Oleg Tikhomirov

Adenosine receptors in regulation of dendritic cell differentiation and function.

Differentiation of functional dendritic cells (DCs) critically depends on the microenvironment. DCs differentiate in hypoxic tumor sites and inflamed or damaged tissue. Because local concentrations of adenosine reach high physiologically relevant levels in these conditions, we assessed the expression of adenosine receptors and the effect of their activation on differentiation of human monocytes and mouse peritoneal macrophages and hematopoietic progenitor cells (HPCs) into myeloid DCs. Stimulation of adenosine receptors skews DC differentiation toward a distinct cell population characterized by expression of both DC and monocyte/macrophage cell surface markers. Pharmacologic analysis and experiments with cells from A(2B) adenosine receptor knockout mice identified A(2B) receptor as the mediator of adenosine effects on DCs. Unlike normal myeloid DCs, adenosine-differentiated DCs have impaired allostimulatory activity and express high levels of angiogenic, pro-inflammatory, immune suppressor, and tolerogenic factors, including VEGF, IL-8, IL-6, IL-10, COX-2, TGF-beta, and IDO. They promoted tumor growth if injected into tumors implanted in mice. Using adenosine desaminase knockout animals, we showed that DCs with proangiogenic phenotype are highly abundant under conditions associated with elevated levels of extracellular adenosine in vivo. Adenosine signaling through A(2B) receptor is an important factor of aberrant DC differentiation and generation of tolerogenic, angiogenic, and proinflammatory cells.

Ectodomain Cleavage of ErbB-4 CHARACTERIZATION OF THE CLEAVAGE SITE AND m80 FRAGMENT

Ectodomain cleavage of the ErbB-4 receptor tyrosine kinase generates a membrane-associated fragment of 80 kDa (m80) that has been subjected to N-terminal sequencing. The sequence obtained shows that the N terminus of this fragment begins with Ser-652 of ErbB-4. When a 12-residue peptide corresponding to ErbB-4 residues 646–657 was incubated with recombinant tumor necrosis factor-α-converting enzyme, fragments representing residues 646–651 and 652–657 were obtained. These data indicate that ectodomain cleavage of ErbB-4 occurs between His-651 and Ser-652, placing the cleavage site within the ectodomain stalk region approximately 8 residues prior to the transmembrane domain. Several experiments have characterized other aspects of the m80 ErbB-4 fragment. Inhibition of ErbB-4 tyrosine kinase activity with pan-ErbB tyrosine kinase inhibitors indicates that kinase activity is stringently required for heregulin-dependent, but not 12-O-tetradecanoylphorbol-13-acetate-induced, ErbB-4 ectodomain cleavage and formation of the m80 fragment. When the m80 ErbB-4 fragment is generated by cell treatment with heregulin or 12-O-tetradecanoylphorbol-13-acetate, the fragment associates with intact ErbB-2. However, this fragment does not associate with the intact ErbB-4 molecule.

Ligand-induced, p38-dependent Apoptosis in Cells Expressing High Levels of Epidermal Growth Factor Receptor and ErbB-2

Increased expression of the epidermal growth factor (EGF) receptor (EGFR) and ErbB-2 is implicated into the development and progression of breast cancer. Constant ligand-induced activation of EGFR and ErbB-2 receptor-tyrosine kinases is thought to be involved in the transformation of fibroblasts and mammary epithelial cells. Data herein show that ligand stimulation of cells that express both the EGFR and the ErbB-2 may result either in cell proliferation or apoptosis depending on the expression levels of EGFR and ErbB-2. Mammary tumor cells that express low levels of both receptors or high levels of ErbB-2 and low levels of EGFR survive and proliferate in the presence of EGF. In contrast, fibroblastic cells or mammary tumor cells, which co-express high levels of EGFR and ErbB-2 invariably undergo apoptosis in response to EGF. In these cells persistent activation of p38 MAPK is an essential element of the apoptotic mechanism. Also, the data implicate a p38-dependent change in mitochondrial membrane permeability as a downstream effector of apoptosis. Ligand-dependent apoptosis in cells co-expressing high levels of EGFR and ErbB-2 could be a natural mechanism that protects tissues from unrestricted proliferation in response to the sustained activation of receptor-tyrosine kinases.

