The adapter 3BP2: how it plugs into leukocyte signaling

KIT mutations and expression: current knowledge and new insights for overcoming IM resistance in GIST

Gastrointestinal stromal tumor (GIST) is the most common sarcoma located in gastrointestinal tract and derived from the interstitial cell of Cajal (ICC) lineage. Both ICC and GIST cells highly rely on KIT signal pathway. Clinically, about 80-90% of treatment-naive GIST patients harbor primary KIT mutations, and special KIT-targeted TKI, imatinib (IM) showing dramatic efficacy but resistance invariably occur, 90% of them was due to the second resistance mutations emerging within the KIT gene. Although there are multiple variants of KIT mutant which did not show complete uniform biologic characteristics, most of them have high KIT expression level. Notably, the high expression level of KIT gene is not correlated to its gene amplification. Recently, accumulating evidences strongly indicated that the gene coding, epigenetic regulation, and pre- or post- protein translation of KIT mutants in GIST were quite different from that of wild type (WT) KIT. In this review, we elucidate the biologic mechanism of KIT variants and update the underlying mechanism of the expression of KIT gene, which are exclusively regulated in GIST, providing a promising yet evidence-based therapeutic landscape and possible target for the conquer of IM resistance. Video Abstract.

Scaffold protein SH3BP2 signalosome is pivotal for immune activation in nephrotic syndrome

Despite clinical use of immunosuppressive agents, the immunopathogenesis of minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) remains unclear. Src homology 3-binding protein 2 (SH3BP2), a scaffold protein, forms an immune signaling complex (signalosome) with 17 other proteins, including phospholipase Cγ2 (PLCγ2) and Rho-guanine nucleotide exchange factor VAV2 (VAV2). Bioinformatic analysis of human glomerular transcriptome (Nephrotic Syndrome Study Network cohort) revealed upregulated SH3BP2 in MCD and FSGS. The SH3BP2 signalosome score and downstream MyD88, TRIF, and NFATc1 were significantly upregulated in MCD and FSGS. Immune pathway activation scores for Toll-like receptors, cytokine-cytokine receptor, and NOD-like receptors were increased in FSGS. Lower SH3BP2 signalosome score was associated with MCD, higher estimated glomerular filtration rate, and remission. Further work using Sh3bp2KI/KI transgenic mice with a gain-in-function mutation showed ~6-fold and ~25-fold increases in albuminuria at 4 and 12 weeks, respectively. Decreased serum albumin and unchanged serum creatinine were observed at 12 weeks. Sh3bp2KI/KI kidney morphology appeared normal except for increased mesangial cellularity and patchy foot process fusion without electron-dense deposits. SH3BP2 co-immunoprecipitated with PLCγ2 and VAV2 in human podocytes, underscoring the importance of SH3BP2 in immune activation. SH3BP2 and its binding partners may determine the immune activation pathways resulting in podocyte injury leading to loss of the glomerular filtration barrier.

PARsylation-mediated ubiquitylation: lessons from rare hereditary disease Cherubism

Modification of proteins by ADP-ribose (PARsylation) is catalyzed by the poly(ADP-ribose) polymerase (PARP) family of enzymes exemplified by PARP1, which controls chromatin organization and DNA repair. Additionally, PARsylation induces ubiquitylation and proteasomal degradation of its substrates because PARsylation creates a recognition site for E3-ubiquitin ligase. The steady-state levels of the adaptor protein SH3-domain binding protein 2 (3BP2) is negatively regulated by tankyrase (PARP5), which coordinates ubiquitylation of 3BP2 by the E3-ligase ring finger protein 146 (RNF146). 3BP2 missense mutations uncouple 3BP2 from tankyrase-mediated negative regulation and cause Cherubism, an autosomal dominant autoinflammatory disorder associated with craniofacial dysmorphia. In this review, we summarize the diverse biological processes, including bone dynamics, metabolism, and Toll-like receptor (TLR) signaling controlled by tankyrase-mediated PARsylation of 3BP2, and highlight the therapeutic potential of this pathway.

Multiple versus solitary giant cell lesions of the jaw: Similar or distinct entities?

