N4BP1 restricts HIV-1 and its inactivation by MALT1 promotes viral reactivation

Abstract

RNA modulating factors not only regulate multiple steps of cellular RNA metabolism, but also emerge as key effectors of the immune response against invading viral pathogens including human immunodeficiency virus type-1 (HIV-1). However, cellular RNA binding proteins involved in the establishment and maintenance of latent HIV-1 reservoirs have not been extensively studied. Here, we screened a panel of 62 cellular RNA binding proteins and identified NEDD4 binding protein 1 (N4BP1) as potent interferon-inducible inhibitor of HIV-1 in primary T cells and macrophages. N4BP1 harbors a prototypical PIN-like RNase domain and inhibits HIV-1 replication by interacting with and degrading viral mRNA species. Upon activation of CD4 + T cells, however, N4BP1 undergoes rapid cleavage at Arg509 by the paracaspase MALT1. Mutational analyses and knockout studies revealed that MALT1-mediated inactivation of N4BP1 facilitates the reactivation of latent HIV-1 proviruses. Taken together, our findings demonstrate that the RNase N4BP1 is an efficient restriction factor of HIV-1 and suggest that inactivation of N4BP1 by induction of MALT1 activation might facilitate elimination of latent HIV-1 reservoirs.

A MALT1 inhibitor suppresses human myeloid DC, effector T-cell and B-cell responses and retains Th1/regulatory T-cell homeostasis

“…(C) and (D) CFSE stained human CD19+ cells were cocultured with FACS sorted CD4 + CXCR5 + CD45RO + T-cells and stimulated for 5 days with SEB 100 ng/ml (n = 6) in the presence or absence of 10 μM Compound 2, 5 μM mepazine or 100 μM z-VRPR-fmk. Proliferation (A) was assessed as CFSE dilution of CD19+ B cells, presence of CD19 + CD27 hi CD38 hi plasmablasts was measured using flow the abolishment of MALT1 protease activity, whereas the development of autoimmunity is not seen in MALT1 knock-out (KO) mice [17]. Actually, MALT1 KO and PD mice have been shown to be protected from experimental allergic encephalitis but only PD mice exhibited autoimmune disease due to the role of MALT1 enzymatic activity during Treg development [17].…”

“…Proliferation (A) was assessed as CFSE dilution of CD19+ B cells, presence of CD19 + CD27 hi CD38 hi plasmablasts was measured using flow the abolishment of MALT1 protease activity, whereas the development of autoimmunity is not seen in MALT1 knock-out (KO) mice [17]. Actually, MALT1 KO and PD mice have been shown to be protected from experimental allergic encephalitis but only PD mice exhibited autoimmune disease due to the role of MALT1 enzymatic activity during Treg development [17]. Our studies indicate that a MALT1 allosteric inhibitor affecting both scaffold and protease activity can be considered as a potential treatment for autoantigen-driven autoimmune pathology due to its effect on TCR-and BCRmediated activation, such as type 1 diabetes and systemic lupus erythematosus.…”

“…In addition to the effects of MALT1 in promoting NF-κB activity, MALT1 protease cleaves the endoribonucleases Regnase-1 and Roquin [10,[11][12][13], and increases the stability of mRNAs in activated T-cells [14][15][16]. It has recently been identified that MALT1 cleaves the RNAse N4BP1 in T-cells and macrophages, an interferon-inducible inhibitor of HIV-1 [17].…”

GRK2 suppresses lymphomagenesis by inhibiting the MALT1 proto-oncoprotein

“…The discovery that in addition to scaffolding activity, MALT1 also possesses proteolytic activity, represented a major step in advancing our understanding of lymphocyte biology and the molecular pathogenesis of CBM-driven lymphomas (17,18,66). Thus far, 10 specific proteolytic substrates of MALT1 have been identified (20,67), and we demonstrate that GRK2 inhibits MALT1-mediated cleavage of 2 of these known substrates, RELB and CYLD. MALT1 protease activity is thought to sustain NF-κB activation and promote lymphomagenesis in part by cleaving RELB, an NF-κB subunit that forms transcriptionally inactive complexes with and thereby inhibits RELA and c-REL (15).…”

Mechanism of negative regulation of NF-κB by N4BP1

“…These data also suggest that other pathways that activate caspase 8 may amplify NF-κB-dependent gene expression by inactivating N4BP1. MALT1 was also reported to cleave N4BP1 in T cells, suggesting that distinct proteases may be induced to cleave N4BP1 in a cell type-and/or ligand-specific manner 34 . In view of the requirement for caspase 8 for normal T cell and B cell proliferation and homeostasis in conditional knockout mice 37,38 and our finding that N4BP1 is also similarly required, we conclude that in some cases the two proteins must function independently, or that the cleavage of N4BP1 promotes event(s) that are needed for lymphocyte homeostasis.…”