The effects of c-Abl mutation on developing B cell differentiation and survival

c-Abl controls BCR signaling and B cell differentiation by promoting B cell metabolism

As a non-receptor tyrosine kinase, c-Abl was first studied in chronic myelogenous leukemia, and its role in lymphocytes has been well characterized. c-Abl is involved in B cell development and CD19 associated B cell antigen receptor (BCR) signaling. Although c-Abl regulates different metabolic pathways, the role of c-Abl is still unknown in B cell metabolism. In this study, B cell specific c-Abl knockout (KO) mice (Mb1^Cre+/- c-Abl^fl/fl ) were used to investigate how c-Abl regulates B cell metabolism and BCR signaling. We found that the levels of activation positive BCR signaling proximal molecules, phosphorylated spleen tyrosine kinase (pSYK) and phosphorylated Bruton tyrosine kinase (pBTK), were decreased, while the level of key negative regulator, phosphorylated SH2-containing inositol phosphatase (pSHIP1), was increased in Mb1^Cre+/- c-Abl^fl/fl mice. Furthermore, we found c-Abl deficiency weakened the B cell spreading, formation of BCR signalosomes, and the polymerization of actin during BCR activation, and also impaired the differentiation of germinal center (GC) B cells both in quiescent condition and after immunization. Moreover, B cell mitochondrial respiration and the expression of B cell metabolism regulating molecules were downregulated in c-Abl deficiency mice. Overall, c-Abl, which involved in actin remodeling and B cell metabolism, positively regulates BCR signaling and promotes GC differentiation. This article is protected by copyright. All rights reserved.

Interferon-γ regulates cell malignant growth via the c-Abl/HDAC2 signaling pathway in mammary epithelial cells

Interferon-γ (IFN-γ) has been used to control cancers in clinical treatment. However, an increasing number of reports have suggested that in some cases effectiveness declines after a long treatment period, the reason being unclear. We have reported previously that long-term IFN-γ treatment induces malignant transformation of healthy lactating bovine mammary epithelial cells (BMECs) in vitro. In this study, we investigated the mechanisms underlying the malignant proliferation of BMECs under IFN-γ treatment. The primary BMECs used in this study were stimulated by IFN-γ (10 ng/mL) for a long term to promote malignancy. We observed that IFN-γ could promote malignant cell proliferation, increase the expression of cyclin D1/cyclin-dependent kinase 4 (CDK4), decrease the expression of p21, and upregulate the expression of cellular-abelsongene (c-Abl) and histone deacetylase 2 (HDAC2). The HDAC2 inhibitor, valproate (VPA) and the c-Abl inhibitor, imatinib, lowered the expression level of cyclin D1/CDK4, and increased the expression level of p21, leading to an inhibitory effect on IFN-γ-induced malignant cell growth. When c-Abl was downregulated, the HDAC2 level was also decreased by promoted proteasome degradation. These data suggest that IFN-γ promotes the growth of malignant BMECs through the c-Abl/HDAC2 signaling pathway. Our findings suggest that long-term application of IFN-γ may be closely associated with the promotion of cell growth and even the carcinogenesis of breast cancer.

Tyrosine kinase c-Abl regulates the survival of plasma cells

Tyrosine kinase c-Abl plays an important role in early B cell development. Its deletion leads to reduced pro- and pre-B cell generation in mice. However, its function in B cell terminal differentiation remains unexplored. Here, we used c-Abl^f/f Aicda^cre/+ mice, in which c-Abl is ablated only in antigen-activated B cells, to study the role of c-Abl in germinal center (GC) B and antibody-secreting plasma cell formation. Upon challenge with a model antigen, we found normal GC and memory B but reduced plasma cells and antigen-specific antibody response in the mutant mice. In-vitro studies revealed that plasma cells lacking c-Abl could be generated but did not accumulate in culture, indicative of survival defect. They also exhibited impaired STAT3 phosphorylation. The plasma cell defects could be rectified by introduction of Bim-deficiency or delivery of colivelin, a STAT3 activator, into c-Abl^f/f Aicda^cre/+ mice. Hence, c-Abl signalling regulates the survival of plasma cells.

