[show abstract][hide abstract] ABSTRACT: The effect of activation and over-expression of the nuclear receptor PPARβ/δ in human MDA-MB-231 (ER-) and MCF7 (ER+) breast cancer cell lines was examined. Target gene induction by ligand activation of PPARβ/δ was increased by over-expression of PPARβ/δ compared to controls. Over-expression of PPARβ/δ caused a decrease in cell proliferation in MCF7 and MDA-MB-231 cells compared to controls while ligand activation of PPARβ/δ further inhibited proliferation of MCF7 but not MDA-MB-231 cells. Over-expression and/or ligand activation of PPARβ/δ in MDA-MB-231 or MCF7 cells had no effect on experimental apoptosis. Decreased clonogenicity was observed in both MDA-MB-231 and MCF7 over-expressing PPARβ/δ in response to ligand activation of PPARβ/δ as compared to controls. Ectopic xenografts developed from MDA-MB-231 and MCF7 cells over-expressing PPARβ/δ were significantly smaller and ligand activation of PPARβ/δ caused an even greater reduction in tumor volume as compared to controls. Interestingly, the decrease in MDA-MB-231 tumor size after over-expressing PPARβ/δ and ligand activation of PPARβ/δ correlated with increased necrosis. These data show that ligand activation and/or over-expression of PPARβ/δ in two human breast cancer cell lines inhibits relative breast cancer tumorigenicity and provide further support for the development of ligands for PPARβ/δ to specifically inhibit breast carcinogenesis. These new cell-based models will be invaluable tools for delineating the role of PPARβ/δ in breast cancer and evaluating the effects of PPARβ/δ agonists.
Molecular Cancer Therapeutics 01/2014; · 5.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: Tec family kinases play critical roles in the activation of immune cells. In particular, Itk is important for the activation of T cells via the T cell Receptor (TcR), however, molecules that cooperate with Itk to activate downstream targets remain little explored. Here we show that Itk interacts with the heterotrimeric G-protein α subunit Gα13 during TcR triggering. This interaction requires membrane localization of both partners, and is partially dependent on GDP- and GTP-bound states of Gα13. Furthermore, we find that Itk interacts with Gα13 via the zinc binding regions within its Tec homology domain. The interaction between Itk and Gα13 also results in tyrosine phosphorylation of Gα13, however this is not required for the interaction. Itk enhances Gα13 mediated activation of serum response factor (SRF) transcriptional activity dependent on its ability to interact with Gα13, but its kinase activity is not required to enhance SRF activity. These data reveal a new pathway regulated by Itk in cells, and suggest cross talk between Itk and G-protein signaling downstream of the TcR.
The international journal of biochemistry & cell biology 02/2013; · 4.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mast cells play a critical role in the development of the allergic response. Upon activation by allergens and IgE via the high affinity receptor for IgE (FcɛRI), these cells release histamine and other functional mediators that initiate and propagate immediate hypersensitivity reactions. Mast cells also secrete cytokines that can regulate immune activity. These processes are controlled, in whole or part, by increases in intracellular Ca(2+) induced by the FcɛRI. We show here that N-(4-(3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl)phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2), a pyrazole derivative, inhibits activation-induced Ca(2+) influx in the rat basophil cell line RBL-2H3 and in bone marrow-derived mast cells (BMMCs), without affecting global tyrosine phosphorylation of cellular proteins or phosphorylation of the mitogen-activated protein kinases Erk1/2, JNK and p38. BTP2 also inhibits activation-induced degranulation and secretion of interleukin (IL)-2, IL-3, IL-4, IL-6, IL-13, tumor necrosis factor (TNF)-α, and granulocyte macrophage-colony stimulating factor (GM-CSF) by BMMCs, which correlates with the inhibition of Nuclear Factor of Activated T cells (NFAT) translocation. In vivo, BTP2 inhibits antigen-induced histamine release. Structure-activity relationship analysis indicates that substitution at the C3 or C5 position of the pyrazole moiety on BTP2 (5-trifluoromethyl-3-methyl-pyrazole or 3-trifluoromethyl-5-methyl-pyrazole, respectively) affected its activity, with the trifluoromethyl group at the C3 position being critical to its activity. We conclude that BTP2 and related compounds may be potent modulators of mast cell responses and potentially useful for the treatment of symptoms of allergic inflammation.
