Objective: To investigate the cross-talk between the PI3K/Akt and MEK/ERK pathways and its role in cell cycle regulation under endoplasmic reticulum stress in human hepatocellular carcinoma cells.
Methods: PI3K inhibitor LY294002 and MEK inhibitor U0126 were used to block the PI3K/Akt and MEK/ERK pathways respectively, and constitutively activated Akt mutant construct was used to activate the PI3K/Akt pathway. Western blot was used to study the potential cross-talk between the PI3K/Akt and MEK/ERK pathways under endoplasmic reticulum stress in human hepatocellular carcinoma cells. the role of the cross-talk between the PI3K/Akt and MEK/ERK pathways in cell cycle regulation was investigated by using propidium iodide staining.
Results: LY294002 not only blocked Akt activation efficiently but also increased ERK phosphorylation markedly under endoplasmic reticulum stress in SMMC-7721 and Hep3B cells. Furthermore, myr-Akt inhibited endoplasmic reticulum stress-mediated ERK phosphorylation. In contrast, MEK inhibitor U0126 had no effect on endoplasmic reticulum stress-induced Akt activation. It is notable that both myr-Akt overexpression and MEK inhibitor U0126 inhibited endoplasmic reticulum stress-induced G0/G1 phase arrest in SMMC-7721 cells.
Conclusion: Endoplasmic reticulum stress-induced Akt activation is mediated through PI3K and the PI3K/Akt pathway inactivation is involved in increased ERK activity in human hepatocellular carcinoma cells. The cross-talk between the PI3K/Akt and MEK/ERK cascades plays an important role in endoplasmic reticulum stress-induced human hepatocellular carcinoma cell cycle arrest.