HOIL1 cleavage by MALT1, the knives are out

Abstract

The paracaspase MALT1 functions as a bifunctional regulator of lymphocyte activation following the engagement of antigen receptors. First, MALT1 scaffolds the CARMA1-BCL10-MALT1 (CBM) signaling complex in charge of activating the NF-kB transcription factor. Second, MALT1 proteolytic activity governs NF-kB fine-tuning and the homeostasis of the immune system. MALT1 is also constitutively activated in the activated B-cell like (ABC) subset of diffuse large B-cell lymphoma (DLBCL), and the discovery that its chemical inhibition is toxic has opened new perspectives of treatment. Yet, the nature of MALT1 substrates continues to be elucidated. Herein, we review the recent identification of the linear ubiquitin assembly chain complex (LUBAC) element HOIL1 as a new substrate for MALT1 in lymphocytes and lymphoma. We discuss how this processing may affect NF-kB signaling and impact on lymphocyte homeostasis.