Lysophosphatidic Acid (LPA) Protects Primary Chronic Lymphocytic Leukemia (CLL) Cells from Apoptosis: Role for LPA as a Survival Factor in CLL.

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of CD19+/CD5+ lymphocytes, and this is achieved primarily through a block in apoptosis. The mechanisms underlying this defect are not fully understood. Several proteins have been shown to protect CLL cells from apoptosis and one of these is albumin that solublizes lipids in the plasma. A lipid found in plasma, lysophosphatidic acid (LPA), protects epithelial and fibroblast cells from apoptosis. We investigated whether LPA could be a survival factor in CLL. Herein, we demonstrate that LPA effectively protects the B cell line BJAB and the CLL-like cell line I-83 from etoposide, fludarabine, and chlorambucil-induced apoptosis. In primary CLL cells, plasma from either healthy or CLL patients significantly reduces spontaneous and drug-induced apoptosis. However, delipidation of the plasma reduces its protective effect. In addition, LPA protects primary CLL cells but not healthy lymphocytes from apoptosis. By western blotting, the LPA receptor 1 (LPA₁) expression is increased in primary CLL cells compared to normal lymphocytes. Treatment of primary CLL cells with the LPA receptor antagonist diacylglycerol pyrophosphate (DGPP) reverses the protective effect of LPA against apoptosis. Over expression of the LPA₁ receptor protects cells from apoptosis and downregulation of the receptor blocks LPA mediated protection against spontaneous apoptosis. The protective effect of LPA is inhibited by blocking activation of the PI-3K/AKT signaling pathway. These results indicate that LPA is a survival factor in primary CLL cells and that drugs targeting the LPA receptors might be an effective therapy for this disease.