Inhibition of the EGF receptor and ERK1/2 signaling pathways rescues the human epidermoid carcinoma A431 cells from IFNγ-induced apoptosis

Interferon gamma (IFN gamma) has been demonstrated to inhibit tumor growth in vivo as well as proliferation of multiple types of cultured transformed cells. In this study, we showed that IFN gamma promoted progressive death in A431 cells, overexpressing EGF receptor (EGFR). Based on the data provided by evaluating cell morphology, MTT assay, FACS analysis and cleaved caspase-3 staining we concluded that the major cause of IFN gamma-induced A431 cell growth inhibition was not cell cycle arrest, but apoptosis. We investigated a role for the EGFR and ERK1/2 MAPK signaling pathways in IFN gamma-induced apoptosis of A431 cells. IFN gamma-induced cell death was accompanied by both an increase of the ERK1/2 MAPK activation and a simultaneous reduction of the EGFR activation. Activation of ERK1/2 was crucial for IFN gamma-induced cell death because MEK1/2 inhibitors, PD0325901 and U0126 efficiently protected cells from apoptosis by suppressing caspase-3 activation. Even though EGFR tyrosine kinase inhibitor AG1478 also rescued A431 cells from IFN gamma-induced apoptosis, unlike MEK1/2 inhibitors, it initiated G(1) arrest. Together, these results suggest that sustained inhibition of both EGFR and ERK1/2 leads to significant protection of the cells from IFN gamma-induced apoptosis, indicating important roles for the EGFR tyrosine kinase and ERK1/2 MAP-kinases in regulating A431 cell death.