Genomic, tissue expression, and protein characterization of pCLCA1, a putative modulator of cystic fibrosis in the pig.

Department of Veterinary Pathology, Freie Universität Berlin, Berlin, Germany.
Journal of Histochemistry and Cytochemistry (Impact Factor: 2.26). 09/2009; 57(12):1169-81. DOI: 10.1369/jhc.2009.954594
Source: PubMed

ABSTRACT Recent studies have identified members of the CLCA (chloride channels, calcium-activated) gene family as potential modulators of the cystic fibrosis (CF) phenotype, but differences between the human and murine CLCA genes and proteins may limit the use of murine CF models. Recently established pig models of CF are expected to mimic the human disease more closely than the available mouse models do. Here, we characterized the porcine CLCA gene locus, analyzed the expression pattern and protein processing of pCLCA1, and compared it to its human ortholog, hCLCA1. The porcine CLCA gene family is located on chromosome 4q25, with a broad synteny with the human and murine clca gene loci, except for a pig-specific gene duplication of pCLCA4. Using pCLCA1-specific antibodies, the protein was immunohistochemically localized in mucin-producing cells, including goblet cells and mucinous glands in the respiratory and alimentary tracts. Similar to hCLCA1, biochemical characterization of pCLCA1 identified a secreted soluble protein that could serve as an extracellular signaling molecule or functional constituent of the protective mucous layers. The results suggest that pCLCA1 shares essential characteristics of hCLCA1, supporting the pig model as a promising tool for studying the modulating role of pCLCA1 in the complex pathology of CF.

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    ABSTRACT: Human Ca(2+)-activated Cl ion channel 1 (hCLCA1) is expressed in goblet cell hyperplasia in the airway of asthmatics, and murine CLCA3 is associated with antigen-sensitized and IL-13-induced goblet cell metaplasia in mice. However, the role of CLCA in goblet cell degranulation is not fully investigated. Niflumic acid (NFA), a relatively specific CLCA inhibitor, inhibits goblet cell metaplasia, but the effect of NFA on goblet cell degranulation has not been determined in an asthma model. Guinea pigs were sensitized with ovalbumin (OA) twice and then challenged with saline, OA, histamine, and one of the Ca(2+)-dependent secretagogues, UTP. The PAS/AB-stained mucus area in the tracheal epithelium was measured with a computer image analysis system, and the morphology of mucus granules was examined by transmission electron microscopy. In the in vitro experiment, goblet cells cultured with IL-13 at the air-liquid interface were stimulated with UTP in the presence or absence of NFA, and the MUC5AC level in cell lysates was measured by ELISA. The mucus areas were smaller in the OA-, histamine-, and UTP-challenged animals than in the saline-challenged animals. NFA inhibited the decrease in mucus area and morphological changes in mucus granules. UTP caused swelling and exocytosis of mucus granules and MUC5AC secretion by cultured goblet cells, and NFA inhibited these changes. NFA inhibited the secretory response of mucus granules in an asthma model, suggesting that CLCA may be associated with goblet cell degranulation and that CLCA inhibitors may be useful for the treatment of hypersecretion in asthma.
    Allergology International 03/2012; 61(1):133-42.
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    ABSTRACT: Despite the discovery of the widely expressed CLCA (chloride channel regulators, calcium-activated) proteins more than 15 years ago, their seemingly diverse functions are still poorly understood. With the recent generation of porcine animal models for cystic fibrosis (CF), members of the porcine CLCA family are becoming of interest as possible modulators of the disease in the pig. Here, we characterize pCLCA2, the porcine ortholog of the human hCLCA2 and the murine mCLCA5, which are the only CLCA members expressed in the skin. Immunohistochemical studies with a specific antibody against pCLCA2 have revealed a highly restricted pCLCA2 protein expression in the skin. The protein is strictly co-localized with filaggrin and trichohyalin in the granular layer of the epidermis and the inner root sheath of the hair follicles, respectively. No differences have been observed between the expression patterns of wild-type pigs and CF transmembrane conductance regulator (-/-) pigs. We speculate that pCLCA2 plays an as yet undefined role in the structural integrity of the skin or, possibly, in specialized functions of the epidermis, including barrier or defense mechanisms.
    Cell and Tissue Research 09/2012; · 3.68 Impact Factor
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    ABSTRACT: CLCA proteins (calcium-activated chloride channel regulators) have been linked to diseases involving secretory disorders, including cystic fibrosis (CF) and asthma. They have been shown to modulate endogenous chloride conductance, possibly by acting as metalloproteases. Based on the differential processing of the subunits after posttranslational cleavage, two subgroups of CLCA proteins can be distinguished. In one subgroup, both subunits are secreted, in the other group, the carboxy-terminal subunit possesses a transmembrane segment, resulting in shedding of only the amino-terminal subunit. Recent data on the post-translational cleavage and proteolytic activity of CLCA are limited to secreted CLCA. In this study, we characterized the cleavage of mCLCA6, a murine CLCA possessing a transmembrane segment. As for secreted CLCA, the cleavage in the endoplasmic reticulum was not observed for a protein with the E157Q mutation in the HEXXH motif of mCLCA6, suggesting that this mutant protein and secreted CLCA family members share a similar autoproteolytic cleavage mechanism. In contrast to secreted CLCA proteins with the E157Q mutation, the uncleaved precursor of the mCLCA6E157Q mutant reached the plasma membrane, where it was cleaved and the amino-terminal subunit was shed into the supernatant. Using crude membrane fractions, we showed that cleavage of the mCLCA6E157Q protein is zinc-dependent and sensitive to metalloprotease inhibitors, suggesting secondary cleavage by a metalloprotease. Interestingly, anchorage of mCLCA6E157Q to the plasma membrane is not essential for its secondary cleavage, because the mCLCA6(Δ™)E157Q mutant still underwent cleavage. Our data suggest that the processing of CLCA proteins is more complex than previously recognized.
    Molecules and Cells 02/2012; 33(3):251-7. · 2.21 Impact Factor

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