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The role of different G protein-coupled receptors (GPCRs) in the cardiovascular system is well understood in cardiomyocytes and vascular smooth muscle cells (VSMCs). In the former, stimulation of Gs-coupled receptors leads to increases in contractility, whereas stimulation of Gq-coupled receptors modulates cellular survival and hypertrophic responses. In VSMCs, stimulation of GPCRs also modulates contractile and cell growth phenotypes. Here, we will focus on the relatively less well-studied effects of GPCRs in cardiac fibroblasts, focusing on key signaling events involved in the activation and differentiation of these cells. We also review the hierarchy of signaling events driving the fibrotic response and the communications between fibroblasts and other cells in the heart. We discuss how such events may be distinct depending on where the GPCRs and their associated signaling machinery are localized in these cells with an emphasis on nuclear membrane-localized receptors. Finally, we explore what such connections between the cell surface and nuclear GPCR signaling might mean for cardiac fibrosis. [ABSTRACT FROM AUTHOR]

Incorporating mechanical cues into cellular responses allows us to experience our direct environment. Specialized cells can perceive and discriminate between different physical properties such as level of vibration, temperature, or pressure. Mechanical forces are abundant signals that also shape general cellular responses such as cytoskeletal rearrangement, differentiation, or migration and contribute to tissue development and function. The molecular structures that perceive and transduce mechanical forces are specialized cytoskeletal proteins, cell junction molecules, and membrane proteins such as ion channels and metabotropic receptors. G protein-coupled receptors (GPCRs) have attracted attention as metabotropic force receptors as they are among the most important drug targets. This review summarizes the function of mechano-sensitive GPCRs, specifically, the angiotensin II type 1 receptor and adrenergic, apelin, histamine, parathyroid hormone 1, and orphan receptors, focusing particularly on the advanced knowledge gained from adhesion-type GPCRs. We distinguish between shear stress and cell swelling/stretch as the two major types of mechano-activation of these receptors and contemplate the potential contribution of the force-fromlipid and force-from-tether models that have previously been suggested for ion channels. [ABSTRACT FROM AUTHOR]

Mechanochemical signal transduction occurs when mechanical forces, such as fluid shear stress, are converted into biochemical responses within the cell. The molecular mechanisms by which endothelial cells (ECs) sense/transduce shear stress into biological signals, including the nature of the mechanosensor, are still unclear. G proteins and G protein-coupled receptors (GPCRs) have been postulated independently to mediate mechanotransduction. In this study, we used in situ proximity ligation assay (PLA) to investigate the role of a specific GPCR/Gαq/11 pair in EC shear stress-induced mechanotransduction. We demonstrated that sphingosine 1-phosphate (S1P) stimulation causes a rapid dissociation at 0.5 min of Gαq/11 from its receptor S1P3, followed by an increased association within 2 min of GPCR kinase-2 (GRK2) and β-arrestin-1/2 with S1P3 in human coronary artery ECs, which are consistent with GPCR/Gαq/11 activation and receptor desensitization/internalization. The G protein activator AlF4 resulted in increased dissociation of Gαq/11 from S1P3, but no increase in association between S1P3 and either GRK2 or β-arrestin-1/2. The G protein inhibitor guanosine 5′-(β-thio) diphosphate (GDP-β-S) and the S1P3 antagonist VPC23019 both prevented S1P-induced activation. Shear stress also caused the rapid activation within 7 s of S1P3/Gαq/11. There were no increased associations between S1P3 and GRK2 or S1P3 and β-arrestin-1/2 until 5 min. GDP-β-S, but not VPC23019, prevented dissociation of Gαq/11 from S1P3 in response to shear stress. Shear stress did not induce rapid dephosphorylation of β-arrestin-1 or rapid internalization of S1P3, indicating no GPCR activation. These findings suggest that Gαq/11 participates in the sensing/transducing of shear stress independently of GPCR activation in ECs. [ABSTRACT FROM AUTHOR]

