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Valproic acid induces autophagy by suppressing the Akt/mTOR pathway in human prostate cancer cells

View Article: PubMed Central - PubMed

ABSTRACT

Previous studies have demonstrated that the chronic administration of valproic acid (VPA) suppresses angiogenesis in vivo; however, the mechanisms implicated in VPA-induced autophagy remain unclear. The current study aimed to assess VPA-induced autophagy in three prostate cancer cell lines (PC3, DU145 and LNCaP), in addition to analyzing the Akt/mammalian target of rapamycin (mTOR) signal pathway. Prostate cancer cell lines were cultured with various doses of VPA. Cell cycle was analyzed using flow cytometry, and autophagy markers [1A/1B-light chain 3 (LC3)-II and Beclin-1] were examined using transmission electron microscopy, fluorescent microscopy and western blotting. Activation of the Akt/mTOR signal pathway was also assessed by western blotting. The results demonstrated that VPA induced autophagosomes and suppressed the Akt/mTOR signal pathway. This was confirmed by detection of increased LC3-II and Beclin-1 in VPA-treated cells compared with untreated controls. Phosphorylated forms of Akt (PC3, P=0.048; DU145, P=0.045; LNCaP, P=0.039) and mTOR (PC3, P=0.012; DU145, P=0.41; LNCaP, P=0.35) were significantly reduced following VPA treatment. These results suggest that VPA may function as a histone deacetylase inhibitor, suppressing the growth of prostate cancer cells by modulating autophagy pathways, including inhibition of the Akt/mTOR pathway. Further experiments are required to determine the significance of all involved pathways regarding VPA-induced growth inhibition.

No MeSH data available.


Effect of VPA on Akt, mTOR and their phosphorylated forms. Western blotting measured the levels of Akt, mTOR, and their phosphorylated forms in (A) PC3, (B) LNCaP and (C) DU145 cells subsequent to VPA treatment at various concentrations. (D) In contrast to the control group, VPA-treated cells were found to demonstrate a dose-dependent decrease in the phosphorylation of Akt and mTOR proteins in DU145, PC3 and LNCaP cells. There was no significant change in the protein levels of total Akt and mTOR. In addition, 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines; 2.5 mmol/l and 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines. *P<0.05. p-, phosphorylated; mTOR, mammalian target of rapamycin; VPA, valproic acid.
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f4-ol-0-0-4880: Effect of VPA on Akt, mTOR and their phosphorylated forms. Western blotting measured the levels of Akt, mTOR, and their phosphorylated forms in (A) PC3, (B) LNCaP and (C) DU145 cells subsequent to VPA treatment at various concentrations. (D) In contrast to the control group, VPA-treated cells were found to demonstrate a dose-dependent decrease in the phosphorylation of Akt and mTOR proteins in DU145, PC3 and LNCaP cells. There was no significant change in the protein levels of total Akt and mTOR. In addition, 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines; 2.5 mmol/l and 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines. *P<0.05. p-, phosphorylated; mTOR, mammalian target of rapamycin; VPA, valproic acid.

Mentions: The Akt/mTOR signaling pathway was investigated in PC3, DU145 and LNCaP cell lines treated with VPA. The relative fold of phosphorylated Akt and mTOR increased as determined by scanning densitometry of the western blot normalized to β-actin. VPA-treated cells were observed to induce a dose-dependent decrease in the phosphorylation of Akt (PC3, P=0.048; DU145, P=0.045; LNCaP, P=0.039) and mTOR (PC3, P=0.012; DU145, P=0.41; LNCaP, P=0.35) protein compared to the control group (Fig. 4) in all cell lines. However, the total protein levels of Akt (PC3, P=0.082; DU145, P=0.065; LNCaP, P=0.059) and mTOR (PC3, P=0.12; DU145, P=0.095; LNCaP, P=0.089) did not change following VPA treatment (P>0.05) (Fig. 4D), which indicates that VPA inflicts a potent inhibitory effect on Akt/mTOR signaling.


