c-Abl stabilizes HDAC2 levels by tyrosine phosphorylation repressing neuronal gene expression in Alzheimer's disease.

In Alzheimer's disease (AD), there is a decrease in neuronal gene expression induced by HDAC2 increase; however, the mechanisms involved are not fully elucidated. Here, we described how the tyrosine kinase c-Abl increases HDAC2 levels, inducing transcriptional repression of synaptic genes. Our data demonstrate that (1) in neurons, c-Abl inhibition with Imatinib prevents the AßO-induced increase in HDAC2 levels; (2) c-Abl knockdown cells show a decrease in HDAC2 levels, while c-Abl overexpression increases them; (3) c-Abl inhibition reduces HDAC2-dependent repression activity and HDAC2 recruitment to the promoter of several synaptic genes, increasing their expression; (4) c-Abl induces tyrosine phosphorylation of HDAC2, a posttranslational modification, affecting both its stability and repression activity; and (5) treatment with Imatinib decreases HDAC2 levels in a transgenic mice model of AD. Our results support the participation of the c-Abl/HDAC2 signaling pathway in the epigenetic blockade of gene expression in AD pathology.

Normal ABL1 is a tumor suppressor and therapeutic target in human and mouse leukemias expressing oncogenic ABL1 kinases.

Leukemias expressing constitutively activated mutants of ABL1 tyrosine kinase (BCR-ABL1, TEL-ABL1, NUP214-ABL1) usually contain at least 1 normal ABL1 allele. Because oncogenic and normal ABL1 kinases may exert opposite effects on cell behavior, we examined the role of normal ABL1 in leukemias induced by oncogenic ABL1 kinases. BCR-ABL1-Abl1(-/-) cells generated highly aggressive chronic myeloid leukemia (CML)-blast phase-like disease in mice compared with less malignant CML-chronic phase-like disease from BCR-ABL1-Abl1(+/+) cells. Additionally, loss of ABL1 stimulated proliferation and expansion of BCR-ABL1 murine leukemia stem cells, arrested myeloid differentiation, inhibited genotoxic stress-induced apoptosis, and facilitated accumulation of chromosomal aberrations. Conversely, allosteric stimulation of ABL1 kinase activity enhanced the antileukemia effect of ABL1 tyrosine kinase inhibitors (imatinib and ponatinib) in human and murine leukemias expressing BCR-ABL1, TEL-ABL1, and NUP214-ABL1. Therefore, we postulate that normal ABL1 kinase behaves like a tumor suppressor and therapeutic target in leukemias expressing oncogenic forms of the kinase.

c-Abl tyrosine kinase promotes adipocyte differentiation by targeting PPAR-gamma 2.

Adipocyte differentiation, or adipogenesis, is a complex and highly regulated process. A recent proteomic analysis has predicted that the nonreceptor tyrosine kinase Abelson murine leukemia viral oncogene (c-Abl) is a putative key regulator of adipogenesis, but the underlying mechanism remained obscure. We found that c-Abl was activated during the early phase of mouse 3T3-L1 preadipocyte differentiation. Moreover, c-Abl activity was essential and its inhibition blocked differentiation to mature adipocytes. c-Abl directly controlled the expression and activity of the master adipogenic regulator peroxisome proliferator-activator receptor gamma 2 (PPARγ2). PPARγ2 physically associated with c-Abl and underwent phosphorylation on two tyrosine residues within its regulatory activation function 1 (AF1) domain. We demonstrated that this process positively regulates PPARγ2 stability and adipogenesis. Remarkably, c-Abl binding to PPARγ2 required the Pro12 residue that has a phenotypically well-studied common human genetic proline 12 alanine substitution (Pro12Ala) polymorphism. Our findings establish a critical role for c-Abl in adipocyte differentiation and explain the behavior of the known Pro12Ala polymorphism.

c-Abl activates janus kinase 2 in normal hematopoietic cells.

