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B56?-related protein phosphatase 2A dysfunction identified in patients with intellectual disability.

ABSTRACT: Here we report inherited dysregulation of protein phosphatase activity as a cause of intellectual disability (ID). De novo missense mutations in 2 subunits of serine/threonine (Ser/Thr) protein phosphatase 2A (PP2A) were identified in 16 individuals with mild to severe ID, long-lasting hypotonia, epileptic susceptibility, frontal bossing, mild hypertelorism, and downslanting palpebral fissures. PP2A comprises catalytic (C), scaffolding (A), and regulatory (B) subunits that determine subcellular anchoring, substrate specificity, and physiological function. Ten patients had mutations within a highly conserved acidic loop of the PPP2R5D-encoded B56? regulatory subunit, with the same E198K mutation present in 6 individuals. Five patients had mutations in the PPP2R1A-encoded scaffolding A? subunit, with the same R182W mutation in 3 individuals. Some A? cases presented with large ventricles, causing macrocephaly and hydrocephalus suspicion, and all cases exhibited partial or complete corpus callosum agenesis. Functional evaluation revealed that mutant A and B subunits were stable and uncoupled from phosphatase activity. Mutant B56? was A and C binding-deficient, while mutant A? subunits bound B56? well but were unable to bind C or bound a catalytically impaired C, suggesting a dominant-negative effect where mutant subunits hinder dephosphorylation of B56?-anchored substrates. Moreover, mutant subunit overexpression resulted in hyperphosphorylation of GSK3?, a B56?-regulated substrate. This effect was in line with clinical observations, supporting a correlation between the ID degree and biochemical disturbance.

SUBMITTER: Houge G

PROVIDER: S-EPMC4623570 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

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B56δ-related protein phosphatase 2A dysfunction identified in patients with intellectual disability.

Houge Gunnar G Haesen Dorien D Vissers Lisenka E L M LE Mehta Sarju S Parker Michael J MJ Wright Michael M Vogt Julie J McKee Shane S Tolmie John L JL Cordeiro Nuno N Kleefstra Tjitske T Willemsen Marjolein H MH Reijnders Margot R F MR Berland Siren S Hayman Eli E Lahat Eli E Brilstra Eva H EH van Gassen Koen L I KL Zonneveld-Huijssoon Evelien E de Bie Charlotte I CI Hoischen Alexander A Eichler Evan E EE Holdhus Rita R Steen Vidar M VM Døskeland Stein Ove SO Hurles Matthew E ME FitzPatrick David R DR Janssens Veerle V

The Journal of clinical investigation 20150713 8

Here we report inherited dysregulation of protein phosphatase activity as a cause of intellectual disability (ID). De novo missense mutations in 2 subunits of serine/threonine (Ser/Thr) protein phosphatase 2A (PP2A) were identified in 16 individuals with mild to severe ID, long-lasting hypotonia, epileptic susceptibility, frontal bossing, mild hypertelorism, and downslanting palpebral fissures. PP2A comprises catalytic (C), scaffolding (A), and regulatory (B) subunits that determine subcellular ...[more]

PMID: 26168268

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Project description:BackgroundWnt signaling is a key regulator of development and tumorigenesis. Protein phosphatase 2A (PP2A), which consists of a catalytic C, a structural A, and a regulatory B subunit, plays diverse roles in Wnt signaling through its B56 subunits. B56 is a multigene family encoding for proteins with a conserved core domain and divergent amino- and carboxy-termini. Ectopic B56alpha and B56gamma reduce beta-catenin abundance and B56alpha reduces Wnt-dependent transcription, suggesting that B56alpha and B56gamma inhibit Wnt signaling. In contrast, B56epsilon is required for Wnt signaling. Knowledge of where and when B56 subunits are expressed during Xenopus development will aid in our understanding of their roles in Wnt signaling.ResultsWe have undertaken expression analyses of B56alpha and B56gamma in Xenopus laevis. We cloned Xenopus B56alpha; it is 88% identical to human B56alpha. Xenopus B56gamma is 94% identical with human B56gamma, however, a novel evolutionarily conserved mixed-isoform transcript was identified that contains a B56delta-like amino-terminal domain and a B56gamma core domain. The B56delta-like variable domain exon is located upstream of the B56gamma variable domain exon at the human B56gamma locus, suggesting that the mixed-isoform transcript is due to alternative splicing. B56gamma transcripts with different 3' ends were identified that lack or possess a 35 base pair sequence, resulting in either a transcript similar to human B56gamma1, or an uncharacterized evolutionarily conserved sequence. Real time RT-PCR analyses revealed that B56alpha is expressed at moderate levels before the midblastula transition (MBT), at reduced levels during gastrulation and neurulation, and at high levels during organogenesis, while B56gamma is expressed at low levels until organogenesis. B56alpha is enriched in the ventral hemisphere pre-MBT, while B56gamma is ventrally enriched post-MBT. Aalpha, Abeta, Calpha and Cbeta are expressed in early Xenopus development, suggesting the presence of a functional heterotrimer.ConclusionOur data suggest that B56 functional diversity is achieved in part through the synthesis of a novel mixed-isoform B56delta/gamma transcript. Our data also suggest that B56alpha functions pre-MBT, inhibiting Wnt signaling on the ventral side of the embryo, and again during organogenesis, while B56gamma functions primarily post-MBT.

Dataset Information

B56?-related protein phosphatase 2A dysfunction identified in patients with intellectual disability.

Publications

B56δ-related protein phosphatase 2A dysfunction identified in patients with intellectual disability.

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