ERK抑制对乳腺癌细胞(MCF-7)PCAF的影响和意义

目的:研究ERK抑制在雌激素对乳腺癌细胞MCF-7促细胞周期转化、抗凋亡过程中核受体辅激活因子PCAF及野生型p53蛋白的表达、转录水平变化,探讨ERK通过PCAF对雌激素受体信号通路的作用和机理.方法:以雌激素受体阳性乳腺癌细胞MCF-7为研究对象,实验分组为17β一雌二醇(17β-estradiol,17β-E2)处理组、17β-E2+ERK抑制剂PD98059处理组和细胞对照组.流式细胞术检测细胞凋亡、细胞周期;Westernblot检测P-ERK1/2、PCAF和野生型P53蛋白水平;RT-PCR检测野生型PCAFmRNA、p53mRNA水平.结果:应用ERK磷酸化抑制剂PD98059后,能抑制17β-E2抗MCF-7细胞凋亡的作用,使细胞早期凋亡率增加,其差异具有统计学意义(P<0.05);能抑制17β-E2促进MCF-7细胞周期转化作用,使G1期细胞增加,s期和G2期细胞减少,其差异具有显著统计学意义(P<0.01);PCAF和P-ERK1/2蛋白表达水平显著降低(P<0.01),PCAFmRNA转录水平差异无统计学意义(P>0.05);野生型P53蛋白表达和p53mRNA转录水平升高(P<0.01).结论:ERK在17β-E2抗乳腺癌细胞MCF-7凋亡、促细胞周期转化中的作用与PCAF增强雌激素受体信号及野生型p53蛋白表达和基因转录水平改变有关.     

Analysis of the P300/CBP-Associated Factor (PCAF) Gene in Astrocytic Tumors

The PCAF gene encodes the p300/CBP-Associated Factor (PCAF), a histone acetyltransferase, which regulates p53 by acetylation of Lys320 in the C-terminal portion of p53. While the p53 gene is one of the most frequently mutated tumor suppressor genes in human tumors, such mutations occur in only 30% of astrocytic tumors. Since PCAF can regulate p53 activity, abrogation of PCAF function by PCAF gene mutation could be an alternate mechanism to inactivate the p53 pathway in tumors lacking p53 mutations. To test this hypothesis, we determined the nucleotide sequence of the entire PCAF coding region in 37 astrocytic tumors (17 glioblastomas, 10 anaplastic astrocytomas, 7 low-grade astrocytomas, and 3 pilocytic astrocytomas). We detected two single-nucleotide alterations that represented non-deleterious polymorphisms (GAG > GAA Glu103Glu, AAT > AGT Asn386Ser) but no obvious functional mutations. Moreover, the frequency of the Asn386Ser allele that contained Ser386 in glioma patients was not statistically different from its frequency in individuals without disease, and no significant association was observed between the PCAF polymorphisms and the presence or absence of p53 mutations in the tumors. We conclude that the PCAF gene is not mutated during the development of the astrocytic tumors studied here.     

A novel histone fold domain-containing protein that replaces TAF6 in Drosophila SAGA is required for SAGA-dependent gene expression

The histone acetyltransferase complex SAGA is well characterized as a coactivator complex in yeast. In this study of Drosophila SAGA (dSAGA), we describe three novel components that include an ortholog of Spt20, a potential ortholog of Sgf73/ATXN7, and a novel histone fold protein, SAF6 (SAGA factor-like TAF6). SAF6, which binds directly to TAF9, functions analogously in dSAGA to TAF6/TAF6L in the yeast and human SAGA complexes, respectively. Moreover, TAF6 in flies is restricted to TFIID. Mutations in saf6 disrupt SAGA-regulated gene expression without disrupting acetylated or ubiquitinated histone levels. Thus, SAF6 is essential for SAGA coactivator function independent of the enzymatic activities of the complex.