binding modes on an ms to μs time scale. The differences in affinities and binding modes are attributed to the differences in charged residues that flank the otherwise identical hydrophobic core sequences of the two SIMs. In addition, within its native context, SIM-N bound intramolecularly to the adjacent N-terminal helical bundle domain of DAXX, thus reducing its apparent affinity for SUMO. This behavior suggests a possible autoregulatory mechanism for DAXX. The interaction of a C-terminal fragment of DAXX with an N-terminal fragment of the sumoylated Ets1 transcription factor was mediated by SIM-C. Importantly, this interaction did not involve any direct contacts between DAXX and Ets1, but rather was derived from the non-covalent binding of SIM-C to SUMO-1, which in turn was covalently linked to the unstructured N-terminal segment of Ets1. These results provide insights into the binding mechanisms and hence biological roles of the DAXX SUMO-interacting motifs.

Transcriptional repression by sumoylation of Epstein-Barr virus BZLF1 protein correlates with association of histone deacetylase

The transition from latent to lytic phases of the Epstein-Barr virus life cycle is triggered by expression of a viral transactivator, BZLF1, that then induces expression of the viral immediate-early and early genes. The BZLF1 protein is post-translationally modified by a small ubiquitin-related modifier-1 (SUMO-1). Here we found that BZLF1 is conjugated at lysine 12 not only by SUMO-1 but also by SUMO-2 and 3. The K12R mutant of BZLF1, which no longer becomes sumoylated, exhibits stronger transactivation than the wild-type BZLF1 in a reporter assay system as well as in the context of virus genome with nucleosomal structures. Furthermore, exogenous supply of a SUMO-specific protease, SENP, caused de-sumoylation of BZLF1 and enhanced BZLF1-mediated transactivation. Immunoprecipitation experiments proved that histone deacetylase 3 preferentially associated with the sumoylated form of BZLF1. Levels of the sumoylated BZLF1 increased as lytic replication progressed. Based on these observations, we conclude that sumoylation of BZLF1 regulates its transcriptional activity through histone modification during Epstein-Barr virus productive replication.

PIASy inhibits LRH-1-dependent CYP11A1 expression by competing for SRC-1 binding

The orphan nuclear receptor LRH-1 (liver receptor homologue-1; NR5A2) plays a critical role in development, bile acid synthesis and cholesterol metabolism. LRH-1 is also expressed in the ovary where it is implicated in the regulation of steroidogenic genes for steroid hormone synthesis. In the present study, we investigated the molecular mechanisms of the transcriptional regulation of CYP11A1 by LRH-1 and found that LRH-1-mediated transactivation was markedly repressed by PIASy [protein inhibitor of activated STAT (signal transducer and activator of transcription) y], the shortest member of the PIAS family. The suppression of LRH-1 activity requires the N-terminal repression domain. Although PIAS proteins also function as E3 SUMO (small ubiquitin-related modifier) ligases and enhance SUMO conjugation, PIASy-mediated repression was independent of LRH-1 SUMOylation status. In addition, histone deacetylase activity was not involved in the inhibition of LRH-1 by PIASy. Immunoprecipitation and mammalian two-hybrid analyses indicated that PIASy interacted with LRH-1 through the C-terminal region, including the AF-2 (activation function-2) motif, which was also involved in the interaction between LRH-1 and the co-activator SRC-1 (steroid receptor co-activator-1). PIASy inhibited the binding of SRC-1 to LRH-1, although overexpression of SRC-1 partially overcame the PIASy inhibition of LRH-1 induction of the CYP11A1 promoter. The results of the present study suggest that competition with co-activators may be an important mechanism underlying the PIASy repression of LRH-1-mediated transactivation.

Sumoylation of CoREST modulates its function as a transcriptional repressor

It is emerging that covalent modifications of many transcription factors and co-factors by the small ubiquitin-like modifier (SUMO) can have a key role in modulating their transcriptional regulation. As SUMO modification is often associated with transcriptional repression, we studied whether it was involved in modulating the repressive activity of CoREST. We showed that CoREST can be modified by SUMO-1 at lysine 294. PIASxbeta interacted with CoREST in vitro and in vivo, and functions as an E3-ligase to mediate its sumoylation. Furthermore, SENP1 mediated the desumoylation of CoREST. Interestingly, mutation of the CoREST sumoylation site compromised its ability as a corepressor. These results demonstrate that SUMO-1 modification modulates the transcriptional repression by CoREST and is needed for its full repressive activity.

