497-P: Fyn-Dependent Tyrosine Phosphorylation of Tgm2 Modulates p53-Tgm2-p62 Complex in Renal Proximal Tubular Epithelial Cells

Abstract

Diabetic kidney disease (DKD) is one of the major diabetic complications, the leading cause of the end stage renal disease (ESRD). Recently autophagy, which is also implicated in diabetes and insulin resistance, was shown to regulate DKD. Previously, we reported that Fyn functions as a muscle mass regulator by suppressing autophagy but it is still not known whether Fyn regulates autophagy in kidney and functions as a pathogenesis of DKD. Recently, we demonstrated that over-expressing of Fyn in HK2 cells as an in vitro cell model of renal proximal tubular epithelial cells inhibits autophagy. SiRNA mediating knockdown of Fyn increased autophagy demonstrating Fyn has important role for autophagy in HK2 cells. Phospho-proteomic analysis revealed that Fyn phosphorylates Transglutaminase 2 (Tgm2), a known autophagic inhibitor through Beclin1, on Y369 and Y617. More recently, we demonstrated that Fyn dependent phosphorylation of Tgm2 could regulate autophagy in HK2 cells. While it has been reported that Tgm2 could cross-link Beclin1 to inhibits its activity, no cross-linking of Beclin1 was seen in Tgm2 expressing HK2 cells, indicating there could be another mechanism of Fyn-Tgm2 regulating autophagy in HK2 cells. Recently, Tgm2 was shown to make a complex with p53 and p62, known autophagy regulator/substrate to degrade p53 in autophagosome in cancer cells. Interestingly, we found that p53 expression was decreased in Tgm2 knock-downed HK2 cells and increased in Tgm2 expressing HK2 cells. More importantly co-immunoprecipitation assay showed that Tgm2-Y369,617F which could not be phosphorylated by Fyn bind to p53 more than WT and dissociated from p62. Taken together, these data suggest that Fyn phosphorylates Tgm2 on Y369, 617 to modulate p53-Tgm2-p62 complex in the renal tubulus cells leading to a pathogenesis of DKD. Disclosure E. Yamada: None. S. Okada: None. C.C. Bastie: None. M. Yamada: None.