Jak2 is involved in cytokine growth factor-stimulated signal transduction, but the mechanism of its activation is largely unknown. Here, we investigated Jak2 activation in a normal hematopoietic cell line, 32D mouse myeloid cells. The bimolecular fluorescence complementation studies showed that c-Abl formed a stable complex with Jak2 in live cells. Co-immunoprecipitation results showed that c-Abl bound to the ßc chain of IL-3/IL-5/GM-CSF receptors. The kinase activities of both c-Abl and Jak2 were stimulated by IL-3 in 32D cells. Decreasing c-Abl protein expression in 32D cells by inducible shRNA decreased Jak2 activity and resulted in the failure of Jak2 activation in response to IL-3. Treatment of IL-3 and serum-starved 32D cells with 1 µM imatinib mysylate inhibited IL-3 stimulated kinase activities of both c-Abl and Jak2. In addition, the kinase-deficient Bcr-Abl mutant (p210K1172R) was defective for activation of Jak2 in 32D cells and impaired IL-3 independent growth, which was rescued by overexpression of c-Abl (+Abl). IL-3 efficiently inhibited apoptosis of 32Dp210K/R+Abl cells induced by imatinib mysylate but not Jak2 kinase inhibitor TG101209. In summary, our findings provide evidence that the kinase function of c-Abl and its C-terminal CT4 region is crucial for its interaction with Jak2 and its activation. c-Abl kinase activity induced by IL-3 is required for IL-3-stimulated Jak2 and Jak1 activation. Our findings reveal a novel regulatory role of c-Abl in Jak2 activation induced by IL-3 cytokine growth factor in 32D hematopoietic cells.

Imatinib mesylate stimulates low-density lipoprotein receptor-related protein 1-mediated ERK phosphorylation in insulin-producing cells.

Low-density lipoprotein receptor-related protein 1 (LRP1) is an endocytic and multi-functional type I cell surface membrane protein, which is known to be phosphorylated by the activated platelet-derived growth factor receptor (PDGFR). The tyrosine kinase inhibitor imatinib, which inhibits PDGFR and c-Abl, and which has previously been reported to counteract ß-cell death and diabetes, has been suggested to reduce atherosclerosis by inhibiting PDGFR-induced LRP1 phosphorylation. The aim of the present study was to study LRP1 function in ß-cells and to what extent imatinib modulates LRP1 activity. LRP1 and c-Abl gene knockdown was performed by RNAi using rat INS-1 832/13 and human EndoC1-ßH1 cells. LRP1 was also antagonized by treatment with the antagonist low-density lipoprotein receptor-related protein associated protein 1 (LRPAP1). We have used PDGF-BB, a PDGFR agonist, and apolipoprotein E (ApoE), an LRP1 agonist, to stimulate the activities of PDGFR and LRP1 respectively. Knockdown or inhibition of LRP1 resulted in increased hydrogen peroxide (H2O2)- or cytokine-induced cell death, and glucose-induced insulin release was lowered in LRP1-silenced cells. These results indicate that LRP1 function is necessary for ß-cell function and that LRP1 is adversely affected by challenges to ß-cell health. PDGF-BB, or the combination of PDGF-BB+ApoE, induced phosphorylation of extracellular-signal-regulated kinase (ERK), Akt and LRP1. LRP1 silencing blocked this event. Imatinib blocked phosphorylation of LRP1 by PDGFR activation but induced phosphorylation of ERK. LRP1 silencing blocked imatinib-induced phosphorylation of ERK. Sunitinib also blocked LRP1 phosphorylation in response to PDGF-BB and induced phosphorylation of ERK, but this latter event was not affected by LRP1 knockdown. siRNA-mediated knockdown of the imatinib target c-Abl resulted in an increased ERK phosphorylation at basal conditions, with no further increase in response to imatinib. Imatinib-induced cell survival of tunicamycin-treated cells was partially mediated by ERK activation. We have concluded that imatinib promotes LRP1-dependent ERK activation, possibly via inhibition of c-Abl, and that this could contribute to the pro-survival effects of imatinib on ß-cells.

A humanin analog decreases oxidative stress and preserves mitochondrial integrity in cardiac myoblasts.

A potent analog (HNG) of the endogenous peptide humanin protects against myocardial ischemia-reperfusion (MI-R) injury in vivo, decreasing infarct size and improving cardiac function. Since oxidative stress contributes to the damage from MI-R we tested the hypotheses that: (1) HNG offers cardioprotection through activation of antioxidant defense mechanisms leading to preservation of mitochondrial structure and that, (2) the activity of either of a pair of non-receptor tyrosine kinases, c-Abl and Arg is required for this protection. Rat cardiac myoblasts (H9C2 cells) were exposed to nanomolar concentrations of HNG and to hydrogen peroxide (H2O2). Cells treated with HNG in the presence of H2O2 demonstrated reduced intracellular reactive oxygen species (ROS), preserved mitochondrial membrane potential, ATP levels and mitochondrial structure. HNG induced activation of catalase and glutathione peroxidase (GPx) within 5 min and decreased the ratio of oxidized to reduced glutathione within 30 min. siRNA knockdown of both Abl and Arg, but neither alone, abolished the HNG-mediated reduction of ROS in myoblasts exposed to H2O2. These findings demonstrate an HNG-mediated, Abl- and Arg-dependent, rapid and sustained activation of critical cellular defense systems and attenuation of oxidative stress, providing mechanistic insights into the observed HNG-mediated cardioprotection in vivo.

