Tissue kallikrein promotes survival and β-catenin degradation in SH-SY5Y cells under nutrient stress conditions via autophagy.

Previous studies by our group showed that tissue kallikrein (TK) exerts neuroprotective effects during cerebral ischemia. Autophagy is an important adaptive response to cellular stress during nutrient deprivation, and β-catenin in known to repress autophagy. The present study investigated the possible involvement of autophagy and β-catenin signaling in the protective effects of TK under nutrient deprivation-induced stress conditions. TK was shown to promote the survival and inhibit the death of SH-SY5Y cells under serum starvation and enhanced autophagic activity in a concentration-dependent manner, as indicated by augmented light chain (LC)3-II levels and Beclin-1 expression. The autophagy inhibitors 3-methyladenine and NH4Cl abolished the protective effects of TK. Of note, although serum starvation alone and TK treatment increased p62 protein levels and mRNA expression, incubation with the lysosome inhibitor NH4Cl increased the accumulation of LC3-II and p62 protein, indicating normal autophagic flux. It was also observed that β-catenin expression was significantly downregulated by TK treatment. TK stimulated the interaction between LC3 and β-catenin, and NH4Cl abolished the effects of TK on β-catenin levels in serum-starved cells, suggesting the autophagic degradation of β-catenin, which may have led to the enhancement of autophagy. In conclusion, the findings of the present study demonstrated that TK promoted cell survival and β-catenin degradation in serum-starved SH-SY5Y cells via increasing autophagy, which indicated the therapeutic potential of TK under nutrient deprivation-associated stress conditions.