Arg Deficiency Does not Influence the Course of Myelin Oligodendrocyte Glycoprotein (MOG35-55)-induced Experimental Autoimmune Encephalomyelitis

Background

Inhibition of Abl kinases has an ameliorating effect on the rodent model for multiple sclerosis, experimental autoimmune encephalomyelitis, and arrests lymphocyte activation. The family of Abl kinases consists of the Abl1/Abl and Abl2/Arg tyrosine kinases. While the Abl kinase has been extensively studied in immune activation, roles for Arg are incompletely characterized. To investigate the role for Arg in experimental autoimmune encephalomyelitis, we studied disease development in Arg^-/- mice.

Methods

Arg^-/- and Arg^+/+ mice were generated from breeding of Arg^+/- mice on the C57BL/6 background. Mice were immunized with the myelin oligodendrocyte glycoprotein (MOG)35-55 peptide and disease development recorded. Lymphocyte phenotypes of wild type Arg^+/+ and Arg^-/- mice were studied by in vitro stimulation assays and flow cytometry.

Results

The breeding of Arg^+/+ and Arg^-/- mice showed skewing in the frequency of born Arg^-/- mice. Loss of Arg function did not affect development of experimental autoimmune encephalomyelitis, but reduced the number of splenic B-cells in Arg^-/- mice following immunization with MOG peptide.

Conclusions

Development of MOG-induced experimental autoimmune encephalomyelitis is not dependent on Arg, but Arg plays a role for the number of B cells in immunized mice. This might suggest a novel role for the Arg kinase in B-cell trafficking or regulation. Furthermore, the results suggest that Arg is important for normal embryonic development.

Critical role of actin-associated proteins in smooth muscle contraction, cell proliferation, airway hyperresponsiveness and airway remodeling

Asthma is characterized by airway hyperresponsiveness and airway remodeling, which are largely attributed to increased airway smooth muscle contractility and cell proliferation. It is known that both chemical and mechanical stimulation regulates smooth muscle contraction. Recent studies suggest that contractile activation and mechanical stretch induce actin cytoskeletal remodeling in smooth muscle. However, the mechanisms that control actin cytoskeletal reorganization are not completely elucidated. This review summarizes our current understanding regarding how actin-associated proteins may regulate remodeling of the actin cytoskeleton in airway smooth muscle. In particular, there is accumulating evidence to suggest that Abelson tyrosine kinase (Abl) plays a critical role in regulating airway smooth muscle contraction and cell proliferation in vitro, and airway hyperresponsiveness and remodeling in vivo. These studies indicate that Abl may be a novel target for the development of new therapy to treat asthma.

Avian influenza viruses inhibit the major cellular signalling integrator c-Abl

The non-structural protein 1 (NS1) of influenza A viruses (IAV) encodes several src homology (SH) binding motifs (bm) (one SH2bm, up to two SH3bm), which mediate interactions with host cell proteins. In contrast to NS1 of human IAV, NS1 of avian strains possess the second SH3bm (SH3(II)bm) consensus sequence. Since our former studies demonstrated an NS1-CRK interaction, mediated by this motif, here, we addressed the regulatory properties of this SH3bm for cellular signalling. Initially, we observed a reduced basal CRK phosphorylation upon infection with avian IAV harbouring an NS1 with an SH3(II)bm in contrast to human IAV. Reduced activity of the tyrosine kinase c-Abl was identified to be responsible for reduced CRK phosphorylation. Further, binding of NS1 to c-Abl was determined, and mutational manipulation of the SH3(II)bm illustrated the necessity of this motif for c-Abl inhibition. Interestingly, Abl kinase inhibition resulted in impaired avian IAV propagation and pathogenicity and mutational analysis linked the pronounced inhibition of c-Abl to cytopathogenic cell alterations upon avian IAV infections. Taken together, NS1 proteins of avian IAV interfere with the kinase activity of c-Abl, a major cellular signalling integrator that controls multiple signalling processes and cell fate regulations apparently including IAV infections.

