Increased expression of REarranged during Transfection (RET) kinase is reported in 10-20 % of lung adenocarcinomas (LUAD) and is associated with metastasis and reduced survival. Ezrin is a scaffold protein that promotes protein interactions with the actin cytoskeleton to regulate cell migration and is also associated with invasion and metastasis in cancers. RET isoforms interact with unique combinations of scaffold proteins to promote distinct signaling pathways. We hypothesized that RET isoforms associate distinctly with Ezrin for cytoskeletal reorganization and LUAD cell migration processes.
HCC1833 and A549 LUAD, SH-SY5Y neuroblastoma or HEK-293 cells expressing RET and Ezrin were stimulated with the RET ligand glial cell line-derived neurotrophic factor (GDNF) and treated with RET, Ezrin or Src inhibitors. Co-immunoprecipitation or pull-down assays coupled to immunoblotting were used to investigate protein activation and interactions. Immunofluorescence confocal microscopy assessed LUAD cytoskeletal reorganization and colocalization of RET and Ezrin. Live-cell fluorescence imaging was used to measure cell migration and chemotaxis.
GDNF promoted activation, interaction and colocalization of RET51 isoform and Ezrin. Inhibition of RET or Src impaired Ezrin interactions with RET and Src. GDNF stimulation enhanced the formation of actin-rich filopodia, in which both RET and Ezrin were enriched, and promoted chemotaxis in LUAD cells. However, inhibition of RET, Src or Ezrin suppressed filopodia formation, reduced colocalization of Ezrin with RET, and impaired cell migration and/ or chemotaxis. We further showed that GDNF-mediated activation of RET and Ezrin promoted RhoA-GTPase activity and signaling of ROCK1 and ROCK2 in LUAD cells.
Expression and activation of RET51 mediates unique protein interactions with Ezrin to promote LUAD cell chemotaxis for cancer cell dissemination, which may have implications in LUAD metastatic progression.

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