Genes and environment: novel, functional polymorphism in the human cathepsin L (CTSL1) promoter disrupts a xenobiotic response element (XRE) to alter transcription and blood pressure.

BACKGROUND: Cathepsin L (CTSL1) catalyzes the formation of peptides that influence blood pressure (BP). Naturally occurring genetic variation or targeted ablation of the Ctsl1 locus in mice yield cardiovascular pathology. Here, we searched for genetic variation across the human CTSL1 locus and probed its functional effects, especially in the proximal promoter. METHODS AND
RESULTS: Systematic polymorphism discovery by re-sequencing across CTSL1 in 81 patients uncovered 38 genetic variants, five of which were relatively common (MAF >5%), creating a single linkage disequilibrium block in multiple biogeographic ancestries. One of these five common variants lay in a functional domain of the gene: promoter C-171A (rs3118869), which disrupts a predicted xenobiotic response element (XRE; match C>A). In transfected CTSL1 promoter/luciferase reporter plasmids, C-171A allele influenced transcription (C>A, P = 3.36E-6), and transcription was also augmented by co-exposure to the aryl hydrocarbon receptor (AHR) complex (AHR:ARNT) in the presence of their ligand dioxin (P = 6.81E-8); allele (C vs. A) and AHR:ARNT/dioxin stimulus interacted to control gene expression (interaction P = 0.033). Endogenous Ctsl1, Ahr, and Arnt transcripts were present in chromaffin cells. Promoter functional C-171A genotype also predicted hypertension (P = 1.0E-3), SBP (P = 4.0E-4), and DBP (P = 3.0E-3), in an additive pattern for diploid genotypes (A/A > C/A > C/C) in 868 patients, and the results were extended by validation analysis into an independent population sample of 986 patients.
CONCLUSION: We conclude that common genetic variation in the proximal CTSL1 promoter, especially at position C-171A, is functional in cells, and alters transcription so as to explain the association of CTSL1 with BP in vivo. At the XRE, endogenous genetic variation plus exogenous aryl hydrocarbon stimulation interact to control CTSL1 gene expression. These results unveil a novel control point whereby heredity and environment can intersect to control a complex trait, and point to new transcriptional strategies for intervention into transmitter biosynthesis and its cardiovascular consequences.