The majority of giant cell lesions of the jaw present as a solitary focus of disease in bones of the maxillofacial skeleton. Less frequently they occur as multifocal lesions. This raises the clinical dilemma if these should be considered distinct entities and therefore each need a specific therapeutic approach. Solitary giant cell lesions of the jaw present with a great diversity of symptoms. Recent molecular analysis revealed that these are associated with somatic gain-of-function mutations in KRAS, FGFR1 or TRPV4 in a large component of the mononuclear stromal cells which all act on the RAS/MAPK pathway. For multifocal lesions, a small group of neoplastic multifocal giant cell lesions of the jaw remain after ruling out hyperparathyroidism. Strikingly, most of these patients are diagnosed with jaw lesions before the age of 20 years, thus before the completion of dental and jaw development. These multifocal lesions are often accompanied by a diagnosis or strong clinical suspicion of a syndrome. Many of the frequently reported syndromes belong to the so-called RASopathies, with germline or mosaic mutations leading to downstream upregulation of the RAS/MAPK pathway. The other frequently reported syndrome is cherubism, with gain-of-function mutations in the SH3BP2 gene leading through assumed and unknown signaling to an autoinflammatory bone disorder with hyperactive osteoclasts and defective osteoblastogenesis. Based on this extensive literature review, a RAS/MAPK pathway activation is hypothesized in all giant cell lesions of the jaw. The different interaction between and contribution of deregulated signaling in individual cell lineages and crosstalk with other pathways among the different germline- and non-germline-based alterations causing giant cell lesions of the jaw can be explanatory for the characteristic clinical features. As such, this might also aid in the understanding of the age-dependent symptomatology of syndrome associated giant cell lesions of the jaw; hopefully guiding ideal timing when installing treatment strategies in the future.

Bayesian Hyper-LASSO Classification for Feature Selection with Application to Endometrial Cancer RNA-seq Data

Feature selection is demanded in many modern scientific research problems that use high-dimensional data. A typical example is to identify gene signatures that are related to a certain disease from high-dimensional gene expression data. The expression of genes may have grouping structures, for example, a group of co-regulated genes that have similar biological functions tend to have similar expressions. Thus it is preferable to take the grouping structure into consideration to select features. In this paper, we propose a Bayesian Robit regression method with Hyper-LASSO priors (shortened by BayesHL) for feature selection in high dimensional genomic data with grouping structure. The main features of BayesHL include that it discards more aggressively unrelated features than LASSO, and it makes feature selection within groups automatically without a pre-specified grouping structure. We apply BayesHL in gene expression analysis to identify subsets of genes that contribute to the 5-year survival outcome of endometrial cancer (EC) patients. Results show that BayesHL outperforms alternative methods (including LASSO, group LASSO, supervised group LASSO, penalized logistic regression, random forest, neural network, XGBoost and knockoff) in terms of predictive power, sparsity and the ability to uncover grouping structure, and provides insight into the mechanisms of multiple genetic pathways leading to differentiated EC survival outcome.

Timed Regulation of 3BP2 Induction Is Critical for Sustaining CD8+ T Cell Expansion and Differentiation

Successful anti-viral response requires the sustained activation and expansion of CD8⁺ T cells for periods that far exceed the time limit of physical T cell interaction with antigen-presenting cells (APCs). The expanding CD8⁺ T cell pool generates the effector and memory cell populations that provide viral clearance and long-term immunity, respectively. Here, we demonstrate that 3BP2 is recruited in cytoplasmic microclusters and nucleates a signaling complex that facilitates MHC:peptide-independent activation of signaling pathways downstream of the TCR. We show that induction of the adaptor molecule 3BP2 is a sensor of TCR signal strength and is critical for sustaining CD8⁺ T cell proliferation and regulating effector and memory differentiation.

Dimitriou et al. show that the adaptor protein 3BP2 lowers the threshold of T cell activation and that the induction of the 3BP2 signaling module at later time points may serve to recapitulate and prolong the biochemical signals emanating from the TCR required for sustained MHC:peptide-independent T cell proliferation.

A 5-gene prognostic nomogram predicting survival probability of glioblastoma patients

BACKGROUND

Glioblastoma (GBM) remains the most biologically aggressive subtype of gliomas with an average survival of 10 to 12 months. Considering that the overall survival (OS) of each GBM patient is a key factor in the treatment of individuals, it is meaningful to predict the survival probability for GBM patients newly diagnosed in clinical practice.

