Disease relevance of F2RL3

• A partial cDNA sequence of a fourth member of this family (PAR4) was identified in an expressed sequence tag database, and the full-length cDNA clone has been isolated from a lymphoma Daudi cell cDNA library [1].
• This was deduced from the findings that a further calcium signal could be observed in human astrocytoma cells stimulated with alpha-thrombin after SFLLRN and the PAR-4-activating peptide GYPGQV also induced a calcium response [2].
• Further mechanistic studies on the actions of PAR-1 and PAR-4 as detrimental in experimental models of Parkinson's disease are warranted [3].
• Here we show that at the relatively high concentration of agonist most likely found at the site of a local thrombus, dual inhibition of the P2Y12 receptor and calcium mobilization result in a complete inhibition of PAR4-induced aggregation, while having no effect on either thrombin or PAR1-mediated platelet aggregation [4].
• Adenocarcinomas were significantly more positive than SCC for PAR-1 (17 vs. 8 cases) and PAR-4 (10 vs. 5 cases) [5].

High impact information on F2RL3

• PAR3 is a cofactor for PAR4 activation by thrombin [6].
• The response mediated by PAR4, however, was limited to platelet aggregation and similar to that triggered in platelets by weaker agonists such as ADP or epinephrine [7].
• COS cells transiently transfected with PAR4 resulted in the formation of intracellular inositol triphosphate when treated with either thrombin or trypsin [1].
• By fluorescence in situ hybridization, the human PAR4 gene was mapped to chromosome 19p12 [1].
• Northern blot showed that PAR4 mRNA was expressed in a number of human tissues, with high levels being present in lung, pancreas, thyroid, testis, and small intestine [1].

Biological context of F2RL3

• The platelet thrombin receptors, PAR (protease-activated receptor) 1 PAR-4 and GPIb-IX-V (glycoprotein Ib-IX-V) have been described as potential contributors of thrombin-induced platelet aggregation [8].
• For example, AYPGKF activated and desensitized PAR4 in platelets and, like thrombin, triggered phosphoinositide hydrolysis but not inhibition of adenylyl cyclase in PAR4-expressing cells [9].
• Studies carried out in the past 12 years have established that activation of protease-activated receptor (PAR)-1 and PAR-4 by thrombin essentially drives human platelet activation [10].
• Biotinylation of cell-surface proteins showed that PAR-4 was internalised after stimulation by thrombin [11].
• The selective activation of each PAR by short synthetic peptides representing these sequences has demonstrated that PAR1, PAR2 and PAR4 play important roles in regulating physiological responses ranging from vasoregulation and cell growth to inflammation and nociception [12].

Anatomical context of F2RL3

• Activation of protease-activated receptor (PAR)-1, PAR-2, and PAR-4 stimulates IL-6, IL-8, and prostaglandin E2 release from human respiratory epithelial cells [13].
• Intracellular Ca2+ levels were assessed in A549 cells and in mouse fibroblasts expressing the human protease activated receptor (PAR)1, PAR2 or PAR4 [14].
• The recent identification of two new thrombin receptors, PAR3 and PAR4, led us to re-examine the basis for endothelial cell responses to thrombin [15].
• Thus, thrombin plays a dual role in modulating the motility of the oesophageal muscularis mucosae, producing contraction via PAR-1 and relaxation via PAR-4 [16].
• Preconditioning with specific local infusion of agonist peptides for PAR-1 and PAR-4 3 days before unilateral 6-OHDA administration (10 mug into the medial forebrain bundle) was tested [3].

Associations of F2RL3 with chemical compounds

• PAR-4 agonist AYPGKF stimulates thromboxane production by human platelets [17].
• PAR-4-induced stimulation is also significantly inhibited by 60 micromol/L genistein [17].
• AYPGKF was relatively specific for PAR4 in part due to the tyrosine at position 2; substitution of phenylalanine or p-fluorophenylalanine at this position produced peptides that activated both PAR1 and PAR4 [9].
• The PAR-4-mediated relaxation was resistant to tetrodotoxin (10 microM), apamin (0.1 microM), charybdotoxin (0.1 microM), L-N(G)-nitroarginine methyl ester (100 microM), indomethacin (3 microM), propranolol (5 microM) or adenosine 3', 5'-cyclic monophosphorothioate, 8-bromo, Rp-isomer (30 microM) [16].
• Platelet activation by thrombin, a serine protease, occurs by binding to and cleavage of the extracellular N-terminal domains of protease-activated receptors 1 and 4 (PAR1 and PAR4) [18].

Other interactions of F2RL3

• This result is consistent with the presence of another thrombin receptor on human platelets, namely PAR-4 [19].
• Whether PAR1 and PAR4 account for activation of human platelets by thrombin, or whether PAR3 or still other receptors contribute, is unknown [20].
• The activation of human platelets by alpha-thrombin is mediated at least in part by cleavage of protease-activated G-protein-coupled receptors, PAR-1 and PAR-4 [21].

Analytical, diagnostic and therapeutic context of F2RL3

• Thus, thrombin activates human platelets independently of PAR-1, i.e., through PAR-4, which we confirmed by PCR analysis [22].
• RESULTS: RT-PCR showed transcripts for PAR-1 and -2 receptors, but not for PAR-4 receptors [23].
• Globally, immunoprecipitation experiments and analysis of the cytoskeleton confirmed that GPIb translocation is powered by a contractile mechanism involving Ca2+ mobilization, actin polymerization, and myosin incorporation into the cytoskeleton and that both PAR-1 and PAR-4 can activate this process [24].

References