Rictor positively regulates B cell receptor signaling by modulating actin reorganization via ezrin

PGRN Inhibits Early B-cell Activation and IgE Production Through the IFITM3-STAT1 Signaling Pathway in Asthma

Progranulin (PGRN) plays a critical role in bronchial asthma and the function of various immune cells. However, the mechanisms by which PGRN influences B-cell receptor (BCR) signaling and immunoglobulin E(IgE) production are not fully understood. The study aimed to elucidate the molecular mechanisms through which PGRN affects BCR signaling, B-cell differentiation, and IgE production. A PGRN knockout mouse model, along with techniques including flow cytometry, the creation of a bone marrow chimeric mouse model, total internal reflection fluorescence (TIRF), and Western blot (WB) analysis is employed, to investigate the link between PGRN and various aspects of B-cell biology. It is discovered that the absence of PGRN in mice alters peripheral B-cell subpopulations, promotes IgE class switching in a cell-intrinsic manner, and affects B-cell subpopulations. Additionally, PGRN modulates B-cell functions by regulating BCR signaling pathways, metabolic processes, and the actin cytoskeleton during early B-cell activation. Significantly, PGRN deficiency results in diminished production of NP-specific antibodies. Moreover, it is found that PGRN inhibits B-cell activation and IgE production through the PGRN-IFITM3-STAT1 signaling pathway. The findings provide new strategies for the targeted treatment of bronchial asthma, highlighting the crucial role of PGRN in B-cell signaling and IgE production.

Profiling of differentially expressed circRNAs and functional prediction in peripheral blood mononuclear cells from patients with rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease associated with an increased risk of death, but its underlying mechanisms are not fully understood. Circular RNAs (circRNAs) have recently been implicated in various biological processes. The aim of this study was to investigate the key circRNAs related to RA.

METHODS

A microarray assay was used to identify the differentially expressed circRNAs (DEcircRNAs) in peripheral blood mononuclear cells (PBMCs) from patients with RA compared to patients with osteoarthritis (OA) and healthy controls. Then, quantitative real-time PCR was applied to verify the DEcircRNAs, and correlations between the levels of DEcircRNAs and laboratory indices were analysed. We also performed extensive bioinformatic analyses including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genome (KEGG) pathway and potential circRNA-miRNA-mRNA network analyses to predict the function of these DEcircRNAs.

RESULTS

A total of 35,342 and 6146 DEcircRNAs were detected in RA patients compared to controls and OA patients, respectively. Nine out of the DEcircRNAs in RA were validated by real-time PCR. There were correlations between the levels of DEcircRNAs and some of the laboratory indices. GO analyses revealed that these DEcircRNAs in RA were closely related to cellular protein metabolic processes, gene expression, the immune system, cell cycle, posttranslational protein modification and collagen formation. Functional annotation of host genes of these DEcircRNAs was implicated in several significantly enriched pathways, including metabolic pathways, ECM-receptor interaction, the PI3K-Akt signalling pathway, the AMPK signalling pathway, leukocyte transendothelial migration, platelet activation and the cAMP signalling pathway, which might be responsible for the pathophysiology of RA.

CONCLUSIONS

The findings of this study may help to elucidate the role of circRNAs in the specific mechanism underlying RA.Key messagesMicroarray assays showed that a total of 35,342 and 6146 DEcircRNAs were detected in RA patients compared to controls and OA patients, respectively.Nine out of the DEcircRNAs in RA were validated by real-time PCR, and the levels of the DEcircRNAs were related to some of the laboratory indices.GO analyses revealed that the DEcircRNAs in RA were closely related to cellular protein metabolic processes, gene expression, the immune system, etc.Functional annotation of host genes of the DEcircRNAs in RA was implicated in several significantly enriched pathways, including metabolic pathways, ECM-receptor interaction, the PI3K-Akt signalling pathway, etc.

