Expression of MALT1 oncogene in hematopoietic stem/progenitor cells recapitulates the pathogenesis of human lymphoma in mice

Abstract

Chromosomal translocations involving the MALT1 gene are hallmarks of mucosa-associated lymphoid tissue (MALT) lymphoma. To date, targeting these translocations to mouse B cells has failed to reproduce human disease. Here, we induced MALT1 expression in mouse Sca1(+)Lin(-) hematopoietic stem/progenitor cells, which showed NF-κB activation and early lymphoid priming, being selectively skewed toward B-cell differentiation. These cells accumulated in extranodal tissues and gave rise to clonal tumors recapitulating the principal clinical, biological, and molecular genetic features of MALT lymphoma. Deletion of p53 gene accelerated tumor onset and induced transformation of MALT lymphoma to activated B-cell diffuse large-cell lymphoma (ABC-DLBCL). Treatment of MALT1-induced lymphomas with a specific inhibitor of MALT1 proteolytic activity decreased cell viability, indicating that endogenous Malt1 signaling was required for tumor cell survival. Our study shows that human-like lymphomas can be modeled in mice by targeting MALT1 expression to hematopoietic stem/progenitor cells, demonstrating the oncogenic role of MALT1 in lymphomagenesis. Furthermore, this work establishes a molecular link between MALT lymphoma and ABC-DLBCL, and provides mouse models to test MALT1 inhibitors. Finally, our results suggest that hematopoietic stem/progenitor cells may be involved in the pathogenesis of human mature B-cell lymphomas.

Fig. 1.

Sca1-MALT1 mice develop extranodal human-like MALT lymphomas. (A) Kaplan–Meier overall survival plots of Sca1-MALT1 mice and WT littermates. Differential survival was analyzed using the log-rank (Mantel–Cox) test: line 86A vs. WT, P = 0.0007; line 86B vs. WT, P = 0.0026; and line 86C vs. WT, P = 0.0173). (B) Macroscopic aspect of the tumors in small intestine, spleen, and kidney of Sca1-MALT1 mice. (C) Tumor location of MALT lymphomas in 26 Sca1-MALT1 mice; note that 65% of mice developed tumors at more than one site.

Fig. 2.

Characterization of human-like MALT lymphomas arising in Sca1-MALT1 mice. (A) Representative hematoxylin–eosin (HE) staining analysis of the mouse lymphomas. A typical lymphoid cell population is present in the small intestine of Sca1-MALT1 mice, infiltrating the lamina propria and the epithelium in small groups, giving rise to lymphoepithelial lesions. (B) Lymphoid tumor cells also infiltrate other tissues. (C) Lymphomas developed in the kidneys showed prominent plasma cells surrounding blood vessels, which were pleomorphic and showed occasional binuclei (marked with arrows). (D) IHC analysis of Pax5 expression in Sca1-MALT1 lymphomas. (E) Gene-expression microarray analysis defined the Sca1-MALT1 lymphoma transcriptional signature. Five Sca1-MALT1 splenic lymphomas and four WT spleen were studied. (F–I) Bioinformatic studies of Sca1-MALT1 murine lymphoma transcriptional signature using GSEA.

Fig. 3.

Sca1-MALT1-p53^−/− mice develop human-like ABC-DLBCL. (A) Kaplan–Meier survival plots of Sca1-MALT1, p53^−/−, p53^−/−, and control WT mice. (B) Macroscopic aspect of the intestine and spleen in Sca1-Malt1,p53^−/− mice vs. WT and p53^−/− age-matched mice. (C) Representative hematoxylin–eosin (HE) staining and IHC analysis for CD20, Foxp1, Mum1, Gcet1, CD10, and Bcl6 in Sca1-Malt1,p53^−/− mice. Appropriate positive and negative control tissues for each antibody were used (see Materials and Methods). (D) Heat-map image showing the Sca1-MALT1,p53^−/− lymphoma transcriptional signature. B220⁺ cells isolated from three Sca1-MALT1,p53^−/− lymphomas and three WT spleens were studied. (E) GSEA showed a significant positive enrichment of the human ABC-DLBCL transcriptional signature in Sca1-MALT1,p53^−/− lymphomas. (F) Sca1-MALT1,p53^−/− lymphomas were significantly enriched in NF-κB target genes. (G and H) B220⁺ splenic B lymphoma cells isolated from three Sca1-MALT1 and three Sca1-MALT1,p53^−/− mice were incubated with (+) or without (−) z-VRPR-fmk (75 μM) (G) or Bay11-7082 (5 μM) (H) for 48 h. Induction of apoptosis was assessed by flow cytometry using annexin V/PI staining. Data represent the means ± SD percentages of apoptotic cells from three independent experiments.