De-dimerization of PTB is catalyzed by PDI and is involved in the regulation of p53 translation.

Polypyrimidine tract-binding protein (PTB) is an RNA binding protein existing both as dimer and monomer and shuttling between nucleus and cytoplasm. However, the regulation of PTB dimerization and the relationship between their functions and subcellular localization are unknown. Here we find that PTB presents as dimer and monomer in nucleus and cytoplasm respectively, and a disulfide bond involving Cysteine 23 is critical for the dimerization of PTB. Additionally, protein disulfide isomerase (PDI) is identified to be the enzyme that catalyzes the de-dimerization of PTB, which is dependent on the CGHC active site of the a' domain of PDI. Furthermore, upon DNA damage induced by topoisomerase inhibitors, PTB is demonstrated to be de-dimerized with cytoplasmic accumulation. Finally, cytoplasmic PTB is found to associate with the ribosome and enhances the translation of p53. Collectively, these findings uncover a previously unrecognized mechanism of PTB dimerization, and shed light on the de-dimerization of PTB functionally linking to cytoplasmic localization and translational regulation.