MUC1-C integrates PD-L1 induction with repression of immune effectors in non-small-cell lung cancer

Immunotherapeutic approaches, particularly PD-1/PD-L1 blockade, have improved the treatment of non-small cell lung cancer (NSCLC), supporting the premise that evasion of immune destruction is of importance for NSCLC progression. However, the signals responsible for upregulation of PD-L1 in NSCLC cells and whether they are integrated with the regulation of other immune-related genes are not known. Mucin 1 (MUC1) is aberrantly overexpressed in NSCLC, activates the NF-κB p65→ZEB1 pathway and confers a poor prognosis. The present studies demonstrate that MUC1-C activates PD-L1 expression in NSCLC cells. We show that MUC1-C increases NF-κB p65 occupancy on the CD274/PD-L1 promoter and thereby drives CD274 transcription. Moreover, we demonstrate that MUC1-C-induced activation of NF-κB→ZEB1 signaling represses the TLR9, IFNG, MCP-1 and GM-CSF genes, and that this signature is associated with decreases in overall survival. In concert with these results, targeting MUC1-C in NSCLC tumors suppresses PD-L1 and induces these effectors of innate and adaptive immunity. These findings support a previously unrecognized central role for MUC1-C in integrating PD-L1 activation with suppression of immune effectors and poor clinical outcome.

DNA methylation by DNMT1 and DNMT3b methyltransferases is driven by the MUC1-C oncoprotein in human carcinoma cells

Aberrant expression of the DNA methyltransferases (DNMTs) and disruption of DNA methylation patterns are associated with carcinogenesis and cancer cell survival. The oncogenic MUC1-C protein is aberrantly overexpressed in diverse carcinomas; however, there is no known link between MUC1-C and DNA methylation. Our results demonstrate that MUC1-C induces the expression of DNMT1 and DNMT3b, but not DNMT3a, in breast and other carcinoma cell types. We show that MUC1-C occupies the DNMT1 and DNMT3b promoters in complexes with NF-κB p65 and drives DNMT1 and DNMT3b transcription. In this way, MUC1-C controls global DNA methylation as determined by analysis of LINE-1 repeat elements. The results further demonstrate that targeting MUC1-C downregulates DNA methylation of the CDH1 tumor suppressor gene in association with induction of E-cadherin expression. These findings provide compelling evidence that MUC1-C is of functional importance to induction of DNMT1 and DNMT3b and, in turn, changes in DNA methylation patterns in cancer cells.

MUC1-C activates BMI1 in human cancer cells

BMI1 is a component of the PRC1 complex that is overexpressed in breast and other cancers, and promotes self-renewal of cancer stem-like cells. The oncogenic mucin 1 (MUC1) C-terminal (MUC1-C) subunit is similarly overexpressed in human carcinoma cells and has been linked to their self-renewal. There is no known relationship between MUC1-C and BMI1 in cancer. The present studies demonstrate that MUC1-C drives BMI1 transcription by a MYC-dependent mechanism in breast and other cancer cells. In addition, we show that MUC1-C blocks miR-200c-mediated downregulation of BMI1 expression. The functional significance of this MUC1-C→BMI1 pathway is supported by the demonstration that targeting MUC1-C suppresses BMI1-induced ubiquitylation of H2A and thereby derepresses homeobox HOXC5 and HOXC13 gene expression. Notably, our results further show that MUC1-C binds directly to BMI1 and promotes occupancy of BMI1 on the CDKN2A promoter. In concert with BMI1-induced repression of the p16^INK4a tumor suppressor, we found that targeting MUC1-C is associated with induction of p16^INK4a expression. In support of these results, analysis of three gene expresssion datasets demonstrated highly significant correlations between MUC1-C and BMI1 in breast cancers. These findings uncover a previously unrecognized role for MUC1-C in driving BMI1 expression and in directly interacting with this stem cell factor, linking MUC1-C with function of the PRC1 in epigenetic gene silencing.

Sequences related to the RNA tumor viruses in the RNA and DNA of human leukemias and lymphomas

DNA-RNA hybridization was used to explore whether human neoplasias contain RNA molecules having sequence homologies to those of the RNA tumor viruses known to cause similar diseases in animals. The pattern of specific RNAs found in the human tumors showed a remarkable concordance with the predictions deducible from the animal systems. Thus human breast cancer contains RNA homologous only to that of the murine mammary tumor virus (MMTV). Human leukemias, sarcomas, and lymphomas (including Hodgkin's and Burkitt's) all contain RNA with sequence homology to the murine leukemia virus (RLV) and not to MMTV RNA. Finally, as in the case of the mouse, none of the human tumors examined contain RNA related in sequence to that of the avian myeloblastosis virus (AMV). The RNA detected in all of the human neoplasias was demonstrated to be of high molecular weight (1 times 10(7) daltons) and encapsulated with a reverse transcriptase in particles having densities between 1.16-1.19 g/ml. Further, the RNA of these human tumor particles was related in sequence to the murine viruses that cause the corresponding neoplasias in mice. Thus, 4 features diagnostic for the murine oncogenic viruses are satisfied by the particles found in the human cancers. Finally, it was shown by "recycling" experiments that the DNA from human leukemic cells and from lymphomatous tissue contained particle-related sequences that could not be detected in normal DNA. This finding was further substantiated by studies with identical twins in which it was shown that the leukemic twin contained particle-related sequences that could not be detected in the leukocytes of his identical healthy sibling. These findings are inconsistent with hypotheses that require chromosomal transmission in the germ line of complete copies of the information required to produce malignancy and the associated virus particles.

