c-Abl Tyrosine Kinase Activity Research Articles

The c-Abl/p73 pathway induces neurodegeneration in a Parkinson's disease model.

Parkinson's disease is the second most common neurodegenerative disorder. Although it is clear that dopaminergic neurons degenerate, the underlying molecular mechanisms are still unknown, and thus, successful treatment is still elusive. One pro-apoptotic pathway associated with several neurodegenerative diseases is the tyrosine kinase c-Abl and its target p73. Here, we evaluated the contribution of c-Abl and p73 in the degeneration of dopaminergic neurons induced by the neurotoxin 6-hydroxydopamine as a model for Parkinson's disease. First, we found that in SH-SY5Y cells treated with 6-hydroxydopamine, c-Abl and p73 phosphorylation levels were up-regulated. Also, we found that the pro-apoptotic p73 isoform TAp73 was up-regulated. Then, to evaluate whether c-Abl tyrosine kinase activity is necessary for 6-hydroxydopamine-induced apoptosis, we co-treated SH-SY5Y cells with 6-hydroxydopamine and Imatinib, a c-Abl specific inhibitor, observing that Imatinib prevented p73 phosphorylation, TAp73 up-regulation, and protected SH-SY5Y cells treated with 6-hydroxydopamine from apoptosis. Interestingly, this observation was confirmed in the c-Abl conditional null mice, where 6-hydroxydopamine stereotaxic injections induced a lesser reduction of dopaminergic neurons than in the wild-type mice significantly. Finally, we found that the intraperitoneal administration of Imatinib prevented the death of dopaminergic neurons induced by injecting 6-hydroxydopamine stereotaxically in the mice striatum. Thus, our findings support the idea that the c-Abl/p73 pathway is involved in 6-hydroxydopamine degeneration and suggest that inhibition of its kinase activity might be used as a therapeutical drug in Parkinson's disease.

C-Abl Activation Linked to Autophagy-Lysosomal Dysfunction Contributes to Neurological Impairment in Niemann-Pick Type A Disease.

Niemann-Pick type A (NPA) disease is a fatal lysosomal neurodegenerative disorder caused by the deficiency in acid sphingomyelinase (ASM) activity. NPA patients present severe and progressive neurodegeneration starting at an early age. Currently, there is no effective treatment for this disease and NPA patients die between 2 and 3 years of age. NPA is characterized by an accumulation of sphingomyelin in lysosomes and dysfunction in the autophagy-lysosomal pathway. Recent studies show that c-Abl tyrosine kinase activity downregulates autophagy and the lysosomal pathway. Interestingly, this kinase is also activated in other lysosomal neurodegenerative disorders. Here, we describe that c-Abl activation contributes to the mechanisms of neuronal damage and death in NPA disease. Our data demonstrate that: 1) c-Abl is activated in-vitro as well as in-vivo NPA models; 2) imatinib, a clinical c-Abl inhibitor, reduces autophagy-lysosomal pathway alterations, restores autophagy flux, and lowers sphingomyelin accumulation in NPA patient fibroblasts and NPA neuronal models and 3) chronic treatment with nilotinib and neurotinib, two c-Abl inhibitors with differences in blood-brain barrier penetrance and target binding mode, show further benefits. While nilotinib treatment reduces neuronal death in the cerebellum and improves locomotor functions, neurotinib decreases glial activation, neuronal disorganization, and loss in hippocampus and cortex, as well as the cognitive decline of NPA mice. Our results support the participation of c-Abl signaling in NPA neurodegeneration and autophagy-lysosomal alterations, supporting the potential use of c-Abl inhibitors for the clinical treatment of NPA patients.

Defying c-Abl signaling circuits through small allosteric compounds.

