The E3 ligase NEDD4L prevents colorectal cancer liver metastasis via degradation of PRMT5 to inhibit the AKT/mTOR signaling pathway

Colorectal cancer is the second most common cause of cancer mortality worldwide, and liver metastasis is the major cause of death in patients with colorectal cancer. Dysfunctional E3 ligase activity has recently been shown to be associated with colorectal cancer. However, the key E3 ligase affecting colorectal cancer liver metastasis remains unknown. Therefore, we used an shRNA library targeting 156 E3 ubiquitin ligases to perform an in vivo loss-of-function screen of a human colorectal cancer cell line in a mouse model of colorectal cancer liver metastasis. The screen revealed that NEDD4L knockdown promoted colorectal cancer liver metastasis. Moreover, overexpression of NEDD4L prevented colorectal cancer liver metastasis. Mechanistic studies revealed that NEDD4L bound to the PPNAY motif in PRMT5 and ubiquitinated PRMT5 to promote its degradation. PRMT5 degradation attenuated the methylation of an arginine residue in AKT1 to inhibit the AKT/mTOR signaling pathway, consequently decreasing colorectal cancer cell proliferation. We are the first to show that PRMT5 is a substrate protein of the E3 ligase NEDD4L and reveals not only the metastasis-inhibiting function of NEDD4L but also a novel mechanism by which NEDD4L suppresses colorectal cancer liver metastasis. These findings may provide a new preventive strategy for liver metastasis.