Islet Endothelial Cells Induce Glycosylation and Increase Cell-surface Expression of Integrin β1 in β Cells

Michael G Spelios,John A Olsen,Lauren A Kenna,Eitan M Akirav

doi:10.1074/jbc.m114.628784

Michael G Spelios, John A Olsen + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m114.628784

Copy DOI

Abstract

The co-culturing of insulinoma and islet-derived endothelial cell (iEC) lines results in the spontaneous formation of free-floating pseudoislets (PIs). We previously showed that iEC-induced PIs display improved insulin expression and secretion in response to glucose stimulation. This improvement was associated with a de novo deposition of extracellular matrix (ECM) proteins by iECs in and around the PIs. Here, iEC-induced PIs were used to study the expression and posttranslational modification of the ECM receptor integrin β1. A wide array of integrin β subunits was detected in βTC3 and NIT-1 insulinomas as well as in primary islets, with integrin β1 mRNA and protein detected in all three cell types. Interestingly, the formation of iEC-induced PIs altered the glycosylation patterns of integrin β1, resulting in a higher molecular weight form of the receptor. This form was found in native pancreas but was completely absent in monolayer β-cells. Fluorescence-activated cell sorting analysis of monolayers and PIs revealed a higher expression of integrin β1 in PIs. Antibody-mediated blocking of integrin β1 led to alterations in β-cell morphology, reduced insulin gene expression, and enhanced glucose secretion under baseline conditions. These results suggest that iEC-induced PI formation may alter integrin β1 expression and posttranslational modification by enhancing glycosylation, thereby providing a more physiological culture system for studying integrin-ECM interactions in β cells.

Highlights

Islet endothelial cells induce pseudoislet formation in ␤ cells and extracellular matrix (ECM) deposition
Integrin ␤1 Is Evenly Distributed in NIT-1 PIs—We have previously reported a rapid method for the formation of PIs using a co-culture system of islet-derived endothelial cell (iEC) and ␤TC3 insulinoma cells [8]
PI forthe expression of different integrin ␤ subunits in insulinoma mation leads to the maturation of integrin ␤1 protein glycosylmonolayers, PIs, and primary islets

Summary

Background

Islet endothelial cells induce pseudoislet formation in ␤ cells and ECM deposition. Results: Pseudoislet formation results in glycosylation and increased cell surface expression of integrin ␤1. The formation of iEC-induced PIs altered the glycosylation patterns of integrin ␤1, resulting in a higher molecular weight form of the receptor. Antibody-mediated blocking of integrin ␤1 led to alterations in ␤-cell morphology, reduced insulin gene expression, and enhanced glucose secretion under baseline conditions These results suggest that iEC-induced PI formation may alter integrin ␤1 expression and posttranslational modification by enhancing glycosylation, thereby providing a more physiological culture system for studying integrin-ECM interactions in ␤ cells. We show that PI formation induces the higher molecular weight native form of integrin ␤1 by protein glycosylation This modification of integrin ␤1 glycosylation is dependent on the presence of iECs and results in an increase in cell surface integrin ␤1 expression. Blockage of integrin ␤1 decreases insulin gene expression and disrupts insulin release in response to increased glucose concentrations

Experimental Procedures

Results

Discussion