Expression and tissue distribution of the mRNAs encoding the human thromboxane A2 receptor (TP) alpha and beta isoforms

The human (h) TXA2 receptor (TP), a G protein-coupled receptor, exists as two isoforms, TPalpha and TPbeta, which arise by alternative mRNA splicing and differ exclusively in their carboxyl terminal cytoplasmic regions. In this study, a reverse transcriptase - polymerase chain reaction (RT-PCR) based strategy was developed to examine the expression of the TPs in tissues of physiologic relevance to TXA2. Although most of the 17 different cell / tissue types examined expressed both TP isoforms, the liver hepatoblastoma HepG2 cell line was found to exclusively express TPalpha mRNA. In most cell types, TPalpha mRNA predominated over TPbeta mRNA. Moreover, although the levels of TPalpha mRNA expression were similar in most of the cell / tissue types examined, extensive differences in the levels of TPbeta mRNA were observed. Consequently, the relative expression of TPalpha : TPbeta mRNA varied considerably due to extensive differences in TPbeta mRNA expression. Most strikingly, primary HUVEC’s were found to express: (i) low levels of TPbeta and (ii) approximately 6- fold greater levels of TPalpha than TPbeta . These data were confirmed in the spontaneously transformed HUVEC derived ECV304 cell line. Expression of TP mRNAs in the various tissue / cells correlated with protein expression, as assessed by radioligand binding using the selective TP antagonist [3H] SQ29,548.Health Research BoardWellcome TrustUniversity College Dublin. President’s Research Awardke,-SB02/09/201

Thromboxane A2 receptor mediated activation of the mitogen activated protein kinase cascades in human uterine smooth muscle cells

Both thromboxane (TX) A2 and 8-epi prostaglandin (PG) F2alpha have been reported to stimulate mitogenesis of vascular smooth muscle (SM) in a number of species. However, TXA2 and 8-epiPGF2alpha mediated mitogenic signalling have not been studied in detail in human vascular SM. Thus, using the human uterine ULTR cell line as a model, we investigated TXA2 receptor (TP) mediated mitogenic signalling in cultured human vascular SM cells. Both the TP agonist U46619 and 8-epiPGF2alpha elicited time and concentration dependent activation of the extracellular signal regulated kinase (ERK)s and c-Jun N-terminal kinase (JNK)s in ULTR cells. Whereas the TP antagonist SQ29,548 abolished U46619-mediated signalling, it only partially inhibited 8-epiPGF2alpha mediated ERK and JNK activation in ULTR cells. Both U46619 and 8-epiPGF2alpha induced ERK activations were inhibited by the protein kinase (PK) C, PKA and phosphoinositide 3-kinase inhibitors GF 109203X, H-89 and wortmannin, respectively, but were unaffected by pertussis toxin. In addition, U46619 mediated ERK activation in ULTR cells involves transactivation of the EGF receptor. In humans, TXA2 signals through two distinct TP isoforms. In investigating the involvement of the TP isoforms in mitogenic signalling, both TPalpha and TPbeta, independently directed U46619 and 8-epiPGF2alpha mediated ERK and JNK activation in human embryonic kidney (HEK) 293 cells over-expressing the individual TP isoforms. However, in contrast to that which occurred in ULTR cells, SQ29,548 abolished 8-epiPGF2alpha mediated ERK and JNK activation through both TPalpha and TPbeta in HEK 293 cells providing further evidence that 8-epiPGF2alpha may signal through alternative receptors, in addition to the TPs, in human uterine ULTR cells.Health Research BoardWellcome TrustIrish Heart FoundationEnterprise Irelandke,ti, -SB01/09/201

Expression and tissue distribution of the mRNAs encoding the human thromboxane A2 receptor (TP) alpha and beta isoforms

The human (h) TXA2 receptor (TP), a G protein-coupled receptor, exists as two isoforms, TPalpha and TPbeta, which arise by alternative mRNA splicing and differ exclusively in their carboxyl terminal cytoplasmic regions. In this study, a reverse transcriptase - polymerase chain reaction (RT-PCR) based strategy was developed to examine the expression of the TPs in tissues of physiologic relevance to TXA2. Although most of the 17 different cell / tissue types examined expressed both TP isoforms, the liver hepatoblastoma HepG2 cell line was found to exclusively express TPalpha mRNA. In most cell types, TPalpha mRNA predominated over TPbeta mRNA. Moreover, although the levels of TPalpha mRNA expression were similar in most of the cell / tissue types examined, extensive differences in the levels of TPbeta mRNA were observed. Consequently, the relative expression of TPalpha : TPbeta mRNA varied considerably due to extensive differences in TPbeta mRNA expression. Most strikingly, primary HUVEC’s were found to express: (i) low levels of TPbeta and (ii) approximately 6- fold greater levels of TPalpha than TPbeta . These data were confirmed in the spontaneously transformed HUVEC derived ECV304 cell line. Expression of TP mRNAs in the various tissue / cells correlated with protein expression, as assessed by radioligand binding using the selective TP antagonist [3H] SQ29,548.Health Research BoardWellcome TrustUniversity College Dublin. President’s Research Awardke,-SB02/09/201

Regulation of Extracellular Signal-Regulated Kinase Cascades by α- and β-Isoforms of the Human Thromboxane A2Receptor