MUC1-C activates the TAK1 inflammatory pathway in colon cancer

The mucin 1 (MUC1) oncoprotein has been linked to the inflammatory response by promoting cytokine-mediated activation of the NF-κB pathway. The TGF-β-activated kinase 1 (TAK1) is an essential effector of proinflammatory NF-κB signaling that also regulates cancer cell survival. The present studies demonstrate that the MUC1-C transmembrane subunit induces TAK1 expression in colon cancer cells. MUC1 also induces TAK1 in a MUC1(+/-)/IL-10(-/-) mouse model of colitis and colon tumorigenesis. We show that MUC1-C promotes NF-κB-mediated activation of TAK1 transcription and, in a positive regulatory loop, MUC1-C contributes to TAK1-induced NF-κB signaling. In this way, MUC1-C binds directly to TAK1 and confers the association of TAK1 with TRAF6, which is necessary for TAK1-mediated activation of NF-κB. Targeting MUC1-C thus suppresses the TAK1NF-κB pathway, downregulates BCL-XL and in turn sensitizes colon cancer cells to MEK inhibition. Analysis of colon cancer databases further indicates that MUC1, TAK1 and TRAF6 are upregulated in tumors associated with decreased survival and that MUC1-C-induced gene expression patterns predict poor outcomes in patients. These results support a model in which MUC1-C-induced TAK1NF-κB signaling contributes to intestinal inflammation and colon cancer progression.

Targeting the MUC1-C oncoprotein downregulates HER2 activation and abrogates trastuzumab resistance in breast cancer cells

Patients with HER2 positive breast cancer often exhibit intrinsic or acquired resistance to trastuzumab treatment. The transmembrane MUC1-C oncoprotein is aberrantly overexpressed in breast cancer cells and associates with HER2. The present studies demonstrate that silencing MUC1-C in HER2-overexpressing SKBR3 and BT474 breast cancer cells results in downregulation of constitutive HER2 activation. Moreover, treatment with the MUC1-C inhibitor, GO-203, was associated with disruption of MUC1-C/HER2 complexes and decreases in tyrosine phosphorylated HER2 (p-HER2) levels. In studies of trastuzumab-resistant SKBR3R and BT474R cells, we found that the association between MUC1-C and HER2 is markedly increased (~20-fold) as compared to that in sensitive cells. Additionally, silencing MUC1-C in the trastuzumab-resistant cells or treatment with GO-203 decreased p-HER2 and AKT activation. Moreover, targeting MUC1-C was associated with downregulation of phospho-p27 and cyclin E, which confer trastuzumab resistance. Consistent with these results, targeting MUC1-C inhibited the growth and clonogenic survival of both trastuzumab-resistant cells. Our results further demonstrate that silencing MUC1-C reverses resistance to trastuzumab and that the combination of GO-203 and trastuzumab is highly synergistic. These findings indicate that MUC1-C contributes to constitutive activation of the HER2 pathway and that targeting MUC1-C represents a potential approach to abrogate trastuzumab resistance.

MUC1-C oncoprotein activates the ZEB1/miR-200c regulatory loop and epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is activated in cancer cells by ZEB1, a member of the zinc finger/homeodomain family of transcriptional repressors. The mucin 1 (MUC1) heterodimeric protein is aberrantly overexpressed in human carcinoma cells. The present studies in breast cancer cells demonstrate that the oncogenic MUC1-C subunit induces expression of ZEB1 by a NF-κB (nuclear factor kappa B) p65-dependent mechanism. MUC1-C occupies the ZEB1 promoter with NF-κB p65 and thereby promotes ZEB1 transcription. In turn, ZEB1 associates with MUC1-C and the ZEB1/MUC1-C complex contributes to the transcriptional suppression of miR-200c, an inducer of epithelial differentiation. The co-ordinate upregulation of ZEB1 and suppression of miR-200c has been linked to the induction of EMT. In concert with the effects of MUC1-C on ZEB1 and miR-200c, we show that MUC1-C induces EMT and cellular invasion by a ZEB1-mediated mechanism. These findings indicate that (i) MUC1-C activates ZEB1 and suppresses miR-200c with the induction of EMT and (ii) targeting MUC1-C could be an effective approach for the treatment of breast and possibly other types of cancers that develop EMT properties.

Oncogenic function of the MUC1 receptor subunit in gene regulation

The mucin 1 (MUC1) oncoprotein is overexpressed by diverse human cancers; however, it has remained largely unclear how MUC1 contributes to tumorigenesis. In this issue of Oncogene and in concert with published work, Behrens et al. report that the MUC1 receptor subunit activates genes involved in invasion, angiogenesis and metastasis.

Immunomodulatory effects of vitamin D: implications for GVHD

GVHD remains a major source of morbidity and mortality after allogeneic BMT. GVHD is mediated by alloreactive T cells derived from the hematopoietic graft that target host tissues. Pre-clinical models have shown that presentation of alloantigens by host DCs results in the activation of donor-derived T cells that mediate GVHD. Strategies that interfere with the Ag-presenting capacity of DCs after allogeneic transplantation may decrease the risk of developing GVHD. Vitamin D is a hormone essential for calcium metabolism that shows immunomodulatory properties. We showed that correction of vitamin D deficiency appeared to mitigate manifestations of GVHD. In pre-clinical studies, we have shown that vitamin D inhibits DC maturation, polarizes T-cell populations toward the expression of Th2 as compared with Th1 cytokines, and blunts allogeneic T-cell proliferation in response to DC stimulation. Exposure to vitamin D resulted in increased expression of IDO, an enzyme responsible for tryptophan metabolism that is upregulated in tolerizing DCs. These data suggest that exposure to vitamin D results in immature DC populations that bias toward tolerizing rather than stimulatory T-cell populations. Vitamin D may therefore have a role in the prevention of GVHD.

MUC1 oncoprotein is targeted to mitochondria by heregulin-induced activation of c-Src and the molecular chaperone HSP90

The MUC1 heterodimeric transmembrane glycoprotein is aberrantly overexpressed by most human carcinomas. The MUC1 C-terminal subunit localizes to mitochondria and blocks stress-induced activation of the intrinsic apoptotic pathway. How MUC1 is delivered to mitochondria is not known. The present studies demonstrate that MUC1 forms intracellular complexes with HSP70 and HSP90. We show that the MUC1 cytoplasmic domain binds directly to HSP70 in vitro. By contrast, binding of MUC1 to HSP90 in vitro is induced by c-Src-mediated phosphorylation of the MUC1 cytoplasmic domain. c-Src also increases binding of MUC1 to HSP90 in cells. In concert with these results, we show that heregulin (HRG), a ligand for ErbB receptors, activates c-Src and, in turn, stimulates binding of MUC1 to HSP90. We also show that inhibitors of c-Src or HSP90 block HRG-induced targeting of MUC1 to mitochondria and integration of MUC1 into the mitochondrial outer membrane. These findings indicate that MUC1 is delivered to mitochondria by a mechanism involving activation of the ErbB receptor-->c-Src pathway and transport by the molecular chaperone HSP70/HSP90 complex.

