Expression of a Cross-reactive Antigen on the Surface of Human Carcinomas Overproducing Epidermal Growth Factor Receptors Shared with RSV induced Tumors

Analysis based on the complement-dependent cytotoxicity (CDC) assays using syngeneic antiserum against a Rous sarcoma virus (RSV)-induced mouse tumor (CSA1M) showed that a cross-reactive antigen with a common tumor-associated cell surface antigen (TASA) of RSV-induced mouse tumors was shared with two human tumors A431 and MDA-468 overexpressing epidermal growth factor receptors (EGFRs). The TASA, however, was not expressed on four human choriocarcinomas, a human lung cancer A2182, and human embryo fibroblasts HEF. Immunofluorescent studies demonstrated that A431 did not express a src gene product detected by rabbit anti-pp60V-src serum. Two variant clones derived from A431 reducing number of EGFRs (cl-15 and cl-16) had almost the same growth rate and expression of transferrin receptor (Tf-R) in comparison with parental A431 cells. These clones, however, decreased the expression of the TASA. Furthermore, CDC assays and enzyme-linked immunosorbent assays (ELISA) revealed that A431 reduced the expression of the TASA by pretreatment of EGF, but not with insulin. A truncated form corresponding to extracellular domain of the EGFR blocked the cytotoxicity of anti-CSA1M serum to A431 and RSV-induced tumor cells. All these findings indicate a close association between a cross-reactive antigen with the TASA of RSV-induced tumors and the EGFR expression