DETECTION OF SILENCER ACTIVITY IN THE LONG CONTROL REGIONS OF HUMAN PAPILLOMAVIRUS TYPE-6 ISOLATED FROM BOTH BENIGN AND MALIGNANT LESIONS

Human papillomavirus type 6 (HPV-6) DNA is the predominant HPV type fo und in condyloma acuminata: it is rarely found in carcinomas. We have previously reported cloning and characterizing an HPV-6 from a vulvar condyloma (HPV6-W50) and an HPV-6 from a vulvar carcinoma (HPV6-T70). The E5, E6 and E7 proteins encoded by the two genomes were identical, however, the two genomes differed in the long control region (LCR). Cl oning of the entire LCR into the enhancerless plasmid pSVEcat showed t hat the two LCRs had comparable enhancer activity. Since the major dif ferences between the two LCRs resided in the 5' end of the LCR, upstre am of the L1 polyadenylation signal, we subcloned the two LCRs to anal yse more closely their effect on cat gene expression. The data indicat ed that LCR subclones of the two genomes had comparable chloramphenico l acetyltransferase (CAT) activity. A negative regulatory region was d etectable when the test plasmids were transfected into HeLa and C33A c ells and in primary keratinocytes. A decrease in CAT activity was also detected when the SV40 early promoter was replaced with the putative HPV-6 E6 promoter. The negative regulatory region functioned in a posi tion- and orientation-independent manner, thus fulfilling the definiti on of a silencer.