Many extracellular and intracellular signals promote the c-Abl tyrosine kinase activity. c-Abl in turn triggers a multitude of changes either in protein phosphorylation or in gene expression in the cell. Yet, c-Abl takes part in diverse signaling routes because of several domains linked to its catalytic core. Complex conformational changes turn on and off its kinase activity. These changes affect surface features of the c-Abl kinase and likely its capability to bind actin and/or DNA. Two specific inhibitors (ATP-competitive or allosteric compounds) regulate the c-Abl kinase through different mechanisms. NMR studies show that a c-Abl fragment (SH3–SH2-linker–SH1) adopts different conformational states upon binding to each inhibitor. This supports an unconventional use for allosteric compounds to unraveling physiological c-Abl signaling circuits.

Abstract A52: Tyrosine kinase activity of c-Abl is essential for p53 dependent transactivation of p21Waf1/Cip1

Abstract c-Abl non-receptor tyrosine kinase is a pivotal upstream positive modulator in cellular response to DNA damage, which attributes to the activation of p53 tumor suppressor protein, hence the expression of the p53 target proteins promoting growth arrest and apoptosis. Nevertheless, the comprehensive function of c-Abl in the activation of p53 mediated by phosphorylation and acetylation is still largely elusive. Thus, in an attempt to determine the significance of tyrosine kinase activity of c-Abl in p53 activation, we examined the extent of p53 activation by exposing cells to Adriamycin (ADR). Under the presence of Abl kinase inhibitor, STI571, p53 dependent transactivation of p21 and Ser15/20 phosphorylation of p53 were markedly impaired. Furthermore, overexpression of the wild type c-Abl in ADR treated cells led to marked increase in p21 expression, whereas that of tyrosine kinase deficient c-Abl led to striking decrease. When U2OS cells were treated with increasing (0, 5, 10 & 15 μM) concentration of STI571, p21 expression gradually diminished with increasing concentration of STI571. In response to DNA damage Atm activates c-Abl, which in turn tyrosine phosphorylates and activates Atm making a positive feedback loop between Atm and c-Abl. We speculate the kinase activity of c-Abl is prerequisite to potentiate Atm activity by this feedback loop resulting in the augmented activation of p53. Preliminary experiments revealed that c-Abl abrogated deacetylation of p53 and Histone protein at p53 target genes promoter mediated by Histone deacetylases (HDACs). Detailed descriptions and significance of these observations will be discussed at the meeting. Citation Format: S. M. Nashir Udden, Masanobu Satake, Shuntaro Ikawa. Tyrosine kinase activity of c-Abl is essential for p53 dependent transactivation of p21Waf1/Cip1. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A52.

Crystal Structure of the Kinase Domain of ABL in Complex with a Potent Rationally-Designed Derivative of the PP1 Inhibitor, AB129

As part of our effort to understand the determinants of drug binding to the Abl tyrosine kinase, we determined the crystal structure of the Abl kinase domain bound to a derivative of the PP1 nucleoside analog. Just as the cancer drug imatinib selectively inhibits the tyrosine kinase activity of c-Abl, c-Kit, and the PDGF receptor, but is a poor inhibitor of the closely related Src kinases (1), PP1 is a selective inhibitor of the Src family (2), c-Kit (3), and PDGFR kinases but not of Abl tyrosine kinase activity (3, 4). In fact, PP1 is 1000X less effective at inhibiting Abl and Bcr-Abl kinases than at inhibiting the Src kinases (3, 4). We rationally designed a derivative of the PP1 compound to introduce hydrogen bonding between it and a strictly conserved lysine residue that coordinates the alpha and beta phosphate groups of ATP in protein kinases (5). By expanding the interactions between the inhibitor and Abl kinase, we sought to make the PP1 derivative, AB129, less selective. Our crystal structure of the Abl kinase domain bound to the AB129 inhibitor shows three important features. First, the compound binds to the kinase domain in the active conformation: alpha C helix is rotated inward facilitating a salt bridge between Lys271 and Glu286 and the conserved Asp-Phe-Gly (DFG) motif is oriented Asp-In. In contrast, the structure of PP1 bound to the Src family kinase Hck is in the inactive conformation (6). Second, the strictly conserved Glu286 residue, not Lys271, hydrogen bonds to the hydroxyl group of AB129. Third, the conformation of the phosphate binding loop (P-loop) is extended. We provide kinetic and calorimetric data to support our rationale for the observed conformational changes.

