TTC4 (tetratricopeptide repeat domain 4) is a nucleoplasmic co-chaperone protein that recruits molecular chaperones Hsp90 and Hsp70 to nascent polypeptides, facilitating proper protein folding 1. TTC4 interacts directly with Hsp70 and stimulates its activity while also binding client proteins including the replication factor CDC6 1. In vascular endothelial cells, TTC4 promotes Hsp70-dependent signaling that inhibits apoptosis through Akt activation and annexin A7 translocation to lysosomes 2. TTC4 additionally functions as a positive regulator of antiviral innate immunity by interacting with TBK1 and promoting Sendai virus-induced immune responses 3. TTC4 exhibits dynamic subcellular localization dependent on the cell cycle, localizing predominantly to the nucleus during G1/S phases 4. Disease relevance includes tumor suppression, as TTC4 maps to chromosome 1, a region frequently deleted in breast cancer 5. Notably, TTC4 harbors mutations in malignant melanoma samples that disrupt CDC6 interaction, suggesting loss of normal tumor-suppressive function contributes to melanoma progression 61. These findings establish TTC4 as a multifunctional protein linking protein quality control, cell cycle regulation, apoptosis resistance, and antiviral immunity.