PCID2 (PCI domain containing 2) is a multifunctional nuclear protein with critical roles in gene expression regulation and cell fate determination. As a component of the TREX-2 complex, PCID2 facilitates mRNA export from the nucleus to the cytoplasm through nuclear pores 1. Beyond classical mRNA export, PCID2 localizes to the centrosome and participates in nuclear protein export through a mechanism distinct from other TREX-2 components 2. PCID2 stabilizes BRCA2 and prevents R-loop-associated DNA damage during transcription 3, while also regulating the SRCAP chr13 remodeling complex to suppress lymphoid differentiation genes. In pluripotent stem cells, PCID2 maintains self-renewal by stabilizing EID1, which blocks CBP/p300 histone acetyltransferase activity and suppresses developmental gene expression 4. PCID2 also functions as part of the REX (Repressor of EXport) complex, preventing export of misprocessed mRNAs and promoting their degradation 5. Clinically, PCID2 is amplified and overexpressed in colorectal and gastric cancers, where it promotes cell cycle progression and metastasis by degrading the tumor suppressor PML and activating Wnt/β-catenin signaling 67. High PCID2 expression correlates with poor prognosis and serves as an independent predictor of cancer recurrence.