Ultra-high static magnetic fields cause immunosuppression through disrupting B-cell peripheral differentiation and negatively regulating BCR signaling

To increase the imaging resolution and detection capability, the field strength of static magnetic fields (SMFs) in magnetic resonance imaging (MRI) has significantly increased in the past few decades. However, research on the side effects of high magnetic field is still very inadequate and the effects of SMF above 1 T (Tesla) on B cells have never been reported. Here, we show that 33.0 T ultra-high SMF exposure causes immunosuppression and disrupts B cell differentiation and signaling. 33.0 T SMF treatment resulted in disturbance of B cell peripheral differentiation and antibody secretion and reduced the expression of IgM on B cell membrane, and these might be intensity dependent. In addition, mice exposed to 33.0 T SMF showed inhibition on early activation of B cells, including B cell spreading, B cell receptor clustering and signalosome recruitment, and depression of both positive and negative molecules in the proximal BCR signaling, as well as impaired actin reorganization. Sequencing and gene enrichment analysis showed that SMF stimulation also affects splenic B cells' transcriptome and metabolic pathways. Therefore, in the clinical application of MRI, we should consider the influence of SMF on the immune system and choose the optimal intensity for treatment.

mTORC2 orchestrates monocytic and granulocytic lineage commitment by an ATF5-mediated pathway

Myeloid hematopoiesis is a finely controlled consecutive developmental process, which is essential to maintain peripheral innate immune homeostasis. Herein, we found that Rictor deletion caused the remarkable reduction of granulocyte-monocyte progenitors (GMPs), monocytes, and macrophages, while the levels of neutrophils were unaffected. Adoptive transfer of Rictor-deleted GMPs or common myeloid progenitors (CMPs) in syngeneic mice showed poor re-constitution of monocytes compared to wild-type GMPs or CMPs. In addition to decreasing the proliferation of CMPs/GMPs, Rictor deletion preferentially inhibited Ly6C+ monocyte differentiation, while enhancing neutrophil differentiation, as determined by colony formation assays. mTORC2 promotes monocyte development by downregulation of the AKT-Foxo4-activating transcription factor 5 (ATF5)-mitochondrial unfolded protein response (mtUPR) pathway. Genetic overexpression of ATF5 or exposure to ethidium bromide significantly rescued monocyte/macrophage differentiation defects of Rictor-deficient myeloid progenitors. Therefore, Rictor is required for CMP/GMP proliferation and acts as an important switch to balance monocytic and granulocytic lineage commitment in bone marrow.

MiR-155 enhances phagocytosis of alveolar macrophages through the mTORC2/RhoA pathway

Alveolar macrophage phagocytosis is significantly reduced in Chronic obstructive pulmonary disease, and cigarette smoke extract is one of the chief reasons for this decrease. Nevertheless, the specific underlying mechanism remains elusive. In this study, the role and possible mechanism of miR-155-5p/mTORC2/RhoA in the phagocytosis of mouse alveolar macrophages (MH-S) were explored. Our results revealed that cigarette smoke extract intervention reduced MH-S cell phagocytosis and miR-155-5p expression. Meanwhile, the dual-luciferase reporter assay validated that Rictor is a target of miR-155-5p. On the one hand, transfecting miR-155-5p mimic, mimic NC, miR-155-5p inhibitor, or inhibitor NC in MH-S cells overexpressing miR-155-5p increased the Alveolar macrophage phagocytotic rate, up-regulated the expression level of RhoA and p-RhoA, and down-regulated that of mTOR and Rictor mRNA and protein. On the other hand, inhibiting the expression of miR-155-5p lowered the phagocytotic rate, up-regulated the expression of mTOR, Rictor mRNA, and protein, and down-regulated the expression of RhoA and p-RhoA, which taken together, authenticated that miR-155-5p participates in macrophage phagocytosis via the mTORC2/RhoA pathway. Finally, confocal microscopy demonstrated that cells overexpressing miR-155-5p underwent cytoskeletal rearrangement during phagocytosis, and the phagocytic function of cells was enhanced, signaling that miR-155-5p participated in macrophage skeletal rearrangement and enhanced alveolar macrophage phagocytosis by targeting the expression of Rictor in the mTORC2/RhoA pathway.

