Abstract
Protocadherin-1 (PCDH1) is a novel susceptibility gene for airway hyperresponsiveness, first identified in families exposed to cigarette smoke and is expressed in bronchial epithelial cells. Here, we asked how mouse Pcdh1 expression is regulated in lung structural cells in vivo under physiological conditions, and in both short-term cigarette smoke exposure models characterized by airway inflammation and hyperresponsiveness and chronic cigarette smoke exposure models. Pcdh1 gene-structure was investigated by Rapid Amplification of cDNA Ends. Pcdh1 mRNA and protein expression was investigated by qRT-PCR, western blotting using isoform-specific antibodies. We observed 87% conservation of the Pcdh1 nucleotide sequence, and 96% conservation of the Pcdh1 protein sequence between men and mice. We identified a novel Pcdh1 isoform encoding only the intracellular signalling motifs. Cigarette smoke exposure for 4 consecutive days markedly reduced Pcdh1 mRNA expression in lung tissue (3 to 4-fold), while neutrophilia and airway hyperresponsiveness was induced. Moreover, Pcdh1 mRNA expression in lung tissue was reduced already 6 hours after an acute cigarette-smoke exposure in mice. Chronic exposure to cigarette smoke induced loss of Pcdh1 protein in lung tissue after 2 months, while Pcdh1 protein levels were no longer reduced after 9 months of cigarette smoke exposure. We conclude that Pcdh1 is highly homologous to human PCDH1, encodes two transmembrane proteins and one intracellular protein, and is regulated by cigarette smoke exposure in vivo.
Highlights
Asthma is a complex disease caused by gene-gene and geneenvironment interactions [1]
We provide a full characterization of the expression pattern of Pcdh1, the murine homologue of PCDH1, a novel airway hyperresponsiveness (AHR) susceptibility gene identified in families exposed to environmental cigarette smoke
We show that the mouse and human genes for Protocadherin-1 are highly homologous, both at the nucleotide and at the amino-acid level, validating the mouse as a relevant model to study Pcdh1 function
Summary
Asthma is a complex disease caused by gene-gene and geneenvironment interactions [1]. Many asthma susceptibility genes have been identified, several of which are expressed in the airway epithelium [2]. We identified protocadherin-1 (PCDH1) as a novel susceptibility gene for airway hyperresponsiveness (AHR) in asthma families [12]. PCDH1 encodes for two main isoforms: a 3 exon and a 5 exon isoform that are expressed in the airway epithelium [12]. In addition a putative third isoform was identified that lacks exon 1 and part of exon 2 [13] Both main isoforms encode a protein containing an extracellular domain with seven cadherin repeats, a transmembrane domain, and an intracellular domain containing several Serine and Tyrosine residues, that have been found to be subject to phosphorylation [14,15]. We previously reported complex splicing patterns of PCDH1 regarding the expression of intracellular conserved motifs, and observed a marked upregulation of PCDH1 during mucociliary differentiation of primary bronchial epithelial cells [13]
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