Raf/MEK/ERK Signaling Pathway Is Involved in the Inhibition of Glioma Cell Proliferation and Invasion in the Ketogenic Microenvironment

Objective:A high-fat,low-carbohydrate ketogenic diet has been used to treat malignant glioma,in which the Raf/MEK/ERK signaling pathway is overactivated.However,whether the Raf/MEK/ERK signaling pathway is involved in the therapeutic effect of ketone bodies remains unknown.In this study,we investigated the effects of a major ketone body,3-hydroxybutyric acid(3-HBA),on the proliferation and metastasis of malignant glioblastoma cells and the underlying mechanism.Methods:Two human malignant glioblastoma cell lines(U87 and U251)were treated with different concentrations of 3-HBA with or without the Raf inhibitor PAF C-16 for 24 h.Cell proliferation,cell cycle,cell invasion,and phospholipase D1(PLD1)activity were determined.Protein and gene expression levels of Raf/MEK/ERK signaling pathway members were examined.Results:3-HBA significantly decreased cell proliferation,invasion,and intracellular PLD1 activity in both U87 and U251 glioblastoma cell lines.3-HBA treatment significantly increased the proportion of cells in the G1 phase and decreased the proportion of cells in S phase in U87 cells.In the U251 line,the proportion of treated cells in S phase was increased and proportion of cells in G2 was decreased.3-HBA treatment also significantly decreased the protein expression levels of Raf,MEK,p-MEK,ERK,p-ERK,and PLD1 while increasing p53 expression;an effect that was similar to treatment with the Raf inhibitor.Co-treatment of 3-HBA with the Raf inhibitor further enhanced the effects of the 3-HBA in both cell lines.Conclusion:We confirmed that a ketogenic microenvironment can inhibit glioma cell proliferation and invasion by downregulating the expression of PLD1 through the Raf/MEK/ERK signaling pathway.