title: Calpain induces N-terminal truncation of β-catenin in normal murine liver development: diagnostic implications in hepatoblastomas.
abstract: Hepatic competence, specification, and liver bud expansion during development depend on precise temporal modulation of the Wnt/β-catenin signaling. Also, loss- and gain-of-function studies have revealed pleiotropic roles of β-catenin in proliferation and hepatocyte and biliary epithelial cell differentiation, but precise mechanisms remain unknown. Here we utilize livers from different stages of murine development to determine β-catenin signaling and downstream targets. Although during early liver development full-length β-catenin is the predominant form, at late stages, where full-length β-catenin localizes to developing biliary epithelial cells only, a 75-kDa truncated β-catenin species is the principal form localizing at the membrane and in the nucleus of differentiating hepatocytes. The truncated species lacks 95 N-terminal amino acids and is transcriptionally active. Our evidence points to proteolytic cleavage of β-catenin by calpain as the mechanism of truncation in cell-free and cell-based assays. Intraperitoneal injection of a short term calpain inhibitor to timed pregnant female mice abrogated β-catenin truncation in the embryonic livers. RNA-seq revealed a unique set of targets transcribed in cells expressing truncated versus full-length β-catenin, consistent with different functionalities. A further investigation using N- and C-terminal-specific β-catenin antibodies on human hepatoblastomas revealed a correlation between full-length versus truncated β-catenin and differentiation status, with embryonal hepatoblastomas expressing full-length β-catenin and fetal hepatoblastomas expressing β-catenin lacking its N terminus. Thus we conclude that calpain-mediated cleavage of β-catenin plays a role in regulating hepatoblast differentiation in mouse and human liver, and the presence of the β-catenin N terminus correlates with differentiation status in hepatoblastomas.
authors.affiliation: Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Abigale
authors.initials: A
authors.lastname: Lade
authors.forename: Sarangarajan
authors.initials: S
authors.lastname: Ranganathan
authors.forename: Jianhua
authors.initials: J
authors.lastname: Luo
authors.forename: Satdarshan P S
authors.initials: SP
authors.lastname: Monga
mesh_terms: D017398:Alternative Splicing / Q000502:physiology; D000818:Animals; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D005260:Female; D057809:HEK293 Cells; D018197:Hepatoblastoma / Q000175:diagnosis* / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000201:enzymology; D006801:Humans; D008099:Liver / Q000196:embryology / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000175:diagnosis* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011247:Pregnancy; D017434:Protein Structure, Tertiary; D051176:beta Catenin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D051176:beta Catenin; D002154:Calpain; C058076:calpain inhibitor III