Molecular cloning of a high-affinity receptor for the growth factor-like lipid mediator lysophosphatidic acid from  Xenopus  oocytes

Abstract

Lysophosphatidic acid (1-acyl-2-lyso-snglycero-3-phosphate, LPA) is a multifunctional lipid mediator found in a variety of organisms that span the phylogenetic tree from humans to plants. Although its physiological function is not clearly understood, LPA is a potent regulator of mammalian cell proliferation; it is one of the major mitogens found in blood serum. In Xenopus laevis oocytes, LPA elicits oscillatory Cl ؊ currents. This current, like other effects of LPA, is consistent with a plasma membrane receptor-mediated activation of G protein-linked signal transduction pathways. Herein we report the identification of a complementary DNA from Xenopus that encodes a functional high-affinity LPA receptor. The predicted structure of this protein of 372 amino acids contains features common to members of the seven transmembrane receptor superfamily with a predicted extracellular amino and intracellular carboxyl terminus. An antisense oligonucleotide derived from the first 5-11 predicted amino acids, selectively inhibited the expression of the endogenous high-affinity LPA receptors in Xenopus oocytes, whereas the same oligonucleotide did not affect the low-affinity LPA receptor. Expression of the full-length cRNA in oocytes led to an increase in maximal Cl ؊ current due to increased expression of the high-affinity LPA receptor, but activation of the low-affinity receptor was, again, unaffected. Oocytes expressing cRNA prepared from this clone showed no response to other lipid mediators including prostaglandins, leukotrienes, sphingosine 1-phosphate, sphingosylphosphorylcholine, and platelet-activating factor, suggesting that the receptor is highly selective for LPA.

Human Lysophosphatidic Acid Acyltransferase

“…This suggests the possibility that, at least in the brain and liver, LPA signaling and metabolism are mediated by additional receptors and enzymes. The cloning from Xenopus oocytes of an LPA receptor cDNA that bears little sequence identity to the mouse brain LPA receptor supports this possibility (9).…”

“…In addition, LPA is a potent promoter of tumor cell growth and invasion (5,6). LPA exerts its biological effects via at least one, but perhaps multiple, specific G protein-coupled receptors (7)(8)(9). Engagement of the receptor results in activation of Ras and the Raf/mitogen-activated protein kinase pathway, stimulation of phospholipases C and D, inhibition of adenylyl cyclase, and tyrosine phosphorylation of focal adhesion proteins along with actin cytoskeleton remodeling (1).…”

Lysophosphatidic Acid Induces Necrosis and Apoptosis in Hippocampal Neurons

“…The responses to this potent biomediator are clearly cell type-specific, as illustrated by the LPA-mediated stimulation of proliferation of many different cell types, including astrocytes; inhibition of proliferation of myeloma cells; and stimulation of differentiation of keratinocytes (van Corven et al, 1989;Tigyi et al, 1994;Tokumura et al, 1994;Piazza et a!., 1995;, as compared with the LPA-induced neuronal degeneration described in this study. There are multiple LPA receptors (van der Bend et al, 1992;Shiono et al, 1993;Thomson et al, 1994;Guo et a!., 1996;Hecht et a!., 1996;Liliom et al, 1996), and these may be one factor in the cell type specificity of LPA responses. In fact, the expression of one LPA receptor in the brain occurs in a temporal and spatial manner consistent with a role for LPA in developmental programmed cell death of neurons (Hecht et a!., 1996).…”

Platelet-activating Factor (PAF) Induces Growth Stimulation, Inhibition, and Suppression of Oncogenic Transformation in NRK Cells Overexpressing the PAF Receptor

“…A thrombin receptor induces mitogenic response in various types of cells (22). Lysophosphatidic acid is considered to be the most potent growth factor in serum (23), and its receptors have been cloned (24,25).…”