Given the fundamental role of β-catenin signaling in intestinal epithelial cell proliferation and the growth-promoting function of protein kinase D1 (PKD1) in these cells, we hypothesized that PKDs mediate cross talk with β-catenin signaling. The results presented here provide several lines of evidence supporting this hypothesis. We found that stimulation of intestinal epithelial IEC-18 cells with the G protein-coupled receptor (GPCR) agonist angiotensin II (ANG II), a potent inducer of PKD activation, promoted endogenous β-catenin nuclear localization in a time-dependent manner. A significant increase was evident within 1 h of ANG II stimulation (P < 0.01), peaked at 4 h (P < 0.001), and declined afterwards. GPCR stimulation also induced a marked increase in β-catenin-regulated genes and phosphorylation at Ser552 in intestinal epithelial cells. Exposure to preferential inhibitors of the PKD family (CRT006610 or kb NB 142-70) or knockdown of the isoforms of the PKD family prevented the increase in β-catenin nuclear localization and phosphorylation at Ser552 in response to ANG II. GPCR stimulation also induced the formation of a complex between PKD1 and β-catenin, as shown by coimmunoprecipitation that depended on PKD1 catalytic activation, as it was abrogated by cell treatment with PKD family inhibitors. Using transgenic mice that express elevated PKD1 protein in the intestinal epithelium, we detected a marked increase in the localization of β-catenin in the nucleus of crypt epithelial cells in the ileum of PKD1 transgenic mice, compared with nontransgenic littermates. Collectively, our results identify a novel cross talk between PKD and β-catenin in intestinal epithelial cells, both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Given the fundamental role of β-catenin signaling in intestinal epithelial cell proliferation and the growth-promoting function of protein kinase D1 (PKD1) in these cells, we hypothesized that PKDs mediate cross talk with β-catenin signaling. The results presented here provide several lines of evidence supporting this hypothesis. We found that stimulation of intestinal epithelial IEC-18 cells with the G protein-coupled receptor (GPCR) agonist angiotensin II (ANG II), a potent inducer of PKD activation, promoted endogenous β-catenin nuclear localization in a time-dependent manner. A significant increase was evident within 1 h of ANG II stimulation (P < 0.01), peaked at 4 h (P < 0.001), and declined afterwards. GPCR stimulation also induced a marked increase in β-catenin-regulated genes and phosphorylation at Ser552 in intestinal epithelial cells. Exposure to preferential inhibitors of the PKD family (CRT006610 or kb NB 142-70) or knockdown of the isoforms of the PKD family prevented the increase in β-catenin nuclear localization and phosphorylation at Ser552 in response to ANG II. GPCR stimulation also induced the formation of a complex between PKD1 and β-catenin, as shown by coimmunoprecipitation that depended on PKD1 catalytic activation, as it was abrogated by cell treatment with PKD family inhibitors. Using transgenic mice that express elevated PKD1 protein in the intestinal epithelium, we detected a marked increase in the localization of β-catenin in the nucleus of crypt epithelial cells in the ileum of PKD1 transgenic mice, compared with nontransgenic littermates. Collectively, our results identify a novel cross talk between PKD and β-catenin in intestinal epithelial cells, both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

The calcium-sensing receptor (CaSR) has played an important role as a target in the treatment of a variety of disease states over the past 20 plus years. In this review, we give an overview of the receptor at the cellular level and then provide details as to how this receptor has been targeted to modulate cellular ion transport mechanisms. As a member of the G proteincoupled receptor (GPCR) family, it has a high degree of homology with a variety of other members in this class, which could explain why this receptor has been identified in so many different tissues throughout the body. This diversity of locations sets it apart from other members of the family and may explain how the receptor interacts with so many different organ systems in the body to modulate the physiology and pathophysiology. The receptor is unique in that it has two large exofacial lobes that sit in the extracellular environment and sense changes in a wide variety of environmental cues including salinity, pH, amino acid concentration, and polyamines to name just a few. It is for this reason that there has been a great deal of research associated with normal receptor physiology over the past 20 years. With the ongoing research, in more recent years a focus on the pathophysiology has emerged and the effects of receptor mutations on cellular and organ physiology have been identified. We hope that this review will enhance and update the knowledge about the importance of this receptor and stimulate future potential investigations focused around this receptor in cellular, organ, and systemic physiology and pathophysiology. [ABSTRACT FROM AUTHOR]

