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Báo cáo khoa học: Characterization of the 5¢ untranslated region of a and b isoforms of the human thromboxane A2 receptor (TP) Differential promoter utilization by the TP isoforms

In humans, thromboxane (TX) A2 signals through two TXA2receptor (TP) isoforms, TPaand TPb,thatdiverge within their carboxyl terminal cytoplasmic (C) tail regions and arise by differential splicing. The human TP gene con-tains three exons E1–E3; while E1 exclusively encodes 5¢ untranslatedregion (UTR) sequence,E2andE3 represent the main coding exons. An additional noncoding exon, E1b was identified within intron 1. Additionally, the TP gene contains twopromoters P1 andP2 located 5¢of E1 andE1b, respectively | Eur. J. Biochem. 269 4058-4073 2002 FEBS 2002 doi 10.1046 j.1432-1033.2002.03098.x Characterization of the 5 untranslated region of a and b isoforms of the human thromboxane A2 receptor TP Differential promoter utilization by the TP isoforms Adrian T. Coyle Sinead M. Miggin and B. Therese Kinsella Department of Biochemistry University College Dublin Ireland In humans thromboxane TX A2 signals through two TXA2 receptor TP isoforms TPa and TPb that diverge within their carboxyl terminal cytoplasmic C tail regions and arise by differential splicing. The human TP gene contains three exons E1-E3 while E1 exclusively encodes 5 untranslated region UTR sequence E2 and E3 represent the main coding exons. An additional noncoding exon E1b was identified within intron 1. Additionally the TP gene contains two promoters P1 and P2 located 5 of E1 and E1b respectively. Herein we investigated the molecular basis of the differential expression of the TP isoforms by characterizing the 5 UTR of the TP transcripts. While E1 and E1b were found associated with TP transcript s their expression was mutually exclusive. 5 rapid amplification of cDNA ends 5 RACE established that the major transcription initiation TI sites were clustered between -115 and -92 within E1 and at -99 within E1b. While E1 and E1b sequences were identified on TPa transcript s neither existed on TPb transcript s . More specifically TPa and TPb transcripts diverged within E2 and the major TI sites for TPb transcripts mapped to -12 -15 therein. Through genetic reporter assays a previously unrecognized promoter termed P3 was identified on the TP gene located immediately 5 of -12. The proximity of P3 to the TI site of TPb suggests a role for P3 in the control of TPb expression and implies that TPa and TPb in addition to being products of differential splicing are under the transcriptional control of distinct promoters. Keywords thromboxane receptor isoforms splicing promoter 5 untranslated region. Thromboxane TX A2 .