Cancer immunotherapy by fusions of dendritic and tumour cells and rh-IL-12

BACKGROUND

Vaccination with fusion cells (FCs) comprising dendritic cells and tumour cells as well as administration of interleukin-12 (IL-12) showed a significant therapeutic effect against established tumours in mouse experimental models. We conducted immunotherapy against various malignant tumours using the FCs and rhIL-12, and investigated the safety and efficacy of the therapy.

MATERIALS AND METHODS

Patients' DCs were mixed with autologous irradiated tumour cells and treated with 50% polyethylene glycol to generate FCs. The FCs were inoculated intradermally, and then 30 ng kg(-1) of rhIL-12 was injected at the same sites 2 and 6 days later. This process was carried out as one cycle, and three of these cycles were repeated at 1-week intervals to comprise one course. After completing the course, its safety and therapeutic effects were estimated.

RESULTS

The most frequently observed adverse event was fever, observed in 26% of patients in the first cycle. Decrease in white blood cell and an increase in serum ALT were observed in 28% and 25%, respectively. Three out of 12 patients with a malignant brain tumour (25%) achieved a partial response (PR), but other patients with a malignant tumour showed no regression of their tumours. Thirteen out of 16 patients with a brain tumour (81%) showed cutaneous delayed hypersensitivity responses. However, only one of 16 patients (6%) with a malignant tumour other than a brain tumour developed such responses.

CONCLUSIONS

Immunotherapy using a FC vaccine and rhIL-12 induced no serious adverse reactions, and provided good therapeutic responses in some of the patients with a brain tumour.

Triterpenoid CDDO-Im downregulates PML/RARα expression in acute promyelocytic leukemia cells

The triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) induces differentiation and apoptosis of diverse human tumor cells. In the present study, we examined the effects of the CDDO imidazolide imide (CDDO-Im) on the NB4 acute promyelocytic leukemia (APL) cell line and primary APL cells. The results show that CDDO-Im selectively downregulates expression of the PML/retinoic receptor alpha fusion protein by a caspase-dependent mechanism and sensitizes APL cells to the differentiating effects of all-trans retinoic acid (ATRA). CDDO-Im treatment of APL cells was also associated with disruption of redox balance and activation of the extrinsic apoptotic pathway. In concert with these results, CDDO-Im sensitizes APL cells to arsenic trioxide (ATO)-induced apoptosis. Our findings indicate that CDDO-Im may be effective in the treatment of APL by: (i) downregulation of PML/RARalpha; (ii) enhancement of ATRA-induced differentiation; and (iii) sensitization of ATO-induced APL cell death.

Immature dendritic cell/tumor cell fusions induce potent antitumour immunity

BACKGROUND

Maturation of dendritic cells (DCs) is important to induce antigen-specific antitumour immunity in cancer immunotherapy with antigen-loaded DCs. However, DCs from tumour-bearing hosts are immature and functionally defective for antigen presentation. We examined whether DCs from tumour-bearing mice could be an effective part of a DC/tumour cell fusion vaccine.

MATERIALS AND METHODS

Dendritic cells from healthy (DC-Hs) or MC38 tumour-bearing mice (DC-TBs) were examined for endocytotic capacity of FITC-labelled dextran, antigen-presenting capacity in allogeneic mixed leucocyte reaction (allo-MLR) and expression of I-Ab, CD80, and CD86. Fusion cells (FCs) of DC-Hs or DC-TBs and MC38 cells (FC-Hs or FC-TBs) were generated by treatment with polyethylene glycol (PEG). Mice vaccinated with FC-Hs or FC-TBs were studied for cytolytic activity of splenocytes and suppressive activity against established MC38 pulmonary metastases.

RESULTS

Dendritic cell-TBs showed higher endocytotic capacity and lower antigen-presenting capacity than did DC-Hs, results indicating that DC-TBs are more immature and functionally defective for antigen presentation than are DC-Hs. Expression of surface molecules, however, was almost same between DC-Hs and DC-TBs. Splenocytes from mice immunized with FC-Hs or FC-TBs induced the same high cytolytic activity against MC38 cells. Vaccination of mice with FC-Hs or FC-TBs resulted in the same significant suppressive effect against established pulmonary metastases of MC38.

CONCLUSION

Dendritic cells from tumour-bearing mice, despite being functionally defective, are effective vehicles for immunotherapy using DC/tumour cell fusion vaccines.

Negative regulation of the SHPTP1 protein tyrosine phosphatase by protein kinase C delta in response to DNA damage

The SHPTP1 protein tyrosine phosphatase is activated by the c-Abl and Lyn tyrosine kinases in the cellular response to genotoxic stress. However, signaling mechanisms involved in the negative regulation of SHPTP1 are unknown. This study demonstrates that protein kinase C delta (PKCdelta) associates with SHPTP1. The PKCdelta catalytic domain binds directly to SHPTP1. The results also demonstrate that PKCdelta is required, at least in part, for phosphorylation and inactivation of SHPTP1. The phosphatase activity of SHPTP1 was attenuated by coincubation with PKCdelta in vitro. In addition, treatment of U-937 human myeloid leukemia cells with 1-beta-D-arabinofuranosylcytosine (ara-C) was associated with induction of the PKCdelta kinase function and inhibition of SHPTP1 activity. Down-regulation of SHPTP1 by ara-C was blocked by the PKCdelta inhibitor rottlerin but not by the PKCalpha and -beta inhibitor Gö6976. Moreover, transient coexpression studies with a dominant-negative mutant of PKCdelta demonstrate that the kinase activity of PKCdelta is required for the down-regulation of SHPTP1. These findings support the functional interaction between PKCdelta and SHPTP1 in the cellular response to DNA damage.