MATERIAL AND METHODS

Using the TCGA dataset and two independent GEO datasets, we identified genes that are associated with the OS and differentially expressed between GBM tissues and the adjacent normal tissues. A robust likelihood-based survival modeling approach was applied to select the best genes for modeling. After the prognostic nomogram was generated, an independent dataset on different platform was used to evaluate its effectiveness.

RESULTS

We identified 168 differentially expressed genes associated with the OS. Five of these genes were selected to generate a gene prognostic nomogram. The external validation demonstrated that 5-gene prognostic nomogram has the capability of predicting the OS of GBM patients.

CONCLUSION

We developed a novel and convenient prognostic tool based on five genes that exhibited clinical value in predicting the survival probability for newly diagnosed GBM patients, and all of these five genes could represent potential target genes for the treatment of GBM. The development of this model will provide a good reference for cancer researchers.

Optimizing intracellular signaling domains for CAR NK cells in HIV immunotherapy: a comprehensive review

Natural killer (NK) cells are innate immune lymphocytes with a key role in host defense against HIV infection. Recent advances in chimeric antigen receptors (CARs) have made NK cells a prime target for expressing recombinant receptors capable of redirecting NK cytotoxic functions towards HIV-infected cells. In this review, we discuss the role of NK cells in HIV and the mechanisms of actions of HIV-targeting CAR strategies. Furthermore, we also review NK cells signal transduction and its application to CAR NK cell strategies to develop new combinations of CAR intracellular domains and to improve CAR NK signaling and cytotoxic functions.

Molecular and cellular characterizations of human cherubism: disease aggressiveness depends on osteoclast differentiation

Background

Cherubism is a rare autosomal dominant disorder of the jaws caused by mutation of the SH3BP2 gene. The bone is replaced by a fibrous granuloma containing multinucleated giant cells. Cells of the cherubism granuloma have never been systematically analyzed. Hence, the aim of this study was to characterize the cells in human cherubism granulomas, to determine the osteoclastic characteristics of the multinucleated giant cells and to investigate the potential role of TNF-α in human cherubism.

Results

Seven granulomas were analyzed in pathology, molecular biology and immunohistochemistry. Granulomas were composed mainly of macrophages or osteoclasts within a fibroblastic tissue, with few lymphoid cells. Myeloid differentiation and nuclear NFATc1 localization were both associated with disease aggressiveness. OPG and RANKL immunohistochemical expression was unexpected in our specimens. Five granuloma cells were cultured in standard and osteoclastogenic media. In culture, cherubism cells were able to differentiate into active osteoclasts, in both osteoclastogenic and standard media. IL-6 was the major cytokine present in the culture supernatants.

Conclusion

Multinucleated giant cells from cherubism granulomas are CD68 positive cells, which differentiate into macrophages in non-aggressive cherubism and into osteoclasts in aggressive cherubism, stimulated by the NFATc1 pathway. This latter differentiation appears to involve a disturbed RANK-L/RANK/OPG pathway and be less TNF-α dependent than the cherubism mouse model.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0907-2) contains supplementary material, which is available to authorized users.

Application of whole genome and RNA sequencing to investigate the genomic landscape of common variable immunodeficiency disorders

Common Variable Immunodeficiency Disorders (CVIDs) are the most prevalent cause of primary antibody failure. CVIDs are highly variable and a genetic causes have been identified in <5% of patients. Here, we performed whole genome sequencing (WGS) of 34 CVID patients (94% sporadic) and combined them with transcriptomic profiling (RNA-sequencing of B cells) from three patients and three healthy controls. We identified variants in CVID disease genes TNFRSF13B, TNFRSF13C, LRBA and NLRP12 and enrichment of variants in known and novel disease pathways. The pathways identified include B-cell receptor signalling, non-homologous end-joining, regulation of apoptosis, T cell regulation and ICOS signalling. Our data confirm the polygenic nature of CVID and suggest individual-specific aetiologies in many cases. Together our data show that WGS in combination with RNA-sequencing allows for a better understanding of CVIDs and the identification of novel disease associated pathways.

