Functional role for the c-Abl tyrosine kinase in meiosis I

The c-Abl tyrosine kinase is activated by ionizing radiation and certain other DNA-damaging agents. The DNA-dependent protein kinase (DNA-PK) and the ataxia telangiectasia mutated (ATM) gene product, effectors in the DNA damage response, contribute to the induction of c-Abl activity. The present study demonstrates that c-Abl is expressed in mouse and rat testes, and predominantly in pachytene spermatocytes of meiosis I. The results also demonstrate that c-Abl interacts directly with meiotic chromosomes. In concert with a requirement for c-Abl at the pachytene stage, we show that, in contrast to wild-type mice, testes from Abl-/- mice exhibit defects in spermatogenesis. These findings provide the first demonstration that c-Abl plays a functional role in meiosis.

Activation of protein kinase C delta by the c-Abl tyrosine kinase in response to ionizing radiation

The c-Abl protein tyrosine kinase is activated by ionizing radiation (IR) and certain other DNA-damaging agents. The present studies demonstrate that c-Abl associates constitutively with protein kinase C delta (PKCdelta). The results show that the SH3 domain of c-Abl interacts directly with PKCdelta. c-Abl phosphorylates and activates PKCdelta in vitro. We also show that IR treatment of cells is associated with c-Abl-dependent phosphorylation of PKCdelta and translocation of PKCdelta to the nucleus. These findings support a functional interaction between c-Abl and PKCdelta in the cellular response to genotoxic stress.

Regulation of Rad51 function by c-Abl in response to DNA damage

The Rad51 protein, a homolog of bacterial RecA, functions in DNA double-strand break repair and genetic recombination. Whereas Rad51 catalyzes ATP-dependent pairing and strand exchange between homologous DNA molecules, regulation of this function is unknown. The c-Abl tyrosine kinase is activated by ionizing radiation and certain other DNA-damaging agents. Here we demonstrate that c-Abl interacts constitutively with Rad51. We show that c-Abl phosphorylates Rad51 on Tyr-54 in vitro. The results also show that treatment of cells with ionizing radiation induces c-Abl-dependent phosphorylation of Rad51. Phosphorylation of Rad51 by c-Abl inhibits the binding of Rad51 to DNA and the function of Rad51 in ATP-dependent DNA strand exchange reactions. These findings represent the first demonstration that Rad51 is regulated by phosphorylation and support a functional role for c-Abl in regulating Rad51-dependent recombination in the response to DNA damage.

Cytochrome c-dependent and -independent induction of apoptosis in multiple myeloma cells

Cytochrome c is a mitochondrial protein that induces apoptosis when accumulated in the cytosol in response to diverse stress inducers. This protein has also been shown to cause apoptosis when added to cell free extracts. In this report, we studied the role of cytochrome c (cyto-c) in dexamethasone (Dex), anti-Fas monoclonal antibody (mAb), and ionizing radiation-induced apoptosis in multiple myeloma cells. The results demonstrate that ionizing radiation-induced apoptosis is associated with an increase in cytosolic cyto-c levels, whereas apoptosis induced by Dex or anti-Fas mAb has no detectable effect on cyto-c release. By contrast, caspase-3 was activated in response to all of these agents. Thus, our findings suggest that Dex or anti-Fas mAb-induced apoptosis is not accompanied by cyto-c release and that there are at least two different pathways leading to activation of caspases and induction of apoptosis in multiple myeloma cells that can be distinguished by accumulation of cytosolic cyto-c.

