A mutation linked to retinitis pigmentosa in HPRP31 causes protein instability and impairs its interactions with spliceosomal snRNPs

Abstract

The AD29 mutation in HPRP31 belongs to a series of mutations that were initially linked with the autosomal dominant disorder retinitis pigmentosa (RP) type 11. The HPRP31 gene encodes the hPrp31 protein that specifically associates with spliceosomal small nuclear ribonucleoprotein particles (snRNPs). Despite intensive research, it is still unclear how the AD29 (Ala216Pro) mutation causes RP. In this study, we report that the expression of this mutant protein affects cell proliferation and alters the structure of nuclear Cajal bodies that are connected with snRNP metabolism. Interestingly, these effects can be reversed by the over-expression of the hPrp6 protein, a binding partner of hPrp31. Although Ala216 is not contained within the U4 or U5 snRNP interacting domains, we present several lines of evidence that demonstrate that the association between the AD29 mutant and snRNPs in the cell nucleus is significantly reduced. Finally, we show that the stability of the AD29 mutant is severely affected resulting in its rapid degradation. Taken together, our results indicate that the Ala216Pro mutation destabilizes the hPrp31 protein structure in turn reducing its interaction with snRNP binding partners and leading to its rapid degradation. These findings significantly impact our understanding of the molecular mechanisms underlying RP and suggest that the insufficiency of the functional hPrp31 protein combined with the potential cytotoxicity associated with the expression the AD29 mutant are at least partially causative of the RP phenotype.

Identification of a PRPF4 Loss-of-Function Variant That Abrogates U4/U6.U5 Tri-snRNP Integration and Is Associated with Retinitis Pigmentosa

“…This mode of binding suggests that p.R192H not only causes a defective integration of PRPF4 into the tri-snRNP, but that it might also lead to the concomitant loss of PPIH, a protein necessary for efficient splicing [30]. Remarkably, a similar mechanism has been proposed for an RP-mutant form of PRPF31 that is thought to sequester its interactor PRPF6 out of the tri-snRNP [31], and an altered composition of the tri-snRNP has also been described for RP-causing missense mutations in PRPF8 [21].…”

Splicing factor U1-70K interacts with the SMN complex and is required for nuclear Gem integrity

“…To probe whether U1-70K interacts with SMN in gems, we employed Förster resonance energy transfer (FRET), which has been utilized previously to detect snRNP interaction partners in Cajal bodies (Staněk and Neugebauer, 2004;Huranová et al, 2009). We expressed YFP-tagged SMN protein together with CFP-tagged U1-70K and measured for increased CFP fluorescence after YFP bleaching (Fig.…”

“…Immunoprecipitation was performed as described previously (Huranová et al, 2009). RNA was extracted using phenol:chloroform, resolved on a 7 M urea denaturing polyacrylamide gel and silver stained.…”

SART3-Dependent Accumulation of Incomplete Spliceosomal snRNPs in Cajal Bodies

“…Immunoprecipitation was performed as previously described (Huranová et al, 2009) using mouse anti-Sm or goat anti-GFP antibodies. RNA was extracted using phenol/chloroform, resolved on a 7 M urea denaturing polyacrylamide gel and silver stained.…”