Tumor necrosis factor-alpha expression in human primary malignant malanoma and it relationship to tumor infiltration by CD3+ cells

Inflammatory signaling compromises cell responses to interferon alpha

Interferon alpha (IFNα) is widely used for treatment of melanoma and certain other malignancies. This cytokine as well as the related IFNβ exerts potent anti-tumorigenic effects; however, their efficacy in patients is often suboptimal. Here, we report that inflammatory signaling impedes the effects of IFNα/β. Melanoma cells can secrete pro-inflammatory cytokines that inhibit cellular responses to IFNα/β via activating the ligand-independent pathway for the phosphorylation and subsequent ubiquitination and accelerated degradation of the IFNAR1 chain of type I IFN receptor. Catalytic activity of the p38 protein kinase was required for IFNAR1 downregulation and inhibition of IFNα/β signaling induced by proinflammatory cytokines such as interleukin 1 (IL-1). Activation of p38 kinase inversely correlated with protein levels of IFNAR1 in clinical melanoma specimens. Inhibition of p38 kinase augmented the inhibitory effects of IFNα/β on cell viability and growth in vitro and in vivo. The roles of inflammation and p38 protein kinase in regulating cellular responses to IFNα/β in normal and tumor cells are discussed.

Increased numbers of tumor-lysing monocytes in cancer patients

Lymphatic infiltration is a well known phenomenon in different tumors including endocrine malignancies. However, little is known about the role of antigen-presenting cells and T cell activation in this context. The aim of our study was to investigate the quantity and function of CD14+/CD56+ monocytes in tumor patients including endocrine malignancies. First, these cells were characterized in peripheral blood of endocrine and non-endocrine cancer patients as well as in tumor tissue samples. Cancer patients had in mean 3.7 times more CD14+/CD56+ monocytes in the peripheral blood compared to healthy controls (p≤0.0001), while the highest frequencies were seen in patients with heavy tumor load. Importantly, these cells additionally expressed several NK cell markers. A proof of CD14+/CD56+ infiltrations into papillary thyroid carcinoma was shown by immunohistochemical analyses. Functional analyses revealed an apoptosis inducing capacity in vitro after IFN-α re-stimulation. Our data indicate the importance of tumor-lysing monocytes in antitumor immunity.

Interleukins 1alpha and 1beta secreted by some melanoma cell lines strongly reduce expression of MITF-M and melanocyte differentiation antigens

We report that melanoma cell lines expressing the interleukin-1 receptor exhibit 4- to 10-fold lower levels of mRNA of microphthalmia-associated transcription factor (MITF-M) when treated with interleukin-1beta. This effect is NF-kappaB and JNK-dependent. MITF-M regulates the expression of melanocyte differentiation genes such as MLANA, tyrosinase and gp100, which encode antigens recognized on melanoma cells by autologous cytolytic T lymphocytes. Accordingly, treating some melanoma cells with IL-1beta reduced by 40-100% their ability to activate such antimelanoma cytolytic T lymphocytes. Finally, we observed large amounts of biologically active IL-1alpha or IL-1beta secreted by two melanoma cell lines that did not express MITF-M, suggesting an autocrine MITF-M downregulation. We estimate that approximately 13% of melanoma cell lines are MITF-M-negative and secrete IL-1 cytokines. These results indicate that the repression of melanocyte-differentiation genes by IL-1 produced by stromal cells or by tumor cells themselves may represent an additional mechanism of melanoma immune escape.

Redox-signaling transmitted in trans to neighboring cells by melanoma-derived TNF-containing exosomes

Hydrogen peroxide is known to be involved in redox signaling pathways that regulate normal processes and disease progression, including cytokine signaling, oxidative stress, and cancer. In studies on immune surveillance against cancer, hydrogen peroxide was found to disrupt cytotoxic T-cell function, thus contributing to tumor escape. In this study, secretion of TNF-containing vesicles of rab9+ endosomal origin, termed exosomes, was investigated using GFP-TNF constructs. We observed a polarized intracellular trafficking and apical secretion of TNF-positive nanovesicles. Cell-to-cell transfer of TNF was observed in exosomes in real-time microscopy, occurring separate from the melanin/melanosome compartment. Exosomes were prepared by ultracentrifugation or immunoisolation on anti-beta2-microglobulin magnetic beads. TNF as well as TNF receptors 1 and 2 were present in the exosomes as determined by Western blot, flow cytometry, and deconvolution microscopy. The functional significance of melanoma-derived exosomes was established by their signaling competence with ability to generate significantly higher ROS levels in T cells compared with sham exosomes (P=0.0006). In conclusion, we report here, for the first time, that TNF is found in tumor cell-derived exosomes and that these exosomes transmit redox signaling in trans to neighboring cells. The results are of importance for a better understanding of tumor escape mechanisms.

