title: Gamma-glutamylcysteine synthetase mediates the c-Myc-dependent response to antineoplastic agents in melanoma cells.
abstract: This study aims to investigate the role of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme for glutathione (GSH) synthesis, in the c-Myc-dependent response to antineoplastic agents. We found that specific c-Myc inhibition depleted cells of GSH by directly reducing the gene expression of both heavy and light subunits of the gamma-GCS enzyme and increased their susceptibility to antineoplastic drugs with different mechanisms of action, such as cisplatin (CDDP), staurosporine (STR), and 5-fluorouracil (5-FU). The effect caused by c-Myc inhibition on CDDP and STR response, but not to 5-FU treatment, is directly linked to the impairment of the gamma-GCS expression, because up-regulation of gamma-GCS reverted drug sensitivity, whereas the interference of GSH synthesis increased drug susceptibility as much as after c-Myc down-regulation. The role of gamma-GCS in the c-Myc-directed drug response depends on the capacity of drugs to trigger reactive oxygen species (ROS) production. Indeed, although 5-FU exposure did not induce any ROS, CDDP- and STR-induced oxidative stress enhanced the recruitment of c-Myc on both gamma-GCS promoters, thus stimulating GSH neosynthesis and allowing cells to recover from ROS-induced drug damage. In conclusion, our data demonstrate that the gamma-GCS gene is the downstream target of c-Myc oncoprotein, driving the response to ROS-inducing drugs. Thus, gamma-GCS impairment might specifically sensitize high c-Myc tumor cells to chemotherapy.
authors.affiliation: Experimental Chemotherapy Laboratory, Experimental Research Center, Regina Elena Cancer Institute, Via delle Messi d'Oro 156, 00158 Rome, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Benassi
authors.forename: Gabriella
authors.initials: G
authors.lastname: Zupi
authors.forename: Annamaria
authors.initials: A
authors.lastname: Biroccio
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D005472:Fluorouracil / Q000494:pharmacology; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism*; D005978:Glutathione / Q000096:biosynthesis; D006801:Humans; D008545:Melanoma / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D016271:Proto-Oncogene Proteins c-myc; D017382:Reactive Oxygen Species; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione; D019311:Staurosporine; D002945:Cisplatin; D005472:Fluorouracil