INTERFERON-ENHANCEMENT OF TYROSINE PHOSPHORYLATION OF EPIDERMAL GROWTH-FACTOR RECEPTORS IN HUMAN BREAST-CARCINOMA CELLS

Interferons have been postulated to inhibit cell growth by modulating the cellular response to growth factors. We now demonstrate that inter feron increases tyrosine phosphorylation of EGFR in the human breast c arcinoma cell line MDA 468, in the presence of EGF. The kinase activit y of EGFR was elevated about two-fold when cells were cultured in the presence of IFN. Antiphosphotyrosine immunoblotting revealed that phos phorylation was increased two-fold on tyrosine residues in EGFR. These results suggest that IFN affects EGF signal transduction, and that su ch changes may play a role in growth inhibition induced by IFN in MDA 468 cells.