Mucosa-associated lymphoid tissue lymphoma translocation protein 1 is a protein that in humans is encoded by the MALT1 gene. [5] [6] [7] It's the human paracaspase.
Mucosa-associated lymphoid tissue lymphoma translocation protein 1 is a protein that in humans is encoded by the MALT1 gene. [5] [6] [7] It's the human paracaspase.
Genetic ablation of the paracaspase gene in mice and biochemical studies have shown that paracaspase is a crucial protein for T and B lymphocytes activation. It has an important role in the activation of the transcription factor NF-κB, in the production of interleukin-2 (IL-2) and in T and B lymphocytes proliferation [8] [9] Two alternatively spliced transcript variants encoding different isoforms have been described for this gene. [10]
In addition, a role for paracaspase has been shown in the innate immune response mediated by the zymosan receptor Dectin-1 in macrophages and dendritic cells, and in response to the stimulation of certain G protein-coupled receptors. [11]
Sequence analysis proposes that paracaspase has an N-terminal death domain, two central immunoglobulin-like domains involved in the binding to the B-cell lymphoma 10 (Bcl10) protein and a caspase-like domain. The death domain and immunoglobulin-like domains participate in binding to BCL10. Activation of MALT1 downstream NF-κB signaling and protease activity occurs when BCL10/MALT1 gets recruited to an activated CARD-CC family protein (CARD9, -10, -11 or -14) in a so-called CBM (CARD-CC/BCL10/MALT1) signaling complex.
Paracaspase has been shown to have proteolytic activity through its caspase-like domain in T lymphocytes. Cysteine 464 and histidine 414 are crucial for this activity. Like metacaspases, the paracaspase cleaves substrates after an arginine residue. To date, several paracaspase substrates have been described (see below). Bcl10 is cut after arginine 228. This removes the last five amino acids at the C-terminus and is crucial for T cell adhesion to fibronectin, but not for NF-κB activation and IL-2 production. However, using a peptide-based inhibitor (z-VRPR-fmk) of the paracaspase proteolytic activity, it has been shown that this activity is required for a sustain NF-κB activation and IL-2 production, suggesting that paracaspase may have others substrates involved in T cell-mediated NF-κB activation. [12] A20, a deubiquitinase, has been shown to be cut by paracaspase in Human and in mouse. Cells expressing an uncleavable A20 mutant is however still capable to activate NF-κB, but cells expressing the C-terminal or the N-terminal A20 cleavage products activates more NF-κB than cells expressing wild-type A20, indicating that cleavage of A20 leads to its inactivation. Since A20 has been described has an inhibitor of NF-κB, this suggests that paracaspase-mediated A20 cleavage in T lymphocytes is necessary for a proper NF-κB activation. [13]
By targeting paracaspase proteolytic activity, it might be possible to develop new drugs that might be useful for the treatment of certain lymphomas or autoimmune disorders.
MALT1 has been shown to interact with BCL10, [14] TRAF6 and SQSTM1/p62.
MALT1 (PCASP1) is part of the paracaspase family and shows proteolytic activity. Since many of the substrates are involved in regulation of inflammatory responses, the protease activity of MALT1 has emerged as an interesting therapeutic target. Currently known protease substrates are (in order of reported discovery):
| Substrate | Reference | Cleavage sequence | |
|---|---|---|---|
| A20 (TNFAIP3) | [13] | LGASR/G | |
| BCL10 | [12] | LRSR/T | |
| CYLD | [15] | FMSR/G | |
| RELB | [16] | LVSR/G | |
| regnase-1/MCPIP1 (ZC3H12A) | [17] | LVPR/G | |
| Roquin-1 (RC3H1) | [18] | LIPR/G | |
| Roquin-2 (RC3H2) | [18] | LISR/S | |
| MALT1 auto-proteolysis | [19] | LCCR/A | |
| MALT1 auto-proteolysis | [20] | HCSR/T | |
| HOIL1 (RBCK1) | [21] [22] [23] | LQPR/G | |
| N4BP1 | [24] | FVSR/G | |
| CARD10 | [25] | LRCR/G | |
| ZC3H12D | [26] | LVPR/G | |
| ZC3H12B | [26] | LVPR/G | |
| TAB3 | [26] | LQSR/G | |
| CASP10 | [26] | LVSR/G | |
| CILK1 | [26] | LISR/S | |
| ILDR2 | [26] | GASR/G LVSR/T GASR/G | |
| TANK | [26] | HIPR/V | |
| Tensin-3 | [27] | R614, R645 |
Specifically by the oncogenic IAP2-MALT1 fusion:
Since MALT1 protease activity is a promising therapeutic target, several different screenings have been performed which have resulted in different types of protease inhibitors. [30] There is active competition between multiple pharma companies and independent research groups in drug development against the MALT1 protease activity. [31]
Granzymes are serine proteases released by cytoplasmic granules within cytotoxic T cells and natural killer (NK) cells. They induce programmed cell death (apoptosis) in the target cell, thus eliminating cells that have become cancerous or are infected with viruses or bacteria. Granzymes also kill bacteria and inhibit viral replication. In NK cells and T cells, granzymes are packaged in cytotoxic granules along with perforin. Granzymes can also be detected in the rough endoplasmic reticulum, golgi complex, and the trans-golgi reticulum. The contents of the cytotoxic granules function to permit entry of the granzymes into the target cell cytosol. The granules are released into an immune synapse formed with a target cell, where perforin mediates the delivery of the granzymes into endosomes in the target cell, and finally into the target cell cytosol. Granzymes are part of the serine esterase family. They are closely related to other immune serine proteases expressed by innate immune cells, such as neutrophil elastase and cathepsin G.
