Glycerol-3-phosphate acyltranferase-2 behaves as a cancer testis gene and promotes growth and tumorigenicity of the breast cancer MDA-MB-231 cell line.

Magali Pellon-Maison,Ezequiel Lacunza,Mercedes C Soler-Gerino,Martin C Abba,Elizabeth R Cattaneo,Rosalind A Coleman,Maria R Gonzalez-Baro,Ivana Y Quiroga,Mauro A Montanaro,Maria B Garcia-Fabiani

doi:10.1371/journal.pone.0100896

Abstract

The de novo synthesis of glycerolipids in mammalian cells begins with the acylation of glycerol-3-phosphate, catalyzed by glycerol-3-phosphate acyltransferase (GPAT). GPAT2 is a mitochondrial isoform primarily expressed in testis under physiological conditions. Because it is aberrantly expressed in multiple myeloma, it has been proposed as a novel cancer testis gene. Using a bioinformatics approach, we found that GPAT2 is highly expressed in melanoma, lung, prostate and breast cancer, and we validated GPAT2 expression at the protein level in breast cancer by immunohistochemistry. In this case GPAT2 expression correlated with a higher histological grade. 5-Aza-2′ deoxycytidine treatment of human cells lines induced GPAT2 expression suggesting epigenetic regulation of gene expression. In order to evaluate the contribution of GPAT2 to the tumor phenotype, we silenced its expression in MDA-MB-231 cells. GPAT2 knockdown diminished cell proliferation, anchorage independent growth, migration and tumorigenicity, and increased staurosporine-induced apoptosis. In contrast, GPAT2 over-expression increased cell proliferation rate and resistance to staurosporine-induced apoptosis. To understand the functional role of GPAT2, we performed a co-expression analysis in mouse and human testis and found a significant association with semantic terms involved in cell cycle, DNA integrity maintenance, piRNA biogenesis and epigenetic regulation. Overall, these results indicate the GPAT2 would be directly associated with the control of cell proliferation. In conclusion, we confirm GPAT2 as a cancer testis gene and that its expression contributes to the tumor phenotype of MDA-MB-231 cells.

Highlights

The de novo synthesis of glycerolipids in mammalian cells begins with the acylation of glycerol-3-phosphate, catalyzed by glycerol3-phosphate acyltransferase (GPAT) [1]
While GPAT1, GPAT3 and GPAT4 are expressed in lipogenic tissues and their activities are associated with triacylglycerol and phospholipid synthesis, the expression pattern of GPAT2 is more prominent in testis [3]
Because GPAT2 has been proposed to be a novel CT gene and in order to validate its high expression in human testis and in cancers, we performed an in silico analysis of GPAT2 mRNA expression

Summary

Introduction

The de novo synthesis of glycerolipids in mammalian cells begins with the acylation of glycerol-3-phosphate, catalyzed by glycerol3-phosphate acyltransferase (GPAT) [1]. As occurs in many other lipid metabolic reactions, several isoforms catalyze this step. At least four different genes encode for GPAT isoforms 1–4, which differ in tissue expression pattern, subcellular localization, fatty acyl-CoA substrate preference, and sensitivity to N-ethylmaleimide. GPAT1 and GPAT2 are mitochondrial isoforms, whereas GPAT3 and GPAT4 are localized in the endoplasmic reticulum [2]. While GPAT1, GPAT3 and GPAT4 are expressed in lipogenic tissues and their activities are associated with triacylglycerol and phospholipid synthesis, the expression pattern of GPAT2 is more prominent in testis [3]. GPAT2, which is expressed in the germ line cells in mouse and rat testis, is highly selective for arachidonoyl-CoA as a substrate [4]. The function of GPAT2 in male reproduction remains unknown, but a recent publication showed that GPAT2 is essential for the biogenesis of piRNA which maintains genome integrity in germ line cells [5]

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Conclusion