Lysophospholipid Receptor-Mediated Calcium Signaling in Human Keratinocytes

Abstract

The lysophospholipids, sphingosine-1-phosphate (S1P) and lysophosphatidic acid (LPA), stimulate chemotaxis and induce differentiation of human keratinocytes. As Ca(2+) plays an important role in keratinocyte differentiation, we studied Ca(2+) signaling by S1P and LPA in these cells, known to express mRNA transcripts of the S1P(1-5) and LPA(1-3) receptors, and the receptor subtypes involved in this process. S1P and LPA caused transient increases in intracellular free Ca(2+) concentration ([Ca(2+)](i)), with pEC(50) values of 8.5+/-0.11 and 7.5+/-0.23, respectively. The [Ca(2+)](i) increases are apparently mediated by stimulation of phospholipase C and involve Ca(2+) mobilization from thapsigargin-sensitive stores and subsequent Ca(2+) influx. The LPA-induced [Ca(2+)](i) increases were not inhibited by the LPA(1/3) receptor antagonist, dioctanoylglycerol pyrophosphate. The S1P-induced [Ca(2+)](i) increases were largely inhibited by the putative S1P(3) antagonist, BML-241, and the S1P(1/3) antagonist, VPC23019. The S1P(1)-specific agonist, SEW2871, did not increase [Ca(2+)](i) but stimulated chemotaxis of keratinocytes, which was fully blocked by S1P(1) antisense oligonucleotides. The data indicate that LPA and S1P potently increase [Ca(2+)](i) in human keratinocytes and that the effect of LPA is mediated by LPA(2), whereas that of S1P is mediated at least to a large part by S1P(3). The S1P(1) receptor, without stimulating [Ca(2+)](i) increases, mediates chemotaxis of keratinocytes.

Selectivity and Specificity of Sphingosine-1-Phosphate Receptor Ligands: Caveats and Critical Thinking in Characterizing Receptor-Mediated Effects

“…In a few studies, however, it has been also used as an S1P 3 receptor antagonist. For example, as mentioned above, Lichte et al (2008), reported that S1P-induced calcium signaling in human keratinocytes is mainly mediated by S1P 3 , because it can be blocked by the putative S1P 3 antagonists BML-241, and VPC23019. Recently, Jongsma et al (2009), using three different assays, have shown that several compounds of the VPC series, including VPC23019, behave as full or partial agonists at S1P 3 receptors.…”

“…Two studies that used higher BML-241/CAY10444 concentrations (50 and 100 μM) did observe an antagonist effect. In one of these studies, the S1P 1 agonist SEW2871 had no effect, while the S1P 1 /S1P 3 receptor antagonist VPC23019 reproduced the effect of BML-241/CAY10444 (Lichte et al, 2008). In the other study, B-cell migration was promoted by a mixed S1P 1 /S1P 3 receptor agonist (VPC24191), but not by the S1P 1 agonist SEW2871.…”

Lysophosphatidic Acid Promotes Cell Migration through STIM1- and Orai1-Mediated Ca 2+ i Mobilization and NFAT2 Activation

“…Binding of LPA to its specific receptors also elicits mobilization of intracellular calcium (Ca 2+ i ) from IP 3 -dependent stores and influx of extracellular Ca 2+ (Ca 2+ o ) mediated by incompletely defined mechanisms (Noguchi et al , 2009). Keratinocytes are known to express LPA 1–3 and respond to LPA with Ca 2+ transients (Anliker and Chun, 2004; Roedding et al , 2006; Ross et al , 2007; Lichte et al , 2008), but the physiological relevance of LPA-induced Ca 2+ fluxes and the downstream signaling pathways in mediating specific physiological effects remain to be defined.…”

SERCA2-Controlled Ca2+-Dependent Keratinocyte Adhesion and Differentiation Is Mediated via the Sphingolipid Pathway: A Therapeutic Target for Darier's Disease

“…Heightened levels of intracellular Sphingosine-1-phosphate (S1P) increase cytosolic Ca 2+ levels by direct mobilization of Ca 2+ from Thapsigargin (TG) sensitive stores (Meyer zu Heringdorf, et al, 2003), while increases in extracellular S1P concentrations activate Store Operated Calcium Entry (SOCE), through activation of G-protein coupled receptors (Mehta, et al, 2005). In keratinocytes, increased intracellular S1P enhances keratinocyte growth and differentiation, and blocks apoptosis (Hong, et al, 2008; Lichte, et al, 2008). Activating sphingosine kinase (SPHK1) increases intracellular S1P; thus, agents that activate this enzyme enhance expression of the differentiation markers filaggrin and involucrin in HaCAT keratinocytes (Hong, et al, 2008).…”