Abstract
BackgroundCLCA is a family of metalloproteases that regulate Ca2+-activated Cl− fluxes in epithelial tissues. In HEK293 cells, CLCA1 promotes membrane expression of an endogenous Anoctamin 1 (ANO1, also termed TMEM16A)-dependent Ca2+-activated Cl− current. Motif architecture similarity with CLCA2, 3 and 4 suggested that they have similar functions. We previously detected the isoform CLCA4L in rat olfactory sensory neurons, where Anoctamin 2 is the principal chemotransduction Ca2+-activated Cl− channel. We explored the possibility that this protein plays a role in odor transduction.ResultsWe cloned and expressed CLCA4L from rat olfactory epithelium in HEK293 cells. In the transfected HEK293 cells we measured a Cl−-selective Ca2+-activated current, blocked by niflumic acid, not present in the non-transfected cells. Thus, CLCA4L mimics the CLCA1 current on its ability to induce the ANO1-dependent Ca2+-activated Cl− current endogenous to these cells. By immunocytochemistry, a CLCA protein, presumably CLCA4L, was detected in the cilia of olfactory sensory neurons co-expressing with ANO2.ConclusionThese findings suggests that a CLCA isoform, namely CLCA4L, expressed in OSN cilia, might have a regulatory function over the ANO2-dependent Ca2+-activated Cl− channel involved in odor transduction.
Highlights
Ca2+-activated Cl− channel regulator (CLCA) is a family of metalloproteases that regulate Ca2+-activated Cl− fluxes in epithelial tissues
Using primers targeting the CLCA4L gene expressed in the rat nervous system allowed isolating three fragments corresponding to the full-length coding sequence of a CLCA gene present in the rat olfactory epithelium, which was named rOECLCA4L (Additional file 1: Figure S1)
We show that transfected CLCA4L mimics CLCA1 on inducing the ANO1-dependent Ca2+-activated Cl− current of HEK293 cells, opening the interesting possibility that in olfactory cilia CLCA4L might play a regulatory role on ANO2
Summary
CLCA is a family of metalloproteases that regulate Ca2+-activated Cl− fluxes in epithelial tissues. In HEK293 cells, CLCA1 promotes membrane expression of an endogenous Anoctamin 1 (ANO1, termed TMEM16A)-dependent Ca2+-activated Cl− current. We previously detected the isoform CLCA4L in rat olfactory sensory neurons, where Anoctamin 2 is the principal chemotransduction Ca2+-activated Cl− channel. 1 (ANO1)-dependent Ca2+-activated Cl− current in HEK293 cells [5] This occurs because CLCA1 somehow promotes the incorporation and stabilization of the ANO1 channel into the plasma membrane [6]. CLCA1 shares its motif architecture with CLCA2, 3 and 4, suggesting that all these proteins are processed and have an analogous function in different cell types [6]. By single-cell PCR in rat olfactory sensory neurons (OSNs), we previously found expression of the isoform CLCA4L as well as CLCA2 mRNAs, being CLCA4L mRNA much more abundant than the latter [7]. The cilium is the cellular compartment where odor transduction takes place, a process in which the principal ionic current is carried by the
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