Novel Mechanistic Link between Focal Adhesion Remodeling and Glucose-stimulated Insulin Secretion

Abstract

Actin cytoskeleton remodeling is well known to be positively involved in glucose-stimulated pancreatic β cell insulin secretion. We have observed glucose-stimulated focal adhesion remodeling at the β cell surface and have shown this to be crucial for glucose-stimulated insulin secretion. However, the mechanistic link between such remodeling and the insulin secretory machinery remained unknown and was the major aim of this study. MIN6B1 cells, a previously validated model of primary β cell function, were used for all experiments. Total internal reflection fluorescence microscopy revealed the glucose-responsive co-localization of focal adhesion kinase (FAK) and paxillin with integrin β1 at the basal cell surface after short term stimulation. In addition, blockade of the interaction between β1 integrins and the extracellular matrix with an anti-β1 integrin antibody (Ha2/5) inhibited short term glucose-induced phosphorylation of FAK (Tyr-397), paxillin (Tyr-118), and ERK1/2 (Thr-202/Tyr-204). Pharmacological inhibition of FAK activity blocked glucose-induced actin cytoskeleton remodeling and glucose-induced disruption of the F-actin/SNAP-25 association at the plasma membrane as well as the distribution of insulin granules to regions in close proximity to the plasma membrane. Furthermore, FAK inhibition also completely blocked short term glucose-induced activation of the Akt/AS160 signaling pathway. In conclusion, these results indicate 1) that glucose-induced activation of FAK, paxillin, and ERK1/2 is mediated by β1 integrin intracellular signaling, 2) a mechanism whereby FAK mediates glucose-induced actin cytoskeleton remodeling, hence allowing docking and fusion of insulin granules to the plasma membrane, and 3) a possible functional role for the Akt/AS160 signaling pathway in the FAK-mediated regulation of glucose-stimulated insulin secretion.

CB1 Cannabinoid Receptors Couple to Focal Adhesion Kinase to Control Insulin Release

“…paxilin, talin, and vinculin and serving to route insulin granules toward the plasma membrane (24). This mechanism rests on focal adhesion kinase (FAK) whose activity regulates FA remodeling and turnover (25,26), and tension signaling (27), facilitating glucose-stimulated insulin secretion (28). This concept is consistent with biphasic insulin release because second phase transport of insulin granules requires F-actin as a motive force (29,30).…”

“…Thus, and considering the formation of vinculin ϩ FA plaques upon CB 1 R activation, we hypothesized that FAK, a tyrosine kinase, might be poised to mediate the interaction between integrins and actin cytoskeleton in response to CB 1 R activation (31). FAK, also activated by growth factors (27) and glucose (26), participates in the multimolecular complex making up focal contact sites (FA plaques) to transduce extracellular signals to i.e. initiate the exocytosis of insulin granules (26).…”

The role of the Src Homology-2 domain containing protein B (SHB) in β cells

“…The delayed cAMP response may be attributed to FAK-regulation of phosphodiesterase activity (Serrels et al 2010), which upon elevated FAK activity promotes the local breakdown of cAMP in the sub-membrane space (Alenkvist et al 2014). Both integrins and glucose promote increased b cell FAK activity with enhanced survival, proliferation and insulin secretion as a result (Rondas et al 2011, Cai et al 2012, Rondas et al 2012, Arous et al 2013. The data of the Shb knockout islets suggest negative effects of FAK as well, operating under conditions of chronic over-activity.…”

Absence of Shb impairs insulin secretion by elevated FAK activity in pancreatic islets

“…FAK has been shown to exert positive cues in glucosestimulated insulin secretion (Rondas et al 2011, Cai et al 2012, Arous et al 2013, but the present data indicate that FAK may serve an inhibitory role in this process as well. FAK inhibition reduced both first-and second-phase glucose-stimulated insulin secretion and reduced the number of docked granules (Rondas et al 2011(Rondas et al , 2012, indicating that the prevailing effect of FAK is to promote the exocytotic process. Shb-knockout islets exhibiting elevated basal FAK activity, on the other hand, display elevated basal insulin secretion, reduced firstphase secretion, and reduced numbers of docked granules (Å kerblom et al 2009), suggesting that the dual effect of FAK becomes most apparent when related with the significant reduction in first-phase secretion noted in the Shb-knockout system.…”