Double PHD fingers protein DPF2 recognizes acetylated histones and suppresses the function of estrogen-related receptor alpha through histone deacetylase 1.

Estrogen-related receptor alpha (ERRalpha) is a member of the nuclear receptor superfamily and regulates many physiological functions, including mitochondrial biogenesis and lipid metabolism. ERRalpha enhances the transactivation function without endogenous ligand by associating with coactivators such as peroxisome proliferator-activated receptor gamma coactivator 1 alpha and beta (PGC-1alpha and -beta) and members of the steroid receptor coactivator family. However, the molecular mechanism by which the transactivation function of ERRalpha is converted from a repressive state to an active state is poorly understood. Here we used biochemical purification techniques to identify ERRalpha-associated proteins in HeLa cells stably expressing ERRalpha. Interestingly, we found that double PHD fingers protein DPF2/BAF45d suppressed PGC-1alpha-dependent transactivation of ERRalpha by recognizing acetylated histone H3 and associating with HDAC1. DPF2 directly bound to ERRalpha and suppressed the transactivation function of nuclear receptors such as androgen receptor. DPF2 was recruited to ERR target gene promoters in myoblast cells, and knockdown of DPF2 derepressed the level of mRNA expressed by target genes of ERRalpha. These results show that DPF2 acts as a nuclear receptor-selective co-repressor for ERRalpha by associating with both acetylated histone H3 and HDAC1.

Coactivation of estrogen receptor beta by gonadotropin-induced cofactor GIOT-4.

Estrogen exerts its diverse effects through two subtypes of estrogen receptors (ER), ERalpha and ERbeta. Each subtype has its own distinct function and expression pattern in its target tissues. Little, however, is known about the transcriptional regulatory mechanism of ERbeta in the major ERbeta-expressing tissues. Using biochemical methods, we identified and described a novel ERbeta coactivator. This protein, designated GIOT-4, was biochemically purified from 293F cells. It coactivated ERbeta in ovarian granulosa cells. GIOT-4 expression was induced by stimulation with follicle-stimulating hormone (FSH). GIOT-4 recruited an SWI/SNF-type complex in a ligand-independent manner to ERbeta as an ER subtype-specific physical bridging factor and induced subsequent histone modifications in the ERbeta target gene promoters in a human ovarian granulosa cell line (KGN). Indeed, two ERbeta-specific target genes were upregulated by FSH at a specific stage of a normal ovulatory cycle in intact mice. These findings imply the presence of a novel regulatory convergence between the gonadotropin signaling cascade and ERbeta-mediated transcription in the ovary.

An hGCN5/TRRAP histone acetyltransferase complex co-activates BRCA1 transactivation function through histone modification.

It is well established that genetic mutations that impair BRCA1 function predispose women to early onset of breast and ovarian cancer. However, the co-regulatory factors that support normal BRCA1 functions remain to be identified. Using a biochemical approach to search for such co-regulatory factors, we identified hGCN5, TRRAP, and hMSH2/6 as BRCA1-interacting proteins. Genetic mutations in the C-terminal transactivation domain of BRCA1, as found in breast cancer patients (Chapman, M. S., and Verma, I. M. (1996) Nature 382, 678-679), caused the loss of physical interaction between BRCA1 and TRRAP and significantly reduced the co-activation of BRCA1 transactivation function by hGCN5/TRRAP. The reported transcriptional squelching between BRCA1 and estrogen receptor alpha (Fan, S., Wang, J., Yuan, R., Ma, Y., Meng, Q., Erdos, M. R., Pestell, R. G., Yuan, F., Auborn, K. J., Goldberg, I. D., and Rosen, E. M. (1999) Science 284, 1354-1356) was rescued by the overexpression of TRRAP or hGCN5. Histone acetyltransferase hGCN5 activity appeared to be indispensable for coregulator complex function in both BRCA1-mediated gene regulation and DNA repair. Biochemical purification of the hGCN5/TRRAP-containing complex suggested that hGCN5/TRRAP formed a complex with hMSH2/hMSH6, presumably as a novel subclass of hGCN5/TRRAP-containing known TFTC (TBP-free TAF-containing)-type histone acetyltransferase complex (hTFTC, hPCAF, and hSTAGA) (Yanagisawa, J., Kitagawa, H., Yanagida, M., Wada, O., Ogawa, S., Nakagomi, M., Oishi, H., Yamamoto, Y., Nagasawa, H., McMahon, S. B., Cole, M. D., Tora, L., Takahashi, N., and Kato, S. (2002) Mol. Cell 9, 553-562). Unlike other subclasses, the isolated complex harbored a previously unknown combination of components including hMSH2 and hMSH6, major components of the BRCA1 genome surveillance repair complex (BASC). Thus, our results suggested that the multiple BRCA1 functions require a novel hGCN5/TRRAP histone acetyltransferase complex subclass.

Repressive domain of unliganded human estrogen receptor alpha associates with Hsc70.

Estrogen receptor (ER) is a hormone-inducible transcription factor as a member of the nuclear receptor gene superfamily. Unliganded ER is transcriptionally silent and capable of DNA binding; however, it is unable to suppress the basal activity of the target gene promoters, unlike non-steroid hormone receptors that associate with corepressors in the absence of their cognate ligands. To study the molecular basis of how unliganded human ERalpha is maintained silent in gene regulation upon the target gene promoters, we biochemically searched interactants for hERalpha, and identified heat shock protein 70 (Hsc70). Hsc70 appeared to associate with the N-terminal hormone binding E domain, that also turned out a transcriptionally repressive domain. Competitive association of Hsc70 with a best known coactivator p300 was observed. Thus, these findings suggest that Hsc70 associates with unliganded hERalpha, and thereby deters hERalpha from recruiting transcriptional coregulators, presumably as a component of chaperone complexes.