Lawton G P, Tang L, Kidd M, Chinery R, Miu K, Modlin I M
Gastrointestinal Surgical Pathobiology Research Group, Department of Surgery, Yale University School of Medicine, New Haven, Connecticut 06520-8062, USA.
J Surg Res. 1996 Feb 1;60(2):293-302. doi: 10.1006/jsre.1996.0046.
Little progress has been made in the understanding of the pathobiology of gastric neoplasia over the past 4 decades. This reflects the paucity of information available regarding the biology of gastric mucosal cell proliferation. More recently it has become apparent that growth factor regulation of cell proliferation is of considerable relevance in initiating mucosal mitogenesis. We have recently identified the histamine secreting enterochromaffin-like (ECL) cell as a pivotal cellular regulator of gastric acid secretion. In addition to its critical role in initiating acid secretion, we have proposed that the ECL cell may produce agents responsible for the regulation of mucosal cell proliferation. We have therefore hypothesized that such a function may be subserved by production of transforming growth factor alpha (TGFalpha). TGFalpha is known to play a significant role both in normal physiology and in the transformation of naive cells into a neoplastic form. We therefore proposed that increased levels of gastrin induced by low acid states might stimulate TGFalpha 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 model using long-term histamine-2 receptor blockade (loxtidine 1 mg/kg/day). In order to evaluate the cell-specific effects, we developed a pure isolated ECL cell system from the mastomys stomach. This utilized pronase digestion (1.0 mg/ml) and EDTA exposure (1 mM) of the mucosa followed by particle size separation with countercurrent elutriation and density purification on a Nycodenz step gradient. ECL cells were obtained with a purity of 90-95%. Histamine secretion from ECL cells was measured by radioimmunoassay (RIA). TGFalpha content was measured by RIA, and TGFalpha expression was measured by RNAse probe protection assay. DNA synthesis was quantified by measuring bromo-deoxyuridine (BrdU) incorporation into cultured cells. TGFalpha 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). TGFalpha message was identified in the ECL cells by RNAse probe protection assay, and was fourfold amplified in ECL cell tumors after 16 weeks of exposure to hypergastrinemia. Gastrin stimulated (10 nM) histamine secretion in isolated naive ECL cells was inhibited by TGFalpha (IC50 5 x 10 (-9) M). DNA synthesis was stimulated by gastrin (EC50 2 X 10 M) and TGFalpha (EC50 5 x 10(-9) M). These data are consistent with the proposal that elevated gastrin levels are associated with ECL cell TGFalpha production and that TGFalpha stimulates ECL cell DNA synthesis.
在过去40年里，人们对胃肿瘤形成的病理生物学的理解进展甚微。这反映出关于胃黏膜细胞增殖生物学的可用信息匮乏。最近，很明显细胞增殖的生长因子调节在启动黏膜有丝分裂中具有相当重要的意义。我们最近已确定分泌组胺的肠嗜铬样（ECL）细胞是胃酸分泌的关键细胞调节因子。除了其在启动胃酸分泌中的关键作用外，我们还提出ECL细胞可能产生负责调节黏膜细胞增殖的因子。因此，我们推测这种功能可能由转化生长因子α（TGFα）的产生来实现。已知TGFα在正常生理学以及幼稚细胞向肿瘤形式的转化中都发挥着重要作用。因此我们提出，低酸状态诱导的胃泌素水平升高可能刺激TGFα分泌，并且这种因子可能能够调节ECL细胞的DNA合成和细胞增殖。我们使用非洲巨鼠建立了一个体内高胃泌素血症模型，方法是长期进行组胺-2受体阻断（洛替丁1毫克/千克/天）。为了评估细胞特异性作用，我们从非洲巨鼠胃中开发了一个纯的分离ECL细胞系统。这利用了对黏膜进行链霉蛋白酶消化（1.0毫克/毫升）和EDTA处理（1毫摩尔），随后通过逆流淘析进行粒度分离，并在Nycodenz梯度上进行密度纯化。获得的ECL细胞纯度为90 - 95%。通过放射免疫测定法（RIA）测量ECL细胞的组胺分泌。通过RIA测量TGFα含量，通过核糖核酸酶探针保护测定法测量TGFα表达。通过测量溴脱氧尿苷（BrdU）掺入培养细胞中来量化DNA合成。高胃泌素血症16周后，胃底黏膜中的TGFα水平从4.3±0.6升高至32.6±2.6飞摩尔/毫克蛋白（P<0.05）。通过核糖核酸酶探针保护测定法在ECL细胞中鉴定出TGFα信息，并且在暴露于高胃泌素血症16周后的ECL细胞瘤中其扩增了四倍。在分离的幼稚ECL细胞中，胃泌素（10纳摩尔）刺激的组胺分泌受到TGFα抑制（半数抑制浓度5×10⁻⁹摩尔）。胃泌素（半数有效浓度2×10摩尔）和TGFα（半数有效浓度5×10⁻⁹摩尔）刺激DNA合成。这些数据与以下提议一致，即升高的胃泌素水平与ECL细胞TGFα产生相关，并且TGFα刺激ECL细胞DNA合成。