FTY720-induced human pulmonary endothelial barrier enhancement is mediated by c-Abl

Strategies to improve pulmonary endothelial barrier function are needed to reverse the devastating effects of vascular leak in acute respiratory distress syndrome. FTY720 is a pharmaceutical analogue of the potent barrier-enhancing phospholipid sphingosine 1-phosphate (S1P). FTY720 decreases vascular permeability by an incompletely characterised mechanism that differs from S1P. Here, we describe its barrier-promoting effects on intracellular signalling and junctional assembly formation in human pulmonary endothelium. Permeability of cultured human pulmonary endothelial cells was assessed using transendothelial electrical resistance and dextran transwell assays. Junctional complex formation was assessed using membrane fractionation and immunofluorescence. Pharmacological inhibitors and small interfering (si)RNA were utilised to determine the effects of individual components on permeability. Unlike S1P, FTY720 failed to induce membrane translocation of adherens junction or tight junction proteins. β-catenin, occludin, claudin-5 or zona occludens protein (ZO)-1/ZO-2 siRNAs did not alter FTY720-induced barrier enhancement. FTY720 induced focal adhesion kinase (FAK) phosphorylation and focal adhesion formation, with FAK siRNA partially attenuating the prolonged phase of barrier enhancement. Inhibition of Src, protein kinase (PK)A, PKG, PKC or protein phosphatase 2A failed to alter FTY720-induced barrier enhancement. FTY720 increased c-Abl tyrosine kinase activity and c-Abl siRNA attenuated peak barrier enhancement after FTY720. FTY720 enhances endothelial barrier function by a novel pathway involving c-Abl signalling.

Novel Anti-Fibrotic Therapies for Experimental Chronic Graft-Versus-Host Disease.

Abstract 4490 BackgroundChronic graft-versus host disease (cGvHD) can result in a scleroderma-like disease with dermal, pulmonary and gastrointestinal fibrosis. The histopathological hallmark of sclerodermatous chronic GvHD is accumulation of extracellular matrix proteins by pathologically activated fibroblasts, caused at least in part by the profibrotic cytokines TGF-β and PDGF. It was shown recently that the family of abl kinases plays an important role in the activation of matrix synthesis. Here we investigated whether imatinib and nilotinib, both targeting specifically TGF-β and PDGF signaling pathways by inhibiting the tyrosine kinase activity of c-abl and PDGF receptors, could reduce cGvHD in a murine model. Material and MethodsRecipient mice (BALB/c, H2d) received total body irradiation (2×6 Gy), followed by 1×10∧6 bone marrow cells and 2×10∧6 splenocytes from B10.D2 donors (H2d, multiple minor mismatches). Recipients receiving syngeneic bone marrow and spleen cells served as control. The treatment of transplanted mice started 12 to 14 days post transplantation. Imatinib (150 mg/kg) was given per os once daily and nilotinib (37.5 mg/kg) was administrated per os twice daily until 6 weeks after bone marrow transplantation. Observed skin changes were documented using a clinical score. After 6 weeks dermal thickness was determined by staining with hematoxylin and eosin and activated fibroblasts by using immunohistochemistry for alpha smooth muscle actin. Collagen concentration in afflicted skin was analyzed with the hydroxyproline assay. ResultsUntreated mice receiving an allogeneic transplant, in contrast to syngeneic controls, showed clinical features of cutaneous cGvHD, including skin lesions with alopecia and a lower mobility, in addition to diarrhea and weight loss until 6 weeks after alloBMT. Treatment of recipients with imatinib and nilotinib resulted in serum concentrations comparable to those achieved in humans by standard dosing. Application of imatinib or nilotinib completely prevented the development of cutaneous cGvHD including alopecia and skin ulceration, and was effective in preventing weight loss. Compared to untreated recipients dermal thickness was decreased by 100 ± 8 % (p = 0.001) with imatinib and by 54 ± 14 % (p = 0.016) with nilotinib. The numbers of myofibroblasts were reduced by 84 ± 16 % (p = 0.001) with imatinib and by 87 ± 18 % (p = 0.002) with nilotinib. Furthermore, the collagen content in afflicted skin was reduced by 83 ± 15 % with imatinib and by 94 ± 14 % with nilotinib. ConclusionsThe combined inhibition of c-abl and PDGFR by imatinib or nilotinib was effective for the prevention of sclerodermatous chronic GvHD. The data support recent clinical observations of the potential effect of imatinib in fibrotic chronic graft-versus-host disease. Disclosures:Spriewald:Novartis: Research Funding. Off Label Use: Imatinib and Nilotinib as anti-fibrotic drug in the prevention and treatment of chronic graft-versus-host disease.. Distler:Novartis: Research Funding.

