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素细胞。紫外线(UV)照射是引起致癌基因组异常的主要危险因素。除了黑色素瘤细胞固有的改变外，原发性黑色素瘤经常有免疫细胞浸润，这表明肿瘤微环境和细胞因子反应在疾病的发生和发展中起着重要作用。紫外线(UV)照射后的持续炎症与黑色素瘤的发生有关，原因是黑素细胞和巨噬细胞之间意外地参与了干扰素-伽马驱动的细胞因子环路。我们假设，一些与黑色素瘤风险增加和色素沉着特征改变有关的遗传倾向也可能影响细胞因子串扰。我们设计了一种整合的生物信息学发现方法，并确定黑色素瘤易感基因IRF4(干扰素调节因子4)是黑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，IRF4被认为是一种淋巴限制性转录因子，可以协调细胞因子的反应，并在某些B细胞恶性肿瘤中扮演家族癌基因的角色，但它对正常黑素细胞和黑色素瘤细胞功能的作用目前尚不清楚。我们发现IRF4在黑色素瘤中高表达，并在黑色素瘤细胞分化和干扰素反应中发挥作用。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IRF4是如何控制黑素细胞分化和细胞因子反应的，并探索其作为免疫治疗潜在决定因素的作用。黑素细胞还通过黑素细胞系转录因子MITF-M(微眼球相关转录因子)提供的一系列专门的受体和信号分子与角质形成细胞和成纤维细胞进行交流。在黑色素瘤的发展过程中，MITF-M变得异质性表达，这可能是由于可变的MITF-M依赖受体的表达而施加了强烈的细胞因子和生长因子信号的上下文依赖性。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)信号级联反应。最近，HGF受到了很多关注，因为高水平的HGF预示着接受BRAF抑制剂治疗的黑色素瘤患者的疗效较差。在大约一半的黑色素瘤中发现了突变和激活的BRAF激酶，一些突变的黑色素瘤对BRAF阻断有强烈的反应，而另一些则不起作用。在这个项目的第二部分，我们的目标是仔细审查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抑制剂耐药中的作用，特别是关于表型异质性，以及描述先进的治疗策略是至关重要的。

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.