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.

Hippocampal Src kinase is required for novelty-induced enhancement of contextual fear extinction.

Exposure to a novel environment enhances the extinction of contextual fear through the "tagging-and-capture" process. However, the underlying molecular mechanisms of novelty-induced enhancement of fear extinction are still unclear. NMDA receptor activity was recently revealed to be required for the enhancement of fear extinction caused by exposure to novelty. Src family kinases (SFKs) act as a molecular hub for regulation of NMDA receptors. We hypothesized that SFKs might be involved in novelty-induced enhancement of fear extinction. We found that the enhancement of fear extinction induced by novelty exposure is accompanied by Src kinase phosphorylation and activation in a restricted time window. Furthermore, intrahippocampal infusion of SFKs inhibitor PP2 inhibits Src kinase phosphorylation and activation, attenuates the activation of NR2B-containing NMDA receptors, and thereby reverses the enhancement of fear extinction induced by novelty exposure. These results suggested that Src kinase may serve as a behavioral tag in the procedural enhancement of fear extinction by novelty exposure.