Orchestrating B cell lymphopoiesis through interplay of IL-7 receptor and pre-B cell receptor signalling

The development of B cells is dependent on the sequential DNA rearrangement of immunoglobulin loci that encode subunits of the B cell receptor. The pathway navigates a crucial checkpoint that ensures expression of a signalling-competent immunoglobulin heavy chain before commitment to rearrangement and expression of an immunoglobulin light chain. The checkpoint segregates proliferation of pre-B cells from immunoglobulin light chain recombination and their differentiation into B cells. Recent advances have revealed the molecular circuitry that controls two rival signalling systems, namely the interleukin-7 (IL-7) receptor and the pre-B cell receptor, to ensure that proliferation and immunoglobulin recombination are mutually exclusive, thereby maintaining genomic integrity during B cell development.

Role of Abl in airway hyperresponsiveness and airway remodeling

BACKGROUND

Asthma is a chronic disease that is characterized by airway hyperresponsiveness and airway remodeling. The underlying mechanisms that mediate the pathological processes are not fully understood. Abl is a non-receptor protein tyrosine kinase that has a role in the regulation of smooth muscle contraction and smooth muscle cell proliferation in vitro. The role of Abl in airway hyperresponsiveness and airway remodeling in vivo is largely unknown.

METHODS

To evaluate the role of Abl in asthma pathology, we assessed the expression of Abl in airway tissues from the ovalbumin sensitized and challenged mouse model, and human asthmatic airway smooth muscle cells. In addition, we generated conditional knockout mice in which Abl expression in smooth muscle was disrupted, and then evaluated the effects of Abl conditional knockout on airway resistance, smooth muscle mass, cell proliferation, IL-13 and CCL2 in the mouse model of asthma. Furthermore, we determined the effects of the Abl pharmacological inhibitors imatinib and GNF-5 on these processes in the animal model of asthma.

RESULTS

The expression of Abl was upregulated in airway tissues of the animal model of asthma and in airway smooth muscle cells of patients with severe asthma. Conditional knockout of Abl attenuated airway resistance, smooth muscle mass and staining of proliferating cell nuclear antigen in the airway of mice sensitized and challenged with ovalbumin. Interestingly, conditional knockout of Abl did not affect the levels of IL-13 and CCL2 in bronchoalveolar lavage fluid of animals treated with ovalbumin. However, treatment with imatinib and GNF-5 inhibited the ovalbumin-induced increase in IL-13 and CCL2 as well as airway resistance and smooth muscle growth in animals.

CONCLUSIONS

These results suggest that the altered expression of Abl in airway smooth muscle may play a critical role in the development of airway hyperresponsiveness and airway remodeling in asthma. Our findings support the concept that Abl may be a novel target for the development of new therapy to treat asthma.

Identification of shared genes and pathways: a comparative study of multiple sclerosis susceptibility, severity and response to interferon beta treatment

Recent genome-wide association studies (GWAS) have successfully identified several gene loci associated with multiple sclerosis (MS) susceptibility, severity or interferon-beta (IFN-ß) response. However, due to the nature of these studies, the functional relevance of these loci is not yet fully understood. We have utilized a systems biology based approach to explore the genetic interactomes of these MS related traits. We hypothesised that genes and pathways associated with the 3 MS related phenotypes might interact collectively to influence the heterogeneity and unpredictable clinical outcomes observed. Individual genetic interactomes for each trait were constructed and compared, followed by prioritization of common interactors based on their frequencies. Pathway enrichment analyses were performed to highlight shared functional pathways. Biologically relevant genes ABL1, GRB2, INPP5D, KIF1B, PIK3R1, PLCG1, PRKCD, SRC, TUBA1A and TUBA4A were identified as common to all 3 MS phenotypes. We observed that the highest number of first degree interactors were shared between MS susceptibility and MS severity (p = 1.34×10⁻⁷⁹) with UBC as the most prominent first degree interactor for this phenotype pair from the prioritisation analysis. As expected, pairwise comparisons showed that MS susceptibility and severity interactomes shared the highest number of pathways. Pathways from signalling molecules and interaction, and signal transduction categories were found to be highest shared pathways between 3 phenotypes. Finally, FYN was the most common first degree interactor in the MS drugs-gene network. By applying the systems biology based approach, additional significant information can be extracted from GWAS. Results of our interactome analyses are complementary to what is already known in the literature and also highlight some novel interactions which await further experimental validation. Overall, this study illustrates the potential of using a systems biology based approach in an attempt to unravel the biological significance of gene loci identified in large GWAS.

