ANKRD52

ANKRD52 is the ankyrin-repeat regulatory subunit of the protein phosphatase 6 (PP6) heterotrimer, where it assembles with the PP6 catalytic subunit and a SAPS-domain PP6R subunit to confer substrate specificity on the complex (PMID:18186651). It was identified by mass spectrometry as a PP6 holoenzyme component, binding the C-terminal scaffold region of PP6R1, which holds separate docking sites for the catalytic and ankyrin-repeat subunits, with endogenous holoenzymes eluting as >440 kDa heterotrimers (PMID:18186651). Functionally, the ANKRD52-PP6 complex maintains the global efficiency of miRNA-mediated silencing by dephosphorylating AGO2 at a conserved S824-S834 cluster; target engagement triggers hierarchical phosphorylation of AGO2 by CSNK1A1, and rapid dephosphorylation by ANKRD52-PPP6C resets AGO2 for productive target binding, with loss of this cycle expanding the AGO2 target repertoire and diluting the active phosphatase-reset pool per target (PMID:28114302). The same complex dephosphorylates PAK1 to restrain cell migration, and ANKRD52 transcription is repressed by TAZ (PMID:33096142). Through its control of miRNA silencing, ANKRD52 sustains miR-155-mediated repression of SOCS1, so its inactivation—or reintroduction of cancer patient mutations—dampens JAK-STAT/interferon-γ signaling and antigen presentation, allowing tumor cells to evade T cell-mediated cytotoxicity (PMID:34853298).

1. 2008 High

   Established that ANKRD52 is not a free-standing protein but an integral ankyrin-repeat regulatory subunit of the PP6 phosphatase heterotrimer, defining the architecture in which a SAPS-domain subunit scaffolds the catalytic and ankyrin-repeat subunits.

   Evidence FLAG Co-IP, mass spectrometry, size-exclusion chromatography and siRNA knockdown with IκBε degradation readout

   PMID:18186651

   Open questions at the time

   • Direct functional role of ANKRD52 itself (vs paralog Ankrd28) was inferred from family behavior
   • No substrate of the ANKRD52-PP6 complex identified at this stage
   • Structural basis of substrate-specificity conferred by the ankyrin repeats unresolved
2. 2017 High

   Answered what physiological substrate the ANKRD52-PP6 complex acts on, showing it dephosphorylates AGO2 to sustain global miRNA silencing through a CSNK1A1-driven phosphorylation/dephosphorylation cycle.

   Evidence Genome-wide CRISPR loss-of-function screen, miRNA fluorescent reporter, AGO2 phospho-site mutagenesis and transcriptome-wide AGO2 CLIP-seq

   PMID:28114302

   Open questions at the time

   • Structural detail of how ANKRD52 recognizes the AGO2 phospho-cluster not resolved
   • Whether ANKRD52 directs other PP6 substrates beyond AGO2 not addressed here
3. 2020 Medium

   Extended the substrate range and added upstream regulation, showing ANKRD52-PP6 dephosphorylates PAK1 to limit migration and that TAZ transcriptionally represses ANKRD52.

   Evidence TAZ knockdown with ANKRD52 promoter-reporter, mass spectrometry, PAK1 phosphorylation assay and cell mobility assay with ANKRD52 overexpression

   PMID:33096142

   Open questions at the time

   • Single-lab findings not independently replicated
   • Direct vs indirect dephosphorylation of PAK1 by the complex not fully separated
   • Mechanism of TAZ-mediated promoter repression not defined
4. 2021 High

   Connected ANKRD52's role in miRNA silencing to tumor immune evasion, showing its loss disrupts miR-155 repression of SOCS1 and thereby dampens interferon-γ responsiveness and T cell killing.

   Evidence CRISPR library screen in syngeneic mouse tumors, T cell co-culture under immune pressure, patient-mutation reintroduction and miR-155/SOCS1 epistasis

   PMID:34853298

   Open questions at the time

   • Whether AGO2 dephosphorylation is the specific node linking ANKRD52 to miR-155 function not directly demonstrated
   • Clinical relevance of specific patient mutations to phosphatase activity not biochemically dissected
5. 2024 Low

   Reaffirmed the PP6 heterotrimer model including ANKRD52 as a scaffold subunit in colorectal cancer, while attributing the stemness phenotype primarily to PP6c-PP6R3.

   Evidence siRNA knockdown of PP6c, colony formation assay, in vivo xenograft and stemness-gene transcriptome analysis

   PMID:39014521

   Open questions at the time

   • ANKRD52's specific contribution not tested; functional data focus on PP6c and PP6R3
   • No direct ANKRD52 knockdown or substrate assay in this context

• How ANKRD52's ankyrin repeats structurally select among PP6 substrates (AGO2, PAK1) and whether additional substrates couple it to other pathways remains unresolved.
• No structure of ANKRD52 within the PP6 holoenzyme or bound to substrate
• Substrate-selection rules conferred by the ankyrin-repeat subunit undefined
• Tissue-specific and physiological scope of ANKRD52-PP6 substrates incomplete