Differentiation-induced changes in promoter usage for transcripts encodingthe human papillomavirus type 31 replication protein E1

The life cycle of human papillomaviruses (HPVs) is tied to keratinocyte dif ferentiation. One key event in the viral life cycle is the differentiation- dependent increase in viral replication. This increase in replication activ ity results in an amplification of the HPV genome from approximately 50 cop ies per cell in basal keratinocytes to thousands of copies of the Viral gen ome per cell in suprabasal keratinocytes. To characterize the events associ ated with this differentiation-dependent increase in HPV replication, we ha ve initiated studies of mRNAs encoding the HPV replication protein E1 durin g the differentiation of cell lines that stably maintain episomal HPV DNA. Differentiation induced the expression of several transcripts that hybridiz ed to an E1-specific probe. One of these messages, a 3.7-kb transcript, did not hybridize to a probe specific for the early promoter upstream of the E 6 open reading frame. RNase protection analysis confirmed an induction of u nspliced messages derived from the differentiation-dependent promoter at nu cleotide 742 in the middle of the E7 open reading frame. These observations demonstrate a differentiation-induced increase in E1 mRNAs derived from th e viral late promoter and suggest a role for increased E1 expression during amplification of the HPV genome. (C) 1999 Academic Press.