Maintaining water balance is a real challenge for amphibians in terrestrial environments. Our previous studies with toad Bombina maxima discovered a 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 import and enhanced exosomes release, which simultaneously regulated aquaporins distribution. Collectively, these findings uncovered that besides membrane integrated aquaporin, a secretory pore-forming protein can facilitate toad water maintaining via macropinocytosis induction and exocytosis modulation, especially in responses to osmotic stress.

In addition to membrane-integrated aquaporins, a novel secretory pore-forming protein, beta gamma-CAT, can facilitate toad water maintaining via macropinocytosis induction and exocytosis modulation, especially in responses to osmotic stress