ALTERNATIVE SPLICING PRODUCES A DIVERGENT CYTOPLASMIC TAIL IN THE HUMAN ENDOTHELIAL THROMBOXANE A(2), RECEPTOR

Thromboxane A(2) (TxA(2)) causes contraction of vascular smooth muscle and aggregation of platelets; paradoxically, it also induces formatio n of the vasodilator and antiaggregant prostacyclin by human endotheli um. To determine if the molecular structure of the endothelial TxA(2) receptor differs from that of the previously characterized receptor fr om placenta, we isolated a putative TxA(2) receptor cDNA from a human endothelial library. The predicted amino acid sequence revealed a stru cture of 369 amino acids, in which a novel cytoplasmic tail replaced t he carboxyl-terminal portion of the previously characterized TxA, rece ptor; this divergence in cytoplasmic domains resulted from the nonspli cing of a potential intron in the placenta TxA(2) receptor. Northern h ybridization reveals that the expression of the TxA(2), receptor in en dothelial RNA decreases 6-fold following stimulation with an endoperox ide analog. Polymerase chain reaction using oligonucleotide primers sp ecific to each cytoplasmic domain revealed that only the novel recepto r was expressed in endothelium, while both receptors were expressed in placenta. Overexpression of the endothelial TxA(2) receptor cDNA in C hinese hamster ovary cells conferred the ability to bind a known recep tor antagonist and mobilize Ca2+ in response to TxA, mimetics. This fi nding of a new TxA(2) receptor in endothelium suggests that a family o f these receptors may result from alternative splicing of the cytoplas mic (carboxyl) tail.