Stable binding to E2F is not required for the retinoblastoma protein to activate transcription, promote differentiation, and suppress tumor cell growth.
The retinoblastoma tumor suppressor protein (pRB) can inhibit cell cycle progression and promote differentiation. pRB interacts with a variety of transcription factors, including members of the E2F and C-EBP protein families and MyoD, and can either repress or activate transcription depending on the promoter under study. These biological and biochemical activities of pRB have been mapped previously to a core domain, referred to as the pRB pocket. Using a panel of synthetic pRB pocket mutants, we found that the acute induction of a G1/S block by pRB is linked to its ability to both bind to E2F and to repress transcription. In contrast, these functions were not required for pRB to promote differentiation, which correlated with its ability to activate transcription in concert with fate-determining proteins such as MyoD. All tumor-derived pRB mutants tested to date failed to bind to E2F and did not repress transcription. Despite an inability to bind to E2F, pRB mutants associated with a low risk of retinoblastoma, unlike high-risk mutants, retained the ability to activate transcription and promote differentiation. Thus, the pRB pocket participates in dual tumor suppressor functions, one linked to cell cycle progression and the other to differentiation control, and these functions can be genetically and mechanistically dissociated.
Sellers
W R
WR
The Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA.
Novitch
B G
BG
Miyake
S
S
Heith
A
A
Otterson
G A
GA
Kaye
F J
FJ
Lassar
A B
AB
Kaelin
W G
WG
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002455:Cell Division; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D016193:G1 Phase; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D011506:Proteins; D012175:Retinoblastoma / Q000378:metabolism / Q000473:pathology; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism*; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D016196:S Phase; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011506:Proteins; C493837:RBL2 protein, human; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D050680:Transcription Factor DP1; D014157:Transcription Factors