Bax activation and translocation to mitochondria mediate EGF-induced programmed cell death

The ErbB family of receptor tyrosine kinases is involved in the regulation of cell proliferation, differentiation and apoptosis. Previous studies indicate that cells expressing elevated levels of the EGFR and ErbB-2 undergo programmed cell death in response to EGF or other EGFR ligands. However, the detailed mechanisms of EGF-induced apoptosis are unclear. This report demonstrates that in the cells undergoing EGF-dependent apoptosis Bax changes its conformation and forms multimeric aggregates, which accumulate on the mitochondrial membrane. Bax activation and translocation to the mitochondria induces a loss of mitochondrial transmembrane potential and cell death. Also, during EGF-induced apoptosis there is downregulation of Bcl-xL, an anti-apoptotic protein. Expression of Bcl-xL in cells susceptible to EGF-dependent apoptosis prevents cell death. The data indicate that addition of EGF does not result in a significant release of cytochrome c from mitochondria and EGF-induced apoptosis is mainly caspase independent.

Tracking NF-κB activity in tumor cells during ovarian cancer progression in a syngeneic mouse model

BackgroundNuclear factor-kappa B (NF-kappaB) signaling is an important link between inflammation and peritoneal carcinomatosis in human ovarian cancer. Our objective was to track NF-kappaB signaling during ovarian cancer progression in a syngeneic mouse model using tumor cells stably expressing an NF-kappaB reporter.MethodsID8 mouse ovarian cancer cells stably expressing an NF-kappaB-dependent GFP/luciferase (NGL) fusion reporter transgene (ID8-NGL) were generated, and injected intra-peritoneally into C57BL/6 mice. NGL reporter activity in tumors was non-invasively monitored by bioluminescence imaging and measured in luciferase assays in harvested tumors. Ascites fluid or peritoneal lavages were analyzed for inflammatory cell and macrophage content, and for mRNA expression of M1 and M2 macrophage markers by quantitative real-time RT-PCR. 2-tailed Mann-Whitney tests were used for measuring differences between groups in in vivo experiments.ResultsIn ID8-NGL cells, responsiveness of the reporter to NF-kappaB activators and inhibitors was confirmed in vitro and in vivo. ID8-NGL tumors in C57BL/6 mice bore histopathological resemblance to human high-grade serous ovarian cancer and exhibited similar peritoneal disease spread. Tumor NF-kappaB activity, measured by the NGL reporter and by western blot of nuclear p65 expression, was markedly elevated at late stages of ovarian cancer progression. In ascites fluid, macrophages were the predominant inflammatory cell population. There were elevated levels of the M2-like pro-tumor macrophage marker, mannose-receptor, during tumor progression, and reduced levels following NF-kappaB inhibition with thymoquinone.ConclusionsOur ID8-NGL reporter syngeneic model is suitable for investigating changes in tumor NF-kappaB activity during ovarian cancer progression, how NF-kappaB activity influences immune cells in the tumor microenvironment, and effects of NF-kappaB-targeted treatments in future studies.

Identification of proteolytic fragments from ErbB-2 that induce apoptosis.

The receptor tyrosine kinase ErbB-2 plays an important role in cell proliferation and differentiation as well as oncogenesis. We have found that ErbB-2 kinase domain fragmentation is important for the induction of apoptosis. Exogenous expression of peptides derived from the ErbB-2 kinase domain induces cells death with the hallmarks of apoptosis. In contrast, transfection of the ErbB-2 carboxy-terminal domain did not induce apoptosis. We have identified a 37-residue segment from the ErbB-2 kinase N-terminal lobe that can strongly induce apoptosis in transfected cells. Cell death was not blocked by the pan-caspase inhibitor z-VAD-FMK. Similar fragments derived from several other receptor tyrosine kinases also induce cell death. These data imply that proteolytic fragmentation of tyrosine kinases liberates apoptotic fragments that can accelerate cell death.

