STUDIES ON MECHANISM OF AUTOCRINE GROWTH OF A HUMAN SALIVARY GLAND ADENOCARCINOMA BY EPIDERMAL GROWTH FACTOR

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The human salivary gland adenocarcinoma cell line HSG proliferates autonomously, with the proliferation mediated by an autocrine growth factor, a Mr.46K epidrmal growth factor(EGF)-like molecule. In this project, the mechanism of autocrine growth of HSG by EGF-like molecule was investigated. Firstly, the expression of the intuitive candidates for the receptor, EGF receptor (EGF-R) and c-erbB2 protooncogene product, p185^<erbB2>, which closely resembles EGF-R and seems also to be a cell surface receptor, was examined. Immunoprecipitation and immunoblotting analyzes using the antibody specific to each protein revealed the expression of both EGF-R and p185^<erbB2> in HSG cells. Northern blotting analyzes also revealed the expression of 5.6 kb EGF-R mRNA and 4.6 kb c-erbB2 mRNA.The co-expression of EGF-R and p185^<erbB2> was also confirmed by immunohistochemical analyzes. When EGF-like molecule was added to the HSG cell cultures, only 170K EGF-R was autophosphorylated, and p185^<erbB2> was not. These result suggested that, although both EGF-R and p185^<erbB2> are co-expressed in HSG cells, the EGF-R is the genuine receptor for the EGF-like molecule. However, there is a possibility that p185^<erbB2> is involved in the signal transduction system. This was examined by using specific antibodies to hEGF-R, p185^<erbB2>, and EGF to inhibit the functions of these molecules. Addition of these three antibodies to the cultures inhibited the growth of HSG cells. Particularly, the effect of the anti-p185^<erbB2> antibody was the strongest in three antibodies. Moreover, the antibodies to EGF-R and p185^<erbB2> caused morphological changes such as disturbances of the plasma membrane, and some cell death. Thus, p185^<erbB2> expressed in EGF as well as EGF-R has an important function in the signal transduction of HSG cell growth.