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Signal transduction typically displays a so‐called bow‐tie topology: Multiple receptors lead to multiple cellular responses but the signals all pass through a narrow waist of central signaling nodes. One such signaling node for several inflammatory and oncogenic signaling pathways is the CARD‐CC/BCL10/MALT1 (CBM) complexes, which get activated by protein kinase C (PKC)‐mediated phosphorylation of the caspase activation and recruitment domain (CARD)‐coiled‐coil domain (CC) component. In humans, there are four CARD‐CC family proteins (CARD9, CARD10, CARD11, and CARD14) and 9 true PKC isozymes (α to ι). At this moment, less than a handful of PKC::CARD‐CC relationships are known. In order to explore the biologically relevant combinatorial space out of all 36 potential permutations in this two‐component signaling event, we made use of CARD10‐deficient human embryonic kidney 293T cells for subsequent pairwise cotransfections of all CARD‐CC family members and all activated PKCs. Upon analysis of NF‐κB‐dependent reporter gene expression, we could define specific PKC::CARD‐CC relationships. Surprisingly, as many as 21 PKC::CARD‐CC functional combinations were identified. CARD10 was responsive to most PKCs, while CARD14 was mainly activated by PKCδ. The CARD11 activation profile was most similar to that of CARD9. We also discovered the existence of mixed protein complexes between different CARD‐CC proteins, which was shown to influence their PKC response profile. Finally, multiple PKCs were found to use a common phosphorylation site to activate CARD9, while additional phosphorylation sites contribute to CARD14 activation. Together, these data reveal the combinatorial space of PKC::CARD‐CC signal transduction nodes, which will be valuable for future studies on the regulation of CBM signaling. [ABSTRACT FROM AUTHOR]

CARD14 gain‐of‐function mutations cause psoriasis in humans and mice. Together with BCL10 and the protease MALT1, mutant CARD14 forms a signaling node that mediates increased NF‐κB signaling and proinflammatory gene expression in keratinocytes. However, it remains unclear whether psoriasis in response to CARD14 hyperactivation is keratinocyte‐intrinsic or requires CARD14 signaling in other cells. Moreover, the in vivo effect of MALT1 targeting on mutant CARD14‐induced psoriasis has not yet been documented. Here, we show that inducible keratinocyte‐specific expression of CARD14E138A in mice rapidly induces epidermal thickening and inflammation as well as increased expression of several genes associated with psoriasis in humans. Keratinocyte‐specific MALT1 deletion as well as oral treatment of mice with a specific MALT1 protease inhibitor strongly reduces psoriatic skin disease in CARD14E138A mice. Together, these data illustrate a keratinocyte‐intrinsic causal role of enhanced CARD14/MALT1 signaling in the pathogenesis of psoriasis and show the potential of MALT1 inhibition for the treatment of psoriasis. Synopsis: Expression of a pathogenic human CARD14 mutant transgene in keratinocytes is sufficient to drive psoriasis‐like dermatitis in mice, which can be inhibited by treatment with a MALT1 protease inhibitor. Keratinocyte‐specific expression of a human psoriasis‐associated CARD14E138A mutant transgene in mice induces skin epidermal thickening and inflammation.CARD14E138A expression in keratinocytes activates MALT1 proteolytic activity in murine skin.Oral treatment of mice with a MALT1 protease inhibitor reduces psoriatic dermatitis in CARD14E138A expressing mice. [ABSTRACT FROM AUTHOR]

Mutations in CARD14 have recently been linked to psoriasis susceptibility. CARD14 is an epidermal regulator of NF-κB 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-κB 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. [ABSTRACT FROM AUTHOR]

Natural killer (NK) cells kill virus-infected or transformed target cells by delivering cytotoxic proteases called granzymes to the target cell cytosol. One of these proteases, granzyme M, is specifically expressed in NK cells and is thought to instigate a form of cell death distinct from that mediated by granzyme A or granzyme B. However, the mechanism of granzyme M-induced cell death is unclear at present, and few substrates for this granzyme have been reported to date. Here we show that the abundant nucleolar phosphoprotein, nucleophosmin (NPM), is cleaved and inactivated by granzyme M. NPM is essential for cell viability as RNA interference-mediated ablation of NPM expression in human cells resulted in spontaneous apoptosis. Significantly, overexpression of wild-type NPM rescued cells treated with NPM small interference RNA, whereas overexpression of the granzyme M-cleaved form of NPM did not. Because NPM is essential for cell viability, these data suggest that targeting of NPM by granzyme M may contribute to tumor cell eradication by abolishing NPM function. [ABSTRACT FROM AUTHOR]

Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is an intracellular cysteine protease (paracaspase) that plays an integral role in innate and adaptive immunity. The phenothiazine mepazine has been shown to inhibit the proteolytic activity of MALT1 and is frequently used to study its biological role. MALT1 has recently been suggested as a therapeutic target in rheumatoid arthritis. Here, we analyzed the effect of mepazine on the receptor activator of nuclear factor κ-B (RANK)-induced osteoclastogenesis. The treatment of mouse bone marrow precursor cells with mepazine strongly inhibited the RANK ligand (RANKL)-induced formation of osteoclasts, as well as the expression of several osteoclast markers, such as TRAP, cathepsin K, and calcitonin. However, RANKL induced osteoclastogenesis equally well in bone marrow cells derived from wild-type and Malt1 knock-out mice. Furthermore, the protective effect of mepazine was not affected by MALT1 deficiency. Additionally, the absence of MALT1 did not affect RANK-induced nuclear factor κB (NF-κB) and activator protein 1 (AP-1) activation. Overall, these studies demonstrate that MALT1 is not essential for RANK-induced osteoclastogenesis, and implicate a MALT1-independent mechanism of action of mepazine that should be taken into account in future studies using this compound. [ABSTRACT FROM AUTHOR]

Rare mutations in CARD14 promote psoriasis by inducing CARD14-BCL10-MALT1 complexes that activate NF-κB and MAP kinases. Here, the downstream signalling mechanism of the highly penetrant CARD14E138A alteration is described. In addition to BCL10 and MALT1, CARD14E138A associated with several proteins important in innate immune signalling. Interactions with M1-specific ubiquitin E3 ligase HOIP, and K63-specific ubiquitin E3 ligase TRAF6 promoted BCL10 ubiquitination and were essential for NF-κB and MAP kinase activation. In contrast, the ubiquitin binding proteins A20 and ABIN1, both genetically associated with psoriasis development, negatively regulated signalling by inducing CARD14E138A turnover. CARD14E138A localized to early endosomes and was associated with the AP2 adaptor complex. AP2 function was required for CARD14E138A activation of mTOR complex 1 (mTORC1), which stimulated keratinocyte metabolism, but not for NF-κB nor MAP kinase activation. Furthermore, rapamycin ameliorated CARD14E138A-induced keratinocyte proliferation and epidermal acanthosis in mice, suggesting that blocking mTORC1 may be therapeutically beneficial in CARD14-dependent psoriasis., (© 2024 The Author(s).)

Immune checkpoint blockade (ICB) has heralded a new era in cancer therapy. Research into the mechanisms underlying response to ICB has predominantly focused on T cells; however, effective immune responses require tightly regulated crosstalk between innate and adaptive immune cells. Here, we combine unbiased analysis of blood and tumors from metastatic breast cancer patients treated with ICB with mechanistic studies in mouse models of breast cancer. We observe an increase in systemic and intratumoral eosinophils in patients and mice responding to ICB treatment. Mechanistically, ICB increased IL-5 production by CD4 + T cells, stimulating elevated eosinophil production from the bone marrow, leading to systemic eosinophil expansion. Additional induction of IL-33 by ICB-cisplatin combination or recombinant IL-33 promotes intratumoral eosinophil infiltration and eosinophil-dependent CD8 + T cell activation to enhance ICB response. This work demonstrates the critical role of eosinophils in ICB response and provides proof-of-principle for eosinophil engagement to enhance ICB efficacy., Competing Interests: Declaration of interests O.S.B., H.G., L.S., L.V., O.I.I., E.v.D., N.B., C.K., M.D., K. Kersten, M.B., D.P., C.-S.H., K.V., E.A.M.R., D.K., L.H., K. Kos, I.S.A., P.K., R.B., and D.S.T. have no competing interests to declare. M.C. reports funding to the institute from BMS and Roche/Genentech and an advisory role for BMS, outside the submitted work. W.S.M.E.T. reports receiving grants from MSD during the conduct of the PEMBRO-RT trial. P.B. reports receiving grants and medication delivery from MSD during the conduct of the PEMBRO-RT trial as well as grants and consultancy fees from BMS outside the submitted work. E.E.V. is legally responsible for all contracts with pharmaceutical companies at the NKI and reports research funding from BMS, outside the submitted work. L.F.A.W. reports funding to the institute from Genmab BV. K.E.d.V. reports research funding from Roche/Genentech and is consultant for Macomics, outside the scope of this work. M.K. reports funding to the institute from BMS, Roche/Genentech, AZ, and an advisory role for BMS, Roche, MSD, and Daiichi Sankyo, outside the submitted work., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)