EPIDERMAL GROWTH-FACTOR RECEPTOR EXPRESSION AND FUNCTION CONTROL CYTOTOXIC RESPONSIVENESS TO TUMOR-NECROSIS-FACTOR IN ME-180 SQUAMOUS CARCINOMA-CELLS

Tumor necrosis factor (TNF) induces dose-dependent but incomplete cytotoxicity in ME-180 cervical carcinoma cells, suggesting that TNF response heterogeneity exists within this cell line. To investigate cellular properties associated with TNF-mediated cytotoxicity, ME-180 cell variants were isolated that stably expressed complete resistance (ME-180R) or sensitivity (ME-180S) to TNF and were compared to the parental cell line. Analysis of I-125-TNF binding on variant and parental cells provided evidence for postreceptor regulation of TNF responsiveness. Epidermal growth factor (EGF) receptor expression in TNF-resistant ME-180R cells was 3-fold higher than that expressed in the parental population and 4-fold higher when compared to TNF-sensitive ME-180S cells. High expression levels correlated with increased EGF receptor tyrosine kinase activity and receptor tyrosine phosphorylation. Southern and Northern blot analysis provided evidence of amplification and overexpression of the EGF receptor gene and its message in ME-180R cells which approached the content and alternate mRNA species expressed in A431 cells. Although 3-fold greater levels of total cellular EGF receptor protein were detected in ME-180R cell lysates, and its cell surface localization was confirmed by immunodetection, these cells were paradoxically unable to bind greater quantities of I-125-EGF or to express greater cytotoxic sensitivity to an EGF-diphtheria toxin fusion protein. Overall, these results suggest that expression of EGF receptor protein, its intrinsic tyrosine kinase activity, or its phosphotyrosine content may alter TNF cytotoxic signal transduction and control TNF responsiveness within the ME-180 cell line. Cell surface expression of an altered EGF receptor may also play a role in suppressing TNF cytotoxic signaling and may represent one mechanism of TNF resistance.