Transforming growth factor beta modulation of the epidermal growth factor Ca2+ signal and c-Fos oncoprotein levels in A431 human epidermoid carcinoma cells.

Transforming growth factor beta (TGF beta) was examined regarding its regulation of the mitogen EGF. A431 human epidermoid carcinoma cells were treated with TGF beta and epidermal growth factor (EGF) (10 ng/ml each) to determine if TGF beta modulates EGF-induced Ca2+ signaling and c-Fos oncoprotein levels. Changes in [Ca2+]i were determined by digital imaging analysis or photon counting. In HBSS + Ca2+ (1.37 mM), EGF 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 nM. In nominally Ca(2+)-free (2-5 muM) HBSS, EGF caused a [Ca2+]i elevation that peaked at 140 nM and returned to baseline. TGF beta in HBSS + Ca2+ did not elicit a [Ca2+]i increase, although affinity labeling revealed types I, II, and III TGF beta receptors. TGF beta added simultaneously 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 treatments increased c-Fos immunoreactivity by around 1 h. In summary, EGF elevated [Ca2+]i in the presence or absence of [Ca2+]e, resulting in high [Ca2+]n, associated with tyrosine and threonine phosphorylation, and increased c-Fos oncoprotein immunoreactivity. TGF beta did not increase [Ca2+]i but did increase c-Fos; TGF beta + EGF added simultaneously altered the EGF-induced [Ca2+]i elevation, and TGF beta pretreatment eliminated EGF-induced [Ca2+]i elevation. This suggests that TGF beta can regulate EGF in A431 cells and that increased c-Fos may not be mediated by Ca2+.