Inhibition of Caspase-8 Activity Caused by Overexpression of BCL10 Contributes to the Pathogenesis of High-Grade MALT Lymphoma,

Abstract 3694

Mucosa-associated lymphoid tissue (MALT) lymphoma comprises approximately 8% of all non-Hodgkin lymphomas and is the most common lymphoma in the gastrointestinal tract. B-cell lymphoma/leukemia 10 (BCL10) overexpression and nuclear expression has been associated with high-grade MALT lymphomas unresponsive to H. pylori eradication treatment. To explore the molecular mechanism of BCL10 overexpression on the pathogenesis and malignant phenotype of MALT lymphoma, we generated EμSR-BCL10 transgenic mice. Results in our previous report showed that predisposition to marginal zone B-cell lymphoma (MZL) development was enhanced in these transgenic mice. MALT lymphoma precursor cells - marginal zone (MZ) B cells - are expanded in BCL10 transgenic mice. Constitutive activation of both canonical and noncanonical NF-κB pathways was identified in these MZ B cells. Elevated expression of BAFF, a NF-κB downstream gene, may be in part responsible for increased tumor cell survival in MALT lymphomas. In this continuing study, quantitative analysis of BCL10 protein levels and the extent of MZ B cell expansion in heterozygous (Tg/+) and homozygous (Tg/Tg) EμSR-BCL10 transgenic mice demonstrated a direct pathogenic effect of BCL10 protein on MALT lymphomagenesis. The activities of caspase-8 and caspase-3, but not caspase-9, were inhibited with increasing BCL10 protein levels in a dose-dependent manner. Apoptosis induced by anti-IgM was selectively inhibited in MZ B cells from transgenic mice, but no differences were observed following treatment with dexamethasone, γ-irradiation or anti-CD95, implying that overexpressed BCL10 exerts anti-apoptotic effects through the B-cell antigen receptor pathway. Expression of API2, another NF-κB downstream gene, was also elevated in a dose-dependent manner with BCL10 protein level in the MZ B cells. Overexpressed BCL10 protein co-immunoprecipitated with caspase-8 and API2, suggesting an in vivo interaction leading to inhibition of caspase-8 activity. Our current data suggests a novel effect of overexpressed BCL10 in the pathogenesis of high-grade MALT lymphoma by increasing expression of API2 and recruitment of API2 and caspase-8 to form a protein complex leading to the suppression of caspase-8 activity in MZ B cells.