Cyclic AMP signals encode information required to differentially regulate a wide variety of cellular responses; yet it is not well understood how information is encrypted within these signals. An emerging concept is that compartmentalization underlies specificity within the cAMP signaling pathway. This concept is based on a series of observations indicating that cAMP levels are distinct in different regions of the cell. One such observation is that cAMP production at the plasma membrane increases pulmonary microvascular endothelial barrier integrity, whereas cAMP production in the cytosol disrupts barrier integrity. To better understand how cAMP signals might be compartmentalized, we have developed mathematical models in which cellular geometry as well as total adenylyl cyclase and phosphodiesterase activities were constrained to approximate values measured in pulmonary microvascular endothelial cells. These simulations suggest that the subcellular localizations of adenylyl cyclase and phosphodiesterase activities are by themselves insufficient to generate physiologically relevant cAMP gradients. Thus, the assembly of adenylyl cyclase, phosphodiesterase, and protein kinase A onto protein scaffolds is by itself unlikely to ensure signal specificity. Rather, our simulations suggest that reductions in the effective cAMP diffusion coefficient may facilitate the formation of substantial cAMP gradients. We conclude that reductions in the effective rate of cAMP diffusion due to buffers, structural impediments, and local changes in viscosity greatly facilitate the ability of signaling complexes to impart specificity within the cAMP signaling pathway. [ABSTRACT FROM AUTHOR]

Receptor ligands, identified as antagonists, based on the absence of stimulation of signaling, can rarely stimulate receptor internalization. D-Tyr-Gly-[(Nle28,31,DTrp30) CCK-26-32]-2-phenylethyl ester (D-Trp-OPE) is such a ligand that binds to the cholecystokinin (CCK) receptor and stimulates internalization. Here, the molecular basis of this trafficking event is explored, with the assumption that ligand binding initiates conformational change, exposing an epitope to direct endocytosis. Ligandstimulated internalization was studied morphologically using fluorescent CCK and D-Trp-OPE. D-Trp-OPE occupation of Chinese hamster ovary cell receptors stimulated internalization into the same region as CCK. Arrestin-biased action was ruled out using morphological translocation of fluorescent arrestin 2 and arrestin 3, moving to the membrane in response to CCK, but not D-Trp-OPE. Possible roles of the carboxyl terminus were studied using truncated receptor constructs, eliminating the proline-rich distal tail, the serine/threoninerich midregion, and the remainder to the vicinal cysteines. None of these constructs disrupted D-Trp-OPE-stimulated internalization. Possible contributions of transmembrane segments were studied using competitive inhibition with peptides that also had no effect. Intracellular regions were studied with a similar strategy using coexpressing cell lines. Peptides corresponding to ends of each loop region were studied, with only the peptide at the carboxyl end of the third loop inhibiting D-Trp-OPE-stimulated internalization but having no effect on CCK-stimulated internalization. The region contributing to this effect was refined to peptide 309-323, located below the recognized G protein-association motif. While a receptor in which this segment was deleted did internalize in response to D-Trp-OPE, it exhibited abnormal ligand binding and did not signal in response to CCK, suggesting an abnormal conformation and possible mechanism of internalization distinct from that being studied. This interpretation was further supported by the inability of peptide 309-323 to inhibit its D-Trp-OPE-stimulated internalization. Thus the 309-323 region of the type 1 CCK receptor affects antagonist-stimulated internalization of this receptor, although its mechanism and interacting partner are not yet clear. [ABSTRACT FROM AUTHOR]

Angiotensin II (AII) binds to G protein-coupled receptor AT1 and stimulates extracellular signal-regulated kinase (ERK), leading to vascular smooth muscle cells (VSMC) proliferation. Proliferation of mammalian cells is tightly regulated by adhesion to the extracellular matrix, which occurs via integrins. To study cross-talk between G protein-coupled receptor- and integrin-induced signaling, we hypothesized that integrins are involved in AII-induced proliferation of VSMC. Using Oligo GEArray and quantitative RT-PCR, we established that messages for α1-, α5-, αV-, and β1-integrins are predominant in VSMC. VSMC were cultured on plastic dishes or on plates coated with either extracellular matrix or poly-d-lysine (which promotes electrostatic cell attachment independent of integrins). AII significantly induced proliferation in VSMC grown on collagen I or fibronectin, and this effect was blocked by the ERK inhibitor PD-98059, suggesting that AII-induced proliferation requires ERK activity. VSMC grown on collagen I or on fibronectin demonstrated approximately three- and approximately sixfold increases in ERK phosphorylation after stimulation with 100 nM AII, respectively, whereas VSMC grown on poly-d-lysine demonstrated no significant ERK activation, supporting the importance of integrin-mediated adhesion. AII-induced ERK activation was reduced by >65% by synthetic peptides containing an RGD (arginine-glycine-aspartic acid) sequence that inhibit α5β1-integrin, and by ~60% by the KTS (lysine-threonine-serine)-containing peptides specific for integrin-α1β1. Furthermore, neutralizing antibody against β1-integrin and silencing of α1, α5, and β1 expression by transfecting VSMC with short interfering RNAs resulted in decreased AII-induced ERK activation. This work demonstrates roles for specific integrins (most likely α5β1 and α1β1) in AII-induced proliferation of VSMC. [ABSTRACT FROM AUTHOR]

