Cellular proliferation and ras oncogene of p21 21,000 expression in relation to the intracellular cyclic adenosine 3':5'-monophosphate levels of a human salivary gland adenocarcinoma cell line in culture.
We have found that reversible differentiation into the myoepithelial cells of a human salivary gland adenocarcinoma cell line (HSG) occurs in growth medium containing dibutyryl cAMP (dB-cAMP). In the current study, the relationship between intracellular cAMP levels and anchorage-dependent and -independent growth or ras oncogene of p21 levels was analyzed in the differentiation process toward myoepithelial cells of HSG cells cultured in the presence of dB-cAMP. Correlation between the concentrations of dB-cAMP and intracellular cAMP in the HSG cells was statistically significant. There was a significant inverse correlation between the concentrations of dB-cAMP and colony-forming ability of the cells in semisolid agar or on a plastic surface. We have found the expression of ras p21 protein in HSG cells. When HSG cells were cultured in the presence of dB-cAMP and were committed to differentiate into myoepithelial cells, it was shown by double-antibody labeling technique and/or immunoblotting that the committed cells expressed myosin with a concomitant decrease of ras p21 protein. Moreover, intracellular cAMP levels were found to be inversely associated with ras p21 content of the cells. These findings indicate that the intracellular cAMP levels regulate significantly cell proliferation and ras p21 expression in HSG cells.