ACC2 Is Expressed at High Levels Human White Adipose and Has an Isoform with a Novel N-Terminus

John C Castle,Jun Kusunoki,Kenji Ohwaki,Jason M Johnson,Yoshikazu Hara,Christopher K Raymond,Philip Garrett-Engele,Zhengyan Kan,Ulrich Zanger

doi:10.1371/journal.pone.0004369

Abstract

Acetyl-CoA carboxylases ACC1 and ACC2 catalyze the carboxylation of acetyl-CoA to malonyl-CoA, regulating fatty-acid synthesis and oxidation, and are potential targets for treatment of metabolic syndrome. Expression of ACC1 in rodent lipogenic tissues and ACC2 in rodent oxidative tissues, coupled with the predicted localization of ACC2 to the mitochondrial membrane, have suggested separate functional roles for ACC1 in lipogenesis and ACC2 in fatty acid oxidation. We find, however, that human adipose tissue, unlike rodent adipose, expresses more ACC2 mRNA relative to the oxidative tissues muscle and heart. Human adipose, along with human liver, expresses more ACC2 than ACC1. Using RT-PCR, real-time PCR, and immunoprecipitation we report a novel isoform of ACC2 (ACC2.v2) that is expressed at significant levels in human adipose. The protein generated by this isoform has enzymatic activity, is endogenously expressed in adipose, and lacks the N-terminal sequence. Both ACC2 isoforms are capable of de novo lipogenesis, suggesting that ACC2, in addition to ACC1, may play a role in lipogenesis. The results demonstrate a significant difference in ACC expression between human and rodents, which may introduce difficulties for the use of rodent models for development of ACC inhibitors.

Highlights

Acetyl-CoA carboxylase alpha (ACC1) and beta (ACC2) catalyze the carboxylation of acetyl-CoA to malonyl-CoA
ACC2 mRNA is present at higher levels in human adipose tissue than ACC1
Expression levels of ACC1 and ACC2 in human tissues, each pooled from multiple donors, were examined using oligonucleotide microarrays [24] and calibrated quantitative real-time Reverse transcription-polymerase chain reaction (RT-PCR) (Figure 1)

Summary

Introduction

Acetyl-CoA carboxylase alpha (ACC1) and beta (ACC2) catalyze the carboxylation of acetyl-CoA to malonyl-CoA. ACC1 is cytosolic and believed to be the primary acetyl-CoA carboxylase (ACC) involved in de novo fatty-acid synthesis. This is supported by observations of high ACC1 expression in rat and mouse lipogenic tissues [14,15]. Immunofluorescence microscopy studies suggest that ACC2 is preferentially localized to the mitochondria, possibly due to the unique ,220 amino acid N-terminus of ACC2 [18]. This N-terminus includes a leader sequence of ,20 hydrophobic residues that has been hypothesized to be responsible for mitochondrial localization and the functional difference between two genes [15]

Methods

Results

Conclusion