Vaccination with allogeneic dendritic cells fused to carcinoma cells induces antitumor immunity in MUC1 transgenic mice

Fusions of autologous tumor cells with allogeneic dendritic cells (DC) represent an approach for the induction of antitumor immunity. In the present studies, we investigated the antitumor effects of vaccinating MUC1-transgenic (MUC1.Tg) mice with MC38/MUC1 carcinoma cells fused to allogeneic DC from BALB/c mice (allo-DC, H-2(d)) or syngeneic DC from C57BL/6 mice (syn-DC, H-2(b)). Both allo and syn fusion cells (FC/MUC1) expressed MHC class II, costimulatory molecules, and the MUC1 antigen. Allo-FC/MUC1 exhibited dual expression of MHC class I haplotypes (H-2(d)/H-2(b))and MUC1 antigen. By contrast, only H-2(b) and MUC1 antigen were expressed by syn-FC/MUC1. CTLs from MUC1.Tg mice immunized with allo- or syn-FC/MUC1 fusion cells lysed MC38/MUC1 targets. Moreover, immunization with allo- or syn-FC/MUC1 was effective in eliminating established MUC1-positive pulmonary metastases in MUC1.Tg mice. These results indicate that immunization of MUC1.Tg mice with syn- or allo-FC/MUC1 is effective in reversing immunologic unresponsiveness to MUC1 antigen and inducing immunity against MUC1-positive tumors. The findings in the present study have broader clinical implications for fusion cell vaccines.

The novel isocoumarin 2-(8-hydroxy-6-methoxy-1-oxo-1H-2-benzopyran-3-yl) propionic acid (NM-3) induces lethality of human carcinoma cells by generation of reactive oxygen species

2-(8-Hydroxy-6-methoxy-1-oxo-1H-2-benzopyran-3-yl) propionic acid (NM-3) is an isocoumarin derivative that has recently entered clinical trials for evaluation as a p.o.-bioavailable, antiangiogenic molecule. NM-3 induces endothelial cell death at low microM concentrations by a nonapoptotic mechanism. The present studies have assessed the direct effects of NM-3 on human carcinoma cells. The results demonstrate that NM-3 treatment is associated with the generation of reactive oxygen species and loss of clonogenic survival. In concert with these findings, we show that exposure to NM-3 is associated with increases in expression of the p53 tumor suppressor. In human MCF-7 and ZR-75-1 breast cancer cells, NM-3 induces the p21 cyclin-dependent kinase inhibitor, cell cycle arrest at G1-S-phase, and necrotic cell death. Moreover, human PA-1 ovarian carcinoma and HeLa cervical carcinoma cells respond to NM-3 with the induction of apoptosis by a reactive oxygen species-dependent mechanism. These findings demonstrate that NM-3 has direct effects on carcinoma cells at clinically achievable concentrations and that this agent could be effective in targeting both the tumor and its vasculature.

Preventive antitumor activity against hepatocellular carcinoma (HCC) induced by immunization with fusions of dendritic cells and HCC cells in mice

BACKGROUND

The prevention of recurrence of hepatocellular carcinoma (HCC) after treatment is very important for improvement of the prognosis of HCC patients. Dendritic cells (DCs) are potent antigen-presenting cells that can prime naive T cells to induce a primary immune response. We attempted to induce preventive antitumor immunity against HCC by immunizing BALB/c mice with fusions of DCs and HCC cells.

METHODS

Murine bone marrow-derived DCs and a murine HCC cell line. BNL cells, were fused by treatment with 50% polyethyleneglvcol (PEG). Fusion efficacy was assessed by the analysis of fusions of BNL cells stained with red fluorescent dye and DCs stained with green fluorescent dye. Mice injected intravenously with DC/BNL fusions were challenged by BNL cell inoculation.

RESULTS

About 30% of the PEG-treated non-adherent cells with both fluorescences were considered to be fusion cells. The cell fraction of DC/BNL fusions showed phenotypes of DCs, MHC class II, CD80, CD86, and intercellular adhesion molecule (ICAM)-1, which were not expressed on BNL cells. Mice immunized with the fusions were protected against the inoculation of BNL tumor cells, whereas injection with a mixture of DCs and BNL cells not treated with PEG did not provide significant resistance against BNL cell inoculation. Splenocytes from DC/BNL fusion-immunized mice showed lytic activity against BNL cells.

CONCLUSIONS

These results demonstrate that immunization with fusions of DCs and HCC cells is capable of inducing preventive antitumor immunity against HCC.

The epidermal growth factor receptor regulates interaction of the human DF3/MUC1 carcinoma antigen with c-Src and beta-catenin

The DF3/MUC1 mucin-like, transmembrane glycoprotein is aberrantly overexpressed in most human carcinomas. The MUC1 cytoplasmic domain interacts with the c-Src tyrosine kinase and thereby increases binding of MUC1 and beta-catenin. In the present work, coimmunoprecipitation studies demonstrate that MUC1 associates constitutively with the epidermal growth factor receptor (EGF-R) in human ZR-75-1 breast carcinoma cells. Immunofluorescence studies show that EGF-R and MUC1 associate at the cell membrane. We also show that the activated EGF-R phosphorylates the MUC1 cytoplasmic tail on tyrosine at a YEKV motif that functions as a binding site for the c-Src SH2 domain. The results demonstrate that EGF-R-mediated phosphorylation of MUC1 induces binding of MUC1 to c-Src in cells. Moreover, in vitro and in vivo studies demonstrate that EGF-R increases binding of MUC1 and beta-catenin. These findings support a novel role for EGF-R in regulating interactions of MUC1 with c-Src and beta-catenin.

Targeting of protein kinase C delta to mitochondria in the oxidative stress response

The cellular response to oxidative stress includes the release of mitochondrial cytochrome c and the induction of apoptosis. Here we show that treatment of diverse cells with hydrogen peroxide (H2O2) induces the targeting of protein kinase C delta (PKCdelta) to mitochondria. The results demonstrate that H2O2-induced activation of PKCdelta is necessary for translocation of PKCdelta from the cytoplasm to the mitochondria. The results also show that mitochondrial targeting of PKCdelta is associated with the loss of mitochondrial transmembrane potential and release of cytochrome c. The functional importance of this event is also supported by the demonstration that H2O2-induced apoptosis is blocked by the inhibition of PKCdelta activation and translocation to mitochondria. These findings indicate that mitochondrial targeting of PKCdelta is required, at least in part, for the apoptotic response of cells to oxidative stress.

