title: Relative resistance to 1,25-dihydroxyvitamin D3 in a keratinocyte model of tumor progression.
abstract: We have examined the effect of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on mitogen-stimulated growth and on c-myc proto-oncogene expression in a keratinocyte model of tumor progression. A dose-dependent inhibition of cell growth by 1,25-(OH)2D3 was demonstrated in both established (HPK1A) and malignant (HPK1A-ras) cells. However, this inhibition was observed with the addition of 1,25-(OH)2D3 at a higher concentration in HPK1A-ras cells than in HPK1A cells. Cell cycle analysis revealed a blockage of the normal progression of the cell cycle from G0 to S phase in the presence of 1,25-(OH)2D3. A higher concentration of 1,25-(OH)2D3 was required in HPK1A-ras cells to overcome the mitogen-stimulated progression into S phase, when compared with HPK1A cells. Analysis of c-myc messenger RNA revealed a strong inhibition of its expression at early time points with higher concentrations of 1,25-(OH)2D3 being required to obtain an inhibition in HPK1A-ras cells similar to that obtained in HPK1A cells. 1,25-(OH)2D3 receptor characterization by sucrose gradient analysis and equilibrium binding demonstrated the presence of a single 3.7 S protein with similar receptor numbers and affinity in both cell lines. These observations therefore demonstrate that an alteration of the growth inhibitory response to 1,25-(OH)2D3 occurs when keratinocytes acquire the malignant phenotype and suggest that the alteration lies beyond the interaction of the ligand with its receptor. In addition, relative resistance to 1,25-(OH)2D3 was also observed in the expression of the cell-cycle associated oncogene c-myc. These studies may therefore have important implications in vivo in the development and growth of epithelial cell cancers.
authors.affiliation: Department of Medicine, McGill University, Montreal, Quebec, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Sebag
authors.forename: J
authors.initials: J
authors.lastname: Henderson
authors.forename: J
authors.initials: J
authors.lastname: Rhim
authors.forename: R
authors.initials: R
authors.lastname: Kremer
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D002117:Calcitriol / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005434:Flow Cytometry; D016259:Genes, myc; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects*; D051379:Mice; D008819:Mice, Nude; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger / Q000378:metabolism; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism
chemical_list: C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D004815:Epidermal Growth Factor; D002117:Calcitriol