title: NUMB controls p53 tumour suppressor activity.
abstract: NUMB is a cell fate determinant, which, by asymmetrically partitioning at mitosis, controls cell fate choices by antagonising the activity of the plasma membrane receptor of the NOTCH family. NUMB is also an endocytic protein, and the NOTCH-NUMB counteraction has been linked to this function. There might be, however, additional functions of NUMB, as witnessed by its proposed role as a tumour suppressor in breast cancer. Here we describe a previously unknown function for human NUMB as a regulator of tumour protein p53 (also known as TP53). NUMB enters in a tricomplex with p53 and the E3 ubiquitin ligase HDM2 (also known as MDM2), thereby preventing ubiquitination and degradation of p53. This results in increased p53 protein levels and activity, and in regulation of p53-dependent phenotypes. In breast cancers there is frequent loss of NUMB expression. We show that, in primary breast tumour cells, this event causes decreased p53 levels and increased chemoresistance. In breast cancers, loss of NUMB expression causes increased activity of the receptor NOTCH. Thus, in these cancers, a single event-loss of NUMB expression-determines activation of an oncogene (NOTCH) and attenuation of the p53 tumour suppressor pathway. Biologically, this results in an aggressive tumour phenotype, as witnessed by findings that NUMB-defective breast tumours display poor prognosis. Our results uncover a previously unknown tumour suppressor circuitry.
authors.affiliation: IFOM, the FIRC Institute for Molecular Oncology Foundation, Via Adamello 16, 20139, Milan, Italy.
authors.forename: Ivan N
authors.initials: IN
authors.lastname: Colaluca
authors.forename: Daniela
authors.initials: D
authors.lastname: Tosoni
authors.forename: Paolo
authors.initials: P
authors.lastname: Nuciforo
authors.forename: Francesca
authors.initials: F
authors.lastname: Senic-Matuglia
authors.forename: Viviana
authors.initials: V
authors.lastname: Galimberti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Viale
authors.forename: Salvatore
authors.initials: S
authors.lastname: Pece
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Di Fiore
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004249:DNA Damage; D019008:Drug Resistance, Neoplasm; D020868:Gene Silencing; D006801:Humans; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D011379:Prognosis; D011485:Protein Binding; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C113026:NUMB protein, human; D016159:Tumor Suppressor Protein p53; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2