Targeting of the c-Abl tyrosine kinase to mitochondria in endoplasmic reticulum stress-induced apoptosis

The ubiquitously expressed c-Abl tyrosine kinase localizes to the nucleus and cytoplasm. Using confocal microscopy, we demonstrated that c-Abl colocalizes with the endoplasmic reticulum (ER)-associated protein grp78. Expression of c-Abl in the ER was confirmed by immunoelectron microscopy. Subcellular fractionation studies further indicate that over 20% of cellular c-Abl is detectable in the ER. The results also demonstrate that induction of ER stress with calcium ionophore A23187, brefeldin A, or tunicamycin is associated with translocation of ER-associated c-Abl to mitochondria. In concert with targeting of c-Abl to mitochondria, cytochrome c is released in the response to ER stress by a c-Abl-dependent mechanism, and ER stress-induced apoptosis is attenuated in c-Abl-deficient cells. These findings indicate that c-Abl is involved in signaling from the ER to mitochondria and thereby the apoptotic response to ER stress.

Mitochondrial targeting of JNK/SAPK in the phorbol ester response of myeloid leukemia cells

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with activation of the stress-activated protein kinase (SAPK) and induction of terminal monocytic differentiation. The present studies demonstrate that TPA targets SAPK to mitochondria by a mechanism dependent on activation of protein kinase C (PKC) beta. Translocation of SAPK to mitochondria in response to TPA is associated with release of cytochrome c, caspase-3 activation and induction of apoptosis. The results show that TPA induces the association of SAPK with the mitochondrial anti-apoptotic Bcl-x(L) protein. Overexpression of Bcl-x(L) attenuated the apoptotic response to TPA treatment. Moreover, expression of Bcl-x(L) mutated at sites of SAPK phosphorylation (Thr-47, -115) was more effective than wild-type Bcl-x(L) in abrogating TPA-induced cytochrome c release and apoptosis. By contrast, expression of Bcl-x(L) had little effect on induction of the monocytic phenotype. These findings indicate that myeloid leukemia cells respond to TPA with targeting of SAPK to mitochondria and that this response contributes to terminal differentiation through the release of cytochrome c and induction of apoptosis.

Interaction of hematopoietic progenitor kinase 1 and c-Abl tyrosine kinase in response to genotoxic stress

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents and regulates induction of the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). The hematopoietic progenitor kinase 1 (HPK1) has also been shown to act upstream to the SAPK/JNK signaling pathway. We report here that exposure of hematopoietic Jurkat T cells to genotoxic agents is associated with activation of HPK1. The results demonstrate that exposure of Jurkat cells to DNA-damaging agents is associated with translocation of active c-Abl from nuclei to cytoplasm and binding of c-Abl to HPK1. Our findings also demonstrate that c-Abl phosphorylates HPK1 in cytoplasm and stimulates HPK1 activity. The functional significance of the c-Abl-HPK1 interaction is supported by the demonstration that this complex regulates SAPK/JNK activation. Overexpression of c-Abl(K-R) inhibits HPK1-induced activation of SAPK/JNK. Conversely, the dominant negative mutant of HPK1 blocks c-Abl-mediated induction of SAPK/JNK. These findings indicate that activation of HPK1 and formation of HPK1/c-Abl complexes are functionally important in the stress response of hematopoietic cells to genotoxic agents.

The novel triterpenoid CDDO induces apoptosis and differentiation of human osteosarcoma cells by a caspase-8 dependent mechanism

The oleanane triterpenoid 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) is a multifunctional molecule that induces monocytic differentiation of human myeloid leukemia cells and inhibits proliferation of diverse human tumor cell lines. The present studies on human osteosarcoma cells demonstrate that CDDO induces mitochondrial cytochrome c release, caspase-3 activation, and internucleosomal DNA fragmentation. Overexpression of the caspase-8 inhibitor CrmA blocked CDDO-induced cytochrome c release and apoptosis. By contrast, overexpression of the antiapoptotic Bcl-x(L) protein blocked CDDO-induced cytochrome c release, but only partly inhibited caspase-3 activation and apoptosis. In concert with these findings, we demonstrate that CDDO: 1) activates caspase-8 and thereby caspase-3 by a cytochrome c-independent mechanism and 2) induces cytochrome c release by caspase-8-dependent cleavage of Bid. The results also demonstrate that treatment of osteosarcoma cells with CDDO induces differentiation, as assessed by alkaline phosphatase activity and osteocalcin production, and that this response is abrogated in cells that overexpress CrmA. These findings demonstrate that CDDO induces both osteoblastic differentiation and apoptosis by caspase-8-dependent mechanisms.

The ARG tyrosine kinase interacts with Siva-1 in the apoptotic response to oxidative stress

The Abl family of mammalian nonreceptor tyrosine kinases consists of c-Abl and ARG (Abl-related gene). Certain insights are available regarding the involvement c-Abl in the response of cells to stress. ARG, however, has no known function in cell signaling. The present studies demonstrate that ARG associates with the proapoptotic Siva-1 protein. The functional significance of the ARG-Siva-1 interaction is supported by the finding that ARG is activated by oxidative stress and that this response involves ARG-mediated phosphorylation of Siva-1 on Tyr(48). The proapoptotic effects of Siva-1 are accentuated in cells stably expressing ARG and are inhibited in ARG-deficient cells. Moreover, the proapoptotic effects of Siva-1 are abrogated by mutation of the Tyr(48) site. We also show that the apoptotic response to oxidative stress is attenuated in ARG-deficient cells and that this defect is corrected by reconstituting ARG expression. These findings support a model in which the activation of ARG by oxidative stress induces apoptosis by a Siva-1-dependent mechanism.

