Retinoic acid and calcium regulation of p53, transforming growth factor-beta 1, and transforming growth factor-alpha gene expression and growth in adenovirus 12-SV40-transformed human tracheal gland epithelial cells.

Abstract

Vitamin A and calcium are important regulators of growth and differentiation of epithelial cells and are intimately involved in preneoplastic and neoplastic transformation. It has been proposed that their effects are mediated by autocrine/paracrine positive and negative regulators of growth. The objectives of this investigation were to examine the effects of all-trans retinoic acid (RA) and Ca2+ on cell proliferation, anchorage-independent growth (AIG), and on the expression of transforming growth factor-alpha (TGF-alpha), transforming growth factor-beta 1 (TGF-beta 1), and p53 tumor suppressor genes in human tracheal gland epithelial (HTGE) cells immortalized by adenovirus 12-simian virus 40 (Ad12-SV40) hybrid. Cells exhibiting the transformed phenotype, AIG, were maintained in serum-free culture conditions. Calcium effects were examined at 0.15, 0.50, 1.0, and 2.0 mM concentrations. The effects of RA were determined with 10(-9), 10(-7), and 10(-6) M concentrations. Gene expression was examined by Northern and Western analyses. Ca2+ had no significant effect on cell proliferation, but it enhanced the expression of TGF-beta 1 gene and slightly inhibited p53 expression. Ca2+ had no effect on TGF-alpha. RA inhibited both cell proliferation and AIG growth, which was accompanied by enhanced expression of p53. RA had no significant effect on the expression of TGF-alpha and TGF-beta 1 genes. These results demonstrate that RA regulates growth of HTGE cells mainly by upregulating the p53 gene; Ca2+, which enhances TGF-beta 1 expression, had no effect on growth.