Two cytodifferentiation agent-induced pathways, differentiation and apoptosis, are distinguished by the expression of human papillomavirus 16 E7 in human bladder carcinoma cells.
Many transformed cells have been found to lose the capacity to proliferate and undergo differentiation following exposure to hybrid polar agents. This study investigates the mechanism by which hexamethylene bisacetamide (HMBA) suppresses the proliferation of the human bladder carcinoma line, T24. We found that following a 24-h exposure to HMBA, T24 proliferation was inhibited, and cells arrested in G1 phase and underwent morphological maturation. HMBA-induced cessation of proliferation was mediated, in part, by effects on cell cycle regulatory proteins. In T24 cells cultured without HMBA, E2F complexes predominantly with p107. In culture with inducer, p107 protein decreased, pRB and p130 were converted to underphosphorylated forms, and E2F was shifted into complexes with pRB and p130. To determine whether the formation of pRB:E2F and p130:E2F complexes was required for the HMBA-induced G1 arrest, the ability of the pocket proteins to bind E2F was blocked by enforced expression of human papillomavirus 16 E7. Following culture with HMBA, the T24 clones expressing E7 died, whereas vector-alone T24 clones arrested in G1 phase. T24/E7-1 cells did not form pRB:E2F or p130:E2F complexes upon culture with HMBA; rather, E2F was present in its free form. T24/E7-1 cells cultured with HMBA initially accumulate in G1. By day 2, they have entered into S phase, and by day 3, over 80% of the cells became apoptotic. Taken together, these studies enlarge the repertoire of demonstrated developmental pathways that may be triggered in transformed cells, depending upon their molecular status, and may provide potential therapeutic opportunities for cancer.
Richon
V M
VM
Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA. v-richon@ski.mskcc.org
Russo
P
P
Venta-Perez
G
G
Cordon-Cardo
C
C
Rifkind
R A
RA
Marks
P A
PA
D000081:Acetamides / Q000494:pharmacology*; D000199:Actins / Q000032:analysis; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D002295:Carcinoma, Transitional Cell / Q000378:metabolism* / Q000821:virology; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D016193:G1 Phase / Q000187:drug effects; D006131:Growth Inhibitors / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D009687:Nuclear Proteins / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000378:metabolism*; D050725:Papillomavirus E7 Proteins; D010750:Phosphoproteins / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D011506:Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D050720:Retinoblastoma-Like Protein p107; D050717:Retinoblastoma-Like Protein p130; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D001749:Urinary Bladder Neoplasms / Q000378:metabolism* / Q000821:virology
D000081:Acetamides; D000199:Actins; D000970:Antineoplastic Agents; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D006131:Growth Inhibitors; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D010750:Phosphoproteins; D011506:Proteins; C493844:RBL1 protein, human; 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; C059731:oncogene protein E7, Human papillomavirus type 16; C014026:hexamethylene bisacetamide