The international journal of biochemistry & cell biology 08/2011; 43(8):1228-39. · 4.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mast cells are critical effector cells in the pathophysiology of allergic asthma and other IgE-mediated diseases. The Tec family of tyrosine kinases Itk and Btk serve as critical signal amplifiers downstream of antigen receptors. Although both kinases are expressed and activated in mast cells following FcεRI stimulation, their individual contributions are not clear. To determine whether these kinases play unique and/or complementary roles in FcεRI signaling and mast cell function, we generated Itk and Btk double knock-out mice. Analyses of these mice show decreased mast cell granularity and impaired passive systemic anaphylaxis responses. This impaired response is accompanied by a significant elevation in serum IgE in Itk/Btk double knock-out mice. In vitro analyses of bone marrow-derived mast cells (BMMCs) indicated that Itk/Btk double knock-out BMMCs are defective in degranulation and cytokine secretion responses downstream to FcεRI activation. These responses were accompanied by a significant reduction in PLCγ2 phosphorylation and severely impaired calcium responses in these cells. This defect also results in altered NFAT1 nuclear localization in double knock-out BMMCs. Network analysis suggests that although they may share substrates, Itk plays both positive and negative roles, while Btk primarily plays a positive role in mast cell FcεRI-induced cytokine secretion.
Journal of Biological Chemistry 01/2011; 286(11):9503-13. · 4.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: Critical physiological roles of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) include the regulation glucose and lipid homeostasis, cellular differentiation, and modulation of inflammation. The potential for targeting PPARβ/δ for the prevention and treatment of metabolic diseases or cancer, is compromised because of major inconsistencies in the literature. This is due primarily to uncertainty regarding the effect of PPARβ/δ and its activation on cell proliferation, apoptosis and cell survival. This review summarizes both the confirmed and conflicting mechanisms that have been described for PPARβ/δ and the potential for targeting this nuclear receptor for the prevention and treatment of colon cancer.
Drug Discovery Today Disease Mechanisms 01/2011; 8(3-4):e85-e93.
[show abstract][hide abstract] ABSTRACT: The putative cardioprotective and chemopreventive properties of the red wine phenolic resveratrol (RES) have made it the subject of a growing body of clinical and basic research. We have begun investigations focusing on the effects of RES on the activity of the aryl hydrocarbon receptor (AHR) complex. Our evidence suggests that RES is a potent repressor of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible gene transcription in estrogen receptor (ER)-positive human breast, lung, and colon cancer cell lines. RES activates the transcription of the ER target genes to the same degree as estradiol (E(2)) in human MCF-7 breast cancer cells. Unlike E(2), which can only diminish TCDD-inducible CYP1A1 gene transcription by approximately 50%, RES can completely abrogate this response. Furthermore, 50% repression of TCDD-inducible transcription can be achieved with 100 nM RES, approximately 2.5 orders of magnitude lower than concentrations required for maximal inhibition, suggesting that multiple mechanisms are responsible for this effect. RES (100 nM) does not prevent ligand binding of a TCDD analog, nor does it prevent AHR from binding to its response element in the 5'-regulatory region of the CYP1A1 gene. Small inhibitory RNAs directed to ERα have demonstrated that RES-mediated repression of CYP1A1 depends on ERα. Whereas CYP1A1 protein levels in MCF-7 cells are refractory to the low-dose transcriptional effects of RES, a concomitant decrease in CYP1A1 protein levels is observed in Caco-2 cells. These results highlight a low-dose RES effect that could occur at nutritionally relevant exposures and are distinct from the high-dose effects often characterized.
Journal of Pharmacology and Experimental Therapeutics 11/2010; 335(2):273-83. · 3.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: Murine models of allergic asthma have been used to understand the mechanisms of development and pathology in this disease. In addition, knockout mice have contributed significantly to our understanding of the roles of specific molecules and cytokines in these models. However, results can vary significantly depending on the mouse strain used in the model, and in particularly in understanding the effect of specific knockouts. For example, it can be equivocal as to whether specific gene knockouts affect the susceptibility of the mice to developing the disease, or lead to resistance. Here we used a house dust mite model of allergic airway inflammation to examine the response of two strains of mice (C57BL/6 and BALB/c) which differ in their responses in allergic airway inflammation. We demonstrate an algorithm that can facilitate the understanding of the behavior of these models with regards to susceptibility (to allergic airway inflammation) (S(aai)) or resistance (R(aai)) in this model. We verify that both C57BL/6 and BALB/c develop disease, but BALB/c mice have higher S(aai) for development. We then use this approach to show that the absence of the Tec family kinase Itk, which regulates the production of Th2 cytokines, leads to R(aai) in the C57BL/6 background, but decreases S(aai) on the BALB/c background. We suggest that the use of such approaches could clarify the behavior of various knockout mice in modeling allergic asthma.