c-Abl regulates Mcl-1 gene expression in chronic lymphocytic leukemia cells.

Chronic lymphocytic leukemia (CLL) is a malignancy characterized by clonal expansion of mature B cells that are resistant to apoptosis. This resistance to apoptosis partly results from Mcl-1 expression because high levels of this protein in CLL cells correlate with poor disease prognosis and resistance to chemotherapy. Thus, understanding the mechanism(s) regulating Mcl-1 expression in CLL cells may be useful in the development of new therapies for this incurable disease. In the present study, we show a strong relationship between c-Abl and Mcl-1 expression in CLL cells. We show that treatment of CLL cells with Abl-specific siRNA or with imatinib, to inhibit c-Abl activity, results in the down-regulation of Mcl-1 protein and mRNA. A major regulator of Mcl-1 gene expression is STAT3. Our data show that CLL cells expressing high levels of c-Abl also show elevated levels of phospho-STAT3, and that STAT3 phosphorylation in CLL cells is dependent on c-Abl activity. However, STAT3 phosphorylation by c-Abl requires activation of nuclear factor-κB, secretion of autocrine interleukin-6, and active protein kinase C. Taken together, our data demonstrate the mechanism involved in c-Abl regulation of Mcl-1 expression in CLL cells, and suggest that c-Abl inhibition has therapeutic application in the treatment of this disease.

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.

An evolutionarily acquired genotoxic response discriminates MyoD from Myf5, and differentially regulates hypaxial and epaxial myogenesis.

Despite having distinct expression patterns and phenotypes in mutant mice, the myogenic regulatory factors Myf5 and MyoD have been considered to be functionally equivalent. Here, we report that these factors have a different response to DNA damage, due to the presence in MyoD and absence in Myf5 of a consensus site for Abl-mediated tyrosine phosphorylation that inhibits MyoD activity in response to DNA damage. Genotoxins failed to repress skeletal myogenesis in MyoD-null embryos; reintroduction of wild-type MyoD, but not mutant Abl phosphorylation-resistant MyoD, restored the DNA-damage-dependent inhibition of muscle differentiation. Conversely, introduction of the Abl-responsive phosphorylation motif converts Myf5 into a DNA-damage-sensitive transcription factor. Gene-dosage-dependent reduction of Abl kinase activity in MyoD-expressing cells attenuated the DNA-damage-dependent inhibition of myogenesis. The presence of a DNA-damage-responsive phosphorylation motif in vertebrate, but not in invertebrate MyoD suggests an evolved response to environmental stress, originated from basic helix-loop-helix gene duplication in vertebrate myogenesis.

Abl-1-bridged tyrosine phosphorylation of VASP by Abelson kinase impairs association of VASP to focal adhesions and regulates leukaemic cell adhesion.

Mena [mammalian Ena (Enabled)]/VASP (vasodilator-stimulated phosphoprotein) proteins are the homologues of Drosophila Ena. In Drosophila, Ena is a substrate of the tyrosine kinase DAbl (Drosophila Abl). However, the link between Abl and the Mena/VASP family is not fully understood in mammals. We previously reported that Abi-1 (Abl interactor 1) promotes phosphorylation of Mena and BCAP (B-cell adaptor for phosphoinositide 3-kinase) by bridging the interaction between c-Abl and the substrate. In the present study we have identified VASP, another member of the Mena/VASP family, as an Abi-1-bridged substrate of Abl. VASP is phosphorylated by Abl when Abi-1 is co-expressed. We also found that VASP interacted with Abi-1 both in vitro and in vivo. VASP was tyrosine-phosphorylated in Bcr-Abl-positive leukaemic cells in an Abi-1-dependent manner. Co-expression of c-Abl and Abi-1 or the phosphomimetic Y39D mutation in VASP resulted in less accumulation of VASP at focal adhesions. VASP Y39D had a reduced affinity to the proline-rich region of zyxin. Interestingly, overexpression of both phosphomimetic and unphosphorylated forms of VASP, but not wild-type VASP, impaired adhesion of K562 cells to fibronectin. These results suggest that the phosphorylation and dephosphorylation cycle of VASP by the Abi-1-bridged mechanism regulates association of VASP with focal adhesions, which may regulate adhesion of Bcr-Abl-transformed leukaemic cells.