GSDMA3 deficiency reprograms cellular metabolism and modulates BCR signaling in murine B cells

Metabolism plays a crucial role in B cell differentiation and function. GSDMA3 is related to mitochondrial metabolism and is involved in immune responses. Here, we used Gsdma3 KO mice to examine the effect of GSDMA3 on B cells. The results demonstrated that GSDMA3 deficiency reprogrammed B cell metabolism, evidenced by upregulating PI3K-Akt-mTOR signaling, along with elevated ROS reproduction and reduced maximal oxygen consumption rate in mitochondria. Moreover, the BCR signaling in the KO B cells was impaired. The reduced BCR signaling was associated with decreased BCR clustering, caused by inhibited activation of WASP. However, GSDMA3 deficiency had no effects on B cell development and functions in humoral immunity, which might be associated with the compensation of upregulated GSDMA2 expression and the fine balance between PI3K signaling and BCR signals interaction. Our observations reveal a previously unknown influence of GSDMA3 on B cells under physiological and immunized states.

The activation of gastric inhibitory peptide/gastric inhibitory peptide receptor axis via sonic hedgehog signaling promotes the bridging of gapped nerves in sciatic nerve injury

Schwann cells play an essential role in peripheral nerve regeneration by generating a favorable microenvironment. Gastric inhibitory peptide/gastric inhibitory peptide receptor (GIP/GIPR) axis deficiency leads to failure of sciatic nerve repair. However, the underlying mechanism remains elusive. In this study, we surprisingly found that GIP treatment significantly enhances the migration of Schwann cells and the formation of Schwann cell cords during recovery from sciatic nerve injury in rats. We further revealed that GIP and GIPR levels in Schwann cells were low under normal conditions, and significantly increased after injury demonstrated by real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Wound healing and Transwell assays showed that GIP stimulation and GIPR silencing could affect Schwann cell migration. In vitro and in vivo mechanistic studies based on interference experiment revealed that GIP/GIPR might promote mechanistic target of rapamycin complex 2 (mTORC2) activity, thus facilitating cell migration; Rap1 activation might be involved in this process. Finally, we retrieved the stimulatory factors responsible for GIPR induction after injury. The results indicate that sonic hedgehog (SHH) is a potential candidate whose expression increased upon injury. Luciferase and chromatin immunoprecipitation (ChIP) assays showed that Gli3, the target transcription factor of the SHH pathway, dramatically augmented GIPR expression. Additionally, in vivo inhibition of SHH could effectively reduce GIPR expression after sciatic nerve injury. Collectively, our study reveals the importance of GIP/GIPR signaling in Schwann cell migration, providing a therapeutic avenue toward peripheral nerve injury.

Analysis of the Role of N-Linked Glycosylation in Cell Surface Expression, Function, and Binding Properties of SARS-CoV-2 Receptor ACE2

Human angiotensin I-converting enzyme 2 (hACE2) is a type I transmembrane glycoprotein that serves as the major cell entry receptor for SARS-CoV and SARS-CoV-2. The viral spike (S) protein is required for the attachment to ACE2 and subsequent virus-host cell membrane fusion. Previous work has demonstrated the presence of N-linked glycans in ACE2. N-glycosylation is implicated in many biological activities, including protein folding, protein activity, and cell surface expression of biomolecules. However, the contribution of N-glycosylation to ACE2 function is poorly understood. Here, we examined the role of N-glycosylation in the activity and localization of two species with different susceptibility to SARS-CoV-2 infection, porcine ACE2 (pACE2) and hACE2. The elimination of N-glycosylation by tunicamycin (TM) treatment, or mutagenesis, showed that N-glycosylation is critical for the proper cell surface expression of ACE2 but not for its carboxiprotease activity. Furthermore, nonglycosylable ACE2 was localized predominantly in the endoplasmic reticulum (ER) and not at the cell surface. Our data also revealed that binding of SARS-CoV or SARS-CoV-2 S protein to porcine or human ACE2 was not affected by deglycosylation of ACE2 or S proteins, suggesting that N-glycosylation does not play a role in the interaction between SARS coronaviruses and the ACE2 receptor. Impairment of hACE2 N-glycosylation decreased cell-to-cell fusion mediated by SARS-CoV S protein but not that mediated by SARS-CoV-2 S protein. Finally, we found that hACE2 N-glycosylation is required for an efficient viral entry of SARS-CoV/SARS-CoV-2 S pseudotyped viruses, which may be the result of low cell surface expression of the deglycosylated ACE2 receptor. IMPORTANCE Understanding the role of glycosylation in the virus-receptor interaction is important for developing approaches that disrupt infection. In this study, we showed that deglycosylation of both ACE2 and S had a minimal effect on the spike-ACE2 interaction. In addition, we found that the removal of N-glycans of ACE2 impaired its ability to support an efficient transduction of SARS-CoV and SARS-CoV-2 S pseudotyped viruses. Our data suggest that the role of deglycosylation of ACE2 on reducing infection is likely due to a reduced expression of the viral receptor on the cell surface. These findings offer insight into the glycan structure and function of ACE2 and potentially suggest that future antiviral therapies against coronaviruses and other coronavirus-related illnesses involving inhibition of ACE2 recruitment to the cell membrane could be developed.