The adaptor 3BP2 is required for KIT receptor expression and human mast cell survival

SH3-binding protein 2 (3BP2) is a cytoplasmic adaptor protein that acts as a positive regulator in mast cell FcεRI-dependent signaling. The KIT receptor whose ligand is the stem cell factor is necessary for mast cell development, proliferation, and survival as well as for optimal IgE-dependent signal. Activating mutations in KIT have been associated with several diseases including mastocytosis. In the present work, we found that 3BP2 silencing impairs KIT signaling pathways, thus affecting phosphoinositide 3-kinase and MAPK pathways in human mast cells (huMCs) from HMC-1, LAD2 (huMC lines), and CD34(+)-derived mast cells. Unexpectedly, silencing of 3BP2 reduces KIT expression in normal huMCs as well as in HMC-1 cells where KIT is mutated, thus increasing cellular apoptosis and caspase-3/7 activity. 3BP2 silencing reduces KIT transcription expression levels. Interestingly, 3BP2 silencing decreased microphthalmia-associated transcription factor (MITF) expression, a transcription factor involved in KIT expression. Reconstitution of 3BP2 in knockdown cells leads to reversal of KIT expression as well as survival phenotype. Accordingly MITF reconstitution enhances KIT expression levels in 3BP2-silenced cells. Moreover, downregulation of KIT expression by miRNA-221 overexpression or the proteasome inhibitor bortezomib also reduced 3BP2 and MITF expression. Furthermore, KIT tyrosine activity inhibition reduced 3BP2 and MITF expression, demonstrating again a tight and reciprocal relationship between these molecules. Taken together, our results show that 3BP2 regulates huMC survival and participates in KIT-mediated signal transduction by directly controlling KIT receptor expression, suggesting its potential as a therapeutic target in mast cell-mediated inflammatory diseases and deregulated KIT disorders.

Cherubism allele heterozygosity amplifies microbe-induced inflammatory responses in murine macrophages

Cherubism is a rare autoinflammatory bone disorder that is associated with point mutations in the SH3-domain binding protein 2 (SH3BP2) gene, which encodes the adapter protein 3BP2. Individuals with cherubism present with symmetrical fibro-osseous lesions of the jaw, which are attributed to exacerbated osteoclast activation and defective osteoblast differentiation. Although it is a dominant trait in humans, cherubism appears to be recessively transmitted in mice, suggesting the existence of additional factors in the pathogenesis of cherubism. Here, we report that macrophages from 3BP2-deficient mice exhibited dramatically reduced inflammatory responses to microbial challenge and reduced phagocytosis. 3BP2 was necessary for LPS-induced activation of signaling pathways involved in macrophage function, including SRC, VAV1, p38MAPK, IKKα/β, RAC, and actin polymerization pathways. Conversely, we demonstrated that the presence of a single Sh3bp2 cherubic allele and pathogen-associated molecular pattern (PAMP) stimulation had a strong cooperative effect on macrophage activation and inflammatory responses in mice. Together, the results from our study in murine genetic models support the notion that infection may represent a driver event in the etiology of cherubism in humans and suggest limiting inflammation in affected individuals may reduce manifestation of cherubic lesions.

Body mass index is associated with gene methylation in estrogen receptor-positive breast tumors

BACKGROUND

Although obesity is associated with breast cancer incidence and prognosis, the underlying mechanisms are poorly understood. Identification of obesity-associated epigenetic changes in breast tissue may advance mechanistic understanding of breast cancer initiation and progression. The goal of this study, therefore, was to investigate associations between obesity and gene methylation in breast tumors.

METHODS

Using the Illumina GoldenGate Cancer I Panel, we estimated the association between body mass index (BMI) and gene methylation in 345 breast tumor samples from phase I of the Carolina Breast Cancer Study, a population-based case-control study. Multivariable linear regression was used to identify sites that were differentially methylated by BMI. Stratification by tumor estrogen receptor (ER) status was also conducted.

RESULTS

In the majority of the 935 probes analyzed (87%), the average beta value increased with obesity (BMI ≥ 30). Obesity was significantly associated with differential methylation (FDR q < 0.05) in just two gene loci in breast tumor tissue overall and in 21 loci among ER-positive tumors. Obesity was associated with methylation of genes that function in immune response, cell growth, and DNA repair.

CONCLUSIONS

Obesity is associated with altered methylation overall, and with hypermethylation among ER-positive tumors in particular, suggesting that obesity may influence the methylation of genes with known relevance to cancer. Some of these differences in methylation by obese status may influence levels of gene expression within breast cells.

