Adipocytes sensitize melanoma cells to environmental TGF-β cues by repressing the expression of miR-211

Transforming growth factor-beta (TGF-beta) superfamily members are critical signals in tissue homeostasis and patho-genesis. Melanoma grows in the epidermis and invades the dermis before metastasizing. This disease progression is accompanied by increased sensitivity to microenvironmental TGF-beta. Here, we found that skin fat cells (adipocytes) promoted metastatic initiation by sensitizing melanoma cells to TGF-beta. Analysis of melanoma clinical samples revealed that adipocytes, usually located in the deeper hypodermis layer, were present in the upper dermis layer within proximity to in situ melanoma cells, an observation that correlated with disease aggressiveness. In a coculture system, adipocytes secreted the cytokines IL-6 and TNF-alpha, which induced a proliferative-to-invasive phenotypic switch in melanoma cells by repressing the expression of the microRNA miR-211. In a xenograft model, miR-211 exhibited a dual role in melanoma progression, promoting cell proliferation while inhibiting metastatic spread. Bioinformatics and molecular analyses indicated that miR-211 directly targeted and repressed the translation of TGFBR1 mRNA, which encodes the type I TGF-beta receptor. Hence, through this axis of cytokine-mediated repression of miR-211, adipocytes increased the abundance of the TGF-beta receptor in melanoma cells, thereby enhancing cellular responsiveness to TGF-beta ligands.The induction of TGF-beta signaling, in turn, resulted in a proliferative-to-invasive phenotypic switch in cultured melanoma cells. Pharmacological inhibition of TGF-beta prevented these effects. Our findings further reveal a molecular link between fat cells and metastatic progression in melanoma that might be therapeutically targeted in patients.