PPP1CB

PPP1CB encodes the β catalytic subunit of protein phosphatase 1 (PP1cβ), a serine/threonine phosphatase that assembles into substrate-specific holoenzymes through regulatory subunits and dephosphorylates diverse targets including myosin regulatory light chain, PLK1, RAF1 (Ser259), p-STAT3, and tau, thereby controlling smooth muscle contraction, mitotic checkpoint signaling, RAS/MAPK pathway output, and neuronal phospho-tau homeostasis (PMID:30185619, PMID:29262732, PMID:30368668, PMID:39119928, PMID:16262633). Regulatory subunit competition governs holoenzyme composition: MYPT1 targets PP1cβ to myosin for contractile regulation, while TIMAP competitively displaces MYPT1 and occludes the PP1cβ active site to inhibit myosin phosphatase activity in endothelial cells, and TRIP12-mediated ubiquitination degrades PP1cβ to relieve dephosphorylation of NF-κB pathway components (PMID:31315927, PMID:39155295). De novo gain-of-function missense mutations in PPP1CB (e.g., Pro49Arg, Ala56Pro) cause a Noonan syndrome–like RASopathy with loose anagen hair (PMID:27264673, PMID:27681385). Loss of PPP1CB phosphatase activity—via a recurrent YPEL5–PPP1CB chimeric transcript in chronic lymphocytic leukemia or via siRNA silencing—promotes leukemic cell proliferation, establishing PP1cβ as a growth-suppressive phosphatase in B-cell malignancy (PMID:23382248).

1. 1994 High

   Molecular cloning and chromosomal mapping established PPP1CB as a distinct PP1 catalytic subunit gene on human 2p23, with tissue-regulated alternative polyadenylation generating multiple transcripts enriched in skeletal muscle.

   Evidence cDNA cloning from human teratocarcinoma library, Northern blotting, FISH mapping in human/rat/mouse

   PMID:7857673 PMID:8312365

   Open questions at the time

   • Functional distinction from PPP1CA and PPP1CG isoforms was not resolved
   • No information on regulatory subunit specificity for PP1cβ versus other isoforms
2. 2000 High

   Identification of PP1 (including PP1cβ) as a resident phosphatase in a macromolecular signaling complex on ryanodine receptor 2 revealed how PP1 is physically targeted to ion channel substrates in cardiac muscle.

   Evidence Cosedimentation, co-immunoprecipitation, and functional channel recording on native cardiac RyR2 complexes

   PMID:10830164

   Open questions at the time

   • PP1 isoform specificity within the RyR2 complex was not distinguished (PP1cα vs PP1cβ)
   • Direct phospho-site on RyR2 dephosphorylated by PP1cβ was not mapped
3. 2005 High

   Reconstituted enzyme–substrate assays demonstrated that PP1 dephosphorylates tau at ten distinct phospho-sites with physiologically relevant kinetics, placing PP1cβ among the phosphatases maintaining neuronal tau phosphorylation balance.

   Evidence In vitro phosphatase assay with purified PP1 and site-specific phospho-tau quantification

   PMID:16262633

   Open questions at the time

   • Relative contribution of PP1cβ versus PP1cα or PP1cγ to tau dephosphorylation in vivo was not determined
   • Regulatory subunit directing PP1 to tau was not identified
4. 2013 High

   Discovery of a recurrent YPEL5–PPP1CB chimeric transcript in >95% of CLL patients, encoding a truncated protein with diminished phosphatase activity, combined with functional knockdown studies, established PP1cβ as a negative regulator of leukemic B-cell proliferation.

   Evidence Paired-end RNA-seq, phosphatase activity assay on chimeric protein, siRNA knockdown with proliferation and colony formation readouts in MEC1/JVM3 cells

   PMID:23382248

   Open questions at the time

   • Direct substrate whose dephosphorylation suppresses CLL cell growth was not identified
   • Whether full-length PPP1CB re-expression rescues the proliferative phenotype was not tested
5. 2016 Medium

   Identification of de novo missense mutations in PPP1CB as the cause of a Noonan-like RASopathy linked PP1cβ dysfunction to RAS/MAPK pathway hyperactivation in a developmental disorder context.

