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Polysome-CAGE of TCL1-driven chronic lymphocytic leukemia revealed induction of multiple N-terminally altered epigenetic regulators and a translation stress signature

ABSTRACT: The transformation of normal to malignant cells is accompanied by substantial changes in gene expression programs through diverse mechanisms. Here we examined the changes in the landscape of transcription start sites (TSSs) and alternative promoter (AP) usage and their impact on the translatome in TCL1-driven chronic lymphocytic leukemia (CLL). Our findings revealed a marked elevation of APs in CLL cells from Eµ-Tcl1 transgenic mice, which are particularly enriched with intragenic promoters that generate N-terminally truncated or modified proteins. Intragenic promoter activation is mediated by (i) loss of function of ‘closed chromatin’ epigenetic regulators due to the generation of inactive N-terminally modified isoforms or reduced expression; (ii) upregulation of transcription factors, including c-Myc, targeting the intragenic promoters and associated enhancers. Exogenous expression of Tcl1 in MEFs is sufficient to induce intragenic promoters of epigenetic regulators and promote c-Myc expression. We further found a dramatic translation downregulation of transcripts bearing CNY cap-proximal tri-nucleotides, reminiscent of cells undergoing metabolic stress. These findings uncovered the role of Tcl1 oncogenic function in altering promoter usage and mRNA translation in leukemogenesis.

ORGANISM(S): Mus musculus

PROVIDER: GSE194265 | GEO | 2022/06/29

REPOSITORIES: GEO

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Project description:B cell chronic lymphocytic leukemia (CLL) is often preceded by a benign monoclonal or oligoclonal CD5+ B cell lymphocytosis. We have generated transgenic mice expressing a catalytically inactive, dominant-negative recombination activating gene 1 (dnRAG1 mice) in the periphery. These animals develop an early-onset indolent CD5+ B cell lymphocytosis, caused in part by a defect in secondary V(D)J rearrangements initiated to alter autoreactive B cell receptor specificity. Hypothesizing that the CD5+ B cells accumulating in dnRAG1 mice represent a CLL precursor, we crossed dnRAG1 mice with CLL-prone Eµ-TCL1 mice to determine whether dnRAG1 expression in Eµ-TCL1 mice accelerates the onset of CLL-like disease. We find that CD5+ B cell expansion and CLL progression occurs more rapidly and uniformly in double-transgenic mice (DTG mice) compared to Eµ-TCL1 mice, but with similar phenotypic and leukemogenic features. To gain insight into genes or pathways responsible for CD5+ B cell accumulation in the transgenic mice, we performed comparative gene expression profiling studies using normal and CD5+ B cells isolated from wild-type and transgenic mice at either 12 weeks of age (pre-leukemia) or at CLL onset in DTG mice (using age-matched wild-type and single-transgenic mice as controls). These analyses confirm the upregulation of tolerogenic genes in CD5+ B cells and reveal a possible role for prolactin signaling in the regulation of receptor editing. This study suggests that a failure to remodel B cell antigen receptor genes in response to autoreactivity may promote the benign accumulation of CD5+ B cells, which may then be subjected to secondary genetic lesions that promote CLL progression. dnRAG1 mice were bred to Eµ-TCL1 mice to obtain cohorts of wild-type (WT), single-transgenic (dnRAG1 and Eµ-TCL1), and DTG mice. Splenic CD19+B220hiCD5- B cells from WT mice or CD19+CD5+ B cells from transgenic mice were purified using fluorescence activated cell sorting (FACS). Biotin end-labeled cDNA prepared from the sorted cells was hybridized to Mouse Gene 1.0 ST Arrays. These experiments were performed two independent times: once with a cohort of 12-week-old mice, and once with older mice (>34 weeks old) consisting of two ill DTG mice and their age-matched counterparts. At least two biological replicates were used where possible.

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Polysome-CAGE of TCL1-driven chronic lymphocytic leukemia revealed induction of multiple N-terminally altered epigenetic regulators and a translation stress signature

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