Abstract
Macroautophagy and chaperone-mediated autophagy (CMA) represent two major lysosomal degradation processes and often compensate for one another to facilitate cell survival. The aim of this study was to determine whether these autophagy pathways could compensate for one another to promote HCC cell survival in the cirrhotic liver. Analysis of normal liver tissue showed no expression of glypican-3 or p62 proteins, suggesting that macroautophagy is the major contributor to autophagic flux under non-pathological conditions. Of 46 cirrhotic livers with HCC examined, 39 (84%) of HCCs showed increased expression of p62, and 36 (78%) showed increased expression of glypican-3, while adjacent non-tumorous hepatocytes were negative for expression of p62 and glypican-3, similar to normal liver tissue. These results suggest that macroautophagy flux is impaired in HCC. Furthermore, more than 95% of HCCs showed altered expression of LAMP-2A compared to the surrounding non-tumorous cirrhotic liver, consistent with induction of CMA in HCC. Elevated expression of glucose-regulated protein 78 (GRP78) and heat shock cognate protein (Hsc70) were detected in 100% of HCC and adjacent non-tumorous cirrhotic livers, suggesting that unresolved ER-stress is associated with HCC risk in liver cirrhosis. Interestingly, inhibition of lysosomal degradation using hydroxychloroquine (HCQ) induced expression of the tumor suppressor p53, promoted apoptosis, and inhibited HCC growth, whereas activation of autophagy using an mTOR inhibitor (Torin1) promoted HCC growth. Results of this study suggest that induction of CMA compensates for the impairment of macroautophagy to promote HCC survival in the cirrhotic liver.
Highlights
Hepatocellular carcinoma (HCC) is a primary malignant tumor in the liver that frequently develops in the background of pre-existing chronic liver diseases
It is well known that HCC develops more frequently in the background of liver cirrhosis, the molecular mechanisms underlying the progression of liver cirrhosis to HCC remain unclear
The endoplasmic reticulum stress (ER stress) and the unfolded protein response (UPR) persist during chronic liver disease and liver cirrhosis related to viral infection (HCV, hepatitis B virus (HBV)) and non-viral etiologies
Summary
Hepatocellular carcinoma (HCC) is a primary malignant tumor in the liver that frequently develops in the background of pre-existing chronic liver diseases. HCC accounts for 80-90% of primary liver cancers, and the incidence of HCC is increasing globally by 3-9% annually [2]. The majority of HCCs develop in patients with liver cirrhosis resulting www.impactjournals.com/oncotarget from infection with either the hepatitis B virus (HBV) or the hepatitis C virus (HCV) [4]. Other conditions, such as alcoholic hepatitis, non-alcoholic fatty liver disease, diabetes, and hemochromatosis contribute to the development of HCC [5, 6]. HCC incidences in Europe and North America are moderate, rates in these regions continue to rise due to the obesity epidemic and other metabolic syndromes [8]
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