EVIDENCE FOR SEPARATE CONTROL MECHANISMS AT THE MESSAGE, PROTEIN, ANDENZYME ACTIVATION LEVELS FOR TRANSGLUTAMINASE DURING CALCIUM-INDUCED DIFFERENTIATION OF NORMAL AND TRANSFORMED HUMAN KERATINOCYTES

We analyzed the effects of three different calcium concentrations on t he RNA and functional protein levels of transglutaminase (TGase) and i nvolucrin (INV) over time in culture, We compared the results in norma l human keratinocytes with those in a squamous cell carcinoma, SCC4. T he highest calcium concentration (1.2 mM) induced the greatest levels of INV and TGase message, INV protein, and rates of CE formation, but not maximal levels of TGase protein, By examining cytosol and membrane fractions of keratinocytes, we found that after synthesis, TGase prot ein shifts, under the influence of calcium (both 0.1 mM and 1.2 mM), f rom the cytosol into the membrane in postconfluent cells, However, onl y 1.2 mM calcium induced significant amounts of TGase activity. These data indicate that elevated calcium (1.2 mM) achieves the expected ind uction in keratinocyte differentiation by regulation of not only INV a nd TGase message levels, but also the translation and activation of TG ase protein. Our data suggest that this calcium-induced activation of TGase protein occurs while the protein is anchored in the membrane. In contrast, despite ample INV and TGase message levels within SCC4 cell s, these RNA levels are not regulated by calcium or translated into pr otein, suggesting that the transformed phenotype of SCC4 cells results not only in a failure of calcium to regulate gene transcription, but also in a defect within the translation machinery of these differentia tion-specific proteins.