CK2 Phospho-Dependent Binding of R2TP Complex to TEL2 Is Essential for mTOR and SMG1 Stability

Abstract

TEL2 interacts with and is essential for the stability of all phosphatidylinositol 3-kinase-related kinases (PIKKs), but its mechanism of action remains unclear. Here, we show that TEL2 is constitutively phosphorylated on conserved serines 487 and 491 by casein kinase 2 (CK2). Proteomic analyses establish that the CK2 phosphosite of TEL2 confers binding to the R2TP/prefoldin-like complex, which possesses chaperon/prefoldin activities required during protein complex assembly. The PIH1D1 subunit of the R2TP complex binds directly to the CK2 phosphosite of TEL2 in vitro and is required for the TEL2-R2TP/prefoldin-like complex interaction in vivo. Although the CK2 phosphosite mutant of TEL2 retains association with the PIKKs and HSP90 in cells, failure to interact with the R2TP/prefoldin-like complex results in instability of the PIKKs, principally mTOR and SMG1. We propose that TEL2 acts as a scaffold to coordinate the activities of R2TP/prefoldin-like and HSP90 chaperone complexes during the assembly of the PIKKs.

Drosophila Spag Is the Homolog of RNA Polymerase II-associated Protein 3 (RPAP3) and Recruits the Heat Shock Proteins 70 and 90 (Hsp70 and Hsp90) during the Assembly of Cellular Machineries

“…Proteomic experiments in Schneider S2 cells showed that dTOR interacts with Pontin, Reptin, Spag, and liquid facet-related, a distant homolog of Tel2 (31,34). In mammalian cells, recruitment of the whole R2TP by Tel2 is necessary to stabilize mammalian TOR (7). Taken together, these data support the conservation of R2TP in the stabilization and assembly of PIKK complexes.…”

“…Later on, we showed that the R2TP is also involved in the early cytoplasmic steps of RNA polymerase II biogenesis (6). Finally, mammalian R2TP also stabilizes proteins from the PI3 kinase-like kinase family (PIKKs), including mammalian TOR and SMG-1, two regulators of protein synthesis (7). This function in PIKK stabilization is dependent on an adaptor called Tel2 (7).…”

“…Finally, mammalian R2TP also stabilizes proteins from the PI3 kinase-like kinase family (PIKKs), including mammalian TOR and SMG-1, two regulators of protein synthesis (7). This function in PIKK stabilization is dependent on an adaptor called Tel2 (7). In all these processes, R2TP appears to stabilize newly synthesized proteins by recruiting Hsp90 and to assemble them into macromolecular complexes by yet poorly understood mechanisms (8).…”

“…Mammalian R2TP is recruited to these kinases via the adaptor Tel2, with a predominant effect on mammalian TOR and SMG1 stability (7). In Drosophila, proteomic data indicate that TOR similarly interacts with Pontin, Reptin, and Lqfr, a distant ortholog of Tel2 (31).…”

Structure of Minimal Tetratricopeptide Repeat Domain Protein Tah1 Reveals Mechanism of Its Interaction with Pih1 and Hsp90

“…Rvb1 and Rvb2 are two highly conserved AAAϩ helicases involved in many different critical complexes in the cell (3,4). The R2TP complex is highly conserved from yeast to mammalian cells and has been shown to be required for the proper assembly of box C/D small nucleolar ribonucleoproteins (5,2), for the assembly of RNA polymerase II (6,7), and for the stability of the phosphatidylinositol 3-kinase-related kinases through binding to TEL2 (8). Furthermore, both human Pih1 (PIH1D1) and human Tah1 (RPAP3) have been shown to regulate apoptosis (9,10).…”