Phosphodiesterase 3B Is Localized in Caveolae and Smooth ER in Mouse Hepatocytes and Is Important in the Regulation of Glucose and Lipid Metabolism

Karin Berger,Rebecka Lindh,Emilia Zmuda-Trzebiatowska,Nils Wierup,Eva Degerman,Andreas Lindqvist,Vincent C Manganiello,Silvana Gaetani

doi:10.1371/journal.pone.0004671

Karin Berger, Rebecka Lindh + Show 6 more

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https://doi.org/10.1371/journal.pone.0004671

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Abstract

Cyclic nucleotide phosphodiesterases (PDEs) are important regulators of signal transduction processes mediated by cAMP and cGMP. One PDE family member, PDE3B, plays an important role in the regulation of a variety of metabolic processes such as lipolysis and insulin secretion. In this study, the cellular localization and the role of PDE3B in the regulation of triglyceride, cholesterol and glucose metabolism in hepatocytes were investigated. PDE3B was identified in caveolae, specific regions in the plasma membrane, and smooth endoplasmic reticulum. In caveolin-1 knock out mice, which lack caveolae, the amount of PDE3B protein and activity were reduced indicating a role of caveolin-1/caveolae in the stabilization of enzyme protein. Hepatocytes from PDE3B knock out mice displayed increased glucose, triglyceride and cholesterol levels, which was associated with increased expression of gluconeogenic and lipogenic genes/enzymes including, phosphoenolpyruvate carboxykinase, peroxisome proliferator-activated receptor γ, sterol regulatory element-binding protein 1c and hydroxyl-3-methylglutaryl coenzyme A reductase. In conclusion, hepatocyte PDE3B is localized in caveolae and smooth endoplasmic reticulum and plays important roles in the regulation of glucose, triglyceride and cholesterol metabolism. Dysregulation of PDE3B could have a role in the development of fatty liver, a condition highly relevant in the context of type 2 diabetes.

Highlights

Cyclic nucleotide phosphodiesterases (PDEs) are important regulators of signal transduction processes mediated by cAMP and cGMP
In this study we demonstrate that, in hepatocytes, PDE3B is localized to caveolae and smooth endoplasmic reticulum (ER) and that the enzyme has an important role in the regulation of triglyceride, cholesterol and glucose metabolism in these cells
In this study we demonstrate that PDE3B is localized to caveolae/lipid raft regions in the plasma membrane as well as in smooth ER

Summary

Introduction

Cyclic nucleotide phosphodiesterases (PDEs) are important regulators of signal transduction processes mediated by cAMP and cGMP. The catalytic domains of PDE3A and B are highly conserved, except for an insertion of 44 unique amino acids that is not found in the catalytic domains of other PDE families and that differs in, and distinguishes, PDE3A and B isoforms [2,3] Their N-terminal regulatory domains are quite divergent, consisting of two hydrophobic regions important for membrane association of these enzymes. Caveolae are special forms of lipid rafts observed as small flask-shaped 50– 100 nM invaginations of the plasma membranes and are abundant in adipocytes. They have a high content of sphingolipids, cholesterol and are stabilized by one or more isoforms of caveolin. Multisite phosphorylation of PDE3s has, for example, been demonstrated in adipocytes, hepatocytes and HeLa cells [8,9] which is believed to be important in the regulation of PDE3 activity and in interaction with other proteins [2,3]

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