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

Author(s)

Iglesia, Rebeca Piatniczka ; Prado, Mariana Brandao ; Cruz, Lilian ; Martins, Vilma Regina ; Santos, Tiago Goss ; Lopes, Marilene Hohmuth

• Document type: Journal article
• Source: STEM CELL RESEARCH & THERAPY; v. 8, APR 17 2017.
• Web of Science Citations: 5

Abstract

Background: Glioblastoma (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. Methods: GSCs 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. Results: We 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. Conclusions: In 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. (AU)

• FAPESP's process: 13/19860-0 - Study of PrPc and STI1 interaction in human glioblastoma stem cells in vivo
• Grantee: Rebeca Piatniczka Iglesia
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• FAPESP's process: 15/04122-9 - Study of the MAPK/ERK pathway in the proliferation of glioblastoma stem cells induced by the PrPc-STI1 complex
• Grantee: Mariana Brandão Prado
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 11/13906-2 - Contribution of the co-chaperone STI1 in mouse development: embryonic stem cell as approach
• Grantee: Marilene Hohmuth Lopes
• Support Opportunities: Research Grants - Young Investigators Grants
• FAPESP's process: 09/14027-2 - Mechanisms associated with the function of prion protein and its ligand STI1/Hop: therapeutic approaches
• Grantee: Vilma Regina Martins
• Support Opportunities: Research Projects - Thematic Grants