title: The role of repair protein Rad51 in synergistic cytotoxicity and mutagenicity induced by epidermal growth factor receptor inhibitor (Gefitinib, IressaR) and benzo[a]pyrene in human lung cancer.
abstract: Rad51 protein is essential for homologous recombination repair of DNA damage, and is over-expressed in chemo- or radioresistant carcinomas. The polycyclic hydrocarbon carcinogen benzo[a]pyrene (B[a]P) affects MAPKs transduction pathways. Gefitinib (IressaR, ZD1839) is a selective epidermal growth factor receptor tyrosine kinase inhibitor that blocks growth factor-mediated cell proliferation and ERK1/2 activation. We hypothesized that gefitinib enhances B[a]P-mediated cytotoxicity by decreasing ERK1/2 activation. Exposure of human lung cancer cells to gefitinib decreased B[a]P-elicited ERK1/2 activation and induced Rad51 protein expression. Gefitinib and B[a]P co-treatment decreased Rad51 protein stability by triggering degradation via a 26S proteasome-dependent pathway. Expression of constitutive active MKK1/2 vectors (MKK1/2-CA) rescues the decreased ERK1/2 activity, and restores Rad51 protein level and stability under gefitinib and B[a]P co-treatment. Gefitinib enhances B[a]P-induced growth inhibition, cytotoxicity and mutagenicity. Co-treatment with gefitinib and B[a]P can further inhibit cell growth significantly after depletion of endogenous Rad51 by siRad51 RNA transfection. Enhancement of ERK1/2 activation by MKK1-CA expression decrease B[a]P- and gefitinib-induced cytotoxicity, and B[a]P-induced mutagenicity. Rad51 protein protects lung cancer cells from synergistic cytotoxic and mutagenic effects induced by gefitinib and B[a]P. Suppression of Rad51 protein expression may be a novel lung cancer therapeutic modality to overcome drug resistance to gefitinib.
authors: Department of Internal Medicine, Hsinchu Hospital, Taiwan.
authors: Jen-Chung
authors: JC
authors: Ko
authors: Jhao-Hao
authors: JH
authors: Hong
authors: Lyu-Han
authors: LH
authors: Wang
authors: Yun-Wei
authors: YW
authors: Lin
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D001564:Benzo(a)pyrene / Q000633:toxicity*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D000077156:Gefitinib; D006801:Humans; D008175:Lung Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D009153:Mutagens / Q000633:toxicity*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011799:Quinazolines / Q000633:toxicity*; D034622:RNA Interference; D051135:Rad51 Recombinase / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D009153:Mutagens; D011799:Quinazolines; D001564:Benzo(a)pyrene; D066246:ErbB Receptors; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D046988:Proteasome Endopeptidase Complex; D000077156:Gefitinib