Non-canonical Function of Prolyl Hydroxylase Domain 2 in Breast Cancer Cell Growth and Progression: Role of Peptidyl-prolyl Cis-trans Isomerase NIMA-interacting 1

Prolyl hydroxylase domain 2 (PHD2) is the primary oxygen sensing enzyme involved in hydroxylation of hypoxia-inducible factor (HIF). Under normoxic conditions, PHD2 hydroxylates specific proline residues in HIF-1α and HIF-2α, promoting their ubiquitination and subsequent proteasomal degradation. Although PHD2 activity decreases in hypoxia, notable residual activity persists, but its function in these conditions remains unclear<i>.</i> Peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (Pin1) targets proteins with phosphorylated serine/threonine-proline (pSer/Thr-Pro) motifs. As PHD2 contains several pSer/Thr-Pro motifs, it may be a potential substrate of Pin1. In the present study, we found Pin1 and PHD2 interactions in human breast cancer MDA-MB-231 cells. The breast cancer tissue array revealed higher levels of PHD2 and Pin1 in tumors compared to adjacent normal tissues. Through liquid chromatography-tandem mass spectrometry spectrometry, three phosphorylation sites (S125, T168, and S174) on PHD2 were identified, with serine 125 as the main site for Pin1 binding. As a new Pin1 binding partner, oncogenic PHD2 could be a potential therapeutic target for breast cancer treatment.