title: Inhibiting tyrosine phosphorylation of protein kinase Cδ (PKCδ) protects the salivary gland from radiation damage.
abstract: Radiation therapy for head and neck cancer can result in extensive damage to normal adjacent tissues such as the salivary gland and oral mucosa. We have shown previously that tyrosine phosphorylation at Tyr-64 and Tyr-155 activates PKCδ in response to apoptotic stimuli by facilitating its nuclear import. Here we have identified the tyrosine kinases that mediate activation of PKCδ in apoptotic cells and have explored the use of tyrosine kinase inhibitors for suppression of irradiation-induced apoptosis. We identify the damage-inducible kinase, c-Abl, as the PKCδ Tyr-155 kinase and c-Src as the Tyr-64 kinase. Depletion of c-Abl or c-Src with shRNA decreased irradiation- and etoposide-induced apoptosis, suggesting that inhibitors of these kinases may be useful therapeutically. Pretreatment with dasatinib, a broad spectrum tyrosine kinase inhibitor, blocked phosphorylation of PKCδ at both Tyr-64 and Tyr-155. Expression of "gate-keeper" mutants of c-Abl or c-Src that are active in the presence of dasatinib restored phosphorylation of PKCδ at Tyr-155 and Tyr-64, respectively. Imatinib, a c-Abl-selective inhibitor, also specifically blocked PKCδ Tyr-155 phosphorylation. Dasatinib and imatinib both blocked binding of PKCδ to importin-α and nuclear import, demonstrating that tyrosine kinase inhibitors can inhibit nuclear accumulation of PKCδ. Likewise, pretreatment with dasatinib also suppressed etoposide and radiation induced apoptosis in vitro. In vivo, pre-treatment of mice with dasatinib blocked radiation-induced apoptosis in the salivary gland by >60%. These data suggest that tyrosine kinase inhibitors may be useful prophylactically for protection of nontumor tissues in patients undergoing radiotherapy of the head and neck.
authors.affiliation: Program in Structural Biology and Biochemistry; Department of Craniofacial Biology, School of Dental Medicine, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Sten M
authors.initials: SM
authors.lastname: Wie
authors.affiliation: Department of Craniofacial Biology, School of Dental Medicine, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Tariq S
authors.initials: TS
authors.lastname: Adwan
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: James
authors.initials: J
authors.lastname: DeGregori
authors.affiliation: Department of Pathology, School of Medicine, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Anderson
authors.affiliation: Department of Craniofacial Biology, School of Dental Medicine, University of Colorado, Anschutz Medical Campus, Aurora, Colorado 80045. Electronic address: mary.reyland@ucdenver.edu.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Reyland
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D017209:Apoptosis; D000081247:CSK Tyrosine-Protein Kinase; D002467:Cell Nucleus / Q000378:metabolism; D004249:DNA Damage; D000069439:Dasatinib; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011485:Protein Binding; D051745:Protein Kinase C-delta / Q000037:antagonists & inhibitors*; D016315:Proto-Oncogene Proteins c-abl / Q000378:metabolism; D011743:Pyrimidines / Q000737:chemistry; D012469:Salivary Glands / Q000201:enzymology* / Q000528:radiation effects*; D013844:Thiazoles / Q000737:chemistry; D014443:Tyrosine / Q000378:metabolism; D028901:alpha Karyopherins / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D011743:Pyrimidines; D013844:Thiazoles; D028901:alpha Karyopherins; D014443:Tyrosine; D000081247:CSK Tyrosine-Protein Kinase; D016315:Proto-Oncogene Proteins c-abl; D019061:src-Family Kinases; C000631346:CSK protein, human; D051745:Protein Kinase C-delta; D000069439:Dasatinib
keywords: Apoptosis; Nonreceptor Tyrosine Kinase; Protein Kinase C (PKC); Radiation Biology; Salivary Gland