Niclosamide blocks glucagon phosphorylation of Ser552 on ß-catenin in primary rat hepatocytes via PKA signalling.

Recently, it has been found that glucagon is able to activate the ß-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 ß-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 ß-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 ß-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 ß-catenin. Interestingly, both niclosamide and the PKA inhibitor H89 blocked the glucagon effect on ß-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 ß-catenin. We have identified a new pathway via glucagon signalling that leads to increased ß-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 ß-catenin activity.

Interleukin-6 is a negative regulator of hepatic glucose production in the isolated rat liver.

The mechanism underlying the increased rate of endogenous glucose production from the liver during exercise remains unknown. The cytokine interleukin-6 (IL-6) is known to be released during exercise and is thought that either IL-6 directly or via a "contraction factor" stimulates the release of stored glucose from the liver. Here we show that IL-6 does not directly increase hepatic glucose output (HGO). Moreover, IL-6 infused at the same time as glucagon caused a significant reduction in HGO. IL-6 infused with epinephrine caused no synergenic increase in HGO. To test if an unknown "contraction factor" was needed along with IL-6 to increase HGO, we used human fasted and exercised plasma perfused with or without IL-6 in our isolated liver system. We found that exercised plasma increased HGO, as expected, but when infused with IL-6, reductions in HGO were found. Our results provide evidence that IL-6 works as a negative regulator of HGO.

Glucagon phosphorylates serine 552 of ß-catenin leading to increased expression of cyclin D1 and c-Myc in the isolated rat liver.

In the last 20 years the prevalence of metabolic disorders, in particular type 2 diabetes (T2D), has more than doubled. Recently, a strong link between T2D and cancer, in particularly liver cancer has been reported. However, the mechanism connecting the development of type 2 diabetes and cancer remains unknown. One of the biggest drivers of liver cancer is alterations in the Wnt/ß-catenin pathway. In this study, we aimed to identify the effect of glucagon on ß-catenin in the isolated rat liver. We found glucagon, which is substantially raised in patients with T2D, rapidly phosphorylates ß-catenin on serine 552 that is associated with increased expression of genes cyclin D1 (CCND1) and c-Myc (MYC), which are known to be involved in liver cancer. This finding may explain the increased risk of liver cancer in people with T2D.