The Hsp90 chaperone controls the biogenesis of L7Ae RNPs through conserved machinery

Abstract

RNA-binding proteins of the L7Ae family are at the heart of many essential ribonucleoproteins (RNPs), including box C/D and H/ACA small nucleolar RNPs, U4 small nuclear RNP, telomerase, and messenger RNPs coding for selenoproteins. In this study, we show that Nufip and its yeast homologue Rsa1 are key components of the machinery that assembles these RNPs. We observed that Rsa1 and Nufip bind several L7Ae proteins and tether them to other core proteins in the immature particles. Surprisingly, Rsa1 and Nufip also link assembling RNPs with the AAA + adenosine triphosphatases hRvb1 and hRvb2 and with the Hsp90 chaperone through two conserved adaptors, Tah1/hSpagh and Pih1. Inhibition of Hsp90 in human cells prevents the accumulation of U3, U4, and telomerase RNAs and decreases the levels of newly synthesized hNop58, hNHP2, 15.5K, and SBP2. Thus, Hsp90 may control the folding of these proteins during the formation of new RNPs. This suggests that Hsp90 functions as a master regulator of cell proliferation by allowing simultaneous control of cell signaling and cell growth.

New insights into the biogenesis of nuclear RNA polymerases?This paper is one of a selection of papers published in this special issue entitled “Canadian Society of Biochemistry, Molecular & Cellular Biology 52nd Annual Meeting — Protein Folding: Principles and Diseases” and has undergone the Journal's usual peer review process.

“…It was therefore proposed that R2TP might be involved in maturation of not only box C/D snoRNPs, but possibly all L7Ae RNPs, of which box C/D snoRNPs are members, along with box H/ACA snoRNPs, U4 snRNP, telomerase, and selenoproteincoding mRNPs. Inhibition of Hsp90 by geldanamycin seems to validate the assumption that Hsp90 and its co-chaperone R2TP might act during L7Ae RNP assembly as it resulted in a decrease in the number of L7Ae proteins (Boulon et al 2008). …”

“…In the network built by Sardiu and colleagues, NUFIP is shown to be a RPAP3/R2TP/ prefoldin-like complex interactor (Sardiu et al 2008), which is not surprising given that both NUFIP and its yeast homologue, RSA1, where able to bind the R2TP components PIH1D1 (PIH1/Nop17), RUVBL1 (TIP49) and RUVBL2 (TIP48) (McKeegan et al 2007;Boulon et al 2008). In both studies a role for NUFIP and their associated factors in box C/D snoRNP (or even all L7Ae family RNP) biogenesis was proposed.…”

“…This protein has 2 tetratricopeptide repeat (TPR) domains that have been shown to mediate interaction with Hsp90 in a similar fashion as another TPR-containing Hsp90 cofactor, Hop/Sti-1 Boulon et al 2008).…”

Selective up-regulation of human selenoproteins in response to oxidative stress

“…Recoding factors are imported into the nucleus to assemble with selenoprotein mRNAs as described in Refs. 40,50,53. mRNPs are built and exported to the cytoplasm to promote efficient translation by the ribosome.…”

Characterization of the UGA-recoding and SECIS-binding activities of SECIS-binding protein 2

“…Inhibition of Hsp90 in cells also prevents the accumulation of SBP2, suggesting a role for Hsp90 in the biogenesis of SBP2. 46 RRL contains abundant amounts of Hsp90 44,47 and Hsp70, 44 which may facilitate the proper folding and expression of SBP2, thereby leading to a more active protein. Even in the absence of understanding the mechanism, it is clear that the in vitro translated SBP2-CT has greater activity and may provide a more sensitive platform for investigating the mechanism of selenocysteine insertion and for probing SBP2 function.…”