Mutations in CARD14 have recently been linked to psoriasis susceptibility. CARD14 is an epidermal regulator of NF-jB activation. However, the ability of CARD14 to activate other signaling pathways as well as the biochemical mechanisms that mediate and regulate its function remain to be determined. Here, we report that in addition to NF-jB signaling, CARD14 activates p38 and JNK MAP kinase pathways, all of which are dependent on the paracaspase MALT1. Mechanistically, we demonstrate that CARD14 physically interacts with paracaspase MALT1 and activates MALT1 proteolytic activity and inflammatory gene expression, which are enhanced by psoriasis-associated CARD14 mutations. Moreover, we show that MALT1 deficiency or pharmacological inhibition of MALT1 catalytic activity inhibits pathogenic mutant CARD14-induced cytokine and chemokine expression in human primary keratinocytes. Collectively, our findings demonstrate a novel role for MALT1 in CARD14-induced signaling and indicate MALT1 as a valuable therapeutic target in psoriasis.

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Mutations in caspase recruitment domain-containing protein 14(CARD14) have been linked to susceptibility to psoriasis. CARD14 is an intracellular scaffold protein that regulates proinflammatory gene expression. Recent studies have offered novel insights into the mechanisms of CARD14-mediated signaling in keratinocytes and the molecular impact of psoriasis-associated CARD14 mutations. CARD14 forms a signaling complex with BCL10 and the paracaspase MALT1, and this process is enhanced upon pathogenic CARD14 mutation, culminating in the activation of MALT1 protease activity and psoriasis-associated gene expression. This review summarizes the current knowledge of CARD14/MALT1-mediated signaling in keratinocytes and its therapeutic implications in psoriasis.