ABSTRACT
BACKGROUND: Glial brain tumors cause considerable mortality and morbidity in children and adults. Innovative targets for therapy are needed to improve survival and reduce long-term sequelae. The aim of this study was to find a candidate tumor-promoting protein, abundantly expressed in tumor cells but not in normal brain tissues, as a potential target for therapy. METHODS: In silico proteomics and genomics, immunohistochemistry, and immunofluorescence microscopy validation were performed. RNA interference was used to ascertain the functional role of the overexpressed candidate target protein. RESULTS: In silico proteomics and genomics revealed pre-B-cell leukemia homeobox (PBX) interacting protein 1 (PBXIP1) overexpression in adult and childhood high-grade glioma and ependymoma compared with normal brain. PBXIP1 is a PBX-family interacting microtubule-binding protein with a putative role in migration and proliferation of cancer cells. Immunohistochemical studies in glial tumors validated PBXIP1 expression in astrocytoma and ependymoma but not in oligodendroglioma. RNAi-mediated PBXIP1-knockdown in glioblastoma cell lines strongly reduced proliferation and migration and induced morphological changes, indicating that PBXIP1 knockdown decreases glioma cell viability and motility through rearrangements of the actin cytoskeleton. Furthermore, expression of PBXIP1 was observed in radial glia and astrocytic progenitor cells in human fetal tissues, suggesting that PBXIP1 is an astroglial progenitor cell marker during human embryonic development. CONCLUSION: PBXIP1 is a novel protein overexpressed in astrocytoma and ependymoma, involved in tumor cell proliferation and migration, that warrants further exploration as a novel therapeutic target in these tumors.
Subject(s)
Astrocytoma/pathology , Brain Neoplasms/pathology , Neoplasm Invasiveness/pathology , Transcription Factors/biosynthesis , Adult , Astrocytoma/metabolism , Blotting, Western , Brain Neoplasms/metabolism , Cell Proliferation , Child , Co-Repressor Proteins , Female , Flow Cytometry , Gene Expression Profiling , Humans , Immunohistochemistry , Male , Microscopy, Fluorescence , Oligonucleotide Array Sequence Analysis , Proteomics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Tissue Array Analysis , Up-RegulationABSTRACT
The Polycomb group (PcG) gene Bmi1 promotes cell proliferation and stem cell self-renewal by repressing the Ink4a/Arf locus. We used a genetic approach to investigate whether Ink4a or Arf is more critical for relaying Bmi1 function in lymphoid cells, neural progenitors, and neural stem cells. We show that Arf is a general target of Bmi1, however particularly in neural stem cells, derepression of Ink4a contributes to Bmi1(-/-) phenotypes. Additionally, we demonstrate haploinsufficient effects for the Ink4a/Arf locus downstream of Bmi1 in vivo. This suggests differential, cell type-specific roles for Ink4a versus Arf in PcG-mediated (stem) cell cycle control.