title: Ionizing radiation stimulates unidentified tyrosine-specific protein kinases in human B-lymphocyte precursors, triggering apoptosis and clonogenic cell death.
abstract: Very little is known regarding the effects of ionizing radiation on cytoplasmic signal transduction pathways. Here, we show that ionizing radiation induces enhanced tyrosine phosphorylation of multiple substrates in human B-lymphocyte precursors. This response to ionizing radiation was also observed in cells pretreated with vanadate, a potent protein-tyrosine-phosphatase (PTPase) inhibitor, and phosphotyrosyl [Val5]angiotensin II phosphatase assays showed no decreased PTPase activity in irradiated cells. Thus, enhanced tyrosine phosphorylation in irradiated B-lymphocyte precursors is not triggered by inhibition of total cellular PTPase activity. Immune-complex kinase assays using anti-phosphotyrosine antibodies demonstrated enhanced protein-tyrosine kinase (PTK) activity in the immunoprecipitates from irradiated cells, and the PTK inhibitors genistein and herbimycin effectively prevented radiation-induced tyrosine phosphorylation. Immune-complex kinase assays on irradiated and unirradiated B-lymphocyte precursors using antibodies prepared against unique amino acid sequences of p59fyn, p56/p53lyn, p55blk, and p56lck demonstrated that these Src-family tyrosine kinases were not the primary PTKs responsible for enhanced tyrosine kinase activity in the anti-phosphotyrosine antibody immunoprecipitates or for enhanced tyrosine phosphorylation of multiple substrates. Thus, our findings favor the hypothesis that ionizing radiation induces enhanced tyrosine phosphorylation in B-lymphocyte precursors by stimulation of as yet unidentified PTKs. Tyrosine phosphorylation appears to be an important proximal step in radiation-induced apoptosis and clonogenic cell death because inhibition of PTK prevents DNA fragmentation and loss of clonogenicity of irradiated B-lymphocyte precursors. Since PTKs play myriad roles in the regulation of cell function and proliferation, the activation of a PTK cascade, as detailed in this report, may explain some of the pleiotropic effects of ionizing radiation on cellular functions of B-lymphocytes and their precursors.
authors.affiliation: Section of Radiation Biology, University of Minnesota, Minneapolis 55455.
authors.forename: F M
authors.initials: FM
authors.lastname: Uckun
authors.forename: L
authors.initials: L
authors.lastname: Tuel-Ahlgren
authors.forename: C W
authors.initials: CW
authors.lastname: Song
authors.forename: K
authors.initials: K
authors.lastname: Waddick
authors.forename: D E
authors.initials: DE
authors.lastname: Myers
authors.forename: J
authors.initials: J
authors.lastname: Kirihara
authors.forename: J A
authors.initials: JA
authors.lastname: Ledbetter
authors.forename: G L
authors.initials: GL
authors.lastname: Schieven
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects*; D001402:B-Lymphocytes / Q000166:cytology / Q000502:physiology*; D016923:Cell Death / Q000187:drug effects / Q000528:radiation effects*; D002460:Cell Line; D002999:Clone Cells; D004307:Dose-Response Relationship, Radiation; D004789:Enzyme Activation; D005720:Gamma Rays; D006801:Humans; D010750:Phosphoproteins / Q000302:isolation & purification; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism / Q000528:radiation effects*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D010750:Phosphoproteins; D014638:Vanadates; D011505:Protein-Tyrosine Kinases