Alpha-fetoprotein/endoplasmic reticulum stress signaling mitigates injury in hepatoma cells

Abstract

Alpha-fetoprotein (AFP) and endoplasmic reticulum (ER) stress play multiple roles in hepatocellular carcinoma. Here, we analyzed the crosstalk between AFP and ER stress in human hepatoma cells. We induced ER stress in human hepatoma cell lines (HepG2 and SK-Hep1 cells) with thapsigargin (TG, an ER stress inducer), and mitigated ER stress with 4-phenylbutyrate acid (4-PBA, an ER stress inhibitor). AFP expression was knocked down by AFP short hairpin RNA and rescued by the pCI-AFP vector. AFP expression and ER stress were examined, and their roles in apoptosis, necroptosis, and proliferation were analyzed. TG significantly induced ER stress, apoptosis, necroptosis, and intracellular AFP protein levels, and reduced proliferation and AFP mRNA expression as well as supernatant AFP protein levels in HepG2 and SK -Hep1 cells. 4-PBA pretreatment partially reversed those changes in HepG2 cells. By contrast to AFP overexpression, knockdown of AFP significantly exacerbated TG-induced ER stress, apoptosis, and necroptosis, and decreased proliferation and the expression of activating transcription factor 6 alpha. In conclusion, ER stress causes the accumulation of AFP protein, which may be related to the reduction of AFP secretion. Accumulated AFP mitigates apoptosis and necroptosis and restores the proliferation of hepatoma cells by reducing ER stress.

Intracellular alpha-fetoprotein mitigates hepatocyte apoptosis and necroptosis by inhibiting endoplasmic reticulum stress

“…The results suggest that the induced AFP expression in the liver by ER stress may enhance the resistance of hepatocytes to apoptosis and necroptosis stimulators, alleviating liver injury. Interestingly, we found that AFP silencing also exacerbated the ER stress, but lowed ATF6 expression in LO2 cells and in hepatocytes of liver tissues in mice, consistent with our previous observation[ 15 ]. These findings suggest that intracellular AFP induced by the ATF6 signaling may feedback-attenuate the ER stress-induced hepatocyte apoptosis and necroptosis, partially by up-regulating ATF6 expression.…”

“…Low levels of serum AFP are detected in patients with chronic liver disease, and are positively correlated with the degrees of liver damages[ 8 , 24 ]. Although high levels of AFP expression were detected in mouse livers, we did not detect abnormally high levels of serum AFP in liver-injured mice, consistent with our observation in hepatoma cells[ 15 ]. These indicated that ER stress induced intracellular AFP expression by limiting its secretion.…”

“…These indicated that during chronic liver diseases, ER stress and other inducers triggered hepatocyte apoptosis and necroptosis and stimulated AFP expression, but limited its secretion, leading to increased levels of intracellular AFP in hepatocytes. These novel data extended our previous study on hepatoma cells[ 15 ], and support the notion that AFP can be induced during the process of chronic liver diseases[ 7 , 23 ]. Our findings may shed light on the liver responses to ER stress in the pathogenic process of chronic liver diseases.…”

“…Aberrant ER stress can activate cell injury reactions, such as apoptosis and necroptosis by activating the C/enhancer binding protein (EBP)-homologous protein (CHOP) pathway, caspase-3 cleavage and mixed lineage kinase domain-like pseudokinase (MLKL) phosphorylation[ 13 , 14 ]. Our previous study has shown that ER stress inhibits the AFP secretion in hepatoma cells and the increase in the levels of intracellular AFP feedback attenuates the ER stress-related apoptosis and necroptosis in hepatoma cells[ 15 ]. However, it is unknown how ER stress can regulate AFP expression and secretion, and how intracellular AFP can modulate the ER stress-induced liver injury during the pathogenic process of chronic liver diseases.…”

Feedback loop between hepatocyte nuclear factor 1α and endoplasmic reticulum stress mitigates liver injury by downregulating hepatocyte apoptosis

“…Then, cells were treated with TG (1.0 μmol/L) for 36 h to induce hepatic ER stress. Previous studies demonstrated that SK-Hep1 cells were more sensitive to ER stress inducers; therefore, an induction dose of 0.25 μmol/L TG was used 62 .…”