Binding of Ku and c-Abl at the kinase homology region of DNA-dependent protein kinase catalytic subunit

The DNA-dependent protein kinase (DNA-PK) controls the repair of double-stranded DNA breaks in mammalian cells. The protein kinase subunit of DNA-PK (DNA-PKcs) is targeted to DNA breaks by association with the Ku DNA-binding heterodimer. Here we show that a Ku association site is present at the carboxyl terminus of DNA-PKcs (amino acids 3002-3850) near the protein kinase domain. Correspondingly, the nuclear c-Abl tyrosine kinase that associates with DNA-PK also binds to the kinase homology domain. The c-Abl SH3 domain binds to amino acids 3414-3850 of DNA-PKcs. c-Abl phosphorylates C-terminal fragments of DNA-PKcs, particularly amino acids 3414-3850. c-Abl phosphorylation of DNA-PKcs disassociates the DNA-PKcs.Ku complex. Thus, Ku and c-Abl provide opposing functions with regard to DNA-PK activity.

Induction of antigen-specific antitumor immunity with adenovirus-transduced dendritic cells

Transduction of dendritic cells (DC) can result in presentation of tumor-associated antigens and induction of immunity against undefined epitopes. The present studies demonstrate adenovirus (Ad)-mediated transduction of the beta-galactosidase gene in mouse DC. Similar transductions have been obtained with the gene encoding the DF3/MUC1 tumor-associated antigen. We show that the Ad-transduced DC are functional in primary allogeneic mixed lymphocyte reactions. Mice immunized with Ad-transduced DC develop cytotoxic T lymphocytes that are specific for the beta-galactosidase or DF3/MUC1 antigens. The results also demonstrate that Ad MUC1-transduced DC induce a specific response which inhibits the growth of DF3/MUC1-positive tumors. These findings support the usefulness of Ad-transduced DC for in vivo immunization against tumor-associated antigens.

Inhibition of phosphatidylinositol 3-kinase by c-Abl in the genotoxic stress response

Activation of phosphatidylinositol (PI) 3-kinase by growth factors results in phosphorylation of phosphatidylinositol lipids at the D3 position. Although PI 3-kinase is essential to cell survival, little is known about mechanisms that negatively regulate this activity. Here we show that the c-Abl tyrosine kinase interacts directly with the p85 subunit of PI 3-kinase. Activation of c-Abl by ionizing radiation exposure is associated with c-Abl-dependent phosphorylation of PI 3-kinase. We also show that phosphorylation of p85 by c-Abl inhibits PI 3-kinase activity in vitro and in irradiated cells. These findings indicate that c-Abl negatively regulates PI 3-kinase in the stress response to DNA damage.

Caspase-3-mediated cleavage of protein kinase C theta in induction of apoptosis

Protein kinase C theta (PKCtheta) is a member of the novel or nPKC family. A functional role for PKCtheta is unknown. The present studies demonstrate that PKCtheta is cleaved in the third variable region (V3) in apoptosis induced by diverse agents. PKCtheta cleavage is blocked in cells that overexpress the anti-apoptotic Bcl-xL or the baculovirus p35 protein. PKCtheta is cleaved by Caspase-3 and by apoptotic cell lysates at a DEVD354/K site. We also show that overexpression of the cleaved kinase-active PKCtheta fragment, but not full-length PKCtheta or a kinase-inactive fragment, results in induction of sub-G1 phase DNA, nuclear fragmentation, and lethality. These findings indicate that proteolytic cleavage of PKCtheta by Caspase-3 induces events characteristic of apoptosis.

Role for Bcl-xL as an inhibitor of cytosolic cytochrome C accumulation in DNA damage-induced apoptosis

Cytochrome C is a mitochondrial protein that induces apoptosis when released into the cytosol or when added to cell-free extracts. Here we show that cells that overexpress the Bcl-2-related protein Bcl-xL fail to accumulate cytosolic cytochrome C or undergo apoptosis in response to genotoxic stress. Coimmunoprecipitation studies demonstrate that Bcl-xL associates with cytochrome C. Cytochrome C binds directly and specifically to Bcl-xL and not to the proapoptotic Bcl-xs protein. The results also demonstrate that Bcl-xs blocks binding of cytochrome C to Bcl-xL. Our findings support a role for Bcl-xL in protecting cells from apoptosis by inhibiting the availability of cytochrome C in the cytosol.

