Synthesis of porcine pCLCA2 protein during late differentiation of keratinocytes of epidermis and hair follicle inner root sheath

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.

NF-κB-regulated transcriptional control of CLCA in a differentiated mouse keratinocyte line

“…A recent paper revealed that CLCA2 is strongly down-regulated by UV radiation and suggested that it may play a role in epidermal differentiation and UV-dependent skin malignancies [12]. Some of the other CLCA members are also reportedly associated with epidermal differentiation [10,11]. In addition to such relationships, based on the in vitro findings of p65-induced CLCA regulation, the possible roles of NF-kB activity in vivo should be taken into consideration since some populations of keratinocytes exhibited nuclear distribution of p65 in the basal and suprabasal layers of native skin and in the organotypic culture.…”

“…Human CLCA2 (hCLCA2) is localized along the basal membrane of basal epithelial cells of the cornea and skin and its expression is elevated during epithelial stratification [8,9]. Porcine CLCA2 was detected in the granular layer [10]. Among the mouse isoforms, mCLCA5 was shown to be expressed in the granular layer of the skin and oral cavity, especially in keratohyalin granules [11].…”

rClca2is associated with epidermal differentiation and is strongly downregulated by ultraviolet radiation

“…The full-length isoform was found mainly in differentiating keratinocytes, and the truncated form in basal keratinocytes. 10 The expression of mCLCA5 and its porcine orthologue, pCLCA2, were found mainly in the granular layer, 11,12 while the human orthologue, hCLCA2, was detected in basal cells. In addition, disturbance of the epidermal homeostasis by UVR caused reversed localization of the truncated CLCA2-t, to the upper cell layers, as previously observed in wounding.…”

“…9 Alternative splicing and proteolytic cleavage with subsequent secretion of the fragment(s) have complicated the analysis of the function of calcium-activated chloride channels (CLCAs). 11,12 rCLCA2 has also been shown to modulate chloride channels and transepithelial Cl À transport in salivary glands and keratinocytes. 11,12 rCLCA2 has also been shown to modulate chloride channels and transepithelial Cl À transport in salivary glands and keratinocytes.…”

“…They may mediate the differentiation-inducing effect of calcium by acting as regulators of chloride channels, 11,12 especially at the initiation of differentiation, 65,66 as intracellular chloride transport induces the expression of differentiation markers and keratinocyte growth inhibition. Their postulated role as tumour suppressors and their ability to respond to changes in calcium levelsimportant in skin homeostasismake them interesting as novel UVB target genes.…”