TRANSCRIPTIONAL REPRESSION OF SMOOTH-MUSCLE ALPHA-ACTIN GENE ASSOCIATED WITH HUMAN PAPILLOMAVIRUS TYPE-16 E7 EXPRESSION

To explore the role of the E7 viral oncogene from human papillomavirus type 16 (HPV16) in the regulation of cytoskeletal organization, we in vestigated alterations in particular cytoskeletal components in rat em bryonal fibroblasts and three transformants of rat embryonal fibroblas t cells produced by transfections with HPV16 E7 alone (TF1), HPV16 E7 plus adenovirus type 5 E1B (TF3), and HPV16 E7 plus activated Ha-ras ( TF4). Marked reductions in smooth-muscle (SM) alpha-actin content and disrupted organization of stress fibers detected by anti-SM alpha-acti n antibody were evident in all the transformants. These cytoskeletal m anifestations were associated with a significant reduction in the mRNA s in these cells. Transcriptional repression by the E7 gene was observ ed after transient transfection of a chloramphenicol acetyltransferase reporter gene with SM alpha-actin gene promoter. Nucleotides-123 to - 39 of the SM alpha-actin gene promoter were required for the HPV16 E7 transcriptional repression as shown by the chloramphenicol acetyltrans ferase assay. The downregulation of this actin isoform mediated by the E7 oncoprotein may play an important role in cell transformation by H PV16. (C) 1995 Wiley-Liss, Inc.