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Targeting PBK/TOPK decreases growth and survival of glioma initiating cells in vitro and attenuates tumor growth in vivo.

ABSTRACT: Glioblastomas are invasive therapy resistant brain tumors with extremely poor prognosis. The Glioma initiating cell (GIC) population contributes to therapeutic resistance and tumor recurrence. Targeting GIC-associated gene candidates could significantly impact GBM tumorigenicity. Here, we investigate a protein kinase, PBK/TOPK as a candidate for regulating growth, survival and in vivo tumorigenicity of GICs.PBK is highly upregulated in GICs and GBM tissues as shown by RNA and protein analyses. We knocked down PBK using shRNA vectors and inhibited the function of PBK protein with a pharmacological PBK inhibitor, HITOPK-032. We assessed viability, tumorsphere formation and apoptosis in three patient derived GIC cultures.Gene knockdown of PBK led to decreased viability and sphere formation and in one culture an increase in apoptosis. Treatment of cells with inhibitor HITOPK-032 (5 ?M and 10 ?M) almost completely abolished growth and elicited a large increase in apoptosis in all three cultures. HI-TOPK-032 treatment (5 mg/kg and 10 mg/kg bodyweight) in vivo resulted in diminished growth of experimentally induced subcutaneous GBM tumors in mice. We also carried out multi-culture assays of cell survival to investigate the relative effects on GICs compared with the normal neural stem cells (NSCs) and their differentiated counterparts. Normal NSCs seemed to withstand treatment slightly better than the GICs.Our study of identification and functional validation of PBK suggests that this candidate can be a promising molecular target for GBM treatment.

SUBMITTER: Joel M

PROVIDER: S-EPMC4470057 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Targeting PBK/TOPK decreases growth and survival of glioma initiating cells in vitro and attenuates tumor growth in vivo.

Joel Mrinal M Mughal Awais A AA Grieg Zanina Z Murrell Wayne W Palmero Sheryl S Mikkelsen Birthe B Fjerdingstad Hege B HB Sandberg Cecilie J CJ Behnan Jinan J Glover Joel C JC Langmoen Iver A IA Stangeland Biljana B

Molecular cancer 20150617

<h4>Background</h4>Glioblastomas are invasive therapy resistant brain tumors with extremely poor prognosis. The Glioma initiating cell (GIC) population contributes to therapeutic resistance and tumor recurrence. Targeting GIC-associated gene candidates could significantly impact GBM tumorigenicity. Here, we investigate a protein kinase, PBK/TOPK as a candidate for regulating growth, survival and in vivo tumorigenicity of GICs.<h4>Methods</h4>PBK is highly upregulated in GICs and GBM tissues as s ...[more]

PMID: 26081429

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Project description:Glioblastomas are deadly cancers that display a functional cellular hierarchy maintained by self-renewing glioblastoma stem cells (GSCs). GSCs are regulated by molecular pathways distinct from the bulk tumor that may be useful therapeutic targets. We determined that A20 (TNFAIP3), a regulator of cell survival and the NF-kappaB pathway, is overexpressed in GSCs relative to non-stem glioblastoma cells at both the mRNA and protein levels. To determine the functional significance of A20 in GSCs, we targeted A20 expression with lentiviral-mediated delivery of short hairpin RNA (shRNA). Inhibiting A20 expression decreased GSC growth and survival through mechanisms associated with decreased cell-cycle progression and decreased phosphorylation of p65/RelA. Elevated levels of A20 in GSCs contributed to apoptotic resistance: GSCs were less susceptible to TNFalpha-induced cell death than matched non-stem glioma cells, but A20 knockdown sensitized GSCs to TNFalpha-mediated apoptosis. The decreased survival of GSCs upon A20 knockdown contributed to the reduced ability of these cells to self-renew in primary and secondary neurosphere formation assays. The tumorigenic potential of GSCs was decreased with A20 targeting, resulting in increased survival of mice bearing human glioma xenografts. In silico analysis of a glioma patient genomic database indicates that A20 overexpression and amplification is inversely correlated with survival. Together these data indicate that A20 contributes to glioma maintenance through effects on the glioma stem cell subpopulation. Although inactivating mutations in A20 in lymphoma suggest A20 can act as a tumor suppressor, similar point mutations have not been identified through glioma genomic sequencing: in fact, our data suggest A20 may function as a tumor enhancer in glioma through promotion of GSC survival. A20 anticancer therapies should therefore be viewed with caution as effects will likely differ depending on the tumor type.

Project description:BackgroundCD44 is a molecular marker associated with cancer stem cell populations and treatment resistance in glioma. More effective therapies will result from approaches aimed at targeting glioma cells high in CD44.MethodsGlioma-initiating cell lines were derived from fresh surgical glioblastoma samples. Expression of tissue transglutaminase 2 (TGM2) was attenuated through lentivirus-mediated short hairpin RNA knockdown. MTT assay [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] was used to evaluate the growth inhibition induced by TGM2 inhibitor. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling was used to evaluate cell apoptosis following TGM2 inhibition. CD44(+) glioma stem cells were sorted by flow cytometry. A nude mice orthotopic xenograft model was used to evaluate the in vivo effect of TGM2 inhibitor.ResultsTGM2 was highly expressed in CD44-high glioblastoma tissues and tumor-derived glioma-initiating cell lines. TGM2 knockdown impaired cell proliferation and induced apoptosis in CD44-high glioma-initiating cell lines. Further studies indicated that expression of inhibitor of DNA binding 1 protein (ID1) is regulated by TGM2 and might be an important mediator for TGM2-regulated cell proliferation in CD44-high glioma-initiating cell lines. TGM2 inhibitor reduces ID1 expression, suppresses cell proliferation, and induces apoptosis in CD44-high glioma-initiating cell lines. Furthermore, TGM2 is highly expressed in CD44(+) glioma stem cells, while pharmacological inhibition of TGM2 activity preferentially eliminates CD44(+) glioma stem cells. Consistently, TGM2 inhibitor treatment reduced ID1 expression and induced apoptosis in our orthotopic mice xenograft model, which can be translated into prolonged median survival in tumor-bearing mice.ConclusionsTGM2 regulates ID1 expression in glioma-initiating cell lines high in CD44. Targeting TGM2 could be an effective strategy to treat gliomas with high CD44 expression.

Dataset Information

Targeting PBK/TOPK decreases growth and survival of glioma initiating cells in vitro and attenuates tumor growth in vivo.

Publications

Targeting PBK/TOPK decreases growth and survival of glioma initiating cells in vitro and attenuates tumor growth in vivo.

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