QSOX1 promotes mitochondrial apoptosis of hepatocellular carcinoma cells during anchorage-independent growth by inhibiting lipid synthesis.

Anoikis is a programmed death of cell induced upon detachment from the extracellular matrix (ECM). Resistance to anoikis is a critical contributor to cancer invasion and metastasis. High frequency of metastatic recurrence is a huge challenge for current therapy of hepatocellular carcinoma (HCC). Our previous study had identified sulfhydryl oxidase 1 (QSOX1) as a suppressor of HCC metastasis. In the present study, we used the anchorage-independent growth condition to mimic the detachment of HCC cells from ECM. We found that QSOX1 was induced in HCC cells under the anchorage-independent growth condition and that could be blocked by endoplasmic reticulum stress (ERS) inhibitor. Overexpression and knockdown of QSOX1 gene were performed on HCC cells. QSOX1 inhibited de novo synthesis of fatty acids (FAs) and cholesterol (ChE) and reduced their content in the detached HCC cells, and thus mediated mitochondrial apoptosis of HCC cells. In conclusion, QSOX1 is induced under detached culture condition via ERS. QSOX1 promotes mitochondrial apoptosis by suppressing the lipid synthesis of HCC cells in detached condition. QSOX1 appears to accelerate anoikis of HCC cells. These findings offer a new insight into how to overcome anoikis resistance of HCC cells and provide a potential target for prevention of HCC metastasis.