Monga S P, Pediaditakis P, Mule K, Stolz D B, Michalopoulos G K
Department of Pathology, University of Pittsburgh, School of Medicine, PA, USA.
Hepatology. 2001 May;33(5):1098-109. doi: 10.1053/jhep.2001.23786.
The wnt/beta-catenin pathway is important during embryogenesis and carcinogenesis. beta-Catenin interaction with E-cadherin has been shown to be crucial in cell-cell adhesion. We report novel findings in the wnt pathway during rat liver regeneration after 70% partial hepatectomy using Western blot analyses, immunoprecipitation studies, and immunofluorescence. We found wnt-1 and beta-catenin proteins to be predominantly localized in hepatocytes. Immediately following partial hepatectomy, we observed an initial increase in beta-catenin protein during the first 5 minutes with its translocation to the nucleus. We show this increase to be the result of decreased degradation of beta-catenin (decrease in serine phosphorylated beta-catenin) as seen by immunoprecipitation studies. We observed activation of beta-catenin degradation complex comprising of adenomatous polyposis coli gene product (APC) and serine-phosphorylated axin protein, beginning at 5 minutes after hepatectomy, leading to its decreased levels after this time. Quantitative changes observed in E-cadherin protein during liver regeneration are, in general, reverse to those seen in beta-catenin. In addition, using immunoprecipitation, we observe elevated levels of tyrosine-phosphorylated beta-catenin at 6 hours onward. Thus, changes in the wnt pathway during regulated growth seem to tightly regulate cytosolic beta-catenin levels and may be contributing to induce cell proliferation and target gene expression. Furthermore, these changes might also be intended to negatively regulate cell-cell adhesion for structural reorganization during the process of liver regeneration.
Wnt/β-连环蛋白信号通路在胚胎发育和肿瘤发生过程中至关重要。β-连环蛋白与E-钙黏蛋白的相互作用已被证明在细胞间黏附中起关键作用。我们运用蛋白质免疫印迹分析、免疫沉淀研究和免疫荧光技术，报告了大鼠70%肝部分切除术后肝脏再生过程中Wnt信号通路的新发现。我们发现Wnt-1和β-连环蛋白主要定位于肝细胞。肝部分切除术后即刻，我们观察到β-连环蛋白在最初5分钟内蛋白水平出现初始升高，并转位至细胞核。通过免疫沉淀研究可见，这种升高是β-连环蛋白降解减少（丝氨酸磷酸化β-连环蛋白减少）的结果。我们观察到由腺瘤性息肉病基因产物（APC）和丝氨酸磷酸化轴蛋白组成的β-连环蛋白降解复合物在肝切除术后5分钟开始激活，导致此后其水平下降。肝脏再生过程中观察到的E-钙黏蛋白定量变化，总体上与β-连环蛋白的变化相反。此外，通过免疫沉淀，我们观察到6小时后酪氨酸磷酸化β-连环蛋白水平升高。因此，在调控生长过程中Wnt信号通路的变化似乎紧密调节细胞溶质β-连环蛋白水平，可能有助于诱导细胞增殖和靶基因表达。此外，这些变化也可能旨在在肝脏再生过程中对细胞间黏附进行负调控，以实现结构重组。
