EWI-2 negatively regulates TGF-β signaling leading to altered melanoma growth and metastasis

• Published in: Cell research 2015-03, Vol.25 (3), p.370-385
• Main Authors: Wang, Hong-Xing, Sharma, Chandan, Knoblich, Konstantin, Granter, Scott R, Hemler, Martin E
• Format: Article
• Language: English
• Subjects: 631/67/1813/1634; 631/67/322; 631/80/86; Animals; Antigens, CD - genetics; Benzamides - pharmacology; Biomedical and Life Sciences; CD81; Cell Biology; Cell Line, Tumor; Cell Movement - genetics; Cell Proliferation - genetics; Dioxoles - pharmacology; HEK293 Cells; Humans; Life Sciences; Melanoma - pathology; Membrane Proteins - genetics; Mice; Mice, Inbred C57BL; Mice, SCID; Neoplasm Invasiveness - pathology; Neoplasm Transplantation; Nerve Tissue Proteins - metabolism; Original; original-article; Prognosis; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - metabolism; Receptors, Nerve Growth Factor - metabolism; Receptors, Transforming Growth Factor beta - antagonists & inhibitors; Receptors, Transforming Growth Factor beta - metabolism; RNA Interference; RNA, Small Interfering; Signal Transduction; Tetraspanin 24 - genetics; Tetraspanin 28 - genetics; Tetraspanin 28 - metabolism; Tetraspanin-29 - genetics; Tetraspanin-29 - metabolism; TGF-β; Transforming Growth Factor beta - metabolism; Transplantation, Heterologous; 信号; 细胞生长; 表面蛋白质; 负调控; 黑素细胞; 黑色素瘤
• ISSN: 1001-0602; 1748-7838
• DOI: 10.1038/cr.2015.17

In normal melanocytes, TGF-β signaling has a cytostatic effect. However, in primary melanoma cells, TGF-β-in- duced cytostasis is diminished, thus allowing melanoma growth. Later, a second phase of TGF-β signaling supports melanoma EMT-like changes, invasion and metastasis. In parallel with these ＂present-absent-present＂ TGF-β signaling phases, cell surface protein EWI motif-containing protein 2 （EWI-2 or IgSF8） is ＂absent-present-absent＂ in melanocytes, primary melanoma, and metastatic melanoma, respectively, suggesting that EWI-2 may serve as a negative regulator of TGF-β signaling. Using melanoma cell lines and melanoma short-term cultures, we performed RNAi and overexpression experiments and found that EWI-2 negatively regulates TGF-β signaling and its downstream events including cytostasis （in vitro and in vivo）, EMT-like changes, cell migration, CD271-dependent invasion, and lung metastasis （in vivo）. When EWI-2 is present, it associates with cell surface tetraspanin proteins CD9 and CD81 -- mole- cules not previously linked to TGF-β signaling. Indeed, when associated with EWI-2, CD9 and CD81 are sequestered and have no impact on TβR2-TpR1 association or TGF-β signaling. However, when EWI-2 is knocked down, CD9 and CD81 become available to provide critical support for TpR2-TβR1 association, thus markedly elevating TGF-β signaling. Consequently, all of those TGF-β-dependent functions specifically arising due to EWI-2 depletion are reversed by blocking or depleting ceil surface tetraspanin proteins CD9 or CD81. These results provide new insights into regulation of TGF-β signaling in melanoma, uncover new roles for tetraspanins CD9 and CD81, and strongly suggest that EWI-2 could serve as a favorable prognosis indicator for melanoma patients.