Induction of ectopic Myc target gene JAG2 augments hypoxic growth and tumorigenesis in a human B-cell model

Abstract

Ectopic Myc expression plays a key role in human tumorigenesis, and Myc dose-dependent tumorigenesis has been well established in transgenic mice, but the Myc target genes that are dependent on Myc levels have not been well characterized. In this regard, we used the human P493-6 B cells, which have a preneoplastic state dependent on the Epstein–Barr viral EBNA2 protein and a neoplastic state with ectopic inducible Myc, to identify putative ectopic Myc target genes. Among the ectopic targets, JAG2 that encodes a Notch receptor ligand Jagged2, was directly induced by Myc. Inhibition of Notch signaling through RNAi targeting JAG2 or the γ-secretase Notch inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-(S)-phenylglycine t-butyl ester (DAPT) preferentially inhibited the neoplastic state in vitro. Furthermore, P493-6 tumorigenesis was inhibited by DAPT in vivo. Ectopic expression of JAG2 did not enhance aerobic cell proliferation, but increased proliferation of hypoxic cells in vitro and significantly increased in vivo tumorigenesis. Furthermore, the expression of Jagged2 in P493-6 tumors often overlapped with regions of hypoxia. These observations suggest that Notch signaling downstream of Myc enables cells to adapt in the tumor hypoxic microenvironment.

IRE1α RNase–dependent lipid homeostasis promotes survival in Myc-transformed cancers

“…First, restimulation of previously c-Mycdepleted P493 cells via tetracycline withdrawal revealed a timedependent increase in LDHA, ERN1, HSPA5, XBP1t, and XBP1s mRNA ( Figure 2F and Supplemental Figure 2E) and protein ( Figure 2G), with maximal expression levels achieved by 24 to 48 hours. Importantly, IRE1α, BiP, XBP1s, and c-Myc protein levels in P493 High Myc cells were comparable to multiple bona fide BL cell lines: Raji, Daudi, Ramos, and EB-2 (Supplemental Figure 2F), consistent with the notion that P493 High Myc cells are a faithful BL model (20). ChIP-sequencing (ChIP-seq) analysis of P493 cells confirmed c-Myc binding to E-box sequences in the ERN1, HSPA5, and XBP1 promoters, confirming that c-Myc activates their transcription directly (Supplemental Figure 2G).…”

MINCR is a MYC-induced lncRNA able to modulate MYC’s transcriptional network in Burkitt lymphoma cells

“…With the aim of identifying MYC-regulated lncRNAs that could play a driving role in lymphoma development, we set up a bioinformatic pipeline to screen for lncRNAs differentially regulated in MYCinducible model cell lines and a set of BL samples. In particular, we used RNA-seq data obtained from (i) hT-RPE-MycER cells, an immortalized retinal pigment epithelial cell line expressing the MycER fusion protein (a cell line shown to be a relevant tool for the study of several aspects of MYC activity in oncogenic transformation) (38,39); (ii) P493-6 cells, an immortalized B-lymphoblastic cell line carrying a tetracyclin-inducible MYC construct that was shown to be a good model to study MYC-induced lymphomas (40,41); and (iii) 91 GC B cell-derived lymphoma samples subjected to RNA-seq in the framework of the International Cancer Genome Consortium project on malignant lymphoma [ICGC MMML-Seq (International Cancer Genome Consortium Molecular Mechanisms in Malignant Lymphoma by Sequencing)], including 16 BLs, 35 DLBCLs, 40 FLs, and 4 controls (normal GC B-cell samples) (Table S1). …”

JAG2 Induction in Hypoxic Tumor Cells Alters Notch Signaling and Enhances Endothelial Cell Tube Formation

“…Several mechanisms have been proposed including direct icN1 stabilization by interaction with HIF proteins (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). As of yet, little attention has been given to Notch ligand regulation and the effects this may have on Notch activation under hypoxia.…”