NUMB is a cytoplasmic adaptor protein of the Numb/Numb-like family with an N-terminal phosphotyrosine-binding (PTB) domain and a C-terminal region carrying DPF and NPF motifs. It associates peripherally with the cytoplasmic face of the plasma membrane, clathrin-coated structures and endosomes, and in mammals acts as an endocytic protein that regulates clathrin-mediated receptor internalization, its activity being regulated by phosphorylation by the AP-2-associated kinase AAK1. In the developing mammalian brain NUMB, redundantly with NUMBL, maintains neural progenitor (radial glial) cells and their cadherin-based adherens junctions, and postnatally supports subventricular zone neurogenesis. The donkey gene encodes several isoforms; this entry is a 506-residue product whose exon structure corresponds to human isoform 5 (PTB insert present, proline-rich-region insert absent).
Summary: Cytoplasm, transferred by TreeGrafter from PANTHER node PTN000132844 (PAINT node seeded by mouse Numb, MGI:107423). NUMB is a soluble cytoplasmic protein that associates peripherally with the cytoplasmic side of the plasma membrane and endosomes.
Reason: The donkey entry is classified in the NUMB subfamily PTHR47368:SF5 together with human P49757 and mouse Q9QZS3, so it lies inside the clade that inherits the PAINT assertion. The human ortholog is a peripheral membrane protein on the cytoplasmic side and is also cytoplasmic. The more specific membrane and vesicle locations are accepted separately; cytoplasm remains a true description of the soluble pool.
Summary: Plasma membrane from the UniProt subcellular-location mapping (cell membrane, peripheral, cytoplasmic side). Human NUMB localizes to the plasma membrane, accumulates there when AAK1 is depleted, and colocalizes with coated-pit markers (PMID:18657069).
Reason: Experimentally supported for the human ortholog (same PANTHER subfamily SF5), where NUMB acts at clathrin-coated pits at the plasma membrane. The donkey isoform keeps the whole PTB domain and the AAK1-site threonine (file:EQUAS/NUMB/NUMB-bioinformatics/RESULTS-rereview.md).
Summary: Basolateral plasma membrane, from the TreeGrafter PANTHER node. The PAINT node is seeded by mouse Numb, which is curated as basolateral (and NOT apical plasma membrane) in radial glial progenitors (PMID:17589506), where it localizes to adherens-junction-associated vesicles and is needed for basolateral insertion of cadherins.
Reason: The PAINT assertion is grounded in experimental mouse Numb localization in polarized neural progenitors; the donkey protein falls inside the NUMB subfamily (PTHR47368:SF5). The cached mouse paper is abstract-only, so the basolateral localization itself is taken from the curators' reading of the full text; the abstract supports the junctional, cadherin-trafficking context.
Summary: Cytoplasmic vesicle, from the TreeGrafter PANTHER node. Human NUMB is found on endosome membranes and redistributes to perinuclear endosomes in an AAK1-dependent manner (PMID:18657069); mouse Numb localizes to adherens-junction-associated vesicles in radial glia (PMID:17589506).
Reason: Consistent with the endocytic role of NUMB and with experimental vesicular localization of the human and mouse orthologs. More specific terms (endosome membrane, clathrin-coated vesicle) are curated for human but were not propagated by PAINT; the vesicle term is the level the PAINT curator chose for the family and is correct as stated.
Summary: Positive regulation of neurogenesis, from the combined IEA pipeline (PANTHER node plus UniRule). This is the biological-process term the PAINT curator placed on the NUMB node, grounded in mouse genetics showing that Numb and Numbl redundantly maintain neural progenitors during embryonic neurogenesis (PMID:12410312) and postnatally in the subventricular zone (PMID:17174898).
Reason: The role is real and phylogenetically grounded (donkey NUMB is in the SF5 subfamily that inherits the PTN000132844 assertion). It is kept as non-core because the evidence is conditional double-knockout genetics in the mouse brain, establishing that NUMB/NUMBL are required for progenitor maintenance, while the cellular activity through which NUMB acts (endocytic adaptor function and adherens-junction maintenance) is what this review records as core. The term is not too general for that evidence, so no refinement is proposed.
mouse numb and numblike (Nbl), two highly conserved homologues of Drosophila numb, play redundant but critical roles in maintaining neural progenitor cells during embryogenesis
Required throughout embryonic neurogenesis to maintain neural progenitor cells
GO:2000369 regulation of clathrin-dependent endocytosis
ISS PMID:18657069 AAK1 regulates Numb function at an early step in clathrin-me...
