title: B cell antigen receptor-mediated activation of cyclin-dependent retinoblastoma protein kinases and inhibition by co-cross-linking with Fc gamma receptors.
abstract: Cross-linking the B cell Ag receptor (BCR) to surface Fc receptors for IgG (Fc gamma R) inhibits G1-to-S progression; the mechanism by which this occurs is not completely known. We investigated the regulation of three key cell cycle regulatory components by BCR-Fc gamma R co-cross-linking: G1-cyclins, cyclin-dependent kinases (Cdks), and the retinoblastoma gene product (Rb). Rb functions to suppress G1-to-S progression in mammalian cells. Rb undergoes cell-cycle-dependent phosphorylation, leading to its inactivation and thereby promoting S phase entry. We demonstrate in this paper for the first time that BCR-induced Rb phosphorylation is abrogated by co-cross-linking with Fc gamma R. The activation of Cdk4/6- and Cdk2-dependent Rb protein kinases is concomitantly blocked. Fc gamma R-mediated inhibition of Cdk2 activity results in part from an apparent failure to express Cdk2 protein. By contrast, inhibition of Cdk4/6 activities is not due to suppression of Cdk4/6 or cyclins D2/D3 expression or inhibition of Cdk-activating kinase activity. Cdk4- and Cdk6-immune complexes recovered from B cells following BCR-Fc gamma R co-cross-linking are devoid of coprecipitated D-type cyclins, indicating that inhibition of their Rb protein kinase activities is due in part to the absence of bound D-type cyclin. Thus, BCR-derived activation signals that up-regulate D-type cyclin and Cdk4/6 protein expression remain intact; however, Fc gamma R-mediated signals block cyclin D-Cdk4/6 assembly or stabilization. These results suggest that assembly or stabilization of D-type cyclin holoenzyme complexes 1) is an important step in the activation of Cdk4/6 by BCR signals, and 2) suffice in providing a mechanism to account for inhibition of BCR-stimulated Rb protein phosphorylation by Fc gamma R.
authors.affiliation: Department of Biology, Boston College, Chestnut Hill, MA 02467, USA.
authors.forename: D
authors.initials: D
authors.lastname: Tanguay
authors.forename: S
authors.initials: S
authors.lastname: Pavlovic
authors.forename: M J
authors.initials: MJ
authors.lastname: Piatelli
authors.forename: J
authors.initials: J
authors.lastname: Bartek
authors.forename: T C
authors.initials: TC
authors.lastname: Chiles
mesh_terms: D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D001402:B-Lymphocytes / Q000201:enzymology / Q000276:immunology / Q000378:metabolism; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D002454:Cell Differentiation / Q000276:immunology; D056741:Cyclin D; D019927:Cyclin E / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D042863:Cyclin-Dependent Kinase 9; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000378:metabolism*; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004247:DNA / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004789:Enzyme Activation / Q000276:immunology; D016193:G1 Phase / Q000276:immunology; D020035:Holoenzymes / Q000096:biosynthesis; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012313:RNA / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D011947:Receptors, Antigen, B-Cell / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D017452:Receptors, IgG / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*; D025521:Tumor Suppressor Proteins; D015854:Up-Regulation / Q000276:immunology; D000095043:Cyclin-Dependent Kinase-Activating Kinase
chemical_list: D000888:Antibodies, Anti-Idiotypic; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D056741:Cyclin D; D019927:Cyclin E; D016213:Cyclins; D020035:Holoenzymes; D007140:Immunoglobulin Fab Fragments; D008869:Microtubule-Associated Proteins; D011518:Proto-Oncogene Proteins; D011947:Receptors, Antigen, B-Cell; D017452:Receptors, IgG; D016160:Retinoblastoma Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D012313:RNA; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; C495902:Cdk4 protein, mouse; C495912:Cdk6 protein, mouse; C467972:Cdk9 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases; D000095043:Cyclin-Dependent Kinase-Activating Kinase