Rb and prohibitin target distinct regions of E2F1 for repression and respond to different upstream signals.
E2F transcription factor is subject to stringent regulation by a variety of molecules. We recently observed that prohibitin, a potential tumor suppressor protein, binds to the retinoblastoma (Rb) protein and represses E2F transcriptional activity. Here we demonstrate that prohibitin requires the marked box region of E2F for repression; further, prohibitin can effectively inhibit colony formation induced by overexpression of E2F1 in T47D cells. Prohibitin was also found to interact with the signaling kinase c-Raf-1, and Raf-1 could effectively reverse prohibitin-mediated repression of E2F activity. Agents such as E1A, p38 kinase, and cyclins D and E had no effect on prohibitin-mediated repression of E2F1, but all of these molecules could reverse Rb function. Similarly, stimulation of the immunoglobulin M signaling pathway in Ramos cells could inactivate prohibitin, but this had no effect on Rb function. Serum stimulation of quiescent Ramos cells inactivated Rb and prohibitin with different kinetics; further, while the serum-dependent inactivation of Rb was dependent on cyclin-dependent kinase activity, the inactivation of prohibitin was not. We believe that prohibitin is a novel regulator of E2F function which channels specific signaling cascades to the cell cycle regulatory machinery.
Wang
S
S
Department of Pathology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
Nath
N
N
Fusaro
G
G
Chellappan
S
S
D001665:Binding Sites; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D003114:Colony-Forming Units Assay; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005786:Gene Expression Regulation; D000091402:Prohibitins; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D020239:Receptor Cross-Talk; D011961:Receptors, Fc / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism*; D056465:Retinoblastoma-Binding Protein 1; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D000091402:Prohibitins; D011506:Proteins; D011961:Receptors, Fc; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors; C035311:immunoglobulin M receptor; D019908:Proto-Oncogene Proteins c-raf; D018844:Cyclin-Dependent Kinases