Repression of transcription by TSGA/Jmjd1a, a novel interaction partner of the ETS protein ER71

The histone demethylase, Jmjd1a, interacts with the myocardin factors to regulate SMC differentiation marker gene expression

We and others have previously shown that the myocardin transcription factors play critical roles in the regulation of smooth muscle cell (SMC) differentiation marker gene expression. In a yeast 2-hybrid screen for proteins that interact with myocardin-related transcription factor-A (MRTF-A), we identified the histone 3 lysine 9 (H3K9)-specific demethylase, Jmjd1a. GST pull-down assays demonstrated that Jmjd1a bound all 3 myocardin family members, and further mapping studies showed that the jumonjiC domain of Jmjd1a was sufficient to mediate this interaction. Overexpression of Jmjd1a in multipotential 10T1/2 cells decreased global levels of di-methyl H3K9, stimulated the SM alpha-actin and SM22 promoters, and synergistically enhanced MRTF-A- and myocardin-dependent transactivation. Using chromatin immunoprecipitation assays, we also demonstrated that TGF-beta-mediated upregulation of SMC differentiation marker gene expression in 10T1/2 cells was associated with decreased H3K9 dimethylation at the CArG-containing regions of the SMC differentiation marker gene promoters. Importantly, knockdown of Jmjd1a in 10T1/2 cells and primary rat aortic SMCs by retroviral delivery of siRNA attenuated TGF-beta-induced upregulation of endogenous SM myosin heavy chain expression. These effects were concomitant with increased H3K9 dimethylation at the SMC differentiation marker gene promoters and with inhibition of MRTF-A-dependent transactivation of the SMC-specific transcription. These results suggest, for the first time, that SMC differentiation marker gene expression is regulated by H3K9 methylation and that the effects of the myocardin factors on SMC-specific transcription may involve the recruitment of Jmjd1a to the SMC-specific promoters.

Concerted activation of the Mdm2 promoter by p72 RNA helicase and the coactivators p300 and P/CAF

A scarcely studied and under-recognized feature of RNA helicases is their ability to regulate gene transcription. In particular, very little is known about the role of p72 RNA helicase in gene regulation. Here, we have analyzed how this helicase may enhance promoter activity. We demonstrate that p72 RNA helicase forms complexes with the homologous coactivators p300 and CBP in vitro and in vivo, especially leading to an enhancement of the transactivation potential of their C-termini. In addition, we show that the p300/CBP-associated protein (P/CAF) also interacts with p72 RNA helicase, and both this interaction and the binding to p300/CBP are mediated by the N-terminal 63 amino acids of p72 RNA helicase. p300, P/CAF and p72 RNA helicase synergize to stimulate selected promoters, including the Mdm2 one. Notably, downregulation of p72 RNA helicase leads to reduced Mdm2 transcription. Furthermore, our data suggest that p72 RNA helicase activates the Mdm2 promoter in a p53 dependent and independent manner. Collectively, our results have unraveled a mechanism of how p72 RNA helicase can regulate gene transcription, namely by cooperating with p300/CBP and P/CAF. Thereby, p72 RNA helicase may not only be involved in the p53-Mdm2 regulatory loop, but also profoundly impact on the transcriptome through various CBP/p300 and P/CAF interacting proteins.

Involvement of RNA helicases p68 and p72 in colon cancer

The homologous proteins p68 and p72 are members of the DEAD box family of RNA helicases. Here, we show that expression of both of these helicases strongly increases during the polyp-->adenoma-->adenocarcinoma transition in the colon. Furthermore, p68 and p72 form complexes with beta-catenin and promote the ability of beta-catenin to activate gene transcription. Conversely, simultaneous knockdown of p68 and p72 leads to reduced expression of the beta-catenin-regulated genes, c-Myc, cyclin D1, c-jun, and fra-1, all of which are proto-oncogenes. Moreover, transcription of the cell cycle inhibitor p21(WAF1/CIP1), whose expression is suppressed by c-Myc, is enhanced on p68/p72 knockdown. Thus, p68/p72 may contribute to colon cancer formation by directly up-regulating proto-oncogenes and indirectly by down-regulating the growth suppressor p21(WAF1/CIP1). Accordingly, knockdown of p68 and p72 in colon cancer cells inhibits their proliferation and diminishes their ability to form tumors in vivo. Altogether, these results suggest that p68/p72 overexpression is not only a potential marker of colon cancer but is also causally linked to this disease. Therefore, p68 and p72 may be novel targets in the combat against colon cancer.

Interactions of the Vitamin D Receptor with the Corepressor Hairless

Atrichia with papular lesions (APL) and hereditary vitamin D-resistant rickets have a similar congenital hair loss disorder caused by mutations in hairless (HR) and vitamin D receptor (VDR) genes, respectively. HR is a VDR corepressor, and it has been hypothesized that VDR.HR suppress gene expression during specific phases of the hair cycle. In this study, we examined the corepressor activity of HR mutants (E583V, C622G, N970S, V1056M, D1012N, V1136D, and Q1176X) previously described as the molecular cause of APL as well as HR variants (P69S, C397Y, A576V, E591G, R620Q, T1022A) due to non-synonymous polymorphisms in the HR gene. We found that the corepressor activities of all but one of the pathogenic HR mutants were completely abolished. HR mutant E583V exhibited normal corepressor activity, suggesting that it may not be pathogenic. In co-immunoprecipitation assays, all of the pathogenic HR mutants bound VDR but exhibited reduced binding to histone deacetylase 1 (HDAC1), suggesting that the impaired corepressor activity is due in part to defective interactions with HDACs. The HR variants exhibited two classes of corepressor activity, those with normal activity (C397Y, E591G, R620Q) and those with partially reduced activity (P69S, A576V, T1022A). All of the variants interacted with VDR and HDAC1 with the exception of P69S, which was degraded. When coexpressed with VDR, all of the HR pathogenic mutants and variants increased the level of VDR protein, demonstrating that this function of HR was not impaired by these mutations. This study of HR mutations provides evidence for the molecular basis of APL.

Activation of androgen receptor by histone demethylases JMJD2A and JMJD2D

The androgen receptor (AR) is a transcription factor that is pivotal for the development of prostate cancer. Here, we have identified two related histone demethylases, JMJD2A and JMJD2D, which form complexes with ligand-bound AR. We found that AR interacts through its ligand binding domain with JMJD2A and JMJD2D. On the other hand, JMJD2A utilizes its catalytic domain or C-terminus to bind to AR, and JMJD2D does so via its C-terminus. Further, overexpression of JMJD2A or D stimulates AR function and this is dependent on JMJD2 catalytic activity. Conversely, downregulation of JMJD2A, which is often overexpressed in prostate tumors, reduces basal transcription of the AR target gene, prostate-specific antigen, in LNCaP prostate cancer cells. Altogether, our data have identified a novel class of AR coactivators, whose (over)expression in prostate tumors could contribute to the constitutive activation of AR and thus to androgen-depletion independency of advanced prostate cancer cells.