TRANSFORMING GROWTH-FACTOR-BETA MODULATION OF THE EPIDERMAL GROWTH-FACTOR CA2-FOS ONCOPROTEIN LEVELS IN A431 HUMAN EPIDERMOID CARCINOMA-CELLS( SIGNAL AND C)

Transforming growth factor beta (TGF beta) was examined regarding its regulation of the mitogen EGF, A431 human epidermoid carcinoma cells w ere treated with TGF beta and epidermal growth factor (EGF) (10 ng/ml each) to determine if TGF beta modulates EGF-induced Ca2+ signaling an d c-Fos oncoprotein levels. Changes in [Ca2+](i) were determined by di gital imaging analysis or photon counting. In HBSS + Ca2+ (1.37 mM), E GF treatment resulted in a transient increase in [Ca2+](i) from 75 to 150 nM, which lasted approximately 3.5 min and re-equilibrated to 90 n M, In nominally Ca2+-free (2-5 mu M) HBSS, EGF caused a [Ca2+](i) elev ation that peaked at 140 nM and returned to baseline, TGF beta in HBSS + Ca2+ did not elicit a [Ca2+](i) increase, although affinity labelin g revealed types I, II, and III TGF beta receptors. TGF beta added sim ultaneously with EGF in HBSS + Ca2+ caused a gradual rise in [Ca2+](i) from 50 to 100 nM over 16 min. Pretreatment with TGF beta (3 h; 10 ng /ml) abolished the EGF-induced [Ca2+](i) elevation. EGF or TGF beta tr eatments increased c-Fos immunoreactivity by around 1 h, In summary, E GF elevated [Ca2+](i) in the presence or absence of [Ca2+](e), resulti ng in high [Ca2+](n), associated with tyrosine and threonine phosphory lation, and increased c-Fos oncoprotein immunoreactivity. TGF beta did not increase [Ca2+](i) but did increase c-Fos; TGF beta + EGF added s imultaneously altered the EGF-induced [Ca2+](i) elevation, and TGF bet a pretreatment eliminated EGF-induced [Ca2+](i) elevation, This sugges ts that TGF beta can regulate EGF in A431 cells and that increased c-F os may not be mediated by Ca2+.