Caenorhabditis elegans ABL-1 antagonizes p53-mediated germline apoptosis after ionizing irradiation.

c-Abl, a conserved nonreceptor tyrosine kinase, integrates genotoxic stress responses, acting as a transducer of both pro- and antiapoptotic effector pathways. Nuclear c-Abl seems to interact with the p53 homolog p73 to elicit apoptosis. Although several observations suggest that cytoplasmic localization of c-Abl is required for antiapoptotic function, the signals that mediate its antiapoptotic effect are largely unknown. Here we show that worms carrying an abl-1 deletion allele, abl-1(ok171), are specifically hypersensitive to radiation-induced apoptosis in the Caenorhabditis elegans germ line. Our findings delineate an apoptotic pathway antagonized by ABL-1, which requires sequentially the cell cycle checkpoint genes clk-2, hus-1 and mrt-2; the C. elegans p53 homolog, cep-1; and the genes encoding the components of the conserved apoptotic machinery, ced-3, ced-9 and egl-1. ABL-1 does not antagonize germline apoptosis induced by the DNA-alkylating agent ethylnitrosourea. Furthermore, worms treated with the c-Abl inhibitor STI-571 (Gleevec; used in human cancer therapy), two newly synthesized STI-571 variants or PD166326 had a phenotype similar to that generated by abl-1(ok171). These studies indicate that ABL-1 distinguishes proapoptotic signals triggered by two different DNA-damaging agents and suggest that C. elegans might provide tissue models for development of anticancer drugs.

Mice deficient in Abl are osteoporotic and have defects in osteoblast maturation.

The c-Abl protein is a non-receptor tyrosine kinase involved in many aspects of mammalian development. c-Abl kinase is widely expressed, but high levels are found in hyaline cartilage in the adult, bone tissue in newborn mice, and osteoblasts and associated neovasculature at sites of endochondrial ossification in the fetus. Mice homozygous for mutations in the gene encoding c-Abl (AIM) display increased perinatal mortality, reduced fertility, foreshortened crania and defects in the maturation of B cells in bone marrow. Here we demonstrate that Abl-/- mice are also osteoporotic. The long bones of mutant mice contain thinner cortical bone and reduced trabecular bone volume. The osteoporotic phenotype is not due to accelerated bone turnover--both the number and activity of osteoclasts are similar to those of control littermates--but rather to dysfunctional osteoblasts. In addition, the rate of mineral apposition in the mutant animals is reduced. Osteoblasts from both stromal and calvarial explants showed delayed maturation in vitro as measured by expression of alkaline phosphatase (ALP), induction of mRNA encoding osteocalcin and mineral deposition.

A myogenic differentiation checkpoint activated by genotoxic stress.

Cell-cycle checkpoints help to protect the genomes of proliferating cells under genotoxic stress. In multicellular organisms, cell proliferation is often directed toward differentiation during development and throughout adult homeostasis. To prevent the formation of differentiated cells with genetic instability, we hypothesized that genotoxic stress may trigger a differentiation checkpoint. Here we show that exposure to genotoxic agents causes a reversible inhibition of myogenic differentiation. Muscle-specific gene expression is suppressed by DNA-damaging agents if applied prior to differentiation induction but not after the differentiation program is established. The myogenic determination factor, MyoD (encoded by Myod1), is a target of the differentiation checkpoint in myoblasts. The inhibition of MyoD by DNA damage requires a functional c-Abl tyrosine kinase (encoded by Abl1), but occurs in cells deficient for p53 (transformation-related protein 53, encoded by Trp53) or c-Jun (encoded by the oncogene Jun). These results support the idea that genotoxic stress can regulate differentiation, and identify a new biological function for DNA damage-activated signaling network.

Met acts through Abl to regulate p53 transcriptional outcomes and cell survival in the developing liver.

