Characterizations of annexin A1-interacting proteins in apical membrane and cytosolic compartments of renal tubular epithelial cells

Annexin A1 (ANXA1) is a multifunctional calcium-binding protein that can bind to membrane phospholipids. Under high-calcium condition, ANXA1 expression increases on renal epithelial cell surface, leading to enhanced adhesion of calcium oxalate (CaOx) crystal (stone material) onto the cells. To regulate various cellular processes, ANXA1 interacts with many other intracellular protein partners. However, components of the ANXA1-interacting protein complex remain unclear. Herein, we characterized the interacting complexes of apical membrane (ApANXA1) and cytosolic (cyANXA1) forms of ANXA1 in apical membrane and cytosolic compartments, respectively, of renal epithelial cells under high-calcium condition using proteomic and bioinformatic ap-proaches. After fractionation, the ApANXA1-and CyANXA1-interacting partners were identified by immuno-precipitation followed by nanoLC-ESI-Qq-TOF tandem mass spectrometry (IP-MS/MS). The ANXA1-interacting partners that were common in both apical membrane and cytosolic compartments and those unique in each compartment were then analyzed for their physico-chemical properties (molecular weight, isoelectric point, amino acid contents, instability index, aliphatic index, and grand average of hydropathicity), secondary structure (& alpha;-helix, & beta;-turn, random coil, and extended strand), molecular functions, biological processes, reactome path-ways and KEGG pathways. The data demonstrated that each set of these interacting proteins exhibited common and unique characteristics and properties. The knowledge from this study may lead to better understanding of the ApANXA1 and CyAXNA1 biochemistry and functions as well as the pathophysiology of CaOx kidney stone formation induced by high-calcium condition.

Automated summary

In this study, the interacting complexes of the apical membrane (ApANXA1) and cytosolic (cyANXA1) forms of ANXA1 in renal epithelial cells under high-calcium condition were characterized using proteomic and bioinformatic approaches. The results showed that the interacting proteins had both common and unique characteristics and properties. This study provides insights into the biochemistry, functions, and pathophysiology of CaOx kidney stone formation induced by high-calcium condition.