Human leptin protein activates the growth of HepG2 cells by inhibiting PERK-mediated ER stress and apoptosis

Abstract

Current treatment modalities for various types of hepatic cancer, which has an increasing incidence rate, are inadequate and novel therapies are required. Therefore, identifying targets for liver cancer is becoming increasingly valuable to develop novel methods for therapy. The aim of the present study was to examine the growth activation mechanism of the leptin protein in the liver cancer cell line HepG2. The effects of the leptin protein on cell death were investigated by 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide analysis. DNA fragmentation and terminal deoxynucleotidyl transferase dUTP nick end labeling analysis were also performed to detect cell apoptosis. The expression of leptin and three endoplasmic reticulum (ER) stress unfolded protein response (UPR) proteins, including activating transcription factor 6, phosphorylated‑PKR‑like ER kinase (p‑PERK) and inositol requiring protein 1, were investigated for the examination of ER stress. The mRNA UPR proteins were also detected by reverse transcription polymerase chain reaction. The apoptosis‑associated caspase 12 and C/EBP homologous protein (CHOP) was detected by western blot analysis. The expression of or incubation with the leptin protein was able to activate cell growth and inhibit cell death and apoptosis. In cells that expressed leptin or were incubated with leptin protein (pep-LPT), cisplatin‑induced ER stress‑associated mRNA transcription and protein activation were inhibited. Levels of the ER stress UPR pathway protein, PERK, increased significantly in leptin‑silenced cells when treated with cisplatin as compared with those in the leptin‑expressing or pep-LPT cells. Furthermore, caspase 12 activation was inhibited in ex‑LPT, pep‑LPT and HepG2 cells. In conclusion, human leptin protein is involved in promoting the proliferation of HepG2 cells through inhibiting the ER stress‑associated apoptotic pathway. The PERK UPR pathway and the apoptotic factor caspase 12 were found to be involved in the inhibition of apoptosis and enhancement of proliferation.

Adipose tissue, obesity and adipokines: role in cancer promotion

“…Liver cancer cells HepG2 have been demonstrated to be sensitive to leptin treatment where leptin promotes cell growth and prevents cell death through its unfolded protein response [45]. Both proliferation and survival are aided by inhibition of ER stress signals, which is a regulatory pathway for apoptosis [45].…”

“…Both proliferation and survival are aided by inhibition of ER stress signals, which is a regulatory pathway for apoptosis [45]. Both PERK and caspase 12 are implicated in inadvertent cell survival and enhanced proliferation [45].…”

“…Both proliferation and survival are aided by inhibition of ER stress signals, which is a regulatory pathway for apoptosis [45]. Both PERK and caspase 12 are implicated in inadvertent cell survival and enhanced proliferation [45]. In the inflammatory condition of hepatitis C virus, human hepatocellular carcinomas (HCC) arise and LEPR has been identified as the most mutated gene in the affected tissue resulting in reduced phosphorylation of STAT3 [46].…”

The role of fibroblast growth factor 21 in the pathogenesis of non-alcoholic fatty liver disease and implications for therapy

“…An increase of ROS levels and oxidative stress triggers the ROS-PKCnuclear factor-κB (NF-κB) pathway and further activates inflammatory signaling pathways that stimulate the infiltration of inflammatory cells [10,20]. Endoplasmic reticulum stress also stimulates cell apoptosis through both CCAAT enhancer binding protein homologous protein (CHOP)-induced and JNK-mediated mitochondria-dependent apoptosis pathways [24,25].…”

Modulation of Cell Death and Survival by Adipokines in the Liver

“…32) Inhibition of endoplasmic reticulum (ER) stress-associated apoptotic pathway was also proposed for leptin-induced increase in hepatic cancer cells. 33) Additionally, methionine adenosyltransferase (MAT) has been demonstrated responsible for mitogenic property of leptin in HepG2 and Huh7 cells. Interestingly, although leptin induces MAT in hepatic cancer cells, this hormone does not show mitogenic properties in human and mouse hepatocytes.…”