Oh Kwang-Jin, Kalinina Anna, Bagchi Srilata
Center for Molecular Biology of Oral Diseases, University of Illinois at Chicago, Chicago, IL 60612, USA.
Virology. 2010 Jan 5;396(1):118-24. doi: 10.1016/j.virol.2009.10.018. Epub 2009 Nov 10.
The HPV oncoprotein E7 promotes proteasomal degradation of the tumor suppressor protein Rb. In this study, we analyzed the regulation of E7-induced Rb proteolysis in HPV-containing Caski cervical cancer cells. We show that the Rb proteolysis is cell cycle dependent; in S phase Rb is stable while in post-mitotic early G1 phase cells and in differentiated cells, Rb is unstable. Similarly, the in vivo Rb/E7 interaction is not detected in S-phase cells, but is readily detected in differentiating Caski cells. The ubiquitinating enzymes involved in Rb proteolysis have not been identified. We find that the E3 ligase MDM2 is not involved in the Rb proteolysis in Caski cells. An in vivo analysis using multiple catalytic site mutant dominant negative E2 enzymes show that the C92A E2-25K most effectively blocks E7-induced Rb proteolysis. Taken together, these results show that E7 induces Rb proteolysis in growth-arrested cells and E2-25K is involved in the proteolysis.
人乳头瘤病毒（HPV）癌蛋白E7可促进肿瘤抑制蛋白Rb的蛋白酶体降解。在本研究中，我们分析了含HPV的Caski宫颈癌细胞中E7诱导的Rb蛋白水解的调控机制。我们发现，Rb蛋白水解依赖于细胞周期；在S期，Rb稳定，而在有丝分裂后的早期G1期细胞和分化细胞中，Rb不稳定。同样，在S期细胞中未检测到体内Rb/E7相互作用，但在分化的Caski细胞中很容易检测到。参与Rb蛋白水解的泛素化酶尚未确定。我们发现E3连接酶MDM2不参与Caski细胞中的Rb蛋白水解。使用多个催化位点突变的显性负性E2酶进行的体内分析表明，C92A E2-25K最有效地阻断了E7诱导的Rb蛋白水解。综上所述，这些结果表明E7在生长停滞的细胞中诱导Rb蛋白水解，且E2-25K参与了该蛋白水解过程。
