title: Regulation of expression of the DNA repair gene O6-methylguanine-DNA methyltransferase via protein kinase C-mediated signaling.
abstract: O6-Alkylguanine is the major mutagenic and cytotoxic DNA lesion induced by alkylating agents, including 2-chloroethyl-N-nitrosourea-based antitumor drugs. This lesion is repaired by O6-methylguanine-DNA methyltransferase (MGMT), the expression of which is highly variable in both normal tissues and in tumor cells. The promoter of the human MGMT gene was found to contain two putative activator protein (AP)-1 sites. Here, we show that the level of MGMT mRNA in HeLa S3 cells was increased 3-5-fold by phorbol-12-myristate-13-acetate (TPA) and 1,2-diacyl-sn-glycerol (DAG), which are activators of protein kinase C (PKC), as well as by okadaic acid, an inhibitor of protein phosphatases. The PKC inhibitor 1-(5-isoquinoline sulfonyl)-2-methylpiperazine-HCl eliminated MGMT activation by TPA and DAG but not by OA. Prior down-regulation of PKC abolished subsequent effects of TPA or DAG. The results indicate AP-1 to be involved in regulation of MGMT expression. This hypothesis was supported by showing AP-1 binding to two target sequences of the MGMT promoter and transactivation of the MGMT promoter upon cotransfection with c-fos and c-jun in F9 cells. That TPA-mediated induction of MGMT caused increased cellular resistance to 2-chloroethyl-N-nitrosourea suggests a therapeutic significance for PKC-mediated MGMT modulation.
authors.affiliation: Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston 77555-1079, USA.
authors.forename: I
authors.initials: I
authors.lastname: Boldogh
authors.forename: C V
authors.initials: CV
authors.lastname: Ramana
authors.forename: Z
authors.initials: Z
authors.lastname: Chen
authors.forename: T
authors.initials: T
authors.lastname: Biswas
authors.forename: T K
authors.initials: TK
authors.lastname: Hazra
authors.forename: S
authors.initials: S
authors.lastname: Grösch
authors.forename: T
authors.initials: T
authors.lastname: Grombacher
authors.forename: S
authors.initials: S
authors.lastname: Mitra
authors.forename: B
authors.initials: B
authors.lastname: Kaina
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology; D004260:DNA Repair; D019008:Drug Resistance, Neoplasm; D015971:Gene Expression Regulation, Enzymologic; D006367:HeLa Cells; D006801:Humans; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000096:biosynthesis / Q000235:genetics*; D019319:Okadaic Acid / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000378:metabolism
chemical_list: D000477:Alkylating Agents; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D019319:Okadaic Acid; D019853:O(6)-Methylguanine-DNA Methyltransferase; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate