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Expression of TGF‐α/EGF and TGF‐p receptors in human colon carcinoma cell lines

Previous studies have established that colon carcinoma cells secrete several polypeptide growth factors, including TGF‐α/EGF and TGF‐ß, suggesting that these and related molecules function in an autocrine/paracrine fashion to modulate tumor‐cell growth. To investigate this possibility, we have studied the expression of transforming growth factor receptors in a panel of human colon carcinoma cell lines and in several untransformed epithelial cell populations. The results have revealed that neoplastic colon cells express receptors for both TGF‐α/EGF and TGF‐ß. Immunoprecipitation identified the TGF‐α/EGF receptor as a structurally intact 170‐kDa protein. No evidence for over‐expression was found. TGF‐α (and EGF) enhanced receptor autophosphorylation, indicating that these receptors were biochemically functional. TGF‐ß blocked DNA synthesis in non‐neoplastic epithelial cells but not in tumorigenic colon populations. There was no correlation with TGF‐ß receptor number or dissociation constant. However, chemical cross‐linking studies revealed a TGF‐ß receptor subtype of 75 kDa in 3 of the 4 colon carcinoma cells which was undetectable in normal IEC epithelial cultures, suggesting a possible association between 75‐kDa receptor expression and refractoriness to growth inhibition of TGF‐ß. Together, these data support the concept that locally‐produced growth regulators can function in an autocrine or paracrine manner to influence the proliferation of colon carcinoma cells.