Gene Expression Changes and Signaling Events Associated with the Direct Antimelanoma Effect of IFN-γ
Abstract
Immunotherapy, including the use of cytokines, vaccines, and adoptive transfer of lymphocytes, has dominated the treatment of melanoma for the past two decades. The development of agents and techniques to generate melanoma-specific T cells and maximally stimulate lymphocytes has been driven by the concept of immune escape, which underscores the importance of overcoming immune tolerance to treat melanoma. But while novel vaccination strategies can generate larger numbers of antigen-specific cytotoxic T cells, and cytokines such as IL-2, IL-12, IFN-γ, and IFN-α can activate multiple different immune effector cells, few patients have benefited from these treatment modalities.
One reason for this lack of success is the resistance of melanoma cells to growth inhibition and apoptosis following adequate recognition by activated effector cells. Resistance to chemotherapy- and death receptor-induced apoptosis is well-described for melanoma, and includes such mechanisms as Apaf-1 downregulation and the upregulation of IAP, survivin, FLIP, and Bcl-2. These are believed to be in part responsible for resistance to granzyme- and/or death receptor-mediated killing by T and NK cells. But T and NK cells also produce IFN-γ and IFN-α following activation and in the context of tumor recognition, and it is well known that these interferons can have direct antiproliferative and proapoptotic effects on melanoma cells. However, the mechanism underlying these effects remains undefined, as does the basis for resistance to the direct antimelanoma effects of the interferons.
IFN-γ production is central to the antitumor effect of IL-12, and tumor cell sensitivity to IFN-γ has been shown to be central to the antiangiogenic/antitumor effect of combination therapy with IL-12 and IL-18. As one hallmark of overcoming immunologic tolerance through vaccination is the generation of IFN-γ-producing T cells, one has to consider the possibility that the direct effects of IFN-γ on melanoma may underlie the antitumor effect of immunostimulatory cytokines and vaccines. In that context, tumor cell resistance to IFN-γ may be as central to immune escape as effector cell tolerance.
To understand the molecular basis of the direct antimelanoma effects of IFN-γ, we undertook an analysis of the gene expression changes and signaling events associated with IFN stimulation in melanoma cell lines that were either sensitive or resistant to the antiproliferative and proapoptotic effects of IFN-γ and IFN-α. In this report, we show how the application of DNA microarray analysis to this system has yielded relatively small sets of genes whose change in expression is associated with the antimelanoma effect of IFN-γ, and provide evidence linking MEK1 and p38 MAP kinase activation to these effects of IFN-γ on gene expression.
Authors
Jared A. Gollob, Catherine J. Sciambi, Zhiqing Huang, and Holly Dressman
Contact
- Jared A. Gollob (gollo001@mc.duke.edu)