Mechanisms by which DNA tumor virus oncoproteins target the Rb family of pocket proteins

Small DNA tumor viruses have evolved different mechanisms to abrogate the function of the retinoblastoma tumor suppressor (pRb). Studies of these viruses have been invaluable in uncovering the central role of the Rb family of pocket proteins in cell cycle control. While the molecular mechanisms by which the viral oncoproteins inactivate the Rb family are still being elucidated, it is clear that targeting of this family is required both for viral replication and for virus-induced transformation of mammalian cells. This review compares and contrasts the approaches DNA tumor viruses have evolved to antagonize Rb family members--ranging from relatively simple equilibrium dissociation of pRb from cellular pRb-binding factors to chaperone-mediated alterations in pocket protein stability and phosphorylation levels. The review will focus on the viral oncoproteins adenovirus E1A, human papillomavirus E7 and the large T antigens of several polyomaviruses. An understanding of these mechanisms may provide further insight into the regulation and functions of Rb family members as well as uncover new targets for the development of novel anti-viral agents, particularly against human papillomavirus, which is a significant cause of human cancer.