title: Retinoic acid-induced AP-1 transcriptional activity regulates B16 mouse melanoma growth inhibition and differentiation.
abstract: Retinoic acid (RA) inhibits growth and induces differentiation of B16 mouse melanoma cells. These effects are accompanied by a large increase in PKCalpha mRNA and protein levels and surprisingly an increase in activating protein-1 (AP-1) transcriptional activity. To further investigate the RA-induced AP-1 activity we established clones of B16 cells stably expressing an AP-1-luciferase reporter gene. Treatment of these clones with phorbol dibutyrate increased AP-1 activity which peaked at 2-4 h and returned to baseline level by 24 h. In contrast, RA treatment resulted in a slow increase in AP-1 activity that reached a maximum level at 48 h and was maintained for the duration of the treatment. We tested the importance of the RA-induced AP-1 activity by establishing clones which stably express a dominant negative fos gene (A-fos) and have greatly diminished AP-1 activity. Growth rates of untreated A-fos expressing cells were similar to wt B16 and clones not expressing A-fos. However, clones expressing the dominant-negative fos had a markedly decreased sensitivity to RA-induced inhibition of anchorage-dependent and -independent growth. Treatment of wt B16 cells for 48 h with RA increased melanin production by two to fourfold, but this effect was completely lost in the A-fos clones. The ability of RA to induce RARbeta and PKCalpha expression was retained in A-fos clones, suggesting that A-fos was not interfering with RAR transcription activation functions. We tested whether the RA-induced AP-1 activity might be mediated by the ERK1/2 MAPK pathway. Inhibition of ERK1/2 phosphorylation stimulated AP-1 activity, which was not additive to that induced by RA. This finding raises the possibility that this MAPK pathway may be a target of retinoid action. Our observations suggest that AP-1 transcriptional activity induced by RA likely plays an important role in the biological changes mediated by this retinoid in B16 melanoma cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, Joan C. Edwards School of Medicine, Marshall University, Huntington, West Virginia 25704, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Huang
authors.forename: Goran
authors.initials: G
authors.lastname: Boskovic
authors.forename: Richard M
authors.initials: RM
authors.lastname: Niles
mesh_terms: D000818:Animals; D001426:Bacterial Proteins; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D005799:Genes, Dominant; D005982:Glutathione Transferase / Q000502:physiology; D007527:Isoenzymes / Q000378:metabolism; D008543:Melanins / Q000037:antagonists & inhibitors; D008545:Melanoma / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism; D051571:Protein Kinase C-alpha; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects* / Q000502:physiology*; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D001426:Bacterial Proteins; D007527:Isoenzymes; D008543:Melanins; D018168:Receptors, Retinoic Acid; D018808:Transcription Factor AP-1; C082925:retinoic acid receptor beta; D015240:Phorbol 12,13-Dibutyrate; D014212:Tretinoin; D005982:Glutathione Transferase; C496630:Prkca protein, mouse; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha