Signal-transducing adaptor protein-2 delays recovery of B lineage lymphocytes during hematopoietic stress

STAP-2-Derived Peptide Suppresses TCR-Mediated Signals to Initiate Immune Responses

Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that contains pleckstrin and Src homology 2-like domains, as well as a proline-rich region in its C-terminal region. Our previous study demonstrated that STAP-2 positively regulates TCR signaling by associating with TCR-proximal CD3ζ ITAMs and the lymphocyte-specific protein tyrosine kinase. In this study, we identify the STAP-2 interacting regions of CD3ζ ITAMs and show that the STAP-2-derived synthetic peptide (iSP2) directly interacts with the ITAM sequence and blocks the interactions between STAP-2 and CD3ζ ITAMs. Cell-penetrating iSP2 was delivered into human and murine T cells. iSP2 suppressed cell proliferation and TCR-induced IL-2 production. Importantly, iSP2 treatment suppressed TCR-mediated activation of naive CD4+ T cells and decreased immune responses in CD4+ T cell-mediated experimental autoimmune encephalomyelitis. It is likely that iSP2 is a novel immunomodulatory tool that modulates STAP-2-mediated activation of TCR signaling and represses the progression of autoimmune diseases.

Possible Therapeutic Applications of Targeting STAP Proteins in Cancer

The signal-transducing adaptor protein (STAP) family, including STAP-1 and STAP-2, contributes to a variety of intracellular signaling pathways. The proteins in this family contain typical structures for adaptor proteins, such as Pleckstrin homology in the N-terminal regions and SRC homology 2 domains in the central regions. STAP proteins bind to inhibitor of kappaB kinase complex, breast tumor kinase, signal transducer and activator of transcription 3 (STAT3), and STAT5, during tumorigenesis and inflammatory/immune responses. STAP proteins positively or negatively regulate critical steps in intracellular signaling pathways through individually unique mechanisms. This article reviews the roles of the novel STAP family and the possible therapeutic applications of targeting STAP proteins in cancer.

Signal-transducing adaptor protein-1 and protein-2 in hematopoiesis and diseases

Inflammatory and immune signals are involved in stressed hematopoiesis under myeloablation, infection, chronic inflammation, and aging. These signals also affect malignant pathogenesis, and the dysregulated immune environment which causes the resistance to treatment. On activation, various types of protein tyrosine kinases in the cytoplasm mediate the cascade, leading to the transcription of target genes in the nucleus. Adaptor molecules are commonly defined as proteins that lack enzymatic activity, DNA-binding or receptor functions and possess protein-protein or protein-lipid interaction domains. By binding to specific domains of signaling molecules, adaptor proteins adjust the signaling responses after the ligation of receptors of soluble factors, including cytokines, chemokines, and growth factors, as well as pattern recognition receptors such as toll-like receptors. The signal-transducing adaptor protein (STAP) family regulates various intracellular signaling pathways. These proteins have a pleckstrin homology domain in the N-terminal region and an SRC-homology 2-like domain in the central region, representing typical binding structures as adapter proteins. Following the elucidation of the effects of STAPs on terminally differentiated immune cells, such as macrophages, T cells, mast cells, and basophils, recent findings have indicated the critical roles of STAP-2 in B-cell progenitor cells in marrow under hematopoietic stress and STAP-1 and -2 in BCR-ABL-transduced leukemogenesis. In this review, we focus on the role of STAPs in the bone marrow.

The Effects of Adoptively Transferred IL-23/IL-18-Polarized Neutrophils on Tumor and Collagen-Induced Arthritis in Mice

Background

Neutrophils present great diverse phenotypes in various microenvironments and play different immune regulatory functions. Neutrophils generally classified into inflammatory phenotype N1 and anti-informatory phenotype N2. Our recent studies showed that IL-23 alone stimulated neutrophils to express IL-17A, IL-17F and IL-22 and displayed a gene transcriptional profile similar to Th17 cells. In the present study, we tried to identify potential cytokines to promote IL-23-induced neutrophil polarization.

Methods

Mouse bone marrow-derived neutrophils and human peripheral blood neutrophils were treated with IL-23 (10 ng/mL) plus IL-18 (25 ng/mL) to induce Th17-like subset in vitro and detected by real-time PCR, flow cytometry, ELISA, immunofluorescence and RNA-seq assays. In vivo, collagen-induced arthritis (CIA) mouse model and EL4 tumor-bearing mouse model were used to characterize the potential roles of N(IL-23+IL-18) in inflammation and tumor.

Results

Real-time PCR, ELISA and flow cytometry assays showed that IL-18 could significantly enhance IL-23-induced IL-17A, IL-17F and IL-22 expressions in mouse and human neutrophils in a synergistic way, although IL-18 alone failed to induce these cytokines expression. RNA-seq and molecular studies showed that the polarization of N(IL-23+IL-18) is mainly mediated by the JNK/p38-STAT3-BATF signaling pathway. Adoptive transfer of the induced N(IL-23+IL-18) neutrophils significantly accelerated the tumor growth in EL4 tumor-bearing mice and enhanced disease progression in the CIA mouse model. IL-17A-deficient N(IL-23+IL-18) neutrophils failed to enhance the CIA pathogenesis in this model, suggesting that IL-17A may be involved in the N(IL-23+IL-18) neutrophils-promoted arthritis in mice.

Conclusion

The Th17-type subpopulation N(IL-23+IL-18) has pro-tumor and pro-inflammatory properties. Recognizing the different functional polarization of neutrophils would significantly help us to understand the distinctive protective/pathological roles of neutrophils in physiological and different pathological situations.

STAP-2 Adaptor Protein Regulates Multiple Steps of Immune and Inflammatory Responses

Signal-transducing adaptor protein (STAP)-2 is an adaptor molecule involved in regulation of several intracellular signaling events in immune cells. STAP-2 contains a pleckstrin homology domain at the N-terminus, an src homology domain in the central portion and a proline-rich region at the C-terminus. STAP-2 also has a YXXQ motif, which is a potential signal transducer and activator of transcription (STAT)3-binding site. STAP-2 influences the STAT3 and STAT5 activity, integrin-mediated T cell adhesion, chemokine-induced T cell migration, Fas-mediated T cell apoptosis, Toll-like receptor-mediated macrophage functions, macrophage colony-stimulating factor-induced macrophage activation, and the high-affinity immunoglobulin E receptor-mediated mast cell activation. This article reviews the current understanding of roles of the STAP-2 during immune and/or inflammatory responses, and discusses possible therapeutic applications of targeting STAP-2 proteins in immune-related disorders.