PLoS ONE 01/2010; 5(6):e11348. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The concept of selective receptor modulators has been established for the nuclear steroid hormone receptors. Such selective modulators have been used therapeutically with great success in the treatment of cancer. However, this concept has not been examined with regard to the aryl hydrocarbon receptor (AHR) because of the latent toxicity commonly associated with AHR activation. AHR-mediated toxicity is primarily derived from AHR binding to its dioxin response element (DRE) and driving expression of CYP1 family members, which have the capacity to metabolize procarcinogens to genotoxic carcinogens. Recent evidence using a non-DRE binding AHR mutant has established the DRE-independent suppression of inflammatory markers by the AHR. We wished to determine whether such DRE-independent repression with wild-type AHR could be dissociated from canonical DRE-dependent transactivation in a ligand-dependent manner and, in doing so, prove the concept of a selective AHR modulator (SAhRM). Here, we identify the selective estrogen receptor (ER) modulator Way-169916 as a dually selective modulator, binding both ER and AHR. Inflammatory gene expression associated with the cytokine-inducible acute-phase response (e.g., SAA1 and CRP) are diminished by Way-169916 in an AHR-dependent manner. Furthermore, activation of AHR by Way-169916 fails to stimulate canonical DRE-driven AHR-mediated CYP1A1 expression, thus eliminating the potential for AHR-mediated genotoxic stress. Such anti-inflammatory activity in the absence of DRE-mediated expression fulfills the major criteria of an SAhRM, which suggests that selective modulation of AHR is possible and renders the AHR a therapeutically viable drug target for the amelioration of inflammatory disease.
[show abstract][hide abstract] ABSTRACT: Store-operated calcium channels are plasma membrane Ca(2+) channels that are activated by depletion of intracellular Ca(2+) stores, resulting in an increase in intracellular Ca(2+) concentration, which is maintained for prolonged periods in some cell types. Increases in intracellular Ca(2+) concentration serve as signals that activate a number of cellular processes, however, little is known about the regulation of these channels. We have characterized the immuno-suppressant compound BTP, which blocks store-operated channel mediated calcium influx into cells. Using an affinity purification scheme to identify potential targets of BTP, we identified the actin reorganizing protein, drebrin, and demonstrated that loss of drebrin protein expression prevents store-operated channel mediated Ca(2+) entry, similar to BTP treatment. BTP also blocks actin rearrangements induced by drebrin. While actin cytoskeletal reorganization has been implicated in store-operated calcium channel regulation, little is known about actin-binding proteins that are involved in this process, or how actin regulates channel function. The identification of drebrin as a mediator of this process should provide new insight into the interaction between actin rearrangement and store-operated channel mediated calcium influx.
The international journal of biochemistry & cell biology 11/2009; 42(2):337-45. · 4.89 Impact Factor
[show abstract][hide abstract] ABSTRACT: In addition to orchestrating an adaptive metabolic response to xenobiotic compounds, the aryl hydrocarbon receptor (AHR) also plays a necessary role in the normal physiology of mice. The AHR is activated by a structurally diverse group of chemicals ranging from carcinogenic environmental pollutants to dietary metabolites and a number of endogenous molecules. Leukotriene A 4 (5,6-LTA 4) metabolites were identified in DRE-driven luciferase reporter assays as activators of AHR signaling. Various LTA 4 metabolites, including several 5,6- and 5,12-DiHETE products, were screened for AHR activity with 6- trans-LTB 4, 6- trans-12- epi-LTB 4, 5( S),6( S)-DiHETE, and 5( S),6( R)-DiHETE eliciting a significant level of AHR transcriptional activity. However, electrophoretic mobility shift assays (EMSAs) revealed that only 5,6-DiHETE isomers were capable of directly binding and activating the AHR to a DNA-binding species in vitro. Furthermore, ligand competition binding experiments confirm the ability of these compounds to directly bind to the AHR. Interestingly, "aged" preparations of 5,6-DiHETE isomers produced an enhanced level of AHR activation while demonstrating an increase in binding affinity for the receptor. Although the reason for this has not been fully determined, the formation of geometric isomers in the conjugated triene region of these molecules may play a role in the observed increase in AHR-mediated transcriptional activity. This work suggests a connection between AHR activation and inflammatory signaling molecules produced by the 5-lipoxygenase pathway.
