Interleukin 8 mediates bcl-xL-induced enhancement of human melanoma cell dissemination and angiogenesis in a zebrafish xenograft model

The protein bcl-xL is able to enhance the secretion of the pro-inflammatory chemokine interleukin 8 (CXCL8) in human melanoma lines. In the present study, we investigate whether the bcl-xL/CXCL8 axis is important for promoting melanoma angiogenesis and aggressiveness in vivo, using angiogenesis and xenotransplantation assays in zebrafish embryos. When injected into wild type embryos, bcl-xL-overexpressing melanoma cells showed enhanced dissemination and angiogenic activity compared with control cells. Human CXCL8 protein elicited a strong pro-angiogenic activity in zebrafish embryos and zebrafish Cxcr2 receptor was identified as the mediator of CXCL8 pro-angiogenic activity using a morpholino-mediated gene knockdown. However, human CXCL8 failed to induce neutrophil recruitment in contrast to its zebrafish homologue. Interestingly, the greater aggressiveness of bcl-xL-overexpressing melanoma cells was mediated by an autocrine effect of CXCL8 on its CXCR2 receptor, as confirmed by an shRNA approach. Finally, correlation studies of gene expression and survival analyses using microarray and RNAseq public databases of human melanoma biopsies revealed that bcl-xL expression significantly correlated with the expression of CXCL8 and other markers of melanoma progression. More importantly, a high level of co-expression of bcl-xL and CXCL8 was associated with poor prognosis in melanoma patients. In conclusion, these data demonstrate the existence of an autocrine CXCL8/CXCR2 signaling pathway in the bcl-xL-induced melanoma aggressiveness, encouraging the development of novel therapeutic approaches for high bcl-xL-expressing melanoma.