THOC5 is a subunit of the THO complex, which forms part of the larger TREX (transcription/export) complex that couples transcription to mRNA processing and nuclear export 1. While THOC5 depletion affects less than 1% of total mRNA export under steady-state conditions, it dramatically influences over 90% of growth factor/cytokine-induced genes, particularly immediate-early response genes 1. THOC5 functions as a selective mRNA export factor, working with adaptor proteins like Aly to facilitate nuclear export of specific mRNAs such as HSP70 2. The protein shuttles between nucleus and cytoplasm in response to M-CSF signaling and regulates transcription factor expression including C/EBP family members during monocytic differentiation 3. THOC5 is essential for maintaining stem cells and mediating growth factor-induced differentiation and proliferation 1. In disease contexts, THOC5 promotes osteoclast formation by facilitating nuclear translocation of c-FMS cleavage products and regulating RANK expression 4. Additionally, THOC5 upregulation in triple-negative breast cancer contributes to radioresistance and stemness by facilitating nuclear export of SOX2 and NANOG transcripts 5. The protein is regulated by necdin, which affects its nucleocytoplasmic distribution and influences dopaminergic neuron development 6.