Department of Radiopharmacy, Tohoku Pharmaceutical Univ., 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan.
Am J Physiol Gastrointest Liver Physiol. 2010 Jul;299(1):G106-14. doi: 10.1152/ajpgi.00365.2009. Epub 2010 May 6.
A neurotransmitter, norepinephrine (NE), amplifies the mitogenic effect of epidermal growth factor (EGF) in the liver by acting on the alpha(1)-adrenergic receptor coupled with G protein, Galpha(h). However, the molecular mechanism is not well understood. Galpha(h) is known as a transglutaminase 2 (TG2), a cross-linking enzyme implicated in hepatocyte proliferation. We investigated the effect of NE on EGF-induced cell proliferation and TG2 activity using hepatocytes isolated in periportal and perivenous regions of the liver, which differ in proliferative capacity. Periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) were isolated by the digitonin-collagenase perfusion technique. EGF or NE receptor binding was analyzed by Scatchard analysis. Changes in NE-induced DNA synthesis, EGF receptor (EGFR) dimerization and phosphorylation, and TG2 activity were measured. NE enhanced EGF-induced DNA synthesis, EGF-induced EGFR dimerization, and its phosphorylation in PVH but not in PPH. [(3)H]NE binding studies indicated that PVH was found to have a greater affinity and number of receptors than PPH. Furthermore, NE treatment decreased TG2 activity and increased phospholipase C activity in PVH although TG2 level showed no change. These results suggest that NE-induced amplification of EGF-induced DNA synthesis especially in PVH is caused by upregulation of EGFR activation through the switching of function from TG2 to Galpha(h).
一种神经递质去甲肾上腺素（NE）通过与 G 蛋白 Galpha(h)偶联的α1-肾上腺素受体作用于表皮生长因子（EGF），从而放大其有丝分裂效应。然而，其分子机制尚不清楚。Galpha(h)被认为是转谷氨酰胺酶 2（TG2），一种与肝实质细胞增殖有关的交联酶。我们使用分离自肝门静脉周围区和肝中央静脉周围区的肝细胞（两者增殖能力不同）研究了 NE 对 EGF 诱导的细胞增殖和 TG2 活性的影响。采用胆酸钠胶原酶灌注技术分离门静脉周围肝细胞（PPH）和肝中央静脉周围肝细胞（PVH）。通过 Scatchard 分析研究 EGF 或 NE 受体结合。测量 NE 诱导的 DNA 合成、EGF 受体（EGFR）二聚化和磷酸化以及 TG2 活性的变化。NE 增强了 PVH 中 EGF 诱导的 DNA 合成、EGFR 二聚化及其磷酸化，但在 PPH 中则没有。[(3)H]NE 结合研究表明，PVH 比 PPH 具有更高的亲和力和受体数量。此外，尽管 TG2 水平没有变化，但 NE 处理降低了 PVH 中的 TG2 活性并增加了磷脂酶 C 活性。这些结果表明，NE 诱导的 EGF 诱导的 DNA 合成的放大，尤其是在 PVH 中，是通过 TG2 向 Galpha(h)的功能转换而上调 EGFR 激活引起的。
