Regulation of ERK1 and ERK2 by glucose and peptide hormones in pancreatic β cells

We showed previously that ERK1/2 were activated by glucose and amino acids in pancreatic β cells. Here we examine and compare signaling events that are necessary for ERK1/2 activation by glucose and other stimuli in β cells. We find that agents that interrupt Ca²⁺ signaling by a variety of mechanisms interfere with glucose- and glucagon-like peptide (GLP-1)-stimulated ERK1/2 activity. In particular, calmodulin antagonists, FK506, and cyclosporin, immunosuppressants that inhibit the calcium-dependent phosphatase calcineurin, suppress ERK1/2 activation by both glucose and GLP-1. Ca²⁺ signaling from intracellular stores is also essential for ERK1/ 2 activation, because thapsigargin blocks ERK1/2 activation by glucose or GLP-1. The glucosesensitive mechanism is distinct from that used by phorbol ester or insulin to stimulate ERK1/2 but shares common features with that used by GLP-1.