Browsing by Author "Kayhan, Merve"
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Item Open Access Adenosine receptor signaling targets both PKA and epac pathways to polarize dendritic cells to a suppressive phenotype(American Association of Immunologists, 2019) Kayhan, Merve; Koyaş, Altay; Akdemir, İmran; Savaş, Ali Can; Çekiç, ÇağlarExtracellular adenosine accumulates in tumors and causes suppression of immune cells. Suppressive adenosine signaling is achieved through adenosine A2A and A2B receptors, which are Gs coupled, and their activation elevates cAMP levels. Gs-coupled GPCR signaling causes cAMP accumulation, which plays an anti-inflammatory role in immune cells. Protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) are two intracellular receptors of cAMP. In this study we showed that adenosine receptor signaling polarizes activated murine dendritic cells (DCs) into a tumor-promoting suppressive phenotype. Adenosine receptor signaling activates cAMP pathway and upregulates the negative regulators of NF-κB but does not influence phosphorylation of immediate inflammatory signaling molecules downstream of TLR signaling. Pharmacologic activation of both PKA and Epac pathways by specific cAMP analogues phenocopied the effects of adenosine signaling on murine DCs, such as suppression of proinflammatory cytokines, elevation of anti-inflammatory IL-10, increased expression of regulators of NF-κB pathway, and finally suppression of T cell activation. Inhibition of effector cytokine, IL-12p40 production, and increased immunosuppressive IL-10 production by adenosine signaling is significantly reversed only when both PKA and Epac pathways were inhibited together. Adenosine signaling increased IL-10 secretion while decreasing IL-12p40 secretion in human monocyte-derived DCs. Stimulation of both PKA and Epac pathways also caused combinatorial effects in regulation of IL-12p40 secretion in human monocyte-derived DCs. Interestingly, PKA signaling alone caused similar increase in IL-10 secretion to that of adenosine signaling in human monocyte-derived DCs. Our data suggest adenosine/cAMP signaling targets both PKA/Epac pathways to fully differentiate DCs into a suppressive phenotype.Item Open Access Interleukin-7 protects CD8+ T cells from adenosine-mediated immunosuppression(American Association for the Advancement of Science (AAAS), 2021-03-16) Koyaş, Altay; Tüçer, Suat; Kayhan, Merve; Savaş, Ali Can; Akdemir, İmran; Çekiç, ÇağlarThe nucleoside adenosine accumulates extracellularly in solid tumors and inhibits CD8+ T cells by activating adenosine receptors. The cytokine interleukin-7 (IL-7), which is produced by various tissues and tumors, promotes the survival and maintenance of T cells. Adenosine and IL-7 signaling are being clinically targeted separately or in combination with other therapies for solid tumor indications. Here, we found that IL-7 signaling promoted the accumulation of tumor-associated CD8+ T cells, in part, by preventing adenosine-mediated immunosuppression. Inhibition of the transcription factor FoxO1 downstream of IL-7 receptor signaling was important for protecting CD8+ T cells from suppression by adenosine. These findings have implications for the development of new approaches for cancer immunotherapies that target the adenosine pathway.Item Open Access Molecular mechanism for adenosine regulation of dendritic cells(2017-05) Kayhan, MerveCell death, inflammation or other cellular stress factors cause accumulation of adenosine in the extracellular space. Adenosine has immunosuppressive effects on antigen presenting cells. However, molecular mechanisms for adenosine regulation of dendritic cells are poorly understood. Here we showed that adenosine receptor signaling promotes an antiinflammatory dendritic cell phenotype. While adenosine receptor signaling increased intracellular cAMP levels, phosphoactivation of major inflammatory pathways such as MAPKs, NF-κB and IRF3 were not affected. Adenosine’s effects were phenocopied by cAMP. Specific cAMP analogs for EPAC and PKA pathways indicated that adenosine activates both intracellular cAMP receptors to inhibit dendritic cell activation. Antiinflammatory cFOS and NR4A receptor family expressions were increased by adenosine or EPAC and PKA specific cAMP analogs. Furthermore, T cells incubated with the medium of dendritic cells, which prestimulated with adenosine receptor agonist and PKAEPAC specific cAMP analogs, produced less IFNγ. Overall our data suggest that dendritic cells are regulated by adenosine through both PKA and EPAC pathways and increased the expression of NR4A nuclear orphan receptors and cFOS. Our findings suggest that for effective targeting of adenosine or other cAMP-inducing receptors both PKA and EPAC are important to modulate immune responsesItem Open Access Reactivation of cAMP pathway by PDE4D inhibition represents a novel druggable axis for overcoming tamoxifen resistance in ER-positive breast cancer(American Association for Cancer Research, 2018) Mishra, Rasmi R.; Belder, Nevin; Ansari, Suhail A.; Kayhan, Merve; Bal, Hilal; Raza, Umar; Ersan, Pelin G.; Tokat, Ünal M.; Eyüpoğlu, Erol; Saatçi, Özge; Jandaghi, P.; Wiemann, S.; Üner, A.; Çekiç, Çağlar; Riazalhosseini, Y.; Şahin, ÖzgürPurpose: Tamoxifen remains an important hormonal therapy for ER-positive breast cancer; however, development of resistance is a major obstacle in clinics. Here, we aimed to identify novel mechanisms of tamoxifen resistance and provide actionable drug targets overcoming resistance. Experimental Design: Whole-transcriptome sequencing, downstream pathway analysis, and drug repositioning approaches were used to identify novel modulators [here: phosphodiesterase 4D (PDE4D)] of tamoxifen resistance. Clinical data involving tamoxifen-treated patients with ER-positive breast cancer were used to assess the impact of PDE4D in tamoxifen resistance. Tamoxifen sensitization role of PDE4D was tested in vitro and in vivo. Cytobiology, biochemistry, and functional genomics tools were used to elucidate the mechanisms of PDE4D-mediated tamoxifen resistance. Results: PDE4D, which hydrolyzes cyclic AMP (cAMP), was significantly overexpressed in both MCF-7 and T47D tamoxifen-resistant (TamR) cells. Higher PDE4D expression predicted worse survival in tamoxifen-treated patients with breast cancer (n ¼ 469, P ¼ 0.0036 for DMFS; n ¼ 561, P ¼ 0.0229 for RFS) and remained an independent prognostic factor for RFS in multivariate analysis (n ¼ 132, P ¼ 0.049). Inhibition of PDE4D by either siRNAs or pharmacologic inhibitors (dipyridamole and Gebr-7b) restored tamoxifen sensitivity. Sensitization to tamoxifen is achieved via cAMP-mediated induction of unfolded protein response/ER stress pathway leading to activation of p38/JNK signaling and apoptosis. Remarkably, acetylsalicylic acid (aspirin) was predicted to be a tamoxifen sensitizer using a drug repositioning approach and was shown to reverse resistance by targeting PDE4D/ cAMP/ER stress axis. Finally, combining PDE4D inhibitors and tamoxifen suppressed tumor growth better than individual groups in vivo. Conclusions: PDE4D plays a pivotal role in acquired tamoxifen resistance via blocking cAMP/ER stress/p38-JNK signaling and apoptosis.