IMPACT

If our results are validated, obesity-associated methylation sites could serve as targets for prevention and treatment research. Cancer Epidemiol Biomarkers Prev; 24(3); 580-6. ©2015 AACR.

The adaptor 3BP2 is required for early and late events in FcεRI signaling in human mast cells

Adaptor molecules are essential in organizing signaling molecules and in coordinating and compartmentalizing their activity. SH3-binding protein 2 (3BP2) is a cytoplasmic adaptor protein mainly expressed by hematopoietic cells that has been shown to act as a positive regulator in T, B, and NK cell signal transduction. 3BP2 is an important regulator of cytotoxic granule release in NK cells. Mast cells (MCs) similarly degranulate following Ag-dependent aggregation of the FcεRI on the cell surface. Activation of these cells induces the release of preformed inflammatory mediators and the de novo synthesis and secretion of cytokines and chemokines. Thus, MCs participate in both innate and acquired responses. We observed that 3BP2 is expressed in human MCs (huMCs) from diverse origins. Moreover, 3BP2 coimmunoprecipitates with essential MC signaling mediators such as Lyn, Syk, and phospholipase C γ; thus, a role for this adaptor in MC function was postulated. In the present work, we used the short hairpin RNA lentiviral targeting approach to silence 3BP2 expression in huMCs. Our findings point to a requirement for 3BP2 in optimal immediate and late MCs responses such as degranulation and IL-8 or GM-CSF secretion. 3BP2 was determined to be necessary for optimal phosphorylation of Syk, linker for activation of T cells, and phospholipase C γ(1), critical signals for calcium release from intracellular stores. Taken together, our results show that by participating in FcεRI- mediated signal transduction 3BP2 is an important regulator of huMC activation. Thus, 3BP2 could be a potential therapeutic target for IgE-dependent MC-mediated inflammatory disease.

The role of SH3BP2 in the pathophysiology of cherubism

Cherubism is a rare bone dysplasia that is characterized by symmetrical bone resorption limited to the jaws. Bone lesions are filled with soft fibrous giant cell-rich tissue that can expand and cause severe facial deformity. The disorder typically begins in children at ages of 2-5 years and the bone resorption and facial swelling continues until puberty; in most cases the lesions regress spontaneously thereafter. Most patients with cherubism have germline mutations in the gene encoding SH3BP2, an adapter protein involved in adaptive and innate immune response signaling. A mouse model carrying a Pro416Arg mutation in SH3BP2 develops osteopenia and expansile lytic lesions in bone and some soft tissue organs. In this review we discuss the genetics of cherubism, the biological functions of SH3BP2 and the analysis of the mouse model. The data suggest that the underlying cause for cherubism is a systemic autoinflammatory response to physiologic challenges despite the localized appearance of bone resorption and fibrous expansion to the jaws in humans.

Loss of Tankyrase-mediated destruction of 3BP2 is the underlying pathogenic mechanism of cherubism

Cherubism is an autosomal-dominant syndrome characterized by inflammatory destructive bony lesions resulting in symmetrical deformities of the facial bones. Cherubism is caused by mutations in Sh3bp2, the gene that encodes the adaptor protein 3BP2. Most identified mutations in 3BP2 lie within the peptide sequence RSPPDG. A mouse model of cherubism develops hyperactive bone-remodeling osteoclasts and systemic inflammation characterized by expansion of the myelomonocytic lineage. The mechanism by which cherubism mutations alter 3BP2 function has remained obscure. Here we show that Tankyrase, a member of the poly(ADP-ribose)polymerase (PARP) family, regulates 3BP2 stability through ADP-ribosylation and subsequent ubiquitylation by the E3-ubiquitin ligase RNF146 in osteoclasts. Cherubism mutations uncouple 3BP2 from Tankyrase-mediated protein destruction, which results in its stabilization and subsequent hyperactivation of the SRC, SYK, and VAV signaling pathways.

