Engrailed-1 Promotes Tumor Progression and Metastasis in Papillary Thyroid Cancer

Background and Objective: Transcription factor Engrailed-1 (EN1) has been implicated as an oncogene in various solid tumors; however, its role in papillary thyroid carcinoma (PTC) is unknown. In the present study, the authors investigate the EN1 expression in PTC clinical specimens and its correlation with clinical outcomes, and then explore its function in PTC progression using in vitro and in vivo models. Methods: A retrospective cohort of 376 paired PTC was collected with informed consent. Immunohistochemistry for EN1 protein expression was evaluated. Clinic pathological data were recorded. EN1-specific shRNAs (or siRNAs) and overexpression plasmids were used. Using En-1 knockdown and overexpression, cell invasion, migration, proliferation, and apoptosis in vitro were detected using Transwell and wound healing assays, MTT, colony formation assay, and flow cytometry assay, respectively. Xenograft tumor models (subcutaneous) and tail-vein injection metastasis models (lung colonization) were established in mice. Results: EN1 is significantly overexpressed in PTC tissues; high EN1 expression is correlated with lymphovascular invasion ( p < 0.05), lymph node metastasis ( p < 0.05), TNM stage ( p < 0.05), and recurrence ( p < 0.05). Functionally enhanced EN1 expression promotes PTC cell invasion and migration, and promotes cell proliferation in vitro . Conversely, EN1 knockdown potently inhibited this invasive phenotype, induced significant apoptosis, and inhibited cell proliferation. EN1 silencing reduced tumor growth and lung metastatic potential in murine models in vivo . EN1 overexpression enhanced these malignant phenotypes in vivo . Conclusions: EN1 may be a novel driver of PTC aggressiveness and metastasis, suggesting its potential utility as a prognostic biomarker and therapeutic target.