Aberrant activation of NF-κB signaling in mammary epithelium leads to abnormal growth and ductal carcinoma in situ

BackgroundApproximately 1 in 5 women diagnosed with breast cancer are considered to have in situ disease, most often termed ductal carcinoma in situ (DCIS). Though recognized as a risk factor for the development of more invasive cancer, it remains unclear what factors contribute to DCIS development. It has been shown that inflammation contributes to the progression of a variety of tumor types, and nuclear factor kappa B (NF-κB) is recognized as a master-regulator of inflammatory signaling. However, the contributions of NF-κB signaling to tumor initiation are less well understood. Aberrant up-regulation of NF-κB activity, either systemically or locally within the breast, could occur due to a variety of commonly experienced stimuli such as acute infection, obesity, or psychological stress. In this study, we seek to determine if activation of NF-κB in mammary epithelium could play a role in the formation of hyperplastic ductal lesions.MethodsOur studies utilize a doxycycline-inducible transgenic mouse model in which constitutively active IKKβ is expressed specifically in mammary epithelium. All previously published models of NF-κB modulation in the virgin mammary gland have been constitutive models, with transgene or knock-out present throughout the life and development of the animal. For the first time, we will induce activation at later time points after normal ducts have formed, thus being able to determine if NF-κB activation can promote pre-malignant changes in previously normal mammary epithelium.ResultsWe found that even a short pulse of NF-κB activation could induce profound remodeling of mammary ductal structures. Short-term activation created hyperproliferative, enlarged ducts with filled lumens. Increased expression of inflammatory markers was concurrent with the down-regulation of hormone receptors and markers of epithelial differentiation. Furthermore, the oncoprotein mucin 1, known to be up-regulated in human and mouse DCIS, was over-expressed and mislocalized in the activated ductal tissue.ConclusionsThese results indicate that aberrant NF-κB activation within mammary epithelium can lead to molecular and morphological changes consistent with the earliest stages of breast cancer. Thus, inhibition of NF-κB signaling following acute inflammation or the initial signs of hyperplastic ductal growth could represent an important opportunity for breast cancer prevention.

Effects of vitamin A deficiency in the postnatal mouse heart: role of hepatic retinoid stores.

To determine whether hepatic depletion of vitamin A (VA) stores has an effect on the postnatal heart, studies were carried out with mice lacking liver retinyl ester stores fed either a VA-sufficient (LRVAS) or VA-deficient (LRVAD) diet (to deplete circulating retinol and extrahepatic stores of retinyl esters). There were no observable differences in the weights or gross morphology of hearts from LRVAS or LRVAD mice relative to sex-matched, age-matched, and genetically matched wild-type (WT) controls fed the VAS diet (WTVAS), but changes in the transcription of functionally relevant genes were consistent with a state of VAD in LRVAS and LRVAD ventricles. In silico analysis revealed that 58/67 differentially expressed transcripts identified in a microarray screen are products of genes that have DNA retinoic acid response elements. Flow cytometric analysis revealed a significant and cell-specific increase in the number of proliferating Sca-1 cardiac progenitor cells in LRVAS animals relative to WTVAS controls. Before myocardial infarction, LRVAS and WTVAS mice had similar cardiac systolic function and structure, as measured by echocardiography, but, unexpectedly, repeat echocardiography demonstrated that LRVAS mice had less adverse remodeling by 1 wk after myocardial infarction. Overall, the results demonstrate that the adult heart is responsive to retinoids, and, most notably, reducing hepatic VA stores (while maintaining circulating levels of VA) impacts ventricular gene expression profiles, progenitor cell numbers, and response to injury.

Abstract 3630: Immunoengineering of tumor associated macrophages using targeted, siRNA delivering nanoparticles

