Induction of common patterns of polypeptide synthesis and phosphorylation by calcium and 12-O-tetradecanoylphorbol-13-acetate in mouse epidermal cell culture.
Terminal differentiation can be induced in cultured basal cells by either increasing the Ca2+ level in the medium from 0.05 to 1.4 mM or by exposure to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). If Ca2+ and TPA act by a common mechanism, then a common pattern of protein synthesis and/or phosphorylation would be expected. Computer-assisted analysis of radioactively labeled polypeptides separated by two-dimensional-polyacrylamide gel electrophoresis was utilized to study protein synthesis and phosphorylation. Within 1 h of increasing the Ca2+ level in the medium, the synthesis of 57 polypeptides was altered by 2-fold or more. Similarly, exposure to TPA for 1 h affected the synthesis of 106 polypeptides. Sixteen polypeptides were affected by both Ca2+ and TPA; the synthesis of nine was increased and seven was decreased, with changes in the same direction for both effectors. By 4 h, the synthesis of 32 polypeptides was similarly modulated by both Ca2+ and TPA. Only one polypeptide which was increased at 1 h was still elevated at 4 h. These results suggest that a common dynamic program of protein synthesis, likely to be related to terminal keratinocyte differentiation, is induced by both Ca2+ and TPA. Overall phosphorylation of epidermal proteins was increased after 30 min of TPA treatment, but was not increased by Ca2+ at this time. Keratin polypeptides were heavily phosphorylated in low Ca2+ medium, but the level or pattern of phosphorylation of these proteins was not altered by either Ca2+ or TPA. Although phosphorylation of a minor polypeptide (pI 5.1/Mr 45,000) was increased 2-3-fold by both Ca2+ and TPA, most of the specific protein phosphorylation changes induced in keratinocytes by Ca2+ and TPA appear to be unique. Thus, if protein phosphorylation is an early signal for epidermal differentiation by each effector, only a single apparent common substrate is involved and multiple kinases are activated. Alternatively, substrate specificity of a single kinase may be differentially altered by each effector.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D003201:Computers; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism*; D007163:Immunosorbent Techniques; D007526:Isoelectric Point; D051379:Mice; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism*; D014176:Protein Biosynthesis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D010750:Phosphoproteins; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium