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

ABSTRACT: In normal melanocytes, TGF-? signaling has a cytostatic effect. However, in primary melanoma cells, TGF-?-induced cytostasis is diminished, thus allowing melanoma growth. Later, a second phase of TGF-? signaling supports melanoma EMT-like changes, invasion and metastasis. In parallel with these "present-absent-present" TGF-? 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-? signaling. Using melanoma cell lines and melanoma short-term cultures, we performed RNAi and overexpression experiments and found that EWI-2 negatively regulates TGF-? 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 - molecules not previously linked to TGF-? signaling. Indeed, when associated with EWI-2, CD9 and CD81 are sequestered and have no impact on T?R2-T?R1 association or TGF-? signaling. However, when EWI-2 is knocked down, CD9 and CD81 become available to provide critical support for T?R2-T?R1 association, thus markedly elevating TGF-? signaling. Consequently, all of those TGF-?-dependent functions specifically arising due to EWI-2 depletion are reversed by blocking or depleting cell surface tetraspanin proteins CD9 or CD81. These results provide new insights into regulation of TGF-? 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.

SUBMITTER: Wang HX 

PROVIDER: S-EPMC4349253 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature