CXCR3 Signaling in BRAF^WT Melanoma Increases IL-8 Expression and Tumorigenicity

Patients with early stage, radial growth phase (RGP) melanoma have a 97% survival rate; however, when the melanoma progresses to the invasive vertical growth phase (VGP), survival rates decrease to 15%. The targets of many clinical trials are the known genetic and molecular mechanisms involved in melanoma progression, with the most common oncogenic mutation being the BRAFV600E. However, less than half of melanomas harbor this mutation, and consequently, do not respond to the current BRAF targeted treatments. It is therefore critical to elucidate alternative mechanisms regulating melanoma progression. Increased expression of the chemokine receptor, CXCR3, on melanoma cells is correlated with increased metastasis and poor patient outcomes, suggesting a role for CXCR3 in the RGP to VGP transition. We found that endogenous CXCR3 can be induced in two RGP cell lines, BOWES (BRAFWT) and WM35 (BRAFV600E), with in vitro environmental stress and nutrient deprivation. Signaling via induced endogenous CXCR3 is linked with IL-8 expression in BOWES cells. Ectopic overexpression of CXCR3 in BOWES cells leads to increased ligand-mediated phERK, cellular migration, and IL-8 expression in vitro, and to increased tumorigenesis and lymph node metastasis in vivo. Our results demonstrate that, in BRAFWT melanomas, CXCR3 signaling mediates significant increases in IL-8 expression, suggesting that CXCR3 expression and signaling may represent a transformative event that drives the progression of BRAFWT melanomas. Implications: Expression of CXCR3 on BRAFWT melanoma cells may be a mediator of melanoma progression.早期放射状生长期（radial growth phase, RGP）黑色素瘤患者的生存率可达97%；然而，当黑色素瘤进展至侵袭性垂直生长期（vertical growth phase, VGP）时，生存率会降至15%。多数临床试验的靶点为黑色素瘤进展相关的已知遗传与分子机制，其中最常见的致癌突变为BRAFV600E。但仅有不到半数的黑色素瘤携带该突变，因此无法对当前的BRAF靶向治疗产生应答，阐明调控黑色素瘤进展的其他替代机制因此至关重要。 黑色素瘤细胞表面的趋化因子受体CXCR3（chemokine receptor CXCR3）表达升高与肿瘤转移增加及患者不良预后相关，提示CXCR3参与了RGP向VGP的转化过程。本研究发现，在体外环境应激与营养剥夺的条件下，两种RGP细胞系——BRAF野生型（BRAFWT）的BOWES细胞与携带BRAFV600E突变的WM35细胞——均可诱导内源性CXCR3的表达。在BOWES细胞中，经诱导的内源性CXCR3的信号转导与白细胞介素8（IL-8）的表达存在关联。 在BOWES细胞中外源过表达CXCR3，可在体外经配体介导提升磷酸化ERK（phERK）水平、增强细胞迁移能力并上调IL-8的表达；在体内则可促进肿瘤发生与淋巴结转移。本研究结果证实，在BRAFWT型黑色素瘤中，CXCR3信号转导可显著上调IL-8的表达，提示CXCR3的表达与信号转导可能是驱动BRAFWT型黑色素瘤进展的关键性转化事件。 研究启示：BRAFWT型黑色素瘤细胞表面CXCR3的表达或可作为黑色素瘤进展的介导因子。