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C-Myc uses Cul4b to preserve genome stability and promote CD8+ T cell-mediated antiviral immune responses

ABSTRACT: During infection, virus-specific CD8+ T cells undergo rapid bursts of proliferation and differentiate into effector cells that kill virus infected cells and reduce viral load. This rapid clonal expansion can put T cells at significant risk for replication-induced DNA damage. We found that c-Myc utilizes the E3 ubiquitin ligase, Cul4b, to inextricably link CD8+ T cell expansion to DNA damage response pathways. Following activation, c-Myc increased levels of Cul4b and other members of the CRL4 complex. Despite having abundant c-Myc expression, Cul4b-deficient CD8+ T cells were unable to expand and clear virus. Cul4b-deficient CD8+ T cells accrued DNA damage and succumbed to proliferative catastrophe early after antigen encounter. Mechanistically, Cul4b ablation induced a protracted accumulation of p21 and Cyclin E2 resulting in replication stress. Our data show that, to support cell proliferation, c-Myc must employ Cul4b to maintain genome stability, thereby directly coupling these two interdependent pathways. These data clarify how CD8+ T cells use c-Myc and Cul4b to sustain their potential for extraordinary population expansion, longevity and antiviral responses.

INSTRUMENT(S): Orbitrap Exploris 480

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): T Cell

SUBMITTER: Hossein Fazelinia

LAB HEAD: Paula M. Olive, PhD

PROVIDER: PXD041220 | Pride | 2023-08-29

REPOSITORIES: Pride

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Project description:Cullin 4B (CUL4B), a scaffold protein that assembles CRL4B ubiquitin ligase complexes, has been reported to be overexpressed in several types of solid tumors and contributes to epigenetic silencing of tumor suppressor. However, its clinical significance and the molecular mechanisms underlying its regulation in gastric cancer (GC) remain largely unknown. Here, we showed that CUL4B was elevated in GC tissues and its overexpression was positively correlated with poor prognosis and lymph node metastasis. CUL4B knockdown in GC cells decreased proliferation, mesenchymal transition and invasion in vitro, as well as tumor growth and metastasis in nude mice, and CUL4B overexpression induced the opposite results. Further studies showed that miR-101 could inhibit CUL4B expression by directly targeting its 3’-UTR and they were inversely correlated in clinical GC specimens. Notably, a positive relationship between CUL4B and HER2 was found in GC clinical specimens, GC cells and GC xenograft tumors. Through bioinformatics analysis of miRNA-seq data and target prediction, we nominated miR-125a as a direct target of CUL4B. ChIP assays demonstrated that CUL4B directly repressed miR-125a expression by physically binding to its promoter. In addition, we confirmed miR-125a is the target of HER2. Consequently, we demonstrated that CUL4B can up-regulate HER2 expression through repressing miR-125a. Most importantly, silencing of HER2 by Herceptin or siRNA partially reversed CUL4B-induced epithelial-to-mesenchymal transition (EMT), cell invasion and metastasis in vitro and in vivo. These findings define a CUL4B-miR-125a-HER2 regulatory mechanism shed light on CUL4B oncogenic mechanisms and reveals promising therapeutic targets for progressive GC. CUL4B proteins are frequently upregulated in human cancer, yet little is known about the underlying molecular mechanisms of CUL4B induced gastric cancer(GC) carcigenesis.Here, we uncover the critical role of CUL4B in gastric cancer growth and metastasis through the regulation of HER2 expression.CUL4B contributes to GC invasion and metastasis by transcriptional repression of HER2 targeting miR-125a, which provide a new insight into how CUL4B regulates GC progression and metastasis.

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C-Myc uses Cul4b to preserve genome stability and promote CD8+ T cell-mediated antiviral immune responses

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