Perk eIF2a Kinase Integrates Proinsulin Quality Control and Insulin Secretion

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 DESCRIPTION (provided by applicant): Monogenic forms of permanent neonatal diabetes and type 2 ß-cell decompensation have highlighted the importance and vulnerability of proinsulin processing in the endoplasmic reticulum (ER). Once thought to be housekeeping functions, the processes of proinsulin folding, ER associated protein degradation (ERAD)- mediated quality and quantity controand trafficking of proinsulin from the ER to the Golgi are all highly regulated as a function of the metabolic state and demand for insulin. We have identified the PERK eIF2a kinase, whose loss of function results in permanent neonatal diabetes in the Wolcott Rallison syndrome, as a key regulator of proinsulin processing in the ER. We postulated a novel and controversial model that PERK regulates proinsulin processing by controlling the expression of key ER chaperone and folding proteins including GRP78 and ERp72, which, in turn, control whether proinsulin is degraded by the ERAD pathway or trafficked forward to the Golgi for proteolytic processing and packaging into secretory granules. In this proposal we will further test this model by manipulating the PERK-eIF2a pathway and the expression of key ER chaperones and assessing the fate and processing state of proinsulin. We will also determine how PERK- eIF2a modulates proinsulin processing in response to fluctuating glucose levels in order to provide the appropriate level of insulin production. Based on preliminary results that Guanabenz, an eIF2a dephosphorylation inhibitor, can reverse the severe proinsulin aggregation seen in PERK deficient ß-cells, we proposed to test its ability to prevent or reverse the severe permanent neonatal diabetes associated with the Wolcott Rallison Syndrome and dominant-negative acting insulin mutants (MIDY). This strategy may also be applicable to treatment of ß-cell dysfunctions associated with type 2 diabetes decompensation. The final Aim is designed to identify the molecular mechanisms underlying PERK-dependent regulation of ER chaperones and is essential for understanding the regulatory context in which PERK plays a central role in regulating ß-cell functions.