γ-Linolenic acid regulates the expression and secretion of SPARC in human cancer cells

Abstract

SPARC (secreted protein acidic and rich in cystein), also known as osteonectin and BM40, is a secreted glycoprotein. It confers matrix adhesion of cells including cancer cells, thus promoting cell migration. SPARC has been shown to be involved in the aggressive nature of cancer. The current study investigated the role of a n-6 polyunsaturated fatty acid, gamma linolenic acid (GLA) on the expression and secretion of SPARC from cancer cells. Human breast cancer cell line MCF-7 and MDA-MB-231, human colon cancer cells HT115 and HRT-18 were used in the study. Cancer cells were treated with GLA or other fatty acids over a range of concentrations. Presence of SPARC in the supernatant and in the cell lysate were analysed using Western blotting. Cellular SPARC was also assessed using immunocytochemistry. SPARC transcript in these cells were studied using RT-PCR. Cell–matrix adhesion was determined using a cell–matrix adhesion assay and cell migration analysis. Treatment of MDA-MB-231 and HT115 cells with GLA, at non-toxic levels, resulted in reduction of SPARC in supernatant as well as in the cell lysate. In contrast, there were little changes in the supernatant SPARC in MCF-7 and in HRT-18 cells. Cellular SPARC, as revealed by immunocytochemistry, also demonstrated a similar trend of changes as seen with protein blotting. Analysis of the SPARC transcript using RT-PCR has shown an up-regulation of SPARC mRNA by the fatty acid. GLA reduced cell–matrix adhesion in these cancer cells. It is concluded that GLA is a regulator of SPARC secretion and expression in cancer cells. It reduces the secretion of SPARC into surrounding environment, which may contribute to the reduction of cancer cells adhesion to the extracellular matrix and cell motility.