Complexation of phospholipase C isozymes regulate cytosolic and nuclear signaling and insulin secretion (796.14)

Insulin secretion from the pancreatic islet β‐cell is stimulated not only by glucose, but also by binding of acetylcholine to the M 3 muscarinic receptor. Acetylcholine binding activates PLCβ2. Postpandrial increases in glucose metabolism by the β‐cell lead to Ca 2+ influx and activates PLCδ1. Thus, the β‐cell has redundant mechanisms to increase the provision of PLC‐derived second messengers of insulin secretion. PLCβ2 and PLCδ1 isozymes can exist in an enzymatically‐inactive complexed state that is dissociated by either cholinergic agonists or by elevated glucose. Dissociation of the PLCβ‐δ complex enables PLC enzymatic activity. Our Co‐IP studies indicate that the PLCβ‐δ complex exists in the INS‐1 β‐cell line, and that treatment with muscarinic agonist, carbachol, led to dissociation of PLCβ2 from PLCδ1. Spatial localization of PLC isozymes was evaluated with indirect immunofluorescence microscopy. At basal conditions, PLCβ2 and PLCδ1 were colocalized throughout the cytosol, but were excluded from the nucleus. Dissociation of the PLCβ‐δ complex occurred with carbachol or high glucose, and notably a pronounced translocation of the PLCδ1 to the nucleus occurred. These data are the first showing that 1.) PLCβ2 and PLCδ1 exist in a complexed state in β‐cell lines, 2.) PLCβ‐δ decomplexation occurs upon cholinergic or glucose stimulation, and 3.) PLCδ1 translocates to the nucleus. Intriguingly, dissociation and activation of the PLC isozymes has the potential to generate both cytosolic and nuclear signaling intermediates. These studies are timely in light of the recent appreciation of the paracrine role of acetylcholine release from islet α‐cells, and the association between variants in human muscarinic receptor gene and increased risk of type 2 diabetes.