title: The cAMP signaling system inhibits the repair of γ-ray-induced DNA damage by promoting Epac1-mediated proteasomal degradation of XRCC1 protein in human lung cancer cells.
abstract: Cyclic AMP is involved in the regulation of metabolism, gene expression, cellular growth and proliferation. Recently, the cAMP signaling system was found to modulate DNA-damaging agent-induced apoptosis by regulating the expression of Bcl-2 family proteins and inhibitors of apoptosis. Thus, we hypothesized that the cAMP signaling may modulate DNA repair activity, and we investigated the effects of the cAMP signaling system on γ-ray-induced DNA damage repair in lung cancer cells. Transient expression of a constitutively active mutant of stimulatory G protein (GαsQL) or treatment with forskolin, an adenylyl cyclase activator, augmented radiation-induced DNA damage and inhibited repair of the damage in H1299 lung cancer cells. Expression of GαsQL or treatment with forskolin or isoproterenol inhibited the radiation-induced expression of the XRCC1 protein, and exogenous expression of XRCC1 abolished the DNA repair-inhibiting effect of forskolin. Forskolin treatment promoted the ubiquitin and proteasome-dependent degradation of the XRCC1 protein, resulting in a significant decrease in the half-life of the protein after γ-ray irradiation. The effect of forskolin on XRCC1 expression was not inhibited by PKA inhibitor, but 8-pCPT-2'-O-Me-cAMP, an Epac-selective cAMP analog, increased ubiquitination of XRCC1 protein and decreased XRCC1 expression. Knockdown of Epac1 abolished the effect of 8-pCPT-2'-O-Me-cAMP and restored XRCC1 protein level following γ-ray irradiation. From these results, we conclude that the cAMP signaling system inhibits the repair of γ-ray-induced DNA damage by promoting the ubiquitin-proteasome dependent degradation of XRCC1 in an Epac-dependent pathway in lung cancer cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Seoul National University College of Medicine, Seoul 110-799, Republic of Korea.
authors.forename: Eun-Ah
authors.initials: EA
authors.lastname: Cho
authors.forename: Yong-Sung
authors.initials: YS
authors.lastname: Juhnn
mesh_terms: D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism*; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005720:Gamma Rays; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D059748:Proteolysis; D015398:Signal Transduction; D025801:Ubiquitin / Q000378:metabolism; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; C116122:RAPGEF3 protein, human; D025801:Ubiquitin; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; D000242:Cyclic AMP; D046988:Proteasome Endopeptidase Complex