Identification of a pathway by which glucose regulates β-catenin signalling via the cAMP/protein kinase A pathway in β-cell models

Abstract

Pancreatic β-cells are highly responsive to changes in glucose, but the mechanisms involved are only partially understood. There is increasing evidence that the β-catenin signalling pathway plays an important role in regulating β-cell function, but the mechanisms regulating β-catenin signalling in these cells is not well understood. In the present study we show that β-catenin levels and downstream signalling are regulated by changes in glucose levels in INS-1E and β-TC6-F7 β-cell models. We found a glucose-dependent increase in levels of β-catenin in the cytoplasm and nucleus of INS-1E cells. Expression of cyclin D1 also increased with glucose and required the presence of β-catenin. This was associated with an increase in phosphorylation of β-catenin on Ser552, which is known to stabilize the molecule and increase its transcriptional activity. In a search for possible signalling intermediates we found forskolin and cell-permeable cAMP analogues recapitulated the glucose effects, suggesting a role for cAMP and PKA (cAMP-dependent protein kinase/protein kinase A) downstream of glucose. Furthermore, glucose caused sustained increases in cAMP. Two different inhibitors of adenylate cyclase and PKA signalling blocked the effects of glucose, whereas siRNA (small interfering RNA) knockdown of PKA blocked the effects of glucose on β-catenin signalling. Finally, reducing β-catenin levels with either siRNA or pyrvinium impaired glucose- and KCl-stimulated insulin secretion. Taken together the results of the present study define a pathway by which changes in glucose levels can regulate β-catenin using a mechanism which involves cAMP production and the activation of PKA. This identifies a pathway that may be important in glucose-dependent regulation of gene expression and insulin secretion in β-cells.

Niclosamide reduces glucagon sensitivity via hepatic PKA inhibition in obese mice: Implications for glucose metabolism improvements in type 2 diabetes

“…To provide support that NENS and Nic block the glucagon signalling pathway, we used CREB serine 133 as a readout, because this is a widely used measure of PKA activity202122. Control mice exposed to glucagon for 15 minutes on both the chow and high fat diets had a significant increase in serine 133 phosphorylation on CREB but both NENS and Nic blocked this effect (Fig.…”

Nutrient-induced intestinal adaption and its effect in obesity

“…Glucose can control β-catenin through a cAMP/PKA pathway 28 or by increasing β-catenin acylation and translocation to the nucleus 29 in other stem cell populations (Fig. 2).…”

C/EBPβ regulates P2X7 receptor expression in response to glucose challenge in intestinal epithelial cells

“…In fact, before reaching the bloodstream and target organs such as the liver and pancreas, glucose is first absorbed and transport by enterocytes of the duodenum and jejunum. Along with its metabolic function, glucose by itself may act as a signaling molecule, not only in fission yeast such as Schizosaccharomyces pombe (Hoffman 2005) but also in mammals, as recently reported in INS-1E pancreatic ␤-cell lines (Cognard et al 2013). Although GLUT2 was proposed to have receptor-like function in ␤-cells and IECs (Leturque et al 2009), the exact cellular entity transmitting the glucose-stimulating effect is not clearly identified, and as such further study is required.…”

“…These results suggested that glucose could activate intracellular signaling pathway(s). In fact, it was previously proposed that changes in glucose levels regulate ␤-catenin signaling through a cAMP/PKA pathway (Cognard et al 2013). Herein, results show that an increase in glucose concentration from 1 to 25 mmol/L was sufficient to increase the luciferase activity associated with CREB promoter transactivation ( Fig.…”