Angiotensin II-induced upregulation of AT1-receptor expression: sequential activation of NF-κB and Elk-1 in neurons. Am J Physiol Cell Physiol 299: C561-C569, 2010. First published June 16, 2010; doi:10.1152/ajpcell.00127.2010.--It has been clearly established that increased circulating angiotensin II (ANG II) with concurrent upregulation of brain and peripheral ANG II type I receptors (AT1R) are important mediators in the pathophysiology of several diseases characterized by sympatho-excitation. In an effort to further understand the regulation of AT1R expression in neurons, we determined the role of sequential activation of the transcription factors nuclear factor-κB (NF-κB) and Ets-like protein 1 (Elk-1) in AT1R upregulation. We used CATH.a neurons as our neuronal cell model. Cells were treated with ANG II (100 nM) over a preset time course. Following ANG II activation, there was a temporal increase in the p65 subunit of NF-κB that was observed at 30 min, peaked at 1 h, and was sustained up to 24 h. There was a concomitant decrease of IκB and increased IκK expression. We also observed an increase in AT1R expression which followed the temporal increase of NF-κB. The activation of NF-κB was blocked by using the inhibitors parthenolide or p65 small interfering RNA (siRNA) which both led to a decrease in AT1R expression. The expression of Elk-1 was upregulated over a time period following ANG II activation and was decreased following NF-κB inhibition, p65-DNA binding was assessed using electrophoretic mobility shift assay, and it was shown that there was a time-dependent increased binding that was inhibited by means of parthenolide pretreatment or siRNA-mediated p65 gene silencing. Therefore, our results suggest a combined role for the transcription factors NF-κB and Elk-1 in the upregulation of AT1R in the CATH.a cell neuronal model. These data imply a positive feedback mechanism that may impact neuronal discharge sensitivity in response to ANG II. [ABSTRACT FROM AUTHOR]

ln vascular endothelial cells, specialized microdomains of plasma membrane termed caveolae modulate various receptor signal transduction pathways regulated by caveolin-1, a resident protein of caveolae. We examined whether transforming growth factor-β1 (TGF-β1), a mu!tifunctional cytokine, alters expression levels of caveolin-1 and influences heterologous receptor signaling. Treatment of cultured bovine aortic endothelial cells (BAEC) with TGF-β1 induces marked decreases in caveolin-1 expression in a timeand dose-dependent fashion at both levels of protein and mRNA. A pharmacological inhibitor of activin receptor-like kinase 5 (ALK-5) counteracts caveolin-1 downregulation by TGF-β1, indicating the involvement of ALK-5 receptor subtype for TGF-β1. Sphingosine 1-phosphate (SIP) is a serum-borne angiogenic lipid growth factor that exerts a wide variety of biological actions. SIP modulates G protein-coupled SIP receptors, activating downstream molecules kinases AMP-activated protein kinase (AMPK), and Akt as well as a small G protein Rac1, ultimately to promote migration. Because SIP receptor signaling is associated with caveolae/caveolin-1, we examined whether pretreatment with TGF-β1 enhances effects of SIP on BAEC. Whereas SIP alone evokes robust BAEC responses to SIP, pretreatment with TGF-β1 leads to even higher magnitudes of SIP-elicited signaling responses and cell migration. Conversely, genetic knockdown of caveolin-1 using small interfering RNA mimics TGF-β1-induced promotion of BAEC responses to SiP. Collectively, these data demonstrate that TGF-β1 downreguiates caveolin-1 of cultured endothelial cells, involving ALK-5 receptor subtype. Because downregulation of caveolin-1 by TGF-β1 promotes subsequent heterologous receptor signaling by SIP, these results may also identify novel point of cross-talk between cytokines and sphingolipids within endothelial signal transduction machineries. [ABSTRACT FROM AUTHOR]