Role of Ets-1 phosphorylation in the effector function of Th cells

The transcription factor Ets-1 critically regulates differentiation and function of T helper (Th) cells. In vitro studies have demonstrated that DNA binding and transcriptional activity of Ets-1 are regulated by phosphorylation. Depending on the site of phosphorylation, Ets-1 function can either be increased or inhibited. In addition, a splice variant lacking several inhibitory phosphorylation sites has been identified, raising the possibility that this splice variant may function differently from the full-length Ets-1. However, it is unclear how the activating and inhibitory phosphorylation events of Ets-1 are coordinated during Th cell activation. Furthermore, the biological consequences of Ets-1 phosphorylation and alternative splicing in regulating the function of Th cells are unknown. We report here that both activating and inhibitory phosphorylation events of Ets-1 occur simultaneously and independently of each other during Th cell activation. We further demonstrate that the effect of Ets-1 phosphorylation is very modest and that full-length Ets-1 and its splice variant are functionally interchangeable in the regulation of cytokine production in Th cells.

PIASy represses CCAAT/enhancer-binding protein delta (C/EBPdelta) transcriptional activity by sequestering C/EBPdelta to the nuclear periphery

CCAAT/enhancer binding proteindelta (C/EBPdelta) plays a key role in mammary epithelial cell G(0) growth arrest, and "loss of function" alterations in C/EBPdelta have been reported in breast cancer and acute myeloid leukemia. C/EBPdelta is regulated at the transcriptional, post-transcriptional, and post-translational levels, suggesting tight control of C/EBPdelta content and function. Protein inhibitors of activated STATs (PIASs) regulate a growing number of transcription factors, including C/EBPs. HC11 nontransformed mammary epithelial cells express PIAS3, PIASxbeta, and PIASy, and all three PIAS family members repress C/EBPdelta transcriptional activity. PIASy is the most potent, however, repressing C/EBPdelta transcriptional activity by >80%. PIASy repression of C/EBPdelta transcriptional activity is dependent upon interaction between the highly conserved PIASy N-terminal nuclear matrix binding domain (SAPD) and the C/EBPdelta transactivation domain (TAD). PIASy repression of C/EBPdelta transcriptional activity is independent of histone deacetylase activity, PIASy E3 SUMO ligase activity, and C/EBPdelta sumoylation status. PIASy expression is associated with C/EBPdelta translocation from nuclear foci, where C/EBPdelta co-localizes with p300, to the nuclear periphery. PIASy-mediated translocation of C/EBPdelta is dependent upon the PIASy SAPD and C/EBPdelta TAD. PIASy reduces the expression of C/EBPdelta adhesion-related target genes and enhances repopulation of open areas within a cell monolayer in the in vitro "scratch" assay. These results demonstrate that PIASy represses C/EBPdelta by a mechanism that requires interaction between the PIASy SAPD and C/EBPdelta TAD and does not require PIASy SUMO ligase activity or C/EBPdelta sumoylation. PIASy alters C/EBPdelta nuclear localization, reduces C/EBPdelta transcriptional activity, and enhances cell proliferation/migration.

SMT3IP1, a nucleolar SUMO-specific protease, deconjugates SUMO-2 from nucleolar and cytoplasmic nucleophosmin

Sumoylation is reversibly regulated by SUMO-specific proteases. We characterized a nucleolar SUMO-specific protease, SMT3IP1, which has a preference for SUMO-2/3. To elucidate SMT3IP1 function, we screened for its interacting proteins that may be its substrates or regulate its activity. By using yeast two-hybrid screening, we identified nucleophosmin (NPM) as an SMT3IP1-binding partner. SMT3IP1 could preferentially remove SUMO-2 from sumoylated NPM. A catalytically inactive SMT3IP1 mutant increased intracellular accumulation of SUMO-2-modified NPM in a dominant-negative manner. Sumoylation of cytoplasmic mutated NPM was markedly elevated in an ARF-dependent manner. Despite the divergence in their localization, ectopic expression of SMT3IP1 could desumoylate a SUMO-2-modified NPM mutant. Additionally, genotoxic drugs caused the dissociation of NPM from nucleolar co-localization with SMT3IP1, but did not affect desumoylation of NPM by SMT3IP1. Our findings suggest that SMT3IP1-mediated desumoylation might control NPM physiological functions at both the nucleolus and other subcellular compartments.

Daxx mediates SUMO-dependent transcriptional control and subnuclear compartmentalization

SUMO (small ubiquitin-related modifier) modification is emerging as an important post-translational control in transcription. In general, SUMO modification is associated with transcriptional repression. Although many SUMO-modified transcription factors and co-activators have been identified, little is known about the mechanism underlying SUMOylation-elicited transcriptional repression. Here, we summarize that SUMO modification of transcription factors such as androgen receptor, glucocorticoid receptor, Smad4 and CBP [CREB (cAMP-response-element-binding protein)-binding protein] co-activator results in the recruitment of a transcriptional co-repressor Daxx, thereby causing transcriptional repression. Such a SUMO-dependent recruitment of Daxx is mediated by the interaction between the SUMO moiety of SUMOylated factors and Daxx SUMO-interacting motif. Interestingly, the transrepression effect of Daxx on these SUMOylated transcription factors can be relieved by SUMOylated PML (promyelocytic leukaemia) via altering Daxx partition from the targeted gene promoter to PML nuclear bodies. Because Daxx SUMO-interacting motif is a common binding site for SUMOylated factors, a model of competition for Daxx recruitment between SUMOylated PML and SUMOylated transcription factors was proposed. Together, our findings strongly suggest that Daxx functions as a SUMO reader in the SUMO-dependent regulation of transcription and subnuclear compartmentalization.

