ZEB1 and Uveal Melanoma Invasiveness

Uveal melanoma (UM) is the most prevalent primary intraocular tumor in adults. Transcription factor ZEB1 is one of the potential master regulators of melanocytes plasticity, because it is recognized as a "driver" of epithelial-to-mesenchymal transitions (EMTs) in carcinomas. We studied the correlation of tumor invasiveness with ZEB1 status and vascular endothelial growth factor/its receptor (VEGF-A/VEGFR2) in UM cells, and also with melanocyte's differentiation rate. Eight UM cell cultures were characterized by melanosomes content using an ETM. ZEB1, VEGF-A and VEGFR2 levels in UM cells were detected by RT-PCR, Western blot, ELISA and flow cytometry. Effects of siRNA-dependent ZEB1 knockdown on UM cell proliferation and their sensitivity to the VEGF-A inhibitor Eylea (aflibercept) were tested by MTT and in a real-time proliferation assay. UMs with an invasive growth type can maintain a high degree of melanocyte differentiation. All ZEB1^low cells were obtained from spindle cell tumors. The sensitivity of UM cells to Eylea inversely correlated with the level of the VEGFR2 receptor. ZEB1 knockdown completely blocked VEGF-A production while anti-VEGF treatment stimulated ZEB1 increase. In UM cell cultures, ZEB1 is a positive regulator of VEGF-A expression. In addition, there is probably a ZEB1 feedback loop that is sensitive to a drop in VEGF-A concentration. The data obtained allow us to consider ZEB1 silencing as an auxiliary link for a combined strategy of killing UM cells.