Valproic acid induces autophagy by suppressing the Akt/mTOR pathway in human prostate cancer cells
Effect of VPA on Akt, mTOR and their phosphorylated forms. Western blotting measured the levels of Akt, mTOR, and their phosphorylated forms in (A) PC3, (B) LNCaP and (C) DU145 cells subsequent to VPA treatment at various concentrations. (D) In contrast to the control group, VPA-treated cells were found to demonstrate a dose-dependent decrease in the phosphorylation of Akt and mTOR proteins in DU145, PC3 and LNCaP cells. There was no significant change in the protein levels of total Akt and mTOR. In addition, 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines; 2.5 mmol/l and 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines. *P<0.05. p-, phosphorylated; mTOR, mammalian target of rapamycin; VPA, valproic acid.
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Related In: Results  -  Collection

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f4-ol-0-0-4880: Effect of VPA on Akt, mTOR and their phosphorylated forms. Western blotting measured the levels of Akt, mTOR, and their phosphorylated forms in (A) PC3, (B) LNCaP and (C) DU145 cells subsequent to VPA treatment at various concentrations. (D) In contrast to the control group, VPA-treated cells were found to demonstrate a dose-dependent decrease in the phosphorylation of Akt and mTOR proteins in DU145, PC3 and LNCaP cells. There was no significant change in the protein levels of total Akt and mTOR. In addition, 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines; 2.5 mmol/l and 5.0 mmol/l VPA treatment induced statistically significant decreases in p-mTOR protein levels in all three cell lines. *P<0.05. p-, phosphorylated; mTOR, mammalian target of rapamycin; VPA, valproic acid.
Mentions: The Akt/mTOR signaling pathway was investigated in PC3, DU145 and LNCaP cell lines treated with VPA. The relative fold of phosphorylated Akt and mTOR increased as determined by scanning densitometry of the western blot normalized to β-actin. VPA-treated cells were observed to induce a dose-dependent decrease in the phosphorylation of Akt (PC3, P=0.048; DU145, P=0.045; LNCaP, P=0.039) and mTOR (PC3, P=0.012; DU145, P=0.41; LNCaP, P=0.35) protein compared to the control group (Fig. 4) in all cell lines. However, the total protein levels of Akt (PC3, P=0.082; DU145, P=0.065; LNCaP, P=0.059) and mTOR (PC3, P=0.12; DU145, P=0.095; LNCaP, P=0.089) did not change following VPA treatment (P>0.05) (Fig. 4D), which indicates that VPA inflicts a potent inhibitory effect on Akt/mTOR signaling.

View Article: PubMed Central - PubMed

ABSTRACT

Previous studies have demonstrated that the chronic administration of valproic acid (VPA) suppresses angiogenesis in vivo; however, the mechanisms implicated in VPA-induced autophagy remain unclear. The current study aimed to assess VPA-induced autophagy in three prostate cancer cell lines (PC3, DU145 and LNCaP), in addition to analyzing the Akt/mammalian target of rapamycin (mTOR) signal pathway. Prostate cancer cell lines were cultured with various doses of VPA. Cell cycle was analyzed using flow cytometry, and autophagy markers [1A/1B-light chain 3 (LC3)-II and Beclin-1] were examined using transmission electron microscopy, fluorescent microscopy and western blotting. Activation of the Akt/mTOR signal pathway was also assessed by western blotting. The results demonstrated that VPA induced autophagosomes and suppressed the Akt/mTOR signal pathway. This was confirmed by detection of increased LC3-II and Beclin-1 in VPA-treated cells compared with untreated controls. Phosphorylated forms of Akt (PC3, P=0.048; DU145, P=0.045; LNCaP, P=0.039) and mTOR (PC3, P=0.012; DU145, P=0.41; LNCaP, P=0.35) were significantly reduced following VPA treatment. These results suggest that VPA may function as a histone deacetylase inhibitor, suppressing the growth of prostate cancer cells by modulating autophagy pathways, including inhibition of the Akt/mTOR pathway. Further experiments are required to determine the significance of all involved pathways regarding VPA-induced growth inhibition.

No MeSH data available.