α-catenin isoforms are regulated by glucose and involved in regulating insulin secretion in rat clonal β-cell models

The recent finding that beta-catenin levels play an important rate-limiting role in processes regulating insulin secretion lead us to investigate whether its binding partner alpha-catenin also plays a role in this process. We find that levels of both alpha-E-catenin and alpha-N-catenin are rapidly up-regulated as levels of glucose are increased in rat clonal beta-cell models INS-1E and INS-832/3. Lowering in levels of either alpha-catenin isoform using siRNA resulted in significant increases in glucose stimulated insulin secretion (GSIS) and this effect was attenuated when beta-catenin levels were lowered indicating these proteins have opposing effects on insulin release. This effect of alpha-catenin knockdown on GSIS was not due to increases in insulin expression but was associated with increases in calcium influx into cells. Moreover, simultaneous depletion of alpha-E catenin and alpha-N catenin decreased the actin polymerisation to a similar degree as latrunculin treatment and inhibition of ARP 2/3 mediated actin branching with CK666 attenuated the alpha-catenin depletion effect on GSIS. This suggests alpha-catenin mediated actin remodelling may be involved in the regulation of insulin secretion. Together this indicates that alpha-catenin and beta-catenin can play opposing roles in regulating insulin secretion, with some degree of functional redundancy in roles of alpha-E-catenin and alpha-N-catenin. The finding that, at least in beta-cell models, the levels of each can be regulated in the longer term by glucose also provides a potential mechanism by which sustained changes in glucose levels might impact on the magnitude of GSIS.