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Title Prostaglandin D2 receptor -mediated desensitization of the alpha isoform of the human thromboxane A2 receptor

Kelley, L.P.; Kinsella, B.T.erese

FASEB Journal 15(4): A219

2001


ISSN/ISBN: 0892-6638
Accession: 035959752

The prostanoid thromboxane (TX)A2 and prostaglandin (PG)D2 mediate opposing actions in platelets and in vascular and non-vascular smooth muscle. TXA2 is a potent stimulator of platelet shape change, aggregation, constriction of vascular and bronchial smooth muscle; whereas PGD2 is a potent inhibitor of platelet aggregation and causes vasodilation. TXA2 and PGD2 mediate their actions by interacting through their specific cell surface G-protein receptors (GPCRs) termed TP and DP, respectively. Alternative mRNA splicing of the human TP gene within exon 3 gives rise to two isoforms termed TPalpha and TPbeta which differ exclusively in their carboxyl cytoplasmic (C) tail region. The aim of this study was to investigate the effects of activation of DP on signalling by TP in both human platelets and human embryonic kidney (HEK) 293 cells overexpressing the individual TPalpha and TPbeta isoforms. Initial studies found that pre-stimulation of platelets with the DP agonist BW245C completely abolished subsequent TP-mediated intracellular calcium mobilisation in response to the TP mimetic U46619. We further investigated if DP mediated desensitisation specifically targets TPalpha, TPbeta or both in HEK 293 cells and compared it to that which occurs in platelets. Our results concluded that signalling by TPalpha, but not TPbeta, was the TP isoform subject to DP mediated desensitisation. A truncated variant of TP containing only those residues common to both TPalpha and TPbeta termed TPDELTA328, was insensitive to prior DP stimulation indicating that the carboxyl terminal tail of TPalpha contains the target-site(s) for DP-mediated desensitisation. We further established that this DP-mediated desensitisation specifically targets a PKA consensus sequence within the unique C-tail of TPalpha's unique C-tail region.

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