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The human telomeric protein TRF2 protects chromosome ends by facilitating their organization into the protective capping structure. Here we show that the stability of TRF2 is regulated via modification by the small ubiquitin-like modifiers (SUMO). TRF2 specifically interacts with and is sumoylated by PIAS1 in mammalian cells. The proteasome inhibitor stabilizes SUMO-conjugated TRF2 without affecting the level of unmodified TRF2, suggesting that SUMO conjugation is required for proteasomal degradation of TRF2. We also show that RNF4, a mammalian SUMO-targeted ubiquitin ligase, interacts with TRF2 in a SUMO-dependent manner and preferentially targets SUMO-conjugated TRF2 for ubiquitination. Collectively, our data demonstrate that the PIAS1-mediated sumoylation status of TRF2 serves as a molecular switch that controls the level of TRF2 at telomeres.

Prospero-related homeobox protein (Prox1) plays essential roles in the development of many tissues and organs. In the present study, we show that Prox1 is modified by the small ubiquitin-like protein SUMO-1 in cultured cells. Mutation analysis identified at least four potential sumoylation sites within the repression domain of Prox1. Our data indicate that sumoylation of Prox1 reduces its interaction with HDAC3 and as a result downregulates its corepressor activity. These findings suggest that sumoylation may serve as a novel mechanism for the regulation of Prox1’s corepressor activity.Structured summaryMINT-6787569:PROX1 (uniprotkb:Q92786) physically interacts (MI:0218) with HDAC3 (uniprotkb:O15379) by anti tag coimmunoprecipitation (MI:0007)MINT-6787767:PROX1 (uniprotkb:Q92786) physically interacts (MI:0218) with SUMO-1 (uniprotkb:P63165) by anti tag coimmunoprecipitation (MI:0007)

PIAS3, a member of the protein inhibitor of activated STAT family, was found to interact in vivo and in vitro with TIF2, a previously described coactivator for nuclear receptors. The interaction is mediated by two distinct non-contiguous regions of TIF2. We found that TIF2–PIAS3 interaction occurs through a unique domain of PIAS3, very rich in acidic residues and conserved throughout the PIAS family. PIAS3 modulates the ability of TIF2 to mediate ligand-enhanced transcription activation positively or negatively, for different steroid receptors. Taken together, our results indicate a potential role of PIAS3 as transcriptional modulator of TIF2-mediated signalling.

Jun-dimerization protein 2 (JDP2) is a member of the activating protein-1 (AP-1) family of transcription factors. JDP2 dimerizes with other AP-1 proteins such as activating transcription factor-2 (ATF2) and Jun to repress transcription from promoters that contain a cyclic AMP-responsive element (CRE). Interferon regulatory factor-2-binding protein-1 (IRF2-BP1), which is reported to be a transcriptional corepressor of IRF2, was isolated as a JDP2-binding protein using an epitope-tagging method. As anticipated from the presence of a RING-finger domain, IRF2-BP1 enhanced the polyubiquitination of JDP2. Moreover, IRF2-BP1 repressed ATF2-mediated transcriptional activation from a CRE-containing promoter.Structured summaryMINT-6699624:JDP2 (uniprotkb:Q8WYK2) physically interacts (MI:0218) with Valyl-tRNA synthetase (uniprotkb:P26640), IRF2-BP1 (uniprotkb:Q8IU81), ATF7 (uniprotkb:P17544), EEF1G (uniprotkb:P26641), EEF1A1 (uniprotkb:P68104), JUND (uniprotkb:P17535), JUNB (uniprotkb:P17275), EF1D2 (uniprotkb:P29692) and RPLP0 (uniprotkb:P05388) by anti tag coimmunoprecipitation (MI:0007).MINT-6699850:JDP2 (uniprotkb:Q8WYK2) binds (MI:0407) to IRF2-BP1 (uniprotkb:Q8IU81) by pull down (MI:0096).MINT-6699684:JDP2 (uniprotkb:Q8WYK2) physically interacts (MI:0218) with JUNB (uniprotkb:P17275), JUND (uniprotkb:P17535), ATF7 (uniprotkb:P17544) and IRF2-BP1 (uniprotkb:Q8IU81) by anti tag coimmunoprecipitation (MI:0007).MINT-6699839:IRF2-BP1 (uniprotkb:Q8IU81) physically interacts (MI:0218) with JDP2 (uniprotkb:Q8WYK2) by anti bait coimmunoprecipitation (MI:0006).MINT-6699748:JDP2 (uniprotkb:Q8WYK2) physically interacts (MI:0218) with ATF2 (uniprotkb:P15336) and c-JUN (uniprotkb:P05412) by anti tag coimmunoprecipitation (MI:0007).MINT-6699865:ATF2 (uniprotkb:P15336) binds (MI:0407) to IRF2-BP1 (uniprotkb:Q8IU81) by pull down (MI:0096).

Both p16(INK4) and p21(Waf1) are very important negative regulators of the cell cycle. In this study we examined the effects of p21(Waf1) on the transcription of p16(INK4). We determined that p21(Waf1) can activate the transcription of p16(INK4), and that this effect is GC-box dependent. We also found that the transcription factor Sp1 plays a key role in this event. Upregulation of Sp1 contributes to the transcriptional activation and protein level of p16(INK4) mediated by p21(Waf1), and is a potential point of cooperation between the p16/pRb and p14 (ARF)/p53 tumor suppressor pathways.

Growth hormone receptor (GHR) signaling involves activation of the Janus Kinases (Jak) and of Stat proteins (signal transducers and activators of transcription). Growth hormone (GH) induces transcriptional activation of c-fos gene and the c-sis inducible element (SIE) of its promoter was shown to bind the Stat proteins. Using cells co-transfected with GHR and Stat 3 expression vectors, we directly demonstrate that GH induces tyrosine phosphorylation of Stat 3 and its binding to the SIE probe. We showed, using mutant forms of GHR, that only the cytoplasmic membrane proximal domain of the receptor, including a conserved proline rich region (box 1), is required for this effect.

DJ-1 is a protein involved in multiple physiological processes, including cancer, Parkinson’s disease, and male fertility. It is unknown how DJ-1 functions in the apparently different systems. The crystal structure of DJ-1 at 1.6 Å resolution shows that DJ-1 is a helix-strand-helix sandwich and forms a dimer. The DJ-1 structure is similar to the members of the intracellular protease PfpI family. However, the catalytic triad of Cys–His–Glu is not strictly conserved in DJ-1, implying that DJ-1 has a different catalytic mechanism if it acts as a protease or DJ-1 serves as a regulatory protein in the physiological processes. The structure shows that Leu166 positions in the middle of a helix and thus predicts that the L166P mutation will bend the helix and impact the dimerization of DJ-1. As a result, the conformational changes may diminish the DJ-1 binding with its partner, leading to the familial Parkinson’s disease caused by the single L166P mutation.