The previously "orphan" G protein-coupled receptor GPR17 is structurally related to both P2Y nucleotide receptors and to receptors for cysteinyl leukotrienes. Genomic analysis revealed two putative open reading frames encoding for a "short" and a "long" receptor isoform of 339and 367-amino acids, respectively, with the latter displaying a 28-amino acid longer NH2 terminus. The short isoform has been recently "deorphanized," revealing dual responses to uracil nucleotides and cysteinyl leukotrienes. No information regarding the ligand specificity, tissue distribution, or pathophysiological roles of the long receptor isoform is available. In the present study, we cloned human long-GPR17, determined its tissue distribution, and characterized its pharmacological specificity in 1321N1 cells by [35S]GTPγS binding (which measures the ability of G proteincoupled receptor agonists to increase GTP binding to G proteins) and whole cell patch-clamp recording measuring receptor coupling to K+ channels. [35S]GTPγS binding in long-GPR17-expressing 1321N1 cells revealed concentration-dependent responses to uracil nucleotides (UDPgalactose = UDP> UDP-glucose) and cysteinyl leukotrienes (LTC4 > LTD4), which were counteracted by a purinergic (cangrelor) and a cysteinyl leukotriene antagonist (montelukast), respectively. The nonhydrolyzable AlP analog ATPγS also acted as an antagonist. GPR17 coupled to Gi and, to a lesser extent, Gq proteins. UDP-glucose and LTD4 also induced increases in overall outward K+ currents, which were antagonized by the purinergic antagonists MRS2179 and cangrelor and by montelukast. We conclude that the previously uncharacterized long-GPR17 isoform is a functional receptor that is stimulated by both uracil nucleotides and cysteinyl leukotrienes. We also show that the signaling pathway of GPR17 involves the generation of outward K+ currents, an important protective mechanism that, in brain, is specifically aimed at reducing neuronal hyperexcitability and resultant neuronal injury. [ABSTRACT FROM AUTHOR]

G protein-coupled receptors (GPCRs) control neuronal functions via ion channel modulation. For voltage-gated ion channels, gating charge movement precedes and underlies channel opening. Therefore, we sought to investigate the effects of G protein activation on gating charge movement. Nonlinear capacitive currents were recorded using the whole cell patch-clamp technique in cultured rat sympathetic neurons. Our results show that gating charge movement depends on voltage with average Boltzmann parameters: maximum charge per unit of linear capacitance (Qmax) = 6.1 ± 0.6 nC/µF, midpoint (Vh) = -29.2 ± 0.5 mV, and measure of steepness (k) = 8.4 ± 0.4 mV. Intracellular dialysis with GTPγS produces a nonreversible ~34% decrease in Qmax, a ~10 mV shift in Vh, and a ~63% increase in k with respect to the control. Norepinephrine induces a ~7 mV shift in Vh and ~40% increase in k. Overexpression of G protein α1γ4 subunits produces a ~13% decrease in Qmax, a ~9 mV shift in Vh, and a ~28% increase in k. We correlate charge movement modulation with the modulated behavior of voltage-gated channels. Concurrently, G protein activation by transmitters and GTP-γS also inhibit both Na+ and N-type Ca2+ channels. These results reveal an inhibition of gating charge movement by G protein activation that parallels the inhibition of both Na+ and N-type Ca2+ currents. We propose that gating charge movement decrement may precede or accompany some forms of GPCR-mediated channel current inhibition or downregulation. This may be a common step in the GPCR-mediated inhibition of distinct populations of voltage-gated ion channels. [ABSTRACT FROM AUTHOR]

