TCF25 emerges as a cytoplasmic regulator of GPRASP2 stability

TCF25 is a conserved eukaryotic protein whose cellular localisation and functional context remain poorly understood. Here, we show that under basal conditions, TCF25 is predominantly cytoplasmic across several human cell types, with a digitonin-resistant perinuclear pool indicative of association to membrane-linked components. Exploration of TCF25's proximal network using proximity labelling further supports enrichment of cytoplasmic and intracellular membrane-associated proteins. Guided by the analysis of public datasets and the proximal proteome data, we show that TCF25 associates with G-protein coupled receptor-associated sorting protein, GPRASP2, and maintains its basal abundance by protecting it from proteasomal degradation. Using structural modelling, we identify a putative interaction interface between the two proteins, involving two closely-spaced helices in the C terminal region of TCF25 that dock to the helical repeat segment of GPRASP2. Consistent with this prediction, deletion of TCF25 amino acids 604-664 disrupted the relationship between TCF25 and GPRASP2. Together, these findings establish a cytoplasmic, membrane-proximal context for TCF25 and identify a C-terminal tract required for its association with GPRASP2. These findings implicate TCF25 in regulating GPRASP2 stability, providing a framework for investigating its role in cellular homeostasis and disease.