Epidermal growth factor receptor gene amplification is correlated with laminin-5 γ2 chain expression in oral squamous cell carcinoma cell lines

Both epidermal growth factor receptor (EGFR) gene amplification and laminin (Ln)-5 γ2 chain overexpression have been reported to be poor prognostic factors in patients with squamous cell carcinoma (SCC) of the head and neck. Here we report our investigation of the relationship between EGFR gene amplification and Ln-5 γ2 chain expression in seven SCC cell lines, since both epidermal growth factor (EGF) signaling and Ln-5 γ2 have been reported to be involved in cell motility. The degree of correlation between EGFR gene amplification and Ln-5 γ2 chain expression was evaluated by Southern and Western blot analyses. EGFR gene amplification was detected in all SCC cell lines at levels 5-50 times those in DNA from normal liver tissue. EGFR gene amplification increased with Ln-5 γ2 chain protein expression in seven cell lines, showing close correlation between EGFR gene amplification and Ln-5 γ2 chain protein expression. In order to show the causal relationship, we analyzed the effects of transforming growth factor-α (TGF-α), tyrosine kinase inhibitor of EGFR, and neutralizing antibody against EGFR, on the expression of Ln-5 γ2 in these cell lines. In two cell lines in which EGFR gene amplification was low, expression of both protein and mRNA of the Ln-5 γ2 chain increased in the presence of TGF-α, and Ln-5 γ2 chain expression was inhibited by neutralizing antibody against EGFR. In all cell lines, Ln-5 γ2 chain expression was inhibited by tyrosine kinase inhibitor which acts selectively on the EGFR signal transduction pathway under the stimulus of TGF-α. These results suggest that EGFR gene amplification and the EGFR signaling pathway can act as positive regulators on the induction of the Ln-5 γ2 chain secreted by tumor cells.