Thromboxane A(2) (TXA(2)) stimulates mitogenic growth of vascular smooth muscle. In humans, TXA(2) signals through two TXA(2) receptor (TP) isoforms, termed TPalpha and TPbeta. To investigate the mechanism of TXA(2)-mediated mitogenesis, regulation of extracellular signal-regulated kinase (ERK) signaling was examined in human embryonic kidney 293 cells stably overexpressing the individual TP isoforms. The TXA(2) mimetic 9,11-dideoxy-9alpha,11alpha-methano epoxy prostaglandin F(2alpha) (U46619) elicited concentration- and time-dependent activation of ERK1 and -2 through both TPs with maximal TPalpha- and TPbeta-mediated ERK activation observed after 10 and 5 min, respectively. U46619-mediated ERK activation was inhibited by the TP antagonist [1S-[1alpha,2beta-(5Z)-3beta,4alpha-]]-7-[3-[[2-(phenylamino)carbonyl]hydrazine] methyl]-7-oxabicyclo[-2,2,1-]hept-2yl]-5-heptenoic acid (SQ29,548), and by the mitogen-activated protein kinase kinase inhibitor 2'-amino-3'-methoxyflavone (PD 98059). Although ERK activation through TPalpha was dependent on 2-[1-(dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide (GF 109203X)-sensitive protein kinase (PK) Cs, ERK activation through TPbeta was only partially dependent on PKCs. ERK activation through both TPalpha and TPbeta was dependent on PKA and phosphoinositide 3-kinase (PI3K) class 1(A), but not class 1(B), and was modulated by Harvey-Ras, A-Raf, c-Raf, and Rap1B/B-Raf and also involved transactivation of the epidermal growth factor receptor. Additionally, PKB/Akt was activated through TPalpha and TPbeta in a PI3K-dependent manner. In conclusion, we have defined the key components of TXA(2)-mediated ERK signaling and have established that both TPalpha and TPbeta are involved. TXA(2)-mediated ERK activation through the TPs is a complex event involving PKC-, PKA-, and PI3K-dependent mechanisms in addition to transactivation of the EGF receptor. TPalpha and TPbeta mediate ERK activation through similar mechanisms, although the time frame for maximal ERK activation and PKC dependence differs

Thromboxane A2 receptor mediated activation of the mitogen activated protein kinase cascades in human uterine smooth muscle cells

Both thromboxane (TX) A2 and 8-epi prostaglandin (PG) F2alpha have been reported to stimulate mitogenesis of vascular smooth muscle (SM) in a number of species. However, TXA2 and 8-epiPGF2alpha mediated mitogenic signalling have not been studied in detail in human vascular SM. Thus, using the human uterine ULTR cell line as a model, we investigated TXA2 receptor (TP) mediated mitogenic signalling in cultured human vascular SM cells. Both the TP agonist U46619 and 8-epiPGF2alpha elicited time and concentration dependent activation of the extracellular signal regulated kinase (ERK)s and c-Jun N-terminal kinase (JNK)s in ULTR cells. Whereas the TP antagonist SQ29,548 abolished U46619-mediated signalling, it only partially inhibited 8-epiPGF2alpha mediated ERK and JNK activation in ULTR cells. Both U46619 and 8-epiPGF2alpha induced ERK activations were inhibited by the protein kinase (PK) C, PKA and phosphoinositide 3-kinase inhibitors GF 109203X, H-89 and wortmannin, respectively, but were unaffected by pertussis toxin. In addition, U46619 mediated ERK activation in ULTR cells involves transactivation of the EGF receptor. In humans, TXA2 signals through two distinct TP isoforms. In investigating the involvement of the TP isoforms in mitogenic signalling, both TPalpha and TPbeta, independently directed U46619 and 8-epiPGF2alpha mediated ERK and JNK activation in human embryonic kidney (HEK) 293 cells over-expressing the individual TP isoforms. However, in contrast to that which occurred in ULTR cells, SQ29,548 abolished 8-epiPGF2alpha mediated ERK and JNK activation through both TPalpha and TPbeta in HEK 293 cells providing further evidence that 8-epiPGF2alpha may signal through alternative receptors, in addition to the TPs, in human uterine ULTR cells.Health Research BoardWellcome TrustIrish Heart FoundationEnterprise Irelandke,ti, -SB01/09/201

Investigation of a functional requirement for isoprenylation by the human prostacyclin receptor

In the current study, we have established that the human (h) prostacyclin receptor (IP) is isoprenylated in whole cells. Through site directed mutagenesis and generation of the isoprenylation defective hIPSSLC, it was established that while isoprenylation of hIP does not influence ligand binding, it is obligatory for agonist activation of adenylyl cyclase and cAMP generation. Overexpression of GαS significantly augmented cAMP generation by the hIP but not by the hIPSSLC. Moreover, GαS co-immunoprecipitated with hIP following agonist activation but did not co-immunoprecipitate with hIPSSLC. Whereas hIP mediated concentration-dependent activation of phospholipase C (PLC); the extent of PLC activation by hIPSSLC was impaired compared to hIP. Co-expression of Gαq significantly augmentated intracellular calcium mobilization by the hIP but not by hIPSSLC. Moreover, whereas Gαq co-immunoprecipitated with hIP, it failed to co-immunoprecipitate with hIPSSLC. While both the hIP and hIPSSLC underwent agonist-induced internalization, the kinetics and extent of hIPSSLC internalization was impaired compared to hIP. Altering the CAAX motif of the hIP from a farnesyl (–CSLC) to a geranylgeranyl (–CSLL) isoprene acceptor, to generate hIPCSLL, did not affect ligand binding and yielded a receptor that exhibited identical signalling through both Gs- and Gq-coupled effectors to that of hIP. Thus, whereas isoprenylation of hIP does not influence ligand binding, it is functionally imperative in regulating post-receptor events including agonist-activation of adenylyl cyclase, for efficient activation of PLC and for receptor internalization. Though the nature of the isoprenoid attached to hIP does not act as a major determinant, the presence of an isoprenoid group, for example farnesyl or geranylgeranyl, is required for functional receptor–G protein interaction and coupling and for efficient agonist- induced receptor internalization