Oncogene-induced MALT1 protease activity drives post-transcriptional gene expression in malignant lymphomas

Constitutive MALT1 activity drives survival of malignant lymphomas addicted to chronic B-cell receptor (BCR) signaling, oncogenic CARD11, or the API2-MALT1 fusion oncoprotein. While MALT1 scaffolding induces NF-kB-dependent survival signaling, MALT1 protease function is thought to augment NF-kB activation by cleaving signaling mediators and transcriptional regulators in B-cell lymphomas. However, the pathological role of MALT1 protease function in lymphomagenesis is not well understood. Here, we show that TRAF6 controls MALT1-dependent activation of NF-kB transcriptional responses, but is dispensable for MALT1 protease activation driven by oncogenic CARD11. To uncouple enzymatic and non-enzymatic functions of MALT1, we analyzed TRAF6-dependent and -independent as well as MALT1 protease-dependent gene expression profiles downstream of oncogenic CARD11 and API2-MALT1. By cleaving and inactivating the RNA binding proteins Regnase-1 and Roquin-1/2, MALT1 protease induces post-transcriptional upregulation of genes like NFKBIZ/IkBz, NFKBID/IkBNS and ZC3H12A/Regnase-1 in activated B-cell-like diffuse large B-cell lymphoma (ABC DLBCL). We demonstrate that oncogene-driven MALT1 activity in ABC DLBCL cells regulates NFKBIZ and NFKBID induction on mRNA level via releasing a brake imposed by Regnase-1 and Roquin-1/2. Furthermore, MALT1 protease drives post-transcriptional gene induction in the context of the API2-MALT1 fusion created by the recurrent t(11;18)(q21;q21) translocation in mucosa-associated lymphoid tissue (MALT) lymphoma. Thus, MALT1 paracaspase acts as a bifurcation point for enhancing transcriptional and post-transcriptional gene expression in malignant lymphomas. Moreover, the identification of MALT1 protease selective target genes will provides specific biomarkers for the clinical evaluation of MALT1 inhibitors. 1)Bulk RNA-Seq profiling of CARD11 L232LI mutant and/or TRAF6 knockout BJAB cells. Additionally, profiling of MLT-748 treatment for TRAF6 KO CARD11 mut cells. 2)Bulk RNA-Seq profiling of (CARD11 L232LI mutant) + (MALT1 C453A protease and/or E795A TRAF6 binding mutant) BJAB cells. 3)Bulk RNA-Seq profiling of API2:MALT1 fusion protein expressing BJAB cells, where MALT1 carries the mutations described in the second bullet point.