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Stabilization of c-Myc protein by CAMKIIγ promotes T-cell lymphoma

ABSTRACT: Although high c-Myc protein expression is observed alongside c-Myc gene amplification in some cancers, in most cases protein overexpression occurs while the amplified gene is largely absent, e.g. T-cell lymphoma (TCL). Here, Ca2+/calmodulin-dependent protein kinase II γ (CAMKIIγ) was shown to stabilize c-Myc protein by directly phosphorylating at serine 62 (S62), which represents a hitherto unknown mechanism of c-Myc protein overexpression. Further, CAMKIIγ was shown to be essential for tumor maintenance. Inhibiting CAMKIIγ with a potent CAMKIIγ-specific inhibitor destabilized c-Myc and reduced tumor burden dramatically. Importantly, high CAMKIIγ in clinical patient specimens positively correlated with increased c-Myc / pS62-c-Myc expression. Together, the CAMKIIγ:c-Myc axis critically influences the development and maintenance of TCL, and represent a novel therapeutic target for TCL.

ORGANISM(S): Mus musculus

PROVIDER: GSE99364 | GEO | 2017/05/27

SECONDARY ACCESSION(S): PRJNA388202

REPOSITORIES: GEO

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Project description:We examined the biological effects of a potent second-generation proteasome inhibitor, ixazomib, in T-cell lymphoma and Hodgkin lymphoma cell lines and human xenograft models. Ixazomib resulted in time- and dose-dependent cytotoxicity and apoptosis in all cell lines (IC50’s <75nM). In vivo studies via SCID tumor xenografts showed significant inhibition of tumor growth (P<0.001) with significantly improved survival (P<0.001) in Jurkat and L540 models with ixazomib-treated mice versus controls. Through global transcriptome and network analyses, ixazomib-treated Jurkat and L540 cells showed significant overlap in biological functions involved in regulation of cell cycle, chromatin modification, and DNA repair processes with a lack of conservation observed in a relatively ixazomib-resistant cell line, L428. Moreover, the predicted activation and inhibition status of tumor suppressors and oncogenes strongly favored ixazomib inhibition of tumor progression. Most notably, ixazomib down-regulated protein levels of MYC and its target genes. Additionally, chromatin immunoprecipitation showed that histone H3 acetylation affected MYC levels and cell death response to ixazomib. Furthermore, inhibition of MYC with JQ1 resulted in synergistic cell death in L428, which was confirmed utilizing MYC knockout. Collectively, ixazomib down-regulated MYC and downstream substrates in TCL and HL, while resistance appeared mediated through MYC- and CHK1-dependent mechanisms. Jurkat (TCL)and L540 cells were treated with ixazomib for 24 hours, RNA was isolated using RNeasy Minikit (Qiagen), following instructions recommended supplied by the manufacturer. Purity and the yield of isolated RNA was determined using Bioanalyzer. These experiments were performed in biological triplicates. Microarray experiment with Jurkat and L540 was performed Affy Human Gene Chip 2.0, at UMASS Medical School Genomic Core facility. Data for Jurkat and L540 cell lines were background adjusted and quantile normalized using RMAExpress. Statistically relevant genes were determined by applying LIMMA with a FDR < 0.05 that resulted in 764 significant genes for the Jurkat experimental group and 5819 significant genes for the L540 experimental group.

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Stabilization of c-Myc protein by CAMKIIγ promotes T-cell lymphoma

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