title: Free tubulin modulates mitochondrial membrane potential in cancer cells.
abstract: Formation of the mitochondrial membrane potential (ΔΨ) depends on flux of respiratory substrates, ATP, ADP, and Pi through voltage-dependent anion channels (VDAC). As tubulin promotes single-channel closure of VDAC, we hypothesized that tubulin is a dynamic regulator of ΔΨ, which in cultured cancer cells was assessed by confocal microscopy of the potential-indicating fluorophore tetramethylrhodamine methylester (TMRM). Microtubule destabilizers, rotenone, colchicine, and nocodazole, and the microtubule stabilizer paclitaxel increased and decreased cellular free tubulin, respectively, and in parallel decreased and increased ΔΨ. Protein kinase A (PKA) activation by cAMP analogues and glycogen synthase kinase 3β (GSK-3β) inhibition decreased ΔΨ, whereas PKA inhibition hyperpolarized, consistent with reports that PKA and GSK-3β decrease and increase VDAC conductance, respectively. Plasma membrane potential assessed by DiBAC(4)(3) was not altered by any of the treatments. We propose that inhibition of VDAC by free tubulin limits mitochondrial metabolism in cancer cells.
authors.affiliation: Center for Cell Death, Injury & Regeneration, Department of Pharmaceutical & Biomedical Sciences, Medical University of South Carolina, Charleston, South Carolina, USA.
authors.forename: Eduardo N
authors.initials: EN
authors.lastname: Maldonado
authors.forename: Jyoti
authors.initials: J
authors.lastname: Patnaik
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Mullins
authors.forename: John J
authors.initials: JJ
authors.lastname: Lemasters
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000503:physiopathology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000502:physiology; D003078:Colchicine / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D003563:Cyclic CMP / Q000031:analogs & derivatives / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D008113:Liver Neoplasms / Q000503:physiopathology; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials; D008870:Microtubules / Q000187:drug effects / Q000502:physiology; D008930:Mitochondria, Liver / Q000187:drug effects / Q000502:physiology; D009369:Neoplasms / Q000503:physiopathology*; D015739:Nocodazole / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012235:Rhodamines / Q000494:pharmacology; D012402:Rotenone / Q000494:pharmacology; D014404:Tubulin / Q000502:physiology*
chemical_list: D012235:Rhodamines; D014404:Tubulin; C401833:tetramethylrhodamine methyl ester; D012402:Rotenone; D003563:Cyclic CMP; C053441:dibutyryl cyclic-3',5'-cytidine monophosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D017868:Cyclic AMP-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D017239:Paclitaxel; D015739:Nocodazole; D003078:Colchicine