Decreased SH3BP2 inhibits osteoclast differentiation and function

Germline mutations in SH3BP2 gene have been identified in patients with cherubism, a skeletal disorder characterized by excessive osteoclastic bone resorption that is limited to the mandible and maxilla. We previously demonstrated that SH3BP2 overexpression in Raw264.7 cells increased RANKL-induced osteoclastogenesis. Here, we examine the effect of decreased SH3BP2 on osteoclastogenesis. shRNA knockdown of SH3BP2 decreased PLCγ2 phosphorylation and NFATc1 expression, and reduced the expression of osteoclast-specific genes. In BMMs knockdown of SH3BP2 led to reductions in both the number and the surface area of TRAP positive and multinucleated osteoclasts. Bone resorptive activity was also dramatically blocked by shRNA knockdown of SH3BP2. Similarly Sh3bp2(-/-) deficient mice BMMs formed smaller osteoclasts that stained less with TRAP than wild-type mice. Taken together, this study demonstrates that SH3BP2 knockdown significantly decreases osteoclast differentiation and function. These results suggest that SH3BP2 plays a critical role in osteoclastogenesis and is a potential target for suppression of pathologic bone resorption.

Enhancement of B-cell receptor signaling by a point mutation of adaptor protein 3BP2 identified in human inherited disease cherubism

Tyrosine phosphorylation of adaptor protein c-Abl-Src homology 3 (SH3) domain-binding protein-2 (3BP2, also referred to SH3BP2) positively regulates the B-cell antigen receptor (BCR)-mediated signal transduction, leading to the activation of nuclear factor of activated T cells (NFAT). Here we showed the effect of the proline to arginine substitution of 3BP2 in which is the most common mutation in patients with cherubism (P418R) on B-cell receptor signaling. Comparing to the wild type, overexpression of the mutant form of 3BP2 (3BP2-P416R, corresponding to P418R in human protein) enhanced BCR-mediated activation of NFAT. 3BP2-P416R increased the signaling complex formation with Syk, phospholipase C-γ2 (PLC-γ2), and Vav1. In contrast, 3BP2-P416R could not change the association with the negative regulator 14-3-3. Loss of the association mutant that was incapable to associate with 14-3-3 could not mimic BCR-mediated NFAT activation in Syk-deficient cells. Moreover, BCR-mediated phosphorylation of extracellular signal regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was not affected by P416R mutation. These results showed that P416R mutation of 3BP2 causes the gain of function in B cells by increasing the interaction with specific signaling molecules.

3BP2-deficient mice are osteoporotic with impaired osteoblast and osteoclast functions

A fine balance between bone resorption by osteoclasts and bone formation by osteoblasts maintains bone homeostasis. In patients with cherubism, gain-of-function mutations in 3BP2, which is encoded by SH3-domain binding protein 2 (SH3BP2), cause cystic lesions with activated osteoclasts that lead to craniofacial abnormalities. However, little is known about the function of wild-type 3BP2 in regulating bone homeostasis. Here we have shown that 3BP2 is required for the normal function of both osteoblasts and osteoclasts. Initial analysis showed that Sh3bp2-/-mice developed osteoporosis as a result of reduced bone formation despite the fact that bone resorption was impaired. We demonstrated using reciprocal bone marrow chimeras, a cell-intrinsic defect of the osteoblast and osteoclast compartments in vivo. Further, Sh3bp2-/- osteoblasts failed to mature and form mineralized nodules in vitro, while Sh3bp2-/- osteoclasts spread poorly and were unable to effectively degrade dentine matrix in vitro. Finally, we showed that 3BP2 was required for Abl activation in osteoblasts and Src activation in osteoclasts, and demonstrated that the in vitro defect of each cell type was restored by the respective expression of activated forms of these kinases. These findings reveal an unanticipated role for the 3BP2 adapter protein in osteoblast function and in coordinating bone homeostatic signals in both osteoclast and osteoblast lineages.

Cherubism gene Sh3bp2 is important for optimal bone formation, osteoblast differentiation, and function

INTRODUCTION

Cherubism is a human genetic disorder that causes bilateral symmetrical enlargement of the maxilla and the mandible in children. It is caused by mutations in SH3BP2. The exact pathogenesis of the disorder is an area of active research. Sh3bp2 knock-in mice were developed by introducing a Pro416Arg mutation (Pro418Arg in humans) in the mouse genome. The osteoclast phenotype of this mouse model was recently described.

METHODS

We examined the bone phenotype of the cherubism mouse model, the role of Sh3bp2 during bone formation, osteoblast differentiation, and osteoblast function.

