G Protein-Coupled Receptor Kinase 6 (GRK6) Regulation of Insulin Processing and Secretion
Abstract
Type 2 Diabetes (T2D) has emerged as a major global health concern that has accelerated in recent years due to poor diets and inactive lifestyles. Afflicted individuals have high blood glucose levels that stem from the inability of the pancreas to make enough insulin to meet demand. For those with chronic disease, drugs are needed to help maintain normal blood glucose levels, but these medicines are outdated and have toxic side effects. 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 beta-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 wild type 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. Moreover, this work highlights previously unappreciated mechanisms within the beta-cell that may unveil new approaches to treat T2D and related metabolic disorders.
Subject Area
Biochemistry|Pharmacology
Recommended Citation
Varney, Matthew J, "G Protein-Coupled Receptor Kinase 6 (GRK6) Regulation of Insulin Processing and Secretion" (2022). ProQuest ETD Collection - Thomas Jefferson University. AAI29992133.
https://jdc.jefferson.edu/dissertations/AAI29992133
