Cysteinyl leukotrienes (CysLTs) are implicated in the pathophysiology of many inflammatory disorders and in particular asthma. Although three CysLT receptor antagonists have been introduced recently as novel therapeutics and two receptors have been clearly identified and cloned, little is known about transcriptional control of receptor expression (Brink et al., 2003 ; Lynch et al., 1999 ; Sarau et al., 1999). The aim of this study was to define the genomic organisation of the Cysteinyl leukotriene receptor 1 (CLTR1).

We performed a polymorphism screen of the CLTR1 coding sequence using as a template genomic DNA from 12 patients treated for asthma with glucocorticoids selected from the Caucasian population. The coding sequence was amplified in two fragments of 556 and 548 bp, purified and sequenced using an ABI Prism 377 DNA sequencer. RACE (Rapid Amplification of cDNA Ends) experiments were performed using the Invitrogen GeneRacer kit and protocol. Three different total RNAs were used as a template: two extracted from human airway smooth muscle cells (HASM) from two different donors and one from peripheral blood monocytes/ lymphocytes (MLs). For each cell type, two RACE experiments were performed using either the GeneRacer OligodT Primer (Invitrogen) or a Gene Specific Primer (GSP) to synthesize the first-strand cDNA.

Polymorphism screening of the coding region of CLTR1 revealed only an already published SNP at position +927 from the ATG. RACE experiments showed 6 different transcripts (5 previously undescribed) containing 2 to 6 exons (see table1). Among them, the published one (Lynch et al., 1999 ; Sarau et al., 1999) was the most common in both cell types, representing more than 75% of the transcripts.

Table1 : Ratio of CLTR1 transcripts obtained from RACE (%).

Different transcripts were found according to the cell line used and most of them seem to be rare. However, it appears that there are two putative promoter regions, one immediately upstream of the 5'UTR of the published sequence and one about 332kb upstream of the 5'UTR of the published sequence.

In summary, CLTR1 is regulated by two promoters and may show cell specific regulation of transcription. The coding region does not contain common polymorphisms altering the amino acid sequence of the receptor.

Lynch KR et al. (1999), Nature 399, 789-793.
Sarau HM et al. (1999), Mol. Pharmacol. 56, 657-663.
Brink C et al. (2003), Pharmacol. Rev. 55, 195-227.