Transforming growth factor-α (TGF-α)-mediated autocrine regulation in human non-small-cell lung cancer (NSCLC) cells NCI-H226 and its brain metastatic variant H226Br were compared. An enhanced TGF-α-induced dose-dependent mitogenic responsiveness in H226Br cells was observed. Neutralising antibody that binds TGF-α inhibits H226Br cell growth more effectively than NCI-H226 cell growth. Binding assay with 125I-labelled epidemlal growth factor (EGF) revealed that H226Br has two types of EGF receptors (EGFRs), whereas the parental cell line, NCI-H226, has only one. H226Br cells contain twice as many EGFRs as H226 cells, as proved by Scatchard analysis and immune kinase assay. Northern analysis indicated that there is more EGFR transcript in H226Br than in NCI-H226, indicating a transcriptional EGFR gene elevation during metastasis progression. The level of accumulated immunoactive TGF-α is lower in the conditioned medium of H226Br than in that of NCI-H226, demonstrating down-regulation of TGF-α transcript. The accumulated data suggest an elevated and sensitive autocrine modulation by TGF-α and EGFR in immortalising the brain metastatic variant cells that were derived from a human NSCLC squamous cell line.
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