title: Tumor-promoting phorbol ester and ras oncogene expression inhibit the glucocorticoid-dependent transcription from the mouse mammary tumor virus long terminal repeat.
abstract: Oncogene activation has been suggested to play some role in determining the hormone independency of tumors. In order to study the role of protein kinase C in mediating the inhibition of the glucocorticoid-dependent transcription from the Mouse Mammary Tumor Virus (MMTV)-Long Terminal Repeat induced by overexpressed activated ras oncogene, we studied the effects of protein kinase C activators [the tumor promoting phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA)] and inhibitors [1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7)] on the dexamethasone (DEX)-mediated activation of a MMTV-Long Terminal Repeat-chloramphenicol acetyltransferase (pMMTV-CAT) chimeric reporter gene transiently transfected into NIH-3T3 cells and in Ha-ras-transformed fibroblasts (T24-NIH-3T3). TPA (30 ng/ml) together with DEX (0.1 microM) treatment of NIH-3T3 cells resulted in a significant decrease of CAT activity from pMMTV-CAT, compared to DEX treatment alone. The addition of H-7 (40 microM) was able to overcome the TPA-induced inhibition of DEX-dependent transcription from pMMTV-CAT. DEX-dependent expression of pMMTV-CAT was significantly reduced in T24-NIH-3T3 with respect to wild-type NIH-3T3 cells. Treatment of T24-NIH-3T3 cells with either H-7 or TPA significantly enhanced or decreased, respectively, the DEX-dependent expression of pMMTV-CAT. TPA and/or H-7 did not affect CAT activity from either pMMTV-CAT in the absence of DEX or from CAT gene under the control of the SV40 promoter. Similar glucocorticoid receptor sites and binding affinities were observed in T24-NIH-3T3 or TPA-treated NIH-3T3 cells compared to wild-type untreated cells. Our data suggest that activation of PKC is involved in the reduced transcriptional regulatory activity of glucocorticoid hormone induced by overexpressed Ha-ras oncogene in NIH-3T3 fibroblasts.
authors.affiliation: Department of Experimental Medicine, University La Sapienza, Rome, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Vacca
authors.forename: I
authors.initials: I
authors.lastname: Screpanti
authors.forename: M
authors.initials: M
authors.lastname: Maroder
authors.forename: E
authors.initials: E
authors.lastname: Petrangeli
authors.forename: L
authors.initials: L
authors.lastname: Frati
authors.forename: A
authors.initials: A
authors.lastname: Gulino
mesh_terms: D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D005696:Galactosidases / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D015967:Gene Expression Regulation, Viral; D005814:Genes, Viral; D011905:Genes, ras / Q000187:drug effects*; D005938:Glucocorticoids / Q000502:physiology*; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection
chemical_list: D005938:Glucocorticoids; D010703:Phorbol Esters; D011965:Receptors, Glucocorticoid; D015500:Chloramphenicol O-Acetyltransferase; D011493:Protein Kinase C; D005696:Galactosidases