Abstract
Membrane-associated ring-CH-type finger (MARCH) proteins belong to the E3 ubiquitin ligase family, which regulates protein stability by increasing ubiquitination. Recent evidence has shown that some MARCH proteins play important roles in cancer development. However, the role of MARCH6 in tumorigenesis, including thyroid tumorigenesis, remains unknown. In this study, we determined that MARCH6 was upregulated in the majority of primary papillary thyroid cancers (PTCs) at both the mRNA and protein levels. Gain-of-function and loss-of-function studies demonstrated that MARCH6 suppressed apoptosis and promoted cell cycle progression, cell proliferation, growth, migration and tumorigenesis in thyroid cancer cells. Mechanistically, MARCH6 interacted with and downregulated DHX9. Knockdown of DHX9 enhanced the proliferative and migratory abilities of thyroid cancer cells. The inhibitory effect of MARCH6 knockdown on thyroid cancer cell growth and migration was also reversed by DHX9 silencing. In addition, MARCH6 activated the AKT/mTOR signaling pathway in a manner dependent on the downregulation of DHX9. Overall, MARCH6 functions as a potential oncogene in thyroid cancer by destabilizing DHX9 and activating AKT/mTOR signaling.