Lysophospholipid Receptor-Mediated Calcium Signaling in Human Keratinocytes

The lysophospholipids, sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA), stimulate chemotaxis and induce differentiation of human keratinocytes. As Ca2+ plays an important role in keratinocyte differentiation, we studied Ca2+ signaling by S1P and LPA in these cells, known to express mRNA transcripts of the S1P1-5 and LPA1-3 receptors, and the receptor subtypes involved in this process. S1P and LPA caused transient increases in intracellular free Ca2+ concentration ([Ca2+]i), with pEC50 values of 8.5±0.11 and 7.5±0.23, respectively. The [Ca2+]i increases are apparently mediated by stimulation of phospholipase C and involve Ca2+ mobilization from thapsigargin-sensitive stores and subsequent Ca2+ influx. The LPA-induced [Ca2+]i increases were not inhibited by the LPA1/3 receptor antagonist, dioctanoylglycerol pyrophosphate. The S1P-induced [Ca2+]i increases were largely inhibited by the putative S1P3 antagonist, BML-241, and the S1P1/3 antagonist, VPC23019. The S1P1-specific agonist, SEW2871, did not increase [Ca2+]i but stimulated chemotaxis of keratinocytes, which was fully blocked by S1P1 antisense oligonucleotides. The data indicate that LPA and S1P potently increase [Ca2+]i in human keratinocytes and that the effect of LPA is mediated by LPA2, whereas that of S1P is mediated at least to a large part by S1P3. The S1P1 receptor, without stimulating [Ca2+]i increases, mediates chemotaxis of keratinocytes.