GDPD5 inhibition alters the choline phospholipid metabolite profile of breast cancer cells toward a less malignant metabolic profile

Abstract

Altered choline phospholipid metabolism is a metabolic hallmark of cancer. Malignant transformation of breast cancer cells results in a switch from high glycerophosphocholine (GPC) and low phosphocholine (PC) to low GPC and high PC. Glycerophosphocholine phosphodiesterase (GPC-PDE; E.C. 3.1.4.2) catalyzes the degradation of GPC to choline (Cho) and glycerol-3-phosphate. The GPC-PDE gene(s) responsible for the relatively low GPC concentration in breast cancer cells have not yet been characterized. Glycerophosphodiester phosphodiesterase domain containing 5 (GDPD5) displays GPC-PDE activity, and is rapidly inhibited by sodium chloride and urea (NaCl/urea). We chemically inhibited GPC-PDE with NaCl/urea in nonmalignant MCF-12A breast epithelial cells, as well as in MCF-7 and MDA-MB-231 breast cancer cells. ¹H magnetic resonance spectroscopy (MRS) of cell extracts demonstrated that exposure of MCF-12A, MCF-7 and MDA-MB-231 cells to NaCl/urea (n=5) significantly increased GPC and decreased PC, resulting in a low [PC]/[GPC] ratio. A high [PC]/[GPC] ratio is associated with high malignancy in breast cancer cell lines. Inhibiting GDPD5 altered the choline phospholipid metabolite profile of breast cancer cells toward a less malignant metabolic profile. Quantitative RT-PCR demonstrated that the two breast cancer cell lines contained significantly elevated GDPD5 mRNA levels compared to nonmalignant cells, which matched the low GPC levels in cancer and high GPC levels in nonmalignant cells. These results indicate that GDPD5 is responsible for the relatively low GPC levels in breast cancer cells, and that it may play an important role in choline phospholipid metabolism of breast cancer.