Thioredoxin interacting protein (Txnip) forms redox sensitive high molecular weight nucleoprotein complexes

Abstract

Thioredoxin interacting protein (Txnip) is an α-arrestin protein that regulates pleiotropic biological responses. Txnip acts as a cancer suppressor and is a critical regulator of energy metabolism. To investigate molecular mechanisms involving Txnip, we searched for its protein binding partners using tandem affinity purification and proteomics analyses and identified several viable candidates, including HSP90, HSP70, and Prp31. We showed, by native PAGE, that Txnip is involved in the formation of high molecular weight complexes (1000–1300 kDa) in the nuclear fraction of cells treated with glucose and bortezomib. DTT treatment partly dissolved these high molecular weight complexes, suggesting that Txnip forms redox sensitive high-order nucleoprotein complexes. RNAse treatment slightly decreased the complex and RNA-seq showed differential expression of RNAs in the complex between Txnip protein overexpressing and control cells, indicating the involvement of RNAs in the complex. These results collectively provide a model whereby Txnip exerts its functions through multiple binding partners, forming transient higher-order complexes to regulate other signaling molecules.