Inhibition of ROS/NUPR1-dependent autophagy antagonises repeated cadmium exposure -induced oral squamous cell carcinoma cell migration and invasion

Cadmium (Cd), an established carcinogen, is a risk factor for oral squamous cell carcinoma (OSCC). Macroautophagy/autophagy is proposed to play a pivotal role in Cd-mediated carcinogenic activity. However, the mechanisms underlying Cd-induced autophagy are poorly understood. In the present study, a CAL27 OSCC cell line exposed to 10(-6) M Cd for 8 weeks was used as a model system. Repeated Cd exposure induced significant migration and invasion of CAL27 cells. Furthermore, we showed that Cd increased the autophagic flux in CAL27 cells, as evidenced by the upregulation of LC3-II and the downregulation of P62/SQSTM1. The genetic blocking of autophagy inhibited Cd-induced migration and invasion, indicating a carcinogenic role of autophagy in Cd-treated CAL27 cells. Cd-induced NUPR1 expression, which contributes to lysosomal biogenesis and expression of autophagy-related gene, was found to mechanistically initiate autophagy in CAL27 cells. Of note, NUPR1 shRNA abolished Cd-induced autophagy both in vitro and in vivo. We also found that Cd triggered the generation of MDA in a xenograft tumour model and that N-acetyl-L-cysteine, a reactive oxygen species (ROS) scavenger, abrogated the effects of Cd on NUPR1-dependent autophagy in vivo. Taken together, these results demonstrate that ROS-dependent NUPR1-mediated autophagy plays an important role in repeated Cd exposure -induced cell growth, migration and invasion in OSCC cells.