Role for Retinoblastoma Protein Family Members in UV‐enhanced Expression from the Human Cytomegalovirus Immediate Early Promoter¶

The expression from a reporter construct driven by a cytomegalovirus (CMV) immediate early (IE) promoter is strongly inducible by UV in human fibroblasts. This response is induced at lower UV fluences in transcription‐coupled repair (TCR)–deficient fibroblasts compared with normal fibroblasts and is absent in their simian virus 40–transformed counterparts. In this study we demonstrate that expression of human papilloma virus (HPV) E7 (but not of HPV E6) can attenuate UV‐induced expression from the human CMV‐IE–driven reporter construct in human fibroblasts. Furthermore, UV‐induced expression from the reporter construct appears impaired in murine fibroblasts harboring inactivating mutations in the retinoblastoma (Rb) gene family members p107 and pRb but not in fibroblasts harboring such mutations in the p53 gene. Taken together, these data suggest that one or more members of the pRb family (but not p53) play an essential role in mediating UV‐induced expression from the CMV‐IE promoter. In this study we report normal UV‐upregulation of reporter expression in xeroderma pigmentosum (XP) group E fibroblasts, consistent with normal TCR. Because XP‐E cells deficient in the p48 subunit of the damaged DNA–binding protein are impaired in E2F‐1–activated transcription, these results also suggest that the (pRb‐regulated) transcription factor E2F‐1 does not play an essential role in UV‐enhanced expression from the CMV‐IE promoter.