Diosmetin Induces Modulation of Igf-1 and Il-6 Levels to Alter Rictor-Akt-PKCα Cascade in Inhibition of Prostate Cancer

Growth signals, which typically originate from the surrounding microenvironment, are important for cells. However, when stimulation by growth factors becomes excessive and exceeds their threshold limit, deleterious effects may ensue. In patients with cancer, maintenance of tumors depends, at least in part, on growth factor stimulation, which can also facilitate cancer progression into advanced stages. This is particularly important when the tumor grows beyond its tissue boundaries or when it invades and colonizes other tissues. These aforementioned malignant events are known to be partly supported by elevated cytokine levels. Among the currently known growth signals, insulin-like growth factor (IGF)-1 and IL-6 have been previously studied for their roles in prostate cancer. Both IGF-1 and IL-6 have been reported to activate the RAPTOR independent companion of MTOR complex 2 (Rictor)/AKT/protein kinase C α (PKCα) signaling pathway as one of their downstream mechanisms. At present, research efforts are mainly focused on the exploration of agents that alter growth factor (such as IGF-1) and cytokine (such as IL-6) signaling for their potential application as therapeutic agents, as both of these have been reported to modulate disease outcome. In the present study, IGF-1 and IL-6 served distinct roles in the androgen responsive LNCaP cell line and in the androgen refractory PC-3 cell line in a dose- and time-dependent manner. Increased phosphorylation of Rictor at the Thr-1135 residue, AKT at the Ser-473 residue and PKCα at the Ser-657 residue were observed after treatment with IGF-1 and IL-6. Subsequently, it was found that diosmetin, a natural plant aglycone, had the potential to modulate the downstream signaling cascade of Rictor/AKT/PKCα to inhibit the progression of prostate cancer. Treatment of LNCaP and PC-3 cells with diosmetin inhibited the phosphorylation of Rictor (Thr-1135), AKT (Ser-473) and PKCα (Ser-657) in a dose-dependent manner. Furthermore, the Bax/Bcl-2 expression ratio was increased in response to diosmetin treatment, which would result in increased apoptosis. Based on these observations, diosmetin may represent a novel therapeutic target for prostate cancer.

CCL2 regulation of MST1-mTOR-STAT1 signaling axis controls BCR signaling and B-cell differentiation

Chemokines are important regulators of the immune system, inducing specific cellular responses by binding to receptors on immune cells. In SLE patients, decreased expression of CCL2 on mesenchymal stem cells (MSC) prevents inhibition of B-cell proliferation, causing the characteristic autoimmune phenotype. Nevertheless, the intrinsic role of CCL2 on B-cell autoimmunity is unknown. In this study using Ccl2 KO mice, we found that CCL2 deficiency enhanced BCR signaling by upregulating the phosphorylation of the MST1-mTORC1-STAT1 axis, which led to reduced marginal zone (MZ) B cells and increased germinal center (GC) B cells. The abnormal differentiation of MZ and GC B cells were rescued by in vivo inhibition of mTORC1. Additionally, the inhibition of MST1-mTORC1-STAT1 with specific inhibitors in vitro also rescued the BCR signaling upon antigenic stimulation. The deficiency of CCL2 also enhanced the early activation of B cells including B-cell spreading, clustering and signalosome recruitment by upregulating the DOCK8-WASP-actin axis. Our study has revealed the intrinsic role and underlying molecular mechanism of CCL2 in BCR signaling, B-cell differentiation, and humoral response.

