Gene silencing of phogrin unveils its essential role in glucose-responsive pancreatic β-cell growth

Abstract

Objective- Phogrin and IA-2, autoantigens in insulin-dependent diabetes mellitus, have been shown to be involved in insulin secretion in pancreatic β-cell, however, implications at a molecular level are confusing from experiment to experiment. We analyzed biological functions of phogrin in β-cells by an RNA interference technique.

Research Design and Methods- Adenovirus-mediated expression of shRNA specific for phogrin (shPhogrin) was conducted using cultured β-cell lines and mouse islets. Both glucose-stimulated insulin secretion and cell proliferation rate were determined in the phogrin-knockdown cells. Further, protein expression was profiled in these cells. To see the binding partner of phogrin in β-cells, coimmunoprecipitation analysis was carried out.

Results- Adenoviral expression of shPhogrin efficiently decreased its endogenous expression in pancreatic β-cells. Silencing of phogrin in β-cells abrogated the glucose-mediated mitogenic effect, which was accompanied by a reduction in the level of IRS2 protein, without any changes in insulin secretion. Phogrin formed a complex with insulin receptor at the plasma membrane, and their interaction was promoted by high glucose stimulation that in turn led to stabilization of IRS2 protein. Corroboratively, phogrin knockdown had no additional effect on the proliferation of β-cell line derived from insulin receptor-knockout mouse.

Conclusions- Phogrin is involved in β-cell growth via regulating stability of IRS2 protein by the molecular interaction with insulin receptor. We propose that phogrin and IA-2 function as an essential regulator of autocrine insulin action in pancreatic b-cells.