title: Tubulin polymerization disrupts cardiac β-adrenergic regulation of late INa.
abstract: OBJECTIVE
  The anticancer drug paclitaxel (TXL) that polymerizes microtubules is associated with arrhythmias and sinus node dysfunction. TXL can alter membrane expression of Na channels (NaV1.5) and Na current (INa), but the mechanisms are unknown. Calcium/calmodulin-dependent protein kinase II (CaMKII) can be activated by β-adrenergic stimulation and regulates INa gating. We tested whether TXL interferes with isoproterenol (ISO)-induced activation of CaMKII and consequent INa regulation.
  
  
  RESULTS
  In wild-type mouse myocytes, the addition of ISO (1 µmol/L) resulted in increased CaMKII auto-phosphorylation (western blotting). This increase was completely abolished after pre-treatment with TXL (100 µmol/L, 1.5 h). The mechanism was further investigated in human embryonic kidney cells. TXL inhibited the ISO-induced β-arrestin translocation. Interestingly, both knockdown of β-arrestin2 expression using small interfering RNA and inhibition of exchange protein directly activated by cAMP (Epac) blocked the ISO-induced CaMKII auto-phosphorylation similar to TXL. The generation of cAMP, however, was unaltered (Epac1-camps). CaMKII-dependent Na channel function was measured using patch-clamp technique in isolated cardiomyoctes. ISO stimulation failed to induce CaMKII-dependent enhancement of late INa and Na channel inactivation (negative voltage shift in steady-state activation and enhanced intermediate inactivation) after pre-incubation with TXL. Consistent with this, TXL also inhibited ISO-induced CaMKII-specific Na channel phosphorylation (at serine 571 of NaV1.5).
  
  
  CONCLUSIONS
  Pre-incubation with TXL disrupts the ISO-dependent CaMKII activation and consequent Na channel regulation. This may be important for patients receiving TXL treatments, but also relevant for conditions of increased CaMKII expression and enhanced β-adrenergic stimulation like in heart failure.
authors.affiliation: Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany.
authors.forename: Nataliya
authors.initials: N
authors.lastname: Dybkova
authors.affiliation: Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany Department of Internal Medicine II, University Hospital Regensburg, Franz-Josef-Strauß-Allee 11, Regensburg 93053, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Wagner
authors.affiliation: Department of Cardiology, Angiology and Pneumology, Ruprecht Karls University Heidelberg, Heidelberg, Germany DZHK, Partner Site Heidelberg, Heidelberg, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Backs
authors.affiliation: Davis Heart and Lung Research Institute, Department of Internal Medicine and Physiology and Cell Biology, Ohio State University Medical Center, Columbus, OH, USA.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Hund
authors.affiliation: Davis Heart and Lung Research Institute, Department of Internal Medicine and Physiology and Cell Biology, Ohio State University Medical Center, Columbus, OH, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Mohler
authors.affiliation: Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Sowa
authors.affiliation: Clinic for Cardiology and Pneumology, Georg-August-University Göttingen, Göttingen, Germany DZHK (German Centre for Cardiovascular Research), Partner Site Göttingen, Göttingen, Germany.
authors.forename: Viacheslav O
authors.initials: VO
authors.lastname: Nikolaev
authors.affiliation: Department of Internal Medicine II, University Hospital Regensburg, Franz-Josef-Strauß-Allee 11, Regensburg 93053, Germany lars.maier@ukr.de.
authors.forename: Lars S
authors.initials: LS
authors.lastname: Maier
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000633:toxicity; D019390:Arrestins / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008870:Microtubules / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D017239:Paclitaxel / Q000633:toxicity; D010766:Phosphorylation; D058105:Polymerization; D055503:Protein Multimerization; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism*; D050257:Tubulin Modulators / Q000633:toxicity; D000071557:beta-Arrestins
chemical_list: D000318:Adrenergic beta-Agonists; D000972:Antineoplastic Agents, Phytogenic; D019390:Arrestins; D011943:Receptors, Adrenergic, beta; D015222:Sodium Channels; D014404:Tubulin; D050257:Tubulin Modulators; D000071557:beta-Arrestins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; C517673:Camk2d protein, mouse; D007545:Isoproterenol; D017239:Paclitaxel
keywords: Adrenergic stimulation; Calcium/calmodulin-dependent protein kinase II; Microtubules; Paclitaxel; Sodium channels