Differential down-regulation of epidermal growth factor receptors expressed in the metastatic variants of human lung cancer adenocarcinoma cell line DMS4C.

The metastatic variants of human lung adenocarcinoma cell line DMS4C were established by selection in vivo. Lung, brain, spleen and liver metastatic tumors derived from intracarotid inoculation of athymic BALB/c mice were collected, and their corresponding variant cell lines established. The epidermal growth factor (EGF) receptor expression of the parental cell line as well as the metastatic variant cell lines were investigated. 125I-labeled EGF binding assays showed that there were two types of EGF receptors in both parental and metastatic variants. Compared to DMS4C, the EGF binding capacities were found to be down-regulated by 70, 79, 85 and 89% for lung, spleen, liver and brain variant, respectively. The dissociation constants of spleen, liver and brain EGF receptors were distinct from that of the parental cell line. The EGF receptor autophosphorylation activity of lung variant was shown to be down-regulated as shown by immune complex kinase assay that corresponded to EGF receptor numbers whereas kinase activities of the liver, spleen and brain variants EGF receptors were completely abolished. However, the 170 kilodalton EGF receptor was shown to be unaltered during metastasis. The results indicated that, during metastasis progression, the proliferation of adenocarcinoma cells may have adopted a different growth regulation that is independent of EGF receptor kinase-modulated autocrine pathway. The result also implies that other oncogene may emerge as the major growth regulator for distant metastasis of adenocarcinoma cancer cells. This work provides a model for understanding tumor metastasis progression of human lung cancer.