The Bcr-Abl SH2-Kinase Domain Interface Is Critical for Leukemogenesis and An Additional Therapeutic Target in CML.

Abstract 37We previously showed that the Abl SH2 domain is an allosteric activator of c-Abl tyrosine kinase activity and substrate phosphorylation (Filippakopoulos et al. (2008) Cell 134(5), 793-803). This effect is exerted directly by docking of the SH2 domain onto the N-lobe of the kinase domain in the active conformation of c-Abl. We also showed that the same structural mechanism is a critical factor for full activation of the oncogenic fusion kinase Bcr-Abl. Disruption of binding of the SH2 domain to the kinase domain in Bcr-Abl by the Ile164Glu mutation in the SH2 domain, led to a strong reduction in in vitro tyrosine kinase activity and Bcr-Abl autophosphorylation. Unexpectedly, we observed a differential attenuation of downstream signaling pathways upon disruption of the SH2-kinase domain interface, indicating different activation thresholds of Bcr-Abl downstream signaling pathways. Here, we show that disrupting the SH2-kinase domain interface abrogates the transforming capacity of Bcr-Abl. Cells expressing the Bcr-Abl Ile164Glu mutant were unable to generate cytokine-independent colonies in vitro. Furthermore, mice transplanted with Bcr-Abl Ile164Glu expressing bone marrow cells did not develop the characteristic MPD-like disease that is caused by wild-type Bcr-Abl. Mice that received Bcr-Abl Ile164Glu cells showed normal survival, blood counts and histology after more than 100 days post-transplant, despite the presence of Bcr-Abl Ile164Glu-expressing cells in all blood lineages. This shows that the formation of the SH2-kinase domain interface is strictly necessary for Bcr-Abl to cause CML. Together with our data that show sensitization to imatinib inhibition of Bcr-Abl Ile164Glu as compared to Bcr-Abl wild-type, this argues for the SH2-kinase domain interface as an additional drug target on Bcr-Abl that may synergize with tyrosine kinase inhibitors and may be useful to inhibit tyrosine kinase inhibitor resistant Bcr-Abl clones. To address possibilities to interfere with the SH2-kinase domain interface, we are using an engineered binding protein that binds to the Abl SH2 domain with high-affinity and specificity and supposedly disrupts the interface with the kinase domain, resulting in a decrease in Bcr-Abl kinase activity. In conclusion, we provide strong evidence that the structural positioning of the SH2 domain is a crucial factor for constitutive activity, signal transduction and leukemogenicity of Bcr-Abl. Besides oligomerization via the N-terminal coiled-coiled domain and loss of the auto-inhibitory N-terminal myristoyl group, the proper positioning of the SH2 domain appears to be another critical factor that is required for constitutive activation of Bcr-Abl. Inhibitors of the SH2-kinase domain interface of Bcr-Abl may comprise alternative or additional points of pharmacological intervention for the treatment of imatinib-sensitive or -resistant CML or Ph+ acute lymphocytic leukemia. Disclosures:No relevant conflicts of interest to declare.