Rictor/mTORC2 is involved in endometrial receptivity by regulating epithelial remodeling

Successful embryo implantation requires well-functioning endometrial luminal epithelial cells to establish uterine receptivity. Inadequate uterine receptivity is responsible for approximately two thirds of implantation failures in humans. However, the regulatory mechanism governing this functional process remains largely unexplored. A previous study revealed that the expression of Rictor, the main member of mTORC2, in mouse epithelial cells is increased on the fourth day of gestation (D4). Here, we provide the first report of the involvement of Rictor in the regulation of endometrial receptivity. Rictor was conditionally ablated in the mouse endometrium using a progesterone receptor cre (PRcre ) mouse model. Loss of Rictor altered polarity remodeling and the Na+ channel protein of endometrial cells by mediating Rac-1/PAK1(pPAK1)/ERM(pERM) and Sgk1/pSgk1 signaling, respectively, ultimately resulting in impaired fertility. In the endometrium of women with infertility, the expression of Rictor was changed, along with the morphological transformation and Na+ channel protein of epithelial cells. Our findings demonstrate that Rictor is crucial for the establishment of uterine receptivity in both mice and humans. The present study may help improve the molecular regulatory network of endometrial receptivity and provide new diagnostic and treatment strategies for infertility.

STAT3 couples with 14-3-3σ to regulate BCR signaling, B-cell differentiation, and IgE production

BACKGROUND

STAT3 or dedicator of cytokinesis protein 8 (Dock8) loss-of-function (LOF) mutations cause hyper-IgE syndrome. The role of abnormal T-cell function has been extensively investigated; however, the contribution of B-cell-intrinsic dysfunction to elevated IgE levels is unclear.

OBJECTIVE

We sought to determine the underlying molecular mechanism of how STAT3 regulates B-cell receptor (BCR) signaling, B-cell differentiation, and IgE production.

METHODS

We used samples from patients with STAT3 LOF mutation and samples from the STAT3 B-cell-specific knockout (KO) mice Mb1CreStat3flox/flox mice (B-STAT3 KO) to investigate the mechanism of hyper-IgE syndrome.

RESULTS

We found that the peripheral B-cell homeostasis in B-STAT3 KO mice mimicked the phenotype of patients with STAT3 LOF mutation, having decreased levels of follicular and germinal center B cells but increased levels of marginal zone and IgE+ B cells. Furthermore, B-STAT3 KO B cells had reduced BCR signaling following antigenic stimulation owing to reduced BCR clustering and decreased accumulation of Wiskott-Aldrich syndrome protein and F-actin. Excitingly, a central hub protein, 14-3-3σ, which is essential for the increase in IgE production, was enhanced in the B cells of B-STAT3 KO mice and patients with STAT3 LOF mutation. The increase of 14-3-3σ was associated with increased expression of the upstream mediator, microRNA146A. Inhibition of 14-3-3σ with R18 peptide in B-STAT3 KO mice rescued the BCR signaling, follicular, germinal center, and IgE+ B-cell differentiation to the degree seen in wild-type mice.

CONCLUSIONS

Altogether, our study has established a novel regulatory pathway of STAT3-miRNA146A-14-3-3σ to regulate BCR signaling, peripheral B-cell differentiation, and IgE production.

CX3CR1 positively regulates BCR signaling coupled with cell metabolism via negatively controlling actin remodeling

As an important chemokine receptor, the role of CX3CR1 has been studied extensively on the migration of lymphocytes including T and B cells. Although CX3CR1+ B cells have immune suppressor properties, little is known about its role on the regulation of BCR signaling and B cell differentiation as well as the underlying molecular mechanism. We have used CX3CR1 KO mice to study the effect of CX3CR1 deficiency on BCR signaling and B cell differentiation. Interestingly, we found that proximal BCR signaling, such as the activation of CD19, BTK and SHIP was reduced in CX3CR1 KO B cells upon antigenic stimulation. However, the activation of mTORC signaling was enhanced. Mechanistically, we found that the reduced BCR signaling in CX3CR1 KO B cells was due to reduced BCR clustering, which is caused by the enhanced actin accumulation by the plasma membrane via increased activation of WASP. This caused an increased differentiation of MZ B cells in CX3CR1 KO mice and an enhanced generation of plasma cells (PC) and antibodies. Our study shows that CX3CR1 regulates BCR signaling via actin remodeling and affects B cell differentiation and the humoral immune response.

PTH(1‑34) activates the migration and adhesion of BMSCs through the rictor/mTORC2 pathway

The ability of intermittent parathyroid hormone (1-34) [PTH(1-34)] treatment to enhance bone-implant osseo-integration was recently demonstrated in vivo. However, the mechanisms through which PTH (1-34) regulates bone marrow-derived stromal cells (BMSCs) remain unclear. The present study thus aimed to investigate the effects of PTH(1-34) on the migration and adhesion of, and rictor/mammalian target of rapamycin complex 2 (mTORC2) signaling in BMSCs. In the present study, BMSCs were isolated from Sprague-Dawley rats treated with various concentrations of PTH(1-34) for different periods of time. PTH(1-34) treatment was performed with or without an mTORC1 inhibitor (20 nM rapamycin) and mTORC1/2 inhibitor (10 µM PP242). Cell migration was assessed by Transwell cell migration assays and wound healing assays. Cell adhesion and related mRNA expression were investigated through adhesion assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively. The protein expression of chemokine receptors (CXCR4 and CCR2) and adhesion factors [intercellular adhesion molecule 1 (ICAM-1), fibronectin and integrin β1] was examined by western blot analysis. The results revealed that various concentrations (1, 10, 20, 50 and 100 nM) of PTH(1-34) significantly increased the migration and adhesion of BMSCs, as well as the expression of CXCR4, CCR2, ICAM-1, fibronectin and integrin β1. In addition, the p-Akt and p-S6 levels were also upregulated by PTH(1-34). BMSCs subjected to mTORC1/2 signaling pathway inhibition or rictor silencing exhibited a markedly reduced PTH-induced migration and adhesion, while no such effect was observed for the BMSCs subjected to mTORC1 pathway inhibition or raptor silencing. These results indicate that PTH(1-34) promotes BMSC migration and adhesion through rictor/mTORC2 signaling in vitro. Taken together, the results of the present study reveal an important mechanism for the therapeutic effects of PTH(1-34) on bone-implant osseointegration and suggest a potential treatment strategy based on the effect of PTH(1-34) on BMSCs.

Rictor promotes cell migration and actin polymerization through regulating ABLIM1 phosphorylation in Hepatocellular Carcinoma

As one of the most ominous malignancies, hepatocellular carcinoma (HCC) is frequently diagnosed at an advanced stage, owing to its aggressive invasion and metastatic spread. Emerging evidence has demonstrated that Rictor, as a unique component of the mTORC2, plays a role in cell migration, as it is dysregulated in various cancers, including HCC. However, the underlying molecular mechanism has not been well-characterized. Here, evaluation on a tissue-array panel and bioinformatics analysis revealed that Rictor is highly expressed in HCC tissues. Moreover, increased Rictor expression predicts poor survival of HCC patients. Rictor knockdown significantly suppressed cell migration and actin polymerization, thereby leading to decreased nuclear accumulation of MKL1 and subsequent inactivation of SRF/MKL1-dependent gene transcription, i.e. Arp3 and c-Fos. Mechanistically, we identified ABLIM1 as a previously unknown phosphorylation target of Rictor. Rictor interacts with ABLIM1 and regulates its serine phosphorylation in HCC cells. We generated ABLIM1 knockout cell lines of HCC, in which dominant negative mutations of Ser 214 and Ser 431 residues inhibited the ABLIM1-mediated actin polymerization and the MKL1 signaling pathway. Overall, ABLIM1 phosphorylation induced by Rictor plays an important role in controlling actin polymerization in HCC cells.

AKT2 deficiency impairs formation of the BCR signalosome

BACKGROUND

AKT2 is one of the key molecules that involves in the insulin-induced signaling and the development of cancer. In B cells, the function of AKT2 is unclear.

METHODS

In this study, we used AKT2 knockout mice model to study the role of AKT2 in BCR signaling and B cell differentiation.

RESULTS

AKT2 promotes the early activation of B cells by enhancing the BCR signaling and actin remodeling. B cells from AKT2 KO mice exhibited defective spreading and BCR clustering upon stimulation in vitro. Disruption of Btk-mediated signaling caused the impaired differentiation of germinal center B cells, and the serum levels of both sepecific IgM and IgG were decreased in the immunized AKT2 KO mice. In addition, the actin remodeling was affected due to the decreased level of the activation of WASP, the actin polymerization regulator, in AKT2 KO mice as well. As a crucial regulator of both BCR signaling and actin remodeling during early activation of B cells, the phosphorylation of CD19 was decreased in the AKT2 absent B cells, while the transcription level was normal.

