title: Nitric Oxide Down-Regulates Topoisomerase I and Induces Camptothecin Resistance in Human Breast MCF-7 Tumor Cells.
abstract: Camptothecin (CPT), a topoisomerase I poison, is an important drug for the treatment of solid tumors in the clinic. Nitric oxide (·NO), a physiological signaling molecule, is involved in many cellular functions, including cell proliferation, survival and death. We have previously shown that ·NO plays a significant role in the detoxification of etoposide (VP-16), a topoisomerase II poison in vitro and in human melanoma cells. ·NO/·NO-derived species are reported to modulate activity of several important cellular proteins. As topoisomerases contain a number of free sulfhydryl groups which may be targets of ·NO/·NO-derived species, we have investigated the roles of ·NO/·NO-derived species in the stability and activity of topo I. Here we show that ·NO/·NO-derived species induces a significant down-regulation of topoisomerase I protein via the ubiquitin/26S proteasome pathway in human colon (HT-29) and breast (MCF-7) cancer cell lines. Importantly, ·NO treatment induced a significant resistance to CPT only in MCF-7 cells. This resistance to CPT did not result from loss of topoisomerase I activity as there were no differences in topoisomerase I-induced DNA cleavage in vitro or in tumor cells, but resulted from the stabilization/induction of bcl2 protein. This up-regulation of bcl2 protein in MCF-7 cells was wtp53 dependent as pifithrine-α, a small molecule inhibitor of wtp53 function, completely reversed CPT resistance, suggesting that wtp53 and bcl2 proteins played important roles in CPT resistance. Because tumors in vivo are heterogeneous and contaminated by infiltrating macrophages, ·NO-induced down-regulation of topoisomerase I protein combined with bcl2 protein stabilization could render certain tumors highly resistant to CPT and drugs derived from it in the clinic.
authors.affiliation: Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Nilesh K
authors.initials: NK
authors.lastname: Sharma
authors.affiliation: Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Kumar
authors.affiliation: Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Amrita
authors.initials: A
authors.lastname: Kumari
authors.affiliation: National Toxicology Program, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Tokar
authors.affiliation: National Toxicology Program, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Waalkes
authors.affiliation: Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Carl D
authors.initials: CD
authors.lastname: Bortner
authors.affiliation: Laboratory of Structural Biology, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Jason
authors.initials: J
authors.lastname: Williams
authors.affiliation: Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Marilyn
authors.initials: M
authors.lastname: Ehrenshaft
authors.affiliation: Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Ronald P
authors.initials: RP
authors.lastname: Mason
authors.affiliation: Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle, Park, Durham, North Carolina, United States of America.
authors.forename: Birandra K
authors.initials: BK
authors.lastname: Sinha
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics*; D002166:Camptothecin / Q000494:pharmacology*; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics*; D005047:Etoposide / Q000494:pharmacology; D019073:HT29 Cells; D006801:Humans; D061986:MCF-7 Cells; D009569:Nitric Oxide / Q000378:metabolism*; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D059004:Topoisomerase I Inhibitors; D009569:Nitric Oxide; D005047:Etoposide; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D002166:Camptothecin