A Regulatory Circuit Controlling Itch-mediated p73 Degradation by Runx

The members of the tumor suppressor p53 family are under tight regulation by distinct ubiquitin-protein isopeptide (E3) ligases. The level of p73 is regulated by the E3 ligase Itch. Itch levels are sharply reduced in response to DNA damage with concomitant p73 accumulation and activation. The mechanism of controlling Itch level is not known. We show that the Itch promoter is a target of the transcription activator Runx. Yes-associated protein (Yap1) is a shared transcription co-activator of Runx and p73. Under normal conditions, the Runx-Yap1 complex binds the Itch promoter and supports its transcription and p73 degradation. In response to DNA damage, Yap1 is phosphorylated by c-Abl at the position Tyr-357. The modified Yap1 does not co-activate Runx in supporting Itch transcription. The subsequent reduction in the Itch level gives rise to p73 accumulation. These results demonstrate how Yap1 supports degradation of p73 via Runx and how it plays an opposite role in response to DNA damage.

Long‐term experience with imatinib therapy in chronic phase chronic myelogenous leukemia—Remarkable activity with room for improvement

Long‐term experience with imatinib therapy in chronic phase chronic myelogenous leukemia—Remarkable activity with room for improvement

C‐Abl activates p38 MAPK independently of its tyrosine kinase activity: Implications in cisplatin‐based therapy

Activation of p38 MAPK is a critical requisite for the therapeutics activity of the antitumor agent cisplatin. In this sense, a growing body of evidences supports the role of c-Abl as a major determinant of p38 MAPK activation, especially in response to genotoxic stress when triggered by cisplatin. Here, we demonstrate that p38 MAPK activation in response to cisplatin does not require the tyrosine kinase activity of c-Abl. Indeed, c-Abl can activate the p38 MAPK signaling pathway by a mechanism that is independent of its tyrosine kinase activity, but that instead involves the ability of c-Abl to increase the stability of MKK6. Similar results were obtained in chronic myeloid leukemia-derived cell lines, in which a chimeric Bcr/Abl protein mimics the effects of c-Abl overexpression on p38 MAPK activation. These findings may explain why a clinically used c-Abl inhibitor, imatinib mesylate, fails to inhibit the p38 MAPK pathway alone or in combination with cisplatin, and provide evidence of a novel signaling mechanism in which these antitumor agents act.

C-Abl-mediated Phosphorylation of WAVE3 Is Required for Lamellipodia Formation and Cell Migration

The activity of the Wiskott-Aldrich syndrome-related WAVE3 protein is critical for the regulation of the Arp2/3-dependent cytoskeleton organization downstream of Rac-GTPase. The Ableson (Abl) non-receptor tyrosine kinase is also involved in the remolding of actin cytoskeleton in response to extracellular stimuli. Here we show that platelet-derived growth factor stimulation of cultured cells results in WAVE3-Abl interaction and localization to the cell periphery. WAVE3-Abl interaction promotes the tyrosine phosphorylation of WAVE3 by Abl, and STI-571, a specific inhibitor of Abl kinase activity, abrogates the Abl-mediated phosphorylation of WAVE3. We have also shown that Abl targets and phosphorylates four tyrosine residues in WAVE3 and that the Abl-dependent phosphorylation of WAVE3 is critical for the stimulation of lamellipodia formation and cell migration. Our results show that the activation of WAVE3 to promote actin remodeling is enhanced by the c-Abl-mediated tyrosine phosphorylation of WAVE3.