Tumor associated macrophages (TAMs) can modify the tumor microenvironment to create a pro-tumor niche. Dysregulation of NF-κB signaling is implicated in creating a pro-tumor phenotype in TAMs. NF-κB signaling consists of a classical pathway and a less understood alternative pathway. Suppression of NF-κB activation in TAMs is predicted to decrease local smoldering inflammation and inhibit the pro-tumor TAM phenotype. However, recent studies have reported anti-tumor macrophage behavior induced by activation of the classical NF-κB pathway. We have successfully used mannosylated polymer nanoparticles (Mn-NP) to deliver siRNA for RNAi of NF-κB proteins in bone marrow derived macrophages (BMDMs) and mouse TAMs in vivo. Mannose serves as a macrophage targeting ligand via the mannose receptor (CD206). This work aims to characterize these nanomaterials for targeted delivery of functional nucleic acid sequences into macrophages in vitro and in vivo. These studies will also use the Mn-NP to investigate the effects of specific manipulation of NF-κB activation on macrophage phenotype. Mn-NPs are micelles formed by self-assembly of triblock polymers with a poly(BMA-co-PAA-co-DMAEMA) core, a DMAEMA siRNA condensing block, and an azide-containing outer block for further functionalization. Alkyne functionalized mannose is then “clicked” on the end of the polymer and presented on the micellar surface. In vitro cell studies carried out with BMDMs from mice that express luciferase as a reporter of total NF-κB activity. Mn-NP delivery of siRNA (50 nM for 24 hrs) against each of several NF-κB pathway proteins confirms efficacious knockdown of total NF-κB activity, comparable to transfection with the commercial agent Lipofectamine. Mn-NPs are also highly biocompatible in vitro and exhibit no significant liver or kidney toxicity in mice at doses of 5 mg/kg. The mannosylated carrier effectively delivers cy3 fluorescently labeled nucleotides to TAMs in multiple model systems, including in primary mammary tumors arising spontaneously in polyoma mice and an implanted ovarian tumor model, . Currently, studies are focused on a potential therapeutic strategy that involves RNAi of an inhibitor of the classical NF-κB pathway, IκBα, in order to strategically activate the classical pathway in TAMs. Quantitative RT-PCR analysis of macrophages treated with Mn-NP formulated with siRNA against IκBα show a decrease in M2 markers, a decrease in smoldering inflammation associated cytokines, and an increase in immune cell recruiting chemokines. Citation Format: Ryan Ortega, Whitney Barham, Oleg Tikhomirov, Kavya Sharman, Fiona Yull, Todd Giorgio. Immunoengineering of tumor associated macrophages using targeted, siRNA delivering nanoparticles. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3630. doi:10.1158/1538-7445.AM2014-3630

Abstract 3010: The role of NF-kappaB in mammary tumor initiation

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Nuclear factor kappa B signaling is accepted as a major component of pro-survival signaling within breast cancer cells. However, less is known about how NF-kappaB could contribute to breast tumor initiation. Inflammatory signaling can be activated within the breast by such common factors as obesity, involution following lactation, aging, and psychological stress. Thus, understanding how activated NF-kappaB could lead to the initiation of breast tumors would provide opportunities to develop prevention strategies. We generated a doxycycline-inducible mouse model to study the effects of constitutively active IKK2 on ductal morphogenesis. In this model, Tet-o-cIKK2 mice are crossed with MMTV-rtTA transgenics to target inducible expression specifically to the mammary epithelium. Expression of cIKK2 in transplanted mammary tissue results in enlarged terminal end-buds, increased lateral branching, and intraductal hyperplasia. Transgene induction for only 3 days in a 6 week old female induces filling of ductal lumens, hypercellularity and loss of strict basal/luminal structure. Quantitative PCR of mammary tissue reveals up-regulated markers of macrophage infiltration such as CCL2 and F4/80 and markers of inflammation including Cox-2, TNF-alpha, and CXCL1. Interestingly, constitutive IKK2 activation also results in a decrease in hormone receptor levels (ERα and PR). Immunofluorescent staining shows that activation of classical NF-kappaB increases nuclear p65, as expected. However, nuclear p52 is also increased in transgene positive cells, suggesting that a subset of the effects resulting from activation of classical NF-kappaB are mediated by cross talk with the alternative pathway. Taken together, we find that activation of NF-kappaB in mammary epithelium is sufficient to induce hyperplastic growth and loss of ductal structure. Ongoing studies seek to define what additional factors, such as the right hormonal context, will cause the lesions to progress to malignancy. Citation Format: Whitney Barham, Oleg Tikhomirov, Lianyi Chen, Ryan Ortega, Halina Onishko, Linda Connelly, Fiona E. Yull. The role of NF-kappaB in mammary tumor initiation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3010. doi:10.1158/1538-7445.AM2014-3010