title: The effects of retinoic acid on rat epidermal cells in vitro: changes in patterns of protein phosphorylation in relation to growth and differentiation.
abstract: Keratinocytes proliferate, stratify, and differentiate in vitro but if the calcium concentration of the medium is reduced to 0.07 mM Ca2+ (low calcium medium) the cells proliferate but do not stratify or differentiate. Keratinocytes proliferating in low calcium medium synthesized DNA at a higher rate than cultures of stratifying keratinocytes and this correlated with increased phosphorylation of a membrane-associated Mr 23,200 phosphoprotein (pp23) relative to cytosolic phosphoproteins of Mr 26,500 (pp27a and pp27b). In both normal and low calcium medium, all-trans-retinoic acid increased phosphorylation of pp23 relative to that of pp27 and increased DNA synthesis after 12-24 h. These results suggest that the phosphoproteins pp23 and pp27 are cell-cycle regulated and that the changes in phosphorylation were a consequence of a stimulation of cell proliferation by retinoic acid. The half-life of all-trans-retinoic acid in these cultures was about 6 h; increased DNA synthesis and concomitant changes in phosphorylation patterns also resulted from a 6-h pulse of retinoic acid followed by an 18-h washout period.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D002470:Cell Survival; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000096:biosynthesis; D003720:Densitometry; D004591:Electrophoresis, Polyacrylamide Gel; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects; D007633:Keratins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D010750:Phosphoproteins; D014212:Tretinoin; D007633:Keratins; D004247:DNA; D002118:Calcium