REGULATION OF MASTOMYS ECL CELL-FUNCTION BY TRANSFORMING GROWTH-FACTOR-ALPHA

Little progress has been made in the understanding of the pathobiology of gastric neoplasia over the past 4 decades. This reflects the pauci ty of information available regarding the biology of gastric mucosal c ell proliferation. More recently it has become apparent that growth fa ctor regulation of cell proliferation is of considerable relevance in initiating mucosal mitogenesis. We have recently identified the histam ine secreting enterochromaffin-like (ECL) cell as a pivotal cellular r egulator of gastric acid secretion. In addition to its critical role i n initiating acid secretion, we have proposed that the ECL cell may pr oduce agents responsible for the regulation of mucosal cell proliferat ion. We have therefore hypothesized that such a function may be subser ved by production of transforming growth factor alpha (TGF alpha). TGF alpha is known to play a significant role both in normal physiology a nd in the transformation of naive cells into a neoplastic form. We the refore proposed that increased levels of gastrin induced by low acid s tates might stimulate TGF alpha secretion and that this agent might be capable of regulating ECL cell DNA synthesis and cell proliferation. We used the mastomys rodent to generate an in vivo hypergastrinemia mo del using long-term histamine-a receptor blockade (loxtidine 1 mg/kg/d ay). In order to evaluate the cell-specific effects, we developed a pu re isolated ECL cell system from the mastomys stomach. This utilized p ronase digestion (1.0 mg/ml) and EDTA exposure (1 mM) of the mucosa fo llowed by particle size separation with countercurrent elutriation and density purification on a Nycodenz step gradient. ECL cells were obta ined with a purity of 90-95%. Histamine secretion from ECL cells was m easured by radioimmunoassay (RIA). TGF alpha content was measured by R IA, and TGF alpha expression was measured by RNAse probe protection as say. DNA synthesis was quantified by measuring bromo-deoxyuridine (Brd U) incorporation into cultured cells. TGF alpha levels were increased in fundic mucosa after 16 weeks of hypergastrinemia (from 4.3 +/- 0.6 to 32.6 +/- 2.6 fmole/mg protein, P < 0.05). TGF alpha message was ide ntified in the ECL cells by RNAse probe protection assay, and was four fold amplified in ECL cell tumors after 16 weeks of exposure to hyperg astrinemia. Gastrin stimulated (10 nM) histamine secretion in isolated naive ECL cells was inhibited by TGF alpha (IC50 2 X 10(-10) M). DNA synthesis was stimulated by gastrin (EC(50) 2 X 10(-11) M) and TGF alp ha (EC(50) 5 X 10(-9) M). These data are consistent with the proposal that elevated gastrin levels are associated with ECL cell TGF alpha pr oduction and that TGF alpha stimulates ECL cell DNA synthesis. (C) 199 6 Academic Press, Inc.