Characterization of the molecular mechanisms for p53-mediated differentiation.
The p53 tumor suppressor protein can induce both apoptosis and cell cycle arrest. Moreover, we and others have shown previously that p53 is a potent mediator of differentiation. For example, expression of ptsp53, a temperature-inducible form of p53, induces differentiation of leukemic monoblastic U-937 cells. The functions of p53 have for long been believed to be dependent on the transactivating capacity of p53. However, recent data show that both p53-induced cell cycle arrest and apoptosis can be induced independently of p53-mediated transcriptional activation, indicating alternative pathways for p53-induced apoptosis and cell cycle arrest. The bcl-2 proto-oncogene contributes to the development of certain malignancies, probably by inhibition of apoptosis. Interestingly, Bcl-2 has been shown to inhibit p53-mediated apoptosis as well as p53-mediated transcriptional activation. Asking whether Bcl-2 would interfere with the p53-mediated differentiation of U-937 cells, we stably transfected bcl-2 to U-937 cells inducibly expressing p53. Although the established Bcl-2-expressing clones were resistant to p53-mediated apoptosis, we did not observe any interference of Bcl-2 with the p53-mediated differentiation, suggesting separable pathways for p53 in mediating apoptosis and differentiation of U-937 cells. Neither did expression of Bcl-2 interfere with p53-induced expression of endogenous p21, suggesting that p53-induced differentiation might be dependent on the transcriptional activity of p53. To further investigate whether the p53-mediated differentiation of U-937 cells depends on the transcriptional activity of p53, we overexpressed transactivation-deficient p53, a transcriptionally inactive p53 mutant in these cells. However, in contrast to the effects of wild-type p53, expression of trans-activation-deficient p53 did neither induce signs of apoptosis nor of differentiation in U-937 cells. Our results indicate that the transcriptional activity of p53 is essential both for p53-mediated apoptosis and differentiation of U-937 cells.
Chylicki
K
K
Department of Hematology, Lund University, Sweden. Kristina.Chylicki@hematologi.lu.se
Ehinger
M
M
Svedberg
H
H
Gullberg
U
U
D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival; D002762:Cholecalciferol / Q000494:pharmacology; D002999:Clone Cells / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D016167:Integrin alphaXbeta2 / Q000378:metabolism; D007700:Kinetics; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020298:U937 Cells
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016167:Integrin alphaXbeta2; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D002762:Cholecalciferol