Interaction between ATM protein and c-Abl in response to DNA damage

The gene mutated in the autosomal recessive disorder ataxia telangiectasia (AT), designated ATM (for 'AT mutated'), is a member of a family of phosphatidylinositol-3-kinase-like enzymes that are involved in cell-cycle control, meiotic recombination, telomere length monitoring and DNA-damage response. Previous results have demonstrated that AT cells are hypersensitive to ionizing radiation and are defective at the G1/S checkpoint after radiation damage. Because cells lacking the protein tyrosine kinase c-Abl are also defective in radiation-induced G1 arrest, we investigated the possibility that ATM might interact with c-Abl in response to radiation damage. Here we show that ATM binds c-Abl constitutively in control cells but not in AT cells. Our results demonstrate that the SH3 domain of c-Abl interacts with a DPAPNPPHFP motif (residues 1,373-1,382) of ATM. The results also reveal that radiation-induction of c-Abl tyrosine kinase activity is diminished in AT cells. These findings indicate that ATM is involved in the activation of c-Abl by DNA damage and this interaction may in part mediate radiation-induced G1 arrest.

Interaction of the DF3/MUC1 breast carcinoma-associated antigen and beta-catenin in cell adhesion

The DF3/MUC1 mucin-like glycoprotein is aberrantly overexpressed in human breast carcinomas. The functional role of DF3 is unknown. The present studies demonstrate that DF3 associates with beta-catenin. Similar findings have been obtained for gamma-catenin but not alpha-catenin. DF3, like E-cadherin and the adenomatous polyposis coli gene product, contains an SXXXXXSSL site that is responsible for direct binding to beta-catenin. The results further demonstrate that interaction of DF3 and beta-catenin is dependent on cell adhesion. These findings and the role of beta-catenin in cell signaling support a role for DF3 in the adhesion of epithelial cells.

Induction of antitumor activity by immunization with fusions of dendritic and carcinoma cells

Dendritic cells (DCs) are potent antigen-presenting cells that prime naive cytotoxic T-cells (CTLs). In this study, we have fused DCs with MC38 carcinoma cells. The fusion cells were positive for major histocompatibility (MHC) class I and II, costimulating molecules and intercellular cell adhesion molecule-1 (ICAM-1). The results show that the fusion cells stimulate naive T cells in the primary mixed lymphocyte reaction (MLR) and induce MC38 tumor-specific CTLs in vivo. Antibody-mediated depletion experiments demonstrate that induction of CD4+ and CD8+ CTLs protects against challenge with tumor cells. We also show that immunization with the fusion cells induces rejection of established metastases. These findings represent the first demonstration that fusions of DCs and tumor cells can be used in the treatment of cancer.

Functional interaction between DNA-PK and c-Abl in response to DNA damage

How DNA damage is converted into intracellular signals that can control cell behaviour is unknown. The c-Abl protein tyrosine kinase is activated by ionizing radiation and certain other DNA-damaging agents, whereas the DNA-dependent protein kinase (DNA-PK), consisting of a serine/threonine kinase and Ku DNA-binding subunits, requires DNA double-strand breaks or other DNA lesions for activation. Here we demonstrate that c-Abl interacts constitutively with DNA-PK. Ionizing radiation stimulates binding of c-Abl to DNA-PK and induces an association of c-Abl with Ku antigen. We show that DNA-PK phosphorylates and activates c-Abl in vitro. Cells deficient in DNA-PK are defective in c-Abl activation induced by ionizing radiation. In a potential feedback mechanism, c-Abl phosphorylates DNA-PK, but not Ku, in vitro. Phosphorylation of DNA-PK by c-Abl inhibits the ability of DNA-PK to form a complex with DNA. We also show that treatment of cells with ionizing radiation results in phosphorylation of DNA-PK that is dependent on c-Abl. Our results support the hypothesis that there are functional interactions between c-Abl and DNA-PK in the response to DNA damage.

Regulation of DNA damage-induced apoptosis by the c-Abl tyrosine kinase

Activation of the c-Abl protein tyrosine kinase by certain DNA-damaging agents contributes to downregulation of Cdk2 and G1 arrest by a p53-dependent mechanism. The present work investigates the potential role of c-Abl in apoptosis induced by DNA damage. Transient transfection studies with wild-type, but not kinase-inactive, c-Abl demonstrate induction of apoptosis. Cells that stably express inactive c-Abl exhibit resistance to ionizing radiation-induced loss of clonogenic survival and apoptosis. Cells null for c-abl are also impaired in the apoptotic response to ionizing radiation. We further show that cells deficient in p53 undergo apoptosis in response to expression of c-Abl and exhibit decreases in radiation-induced apoptosis when expressing inactive c-Abl. These findings suggest that c-Abl kinase regulates DNA damage-induced apoptosis.

Therapeutic antitumor response after immunization with an admixture of recombinant vaccinia viruses expressing a modified MUC1 gene and the murine T-cell costimulatory molecule B7

Tumor-associated antigens have considerable promise not only as diagnostic or prognostic markers but also as targets for active or passive immunotherapy. DF3/MUC1 is a tumor-associated antigen that is overexpressed with an abnormal glycosylation pattern in breast, ovarian, lung, and pancreatic cancers. The major extracellular portion of MUC1 is composed of tandem repeat units of 20 amino acids. Recombinant vaccinia viruses encoding mucin molecules have been constructed by several groups. However, these recombinants have met with limited success in protecting animals from MUC1-expressing tumors because of the vaccinia genome being subject to high-frequency homologous recombination, therefore being unstable in expression of the tandem repeats. In light of these studies, two concurrent strategies were used to improve immune responses to MUC1: a recombinant vaccinia virus was constructed containing a modified "mini" MUC1 gene containing only 10 tandem repeat sequences to minimize vaccinia-mediated rearrangement (designated rV-MUC1); and an admixture was used containing rV-MUC1 and a recombinant vaccinia virus containing the gene for the murine T-cell costimulatory molecule B7-1 (rV-B7). The rV-MUC1 gene product maintained a consistent molecular weight throughout several passages, indicating stability of the inserted gene. Mice inoculated with rV-MUC1 demonstrated MUC1-specific cytolytic responses that were further enhanced by admixture with rV-B7. In a MUC1-expressing pulmonary metastases prevention model, mice inoculated two times with rV-MUC1 were protected from the establishment of metastases. No additive effect on antitumor immunity (> 90% with rV-MUC1 alone) was observed in mice primed with an admixture of rV-MUC1 and rV-B7 and boosted with rV-MUC1. When rV-MUC1 was used to treat established MUC1 positive metastases, however, three administrations of rV-MUC1 were not sufficient to confer antitumor effects. In contrast, when tumor-bearing mice were primed with an admixture of rV-MUC1 and rV-B7, followed by two boosts with rV-MUC1, there was a significant reduction in pulmonary metastases (p = < 0.0001), which correlated to 100% survival. Coexpression of the B7 molecule, although not necessary for the induction of an immune response of sufficient magnitude to prevent MUC1 tumors, was thus essential in a treatment setting.

Proteolytic activation of protein kinase C delta by an ICE/CED 3-like protease induces characteristics of apoptosis

Recent studies have shown that protein kinase C (PKC) delta is proteolytically activated at the onset of apoptosis induced by DNA-damaging agents, tumor necrosis factor, and anti-Fas antibody. However, the relationship of PKC delta cleavage to induction of apoptosis is unknown. The present studies demonstrate that full-length PKC delta is cleaved at DMQD330N to a catalytically active fragment by the cysteine protease CPP32. The results also demonstrate that overexpression of the catalytic kinase fragment in cells is associated with chromatin condensation, nuclear fragmentation, induction of sub-G1 phase DNA and lethality. By contrast, overexpression of full-length PKC delta or a kinase inactive PKC delta fragment had no detectable effect. The findings suggest that proteolytic activation of PKC delta by a CPP32-like protease contributes to phenotypic changes associated with apoptosis.