BACKGROUND & AIMS: Genetic studies indicate that distinct signaling modulators are each necessary but not individually sufficient for embryonic hepatocyte survival in vivo. Nevertheless, how signaling players are interconnected into functional circuits and how they coordinate the balance of cell survival and death in developing livers are still major unresolved issues. In the present study, we examined the modulation of the p53 pathway by HGF/Met in embryonic livers. METHODS: We combined pharmacological and genetic approaches to biochemically and functionally evaluate p53 pathway modulation in primary embryonic hepatocytes and in developing livers. RT-PCR arrays were applied to investigate the selectivity of p53 transcriptional response triggered by Met. RESULTS: Met recruits p53 to regulate the liver developmental program, by qualitatively modulating its transcriptional properties: turning on the Mdm2 survival gene, while keeping death and cell-cycle arrest genes Pmaip1 and p21 silent. We investigated the mechanism leading to p53 regulation by Met and found that Abl and p38MAPK are required for p53 phosphorylation on S(389), Mdm2 upregulation, and hepatocyte survival. Alteration of this signaling mechanism switches p53 properties, leading to p53-dependent cell death in embryonic livers. RT-PCR array studies affirmed the ability of the Met-Abl-p53 axis to modulate the expression of distinct genes that can be regulated by p53. CONCLUSIONS: A signaling circuit involving Abl and p38MAPK is required downstream of Met for the survival of embryonic hepatocytes, via qualitative regulation of the p53 transcriptional response, by switching its proapoptotic into survival properties.

c-Abl mediates endothelial apoptosis induced by inhibition of integrins alphavbeta3 and alphavbeta5 and by disruption of actin.

Inhibition of integrins alphavbeta3 and alphavbeta5 in human brain microvascular endothelial cells (HBMECs) by the function-blocking peptide RGDfV induces loss of spreading on vitronectin, cell detachment, and apoptosis. We demonstrate that cell detachment is not required for apoptosis because plating on bovine serum albumin-blocked poly-L-lysine (allows attachment, but not integrin ligation and cell spreading) also induced apoptosis. Latrunculin B (LatB), which inhibits F-actin polymerization, induced transient loss of HBMEC spreading on vitronectin, but not their detachment, and induced apoptosis despite recovery of cell spreading. However, LatB did not cause apoptosis in 5 tumor cell lines. In HBMECs, both LatB and RGDfV induced transient Y412 and Y245 phosphorylation of endogenous c-Abl, a nonreceptor tyrosine kinase that reciprocally regulates F-actin. LatB also induced nuclear translocation of c-Abl in HBMECs. STI-571 (imatinib), a targeted therapy for BCR-ABL1(+) leukemias and inhibitor of c-Abl, platelet-derived growth factor receptor, and c-Kit, decreased endothelial apoptosis. LatB-induced HBMEC apoptosis, and its inhibition by STI-571 also occurred in a 3-dimensional collagen model, supporting physiologic relevance. Last, siRNA to c-Abl (but not nonspecific siRNA) also inhibited RGDfV- and LatB-induced apoptosis. Thus, endogenous c-Abl mediates endothelial apoptosis induced by inhibition of integrins alphavbeta3/alphavbeta5 or by LatB-induced disruption of F-actin.

Moderate caveolin-1 downregulation prevents NADPH oxidase-dependent endothelial nitric oxide synthase uncoupling by angiotensin II in endothelial cells.

OBJECTIVE: We analyzed the role of caveolin-1 (Cav-1) in the cross-talk between NADPH oxidase and endothelial nitric oxide synthase (eNOS) signaling in endothelial caveolae. METHODS AND RESULTS: In intact endothelial cells, angiotensin II (AII) concurrently increased NO and O(2)(-·) production (to 158±12% and 209±5% of control). NO production was sensitive to inhibition of NADPH oxidase and small interfering RNA downregulation of nonreceptor tyrosine kinase cAbl. Reciprocally, N-nitro-l-arginine methyl ester, a NOS inhibitor, partly inhibited O(2)(-·) stimulated by AII (by 47±11%), indicating eNOS uncoupling, as confirmed by increased eNOS monomer/dimer ratio (by 35%). In endothelial cell fractions separated by isopycnic ultracentrifugation, AII promoted colocalization of cAbl and the NADPH oxidase subunit p47phox with eNOS to Cav-1-enriched fractions, as confirmed by proximity ligation assay. Downregulation of Cav-1 by small interfering RNA (to 50%), although it preserved eNOS confinement, inhibited AII-stimulated p47phox translocation and NADPH oxidase activity in Cav-1-enriched fractions and reversed eNOS uncoupling. AII infusion produced hypertension and decreased blood hemoglobin-NO in Cav-1(+/+) mice but not in heterozygote Cav-1(+/-) mice with similar Cav-1 reduction. CONCLUSIONS: Cav-1 critically regulates reactive oxygen species-dependent eNOS activation but also eNOS uncoupling in response to AII, underlining the possibility to treat endothelial dysfunction by modulating Cav-1 abundance.

