title: Loss of the tumor suppressor spinophilin (PPP1R9B) increases the cancer stem cell population in breast tumors.
abstract: The spinophilin (Spn, PPP1R9B) gene is located at 17q21.33, a region frequently associated with microsatellite instability and loss of heterozygosity, especially in breast tumors. Spn is a regulatory subunit of phosphatase1a (PP1), which targets the catalytic subunit to distinct subcellular locations. Spn downregulation reduces PPP1CA activity against the retinoblastoma protein, pRb, thereby maintaining higher levels of phosphorylated pRb. This effect contributes to an increase in the tumorigenic properties of cells in certain contexts. Here, we explored the mechanism of how Spn downregulation contributes to the malignant phenotype and poor prognosis in breast tumors and found an increase in the stemness phenotype. Analysis of human breast tumors showed that Spn mRNA and protein are reduced or lost in 15% of carcinomas, correlating with a worse prognosis, a more aggressive tumor phenotype and triple-negative tumors, whereas luminal tumors showed high Spn levels. Downregulation of Spn by shRNA increased the stemness properties along with the expression of stem-related genes (Sox2, KLF4, Nanog and OCT4), whereas ectopic overexpression of Spn cDNA reduced these properties. Breast tumor stem cells appeared to have low levels of Spn mRNA, and Spn loss correlated with increased stem-like cell appearance in breast tumors as indicated by an increase in CD44+/CD24- cells. A reduction of the levels of PPP1CA mimicked the cancer stem-like cell phenotype of Spn downregulation, suggesting that the mechanism of Spn involves PP1a. These increased cancer stem cell-like properties with reduced Spn might account for the malignant phenotype observed in Spn-loss tumors and may contribute to a worse patient prognosis.
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Ferrer
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.
authors.forename: E M
authors.initials: EM
authors.lastname: Verdugo-Sivianes
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Castilla
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Melendez
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.|Department of Preventive Medicine and Public Health, Seville University, Seville, Spain.
authors.forename: J J
authors.initials: JJ
authors.lastname: Marin
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Muñoz-Galvan
authors.affiliation: Department of Radiation Oncology, University Hospital Virgen Del Rocío, Seville, Spain.
authors.forename: J L
authors.initials: JL
authors.lastname: Lopez-Guerra
authors.affiliation: Department of Pathology, University Hospital Virgen Del Rocío, Seville, Spain.
authors.forename: B
authors.initials: B
authors.lastname: Vieites
authors.affiliation: Department of Radiation Oncology, University Hospital Virgen Del Rocío, Seville, Spain.
authors.forename: M J
authors.initials: MJ
authors.lastname: Ortiz-Gordillo
authors.affiliation: Unidad Funcional de Patología Mamaria, University Hospital Virgen Del Rocío, Seville, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: De León
authors.affiliation: Methodology Unit- Fundación Pública Andaluza para la Gestión de la Investigación en Salud de Sevilla, Virgen del Rocío University Hospital, Seville, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Praena-Fernandez
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Perez
authors.affiliation: Department of Pathology, University Hospital Ramon y Cajal, Madrid, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Palacios
authors.affiliation: Instituto de Biomedicina de Sevilla (IBIS/HUVR/CSIC/Universidad de Sevilla), Seville, Spain.|Consejo Superior de Investigaciones Cientificas, Sevilla, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Carnero
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D015331:Cohort Studies; D005260:Female; D006801:Humans; D000090062:Kruppel-Like Factor 4; D008840:Microfilament Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000473:pathology*; D009419:Nerve Tissue Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D011379:Prognosis; D000099273:Neurabins
chemical_list: D000090062:Kruppel-Like Factor 4; D008840:Microfilament Proteins; D009419:Nerve Tissue Proteins; D000099273:Neurabins; C000715467:KLF4 protein, human