Androgen-mediated cholesterol metabolism in LNCaP and PC-3 cell lines is regulated through two different isoforms of acyl-coenzyme A:Cholesterol Acyltransferase (ACAT)

BACKGROUND

The objective of this work was to determine the effect of an androgen agonist, R1881, on intracellular cholesterol synthesis and esterification in androgen-sensitive (AS) prostate cancer (LNCaP) cells.

METHODS

We investigated the activity and expression of cholesterol metabolism enzymes, HMG-CoA-reductase and ACAT in the LNCaP and PC-3 (androgen-independent control) models.

RESULTS

Microsomal PC-3 HMG-CoA-reductase activity was increased with R1881 despite having similar cholesterol levels while increased cholesterol levels in microsomes from LNCaPs treated with R1881 (L+) were associated with increased HMG-CoA reductase activity. Increased intracellular cholesteryl esters (CE) found in (L+) were not associated with an increased ACAT1 activity. There was no effect from androgen treatment on ACAT1 protein expression in theses cells; however, ACAT2 expression was induced upon R1881 treatment. In contrast, we found an increase in the in vitro ACAT1 activity in PC-3 cells treated with androgen (P+). Only ACAT1 expression was induced in P+. We further assessed the expression of STAT1 alpha, a transcriptional activator that modulates ACAT1 expression. STAT1 alpha expression and phosphorylation were induced in P+. To determine the role of the AR on ACAT1 expression and esterification, we treated PC-3 cells overexpressing the androgen receptor with R1881 (PAR+). AR expression was decreased in PAR+ cells; ACAT1 protein expression and cholesterol ester levels were also decreased, however, ACAT2 remained unchanged. STAT1 alpha expression was decreased in PAR+.

CONCLUSIONS

Overall, these findings support the importance of cholesterol metabolism regulation within prostate cancer cells and unravel a novel role for STAT1 alpha in prostate cancer metabolism.

PIASy controls ubiquitination-dependent proteasomal degradation of Ets-1

The ETS transcription factor Ets-1 (E26 transformation-specific-1) plays a critical role in many physiological processes including angiogenesis, haematopoietic development and tumour progression. Its activity can be regulated by post-translational modifications, such as phosphorylation. Recently, we showed that Ets-1 is a target for SUMO (small ubiquitin-like modifier) modification and that PIASy [protein inhibitor of activated STAT (signal transducer and activator of transcription) Y], a specific SUMO-E3 ligase for Ets-1, represses Ets-1-dependent transcription. In the present study, we demonstrated that Ets-1 is degraded by the proteasome and that overexpression of PIASy increased the stability of endogenous and ectopically expressed Ets-1 protein by preventing proteasomal degradation. Moreover, knockdown of the endogenous PIASy expression by RNA interference reduced the protein level of endogenous Ets-1. The proteasome inhibitor MG132 reversed this effect. Deletion analysis showed that the TAD (transcriptional activation domain), which has been identified as the interaction domain with PIASy, was also required for Ets-1 ubiquitination and proteasomal degradation. However, the Ets-1 stabilization by PIASy was not due to reduced ubiquitination of Ets-1. Our results suggested that PIASy controls Ets-1 function, at least in part, by inhibiting Ets-1 protein turnover via the ubiquitin-proteasome system.

Repression of E1AF transcriptional activity by sumoylation and PIASy

E1AF is a member of the Ets transcriptional factor family, and it plays a crucial role in tumor metastasis. However, the molecular mechanisms regulating its activity are not well characterized. In this study, we show that E1AF is sumoylated at four lysine residues, both in vivo and in vitro. Replacement of these lysines by arginine enhanced the transcriptional activity of E1AF, suggesting that sumoylation negatively regulates E1AF activity. We further demonstrated that PIASy enhanced sumoylation of E1AF as a specific SUMO-E3 ligase. In addition, PIASy repressed the transcriptional activity of both the wild-type and sumoylation defective mutants. However, the C342A mutant of PIASy, which abrogates SUMO-E3 ligase activity, had a significantly decreased ability to repress E1AF activity. Taken together, our results indicate that PIASy negatively regulates E1AF-mediated transcription by both E1AF sumoylation in a dependent and independent fashion.