MALT lymphoma is a form of lymphoma involving the mucosa-associated lymphoid tissue (MALT), frequently of the stomach, but virtually any mucosal site can be affected. It is a cancer originating from B cells in the marginal zone of the MALT.
The B-cell receptor (BCR) is a transmembrane protein on the surface of a B cell. A B-cell receptor is composed of a membrane-bound immunoglobulin molecule and a signal transduction moiety. The former forms a type 1 transmembrane receptor protein, and is typically located on the outer surface of these lymphocyte cells. Through biochemical signaling and by physically acquiring antigens from the immune synapses, the BCR controls the activation of the B cell. B cells are able to gather and grab antigens by engaging biochemical modules for receptor clustering, cell spreading, generation of pulling forces, and receptor transport, which eventually culminates in endocytosis and antigen presentation. B cells' mechanical activity adheres to a pattern of negative and positive feedbacks that regulate the quantity of removed antigen by manipulating the dynamic of BCR–antigen bonds directly. Particularly, grouping and spreading increase the relation of antigen with BCR, thereby proving sensitivity and amplification. On the other hand, pulling forces delinks the antigen from the BCR, thus testing the quality of antigen binding.
Paracaspases are members of the C14 family of cysteine proteases. Paracaspases are proteins related to caspases present in animals and slime mold, in contrast to metacaspases, which are present in plants, fungi, and "protists". The phylogenetic distribution is a bit confusing, since slime mold diverged earlier than the animal/fungal split.
NF-kappa-B essential modulator (NEMO) also known as inhibitor of nuclear factor kappa-B kinase subunit gamma (IKK-γ) is a protein that in humans is encoded by the IKBKG gene. NEMO is a subunit of the IκB kinase complex that activates NF-κB. The human gene for IKBKG is located on the chromosome band Xq28. Multiple transcript variants encoding different isoforms have been found for this gene.
Caspase-8 is a caspase protein, encoded by the CASP8 gene. It most likely acts upon caspase-3. CASP8 orthologs have been identified in numerous mammals for which complete genome data are available. These unique orthologs are also present in birds.
IKK-β also known as inhibitor of nuclear factor kappa-B kinase subunit beta is a protein that in humans is encoded by the IKBKB gene.
Nuclear factor NF-kappa-B p105 subunit is a protein that in humans is encoded by the NFKB1 gene.
The IκB kinase is an enzyme complex that is involved in propagating the cellular response to inflammation, specifically the regulation of lymphocytes.
Transcription factor RelB is a protein that in humans is encoded by the RELB gene.
Baculoviral IAP repeat-containing protein3 is a protein that in humans is encoded by the BIRC3 gene.
B-cell lymphoma/leukemia 10 is a protein that in humans is encoded by the BCL10 gene. Like BCL2, BCL3, BCL5, BCL6, BCL7A, and BCL9, it has clinical significance in lymphoma.
Tumor necrosis factor, alpha-induced protein 3 or A20 is a protein that in humans is encoded by the TNFAIP3 gene.
Caspase recruitment domain-containing protein 11 also known as CARD-containing MAGUK protein 1 is a protein in the CARD-CC protein family that in humans is encoded by the CARD11 gene. CARD 11 is a membrane associated protein that is found in various human tissues, including the thymus, spleen, liver, and peripheral blood leukocytes. Similarly, CARD 11 is also found in abundance in various lines of cancer cells.
Caspase recruitment domain-containing protein 10 is a protein in the CARD-CC protein family that in humans is encoded by the CARD10 gene.
Marginal zone lymphomas, also known as marginal zone B-cell lymphomas (MZLs), are a heterogeneous group of lymphomas that derive from the malignant transformation of marginal zone B-cells. Marginal zone B cells are innate lymphoid cells that normally function by rapidly mounting IgM antibody immune responses to antigens such as those presented by infectious agents and damaged tissues. They are lymphocytes of the B-cell line that originate and mature in secondary lymphoid follicles and then move to the marginal zones of mucosa-associated lymphoid tissue (MALT), the spleen, or lymph nodes. Mucosa-associated lymphoid tissue is a diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of the body such as the gastrointestinal tract, mouth, nasal cavity, pharynx, thyroid gland, breast, lung, salivary glands, eye, skin and the human spleen.
The Interleukin-1 family is a group of 11 cytokines that plays a central role in the regulation of immune and inflammatory responses to infections or sterile insults.
Caspase-8 deficiency (CEDS) is a very rare genetic disorder of the immune system. It is caused by mutations in the CASP8 gene that encodes the protein caspase-8. The disorder is characterized by splenomegaly and lymphadenopathy, in addition to recurrent sinopulmonary infections, recurrent mucocutaneous herpesvirus or other viral infections, and hypogammaglobulinemia. Investigators in the laboratory of Dr. Michael Lenardo at the National Institutes of Health described this condition in two siblings from a consanguineous family in 2002, and several more affected family members have since been identified.
The CARD-CC protein family is defined by an evolutionary conserved "caspase activation and recruitment domain" (CARD) and a coiled-coil (CC) domain. Coiled-coils (CC) act as oligomerization domains for many proteins such as structural and motor proteins, and transcription factors. This means that monomers are converted to macromolecular complexes by polymerization. In humans and other jawed vertebrates, the family consists of CARD9 and the three "CARD-containing MAGUK protein" (CARMA) proteins CARD11 (CARMA1), CARD14 (CARMA2) and CARD10 (CARMA3). Although the MAGUK protein DLG5 contains both a CARD domain and a CC domain, it does not belong to the same family as the CARD-CC proteins since the evolutionary origin of its CARD domain is very likely to be different.
Vishva Mitra Dixit is a physician of Indian origin who is the current Vice President of Discovery Research at Genentech.
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