Differential effects of sPLA 2 -GV and GX on cellular proliferation and lipid accumulation in HT29 colon cancer cells

Secretory phospholipase A 2 (sPLA 2 ) group of enzymes have been shown to hydrolyze phospholipids, among which sPLA 2 Group V (GV) and Group X (GX) exhibit high selectivity towards phosphatidylcholine-rich cellular plasma membranes. The enzymes have recently emerged as key regulators in lipid droplets formation and it is hypothesized that sPLA 2 -GV and GX enhanced cell proliferation and lipid droplet accumulation in colon cancer cells (HT29). In this study, cell viability and lipid droplet accumulation were assessed by Resazurin assay and Oil-Red-O staining. Interestingly, both sPLA 2 -GV and GX enzymes reduced intracellular lipid droplet accumulation and did not significantly affect cell proliferation in HT29 cells. Incubation with varespladib, a pan-inhibitor of sPLA 2 -Group IIA/V/X, further suppressed lipid droplets accumulation in sPLA 2 -GV but have no effects in sPLA 2 -GX-treated cells. Further studies using catalytically inactive sPLA 2 enzymes showed that the enzymes intrinsic catalytic activity is required for the net reduction of lipid accumulation. Meanwhile, inhibition of intracellular phospholipases (iPLA 2 -γ and cPLA 2 -α) unexpectedly enhanced lipid droplet accumulation in both sPLA 2 -GV and GX-treated cells. The findings suggested an interconnected relationship between extracellular and intracellular phospholipases in lipid cycling. Previous studies indicated that sPLA 2 enzymes are linked to cancer development due to their ability to induce release of arachidonic acid and eicosanoids as well as the stimulation of lipid droplet formation. This study showed that the two enzymes work in a distinct manner and they neither confer proliferative advantage nor enhanced the net lipid droplet accumulation in HT29 cells.