Oncogenic activation of c-Abl in non-small cell lung cancer cells lacking FUS1 expression: inhibition of c-Abl by the tumor suppressor gene product Fus1

In lung cancer, frequent loss of one allele of chromosome 3p is seen in both small cell lung cancer and non-small cell lung cancer (NSCLC), providing evidence of tumor suppressor genes (TSGs) in this chromosomal region. The mechanism of Fus1 tumor suppressor activity is unknown. We have found that a Fus1 peptide inhibits the Abl tyrosine kinase in vitro (IC(50) 35 microM). The inhibitory Fus1 sequence was derived from a region that was deleted in a mutant FUS1 gene (FUS1 (1-80)) detected in some lung cancer cell lines. Importantly, a stearic acid-modified form of this peptide was required for the inhibition, but stearic acid alone was not inhibitory. Two NSCLC cell lines, which lack expression of wild-type Fus1, contain activated c-Abl. Forced expression of an inducible FUS1 cDNA in H1299 NSCLC cells decreased levels of activated c-Abl and inhibited its tyrosine kinase activity. Similarly, treatment of c-Abl immune complexes with the inhibitory Fus1 peptide also reduced the level of c-Abl in these immune complexes. The size and number of colonies of the NSCLC cell line, H1,299, in soft agar was strongly inhibited by the Abl kinase inhibitor imatinib mesylate. Co-expression of FUS1 and c-ABL in COS1 cells blocked activation of c-Abl tyrosine kinase. In contrast, co-expression of mutant FUS1 (1-80) with c-ABL had little inhibitory activity against c-Abl. These findings provide strong evidence that c-Abl is a possible target in NSCLC patients that have reduced expression of Fus1 in their tumor cells.

C-Abl acetylation by histone acetyltransferases regulates its nuclear-cytoplasmic localization.

c-Abl function is strictly dependent on its subcellular localization. Using an in vitro approach, we identify c-Abl as a new substrate for p300, CBP (CREB-binding protein) and PCAF (p300/CBP-associated factor) histone acetyltransferases. Remarkably, acetylation markedly alters its subcellular localization. Point mutagenesis indicated that Lys 730, located in the second nuclear localization signal, is the main target of p300 activity. It has previously been reported that c-Abl accumulates in the cytoplasm during myogenic differentiation. Here, we show that c-Abl protein is acetylated at early stages of myogenic differentiation. Indeed, acetylation on Lys 730 drives c-Abl accumulation in the cytoplasm and promotes differentiation. Thus, Lys 730 acetylation is a novel post-translational modification of c-Abl and a novel mechanism for modulating its subcellular localization that contributes to myogenic differentiation.

Physical and Functional Interaction between hMSH5 and c-Abl

Despite being a member of the mismatch repair family of proteins, the biological functions of hMSH5 in human cells are presently elusive. Here, we report a novel physical and functional interaction between hMSH5 and c-Abl; the latter is a critical non-receptor tyrosine kinase involved in many critical cellular functions including DNA damage response, in which the kinase activity is normally suppressed in the absence of biological challenges. Our data indicate that hMSH5 associates with c-Abl in vivo, which is mediated by a direct physical interaction between the NH2 terminus (residues 1-109) of hMSH5 and the c-Abl SH3 domain. This physical interaction facilitates the activation of c-Abl tyrosine kinase and the phosphorylation of hMSH5 in response to ionizing radiation. Our data also indicate that the hMSH5 P29S variant overactivates the c-Abl tyrosine kinase activity. Furthermore, it seems that the tyrosine phosphorylation of hMSH5 promotes the dissociation of hMSH4-hMSH5 heterocomplex. Together, the revealed physical and functional interaction of hMSH5 with c-Abl implies that the interplay between hMSH5 and c-Abl could manipulate cellular responses to ionizing radiation-induced DNA damages.

