CircATRNL1 activates Smad4 signaling to inhibit angiogenesis and ovarian cancer metastasis via miR‐378

Ovarian cancer is one of the most frequent carcinomas in females, and the occurrence rate is still rising despite many advances made. The pathogenesis of ovarian cancer remains greatly unclear. Here, we investigated the mechanisms of ovarian cancer, with the focus on circATRNL1. Human ovarian cancer tissues and cell lines were used to examine levels of circATRNL1, miR-378, Smad4, AKT, and other proliferation-related and migration-related proteins. Cellular assays were used to determine cancer cell proliferation, invasion, migration, apoptosis, and angiogenesis. We validated the interactions of circATRNL1/miR-378 and miR-378/Smad4, and a mouse tumor xenograft model was employed to assess the effect of circATRNL1 on tumor growth and metastasis in vivo. We found that circATRNL1 was decreased while miR-378 was increased in human ovarian cancer tissues and cells. circATRNL1 bound to miR-378 while miR-378 directly targeted Smad4. Overexpression of circATRNL1 or knockdown of miR-378 suppressed angiogenesis and ovarian cancer cell proliferation, invasion, and migration via decreasing proliferation- and migration-related proteins via miR-378 or Smad4, respectively. Overexpression of circATRNL1 restrained ovarian cancer growth and abdominal metastasis in vivo. Our findings indicate that circATRNL1 acts as a miR-378 sponge to active Smad4 signaling and suppresses angiogenesis and ovarian cancer metastasis.