NEW
Summary: Human NUMB is an endocytic protein that acts at an early step of clathrin-mediated endocytosis; a phosphorylation-site mutant (T102A) enriched at coated pits disrupts transferrin and LDL internalization (PMID:18657069). UniProt records this as curated, publication-backed function for human NUMB.
Reason: Participation test: NUMB itself is a component at clathrin-coated pits whose state (regulated by AAK1 phosphorylation at Thr-102) changes receptor internalization, so it does part of the regulatory work rather than being a cargo. Evolutionary basis: donkey NUMB and human NUMB are in the same PANTHER subfamily (PTHR47368:SF5, 1:1 orthologs), and the donkey isoform conserves the PTB domain, the Thr-102 equivalent and the C-terminal DPF/NPF motifs. Comparator: human NUMB carries regulation of endocytosis (IMP); PAINT did not propagate an endocytosis term on PTN000132844, so this is proposed as a direct ortholog (ISS) transfer from human experimental data, not as an inherited family-level function.
It retains the complete PTB (PID) domain, the threonine equivalent to human Thr-102
Core Functions
Endocytic adaptor at the cytoplasmic face of the plasma membrane and endosomes that regulates clathrin-mediated receptor internalization, under control of AAK1 phosphorylation.
Q: Which molecular activity term best captures NUMB's role at coated pits (cargo-specific adaptor via its PTB domain, or AP-2/EH-protein scaffold via the C-terminal DPF/NPF motifs), and why do neither human nor mouse NUMB carry a Notch signalling-pathway annotation despite the classical Notch-antagonist literature?
Q: Should the endocytic terms curated experimentally for human and mouse NUMB (clathrin-coated pit, endosome membrane, regulation of endocytosis) be propagated at PAINT node PTN000132844, which currently carries only cytoplasm, basolateral plasma membrane, cytoplasmic vesicle and positive regulation of neurogenesis?
Q: Which NUMB isoforms are expressed in donkey tissues, and does the isoform-5-like model (lacking the human 219-316 segment) represent a major transcript?
Suggested Experiments
Experiment: Profile NUMB transcripts in donkey brain and epithelial tissues by long-read RNA-seq to determine which isoforms (PTB and proline-rich-region inserts, 219-316 segment) are expressed.
External Prediction Reviews
These computational predictions are reviewed separately from the GOA annotation set used for this review. The assessments below are from this project and do not constitute official GO annotations or endorsement by GO/UniProt. They are not included in the existing annotation review above.
Assessment of 1 ProtNLM2 GO prediction for donkey NUMB (A0A9L0IQ95), judged against the donkey GOA record (cytoplasm, plasma membrane, basolateral plasma membrane, cytoplasmic vesicle, positive regulation of neurogenesis), the human ortholog P49757 and the AAK1/endocytosis study PMID:18657069, and a donkey-human alignment (97% identity). The plasma membrane prediction is correct and already in donkey GOA (CNN). ProtNLM2 emitted no non-GO outputs (function text or subcellular location) for this accession in the frozen snapshot.
Prediction method: ProtNLM2 · Version: UniProt API snapshot 2026-10-14
Review rationale: Human NUMB localizes to the cytoplasmic face of the plasma membrane, where it acts at clathrin-coated pits and accumulates when AAK1 is depleted (PMID:18657069); the donkey protein is 97% identical to human NUMB with a conserved PTB domain. The exact term is already present in donkey GOA (UniProt subcellular-location mapping), and donkey GOA also carries the more specific basolateral plasma membrane from the PANTHER node. The prediction is therefore correct but not novel. Training-set membership is unknown.
Supporting Evidence:
PMID:18657069: "kinase depletion causes Numb to accumulate at the plasma membrane"