Engagement of cellular prion protein with the co-chaperone Hsp70/90 organizing protein regulates the proliferation of glioblastoma stem-like cells

Abstract

BackgroundGlioblastoma (GBM), a highly aggressive brain tumor, contains a subpopulation of glioblastoma stem-like cells (GSCs) that play roles in tumor maintenance, invasion, and therapeutic resistance. GSCs are therefore a promising target for GBM treatment. Our group identified the cellular prion protein (PrPC) and its partner, the co-chaperone Hsp70/90 organizing protein (HOP), as potential target candidates due to their role in GBM tumorigenesis and in neural stem cell maintenance.MethodsGSCs expressing different levels of PrPC were cultured as neurospheres with growth factors, and characterized with stem cells markers and adhesion molecules markers through immunofluorescence and flow cytometry. We than evaluated GSC self-renewal and proliferation by clonal density assays and BrdU incorporation, respectively, in front of recombinant HOP treatment, combined or not with a HOP peptide which mimics the PrPC binding site. Stable silencing of HOP was also performed in parental and/or PrPC-depleted cell populations, and proliferation in vitro and tumor growth in vivo were evaluated. Migration assays were performed on laminin-1 pre-coated glass.ResultsWe observed that, when GBM cells are cultured as neurospheres, they express specific stemness markers such as CD133, CD15, Oct4, and SOX2; PrPC is upregulated compared to monolayer culture and co-localizes with CD133. PrPC silencing downregulates the expression of molecules associated with cancer stem cells, upregulates markers of cell differentiation and affects GSC self-renewal, pointing to a pivotal role for PrPC in the maintenance of GSCs. Exogenous HOP treatment increases proliferation and self-renewal of GSCs in a PrPC-dependent manner while HOP knockdown disturbs the proliferation process. In vivo, PrPC and/or HOP knockdown potently inhibits the growth of subcutaneously implanted glioblastoma cells. In addition, disruption of the PrPC-HOP complex by a HOP peptide, which mimics the PrPC binding site, affects GSC self-renewal and proliferation indicating that the HOP-PrPC complex is required for GSC stemness. Furthermore, PrPC-depleted GSCs downregulate cell adhesion-related proteins and impair cell migration indicating a putative role for PrPC in the cell surface stability of cell adhesion molecules and GBM cell invasiveness, respectively.ConclusionsIn conclusion, our results show that the modulation of HOP-PrPC engagement or the decrease of PrPC and HOP expression may represent a potential therapeutic intervention in GBM, regulating glioblastoma stem-like cell self-renewal, proliferation, and migration.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-017-0518-1) contains supplementary material, which is available to authorized users.

Melatonin and 5‐fluorouracil co‐suppress colon cancer stem cells by regulating cellular prion protein‐Oct4 axis

“…Although PrP C is involved in tumor biology, its mechanistic association with colorectal cancer stem cells is largely unexplored. A few studies have previously shown that in glioblastoma, the expression of Oct4, Sox2, and PrP C was significantly increased in neurospheres (stem‐like condition), compared with monolayer (nonstem condition) . Although the level of Oct4 during differentiation by retinoic acid was negatively correlated with the expression of PrP C in mouse embryonic stem cells, the knockdown of PrP C did not show the corresponding correlation with Oct4 .…”

Molecular Chaperones in Cancer Stem Cells: Determinants of Stemness and Potential Targets for Antitumor Therapy

“…For instance, the co-chaperone p23 was shown to contribute to the acquisition by prostate cancer cells of a more aggressive (CSC-resembling) phenotype with higher cell motility and pronounced capacity for invasion and metastasis formation [90]. There was a report that the co-chaperone Hop (HSP70/HSP90 organizing protein) and its complexes with cellular prion protein maintain the stemness in gliomas by ensuring proliferation and self-renewal in glioma SCs [91]. Meanwhile, both p23 and Hop are obligatory components of the HSP90/HSP70 chaperone machine (see Figure 2 and [49][50][51]).…”

The cellular prion protein is a stress protein secreted by renal tubular cells and a urinary marker of kidney injury

“…Furthermore, our unpublished data indicate a strong correlation between PRNP gene expression and the UPR as well as XBP1-dependent transcription in kidney renal clear cell carcinoma. Incidentally, PrP C overexpression has been reported in several types of cancer 41 and a consensus view is that increased levels of PrP C endow cells with proliferative 42,43 migratory and invasive capacities [44][45][46] , which are also features supporting tissue remodeling in CKD 3,47 . ER stressed cells shape tissue remodeling since cells upon ER stress secrete numerous specific mediators that promote inflammation, such as Interleukins 6 and 8 and Chemokine (C-X-C) Ligand 3 (CXCL3); angiogenesis through Vascular Endothelial Growth Factor (VEGF) and basic Fibroblast Growth Factor (bFGF); tissue remodeling through the production of collagen 1A2 and the metalloprotease ADAMTS3; apoptosis through the production of Prostate Apoptosis Response 4 (Par-4); and proteostasis with the chaperon ERdj3, which is a critical regulator of tissue homeostasis 1 .…”