Probable serine protease that plays a role in hearing. Acts as a permissive factor for cochlear hair cell survival and activation at the onset of hearing and is required for saccular hair cell survival (By similarity). Activates ENaC (in vitro). Expressed in many tissues including fetal cochlea. Isoform T is found at increased levels in some carcinomas. Undergoes autoproteolytic activation. The disease is caused by variants affecting the gene represented in this entry. Has a predicted N-terminal signal sequence, indicating it may be secreted. Expressed in retina, lung, liver, pancreas, placenta and kidney. Belongs to the peptidase S1 family.