Zeng Shelya X, Dai Mu-Shui, Keller David M, Lu Hua
Department of Biochemistry and Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97201, USA.
EMBO J. 2002 Oct 15;21(20):5487-97. doi: 10.1093/emboj/cdf540.
The p53 homolog p63 is a transcriptional activator. Here, we describe the identification of an HMG1-like protein SSRP1 as a co-activator of p63. Over expression of wild-type, but not deletion mutant, SSRP1 remarkably enhanced p63gamma-dependent luciferase activity, G1 arrest, apoptosis and expression of endogenous PIG3, p21(Waf1/cip1) and MDM2 in human p53-deficient lung carcinoma H1299 cells and mouse embryonic fibroblasts. Also, SSRP1 interacted to p63gamma in vitro and in cells, and resided with p63gamma at the p53-responsive DNA element sites of the cellular endogenous MDM2 and p21(Waf1/cip1) promoters. Moreover, N-terminus-deleted p63 (DeltaN-p63) bound to neither SSRP1 nor its central domain in vitro. Accordingly, SSRP1 was unable to stimulate DeltaN-p63-mediated residual luciferase activity and apoptosis in cells. Finally, the ectopic expression of the central p63-binding domain of SSRP1 inhibited p63-dependent transcription in cells. Thus, these results suggest that SSRP1 stimulates p63 activity by associating with this activator at the promoter.
p53 同源物 p63 是一种转录激活因子。在此，我们描述了一种类 HMG1 蛋白 SSRP1 作为 p63 共激活因子的鉴定过程。在人 p53 缺陷型肺癌 H1299 细胞和小鼠胚胎成纤维细胞中，野生型而非缺失突变型 SSRP1 的过表达显著增强了 p63γ 依赖的荧光素酶活性、G1 期阻滞、细胞凋亡以及内源性 PIG3、p21（Waf1/cip1）和 MDM2 的表达。此外，SSRP1 在体外和细胞内与 p63γ 相互作用，并与 p63γ 共同定位于细胞内源性 MDM2 和 p21（Waf1/cip1）启动子的 p53 反应性 DNA 元件位点。而且，N 端缺失的 p63（ΔN-p63）在体外既不与 SSRP1 结合，也不与其中央结构域结合。相应地，SSRP1 无法刺激细胞中 ΔN-p63 介导的残余荧光素酶活性和细胞凋亡。最后，SSRP1 的中央 p63 结合结构域的异位表达抑制了细胞中 p63 依赖的转录。因此，这些结果表明 SSRP1 通过在启动子处与该激活因子结合来刺激 p63 活性。
