The Secretion of miR-200s by a PKCζ/ADAR2 Signaling Axis Promotes Liver Metastasis in Colorectal Cancer

Abstract

Most colorectal cancer (CRC)-related deaths are due to liver metastases. PKCζ is a tumor suppressor in CRC with reduced expression in metastasis. Given the importance of microRNAs (miRNAs) in regulating cellular plasticity, we performed an unbiased screening and identified the miR-200 family as the most relevant miRNAs downregulated by PKCζ deficiency. The regulation of the intracellular levels of miR-200 by PKCζ is post-transcriptional and involves their secretion in extracellular vesicles. Here, we identified ADAR2 as a direct substrate of PKCζ in CRC cells. Phosphorylation of ADAR2 regulates its editing activity, which is required to maintain miR-200 steady-state levels, suggesting that the PKCζ/ADAR2 axis regulates miR-200 secretion through RNA editing. Loss of this axis results in epithelial-to-mesenchymal transition (EMT) and increased liver metastases, which can be inhibited in vivo by blocking miR-200 release. Therefore, the PKCζ/ADAR2 axis is a critical regulator of CRC metastases through modulation of miR-200 levels. Shelton et al. demonstrate that the loss of the tumor suppressor PKCζ in colorectal cancer cells results in the downregulation of miR-200, leading to increased epithelial-to-mesenchymal transition, cell invasion, and liver metastasis. This is mediated by an increase in miR-200 secretion through the inactivation of the RNA editing enzyme ADAR2, identifying a key vulnerability in liver metastasis.