Cocaine- and Amphetamine-regulated Transcript (CART) Protects Beta Cells against Glucotoxicity and Increases Cell Proliferation

Ramasri Sathanoori,Björn Olde,David Erlinge,Olga Göransson,Nils Wierup

doi:10.1074/jbc.m112.437145

Abstract

Cocaine- and amphetamine-regulated transcript (CART) is an islet peptide that promotes glucose-stimulated insulin secretion in beta cells via cAMP/PKA-dependent pathways. In addition, CART is a regulator of neuronal survival. In this study, we examined the effect of exogenous CART 55-102 on beta cell viability and dissected its signaling mechanisms. Evaluation of DNA fragmentation and chromatin condensation revealed that CART 55-102 reduced glucotoxicity-induced apoptosis in both INS-1 (832/13) cells and isolated rat islets. Glucotoxicity in INS-1 (832/13) cells also caused a 50% reduction of endogenous CART protein. We show that CART increased proliferation in INS-1 (832/13) cells, an effect that was blocked by PKA, PKB, and MEK1 inhibitors. In addition, CART induced phosphorylation of CREB, IRS, PKB, FoxO1, p44/42 MAPK, and p90RSK in INS-1 (832/13) cells and isolated rat islets, all key mediators of cell survival and proliferation. Thus, we demonstrate that CART 55-102 protects beta cells against glucotoxicity and promotes proliferation. Taken together our data point to the potential use of CART in therapeutic interventions targeted at enhancing functional beta cell mass and long-term insulin secretion in T2D.

Highlights

Cocaine- and amphetamine-regulated transcript (CART) potentiates GSIS in pancreatic beta cells and confers neuroprotection
We show that CART, in addition to increasing cAMP production, induces phosphorylation of cAMP-response element-binding protein (CREB), insulin receptor substrate protein (IRS), protein kinase B (PKB)/forkhead box protein O1 (FoxO1), and p44/42-mitogen-activated protein kinase (p44/42 MAPK)/p90 ribosomal S6 kinase (p90RSK) in the INS-1 (832/13) cells and rat islets
CART Is Expressed in INS-1 (832/13) Clonal Beta Cells and Is Regulated by Glucose—INS-1 (832/13) cells are rat insulinoma cells stably transfected with a plasmid coding for human proinsulin [21, 22]

Summary

Background

CART potentiates GSIS in pancreatic beta cells and confers neuroprotection. Results: CART reduced beta cell apoptosis, induced phosphorylation of IRS, PKB, p44/42 MAPK, and CREB, and increased proliferation. CART regulates islet hormone secretion and glucose homeostasis and potentiates the effect of glucagon-like peptide-1 (GLP-1) on glucose-stimulated insulin secretion in INS-1 (832/13) cells and isolated islets from both normal and diabetic GK rats in a 3Ј-5Ј-cyclic adenosine monophosphate/ protein kinase A (cAMP/PKA)-dependent manner [12, 13]. Together these findings suggest that CART is important for normal beta cell function. We show that CART, in addition to increasing cAMP production, induces phosphorylation of cAMP-response element-binding protein (CREB), insulin receptor substrate protein (IRS), protein kinase B (PKB)/forkhead box protein O1 (FoxO1), and p44/42-mitogen-activated protein kinase (p44/42 MAPK)/p90 ribosomal S6 kinase (p90RSK) in the INS-1 (832/13) cells and rat islets

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION