title: Usp28 counteracts Fbw7 in intestinal homeostasis and cancer.
abstract: The stability of several oncoproteins, including c-Myc, is regulated by ubiquitin-dependent degradation mediated by the SCF(Fbw7) ubiquitin ligase. This activity is antagonized by the deubiquitinase Usp28, which is highly expressed in murine and human intestinal cancers. Usp28 was previously shown to interact with its substrates via a "piggyback" interaction with Fbw7, which suggested that Fbw7 is required for Usp28 activity. Unexpectedly, we found that genetic deletion of Usp28 rescued the lethality of Fbw7-deficient primary fibroblasts. Moreover, Usp28 inactivation in the intestine (Usp28(ΔIEC)) ameliorated the hyperproliferation and the impaired goblet and Paneth cell differentiation observed in Fbw7(ΔIEC) mice. The aggressive intestinal tumor formation of APC(Min/+); Fbw7(ΔIEC) mice was restrained when Usp28 was inactivated concomitantly. In both fibroblasts and intestinal cells, Usp28 deficiency corrected the accumulation of SCF(Fbw7) substrate proteins, including NICD1, c-Jun, and c-Myc. These findings suggested that Usp28 function does not depend on the presence of Fbw7, but instead independently recognizes and deubiquitylates the same substrates as SCF(Fbw7). Fbw7 binds to a phosphorylated motif termed the phosphodegron and we found that Usp28 also interacted with this same motif, but only when it is unphosphorylated, offering a mechanistic explanation for identical substrate selection by Fbw7 and Usp28. Our results indicate an unusually direct antagonism between an E3 ligase and a deubiquitinase, Fbw7 and Usp28, in modulating intestinal homeostasis and cancer.
authors.affiliation: Mammalian Genetics Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, Lincoln's Inn Fields, London, United Kingdom.
authors.forename: Markus E
authors.initials: ME
authors.lastname: Diefenbacher
authors.affiliation: Mammalian Genetics Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, Lincoln's Inn Fields, London, United Kingdom.
authors.forename: Atanu
authors.initials: A
authors.lastname: Chakraborty
authors.affiliation: Mammalian Genetics Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, Lincoln's Inn Fields, London, United Kingdom.
authors.forename: Sophia M
authors.initials: SM
authors.lastname: Blake
authors.affiliation: Bioinformatics and Biostatistics, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, Lincoln's Inn Fields, London, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Mitter
authors.affiliation: University of Würzburg, Comprehensive Cancer Center Mainfranken, Würzburg, Germany.
authors.forename: Nikita
authors.initials: N
authors.lastname: Popov
authors.affiliation: Department of Biochemistry and Molecular Biology, Theodor Boveri Institute, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Eilers
authors.affiliation: Mammalian Genetics Laboratory, Cancer Research UK London Research Institute, Lincoln's Inn Fields Laboratories, Lincoln's Inn Fields, London, United Kingdom. School of Medicine, King's College London, Guy's Campus, London, United Kingdom. axel.behrens@cancer.org.uk.
authors.forename: Axel
authors.initials: A
authors.lastname: Behrens
mesh_terms: D000818:Animals; D063646:Carcinogenesis / Q000378:metabolism; D002454:Cell Differentiation; D049109:Cell Proliferation; D044783:F-Box Proteins / Q000378:metabolism*; D000073979:F-Box-WD Repeat-Containing Protein 7; D045325:HCT116 Cells; D006706:Homeostasis; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007414:Intestinal Neoplasms / Q000378:metabolism*; D007422:Intestines / Q000473:pathology; D008822:Mice, Transgenic; D043222:Ubiquitin Thiolesterase / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C513272:Fbxw7 protein, mouse; C000595271:USP28 protein, mouse; D044767:Ubiquitin-Protein Ligases; D043222:Ubiquitin Thiolesterase