CONCLUSIONS

AKT2 involves in the humoral responses, and promotes the BCR signaling and actin remodeling to enhance the activation of B cells via regulating CD19 phosphorylation. Video Abstract.

STING couples with PI3K to regulate actin reorganization during BCR activation

The adaptor protein, STING (stimulator of interferon genes), has been rarely studied in adaptive immunity. We used Sting KO mice and a patient's mutated STING cells to study the effect of STING deficiency on B cell development, differentiation, and BCR signaling. We found that STING deficiency promotes the differentiation of marginal zone B cells. STING is involved in BCR activation and negatively regulates the activation of CD19 and Btk but positively regulates the activation of SHIP. The activation of WASP and accumulation of F-actin were enhanced in Sting KO B cells upon BCR stimulation. Mechanistically, STING uses PI3K mediated by the CD19-Btk axis as a central hub for controlling the actin remodeling that, in turn, offers feedback to BCR signaling. Overall, our study provides a mechanism of how STING regulates BCR signaling via feedback from actin reorganization, which contributes to positive regulation of STING on the humoral immune response.

Methyltransferase Nsd2 Ensures Germinal Center Selection by Promoting Adhesive Interactions between B Cells and Follicular Dendritic Cells

Antibody affinity maturation, which is an antigen-based selection process for B cells, occurs in germinal centers (GCs). GCB cells must efficiently recognize, acquire, and present antigens from follicular dendritic cells (FDCs) to receive positive selection signals from T helper cells. Previous studies showed that GCB cells undergo adhesive interactions with FDCs, but the regulatory mechanisms underlying the cell adhesions and their functional relevance remain unclear. Here, we identified H3K36me2 methyltransferase Nsd2 as a critical regulator of GCB cell-FDC adhesion. Nsd2 deletion modestly reduced GC responses but strongly impaired B cell affinity maturation. Mechanistically, Nsd2 directly regulated expression of multiple actin polymerization-related genes in GCB cells. Nsd2 loss reduced B cell adhesion to FDC-expressed adhesion molecules, thus affecting both B cell receptor (BCR) signaling and antigen acquisition. Overall, Nsd2 coordinates GCB positive selection by enhancing both BCR signaling and T cell help.

Sin1-mediated mTOR signaling in cell growth, metabolism and immune response

The mammalian target of rapamycin (mTOR) is an evolutionarily conserved Ser/Thr protein kinase with essential cellular function via processing various extracellular and intracellular inputs. Two distinct multi-protein mTOR complexes (mTORC), mTORC1 and mTORC2, have been identified and well characterized in eukaryotic cells from yeast to human. Sin1, which stands for Sty1/Spc1-interacting protein1, also known as mitogen-activated protein kinase (MAPK) associated protein (MAPKAP)1, is an evolutionarily conserved adaptor protein. Mammalian Sin1 interacts with many cellular proteins, but it has been widely studied as an essential component of mTORC2, and it is crucial not only for the assembly of mTORC2 but also for the regulation of its substrate specificity. In this review, we summarize our current knowledge of the structure and functions of Sin1, focusing specifically on its protein interaction network and its roles in the mTOR pathway that could account for various cellular functions of mTOR in growth, metabolism, immunity and cancer.

Dedicator of cytokinesis protein 2 couples with lymphoid enhancer-binding factor 1 to regulate expression of CD21 and B-cell differentiation

BACKGROUND

B-cell receptor (BCR) signaling, combined with CD19 and CD21 signals, imparts specific control of B-cell responses. Dedicator of cytokinesis protein 2 (DOCK2) is critical for the migration and motility of lymphocytes. Although absence of DOCK2 leads to lymphopenia, little is known about the signaling mechanisms and physiologic functions of DOCK2 in B cells.

OBJECTIVE

We sought to determine the underlying molecular mechanism of how DOCK2 regulates BCR signaling and peripheral B-cell differentiation.

METHODS

In this study we used genetic models for DOCK2, Wiskott-Aldrich syndrome protein (WASP), and lymphoid enhancer-binding factor 1 deficiency to study their interplay in BCR signaling and B-cell differentiation.