The c-Src tyrosine kinase regulates signaling of the human DF3/MUC1 carcinoma-associated antigen with GSK3 beta and beta-catenin

The DF3/MUC1 mucin-like glycoprotein is aberrantly overexpressed in most human carcinomas. The cytoplasmic domain of MUC1 interacts with glycogen synthase kinase 3 beta (GSK3 beta) and thereby decreases binding of MUC1 and beta-catenin. The present studies demonstrate that MUC1 associates with the c-Src tyrosine kinase. c-Src phosphorylates the MUC1 cytoplasmic domain at a YEKV motif located between sites involved in interactions with GSK3 beta and beta-catenin. The results demonstrate that the c-Src SH2 domain binds directly to pYEKV and inhibits the interaction between MUC1 and GSK3 beta. Moreover and in contrast to GSK3 beta, in vitro and in vivo studies demonstrate that c-Src-mediated phosphorylation of MUC1 increases binding of MUC1 and beta-catenin. The findings support a novel role for c-Src in regulating interactions of MUC1 with GSK3 beta and beta-catenin.

Targeting of the c-Abl tyrosine kinase to mitochondria in the necrotic cell death response to oxidative stress

The ubiquitously expressed c-Abl tyrosine kinase is activated in the response of cells to genotoxic and oxidative stress. The present study demonstrates that reactive oxygen species (ROS) induce targeting of c-Abl to mitochondria. We show that ROS-induced localization of c-Abl to mitochondria is dependent on activation of protein kinase C (PKC)delta and the c-Abl kinase function. Targeting of c-Abl to mitochondria is associated with ROS-induced loss of mitochondrial transmembrane potential. The results also demonstrate that c-Abl is necessary for ROS-induced depletion of ATP and the activation of a necrosis-like cell death. These findings indicate that the c-Abl kinase targets to mitochondria in response to oxidative stress and thereby mediates mitochondrial dysfunction and cell death.

The Human DF3/MUC1 carcinoma-associated antigen signals nuclear localization of the catenin p120(ctn)

The human DF3/MUC1 glycoprotein is aberrantly overexpressed by carcinoma cells. The present studies show that MUC1 associates with the Armadillo protein, p120(ctn). The cytoplasmic domain of MUC1 binds directly to p120. The functional significance of the MUC1-p120 association is supported by the demonstration that MUC1 induces nuclear localization of p120. These findings demonstrate that MUC1 confers cell membrane to nuclear signaling by interactions with p120.

Phorbol ester-induced generation of reactive oxygen species is protein kinase cbeta -dependent and required for SAPK activation

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with protein kinase C (PKC) betaII-mediated activation of the stress-activated protein kinase (SAPK) pathway. The present studies demonstrate that the TPA response of U-937 cells includes the generation of reactive oxygen species (ROS). By contrast, the TPA-resistant U-937 cell variant (TUR), which is deficient in PKCbetaII expression, failed to respond to TPA with the induction of ROS. Moreover, we show that TPA-induced ROS production is restored in TUR cells stably transfected to express PKCbetaII. The results also demonstrate that TPA-induced ROS production is required for activation of the MEK kinase-1 (MEKK-1)--> SAPK pathway. In concert with this observation, treatment of U-937 with H(2)O(2) as a source of ROS is associated with activation of the MEKK-1-->SAPK cascade. These findings indicate that PKCbetaII is required for TPA-induced ROS production and that the MEKK-1-->SAPK pathway is activated by a ROS-mediated mechanism.

Induction of antitumor immunity by vaccination of dendritic cells transfected with MUC1 RNA

Dendritic cells (DC) are potent APCs. In this study, murine bone marrow-derived DC were transfected with RNA encoding the MUC1 Ag that is aberrantly overexpressed in human breast and other carcinomas. The MUC1 RNA-transfected DC exhibited cell surface expression of MUC1 and costimulatory molecules. After injection at the base of the tail, the transfected DC were detectable in inguinal lymph nodes by dual immunochemical staining. Vaccination of wild-type mice with MUC1 RNA-transfected DC induced anti-MUC1 immune responses against MUC1-positive MC38/MUC1, but not MUC1-negative, tumor cells. Mice immunized with the transfected DC were protected against challenge with MC38/MUC1 tumor cells. Furthermore, mice with established MC38/MUC1 tumors were eliminated after receiving the vaccination. CTLs isolated from mice immunized with the transfected DC exhibited specific cytolytic activity against MC38/MUC1 tumor cells. In contrast to these findings, there was little if any anti-MUC1 immunity induced with the transfected DC in MUC1 transgenic (MUC1.Tg) mice. However, coadministration of the transfected DC and IL-12 reversed the unresponsiveness to MUC1 Ag in MUC1.Tg mice and induced MUC1-specific immune responses. These findings demonstrate that vaccination of DC transfected with MUC1 RNA and IL-12 reverses tolerance to MUC1 and induces immunity against MUC1-positive tumors.

Selection and characterization of MUC1-specific CD8+ T cells from MUC1 transgenic mice immunized with dendritic-carcinoma fusion cells

Mice transgenic for the human MUC1 carcinoma-associated antigen (MUC1.Tg) are tolerant to immunization with MUC1 antigen. Recent studies, however, have demonstrated that immunization of MUC1.Tg mice with fusions of MUC1-positive tumour and dendritic cells (FC/MUC1) reverses MUC1 unresponsiveness and results in rejection of established MUC1-positive pulmonary metastases. Here we demonstrate that lymph node cells from MUC1.Tg mice immunized with the FC/MUC1 fusion cells proliferate in response to MUC1 antigen by a mechanism dependent on the function of CD4, major histocompatibility complex (MHC) class II, B7-1, B7-2, CD28, CD40 and CD40 ligand. The findings demonstrate that stimulation of lymph node cells with MUC1 results in selection of MUC1-specific CD8+ T cells. We show that the CD8+ T cells exhibit MUC1-specific cytotoxic T lymphocyte (CTL) activity by recognition of MUC1 peptides presented in the context of MHC class I molecules Kb and Db. The MUC1-specific CD8+ T cells also exhibit antitumour activity against MUC1-positive metastases, but with no apparent reactivity against normal tissues. These results indicate that immunization of MUC1.Tg mice with FC/MUC1 reverses immunological unresponsiveness to MUC1 by presentation of MUC1 peptides in the presence of costimulatory signals and generates MHC-restricted MUC1-specific CD8+ T cells.