C-Abl tyrosine kinase regulates c- fos gene expression via phosphorylating RNA polymerase II

c-Abl tyrosine kinase, predominantly distributed in nucleus, has been implicated in many important cellular processes including the regulation of gene transcription. In this study, we showed that c-Abl promoted the transcription of c- fos gene, both exogenously and endogenously. The nuclear localization and tyrosine kinase activity of c-Abl were required for the activation of c- fos gene. c-Abl was associated with RNA polymerase II (RNAP II) in vivo and augmented the tyrosine phosphorylation of the largest subunit of RNAP II. In addition, c-Abl and RNAP II could be recruited to the region of c- fos promoter. The combined results suggest that c-Abl plays an important role in the transcriptional regulation of c- fos gene and the tyrosine phosphorylation of the largest subunit of RNAP II by c-Abl is involved in the regulating process.

Imatinib mesylate blocks a non‐Smad TGF‐β pathway and reduces renal fibrogenesis in vivo

Transforming growth factor-beta (TGF-beta) is the single most important cytokine promoting renal fibrogenesis. p21-activated kinase-2 (PAK2) and activation of abelson nonreceptor tyrosine kinase (c-abl) have been shown recently to be smad-independent, fibroblast-specific targets downstream of the activated TGF-beta receptor. In the current study we show that in cultured NRK49F-renal fibroblasts (but not in tubular or mesangial cells) TGF-beta similarly activates PAK2 as well as c-abl and induces cell proliferation. Inhibition of the c-abl kinase with imatinib mesylate prevents increased proliferation after TGF-beta addition without affecting PAK2. These in vitro findings were extended to rats with unilateral obstructive nephropathy, a disease model of TGF-beta-driven renal fibrogenesis. In obstructed kidneys, PAK2 and c-abl activity were increased but only c-abl activation was blocked by imatinib. Treatment with imatinib did not prevent renal interstitial infiltration of macrophages or phosphorylation and nuclear translocation of smad2/3 in obstructed kidneys. In contrast, imatinib substantially inhibited an increase in the number of interstitial fibroblasts and myofibroblasts and reduced the expression and interstitial accumulation of collagen type III, collagen type IV and fibronectin. These findings indicate that TGF-beta-induced activation of the nonreceptor c-abl tyrosine kinase regulates fibroblast proliferation and, by this means, is a costimulatory signal in TGF-beta-dependent renal fibrogenesis. Inhibition of c-abl activity with imatinib mesylate ameliorates experimental renal fibrosis in rats.

Activation of the neuronal c-Abl tyrosine kinase by amyloid-β-peptide and reactive oxygen species

The deposition and accumulation of amyloid-beta-peptide (Abeta) in the brain are considered a sine qua non for Alzheimer's disease. The experimental delivery of fibrilized Abeta serves as a cellular model for several facets of the disease including the induction of synaptic dysfunction and apoptosis. c-Abl kinase is involved in the regulation of apoptosis and its pro-apoptotic function is in part mediated by its interaction with p73, a p53 homologue. We found that c-Abl activation is involved in cell signals that regulate neuronal death response to Abeta fibrils. Abeta peptide fibrils induced an increase of the c-Abl activity in rat hippocampal neurons as well as an increase in nuclear p73 protein levels and the p73-c-Abl complex. The neuronal cell death induced by Abeta fibrils was prevented by the inhibition of c-Abl with imatinib mesylate (Gleevec or STI571) and by the inhibition c-Abl expression by RNAi. These results directly point to a therapeutic strategy for the treatment of Alzheimer's disease.

