Abstract
BACKGROUND: VDAC controls the flux of hydrophilic metabolites into mitochondria. In vitro, tubulin closes VDAC and in situ free tubulin dynamically modulates ΔΨ. Erastin, a ligand for VDAC, increases ΔΨ in HepG2 cells. Here, we hypothesize that VDAC regulates mitochondrial metabolism and that free tubulin decreases and erastin increases VDAC conductance. Our AIM was to determine ΔΨ, ATP, NADH, and response to free tubulin and erastin after VDAC knockdown (KD). METHODS: HepG2 cells were transfected with siRNAs (5 nM, Ambion) against VDAC1/2/3. At 48 h after transfection, ΔΨ was assessed by fluorescence of tetramethylrhodamine methylester (TMRM) and NADH by autofluorescence using confocal/multiphoton microscopy. Fluorescent beads were fiduciary markers. Adenine nucleotides were determined by HPLC. RESULTS: siRNA decreased mRNA and protein for each VDAC isoform by ∼90%. Double KD of VDAC1/2, VDAC1/3 and VDAC2/3 decreased TMRM fluorescence by ∼20, 55 and 73%, respectively, compared to 100% for non-target siRNA. In reconstituted bilayers, VDAC from HepG2 formed typical anion selective and voltage-gated channels reversibly blocked by dimeric tubulin. Nocodazole decreased ΔΨ by ∼61% in non-target cells and 43, 14 and 17% after KD of VDAC1/2, VDAC1/3 and VDAC2/3. VDAC3 KD decreased ATP by ∼48%, total adenine nucleotides by ∼45%, NADH by ∼33% and the NADH/NAD ratio by ∼60%. Erastin increased ΔΨ by ∼46-48% in non-target and VDAC1/2 KD cells but failed to return ΔΨ to baseline levels after VDAC1/3 and VDAC2/3 KD. Erastin also blocked and reversed depolarization induced by nocodazole. CONCLUSION: VDAC3, the least abundant isoform, contributes most to maintenance of mitochondrial metabolism in HepG2 cells. Erastin antagonizes the inhibitory effect of free tubulin. These results indicate that VDAC, especially VDAC3, regulates mitochondrial metabolism in hepatoma cells.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
