A CLCA regulatory protein present in the chemosensory cilia of olfactory sensory neurons induces a Ca 2+ -activated Cl - current when transfected into HEK293.

Background: CLCA is a family of metalloproteases that regulate Ca ²⁺ -activated Cl ^- fluxes in epithelial tissues. In HEK293 cells, CLCA1 promotes membrane expression of an endogenous Anoctamin 1 (ANO1, also termed TMEM16A)-dependent Ca ²⁺ -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 Ca ²⁺ -activated Cl ^- channel. We explored the possibility that this protein plays a role in odor transduction.
Results: We cloned and expressed CLCA4L from rat olfactory epithelium in HEK293 cells. In the transfected HEK293 cells we measured a Cl ^- -selective Ca ²⁺ -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 Ca ²⁺ -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.
Conclusion: These findings suggests that a CLCA isoform, namely CLCA4L, expressed in OSN cilia, might have a regulatory function over the ANO2-dependent Ca ²⁺ -activated Cl ^- channel involved in odor transduction.