Identification of the E2A gene products as regulatory targets of the G1 cyclin-dependent kinases.
The E2A gene products, E12 and E47, are multifunctional transcription factors that as homodimers regulate B cell development, growth, and survival. In this report, the E2A gene products are shown to be targets for regulation by the G1 cyclin-dependent kinases. Two novel G1 cyclin-dependent kinase sites are identified on the N-terminal domain of E12/E47. One site displays homology to a preferential D-type cyclin-dependent kinase site (serine 780) on the retinoblastoma susceptibility gene product (pRB) and, consistent with this homology, is more efficiently phosphorylated by cyclin D1-CDK4 than by the other cyclin-dependent kinases (CDK) that were tested. The second kinase site is phosphorylated by both cyclin D1-CDK4 and cyclin A/E-CDK2 complexes. Mutation studies indicated that phosphorylation of the cyclin D1-CDK4 site, or more potently, of both the cyclin D1-CDK4 and cyclin A/E-CDK2 sites, negatively regulates the growth suppressor function associated with the N-terminal domain of E12/E47. Transient expression studies showed that ectopic expression of cyclin D1 or E negatively regulates sequence-specific activation of gene transcription by E12/E47. Analysis of site mutants, however, indicated that inhibition of E12/E47 transcriptional activity did not require the N-terminal G1 cyclin-dependent kinase sites. Together, the results suggest that the growth suppressor and transcriptional activator functions of E12/E47 are targets for regulation by G1 cyclin-dependent kinases but that the mechanisms of regulation for each function are distinct.
Chu
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Department of Pathology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Kohtz
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DS
D000818:Animals; D042846:CDC2-CDC28 Kinases; D002455:Cell Division; D002460:Cell Line; D056746:Cyclin G; D056766:Cyclin G1; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D016213:Cyclins / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D051379:Mice; D008809:Mice, Inbred C3H; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D051820:TCF Transcription Factors; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D015533:Transcriptional Activation
C534703:Ccng1 protein, mouse; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D051820:TCF Transcription Factors; C544913:Tcf7l1 protein, mouse; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; C495902:Cdk4 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases