Emilin1 degradation and secretion in exosomes inactivate its tumor- and metastasis-suppressive role in melanoma mouse models

Several studies have demonstrated that melanoma-derived exosomes home in sentinel lymph nodes favoring metastasis. Here, we determined the proteomic signature in exosomes derived from lymph node metastatic models. We found a signature of genes over-expressed and proteins hyper-secreted in exosomes related to lymph node metastasis in the B16 mouse melanoma model. Out of these candidates, we found that Emilin1, a protein with an important function in lymph node physiology, was hyper-secreted in exosomes. Interestingly, we found that Emilin1 is degraded and secreted in exosomes as a mechanism favoring metastasis. Indeed, we found that Emilin1 has a tumor suppressor-like role regulating negatively cell viability and migration. Importantly, our in vivo studies demonstrate that Emilin1 overexpression reduced primary tumor growth and metastasis in mouse melanoma models. Analysis in human melanoma samples showed that cells expressing high levels of EMILIN1 are reduced in metastatic lesions. Overall, our analysis suggests a novel mechanism involved in the inactivation of Emilin1 in melanoma favouring melanoma progression and metastasis.