Research ArticleCancer

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

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Science Signaling  23 Jul 2019:
Vol. 12, Issue 591, eaav6847
DOI: 10.1126/scisignal.aav6847

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Fat triggers metastasis

In melanoma patient samples, tumors appear to grow in a lateral, proliferative phase within the upper epidermal layer of the skin but switch to a vertical, invasive phase when they grow into the deeper layers where adipose (fat) exists. Golan et al. examined cocultures of melanoma cells and adipocytes and identified a direct role for fat cells in this metastatic switch. The authors found that adipocytes secreted cytokines that signaled through their receptors on melanoma cells to repress the expression of a microRNA that promotes proliferative and suppresses invasive phenotypes. The microRNA also represses the expression of a receptor for the growth factor TGF-β, which is implicated in metastatic disease and abundant in the dermal layer. Blocking TGF-β signaling prevented the invasive switch in cultured melanoma cells and, therefore, may suppress metastasis in patients.

Abstract

Transforming growth factor–β (TGF-β) superfamily members are critical signals in tissue homeostasis and pathogenesis. Melanoma grows in the epidermis and invades the dermis before metastasizing. This disease progression is accompanied by increased sensitivity to microenvironmental TGF-β. Here, we found that skin fat cells (adipocytes) promoted metastatic initiation by sensitizing melanoma cells to TGF-β. 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-α, 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-β receptor. Hence, through this axis of cytokine-mediated repression of miR-211, adipocytes increased the abundance of the TGF-β receptor in melanoma cells, thereby enhancing cellular responsiveness to TGF-β ligands. The induction of TGF-β signaling, in turn, resulted in a proliferative-to-invasive phenotypic switch in cultured melanoma cells. Pharmacological inhibition of TGF-β 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.

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