Genotoxic drugs induce interaction of the c-Abl tyrosine kinase and the tumor suppressor protein p53

The function of the c-Abl protein tyrosine kinase is unknown. The present studies demonstrate that the antimetabolite 1-beta-D-arabinofuranosylcytosine (ara-C) induces binding of c-Abl and p53. Ara-C treatment of cells that express wild type or a dominant negative, kinase-inactive c-Abl(K-R) was associated with formation of c-Abl-p53 complexes and increased expression of the cyclin-dependent kinase (Cdk) inhibitor p21. However, down-regulation of Cdk2 by ara-C was found in cells expressing wild type c-Abl and not in cells expressing c-Abl(K-R) or those deficient in p53. Similar findings were obtained following treatment of cells with the alkylating agent methyl methanesulfonate (MMS). Cells that express the c-Abl dominant negative or are null for c-Abl exhibited partial abrogation of Cdk2 down-regulation and G1 arrest in response to MMS exposure. Cells lacking the c-abl gene also responded to ara-C and MMS with increases in p53 levels and induction of p21. These findings indicate that the cellular response to certain genotoxic drugs involves binding of c-Abl to p53 and down-regulation of Cdk2 by a c-Abl kinase/p53-dependent mechanism.

Activation of p38 mitogen-activated protein kinase by c-Abl-dependent and -independent mechanisms

The p38 mitogen-activated protein (MAP) kinase defines a subgroup of the mammalian MAP kinases that are induced in response to lipopolysaccharide, hyperosmolarity, and interleukin 1. p38 MAP kinase appears to play a role in regulating inflammatory responses, including cytokine secretion and apoptosis. Here we show that diverse classes of DNA-damaging agents such as cisplatinum, 1-beta-D-arabinofuranosylcytosine, UV light, ionizing radiation, and methyl methanesulfonate activate p38 MAP kinase. We also demonstrate that cells deficient in c-Abl fail to activate p38 MAP kinase after treatment with cisplatinum and 1-beta-D-arabinofuranosylcytosine but not after exposure to UV and methyl methanesulfonate. Reconstitution of c-Abl in the Abl-/- cells restores that response. Similar results were obtained for induction of the Jun-NH2-kinase/stress-activated protein kinase. These findings indicate that p38 MAP and Jun-NH2-kinase/stress-activated protein kinases are differentially regulated in response to different classes of DNA-damaging agents.

Interaction of cyclin-dependent kinase 2 and the Lyn tyrosine kinase in cells treated with 1-beta-D-arabinofuranosylcytosine

The cyclin dependent kinase 2 (Cdk2) is required for initiation and progression of DNA replication. Activation of Cdk2 involves binding to cyclin E or cyclin A and dephosphorylation of Tyr15. The present studies demonstrate that treatment of U-937 cells with 1-beta-D-arabinofuranosylcytosine (ara-C) is associated with tyrosine phosphorylation of Cdk2 and inhibition of Cdk2 activity. The results also demonstrate that Cdk2 directly associates with the Src-like tyrosine kinase Lyn as a consequence of ara-C-treatment. Confocal microscopy studies show that Lyn is detectable in the nucleus and that it colocalises with Cdk2. Subcellular fractionation and coimmunoprecipitation studies further demonstrate nuclear binding of Lyn and Cdk2. We also show that Lyn phosphorylates Tyr15 of Cdk2 and that incubation of Lyn with Cdk2 results in inhibition of Cdk2 activity. These findings suggest that the association of Lyn and Cdk2 in ara-C-treated cells may contribute to regulation of Cdk2-dependent cell cycle checkpoints.

