Proteins of the Wnt signaling pathway as targets for the regulation of CD133+ cancer stem cells in glioblastoma

Glioblastoma multiforme (GBM) is one of the most aggressive types of brain tumor and is highly resistant to therapy. The median survival time for patients with GBM is 15 months. GBM resistance to treatment is associated with cancer stem cells (CSCs). CD133 membrane glycoprotein is the best-known marker of GBM CSCs. The Wnt signaling pathway plays an important role in the proliferation of all stem cells. To the best of our knowledge, the present study was the first to examine the expression levels of proteins associated with the Wnt signaling pathway in CD133(+) CSCs of human GBM. Furthermore, potential targets that may regulate CD133(+) CSCs in human GBM were investigated. The human GBM U-87MG cell line was cultured in neurobasal medium supplemented with B27, fibroblast growth factor, epidermal growth factor and no serum. Immunohistochemical characteristics of glioma spheres were investigated based on the expression of key markers of CSCs. CD133(+) cells were extracted from glioma spheres by cell sorting and then lysed. High-performance liquid chromatography-mass spectrometry was used for proteome analysis. Lysates of CD133(-) cells in GBM were used for comparison. The present study was the first to describe the conceptual proteome differences between GBM and CD133(+) CSCs of the common pool. Major differences were identified in the glycolysis/gluconeogenesis, focal adhesion, tight junction and Wnt signaling pathways. This study aimed to analyze the crucial role that proteins of the Wnt signaling pathway play in stem cell proliferation. The identified proteins were analyzed for their association with the Wnt signaling pathway using the international open databases PubMed, Protein Analysis Through Evolutionary Relationships, Gene Ontology, Kyoto Encyclopedia of Genes and Genomes and Search Tool for the Retrieval of Interacting Genes/Proteins. An increased expression of 12 proteins associated with the Wnt signaling pathway were identified in GBM CD133(+) CSCs, which included catenin beta-1, disheveled associated activator of morphogenesis 1, RAC family small GTPase 2 and RAS homolog gene family member A, a number of which are also associated with adherens junctions. The Wnt signaling pathway is not upregulated in CSCs; however, the high expression levels of adenomatous polyposis coli, beta-catenin, C-terminal binding protein (CtBP) and RuvB-like AAA ATPase 1 (RUVBL1 or Pontin52) proteins suggest the possibility of alternative activation of specific genes in the nuclei of these cells. Calcyclin-binding protein, casein kinase II alpha, casein kinase II beta, CtBP1, CtBP2, CUL1 and RUVBL1 proteins may be used as targets for the pharmaceutical regulation of CSCs in complex GBM treatment.