RESULTS

We observed delays in early postnatal development of homozygous Sh3bp2(KI/KI) mice, which exhibited increased growth plate thickness and significantly decreased trabecular bone thickness and bone mineral density. Histomorphometric and microcomputed tomography analyses showed bone loss in the cranial and appendicular skeletons. Sh3bp2(KI/KI) mice also exhibited a significant decrease in osteoid formation that indicated a defect in osteoblast function. Calvarial osteoblast cell cultures had decreased alkaline phosphatase expression and mineralization, suggesting reduced differentiation potential. Gene expression of osteoblast differentiation markers such as collagen type I, alkaline phosphatase, and osteocalcin were decreased in osteoblast cultures from Sh3bp2(KI/KI) mice.

CONCLUSIONS

These data suggest that Sh3bp2 regulates bone homeostasis through not only osteoclast-specific effects, but also through effects on osteoblast differentiation and function.

3BP2 adapter protein is required for receptor activator of NFκB ligand (RANKL)-induced osteoclast differentiation of RAW264.7 cells

The adapter protein 3BP2 (also known as SH3BP2 and Abl SH3-binding protein 2) has been involved in leukocyte signaling and activation downstream immunoreceptors. Genetic studies have further associated 3BP2 mutations to the human disease cherubism and to inflammation and bone dysfunction in mouse. However, how wild type 3BP2 functions in macrophage differentiation remains poorly understood. In this study, using small interfering RNA-mediated silencing of 3BP2 in the RAW264.7 monocytic cell line, we show that 3BP2 was required for receptor activator of NFkappaB ligand (RANKL)-induced differentiation of RAW264.7 cells into multinucleated mature osteoclasts but not for granulocyte macrophage-colony stimulating factor/interleukin-4-induced differentiation into dendritic cells. 3BP2 silencing was associated with impaired activation of multiple signaling events downstream of RANK, including actin reorganization; Src, ERK, and JNK phosphorylation; and up-regulation of osteoclastogenic factors. In addition, 3BP2 knockdown cells induced to osteoclast by RANKL displayed a reduced increase of Src and nuclear factor of activated T cells (NFATc1) mRNA and protein expression. Importantly, 3BP2 interacted with Src, Syk, Vav, and Cbl in monocytic cells, and the introduction of constitutively active mutants of Src and NFATc1 in 3BP2-deficient cells restored osteoclast differentiation. Finally, the expression of a 3BP2 cherubism mutant was found to promote increased Src activity and NFAT-dependent osteoclast formation. Together, this study demonstrates that wild type 3BP2 is a key regulator of RANK-mediated macrophage differentiation into osteoclast through Src and NFATc1 activation.

Tyrosine phosphorylation of 3BP2 regulates B cell receptor-mediated activation of NFAT

Adaptor protein c-Abl SH3 domain-binding protein-2 (3BP2, also referred to SH3BP2) regulates immune receptor-mediated signal transduction. In this report we focused on the molecular mechanism of 3BP2 function in B cell receptor (BCR) signaling. Engagement of BCR induces tyrosine phosphorylation of 3BP2. Genetic analysis demonstrated that Syk is critical for BCR-mediated tyrosine phosphorylation of 3BP2. Mutational analysis of 3BP2 revealed that both Tyr(183) and Src homology 2 (SH2) domain are necessary for 3BP2-mediated BCR-induced activation of nuclear factor of activated T cells (NFAT). Point mutation of Tyr(183) or Arg(486) in the SH2 domain of 3BP2 diminished BCR-mediated tyrosine phosphorylation of 3BP2. Endogenous 3BP2 forms a complex with tyrosine-phosphorylated cellular signaling molecules. Peptide binding experiments demonstrated that only phosphorylated Tyr(183) in 3BP2 could form a complex with the SH2 domain(s) of phospholipase Cgamma2 and Vav1 from B cell lysates. These interactions were represented by using bacterial glutathione S-transferase-phospholipase Cgamma2 or -Vav1 SH2 domain. Furthermore, pulldown and Far Western experiments showed that the 3BP2-SH2 domain directly binds to B cell linker protein (BLNK) after BCR stimulation. These results demonstrated that 3BP2 induces the protein complex with cellular signaling molecules through phosphorylation of Tyr(183) and SH2 domain leading to the activation of NFAT in B cells.