Expression of secretory phospholipase A2 in colon tumor cells potentiates tumor growth

Secretory phospholipase A(2) (sPLA(2)-IIA) has been shown to attenuate intestinal tumorigenesis in Apc(Min) mice, demonstrating that it is a tumor modifier. To further explore the actions of sPLA2-IIA in tumorigenesis, sPLA2-IIA was overexpressed in two cell lines where it is normally absent, the murine colon tumor cell line AJ02nm(0), and human colon carcinoma cell line HCT-116. Two allelic variants of sPLA2-IIA were tested in this study; sPLA2-IIA(AKR) and sPLA(2)-IIA(SWR), which are derived from AKR/J and SWR/J mice, respectively, and differ by a single amino acid at position 63 in the calcium- and receptor-binding domain. There was no change in cell-doubling time for either allele when compared to vector controls. Furthermore, sodium butyrate and arachidonic acid (AA)-induced cell death were unchanged in control and transfected cells. Addition of the sPLA(2) substrate, palmitoyl-arachidonoyl-phosphatidic acid (PAPA), to AJ02nm(0) cells resulted in a modest (12%-24%), but significant (P < 0.01), inhibition of growth that was dependent on sPLA2-IIA expression. However, when AJ02nm(0) and HCT-116 cells were injected subcutaneously (sc) into nude mice, Pla2g2a expression resulted in a 2.5-fold increase in tumor size. In addition, sPLA(2)-IIA. expressing HCT-116 tumors were found to be more infiltrative than controls. We conclude that the ability of sPLA(2)-IIA to slow tumor cell growth is dependent upon the availability of substrate, and that in some instances sPLA(2)-IIA may actually enhance tumor growth. Mechanisms that may account for differences between the tumor explant model versus the Apc(Min) model of intestinal cancer are discussed. (c) 2006 Wiley-Liss, Inc.