Disruption of retinoblastoma protein family function by human papillomavirus type 16 E7 oncoprotein inhibits lens development in part through E2F-1

Complexes between the retinoblastoma protein (pRb) and the transcription fa ctor E2F-1 are thought to be important for regulating cell proliferation. W e have shown previously that the E7 oncoprotein from human papillomavirus t ype 16, dependent upon its binding to pRb proteins, induces proliferation, disrupts differentiation, and induces apoptosis when expressed in the diffe rentiating, or fiber, cells of the ocular lenses in transgenic mice, Mice t hat carry a null mutation in E2F-1 do not exhibit any defects in proliferat ion and differentiation in the lens. By examining the lens phenotype in mic e that express E7 on an E2F-1 null background, we now show genetic evidence that E7's ability to alter the fate of fiber cells is partially dependent on E2F-1. On the other hand, E2F-1 status does not affect E7-induced prolif eration in the undifferentiated lens epithelium. These data provide genetic evidence that E2F-1, while dispensible for normal fiber cell differentiati on, is one mediator of E7's activity in vivo and that the requirement for E 2F-1 is context dependent. These data suggest that an important role for pR b-E2F-1 complex during fiber cell differentiation is to negatively regulate cell cycle progression, thereby allowing completion of the differentiation program to occur.