Calcium Signaling of Dioleoyl Phosphatidic Acid via Endogenous LPA Receptors: A Study Using HCT116 and HT29 Human Colon Cancer Cell Lines

Lysophosphatidylethanolamine increases intracellular Ca(2+) through LPA(1) in PC-12 neuronal cells

G protein-coupled receptors (GPCRs) have been implicated in lysophosphatidylethanolamine (LPE)-induced increases in intracellular Ca(2+) ([Ca(2+)]i), but in different cell types, this response may be dependent or independent of lysophosphatidic acid (LPA) GPCR. The effects of LPEs from Grifola frondosa on the neuronal differentiation and apoptosis of PC-12 neuronal cells have been previously reported. In the present study, the authors sought to identify the mechanism responsible for the effects of LPEs in PC-12 neuronal cells. LPE increase [Ca(2+)]i concentration-dependently in PC-12 neuronal cells, but this LPE-induced [Ca(2+)]i increase was less than that elicited by LPA. Studies using specific inhibitors showed that LPE-induced Ca(2+) response was mediated via pertussis toxin-sensitive Gi/o proteins, edelfosine-sensitive phospholipase C, and 2-APB-sensitive IP3 receptor and by Ca(2+) influx across the cell membrane, and that this did not involve the conversion of LPE to LPA. Furthermore, LPE- and LPA-induced responses were found to show homologous and heterologous desensitization in PC-12 cells. VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases. Furthermore, AM-095 (a specific inhibitor of LPA1) inhibited LPE-induced Ca(2+) response completely in PC-12 cells. These findings indicate LPE increases [Ca(2+)]i via a LPA1/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise/Ca(2+) influx pathway in PC-12 neuronal cells.

Lysophosphatidylethanolamine utilizes LPA(1) and CD97 in MDA-MB-231 breast cancer cells

Lysophosphatidylethanolamine (LPE) is a lyso-type metabolite of phosphatidylethanolamine (a plasma membrane component), and its intracellular Ca(2+) ([Ca(2+)]i) increasing actions may be mediated through G-protein-coupled receptor (GPCR). However, GPCRs for lysophosphatidic acid (LPA), a structurally similar representative lipid mediator, have not been implicated in LPE-mediated activities in SK-OV3 or OVCAR-3 ovarian cancer cells or in receptor over-expression systems. In the present study, LPE-induced [Ca(2+)]i increase was observed in MDA-MB-231 cells but not in other breast cancer cell lines. In addition, LPE- and LPA-induced responses showed homologous and heterologous desensitization. Furthermore, VPC32183 and Ki16425 (antagonists of LPA1 and LPA3) inhibited LPE-induced [Ca(2+)]i increases, and knockdown of LPA1 by transfection with LPA1 siRNA completely inhibited LPE-induced [Ca(2+)]i increases. Furthermore, the involvement of CD97 (an adhesion GPCR) in the action of LPA1 in MDA-MB-231 cells was demonstrated by siRNA transfection. Pertussis toxin (a specific inhibitor of Gi/o proteins), edelfosine (an inhibitor of phospholipase C), or 2-APB (an inhibitor of IP3 receptor) completely inhibited LPE-induced [Ca(2+)]i increases, whereas HA130, an inhibitor of autotaxin/lysophospholipase D, did not. Therefore, LPE is supposed to act on LPA1-CD97/Gi/o proteins/phospholipase C/IP3/Ca(2+) rise in MDA-MB-231 breast cancer cells.