Cancer Letters

Cancer Letters

Volume 182, Issue 2, 28 August 2002, Pages 175-182
Cancer Letters

Expression of cytosolic and group X secretory phospholipase A2 genes in human colorectal adenocarcinomas

https://doi.org/10.1016/S0304-3835(02)00081-2Get rights and content

Abstract

Gene expression of cytosolic phospholipase A2 (cPLA2) and protein level of secretory PLA2 group X (sPLA2-X) are upregulated in human colorectal cancer and provide cyclooxygenase-2 (COX-2) with arachidonic acid, resulting in increased levels of PGE2. Mutated ras-genes are suggested to be involved in the regulatory pathway of cPLA2 in lung cancer cells. We analysed the gene expression of cPLA2 and sPLA2-X in 42 and 38 primary colorectal tumours, respectively, with and without K-ras mutations. We found an up-regulation of cPLA2 mRNA but the induction in tumour tissues does not correlate with Ras-gene mutations. Moreover, our results cannot consistently reflect an overexpression of sPLA2-X gene in colorectal cancer tissues.

Introduction

Phospholipases A2 (PLA2s) comprise a large family of structurally and mechanistically distinct enzymes that catalyse fatty acid release from the sn-2 position of glycerophospholipids [1]. Among the forms of PLA2s expressed in human tissues the cytosolic high molecular weight 85 kDa PLA2 (cPLA2) and secretory low molecular weight 14 kDa group X PLA2 (sPLA2-X) have turned out to be arachidonyl selective and thus release arachidonic acid [2], [3]. Subsequently, the arachidonic acid will serve as a substrate for cyclooxygenase-2 (COX-2) which generates eicosanoids, such as the mitogenic prostaglandin E2 (PGE2) [4]. Experimental, clinical and epidemiological studies have implicated that increased COX-2 activity has a putative role in colorectal carcinogenesis [5], [6], [7], [8] and there is some evidence for a correlation between increased levels of PGE2 and tumourigenesis [9].

Increased gene and protein expression of group II PLA2 (PLA2-II), are thought to participate in inflammatory reactions and have also demonstrated to be upregulated in human colorectal adenomas from familial adenomatous polyposis (FAP) patients [10]. Genetic studies have provided evidence that inactivating mutation of PLA2-II enhances the development of intestinal neoplasias in the Min mouse which carries a mutation in the adenomatous polyposis coli (APC) gene [11]. PLA2-II was concluded to confer resistance to mouse intestinal tumourigenesis. Corresponding findings have not been substantiated in human colorectal cancer [12], [13]. Recent studies have shown that deletion of cPLA2 in laboratory mouse strains (Min mouse and ApcΔ716 knockout mouse) suppresses intestinal tumourigenesis [14], [15]. In addition, other studies have shown that cPLA2 mRNA and sPLA2-X protein are elevated in human colon cancer [16], [17].

A model of colorectal carcinogenesis suggests that tumour development is a multistep process based on alterations in multiple genes, e.g. APC, p53 and K-ras [18]. K-ras mutations are found as an early event in the adenoma–carcinoma sequence and mutations occurring in codons 12 and 13 of the K-ras gene have regularly been found in 30–50% of colorectal tumours [19], [20]. Ras binds GTP and exhibits GTPase activity, which activates the mitogen-activated protein (MAP) kinase cascade and thereby promote DNA synthesis and cell division [21]. Oncogenic forms of Ras-protein decrease the GTPase activity, which prevents deactivation of the MAP-kinase cascade leading to prolonged stimulation of DNA synthesis [21].

In human lung cancer cells it has been shown that oncogenic ras has a putative role in carcinogenesis by inducing gene expression of cPLA2 and COX-2 [22], but little is known about the interplay between K-ras mutations and cPLA2 mRNA expression and the role of sPLA2-X in colorectal carcinogenesis. In this study we analysed the relation between cPLA2 and sPLA2-X expression and mutations in the K-ras gene in human colorectal adenocarcinomas.

Section snippets

Patients and samples

For analysis of cPLA2 gene expression and K-ras mutation, the study comprises tissue samples from 42 patients (18 male and 24 female) undergoing surgical resection for primary colorectal adenocarcinomas diagnosed at the Department of Surgery, Ryhov County Hospital, Jönköping, Sweden. Tumour tissue and paired normal colonic control tissue, 5–10 cm from the tumour, was surgically resected and immediately frozen at −70 °C. The age of the patients ranged from 25 to 93 (median age 72) years, and the

Results

The gene expression of cPLA2 and sPLA2-X was examined using RT–PCR and dot-blot analysis in human colorectal tumour tissue and matched normal mucosa. For normalization of RNA loading between samples, the gene expression of β2-microglobulin was used as a housekeeping gene. A representative dot-blot from three colorectal tumours with matched normal mucosa is shown (Fig. 1). The median mRNA expression of cPLA2 was significantly increased compared to the corresponding control level in normal

Discussion

Genetic studies on laboratory mouse strains have shown that cPLA2 plays a role in the progression of polyps in the intestine [14], [15]. Recently it has been reported that expression of oncogenic forms of H-Ras directly increases cPLA2 expression in normal rat lung epithelial cells and that the induction of cPLA2 represents a novel downstream effector of Ras [24]. Moreover, increased expression of cPLA2 has also been reported in Ras-transformed fibroblasts [25].

In human lung cancer cells with

Acknowledgments

We thank Dr Anders Hugander, Department of Surgery, Ryhov County Hospital, Jönköping, Sweden, for kindly collecting the samples. We also thank Dr Marietta Kaszkin, Pharmazentrum Frankfurt, Germany, for the generous gift of the human group X sPLA2 antiserum. This work was supported by grants from the County Council of Jönköping, and the Swedish Cancer Foundation, Sweden.

References (31)

  • V. Van Putten et al.

    Induction of cytosolic phospholipase A2 by oncogenic ras is mediated through the JNK and ERK pathway in rat epithelial cells

    J. Biol. Chem.

    (2001)
  • M.-H. Yoo et al.

    Role of cytosolic phospholipase A2-linked cascade in the signaling by an oncogenic, constitutively-active H-ras isoform

    J. Biol. Chem.

    (2001)
  • S. Akiba et al.

    Secretory phospholipase A2 mediates cooperative prostaglandin generation by growth factor and cytokine independently of preceding cytosolic phospholipase A2 expression in rat gastric epithelial cells

    J. Biol. Chem.

    (2001)
  • K. Hanasaki et al.

    Purified group X secretory phospholipase A2 induced prominent release of arachidonic acid from human myeloid leukemia cells

    J. Biol. Chem.

    (1999)
  • S. Bezzine et al.

    Exogenously added human group X secreted phospholipase A2 but not the group IB, IIA, and V enzymes efficiently release arachidonic acid from adherent mammalian cells

    J. Biol. Chem.

    (2000)

    • Cited by (0)

    View full text
    Copyright © 2002 Elsevier Science Ireland Ltd. All rights reserved.