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Wang D, Pierce A, Veo B, Fosmire S, Danis E, Donson A, Venkataraman S, Vibhakar R. A Regulatory Loop of FBXW7-MYC-PLK1 Controls Tumorigenesis of MYC-Driven Medulloblastoma. Cancers (Basel) 2021; 13:cancers13030387. [PMID: 33494392 PMCID: PMC7865656 DOI: 10.3390/cancers13030387] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Revised: 01/09/2021] [Accepted: 01/15/2021] [Indexed: 12/14/2022] Open
Abstract
Simple Summary Group 3 medulloblastoma (MB) is often accompanied by MYC amplification and has a poor prognosis. FBXW7, a critical tumor suppressor in many types of cancer, regulates the proteasome-mediated degradation of oncoproteins including MYC. However, the role of FBXW7 in the tumorigenesis of group 3 MB has not been well studied. In this study, we show that FBXW7 is downregulated in group 3 MB patient samples, and FBXW7 stabilization is crucial for inhibiting c-MYC. We identified a FBXW7-MYC-PLK1 regulatory loop in MYC-driven MB, which provides a mechanism of using protein kinase inhibitors for translation in the future. Abstract Polo-like kinase 1 (PLK1) is highly expressed in group 3 medulloblastoma (MB), and it has been preclinically validated as a cancer therapeutic target in medulloblastoma. Here, we demonstrate that PLK1 inhibition with PCM-075 or BI6727 significantly reduces the growth of MB cells and causes a decrease of c-MYC mRNA and protein levels. We show that MYC activates PLK1 transcription, while the inhibition of PLK1 suppresses MB tumor development and causes a decrease in c-MYC protein level by suppressing FBXW7 auto poly-ubiquitination. FBXW7 physically interacts with PLK1 and c-MYC, facilitating their protein degradation by promoting ubiquitination. These results demonstrate a PLK1-FBXW7-MYC regulatory loop in MYC-driven medulloblastoma. Moreover, FBXW7 is significantly downregulated in group 3 patient samples. The overexpression of FBXW7 induced apoptosis and suppressed proliferation in vitro and in vivo, while constitutive phosphorylation mutation attenuated its tumor suppressor function. Altogether, these findings demonstrated that PLK1 inhibition stabilizes FBXW7 in MYC-driven MB, thus revealing an important function of FBXW7 in suppressing medulloblastoma progression.
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Affiliation(s)
- Dong Wang
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
| | - Angela Pierce
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
| | - Bethany Veo
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
| | - Susan Fosmire
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
| | - Etienne Danis
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
| | - Andrew Donson
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
| | - Sujatha Venkataraman
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
- Morgan Adams Foundation Pediatric Brain Tumor Research Program, Children’s Hospital Colorado, Aurora, CO 80045, USA
| | - Rajeev Vibhakar
- Department of Pediatrics, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045, USA; (D.W.); (A.P.); (B.V.); (S.F.); (E.D.); (A.D.); (S.V.)
- Morgan Adams Foundation Pediatric Brain Tumor Research Program, Children’s Hospital Colorado, Aurora, CO 80045, USA
- Department of Neurosurgery, University of Colorado Denver, Aurora, CO 80045, USA
- Correspondence:
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cMYC expression in infiltrating gliomas: associations with IDH1 mutations, clinicopathologic features and outcome. J Neurooncol 2013; 115:249-59. [PMID: 23934175 DOI: 10.1007/s11060-013-1221-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Accepted: 08/04/2013] [Indexed: 12/28/2022]
Abstract
Gliomas are among the most frequent adult primary brain tumors. Mutations in IDH1, a metabolic enzyme, strongly correlate with secondary glioblastomas and increased survival. cMYC is an oncogene also implicated in aberrant metabolism, but its prognostic impact remains unclear. Recent genotyping studies also showed SNP variants near the cMYC gene locus, associate with an increased risk for development of IDH1/2 mutant gliomas suggesting a possible interaction between cMYC and IDH1. We evaluated nuclear cMYC protein levels and IDH1 (R132H) by immunohistochemistry in patients with oligodendroglioma/oligoastrocytomas (n = 20), astrocytomas (grade II) (n = 19), anaplastic astrocytomas (n = 21) or glioblastomas (n = 111). Of 158 tumors with sufficient tissue, 110 (70 %) showed nuclear cMYC immunopositivity--most frequent (95 %, χ(2) p = 0.0248) and intense (mean 1.33, ANOVA p = 0.0179) in anaplastic astrocytomas versus glioblastomas (63 %) or low grade gliomas (74 %). cMYC expression associated with younger age as well as p53 immunopositivity (OR = 3.6, p = 0.0332) and mutant IDH1 (R132H) (OR = 7.4, p = 0.06) among malignant gliomas in our cohort. Independent analysis of the publically available TCGA glioblastoma dataset confirmed our strong association between cMYC and mutant IDH1 expression. Both IDH1 (R132H) and cMYC protein expression were associated with improved overall survival by univariate analysis. However, cMYC co-expression associated with shortened time to malignant transformation and overall survival among IDH1 (R132H) mutants in both univariate and multivariate analyses. In summary, our findings suggest that cMYC may be associated with a unique clinicopathologic and biologic group of infiltrating gliomas and help mediate the malignant transformation of IDH1 mutant gliomas.
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Abstract
Medulloblastoma, the most common malignant paediatric brain tumour, is currently diagnosed and stratified using a combination of clinical and demographic variables. Recent transcriptomic approaches have demonstrated that the histological entity known as medulloblastoma is comprised of multiple clinically and molecularly distinct subgroups. The current consensus is that four defined subgroups of medulloblastoma exist: WNT, SHH, Group 3, and Group 4. Each subgroup probably contains at least one additional level of hierarchy, with some evidence for multiple subtypes within each subgroup. The demographic and clinical differences between the subgroups present immediate and pressing questions to be addressed in the next round of clinical trials for patients with medulloblastoma. Many of the genetically defined targets for rational medulloblastoma therapies are unique to a given subgroup, suggesting the need for subgroup-specific trials of novel therapies. The development of practical, robust and widely accepted subgroup biomarkers that are amenable to the conditions of a prospective clinical trial is, therefore, an urgent need for the paediatric neuro-oncology community. In this Review, we discuss the clinical implications of molecular subgrouping in medulloblastoma, highlighting how these subgroups are transitioning from a research topic in the laboratory to a clinically relevant topic with important implications for patient care.
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