Synaptic clustering of PSD-95 is regulated by c-Abl through tyrosine phosphorylation.

The c-Abl tyrosine kinase is present in mouse brain synapses, but its precise synaptic function is unknown. We found that c-Abl levels in the rat hippocampus increase postnatally, with expression peaking at the first postnatal week. In 14 d in vitro hippocampal neuron cultures, c-Abl localizes primarily to the postsynaptic compartment, in which it colocalizes with the postsynaptic scaffold protein postsynaptic density protein-95 (PSD-95) in apposition to presynaptic markers. c-Abl associates with PSD-95, and chemical or genetic inhibition of c-Abl kinase activity reduces PSD-95 tyrosine phosphorylation, leading to reduced PSD-95 clustering and reduced synapses in treated neurons. c-Abl can phosphorylate PSD-95 on tyrosine 533, and mutation of this residue reduces the ability of PSD-95 to cluster at postsynaptic sites. Our results indicate that c-Abl regulates synapse formation by mediating tyrosine phosphorylation and clustering of PSD-95.

Oxidative stress activates the c-Abl/p73 proapoptotic pathway in Niemann-Pick type C neurons.

Niemann-Pick type C (NPC) is a neurodegenerative disease characterized by the intralysosomal accumulation of cholesterol leading to neuronal apoptosis. We have previously reported the activation of the c-Abl/p73 proapoptotic pathway in the cerebellum of NPC mice; however, upstream signals underlying the engagement of this pathway remain unknown. Here, we investigate the possible role of oxidative stress in the activation of c-Abl/p73 using different in vitro and in vivo NPC models. Our results indicate a close temporal correlation between the appearance of nitrotyrosine (N-Tyr; a post-translational tyrosine modification caused by oxidative stress) and the activation of c-Abl/p73 in NPC models. To test the functional role of oxidative stress in NPC, we have treated NPC neurons with the antioxidant NAC and observed a dramatic decrease of c-Abl/p73 activation and a reduction in the levels of apoptosis in NPC models. In conclusion, our data suggest that oxidative stress is the main upstream stimulus activating the c-Abl/p73 pathway and neuronal apoptosis in NPC neurons.

Controlling Abl: auto-inhibition and co-inhibition?

Auto-inhibition describes the capacity of proteins to adopt a self-imposed latent conformation. Recently, a crystal structure of the Abl tyrosine kinase has revealed its ability to auto-inhibit. However, a separate body of work suggests that other cellular proteins also inhibit Abl. To reconcile the crystal structure with Abl inhibitors, I propose that Abl is controlled by cellular 'co-inhibitors' that bind Abl, stabilizing the auto-inhibited conformation. The implication of co-inhibition on Abl function is discussed.

c-Abl kinase is required for beta 2 integrin-mediated neutrophil adhesion.

Integrin regulation in neutrophil adhesion is essential for innate immune response. c-Abl kinase is a nonreceptor tyrosine kinase and is critical for signaling transduction from various receptors in leukocytes. Using neutrophils and dHL-60 (neutrophil-like differentiation of HL-60) cells, we show that c-Abl kinase is activated by beta(2) integrin engagement and is required for beta(2) integrin-dependent neutrophil sustained adhesion and spreading. The expression of beta(2) integrin on neutrophils induced by TNF-alpha is not affected by c-Abl kinase inhibitor STI571, suggesting that c-Abl kinase is not involved in TNF-alpha-induced integrin activation. The recruitment of c-Abl kinase to beta(2) integrin is dependent on talin head domain, which constitutively interacts with beta(2) integrin cytoplasmic domain. After activated, c-Abl kinase increases the tyrosine phosphorylation of Vav. The SH3 domain of c-Abl kinase is involved in its interaction with talin and Vav. Thus, c-Abl kinase plays an essential role in the activation of Vav induced by beta(2) integrin ligation and in regulating neutrophil-sustained adhesion and spreading.