We have recently characterized the growth-inhibitory and cellular responses [carcinoembryonic antigen (CEA) secretion, protein secretion, protein expression, fibronectin and laminin synthesis] of the human colon carcinoma MOSER cell line to transforming growth factor-β (TGF-β) (Cancer Res., 47: 2950, 1987; 48: 4059, 1988). We have also recently isolated a subline (MOSER R2) from the parental MOSER cells which, unlike the parental line, is relatively resistant to the growth-inhibitory effect of TGF-β (Biochem. Biophys. Res. Commun., 150: 711, 1988). We now report on the characterization of the cellular responses of this resistant MOSER R2 subline to TGF-β and compare its responses to that of the highly growth-inhibition-sensitive MOSER cell line. In view of the reported relationship between CEA expression and differentiation in colon cancer and the ability of colon-derived substrata material to modulate the phenotypic properties of colon cancer cells, additional characterization and direct comparison of the effects of TGF-β on the two cell lines were also performed with respect to (a) cellular expression of CEA and CEA cross-reactive glycoproteins; and (b) colon-derived substrata material.
Unlike the growth-inhibition-sensitive MOSER cells, TGF-β had no effects on fibronectin/laminin synthesis nor on the cellular morphology of the resistant MOSER R2 cells. TGF-β was also unable to modulate protein secretion and deposition of substrata material by these cells. However, several other responses of the resistant cells to TGF-β were found to be similar to that of the sensitive MOSER cells. These responses include: (a) a prolonged and stable secretion of CEA; (b a prolonged and stable induction of elevated cellular expression of CEA and CEA cross-reactive glycoproteins; and (c) enhancement of the expression of three cellular proteins with molecular weights corresponding to 52,000, 48,000, and 42,000. We further report that the differences observed in the responses to TGF-β in the two cell lines were not due to differences in TGF-β binding or other receptor parameters such as the expression of distinct TGF-β receptor subspecies.
Supported by USPHS Grant CA47775 (S. C.) and by ACS Grant PDT-324 (J. V.).