Cytokines and antitumor immunity

Currently, the notion of immunosurveillance against tumors is enjoying something of a renaissance. Even if we still refuse to accept that tumors arising in the normal host are unable to trigger an immune response because of the lack of initiation ("danger") signals, there is no doubt that the immune system can be manipulated experimentally and by implication therapeutically to exert anti-tumor effects. For this activity to be successful, the appropriate cytokine milieu has to be provided, making cytokine manipulation central to immunotherapy. On the other hand, the major hurdle currently preventing successful immunotherapy is the ability of tumors to evolve resistant variants under the pressure of immune selection. Here, too, the cytokine milieu plays an essential role. The purpose of this brief review is to consider the current status of the application of cytokines in facilitating antitumor immunity, as well their role in inhibiting responses to tumors. Clearly, encouraging the former but preventing the latter will be the key to the effective clinical application of cancer immunotherapy.

Thioredoxin, thioredoxin reductase and tumour necrosis factor-alpha expression in melanoma cells: correlation to resistance against cytotoxic attack

Although malignant melanomas are often associated with cytotoxic lymphocyte infiltration, these cells are largely ineffective in inducing tumour cell kill, indicating that the melanoma cells have protective mechanisms. These mechanisms are not fully understood, but cytokines and redox-active antioxidant proteins such as catalase, superoxide dismutase, thioredoxin (Trx) and Trx reductase (TrxR) present in the tumour cells constitute part of this protection. In this study firstly we investigated the constitutive intracellular expression of Trx, TrxR, the cytokines interleukin (IL)-1alpha, IL1beta, IL2, IL4, IL6, IL8, IL10, tumour necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma) in normal melanocytes and ten primary and metastatic malignant melanoma cell lines. Secondly, we analysed whether redox stimulation by Trx alone or in combination with the phorbol ester PMA affected the expression and release of TNFalpha. Thirdly, we explored the possible correlation between Trx/TrxR expression and resistance to exogenous TNFalpha. All the cultured cells showed intracellular overexpression of Trx and TrxR, which was not always the case for melanoma cells in vivo (tissue sections). The predominant intracellular cytokines found were TNFalpha, IL1alpha and IL1beta. In spite of its presence in the Golgi apparatus, none of the cell lines secreted TNFalpha constitutively, and only one melanoma, FM3, released detectable amounts after stimulation. In contrast, U-937 monocyte control cells released high amounts of TNFalpha on identical stimulation. All the melanoma cell lines were relatively resistant against exogenous TNFalpha, and there was a significant correlation (P < 0.01) between intracellular Trx/TrxR expression and TNFalpha resistance (IC50). In conclusion, Trx and TrxR, as well as TNFalpha, IL1alpha and IL1beta, were highly expressed in cultured normal skin melanocytes and malignant melanoma cell lines. In contrast to U-937 monocytic cells, TNFalpha showed a secretory block in these cells, suggesting a cytoprotective and possible autocrine role for TNFalpha. The intracellular expression of Trx and TrxR together with endogenous TNFalpha was correlated with the resistance to TNFalpha-induced cytotoxicity.

Endogenous tumour necrosis factor-alpha sensitise melanoma cells to glucosaminylmuramyl dipeptide

Flow cytometry was used to demonstrate that cultured human melanoma BRO cells expressed membrane-bound tumour necrosis factor-alpha (TNF-alpha) and were able to release TNF-alpha upon treatment with glucosaminylmuramyl dipeptide (GMDP). The released TNF-alpha was shown to prime melanoma cells, previously unable to respond to GMDP by increasing expression of melanoma-associated antigens, making them sensitive to GMDP treatment.