The role of transforming growth factor-alpha (TGF-alpha) and the epidermal growth factor (EGF) receptor in the growth of human colon carcinoma cell lines will be examined. We hypothesize that altered processing of and response to TGF-alpha and the EGF receptor may be responsible for the heterogeneous growth properties of colon carcinoma cells. There are qualitative and quantitative differences in TGF-alpha secreted by different colon cell lines. Further characterization of the biosynthesis and secretion of TGF-alpha, including the possible role of protein kinase C in the regulation of TGF-alpha processing, will be addressed. This involves immunoprecipitation of biosynthetically labeled TGF-alpha with antibodies specific to different domains of the precursor molecule and analysis by polyacrylamide gel electrophoresis. The role of the differentiation agent N,N-dimethylformamide in TGF-alpha secretion and processing will also be examined. Experiments using antibodies to TGF-alpha and the EGF receptor showed that the well differentiated colon cells utilize TGF-alpha as an autocrine growth factor while these antibodies do not alter the growth of poorly differentiated cells. The differences in EGF receptor processing in the different colon cells will be addressed to determine if this is related to the different response to TGF-alpha. Possible constitutive expression of the EGF receptor kinase activity or components of the signal transduction pathway will be explored. Culture of the poorly differentiated HAT 116 cell line in the presence of EGF results in a 2-fold slower growth rate on extracellular matrix (ECM) compared to growth on plastic. EGF itself does not alter the growth rate of these cells. This phenotype will be characterized with respect to alteration in the synthesis or degradation of individual ECM components and their receptors. Information concerning the involvement of TGF-alpha and the EGF receptor in the growth control mechanisms in colon carcinoma cells will be useful for the development of new drugs against colon cancer.
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