Angiotensin II (ANG II) type I (AT1) receptors, similar to other G protein-coupled receptors, undergo desensitization and internalization, and potentially nuclear localization, subsequent to agonist interaction. Evidence suggests that the carboxy-terminal tail may be involved in receptor nuclear localization. In the present study, we examined the carboxy- terminal tail of the receptor for specific regions responsible for the nuclear translocation phenomenon and resultant nuclear activation. Human embryonic kidney cells stably expressing either a wild-type AT1A receptor-green fluorescent protein (AT1AR/GFP) construct or a site-directed mutation of a putative nuclear localization sequence (NLS) [K307Q]AT1AR/GFP (KQ/AT1AR/GFP), were examined for differences in receptor nuclear trafficking and nuclear activation. Receptor expression, intracellular signaling, and ANG II-induced internalization of the wild-type/GFP construct and of the KQ/AT1AR/GFP mutant was similar. Laser scanning confocal microscopy showed that in cells expressing the AT1AR/GFP, trafficking of the receptor to the nuclear area and colocalization with lamin B occurred within 30 mm of ANG II (100 nM) stimulation, whereas the KQ/AT1AR/GFP mutant failed to demonstrate nuclear localization. Immunoblotting of nuclear lysates with an anti-GFP antibody confirmed these observations. Nuclear localization of the wild-type receptor correlated with increase transcription for both EGR-1 and PTGS-2 genes while the nuclear-deficient KQ/AT1AR/GFP mutant demonstrated increases for only the EGR-1 gene. These results suggest that a NLS (KKFKKY; aa307-312) is located within the cytoplasmic tail of the AT1A receptor and that nuclear localization of the receptor corresponds with specific activation of transcription for the COX-2 gene PTGS-2. [ABSTRACT FROM AUTHOR]

Sphingosine 1-phosphate (SIP) is a platelet-derived angiogenic lipid growth factor, modulating G-protein-coupled SIP1 receptors (SIP1-R) to activate endothelial nitric oxide synthase (eNOS), as well as MAPK pathways in endothelial cells. We explored whether and how hydrogen peroxide (H2O2), a representative reactive oxygen species, alters SIP1-R expression and influences SIP signaling in cultured bovine aortic endothelial cells (BAECs). When BAECs are treated with pathophysiologically relevant concentrations of H2O2 (150 µM for 30 mm), SIP1-R protein expression levels are acutely augmented by ~30-fold in a dose-dependent fashion. When BAECs have been pretreated with H2O2, subsequent SIP stimulation (100 nM) leads to a higher degree of eNOS enzyme activation (assessed as intracellular cGMP content, 1.7 ± 0.2-fold vs. no H2O2 pretreatment groups, P < 0.05), associated with a higher magnitude of phosphorylation responses of eNOS and MAPK ERK1/2. PP2, an inhibitor of Src-family tyrosine kinase, abolished the effects of H2O2 on both SIP1-R protein upregulation and enhanced BAEC responses to SIP. H2O2 does not augment SIP1 mRNA expression, whereas VEGF under identical cultures leads to increases in SIP1 mRNA signals. Whereas H2O2 attenuates proliferation of BAECs, addition of SIP restores growth responses of these cells. These results demonstrate that extracellularly administered H2O2 increases SIP1-R expression and promotes endothelial responses for subsequent SIP treatment. These results may identify potentially important points of cross-talk between reactive oxygen species and sphingolipid pathways in vascular responses. [ABSTRACT FROM AUTHOR]

Lysophosphatidic acid (LPA) refers to a family of small phospholipid mediators that are generated in response to agonist stimulation in diverse cell types. LPA binds to G protein-coupled receptors to elicit numerous biological responses, including proliferation and inflammation. In this study, LPA production and response were characterized in a human corneal epithelial cell line, 2.040 pRSV-T. LPA levels in cells and medium are increased by exogenous 18:1 LPA (oleoyl-LPA), LPS, 1L-1β, and TNF-α. LPS, IL-1β, and TNF-α, which mediate ocular inflammation, stimulate activation of p38, ERK, and Akt kinases in the corneal cell line. Similar responses are elicited by 18:1 LPA. Pertussis toxin (PTX) blocks LPA-induced activation of p38 and ERK but only slightly inhibits LPA-induced activation of Akt. All of the agonists tested, including LPA, stimulate proliferation of 2.040 pRSV-T cells. In these cells, both Akt and ERK pathways are important for LPA-induced proliferation. Thus PTX only partially suppresses the mitogenic response to LPA. Transcripts for the LPA receptors LPA1/EDG-2, LPA2/EDG-4, and LPA3/EDG-7 are expressed by the corneal cell line. Ki16425, an antagonist for LPA receptors, was used to explore the autocrine role of LPA. LPA-induced activations of p38, ERK, and Akt kinases, as well as proliferation, are inhibited by Ki16425. Ki16425 partially inhibits signal transduction and proliferation induced by the inflammatory agents tested. We conclude that LPA, produced in corneal epithelial cells in response to inflammatory agonists, contributes to mediating the mitogenic responses to these agonists in an autocrine fashion. [ABSTRACT FROM AUTHOR]