title: Early phosphorylation of the retinoblastoma gene product regulates protein binding to the c-fos retinoblastoma control element during T cell activation.
abstract: Function of the retinoblastoma tumor suppressor protein [pRb] is regulated by phosphorylation during the G1 and S phases of the cell cycle. pRb regulates transcription of several genes, including c-fos. However, since c-fos is regulated during exit from G0, it has remained unclear how pRb participates in c-fos regulation. We have identified a protein complex, the retinoblastoma control factor A [RCF-A] which binds to the c-fos retinoblastoma control element [RCE] and is regulated by pRb within 10 min after T cell activation. We demonstrate that pRb control of RCF-A is dependent upon the state of phosphorylation of pRb. pRb becomes hyperphosphorylated on specific peptides at 10 min after mitogenic stimulation and pRb is dephosphorylated by 30 min. This time course coincides with RCF-A DNA binding. RCF-A binds RCE DNA longer when cells are treated with okadaic acid, and okadaic acid prevents pRb dephosphorylation. Dephosphorylated pRb inhibits RCF-A binding in vitro but phosphorylated pRb does not. Thus, in addition to the described G1/S regulation of pRb, transient inactivation by phosphorylation of pRb in T cells may also be important as resting cells leave G0.
authors.affiliation: Department of Microbiology, University of Kansas, Lawrence 66045, USA.
authors.forename: L K
authors.initials: LK
authors.lastname: Felzien
authors.forename: M G
authors.initials: MG
authors.lastname: Branden
authors.forename: S H
authors.initials: SH
authors.lastname: Benedict
mesh_terms: D000328:Adult; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016193:G1 Phase / Q000235:genetics; D005786:Gene Expression Regulation; D016762:Genes, fos / Q000502:physiology*; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding; D012045:Regulatory Sequences, Nucleic Acid; D016192:Resting Phase, Cell Cycle / Q000235:genetics; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase / Q000235:genetics; D013601:T-Lymphocytes / Q000276:immunology*; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D007476:Ionophores; D016160:Retinoblastoma Protein; D014157:Transcription Factors; D019319:Okadaic Acid; D004247:DNA