Identification in mice of two isoforms of the cysteinyl leukotriene 1 receptor that result from alternative splicing

Two classes of human G protein-coupled receptors, cysteinyl leukotriene 1 ( CysLT(1)) and CysLT(2) receptors, recently have been characterized and clon ed. Because the CysLT(1) receptor blockers are effective in treating human bronchial asthma and the mouse is often used to model human diseases, we is olated the mouse CysLT(1) receptor from a mouse lung cDNA library and found two isoforms. A short isoform cDNA containing two exons encodes a polypept ide of 339 aa with 87.3% amino acid identity to the human CysLT(1) receptor . A long isoform has two additional exons and an in-frame upstream start co don resulting in a 13-aa extension at the N terminus. Northern blot analysi s revealed that the mouse CysLT(1) receptor mRNA is expressed in lung and s kin; and reverse transcription-PCR showed wide expression of the long isofo rm with the strongest presence in lung and skin. The gene for the mouse Cys LT(1) receptor was mapped to band XD. Leukotriene (LT) Dq induced intracell ular calcium mobilization in Chinese hamster ovary cells stably expressing either isoform of the mouse CysLT(1) receptor cDNA. This agonist effect of LTD4 was fully inhibited by the CysLT(1) receptor antagonist, MK-571. Micro somal membranes from each transformant showed a single class of binding sit es for [H-3]LTD4; and the binding was blocked by unlabeled LTs, with the ra nk order of affinities being LTD4 >> LTE4 = LTC4 >> LTB4. Thus, the dominan t mouse isoform with the N-terminal amino acid extension encoded by an addi tional exon has the same ligand response profile as the spliced form and th e human receptor.