Disruption of the Rb--Raf-1 interaction inhibits tumor growth and angiogenesis.
The retinoblastoma tumor suppressor protein (Rb) plays a vital role in regulating mammalian cell cycle progression and inactivation of Rb is necessary for entry into S phase. Rb is inactivated by phosphorylation upon growth factor stimulation of quiescent cells, facilitating the transition from G(1) phase to S phase. Although the signaling events after growth factor stimulation have been well characterized, it is not yet clear how these signals contact the cell cycle machinery. We had found previously that growth factor stimulation of quiescent cells lead to the direct binding of Raf-1 kinase to Rb, leading to its inactivation. Here we show that the Rb-Raf-1 interaction occurs prior to the activation of cyclin and/or cyclin-dependent kinases and facilitates normal cell cycle progression. Raf-1-mediated inactivation of Rb is independent of the mitogen-activated protein kinase cascade, as well as cyclin-dependent kinases. Binding of Raf-1 seemed to correlate with the dissociation of the chromatin remodeling protein Brg1 from Rb. Disruption of the Rb-Raf-1 interaction by a nine-amino-acid peptide inhibits Rb phosphorylation, cell proliferation, and vascular endothelial growth factor-mediated capillary tubule formation. Delivery of this peptide by a carrier molecule led to a 79% reduction in tumor volume and a 57% reduction in microvessel formation in nude mice. It appears that Raf-1 links mitogenic signaling to Rb and that disruption of this interaction could aid in controlling proliferative disorders.
Department of Interdisciplinary Oncology, H. Lee Moffitt Cancer Center and Research Institute, University of South Florida, 12902 Magnolia Dr., Tampa, FL 33612, USA.
Piyali
P
Dasgupta
Jiazhi
J
Sun
Sheng
S
Wang
Gina
G
Fusaro
Vicki
V
Betts
Jaya
J
Padmanabhan
Saïd M
SM
Sebti
Srikumar P
SP
Chellappan
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D056741:Cyclin D; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D050684:E2F Transcription Factors; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000098:blood supply* / Q000378:metabolism / Q000473:pathology*; D009389:Neovascularization, Pathologic; D009687:Nuclear Proteins / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding / Q000187:drug effects; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016196:S Phase / Q000187:drug effects; D044967:Serum; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors / Q000494:pharmacology
D018797:Cell Cycle Proteins; D056741:Cyclin D; D016213:Cyclins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D009687:Nuclear Proteins; D010446:Peptide Fragments; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D019908:Proto-Oncogene Proteins c-raf; D018844:Cyclin-Dependent Kinases; D020930:MAP Kinase Kinase Kinases; C084108:SMARCA4 protein, human; C513194:Smarca4 protein, mouse; D004265:DNA Helicases