title: The embryonic type of SPP1 transcriptional regulation is re-activated in glioblastoma.
abstract: Osteopontin (SPP1, a secreted phosphoprotein 1) is primarily involved in immune responses, tissue remodelling and biomineralization. However, it is also overexpressed in many cancers and regulates tumour progression by increasing migration, invasion and cancer stem cell self-renewal. Mechanisms of SPP1 overexpression in gliomas are poorly understood. We demonstrate overexpression of two out of five SPP1 isoforms in glioblastoma (GBM) and differential isoform expression in glioma cell lines. Up-regulated SPP1 expression is associated with binding of the GLI1 transcription factor to the promoter and OCT4 (octamer-binding transcription factor 4) to the first SPP1 intron of the SPP1 gene in human glioma cells but not in non-transformed astrocytes. GLI1 knockdown reduced SPP1 mRNA and protein levels in glioma cells. GLI1 and OCT4 are known regulators of stem cell pluripotency. GBMs contain rare cells that express stem cell markers and display ability to self-renew. We reveal that SPP1 is overexpressed in glioma initiating cells defined by high rhodamine 123 efflux, sphere forming capacity and stemness marker expression. Forced differentiation of human glioma spheres reduced SPP1 expression. Knockdown of SPP1, GLI1 or CD44 with siRNAs diminished sphere formation. C6 glioma cells stably depleted of Spp1 displayed reduced sphere forming capacity and downregulated stemness marker expression. Overexpression of the wild type Spp1, but not Spp1 lacking a Cd44 binding domain, rescued cell ability to form spheres. Our findings show re-activation of the embryonic-type transcriptional regulation of SPP1 in malignant gliomas and point to the importance of SPP1-CD44 interactions in self-renewal and pluripotency glioma initiating cells.
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Kijewska
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Kocyk
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Kloss
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Karolina
authors.initials: K
authors.lastname: Stepniak
authors.affiliation: Laboratory of Molecular Bases of Aging, The Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Korwek
authors.affiliation: Jean-Pierre Aubert Research Center, INSERM U837, Lille, France.
authors.forename: Renata
authors.initials: R
authors.lastname: Polakowska
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Michal
authors.initials: M
authors.lastname: Dabrowski
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Gieryng
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Bartosz
authors.initials: B
authors.lastname: Wojtas
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Iwona A
authors.initials: IA
authors.lastname: Ciechomska
authors.affiliation: Laboratory of Molecular Neurobiology, The Nencki Institute of Experimental Biology of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: Bozena
authors.initials: B
authors.lastname: Kaminska
mesh_terms: D000818:Animals; D001932:Brain Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation / Q000235:genetics; D045744:Cell Line, Tumor; D000066673:Cell Self Renewal; D015972:Gene Expression Regulation, Neoplastic; D005909:Glioblastoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006367:HeLa Cells; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D053495:Osteopontin / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D034622:RNA Interference; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018874:Spheroids, Cellular / Q000378:metabolism; D015533:Transcriptional Activation; D000071676:Zinc Finger Protein GLI1 / Q000235:genetics / Q000378:metabolism
chemical_list: C497483:CD44 protein, human; C400551:GLI1 protein, human; D018960:Hyaluronan Receptors; D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; C506895:SPP1 protein, human; D000071676:Zinc Finger Protein GLI1; D053495:Osteopontin
keywords: glioma initiating cells; osteopontin; self-renewal; stemness factors; transcription factors