Increased activity of the transcription factor NF-kB is an important contribution to the creation and development of numerous cancers. MALT lymphomas and certain diffuse large B-cell lymphoma (DLBCL) exhibit genetic changes in CARD11, BCL10 and MALT1, all resulting in MALT1-mediated activation of NF-kB. CARD11, BCL10 enMALT1 are essential components of the antigen receptor signaling to NF-kB. Recently we discovered that MALT1 has proteolytic activity. It is our overall goal to further elucidate the molecular mechanisms of MALT1-mediated NF-kB activation, which we mainly study the function and regulation of MALT1 proteolytic activity in vitro and in vivo models (transgenic mice). The insights gained will possibly be used for the development and validation of specific inhibitors of MALT1 protease activity.