Molecular Cloning and Characterization of a Lysophosphatidic Acid Receptor, Edg-7, Expressed in Prostate

Abstract

Two G protein-coupled receptors (Edg-2) and (Edg-4) for the lysolipid phosphoric acid mediator lysophosphatidic acid have been described by molecular cloning. However, the calcium-mobilizing receptor Edg-4 is not expressed in some cell lines that exhibit robust calcium responses to this ligand, thus predicting the existence of additional receptor subtypes. We report here on the characterization of a third human lysophosphatidic acid receptor subtype, Edg-7, which mediates lysophosphatidic acid-evoked calcium mobilization. In a rat hepatoma Rh7777 cell line that lacks endogenous responses to lysophosphatidic acid, this lipid mediator, but not others, evokes calcium transients when the cells have been transfected with Edg-7 or Edg-4 DNAs. Furthermore, frog oocytes exhibit a calcium-mediated chloride conductance in response to mammalian-selective lysophosphatidic acid mimetics after injection of Edg-7 mRNA. Edg-7-expressing Rh7777 cells do not show inhibition of forskolin-driven rises in cAMP in response to lysophosphatidic acid. However, membranes from HEK293T cells cotransfected with Edg-7 and G(i2)alpha protein DNAs show lysophosphatidic acid dose-dependent increases in [gamma-(35)S]GTP binding with an EC(50) value of 195 nM. When we used this assay to compare various synthetic LPA analogs at Edg-2, Edg-4, and Edg-7 receptors, we found that ethanolamine-based compounds, which are full LPA mimetics at Edg-2 and Edg-4, exhibit little activity at the Edg-7 receptor. Edg-7 RNA was detected in extracts of several rat and human tissues including prostate. Together, our data indicate that Edg-7 is a third lysophosphatidic acid receptor that couples predominantly to G(q/11)alpha proteins.

Enhancement of survival by LPA via Erk1/Erk2 and PI 3-kinase/Akt pathways in a murine hepatocyte cell line

“…It has been accepted that hepatocytes and the liver lack LPA receptors (1,21,25). Particularly, no Edg2 mRNA was detected in liver tissue during Northern blotting (1,15,21).…”

“…LPA also evokes cellular effector functions, which are dependent on cytoskeletal responses such as contraction, secretion, adhesion, and chemotaxis. The cellular effects of LPA are mediated predominantly via G protein-coupled receptors, encoded by the endothelial differentiation genes Edg2, Edg4, and Edg7 (1,21,25). As it binds to Edg receptor, LPA recruits G i proteins, which may lead to a downstream activation of Erk1/Erk2 mitogen-activated protein (MAP) kinases and, via several intermediate effectors, induction of the serum response element (SRE)-driven cell proliferation (30,39).…”

Lysophosphatidic Acid-induced Mitogenesis Is Regulated by Lipid Phosphate Phosphatases and Is Edg-receptor Independent

“…Edg-2 is widely expressed, with highest mRNA levels appearing in brain (20), reflecting expression in Schwann cells and oligodendrocytes (29,30). Edg-4 is most highly expressed in testis and leukocytes (20), whereas Edg-7 is very highly expressed in kidney and prostate (21,22). When stably transfected into the LPA-unresponsive cell line RH7777 (Rat Hepatoma), Edg-2 mediates inhibition of cAMP accumulation, whereas Edg-4 and Edg-7 mediate calcium mobilization (22).…”

“…To date, eight members of the Edg cluster have been described. Edg-2 (15,19), -4 (20), and -7 (21,22) have been shown to be LPA receptors and Edg-1 (23,24), -3, -5 (25), -6 (26,27), and -8 (28) are receptors for the structurally related phospholipid sphingosine 1-phosphate. The LPA receptors differ with respect to distribution and G-protein coupling.…”

Lysophospholipid signaling: Beyond the EDGs

“…The McArtl rat hepatoma cell line 7777 (RH7777) cells are frequently used in studies utilizing the ectopic expression of LPA receptors, since these cells do not express the EDG-family LPA receptors and do not respond to LPA through any endogenous receptors as judged by calcium mobilization or inhibition of cAMP accumulation [15,23,24]. Other cell lines previously reported to be devoid of EDG-family receptors are HTC4 [25], LPA 1&2 −/− double knock-out mouse embryonic fibroblasts (DKO MEFs) [11] and the B103 rat neuroblastoma cell line [26].…”