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Ahmed_Shireman Brain 2021 ChIPSeq

ABSTRACT: Glioblastoma is a primary brain cancer with a near 100% recurrence rate. Upon recurrence, the tumor is resistant to all conventional therapies, and because of this, 5-year survival is dismal. One of the major drivers of this high recurrence rate is the ability of GBM cells to adapt to complex changes within the tumor microenvironment. To elucidate the molecular mechanisms of this adaptation, specifically during chemotherapy, we employed ChIP-Sequencing and gene expression analysis. We identified a molecular circuit in which the expression of ciliary protein ALR13B is epigenetically regulated to promote adaptation to chemotherapy. Immuno-precipitation combined with Liquid Chromatography-Mass Spectrometry binding partner analysis revealed that that ARL13B interacts with the purine biosynthetic enzyme IMPDH2. Further, radioisotope tracing revealed that this interaction function as a negative regulator for purine salvaging. Inhibition of ARL13B-IMPDH2 interaction enhances temozolomide (TMZ)-induced DNA damage by forcing GBM cells to rely on the purine salvage pathway. Targeting the ARLI3B-IMPDH2 circuit can be achieved by using an FDA-approved drug, Mycophenolate Mofetil, that can block the IMPDH2 activity and enhance the therapeutic efficacy of TMZ. Our results suggest and support clinical evaluation of MMF in combination with TMZ treatment in glioma patients.

ORGANISM(S): Homo sapiens

PROVIDER: GSE164352 | GEO | 2021/01/07

REPOSITORIES: GEO

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Project description:Glioblastoma (GBM) carries a dismal prognosis largely due to acquired resistance to the standard treatment, which incorporates the chemotherapy temozolomide (TMZ). Inhibiting the proteasomal pathway is an emerging strategy, where combination treatments are under clinical investigation. We hypothesized that pre-treatment of GBM with bortezomib (BTZ) might sensitize glioblastoma to TMZ by abolishing autophagy survival signals to augment DNA damage and apoptosis. P3 patient-derived GBM cells as well as the tumor cell lines U87, HF66, A172 and T98G were investigated for clonogenic survival after single or combined treatment with TMZ and BTZ in vitro. Change in autophagic flux was examined after experimental treatments in conjunction with inhibitors of autophagy or downregulation of autophagy-related genes -5 and -7 (ATG5 and ATG7, respectively). Autophagic flux was increased in TMZ-resistant P3 and T98G cells as indicated by diminished levels of the autophagy markers LC3A/B-II and increased STX17, higher protein degradation and no formation of p62 bodies nor induction of apoptosis. In contrast, BTZ treatment attenuated ULK1 mRNA, total and phosphorylated protein, and accumulated LC3A/B-II, p62 and autophagosomes analogously to Baf1 and chloroquine autophagy inhibitors. These autophagosomes did not fuse with lysosomes, indicated by attenuated STX17 expression and reduced degradation of long-lived proteins, which culminated in enhanced caspase-3/8 dependent apoptosis. BTZ synergistically enhanced TMZ efficacy, attenuated tumor cell proliferation, triggered ATM/Chk2 DNA damage signalling to further augment caspase-3/8 mediated apoptosis in the TMZ resistant P3 and T98G GBM cells. Genetic or chemical inhibition of autophagy (with CRISPR-CAs9 ATG5, ATG7 shRNA, MRT68921 or VPS34-IN1) abrogated BTZ efficacy and rescued BTZ+ TMZ treated GBM cells from death. We conclude that Bortezomib ameliorates temozolomide resistance through ATG5/7-dependent abrogated autophagic flux and may be amenable in combination treatment regimens for TMZ refractory GBM patients.

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Ahmed_Shireman Brain 2021 ChIPSeq

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