The retinoblastoma gene is one of the best characterized tumor suppressor genes. The loss of Rb function has been correlated with the etiology of a subset of human neoplasias such as retinoblastomas, osteosarcomas, small lung carcinomas, breast carcinomas, etc. The Rb protein is also an important regulator of normal cell proliferation and has been shown to bind DNA tumor virus oncoproteins, such as adenovirus EIA, papillomavirus E7 and SV40 T antigen. Thus elucidation of the normal role of Rb protein and identification of the cellular targets of its interactions is critically important. Rb protein has been shown to interact with cellular transcription factors E2F. The interactions of Rb with E2F are particularly significant as E2F has been shown to be involved in the transcription of several proliferation associated genes. The work described is based on the principal investigator's recent observation that Rb protein in the from of a cellular complex, E2F-I, inhibits the DNA binding activity of the transcription factor E2F by forming an E2F/E2F-I complex. In this proposal: i) we plan to characterize the Rb associated proteins that cooperate with Rb to reconstitute the E2F-I activity. ii) analyze the cell cycle dependent biochemical alterations of E2F-I, which will enable us to correlate the growth suppressor function of Rb with its regulation of E2F DNA binding activity. %%% The retinoblastoma (Rb) protein has been shown to act as a suppressor of cell growth which suggests it is an important regulator of normal cell proliferation. Rb has been shown to bind DNA tumor virus oncoproteins (proteins which in mutated forms can cause uncontrolled cell growth). The elucidation of the normal role of Rb protein and identification of the cellular targets of its interactions is a fundamental question in understanding cell growth. Rb protein has been shown to interact with a cellular protein E2F. The interactions of Rb with E2F are particularly significant as E2F has been shown to regulate several cell growth associated genes. A recent observation is that Rb protein forms a cellular complex, E2F-I, which inhibits E2F by forming an E2F/E2F-I complex. Proposed research involves: i) characterizing the Rb associated proteins and reconstituting the E2F-I activity; and ii) analyze the cell cycle regulation of the factor E2F-I, which will enable the correlation of the growth suppressor function of Rb with its regulation of E2F DNA binding activity.
