Notch1 binds and induces degradation of Snail in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common, highly invasive malignant tumor associated with a high mortality rate. We previously reported that the aberrant expression of Snail via activation of reactive oxygen species contributes to the invasive property of HCC, in part by downregulation of E-cadherin through both transcriptional repression and epigenetic modification of the E-cadherin promoter. Having demonstrated the ability of Snail to bind and recruit histone deacetylase 1 and DNA methyltransferase 1 in this context, we set out to look for other interactions that could affect its ability to promote oncogenic transformation and cancer cell invasion.

Using cells that stably expressed Snail, we characterized Snail protein interactors by tandem affinity purification and mass spectrometry. Immunoprecipitation and subcellular colocalization studies were performed to confirm our identification of the Notch1 intracellular domain (NICD) as a novel Snail-binding partner. NICD interaction with Snail was found to induce ubiquitination and MDM2-dependent degradation of Snail. Interestingly, NICD inhibited Snail-dependent invasive properties in both HCC cells and mouse embryonic fibroblasts.

Our study demonstrates that NICD can oppose Snail-dependent HCC cell invasion by binding and inducing proteolytic degradation of Snail. Although Notch signaling and Snail are both widely considered tumor-promoting factors, our findings indicate that the individual oncogenic contribution of Notch1 and Snail in malignant systems should be interpreted carefully, particularly when they are conjointly expressed.