Anticarcinogenic action of quercetin by downregulation of phosphatidylinositol 3-kinase (PI3K) and protein kinase C (PKC) via induction of p53 in hepatocellular carcinoma (HepG2) cell line.

Protein kinase C (PKC) is a key regulator of cell growth and differentiation in mammalian cells and hyperactivation of PKC is believed to play an important role in tumor progression. PKC is downstream to signaling protein of phosphatidylinositol 3-Kinase (PI3K), a known up-regulator of cell proliferation and survival. Accumulation of reactive oxygen species (ROS) triggers oxidative stress in the tumor microenvironment, leading to the hyperactivation of various oxidative stress-stimulated signaling molecules. Quercetin (QUE) is a naturally occurring dietary flavonoid having antioxidant properties. QUE is reported to show antitumor activity both in vitro and in vivo; however, the molecular mechanism is yet to be thoroughly explored. HepG2 cells display cellular functions similar to the normal hepatocytes with high degree of morphological and functional differentiation, therefore HepG2 cell line is chosen as the suitable model for drug targeting. Present study is aimed to establish the signaling pathway involved in the anticarcinogenic action of QUE in HepG2 cell line. HepG2 cells were treated with different doses of QUE. Protein level and gene expression were analysed by Western blotting and RT-PCR, respectively. PKC activity was measured by non-radioactive-tagged phosphorylation. Results showed downregulation of expression of PI3K, PKC, COX-2 and ROS caused by QUE. Additionally, QUE enhanced the expression of p53 and BAX in HepG2 cells. Overall, results of the current study suggested that QUE elicited anticarcinogenic action by upregulation of p53 and BAX in HepG2 cells via downregulation of ROS, PKC, PI3K and COX-2, confirming our earlier report on the animal model.