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Identification of DHC2 associated nuclear proteins in DHC2 knockdown U87 cells

ABSTRACT: The acquisition of temozolomide resistance is a major clinical challenge for glioblastoma treatment. Chemoresistance in glioblastoma is largely attributed to repair of temozolomide-induced DNA lesions by MGMT. However, many MGMT-negative glioblastomas are still resistant to temozolomide, and the underlying molecular mechanisms remain unclear. We found that DHC2 was highly expressed in MGMT-negative recurrent glioblastoma specimens and its expression strongly correlated to poor progression-free survival in MGMT-negative glioblastoma patients. In vivo and in vitro, silencing DHC2 enhanced temozolomide-induced DNA damage and significantly improved the efficiency of temozolomide treatment in MGMT-negative glioblastoma cells. It is known DHC2 is related to intracellular cargo transportation. To identify the potential interacted “cargo” DHC2 transported and explore the underlying molecular mechanisms of DHC2-midiated DNA damage repair, we performed subcellular proteomic and bioinformatic analyses.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture, Glioblast (sensu Nematoda And Protostomia)

DISEASE(S): Brain Glioblastoma Multiforme

SUBMITTER: Yawei Liu

LAB HEAD: Yawei Liu

PROVIDER: PXD012032 | Pride | 2022-02-28

REPOSITORIES: Pride

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Project description:Transcriptional repressor Growth factor independence 1 (GFI1) is a key regulator of haematopoiesis. We previously established that the germline variant GFI1-36N promotes acute myeloid leukemia (AML) development, however the mechanism is not full elucidated. Here using multi-omics approach, we show GFI1-36N expression impedes DNA repair in leukemic cells. We demonstrate the presence of GFI1-36N is associated with increased frequency of chromosomal aberrations and mutational burden in murine and human AML cells. In particular, GFI1-36N modulates DNA repair pathways, O6-methylguanine-DNA-methyltransferase (MGMT) and homologous recombination repair (HR). Mechanistically, GFI1-36N exhibits impaired binding to Ndrg1 promoter element compared to GFI1-36S (wild type), causing decreased NDRG1 levels consequently leading to suppression of MGMT expression, imprinted at the transcriptome and proteome, thus leaving the AML cells vulnerable to DNA damaging agents. Targeting MGMT via temozolomide and HR via olaparib caused specifically extensive lethality in in vitro and ex vivo human and AML samples expressing GFI1-36N. Whereas the effects were insignificant on non-malignant GFI1-36S or GFI1-36N cells. Further, mice transplanted with GFI1-36N leukemic cells treated with combination of temozolomide and olaparib had a significantly longer AML-free survival than mice transplanted with GFI1-36S leukemic cells. In summary, we show that GFI1-36N disturbs DNA repair activity via NDRG1-MGMT axis and thus provides critical insights into novel therapeutic option for AML presented with GFI1-36N variant. Key Points Presence of GFI1-36N impedes Homologous DNA and MGMT DNA repair selectively in AML cells via the NDRG1-MGMT axis. Use of temozolomide and olaparib allows selectively targeting GFI1-36N leukemic cells. Introduction Gfi1 is a transcription factor which regulates the development of haematopoietic cells as well as neuronal and intestinal epithelial cells 1-5. We reported that a variant of GFI1, denominated GFI1-36N (characterized by an exchange of serine to asparagine at position 36), has a prevalence of 5-7% in a healthy control population but is found at an increased frequency of 10-15% among MDS and AML patients 6,7. The expression of germline variant GFI1-36N predisposes the carriers to develop de novo AML and MDS and correlates with a poor prognosis 6,7. Recently, we and other showed that malignant cells with GFI1-36N variant have increased H3K9-acetylation at target genes resulting in higher expression of genes required for cell survival and proliferation 8. GFI1 exerts its repressive role by recruiting histone-modifying enzymes (deacetylases HDAC1-3, demethylase LSD1, methyl transferase G9a) and regulates the accessibility of DNA to its target genes such as Hoxa9, Pbx1, Meis1, CSF1 and CSFR1 9-15. We also showed that GFI1 regulates apoptosis through its regulation of p53 in lymphoblastic leukemia 16 and we have demonstrated that GFI1 facilitates DNA repair 17. However, it is not known how these activities are affected in the GFI1-36N variant and whether the ability of GFI1 to regulate DNA repair pathways is maintained and how this might affect the development of myeloid malignancies. In this study, we leveraged multi-omics profiling to gain mechanistic insights into the molecular architecture that drives leukemia in the presence of GFI1-36N. We provide evidence that GFI1-36N interferes with DNA in leukemic myeloid cells, which leads to a higher frequency of genetic aberrations in MDS/AML cells. We also show that GFI1-36N myeloid leukemic cells are more sensitive to targeting MGMT and HR repair deficient cells, which opens a new selective therapeutic window to treat AML/MDS.

Project description:Angiogenesis inhibitors, such as sunitinib, represent a promising strategy to improve glioblastoma (GBM) tumor response. In this study, we used the O6-methylguanine methyltransferase (MGMT)-negative GBM cell line U87MG stably transfected with MGMT (U87/MGMT) to assess whether MGMT expression affects the response to sunitinib. We showed that the addition of sunitinib to standard therapy (temozolomide [TMZ] and radiation therapy [RT]) significantly improved the response of MGMT positive but not of MGMT-negative cells. Gene expression profiling revealed alterations in the angiogenic profile, as well as differential expression of several receptor tyrosine kinases targeted by sunitinib. MGMT-positive cells displayed higher levels of vascular endothelial growth factor receptor 1 (VEGFR-1) compared with U87/EV cells, whereas they displayed decreased levels of VEGFR-2. Depleting MGMT using O6-benzylguanine suggested that the expression of these receptors was directly related to the MGMT status. Also, we showed that MGMT expression was associated with a dramatic increase in the soluble VEGFR-1/VEGFA ratio, thereby suggesting a decrease in bioactive VEGFA and a shift towards an antiangiogenic profile. The reduced angiogenic potential of MGMT-positive cells is supported by: (i) the decreased ability of their secreted factors to induce endothelial tube formation in vitro and (ii) their low tumorigenicity in vivo compared with the MGMT-negative cells. Our study is the first to show a direct link between MGMT expression and decreased angiogenicity and tumorigenicity of GBM cells and suggests the combination of sunitinib and standard therapy as an alternative strategy for GBM patients with MGMT-positive tumors. RNA was isolated from parental U87 (U87_EV) and MGMT-transfected U87 (U87_MGMT) triplicate. Pairwise gene expression differences were compared between the two cell lines. Features selected had more than 2-fold up-or down-regulated (P values of >05, unpaired Studentâs t-test with Bonferroni multiple testing correction) were identified. Database for annotation, visualization, and integrated discovery23 was used to identify enriched gene ontology (GO) biological themes.24 The GO data mining was conducted at a term specificity level 3.25 The EASE score was set at 0.05 and the minimum number of genes in a category was 5.

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Identification of DHC2 associated nuclear proteins in DHC2 knockdown U87 cells

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