title: Protein kinase C delta negatively modulates canonical Wnt pathway and cell proliferation in colon tumor cell lines.
abstract: The tumor suppressor Adenomatous Polyposis coli (APC) gene is mutated or lost in most colon cancers. Alterations in Protein kinase C (PKC) isozyme expression and aberrant regulation also comprise early events in intestinal carcinomas. Here we show that PKCδ expression levels are decreased in colon tumor cell lines with respect to non-malignant cells. Reciprocal co-immunoprecipitation and immunofluorescence studies revealed that PKCδ interacts specifically with both full-length (from non-malignant cells) and truncated APC protein (from cancerous cells) at the cytoplasm and at the cell nucleus. Selective inhibition of PKCδ in cancer SW480 cells, which do not possess a functional β-catenin destruction complex, did not affect β-catenin-mediated transcriptional activity. However, in human colon carcinoma RKO cells, which have a normal β-catenin destruction complex, negatively affected β-catenin-mediated transcriptional activity, cell proliferation, and the expression of Wnt target genes C-MYC and CYCLIN D1. These negative effects were confirmed by siRNA-mediated knockdown of PKCδ and by the expression of a dominant negative form of PKCδ in RKO cells. Remarkably, the PKCδ stably depleted cells exhibited augmented tumorigenic activity in grafted mice. We show that PKCδ functions in a mechanism that involves regulation of β-catenin degradation, because PKCδ inhibition induces β-catenin stabilization at the cytoplasm and its nuclear presence at the C-MYC enhancer even without Wnt3a stimulation. In addition, expression of a dominant form of PKCδ diminished APC phosphorylation in intact cells, suggesting that PKCδ may modulate canonical Wnt activation negatively through APC phosphorylation.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico City, Mexico.
authors.forename: José G
authors.initials: JG
authors.lastname: Hernández-Maqueda
authors.forename: Luis Bernardo
authors.initials: LB
authors.lastname: Luna-Ulloa
authors.forename: Paula
authors.initials: P
authors.lastname: Santoyo-Ramos
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Castañeda-Patlán
authors.forename: Martha
authors.initials: M
authors.lastname: Robles-Flores
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D049109:Cell Proliferation; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D010766:Phosphorylation / Q000235:genetics; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D055550:Protein Stability; D059748:Proteolysis; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D060449:Wnt Signaling Pathway; D060509:Wnt3A Protein / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism
chemical_list: C555337:APC protein, human; D025601:Adenomatous Polyposis Coli Protein; C530104:CCND1 protein, human; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; C555510:WNT3A protein, human; D060509:Wnt3A Protein; D051176:beta Catenin; D019938:Cyclin D1; C497258:PRKCD protein, human; D051745:Protein Kinase C-delta