Nuclear signaling induced by ionizing radiation involves colocalization of the activated p56/p53lyn tyrosine kinase with p34cdc2

The Src-like protein-tyrosine kinase p56/p53lyn associates with cell membranes and transduces signals from activated cell surface receptors. In the present work, cell fractionation and confocal microscopy studies demonstrate expression of Lyn in the nucleus. We also demonstrate that exposure of intact cells to ionizing radiation is associated with selective activation of nuclear Lyn. Similar findings have been obtained following irradiation of purified nuclei. Immunoprecipitation studies of nuclear lysates demonstrate radiation-induced binding of Lyn to p34cdc2. Nuclear colocalization of Lyn with Cdc2 has been confirmed by confocal microscopy. Other studies with glutathione S-transferase-Lyn fusion proteins demonstrate that the binding of Lyn to nuclear Cdc2 is associated with inhibition of Cdc2 activity. These findings suggest that the association of activated Lyn with Cdc2 in the nucleus may contribute to regulation of a DNA damage-dependent premitotic checkpoint.

Role for c-Abl tyrosine kinase in growth arrest response to DNA damage

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents, and its overexpression causes arrest in the G1 phase of the cell cycle by a mechanism dependent on the tumour-suppressor protein p53 (refs 2-4). Here we investigate the possible role of c-Abl in growth arrest induced by DNA damage. Transient transfection experiments using wild-type or inactivated c-Abl show that both induce expression of p21, an effector of p53, but only wild-type c-Abl downregulates the activity of the cyclin-dependent kinase Cdk2 and causes growth arrest. Exposure to ionizing radiation of cells that stably express active or inactive c-Abl is associated with induction of c-Abl/p53 complexes and p21 expression. However, cells expressing the dominant-negative c-Abl mutant and cells lacking the c-abl gene are impaired in their ability to downregulate Cdk2 or undergo G1 arrest in response to ionizing radiation. We also show that expression of c-Abl kinase in p21(-1-), but not in p53(-1-), cells results in downregulation of Cdk2. Our results suggest that c-Abl kinase contributes to the regulation of growth arrest induced by ionizing radiation by a p53-dependent, p21-independent mechanism.

The stress response to ionizing radiation involoves c-Abl-dependent phosphorylation of SHPTP1

c-Abl is a nonreceptor tyrosine kinase that is activated by certain DNA-damaging agents. The present studies demonstrate that nuclear c-Abl binds constitutively to the protein tyrosine phosphatase SHPTP1. Treatment with ionizing radiation is associated with c-Abl-dependent tyrosine phosphorylation of SHPTP1. The results demonstrate that the SH3 domain of c-Abl interacts with a WPDHGVPSEP motif (residues 417-426) in the catalytic domain of SHPTP1 and that c-Abl phosphorylates C terminal Y536 and Y564 sites. The functional significance of the c-Abl-SHPTP1 interaction is supported by the demonstration that, like c-Abl, SHPTP1 regulates the induction of Jun kinase activity following DNA damage. These findings indicate that SHPTP1 is involved in the response to genotoxic stress through a c-Abl-dependent mechanism.

Activation of protein kinase Cdelta in human myeloid leukemia cells treated with 1-beta-D-arabinofuranosylcytosine

Treatment of human myeloid leukemia cells with 1-beta-D-arabinofuranosylcytosine (ara-C) is associated with induction of protein kinase activity and early-response gene expression. The present studies in ara-C-treated U-937 cells extend these findings by demonstrating activation of a protein kinase that phosphorylates myelin basic protein (MBP). Purification by sequential ion-exchange chromatography and gel filtration supports the detection of a 40-kD MBP kinase. Substrate and inhibitor studies further support a pattern similar to that of protein kinase C (PKC) isozymes. Results of N-terminal amino acid sequencing and immunoblot analysis demonstrate detection of a 40-kD catalytic fragment of PKCdelta. The results also demonstrate the activation and cleavage of PKCdelta (1) is inhibited by expression of antiapoptotic proteins, and (2) is induced by camptothecin (CAM) and mitomycin C (MMC). These findings support proteolytic activation of PKCdelta in the cellular response to ara-C and other DNA-damaging agents.