457 The lack of CD271 favors melanoma metastasis in zebrafish and is associated with a reduced cell-cell adhesion

Melanoma is the deadliest form of skin cancer, and the mechanisms underlying its progression have not been completely clarified. CD271, also known as p75NTR, is the common neurotrophin receptor. We have recently shown that the expression of CD271 decreases from early stages to more advanced melanomas. We have also demonstrated that the absence of CD271 in melanoma spheroids significantly increases their proliferative and invasive capacity in vitro. The aim of the present study was to confirm the role of CD271 in vivo by using the zebrafish melanoma model. Zebrafish larvae were xenotraplanted with the following melanoma cells: 1. CD271+/- cells sorted from SKMEL28 cell lines; 2. CD271 siRNA WM115 cell lines; 3. 1205Lu cell lines infected with CD271 viral vector. CD271- and CD271 silenced cells markedly increased the percentage of metastases in zebrafish at 7days post injection (p<0.01). On the contrary, CD271 overexpressing melanoma cells decreased the percentage of metastases in zebrafish (p<0.01). A higher number of “full” (>10 cells) and “medium” (5-10 cells) metastases were observed in absence of CD271, while zebrafish injected with SKMEL28 CD271+ and 1205Lu CD271 infected cells displayed mostly “no metastases” (0 cells) and “initial metastasis” (2-4 cells). To better understand the mechanism underlying the role of CD271 in melanoma progression, we hypothesized a correlation between adhesion molecules and CD271 levels. Reduced levels of β1-integrin were observed in metastatic cell lines, as compared to primary cell lines. CD271 silencing down-regulated β1-integrin and reduced cell-cell adhesion, while its overexpression induced β1-integrin upregulation and an increase in cell-cell adhesion. These results demonstrate that the lack of CD271 promotes melanoma progression and invasion in vivo, and that CD271 correlates with cell-cell adhesion.