Thromboxane A 2 receptor mediated activation of the mitogen activated protein kinase cascades in human uterine smooth muscle cells

Abstract

Both thromboxane (TX) A 2 and 8-epi prostaglandin (PG) F 2α have been reported to stimulate mitogenesis of vascular smooth muscle (SM) in a number of species. However, TXA 2 and 8-epiPGF 2α mediated mitogenic signalling has not been studied in detail in human vascular SM. Thus, using the human uterine ULTR cell line as a model, we investigated TXA 2 receptor (TP) mediated mitogenic signalling in cultured human vascular SMCs. Both the TP agonist U46619 and 8-epiPGF 2α 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 SQ29548 abolished U46619 mediated signalling, it only partially inhibited 8-epiPGF 2α mediated ERK and JNK activation in ULTR cells. Both U46619 and 8-epiPGF 2α induced ERK activations were inhibited by the protein kinase (PK) C, PKA and phosphoinositide 3-kinase inhibitors GF109203X, H-89 and wortmannin, respectively, but were unaffected by pertussis toxin. In addition, U46619 mediated ERK activation in ULTR cells involves transactivation of the epidermal growth factor (EGF) receptor. In humans, TXA 2 signals through two distinct TP isoforms. In investigating the involvement of the TP isoforms in mitogenic signalling, both TPα and TPβ independently directed U46619 and 8-epiPGF 2α 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, SQ29548 abolished 8-epiPGF 2α mediated ERK and JNK activation through both TPα and TPβ in HEK 293 cells providing further evidence that 8-epiPGF 2α may signal through alternative receptors, in addition to the TPs, in human uterine ULTR cells.