title: Pathobiological implications of the d16HER2 splice variant for stemness and aggressiveness of HER2-positive breast cancer.
abstract: We have previously shown that the d16HER2 splice variant is linked to HER2-positive breast cancer (BC) tumorigenesis, progression and response to Trastuzumab. However, the mechanisms by which d16HER2 contributes to HER2-driven aggressiveness and targeted therapy susceptibility remain uncertain. Here, we report that the d16HER2-positive mammary tumor cell lines MI6 and MI7, derived from spontaneous lesions of d16HER2 transgenic (tg) mice and resembling the aggressive features of primary lesions, are enriched in the expression of Wnt, Notch and epithelial-mesenchymal transition pathways related genes compared with full-length wild-type (WT) HER2-positive cells (WTHER2_1 and WTHER2_2) derived from spontaneous tumors arising in WTHER2 tg mice. MI6 cells exhibited increased resistance to anoikis and significantly higher mammosphere-forming efficiency (MFE) and self-renewal capability than the WTHER2-positive counterpart. Furthermore, d16HER2-positive tumor cells expressed a higher fraction of CD29High/CD24+/SCA1Lowcells and displayed greater in vivo tumor engraftment in serial dilution conditions than WTHER2_1 cells. Accordingly, NOTCH inhibitors impaired mammosphere formation only in MI6 cells. A comparative analysis of stemness-related features driven by d16HER2 and WTHER2 in ad hoc engineered human BC cells (MCF7 and T47D) revealed a higher MFE and aldehyde dehydrogenase-positive staining in d16HER2- vs WTHER2-infected cells, sustaining consistent BC-initiating cell enrichment in the human setting. Moreover, marked CD44 expression was found in MCF7_d16 and T47D_d16 cells vs their WTHER2 and Mock counterparts. Clinically, BC cases from two distinct HER2-positive cohorts characterized by high levels of expression of the activated-d16HER2 metagene were significantly enriched in the Notch family and signal transducer genes vs those with low levels of the metagene.
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Castagnoli
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: G C
authors.initials: GC
authors.lastname: Ghedini
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Koschorke
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: T
authors.initials: T
authors.lastname: Triulzi
authors.affiliation: Functional Genomics and Bioinformatics Core Facility, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Dugo
authors.affiliation: Tumor Genomics Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Gasparini
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Casalini
authors.affiliation: Laboratory of Immunology and Biology of Metastases, Department of Experimental, Diagnostic and Specialty Medicine, University of Bologna, Bologna, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Palladini
authors.affiliation: CESI Aging Research Center, Department of Medicine and Aging Sciences, G D'Annunzio University, Via Colle dell'Ara, Chieti Scalo, Chieti, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Iezzi
authors.affiliation: CESI Aging Research Center, Department of Medicine and Aging Sciences, G D'Annunzio University, Via Colle dell'Ara, Chieti Scalo, Chieti, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Lamolinara
authors.affiliation: Laboratory of Immunology and Biology of Metastases, Department of Experimental, Diagnostic and Specialty Medicine, University of Bologna, Bologna, Italy.
authors.forename: P L
authors.initials: PL
authors.lastname: Lollini
authors.affiliation: Laboratory of Immunology and Biology of Metastases, Department of Experimental, Diagnostic and Specialty Medicine, University of Bologna, Bologna, Italy.
authors.forename: P
authors.initials: P
authors.lastname: Nanni
authors.affiliation: Molecular Immunology Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Chiodoni
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Tagliabue
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology and Molecular Medicine, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.
authors.forename: S M
authors.initials: SM
authors.lastname: Pupa
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D015415:Biomarkers; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D016000:Cluster Analysis; D018450:Disease Progression; D058750:Epithelial-Mesenchymal Transition / Q000235:genetics; D005260:Female; D015870:Gene Expression; D020869:Gene Expression Profiling; D006801:Humans; D051379:Mice; D009154:Mutation; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics* / Q000378:metabolism; D051880:Receptors, Notch / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D015415:Biomarkers; D018719:Erb-b2 Receptor Tyrosine Kinases; D051880:Receptors, Notch