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

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 II-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 knock-down 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 knock-down 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 pro -insulin 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 pro-cessing, 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.

Automated summary

Recent studies have found a link between a specific mutation in the GRK6 gene and type 2 diabetes. In the study, researchers used pharmacological inhibition and genetic knockdown to investigate the role of GRK6 in insulin dynamics. They found that inhibition of GRK5 and GRK6 increased insulin secretion but reduced insulin processing, while knockdown of GRK6 resulted in defects in insulin processing and reduced levels of cellular insulin. The study also explored how the specific mutation GRK6-P384S found in T2D patients affects insulin processing and found that it has a different distribution pattern in cells compared to normal GRK6. The findings suggest that GRK6 plays a role in regulating insulin processing and secretion, providing a better understanding of its contribution to T2D.