PIH1D1 is a key adapter protein within the R2TP chaperone complex that facilitates assembly of diverse macromolecular complexes essential for cellular homeostasis. The protein functions as part of the HSP90 co-chaperone system, consisting of RUVBL1/RUVBL2 AAA+ ATPases, RPAP3, and PIH1D1 1. PIH1D1 contains a specialized PIH phospho-binding domain that recognizes CK2 phosphorylation sites on client proteins, enabling phosphorylation-dependent recruitment to the HSP90 system 2. The protein plays critical roles in assembling C/D box small nucleolar ribonucleoprotein particles and supports the stability of PIKK family kinases including MTOR and SMG1 through interaction with the TELO2-TTI1-TTI2 complex 3. PIH1D1 also facilitates assembly of the Tuberous Sclerosis Complex (TSC) by directly binding TSC1, while RPAP3 and HSP90 recruit TSC2 1. Additionally, PIH1D1 regulates MRE11 stability through CK2-dependent interactions, supporting DNA damage repair processes 4. Clinically, PIH1D1 expression correlates with poor prognosis in diffuse large B-cell lymphoma, suggesting roles in oncogenesis 5. The protein's diverse functions highlight its importance in protein homeostasis, signaling pathways, and disease development 6.