XIAP regulates DNA damage-induced apoptosis downstream of caspase-9 cleavage

The IAP (inhibitor of apoptosis) family of anti-apoptotic proteins regulates programmed cell death. Of the six known human IAP-related proteins, XIAP is the most potent inhibitor. To study the mechanistic effects of XIAP on DNA damage-induced apoptosis, we prepared U-937 cells that stably overexpress XIAP. The results demonstrate that XIAP inhibits apoptosis induced by 1-[beta-d-arabinofuranosyl]cytosine (ara-C) and other genotoxic agents. XIAP had no detectable effect on ara-C-induced release of mitochondrial cytochrome c and attenuated cleavage of procaspase-9. In addition, we show that ara-C induces the association of XIAP with the cleaved fragments of caspase-9 and thereby inhibition of caspase-9 activity. The results also demonstrate that ara-C induces cleavage of procaspase-3 by a caspase-8-dependent mechanism and that XIAP inhibits caspase-3 activity. These results demonstrate that XIAP functions downstream of procaspase-9 cleavage as an inhibitor of both proteolytically processed caspase-9 and -3 in the cellular response to genotoxic stress.

Negative regulation of cytochrome c-mediated oligomerization of Apaf-1 and activation of procaspase-9 by heat shock protein 90

The release of cytochrome c from mitochondria results in the formation of an Apaf-1-caspase-9 apoptosome and induces the apoptotic protease cascade by activation of procaspase-3. The present studies demonstrate that heat shock protein 90 (Hsp90) forms a cytosolic complex with Apaf-1 and thereby inhibits the formation of the active complex. Immunodepletion of Hsp90 depletes Apaf-1 and thereby inhibits cytochrome c-mediated activation of caspase-9. Addition of purified Apaf-1 to Hsp90-depleted cytosolic extracts restores cytochrome c-mediated activation of procaspase-9. We also show that Hsp90 inhibits cytochrome c-mediated oligomerization of Apaf-1 and thereby activation of procaspase-9. Furthermore, treatment of cells with diverse DNA-damaging agents dissociates the Hsp90-Apaf-1 complex and relieves the inhibition of procaspase-9 activation. These findings provide the first evidence for a negative cytosolic regulator of cytochrome c-dependent apoptosis and for involvement of a chaperone in the caspase cascade.

Requirement for caspase activation in monocytic differentiation of myeloid leukemia cells

Human myeloid leukemia cells respond to 12-tetradecanoylphorbol-13-acetate (TPA) and other activators of protein kinase C (PKC) with the induction of terminal monocytic differentiation. The present studies demonstrate that TPA treatment of U-937 leukemia cells is associated with release of mitochondrial cytochrome c, activation of caspase-3 and induction of internucleosomal DNA fragmentation. By contrast, the TUR cell variant, which is deficient in PKCbeta, failed to respond to TPA with release of cytochrome c and induction of the caspase-3 cascade. Moreover, stable overexpression of PKCbeta in TUR cells reconstituted sensitivity to TPA-induced cytochrome c release and activation of caspase-3. The results also demonstrate that treatment of cells with the caspase inhibitor Z-VAD-fmk blocks both TPA-induced apoptosis and monocytic differentiation. Similar results were obtained in U-937 cells stably expressing the CrmA caspase inhibitor. These findings demonstrate that TPA induces cytochrome c release by a PKCbeta-dependent mechanism and that activation of caspase-mediated signaling is required for induction of the differentiated monocytic phenotype.

Fusions of human ovarian carcinoma cells with autologous or allogeneic dendritic cells induce antitumor immunity

Human ovarian carcinomas express the CA-125, HER2/neu, and MUC1 tumor-associated Ags as potential targets for the induction of active specific immunotherapy. In the present studies, human ovarian cancer cells were fused to human dendritic cells (DC) as an alternative strategy to induce immunity against known and unidentified tumor Ags. Fusions of ovarian cancer cells to autologous DC resulted in the formation of heterokaryons that express the CA-125 Ag and DC-derived costimulatory and adhesion molecules. Similar findings were obtained with ovarian cancer cells fused to allogeneic DC. The fusion cells were functional in stimulating the proliferation of autologous T cells. The results also demonstrate that fusions of ovarian cancer cells to autologous or allogeneic DC induce cytolytic T cell activity and lysis of autologous tumor cells by a MHC class I-restricted mechanism. These findings demonstrate that fusions of ovarian carcinoma cells and DC activate T cell responses against autologous tumor and that the fusions are functional when generated with either autologous or allogeneic DC.

Role for Lyn tyrosine kinase as a regulator of stress-activated protein kinase activity in response to DNA damage

The cellular response to DNA damage includes activation of the nuclear Lyn protein tyrosine kinase. Using cells deficient in Lyn expression, the present studies demonstrate that Lyn is required in part for induction of the stress-activated protein kinase (SAPK) in the response to 1-beta-D-arabinofuranosylcytosine (ara-C) and other genotoxic agents. By contrast, exposure of Lyn-deficient cells to ara-C, ionizing radiation, or cisplatin had no effect on activation of extracellular signal-regulated protein kinase or p38 mitogen-activated protein kinase. Similar findings were obtained in cells stably expressing a kinase-inactive, dominant-negative Lyn(K-R) mutant. Coexpression studies demonstrate that Lyn, but not Lyn(K-R), induces SAPK activity. In addition, the results demonstrate that Lyn activates SAPK by an MKK7-dependent, SEK1-independent mechanism. As MEKK1 functions upstream to MKK7 and SAPK, the finding that a dominant-negative MEKK1(K-M) mutant blocks Lyn-induced SAPK activity supports involvement of the MEKK1-->MKK7 pathway. The results also demonstrate that inhibition of Lyn-induced SAPK activity abrogates the apoptotic response of cells to genotoxic stress. These findings indicate that activation of SAPK by DNA damage is mediated in part by Lyn and that the Lyn-->MEKK1-->MKK7-->SAPK pathway is functional in the induction of apoptosis by genotoxic agents.

