Lysophosphatidic acid is a major regulator of growth-regulated oncogene α in ovarian cancer

Growth-regulated oncogene α (GROα), a member of the chemokine superfamily, is commonly expressed in transformed cells and contributes to angiogenesis and tumorigenesis. Here, we report that increased GROα levels are detected in the plasma and ascites of ovarian cancer patients. Ovarian cancer cell lines in culture express and secrete GROα. However, when they are starved in serum-free medium, ovarian cancer cells ceased producing GROα, suggesting that GROα is not constitutively expressed but rather is produced in response to exogenous growth factors in ovarian cancer cells. The prototype peptide growth factors present in serum such as platelet-derived growth factor, insulin-like growth factor I, and insulin do not stimulate GROα production by ovarian cancer cells. In contrast, lysophosphatidic acid (LPA), a glycerol backbone phospholipid mediator present in serum and ascites of ovarian cancer patients, is a potent inducer of GROα expression in ovarian cancer cell lines. Treatment of ovarian cancer cells with LPA leads to transcriptional activation of the GROα gene promoter and robust accumulation of GROα protein in culture supernatants. The action of LPA on GROα expression is mediated by LPA receptors, particularly the LPA₂ receptor in that ectopic expression of these receptors restores the LPA-dependent GROα production in nonresponsive cells. Down-regulation of LPA₂ expression by small interfering RNA (siRNA) in ovarian cancer cells desensitizes GROα production in response to LPA. The effect of serum on GROα production is also significantly decreased by siRNA inhibition of LPA₂ expression. These studies identify LPA as a primary regulator of GROα expression in ovarian cancer.