[show abstract][hide abstract] ABSTRACT: The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates most of the toxic effects of numerous chlorinated (e.g., TCDD) and nonchlorinated polycyclic aromatic compounds (e.g., benzo[ a]pyrene). Studies in AhR null mice suggested that this receptor may also play a role in the modulation of immune responses. Recently, two drugs, namely, M50354 and M50367 (ethyl ester derivative of M50354), were described as AhR ligands with high efficacy toward reducing atopic allergic symptoms in an AhR-dependent manner by skewing T helper cell differentiation toward a T H1 phenotype [Negishi et al. (2005) J. Immunol. 175 (11), 7348-7356]. Surprisingly, these drugs were shown to have minimal activity toward inducing classical dioxin responsive element-driven AhR-mediated CYP1A1 transcription. We synthesized and reevaluated the ability of these drugs to regulate AhR activity. In contrast to previously published data, both M50354 and M50367 were found to be potent inducers of several AhR target genes, namely, CYP1A1, CYP1B1, and UGT1A2. M50367 was a more effective agonist than M50354, perhaps accounting for its higher bioavailability in vivo. However, M50354 was capable of displacing an AhR-specific radioligand more effectively than M50367. This is consistent with M50354 being the active metabolite of M50367. In conclusion, two selective inhibitors of TH2 differentiation are full AhR agonists.
Chemical Research in Toxicology 03/2008; 21(2):472-82. · 3.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. The toxicity of the potent AhR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin is almost exclusively mediated through this receptor. However, the key alterations in gene expression that mediate toxicity are poorly understood. It has been established through characterization of AhR-null mice that the AhR has a required physiological function, yet how endogenous mediators regulate this orphan receptor remains to be established. A picture as to how the AhR/ARNT heterodimer actually mediates gene transcription is starting to emerge. The AhR/ARNT complex can alter transcription both by binding to its cognate response element and through tethering to other transcription factors. In addition, many of the coregulatory proteins necessary for AhR-mediated transcription have been identified. Cross talk between the estrogen receptor and the AhR at the promoter of target genes appears to be an important mode of regulation. Inflammatory signaling pathways and the AhR also appear to be another important site of cross talk at the level of transcription. A major focus of this review is to highlight experimental efforts to characterize nonclassical mechanisms of AhR-mediated modulation of gene transcription.
[show abstract][hide abstract] ABSTRACT: The regulation of the aryl hydrocarbon receptor (AhR) protein levels has been an area of keen interest, given its important role in mediating the cellular adaptation and toxic response to several environmental pollutants. The carboxyl terminus of hsc70-interacting protein (CHIP) ubiquitin ligase was previously associated with the regulation of the aryl hydrocarbon receptor, although the mechanisms were not directly demonstrated. In this study, we established that CHIP could associate with the AhR at cellular levels of these two proteins, suggesting a potential role for CHIP in the regulation of the AhR complex. The analysis of the sucrose-gradient-fractionated in vitro translated AhR complexes revealed that CHIP can mediate hsp90 ubiquitination while cooperating with unidentified factors to promote the ubiquitination of mature unliganded AhR complexes. In addition, the immunophilin-like protein XAP2 was able to partially protect the AhR from CHIP-mediated ubiquitination in vitro. This protection required the direct interaction of the XAP2 with the AhR complex. Surprisingly, CHIP silencing in Hepa-1c1c7 cells by siRNA methods did not reveal the function of CHIP in the AhR complex, because it did not affect well-characterized activities of the AhR nor affect its steady-state protein levels. However, the presence of potential compensatory mechanisms may be confounding this particular observation. Our results suggest a model where the E3 ubiquitin ligase CHIP cooperates with other ubiquitination factors to remodel native AhR-hsp90 complexes and where co-chaperones such as the XAP2 may affect the ability of CHIP to target AhR complexes for ubiquitination.