   Evidence Whole-exome sequencing of affected individuals, Sanger validation, clinical phenotyping

   PMID:27264673 PMID:27681385

   Open questions at the time

   • Biochemical impact of Pro49Arg and Ala56Pro on phosphatase activity and regulatory subunit binding was predicted but not directly measured
   • No patient-derived cellular models or animal models reported
   • Gain-of-function versus loss-of-function mechanism was inferred, not demonstrated
6. 2018 High

   Three contemporaneous studies defined PP1cβ holoenzyme biochemistry in specific tissues: MYPT1-PP1cβ dephosphorylates PLK1 during DNA damage (controlled by Chk1-mediated MYPT1 Ser20 phosphorylation), LZTR1 scaffolds RAF1-PP1cβ for RAF1 Ser259 dephosphorylation in RAS signaling, and conditional knockout showed PP1cβ is the dominant PP1 isoform (>90%) controlling myosin RLC dephosphorylation and smooth muscle contractility.

   Evidence In vitro kinase assay and Ser20 mutagenesis (Chk1–MYPT1–PP1cβ); endogenous IP and siRNA (LZTR1–RAF1–PP1cβ); smooth-muscle-specific Cre-lox KO with ex vivo contractility and isoform quantification

   PMID:29262732 PMID:30185619 PMID:30368668

   Open questions at the time

   • Whether MYPT1-PP1cβ is the sole PLK1 phosphatase during mitotic damage or acts redundantly was not resolved
   • Structural basis for PP1cβ isoform preference of MYPT1 over PP1cα/γ was not determined
7. 2019 High

   TIMAP was shown to inhibit the MYPT1-PP1cβ myosin phosphatase by competitively binding PP1cβ and occluding its active site, establishing regulatory subunit competition as a mechanism controlling PP1cβ holoenzyme identity and output in endothelial cells.

   Evidence Recombinant pulldown, TIMAP-PP1cβ binding mutant, microcystin-LR active-site competition, TIMAP-KO mouse tissue

   PMID:31315927

   Open questions at the time

   • Quantitative binding affinities for TIMAP vs MYPT1 for PP1cβ were not determined
   • In vivo endothelial phenotype of TIMAP-PP1cβ disruption was not fully characterized
8. 2015 Medium

   PPP1CB was identified as an adipogenic activator that links p38 MAPK signaling to C/EBPδ expression during early clonal expansion of preadipocytes, extending PP1cβ function to metabolic differentiation.

   Evidence siRNA knockdown in 3T3-L1 cells, oil red O staining, qRT-PCR and western blotting for adipogenic markers

   PMID:26449462

   Open questions at the time

   • Direct substrate of PP1cβ in the p38–C/EBPδ axis was not identified
   • In vivo adipose tissue phenotype upon PPP1CB loss was not tested
9. 2024 Medium

   Two studies expanded the substrate and regulatory landscape of PP1cβ: NSD3 scaffolds PP1cβ to dephosphorylate p-STAT3 and suppress glycolysis in lung adenocarcinoma, while TRIP12-mediated ubiquitination degrades PP1cβ to activate NF-κB signaling and promote chemoresistance in bladder cancer.

   Evidence Co-IP of NSD3–PPP1CB–p-STAT3 trimeric complex with in vivo tumor models; Co-IP and CRISPR/siRNA defining TRIP12–OIP5-mediated PPP1CB ubiquitination with NF-κB reporter assays

   PMID:39119928 PMID:39155295

   Open questions at the time

   • NSD3-directed dephosphorylation of STAT3 by PP1cβ has not been reconstituted with purified components
   • Whether TRIP12-mediated degradation is PP1cβ-isoform-specific is unknown
   • CO2/pH sensitivity of PP1cβ phosphatase activity reported in the NSD3 study awaits independent replication

• Key unresolved questions include the structural basis for PP1cβ isoform-selective regulatory subunit binding, the direct biochemical mechanism of RASopathy-causing mutations, and the identity of the PP1cβ substrate(s) mediating its growth-suppressive role in CLL.
• No crystal structure of a PP1cβ-specific holoenzyme distinguishing it from PP1cα or PP1cγ complexes
• Biochemical characterization of Noonan-associated PPP1CB missense mutants is lacking
• CLL-relevant PP1cβ substrates remain unidentified