Hepatocellular carcinoma-associated depletion of the netrin-1 receptor Uncoordinated Phenotype-5A (UNC5A) skews the hepatic unfolded protein response towards prosurvival outcomes.

ABSTRACT

In the liver, HBV and HCV infections, exposure to toxics, genetic and metabolic disorders may induce endoplasmic reticulum (ER) stress and the unfolding protein response (UPR). The UPR allows cells to reach ER homeostasis after lumen overload, but also fosters survival of damaged cells and therefore HCC onset. Dependence receptors such as UNC5A trigger apoptosis when unbound to their ligands. We have previously shown that the main dependence receptor ligand, netrin-1, could protect cells against UPR-induced apoptosis through sustained translation. In this study, we show that UNC5A is cumulatively downregulated by the UPR at the transcriptional level in vitro and at the translational level both in vitro and in vivo. We have found that the 5'-untranslated region of the UNC5A mRNA shares a certain homology degree with that of netrin-1, suggesting linked translational regulatory mechanisms, at least during the initial stages of the UPR. RNAi and forced expression studies identified UNC5A as a modulator of cell death in the context of the UPR. UNC5A decrease of association with polysomes and expression oriented cells towards UPR-associated hepatocytic survival. Such data indicate that cooperation between the UPR and UNC5A depletion as previously observed by ourselves in HCC patients samples may foster liver cancer development and growth.