Chowdhury Md Kamrul H, Wu Lindsay E, Coleman James L J, Smith Nicola J, Morris Margaret J, Shepherd Peter R, Smith Greg C
Department of Pharmacology, UNSW Australia, Sydney, NSW 2052, Australia.
Victor Chang Cardiac Research Institute, Sydney, NSW 2010, Australia.
Biochem J. 2016 May 1;473(9):1247-55. doi: 10.1042/BCJ20160121. Epub 2016 Mar 10.
Recently, it has been found that glucagon is able to activate the β-catenin signalling pathway leading to increased cyclin D1 and c-Myc expression in liver. Therefore the main aim of the present study is to determine whether the effect of glucagon activating β-catenin signalling leading to increased target gene expression is mediated through cAMP activation of PKA (protein kinase A). Primary rat hepatocytes were incubated with insulin, glucagon or adrenaline (epinephrine) and a range of inhibitors of PI3K (phosphoinositide 3-kinase), Wnt, mitochondrial uncoupler (niclosamide) or PKA inhibitors to dissect out the pathway leading to increased Ser(552) phosphorylation on β-catenin following glucagon exposure. In primary rat hepatocytes, we found that short exposure to glucagon or adrenaline caused a rapid increase in Ser(552) phosphorylation on β-catenin that leads to increased cyclin D1 and c-Myc expression. A range of PI3K and Wnt inhibitors were unable to block the effect of glucagon phosphorylating β-catenin. Interestingly, both niclosamide and the PKA inhibitor H89 blocked the glucagon effect on β-catenin signalling, leading to a reduction in target gene expression. Likewise, niclosamide inhibited cAMP levels and the direct addition of db-cAMP (dibutyryl-cAMP sodium salt) also resulted in Ser(552) phosphorylation of β-catenin. We have identified a new pathway via glucagon signalling that leads to increased β-catenin activity that can be reversed with the antihelminthic drug niclosamide, which has recently shown promise as a potential treatment of T2D (Type 2 diabetes). This novel finding could be useful in liver cancer treatment, particularly in the context of T2D with increased β-catenin activity.
最近，人们发现胰高血糖素能够激活β-连环蛋白信号通路，导致肝脏中细胞周期蛋白D1和c-Myc表达增加。因此，本研究的主要目的是确定胰高血糖素激活β-连环蛋白信号通路导致靶基因表达增加的作用是否通过蛋白激酶A（PKA）的cAMP激活介导。将原代大鼠肝细胞与胰岛素、胰高血糖素或肾上腺素孵育，并使用一系列磷脂酰肌醇3-激酶（PI3K）、Wnt、线粒体解偶联剂（氯硝柳胺）或PKA抑制剂，以剖析胰高血糖素暴露后导致β-连环蛋白Ser(552)磷酸化增加的信号通路。在原代大鼠肝细胞中，我们发现短时间暴露于胰高血糖素或肾上腺素会导致β-连环蛋白Ser(552)磷酸化迅速增加，进而导致细胞周期蛋白D1和c-Myc表达增加。一系列PI3K和Wnt抑制剂无法阻断胰高血糖素使β-连环蛋白磷酸化的作用。有趣的是，氯硝柳胺和PKA抑制剂H89均阻断了胰高血糖素对β-连环蛋白信号通路的作用，导致靶基因表达降低。同样，氯硝柳胺抑制了cAMP水平，直接添加二丁酰环磷腺苷（db-cAMP）也导致β-连环蛋白的Ser(552)磷酸化。我们已经确定了一条通过胰高血糖素信号传导导致β-连环蛋白活性增加的新途径，该途径可被抗蠕虫药物氯硝柳胺逆转，氯硝柳胺最近已显示出作为2型糖尿病（T2D）潜在治疗方法的前景。这一新发现可能对肝癌治疗有用，特别是在β-连环蛋白活性增加的T2D背景下。