Combined administration of imatinib mesylate and ionizing radiation leads to increased radiosensitivity in the human glioblastoma cell line RuSi RS1

1564 Background: The selective tyrosine kinase inhibitor imatinib mesylate (Gleevec) effectively inhibits the activity of the abl, PDGF receptor (PDGFR) and c-kit tyrosine kinases. Because of the specific target profile of this orally available and generally well tolerated drug, imatinib is under intensive investigation for the potential treatment of other diseases. Malignant gliomas frequently show a high expression of PDGF receptor which is involved in tumorigenesis by formation of an autocrine loop. A role in DNA repair carried out through c-abl and c-kit was previously described both for c-abl and c-kit. In this study we address the potential use of imatinib mesylate and concomitant ionizing radiation (IR) to improve the radiosensitivity of the glioblastoma cell line RuSi RS1. Methods: Cells of the primary glioblastoma cell line RuSi RS1, as well as of the colon cancer cell line WiDr and of BT20, a human breast cancer cell line, were incubated with different concentrations of imatinib mesylate 30 minutes prior to irradiation (doses between 0 and 16 Gy). Western blots were done comparing the different expression of c-abl, PDGFR alpha and beta, and c-kit in the different cell lines. Immunoprecipitation was performed to assess inhibition of the different kinases by imatinib mesylate. Results: Under combined treatment with imatinib and IR a significant shift of the IC50 (dose needed to reduce the survival fraction by 50%) was detected in RuSi RS1 compared to IR alone. This effect was not seen in WiDr or BT20. RuSi RS1 showed an overexpression of PDGFR beta. Inhibition of tyrosine kinase phosphorylation by imatinib could be shown for PDGFR beta and c-abl (the IP failed for c-kit). Conclusion: Concomitant administration of imatinib mesylate and ionizing radiation increases the radiosensitivity of the glioblastoma cell line RuSi RS1. This effect might partly be due to disruption of an autocrine loop of the PDGF/PDGFR system. Inhibition of DNA repair mechanisms in which the tyrosine kinase activity of c-abl and c-kit is involved might be important causes of this observed phenomenon as well. No significant financial relationships to disclose.

Combined administration of imatinib mesylate and ionizing radiation leads to increased radiosensitivity in the human glioblastoma cell line RuSi RS1

1564 Background: The selective tyrosine kinase inhibitor imatinib mesylate (Gleevec) effectively inhibits the activity of the abl, PDGF receptor (PDGFR) and c-kit tyrosine kinases. Because of the specific target profile of this orally available and generally well tolerated drug, imatinib is under intensive investigation for the potential treatment of other diseases. Malignant gliomas frequently show a high expression of PDGF receptor which is involved in tumorigenesis by formation of an autocrine loop. A role in DNA repair carried out through c-abl and c-kit was previously described both for c-abl and c-kit. In this study we address the potential use of imatinib mesylate and concomitant ionizing radiation (IR) to improve the radiosensitivity of the glioblastoma cell line RuSi RS1. Methods: Cells of the primary glioblastoma cell line RuSi RS1, as well as of the colon cancer cell line WiDr and of BT20, a human breast cancer cell line, were incubated with different concentrations of imatinib mesylate 30 minutes prior to irradiation (doses between 0 and 16 Gy). Western blots were done comparing the different expression of c-abl, PDGFR alpha and beta, and c-kit in the different cell lines. Immunoprecipitation was performed to assess inhibition of the different kinases by imatinib mesylate. Results: Under combined treatment with imatinib and IR a significant shift of the IC50 (dose needed to reduce the survival fraction by 50%) was detected in RuSi RS1 compared to IR alone. This effect was not seen in WiDr or BT20. RuSi RS1 showed an overexpression of PDGFR beta. Inhibition of tyrosine kinase phosphorylation by imatinib could be shown for PDGFR beta and c-abl (the IP failed for c-kit). Conclusion: Concomitant administration of imatinib mesylate and ionizing radiation increases the radiosensitivity of the glioblastoma cell line RuSi RS1. This effect might partly be due to disruption of an autocrine loop of the PDGF/PDGFR system. Inhibition of DNA repair mechanisms in which the tyrosine kinase activity of c-abl and c-kit is involved might be important causes of this observed phenomenon as well. No significant financial relationships to disclose.