Mitochondrial translocation of protein kinase C delta in phorbol ester-induced cytochrome c release and apoptosis

Apoptosis is induced by the release of cytochrome c from mitochondria to the cytoplasm. The present studies demonstrate that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) induces translocation of protein kinase C (PKC) delta from the cytoplasm to mitochondria. The results also show that translocation of PKCdelta results in release of cytochrome c. The functional significance of this event is further supported by the demonstration that PKCdelta translocation is required for TPA-induced apoptosis. These findings demonstrate that translocation of PKCdelta to mitochondria is responsible, at least in part, for inducing cytochrome c release and apoptosis.

Immune reconstitution following high-dose chemotherapy with stem cell rescue in patients with advanced breast cancer

The present study examines the nature of humoral and cellular immune reconstitution in 28 patients with advanced breast cancer following high-dose chemotherapy with stem cell rescue. Patients underwent testing of T, B, NK and dendritic cell function at serial time points until 1 year post transplant or until the time of disease progression. Abnormalities in T cell phenotype and function were observed following high-dose chemotherapy that persisted for at least 6-12 months. The vast majority of patients experienced an inversion of the CD4/CD8 ratio and demonstrated an anergic response to candida antigen. Mean T cell proliferation in response to PHA and to co-culture with allogeneic monocytes was significantly compromised. In contrast, mean IgG and IgA levels were normal 6 months post transplant and NK cell yields and function were transiently elevated following high-dose chemotherapy. Dendritic cells generated from peripheral blood progenitors displayed a characteristic phenotype and were potent inducers of allogeneic T cell proliferation in the post-transplant period. The study demonstrates that patients undergoing autologous transplantation for breast cancer experience a prolonged period of T cell dysfunction. In contrast, B, NK, and DC recover more rapidly. These findings carry significant implications for the design of post-transplant immunotherapy.

Activation of MEK kinase 1 by the c-Abl protein tyrosine kinase in response to DNA damage

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents and regulates induction of the stress-activated c-Jun N-terminal protein kinase (SAPK). Here we show that nuclear c-Abl associates with MEK kinase 1 (MEKK-1), an upstream effector of the SEK1-->SAPK pathway, in the response of cells to genotoxic stress. The results demonstrate that the nuclear c-Abl binds to MEKK-1 and that c-Abl phosphorylates MEKK-1 in vitro and in vivo. Transient-transfection studies with wild-type and kinase-inactive c-Abl demonstrate c-Abl kinase-dependent activation of MEKK-1. Moreover, c-Abl activates MEKK-1 in vitro and in response to DNA damage. The results also demonstrate that c-Abl induces MEKK-1-mediated phosphorylation and activation of SEK1-SAPK in coupled kinase assays. These findings indicate that c-Abl functions upstream of MEKK-1-dependent activation of SAPK in the response to genotoxic stress.

Proteolytic cleavage and activation of protein kinase C [micro] by caspase-3 in the apoptotic response of cells to 1-beta -D-arabinofuranosylcytosine and other genotoxic agents

Protein kinase C (PKC) mu is a novel member of the PKC family that differs from the other isozymes in structural and biochemical properties. The precise function of PKCmu is not known. The present studies demonstrate that PKCmu is cleaved during apoptosis induced by 1-beta-d-arabinofuranosylcytosine (ara-C) and other genotoxic agents. PKCmu cleavage is blocked in cells that overexpress the anti-apoptotic Bcl-x(L) protein or the baculovirus p35 protein. Our results demonstrate that PKCmu is cleaved by caspase-3 at the CQND(378)S site. Cleavage of PKCmu is associated with release of the catalytic domain and activation of its kinase function. We also show that, unlike the cleaved fragments of PKCdelta and theta, overexpression of the PKCmu catalytic domain is not lethal. Cells stably expressing the catalytic fragment of PKCmu, however, are more sensitive to apoptosis induced by genotoxic stress. In addition, expression of the caspase-resistant PKCmu mutant partially inhibits DNA damage-induced apoptosis. These findings demonstrate that PKCmu is cleaved by caspase-3 and that expression of the catalytic domain sensitizes cells to the cytotoxic effects of ara-C and other anticancer agents.

Activation of the cytoplasmic c-Abl tyrosine kinase by reactive oxygen species

The ubiquitously expressed c-Abl protein tyrosine kinase localizes to both the nucleus and cytoplasm. The nuclear form of c-Abl is activated in the cellular response to genotoxic stress. Here we show that cytoplasmic c-Abl is activated by oxidative stress. The results also demonstrate that mitochondrial cytochrome c is released in the cellular response to H(2)O(2) and that this effect is mediated by a c-Abl-dependent mechanism. In concert with these results, we show that H(2)O(2)-induced apoptosis is attenuated in c-Abl-deficient cells. These findings demonstrate that cytoplasmic c-Abl is involved in the apoptotic response of cells to oxidative stress.

Regulation of the hTERT telomerase catalytic subunit by the c-Abl tyrosine kinase

BACKGROUND

Telomeres consist of repetitive (TTAGGG) DNA sequences that are maintained by the multisubunit telomerase ribonucleoprotein. Telomerase consists of an RNA, which serves as template for the sequence tracts, and a catalytic subunit that functions in reverse transcription of the RNA template. Cloning and characterization of the human catalytic subunit of telomerase (hTERT) has supported a role in cell transformation. How telomerase activity is regulated, however, is largely unknown.

RESULTS

We show here that hTERT associates directly with the c-Abl protein tyrosine kinase. We also found that c-Abl phosphorylates hTERT and inhibits hTERT activity. Moreover, our findings demonstrate that exposure of cells to ionizing radiation induces tyrosine phosphorylation of hTERT by a c-Abl-dependent mechanism. The functional significance of the c-Abl-hTERT interaction is supported by the demonstration that cells deficient in c-Abl show telomere lengthening.

CONCLUSIONS

The ubiquitously expressed c-Abl tyrosine kinase is activated by DNA double-strand breaks. Our finding of telomere lengthening in c-Abl-deficient cells and the functional interactions between c-Abl and hTERT support a role for c-Abl in the regulation of telomerase function.