A pore-forming protein drives macropinocytosis to facilitate toad water maintaining

Abstract

Maintaining water balance is a real challenge for amphibians in terrestrial environments. Our previous studies with toad Bombina maxima discovered a secretory aerolysin family pore-forming protein and trefoil factor complex {beta}{gamma}-CAT, which is assembled under tight regulation depending on environmental cues. Here we report an unexpected role for {beta}{gamma}-CAT in toad water maintaining. Deletion of toad skin secretions, in which {beta}{gamma}-CAT is a major component, increased animal mortality under hypertonic stress. {beta}{gamma}-CAT was constitutively expressed in toad osmoregulatory organs, which was inducible under the variation of osmotic conditions. The protein induced and participated in macropinocytosis in vivo and in vitro. During extracellular hyperosmosis, {beta}{gamma}-CAT stimulated macropinocytosis to facilitate water intake and enhanced exosomes release, which simultaneously regulated aquaporins distribution. Collectively, these findings uncovered that besides membrane integrated aquaporins, a secretory pore-forming protein can facilitate toad water maintaining via macropinocytosis induction and exocytosis modulation, especially in responses to osmotic stress.