RESULTS

We found that the absence of DOCK2 led to downregulation of proximal and distal BCR signaling molecules, including CD19, but upregulation of SH2-containing inositol 5 phosphatase 1, a negative signaling molecule. Interestingly, DOCK2 deficiency reduced CD19 and CD21 expression at the mRNA and/or protein levels and was associated with reduced numbers of marginal zone B cells. Additionally, loss of DOCK2 reduced activation of WASP and accelerated degradation of WASP, resulting into reduced actin accumulation and early activation of B cells. Mechanistically, the absence of DOCK2 upregulates the expression of lymphoid enhancer-binding factor 1. These differences were associated with altered humoral responses in the absence of DOCK2.

CONCLUSIONS

Overall, our study has provided a novel underlying molecular mechanism of how DOCK2 deficiency regulates surface expression of CD21, which leads to downregulation of CD19-mediated BCR signaling and marginal zone B-cell differentiation.

The "other" mTOR complex: New insights into mTORC2 immunobiology and their implications

A central role of the mechanistic target of rapamycin (mTOR) in regulation of fundamental cell processes is well recognized. mTOR functions in two distinct complexes: rapamycin-sensitive mTOR complex (C) 1 and rapamycin-insensitive mTORC2. While the role of mTORC1 in shaping immune responses, including transplant rejection, and the influence of its antagonism in promoting allograft tolerance have been studied extensively using rapamycin, lack of selective small molecule inhibitors has limited understanding of mTORC2 biology. Within the past few years, however, intracellular localization of mTORC2, its contribution to mitochondrial fitness, cell metabolism, cytoskeletal modeling and cell migration, and its role in differentiation and function of immune cells have been described. Studies in mTORC2 knockdown/knockout mouse models and a new class of dual mTORC1/2 inhibitors, have shed light on the immune regulatory functions of mTORC2. These include regulation of antigen-presenting cell, NK cell, T cell subset, and B cell differentiation and function. mTORC2 has been implicated in regulation of ischemia/reperfusion injury and graft rejection. Potential therapeutic benefits of antagonizing mTORC2 to inhibit chronic rejection have also been described, while selective in vivo targeting strategies using nanotechnology have been developed. We briefly review and discuss these developments and their implications.

Dock5 controls the peripheral B cell differentiation via regulating BCR signaling and actin reorganization

As an atypical guanine nucleotide exchange factor (GEF), Dock5 has been extensively studied in cellular functions. However, the role of Dock5 on B-cell immunity still remain elusive. In this study, we generated a Dock5 knockout mouse model to study the effect of Dock5 deficiency on B cell development, differentiation and BCR signaling. We found that the absence of Dock5 leads to a moderate effect on B cell development in the bone marrow and reduces follicular (FO) and marginal zone (MZ) B cells. Mechanistically, the key positive upstream B-cell receptor (BCR) signaling molecules, CD19 and Brutons tyrosine kinase (Btk), whose activation determines the fate of FO and MZ B cells, is reduced in Dock5 KO B cells upon antigenic stimulation by using total internal reflection fluorscence microscopy (TIRF) and immunoblot. Interestingly we found that the cellular filamentous actin (F-actin), also decreased in Dock5 KO B cells upon stimulation, which, in turn, offers feedback to BCR signaling. Our study has unveiled that Dock5 regulates the peripheral B cell differentiation via controlling the CD19-Btk signaling axis as well as actin reorganization.

The Coordination Between B Cell Receptor Signaling and the Actin Cytoskeleton During B Cell Activation

B-cell activation plays a crucial part in the immune system and is initiated via interaction between the B cell receptor (BCR) and specific antigens. In recent years with the help of modern imaging techniques, it was found that the cortical actin cytoskeleton changes dramatically during B-cell activation. In this review, we discuss how actin-cytoskeleton reorganization regulates BCR signaling in different stages of B-cell activation, specifically when stimulated by antigens, and also how this reorganization is mediated by BCR signaling molecules. Abnormal BCR signaling is associated with the progression of lymphoma and immunological diseases including autoimmune disorders, and recent studies have proved that impaired actin cytoskeleton can devastate the normal activation of B cells. Therefore, to figure out the coordination between the actin cytoskeleton and BCR signaling may reveal an underlying mechanism of B-cell activation, which has potential for new treatments for B-cell associated diseases.