Control of cytokine responses through the MITF-IRF4 transcription factor network in melanoma

恶性黑色素瘤是一种侵袭性皮肤癌，起源于产生色素的黑色素细胞。紫外线（UV）照射是导致致癌基因组畸变的主要危险因素。除了黑色素瘤细胞内在的改变，原发性黑色素瘤经常有免疫细胞浸润，表明肿瘤微环境和细胞因子反应在疾病的发展和进展中的重要作用。紫外线（UV）照射后的持续炎症与黑色素瘤的发生有关，这是由于黑色素细胞和巨噬细胞之间的干扰素-γ驱动的细胞因子环的意外参与。我们假设，与黑色素瘤风险增加和色素沉着特征改变相关的一些遗传易感性也可能影响细胞因子串扰。我们设计了一种综合的生物信息学发现方法，并确定了黑色素瘤易感基因IRF 4（干扰素调节因子4）作为黑色素细胞和黑色素瘤细胞中细胞因子反应的潜在决定因素。到目前为止，IRF 4被认为是一种淋巴限制性转录因子，其协调细胞因子反应并在某些B细胞恶性肿瘤中充当谱系癌基因，但其对正常黑素细胞和黑色素瘤细胞功能的贡献目前尚不清楚。我们发现IRF 4在黑色素瘤中高表达，并在黑色素瘤细胞分化和干扰素应答中发挥作用。在这个项目的第一部分，我们将仔细研究黑色素瘤易感基因IRF 4如何控制黑色素细胞的分化和细胞因子的反应，并探讨其作为免疫治疗的潜在决定因素的作用。黑色素细胞也通过黑色素细胞谱系转录因子MITF-M（小眼症相关转录因子）提供的受体和信号分子的专门库与角质形成细胞和成纤维细胞进行通信。在黑色素瘤进展过程中，MITF-M变得不均一地表达，并且由于可变的MITF-M依赖性受体表达，这可能强加细胞因子和生长因子信号传导的强背景依赖性。基于文献，我们假设一个临床相关的例子是HGF（肝细胞生长因子）信号级联。最近，HGF受到了很多关注，因为高水平的HGF预示着用BRAF抑制剂治疗的黑色素瘤患者中的不良反应。BRAF激酶的突变和活化形式在大约一半的黑色素瘤中发现，一些BRAF突变的黑色素瘤对BRAF阻断有强烈反应，而其他黑色素瘤则没有。在该项目的第二部分中，我们的目标是仔细检查HGF信号级联的上下文依赖性，因为这对于我们进一步了解HGF在BRAF抑制剂耐药性中的作用至关重要，特别是在表型异质性方面，以及描绘先进的治疗策略。

Malignant melanoma is an aggressive skin cancer that originates from pigment producing melanocytes. Ultraviolet light (UV) irradiation is a major risk factor that causes oncogenic genomic aberrations. Besides melanoma cell intrinsic alterations, primary melanomas frequently have immune cell infiltrates indicating an important role of the tumor microenvironment and cytokine responses in the development and progression of the disease. Sustained inflammation following ultraviolet light (UV) irradiation has been linked to melanomagenesis through the unexpected involvement of an interferon-gamma driven cytokine loop between melanocytes and macrophages. We hypothesized that some genetic predispositions linked to increased melanoma risk and altered pigmentation traits might also affect cytokine crosstalk. We devised an integrative bioinformatic discovery approach and identified the melanoma susceptibility gene IRF4 (interferon-regulatory factor 4) as potential determinant of cytokine responses in melanocytes and melanoma cells. So far, IRF4 is considered as a lymphoid restricted transcription factor that orchestrates cytokine responses and acts as lineage oncogene in certain B cell malignancies, but its contribution to normal melanocyte and melanoma cell function is currently unknown. We found high expression of IRF4 in melanomas and a role in melanoma cell differentiation and interferon responses. In this first part of the project we will scrutinize how the melanoma susceptibility gene IRF4 controls melanocytic differentiation and cytokine responses and explore its role as potential determinant for immunotherapies.Melanocytes also communicate with keratinocytes and fibroblasts through a specialized repertoire of receptors and signaling molecules provided by the melanocytic lineage transcription factor MITF-M (microphthalmia-associated transcription factor). In the course of melanoma progression MITF-M becomes heterogeneously expressed and this likely imposes a strong context dependency of cytokine and growth factor signaling due to variable MITF-M dependent receptor expression. Based on literature we hypothesize that one clinically relevant example is the HGF (hepatocyte growth factor) signaling cascade. Recently, HGF received a lot of attention because high levels of HGF predicted poor responders among melanoma patients treated with BRAF inhibitors. A mutated and activated form of the BRAF kinase is found in about the half of all melanomas and some BRAF mutated melanomas strongly respond to BRAF blockade whereas others do not. In this second part of the project we aim to scrutinize the context-dependency the HGF signaling cascade, as this is critical for our further understanding of the role of HGF in BRAF inhibitor resistance, in particular with respect to phenotypic heterogeneity, and the delineation of advanced therapeutic strategies.