myeloid-innate-signaling-pathway-regulation-malt1-paracaspase

Myeloid Innate Signaling Pathway Regulation by MALT1 Paracaspase Activity

Besides its function in lymphoid cells, which has been addressed by numerous studies, the paracaspase MALT1 also plays an important role in innate cells ...

Novartis Institutes for BioMedical Research

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is essential for immune responses triggered by antigen receptors but the contribution of its paracaspase activity is not fully understood. Here, we studied how MALT1 proteolytic function regulates T-cell activation and fate after engagement of the T-cell receptor pathway. We show that MLT-827, a potent and selective MALT1 paracaspase inhibitor, does not prevent the initial phase of T-cell activation, in contrast to the pan-protein kinase C inhibitor AEB071. However, MLT-827 strongly impacted cell expansion after activation. We demonstrate this is the consequence of profound inhibition of IL-2 production as well as reduced expression of the IL-2 receptor alpha subunit (CD25), resulting from defective canonical NF-κB activation and accelerated mRNA turnover mechanisms. Accordingly, MLT-827 revealed a unique transcriptional fingerprint of MALT1 protease activity, providing evidence for broad control of T-cell signaling pathways. Altogether, this first report with a potent and selective inhibitor elucidates how MALT1 paracaspase activity integrates several T-cell activation pathways and indirectly controls gamma-chain receptor dependent survival, to impact on T-cell expansion.

The T-cell fingerprint of MALT1 paracaspase revealed by selective inhibition.

A CARD10-Dependent Tonic Signalosome Activates MALT1 Paracaspase and Regulates IL-17/TNF-α-Driven Keratinocyte Inflammation.

The MALT1 (Mucosa associated lymphoid tissue lymphoma translocation protein 1) paracaspase couples antigen receptors on lymphocytes to downstream signaling events. Activation of MALT1 is known to involve stimulus-dependent CBM complex formation, that is, the recruitment of BCL10-bound MALT1 to a CARD-Coiled Coil protein. Beyond this canonical, CBM-dependent mechanism of MALT1 activation, recent studies suggest that MALT1 protease activity may be triggered by alternative mechanisms. For instance, the E3-ligase TRAF6 can activate MALT1 proteolytic function and induce MALT1 auto-cleavage. However, the interplay between CBM and TRAF6 with regard to MALT1 activation has remained incompletely elucidated. Here, by generating CRISPR/Cas9-derived knock-out Jurkat T-cells, we show that TRAF6 was dispensable for CARD11/BCL10-dependent MALT1 activation upon T-cell stimulation. However, ectopically-expressed TRAF6 could induce MALT1 activity in Jurkat T-cells devoid of either CARD11 or BCL10. These data provide unequivocal evidence that TRAF6-mediated MALT1 activation does not require the upstream scaffold CARD11 or the interaction between MALT1 and BCL10. Thus, TRAF6 may be part of a previously unidentified non-canonical pathway that triggers MALT1 protease activity independently of canonical CBM signalosomes.

Article	Year
The T-cell fingerprint of MALT1 paracaspase revealed by selective inhibition. Immunology and cell biology\| PubMed ID: 29359407	2018
A CARD10-Dependent Tonic Signalosome Activates MALT1 Paracaspase and Regulates IL-17/TNF-α-Driven Keratinocyte Inflammation. The Journal of investigative dermatology\| PubMed ID: 29571942	2018
MALT1 activation by TRAF6 needs neither BCL10 nor CARD11. Biochemical and biophysical research communications\| PubMed ID: 30336982	2018

Adeline Unterreiner

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