Razani B, Altschuler Y, Zhu L, Pestell R G, Mostov K E, Lisanti M P
Department of Molecular Pharmacology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461, USA.
Biochemistry. 2000 Nov 14;39(45):13916-24. doi: 10.1021/bi001489b.
Squamous cell carcinomas of the lung and cervix arise by neoplastic transformation of their respective tissue epithelia. In the case of cervical carcinomas, an increasing body of evidence implicates the human papillomavirus, HPV (types 16 and 18), as playing a pivotal role in this malignant transformation process. The HPV early genes E6 and E7 are known to inactivate the tumor suppressors p53 and Rb, respectively; this leads to disruption of cell cycle regulation, predisposing cells to a cancerous phenotype. However, the role of caveolin-1 (a putative tumor suppressor) in this process remains unknown. Here, we show that caveolin-1 protein expression is consistently reduced in a panel of lung and cervical cancer derived cell lines and that this reduction is not due to hyperactivation of p42/44 MAP kinase (a known negative regulator of caveolin-1 transcription). Instead, we provide evidence that this down-regulation event is due to expression of the HPV E6 viral oncoprotein, as stable expression of E6 in NIH 3T3 cells is sufficient to dramatically reduce caveolin-1 protein levels. Furthermore, we demonstrate that p53-a tumor suppressor inactivated by E6-is a positive regulator of caveolin-1 gene transcription and protein expression. SiHa cells are derived from a human cervical squamous carcinoma, harbor a fully integrated copy of the HPV 16 genome (including E6), and show dramatically reduced levels of caveolin-1 expression. We show here that adenoviral-mediated gene transfer of the caveolin-1 cDNA to SiHa cells restores caveolin-1 protein expression and abrogates their anchorage-independent growth in soft agar. Taken together, our results suggest that the HPV oncoprotein E6 down-regulates caveolin-1 via inactivation of p53 and that replacement of caveolin-1 expression can partially revert HPV-mediated cell transformation.
肺癌和宫颈癌中的鳞状细胞癌分别起源于各自组织上皮的肿瘤性转化。就宫颈癌而言，越来越多的证据表明人乳头瘤病毒（HPV，16型和18型）在这种恶性转化过程中起关键作用。已知HPV早期基因E6和E7分别使肿瘤抑制因子p53和Rb失活；这导致细胞周期调控紊乱，使细胞易于出现癌性表型。然而，小窝蛋白-1（一种假定的肿瘤抑制因子）在此过程中的作用仍不清楚。在这里，我们表明在一组肺癌和宫颈癌来源的细胞系中，小窝蛋白-1蛋白表达持续降低，并且这种降低并非由于p42/44丝裂原活化蛋白激酶（一种已知的小窝蛋白-1转录负调节因子）的过度激活。相反，我们提供证据表明这种下调事件是由于HPV E6病毒癌蛋白的表达，因为E6在NIH 3T3细胞中的稳定表达足以显著降低小窝蛋白-1蛋白水平。此外，我们证明p53（一种被E6失活的肿瘤抑制因子）是小窝蛋白-1基因转录和蛋白表达的正调节因子。SiHa细胞源自人宫颈鳞状癌，含有HPV 16基因组的完全整合拷贝（包括E6），并显示小窝蛋白-1表达水平显著降低。我们在此表明，腺病毒介导的小窝蛋白-1 cDNA基因转移至SiHa细胞可恢复小窝蛋白-1蛋白表达，并消除它们在软琼脂中的不依赖贴壁生长。综上所述，我们的结果表明HPV癌蛋白E6通过使p53失活而下调小窝蛋白-1，并且小窝蛋白-1表达的恢复可部分逆转HPV介导的细胞转化。
