title: Cell growth inhibition by okadaic acid involves gut-enriched Kruppel-like factor mediated enhanced expression of c-Myc.
abstract: Human breast cancer (HBC) cell growth suppression by okadaic acid (OA) was previously found to involve elevated expression of oncogenes c-myc and c-fos and apoptosis. Since, c-Myc influences diverse pathways of cell growth, we hypothesized that elevated levels of c-Myc are involved in HBC growth suppression. Here, we investigated whether induction of c-Myc by OA or protein synthesis inhibitor cycloheximide contributed to HBC growth inhibition and the mechanisms involved. OA, cycloheximide, or the chemotherapeutic drug Taxol suppressed HBC cell growth. However, OA or cycloheximide treatments over 6 or 10 h, respectively, induced c-Myc expression. Depletion of c-Myc, on the other hand, resulted in enhanced HBC cell viabilities when exposed to OA or cycloheximide, but not by Taxol. OA induced c-myc transcription by targeting an 80-bp region from positions -11 to +70, relative to the P1 transcription start of mouse c-myc promoter. Gel mobility shift assays revealed binding of HBC cell nuclear proteins to the OA-responsive c-myc promoter fragment, whereas binding of one complex was elevated in the case of the OA-treated or cycloheximide-treated HBC cell nuclear extracts. Database search revealed presence of a consensus sequence for zinc finger protein gut-enriched Kruppel-like factor (GKLF) in OA-responsive region of the c-myc promoter. Mutation of GKLF consensus sequences abrogated OA responsiveness of the c-myc promoter, and OA treatments caused enhanced expression of GKLF in HBC cells. Thus, OA-dependent attenuation of HBC growth is accomplished, in part, by zinc finger transcription factor GKLF-mediated enhanced transcription of c-myc.
authors.affiliation: John D. Dingell V.A. Medical Center and Department of Internal Medicine, Wayne State University, Detroit, Michigan 48201, USA.
authors.forename: Liyue
authors.initials: L
authors.lastname: Zhang
authors.forename: Anil
authors.initials: A
authors.lastname: Wali
authors.forename: Chilakamarti V
authors.initials: CV
authors.lastname: Ramana
authors.forename: Arun K
authors.initials: AK
authors.lastname: Rishi
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000502:physiology*; D019319:Okadaic Acid / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000032:analysis / Q000235:genetics*; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: C000715467:KLF4 protein, human; C000715468:Klf4 protein, mouse; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D016271:Proto-Oncogene Proteins c-myc; D019319:Okadaic Acid; D003513:Cycloheximide