PPP3CC

PPP3CC encodes the catalytic γ-subunit of calcineurin, a serine/threonine phosphatase that operates at the intersection of neuronal synapse regulation and NF-κB-dependent signaling in cancer (PMID:32249816, PMID:28041912). In neurons, PPP3CC is a direct substrate of UBE3B-mediated ubiquitination, and its abundance sets dendritic spine density: elevated PPP3CC phenocopies the increased spine number seen upon Ube3b loss, establishing PPP3CC as the effector through which this ubiquitin ligase controls synapse number (PMID:32249816). PPP3CC also constrains NF-κB signaling, and its loss permits constitutive NF-κB activation that promotes tumor cell invasion and proliferation; in glioma this loss is enforced transcriptionally by ZEB1, which binds the PPP3CC promoter to repress its expression, while restoring PPP3CC suppresses NF-κB activity (PMID:29294030). Conversely, in castration-resistant prostate cancer PPP3CC participates in a feedforward circuit with IκBα/NF-κB(p65), miR-196b-3p and Meis2 that drives tumorigenicity through IKKβ-independent NF-κB activation (PMID:28041912). PPP3CC additionally interacts with ITPKC, stabilizing it by inhibiting its phosphorylation and thereby limiting IP3 levels, positioning PPP3CC as a feedback regulator of IP3-Ca²⁺ signaling (PMID:23747857).

1. 2013 Medium

   Established a biochemical role for PPP3CC in Ca²⁺ signaling by showing it physically stabilizes ITPKC and feeds back on IP3 levels, moving beyond a generic phosphatase annotation.

   Evidence Yeast two-hybrid, GST pull-down, Co-IP, co-localization and protein stability assays

   PMID:23747857

   Open questions at the time

   • Direct dephosphorylation of ITPKC by PPP3CC not demonstrated enzymatically
   • Physiological context of the IP3-Ca²⁺ feedback not defined in tissue
2. 2016 Medium

   Placed PPP3CC within a constitutively active feedforward NF-κB circuit driving castration-resistant prostate cancer, defining a tumorigenic role distinct from canonical IKKβ signaling.

   Evidence Genetic knockdown/overexpression of circuit components with in vitro and in vivo tumor growth and epistasis analysis

   PMID:28041912

   Open questions at the time

   • Whether PPP3CC acts catalytically within the circuit is unresolved
   • Direct phosphatase substrates in the NF-κB pathway not identified
3. 2018 Medium

   Identified ZEB1 as a direct transcriptional repressor of PPP3CC and linked PPP3CC loss to constitutive NF-κB activation and glioma aggressiveness, framing PPP3CC as a negative regulator of NF-κB.

   Evidence ChIP, luciferase reporter, ZEB1 knockdown with PPP3CC rescue, NF-κB ELISA, invasion and proliferation assays

   PMID:29294030

   Open questions at the time

   • Which NF-κB pathway components PPP3CC dephosphorylates not defined
   • Mechanistic reconciliation with the pro-tumorigenic CRPC circuit role not addressed
4. 2020 High

   Defined PPP3CC as a direct UBE3B ubiquitination substrate whose level controls dendritic spine density, providing the mechanistic link between an E3 ligase and synapse number.

   Evidence In vitro ubiquitination assay, genetic overexpression phenocopy, and Ube3b knockout spine morphology analysis in mouse neurons

   PMID:32249816

   Open questions at the time

   • Phosphatase substrates relevant to spine regulation not identified
   • Ubiquitination sites and degradation kinetics not mapped
5. 2021 Low

   Connected PPP3CC to apoptotic effectors in ovarian cancer as a miR-200c-3p target, supporting a tumor-suppressor role.

   Evidence miRNA overexpression/RNAi in EOC cell lines, qRT-PCR, western blot for BCL2 and p-AKT, with CCLE/TCGA correlation

   PMID:34573382

   Open questions at the time

   • Pathway placement inferred from downstream marker modulation without direct PPP3CC binding or enzymatic assay
   • Direct miR-200c-3p targeting of PPP3CC 3'UTR not validated by reporter
6. 2024 Low

   Associated PPP3CC upregulation with JNK/P38/MAPK activation and anti-proliferative effects of shikonin in NSCLC.

   Evidence RNA-seq, qPCR, western blot, CCK8 and wound healing assays with GO/KEGG analysis

   PMID:38167059

   Open questions at the time

   • Causal role of PPP3CC inferred from expression changes and bioinformatics without direct mechanistic assay
   • Link between PPP3CC and MAPK pathway not established at the protein level

• The direct enzymatic substrates of PPP3CC phosphatase activity in both synaptic and NF-κB contexts remain unidentified, leaving the catalytic mechanism underlying its phenotypes undefined.
• No dephosphorylation substrate directly demonstrated
• No structural model of PPP3CC in complex with regulatory partners
• Reconciliation of pro- and anti-tumorigenic roles unresolved