Telomere loss in Philadelphia-negative hematopoiesis after successful treatment of chronic myeloid leukemia: evidence for premature aging of the myeloid compartment

Telomere shortening, a well-known marker of aging and cellular stress, occurs under several conditions in the hematopoietic compartment, including aplastic anemia and following iatrogenic noxae. We decided to verify whether pathological telomere erosion also arises in restored Philadelphia-negative (Ph-negative) hematopoiesis following successful treatment of chronic myeloid leukemia (CML). Eighty-one CML patients in complete cytogenetic remission were compared to 76 age-matched healthy subjects. Myeloid cells of CML patients had shorter telomeres than controls (6521 bp vs 7233 bp, p<0.001). This difference was specific for the myeloid compartment, since it was not observed in lymphoid cells (6774 bp vs 6909 bp, p=0.620). Acquired Ph-negative cytogenetic abnormalities (p=0.010), lack of complete molecular remission (p=0.016) and age (p=0.013) were independent predictors of telomere shortening. Telomere dynamics were assessed over a median follow-up period of 22 months. We documented accelerated non-physiological ongoing telomere shortening in 17/59 CML patients (28%). Patients experiencing grade 2-4 hematological toxicity, during CML remission possessed significantly shorter telomeres compared to those lacking toxicity (p=0.005 for any toxicity, p=0.007 for anemia). CML patients suffer from significant and often ongoing telomere stress resulting in premature and selective aging of the myeloid compartment which might have long-term consequences on function and integrity of Ph-negative hematopoiesis.

Functional mechanisms and roles of adaptor proteins in abl-regulated cytoskeletal actin dynamics

Abl is a nonreceptor tyrosine kinase and plays an essential role in the modeling and remodeling of F-actin by transducing extracellular signals. Abl and its paralog, Arg, are unique among the tyrosine kinase family in that they contain an unusual extended C-terminal half consisting of multiple functional domains. This structural characteristic may underlie the role of Abl as a mediator of upstream signals to downstream signaling machineries involved in actin dynamics. Indeed, a group of SH3-containing accessory proteins, or adaptor proteins, have been identified that bind to a proline-rich domain of the C-terminal portion of Abl and modulate its kinase activity, substrate recognition, and intracellular localization. Moreover, the existence of signaling cascade and biological outcomes unique to each adaptor protein has been demonstrated. In this paper, we summarize functional roles and mechanisms of adaptor proteins in Abl-regulated actin dynamics, mainly focusing on a family of adaptor proteins, Abi. The mechanism of Abl's activation and downstream signaling mediated by Abi is described in comparison with those by another adaptor protein, Crk.

ABL tyrosine kinases: evolution of function, regulation, and specificity

ABL-family proteins comprise one of the best conserved branches of the tyrosine kinases. Each ABL protein contains an SH3-SH2-TK (Src homology 3-Src homology 2-tyrosine kinase) domain cassette, which confers autoregulated kinase activity and is common among nonreceptor tyrosine kinases. This cassette is coupled to an actin-binding and -bundling domain, which makes ABL proteins capable of connecting phosphoregulation with actin-filament reorganization. Two vertebrate paralogs, ABL1 and ABL2, have evolved to perform specialized functions. ABL1 includes nuclear localization signals and a DNA binding domain through which it mediates DNA damage-repair functions, whereas ABL2 has additional binding capacity for actin and for microtubules to enhance its cytoskeletal remodeling functions. Several types of posttranslational modifications control ABL catalytic activity, subcellular localization, and stability, with consequences for both cytoplasmic and nuclear ABL functions. Binding partners provide additional regulation of ABL catalytic activity, substrate specificity, and downstream signaling. Information on ABL regulatory mechanisms is being mined to provide new therapeutic strategies against hematopoietic malignancies caused by BCR-ABL1 and related leukemogenic proteins.