G protein-coupled receptor kinase 6 (GRK6) regulates insulin processing and secretion via effects on proinsulin conversion to insulin.

Content Provider	Europe PMC
Author	Varney, Matthew J. Steyaert, Wouter Coucke, Paul J. Delanghe, Joris R. Uehling, David E. Joseph, Babu Marcellus, Richard Al-awar, Rima Benovic, Jeffrey L.
Copyright Year	2022
Abstract	Recent studies identified a missense mutation in the gene coding for G protein–coupled receptor kinase 6 (GRK6) that segregates with type 2 diabetes (T2D). To better understand how GRK6 might be involved in T2D, we used pharmacological inhibition and genetic knockdown in the mouse β-cell line, MIN6, to determine whether GRK6 regulates insulin dynamics. We show inhibition of GRK5 and GRK6 increased insulin secretion but reduced insulin processing while GRK6 knockdown revealed these same processing defects with reduced levels of cellular insulin. GRK6 knockdown cells also had attenuated insulin secretion but enhanced proinsulin secretion consistent with decreased processing. In support of these findings, we demonstrate GRK6 rescue experiments in knockdown cells restored insulin secretion after glucose treatment. The altered insulin profile appears to be caused by changes in the proprotein convertases, the enzymes responsible for proinsulin to insulin conversion, as GRK6 knockdown resulted in significantly reduced convertase expression and activity. To identify how the GRK6-P384S mutation found in T2D patients might affect insulin processing, we performed biochemical and cell biological assays to study the properties of the mutant. We found that while GRK6-P384S was more active than WT GRK6, it displayed a cytosolic distribution in cells compared to the normal plasma membrane localization of GRK6. Additionally, GRK6 overexpression in MIN6 cells enhanced proinsulin processing, while GRK6-P384S expression had little effect. Taken together, our data show that GRK6 regulates insulin processing and secretion in a glucose-dependent manner and provide a foundation for understanding the contribution of GRK6 to T2D.
ISSN	00219258
Volume Number	298
PubMed Central reference number	PMC9526158
Issue Number	10
PubMed reference number	36030052
Journal	The Journal of Biological Chemistry [J. Biol. Chem]
e-ISSN	1083351X
DOI	10.1016/j.jbc.2022.102421
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	2022-08-25
Access Restriction	Open
Rights License	This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). © 2022 The Authors
Subject Keyword	G protein–coupled receptor G protein–coupled receptor kinase insulin proinsulin proprotein convertase type 2 diabetes BSA, bovine serum albumin CPE, carboxypeptidase E DPBS, Dulbecco’s phosphate buffered saline FBS, fetal bovine serum GPCR, G protein-coupled receptor GSIS, glucose stimulated insulin secretion KRBH, Krebs Ringer bicarbonate buffer with Hepes MOI, multiplicity of infection PBS/T, phosphate buffered saline with Tween-20 T2D, type 2 diabetes TBS/T, Tris buffer saline with Tween-20
Content Type	Text
Resource Type	Article
Subject	Cell Biology Molecular Biology Biochemistry