title: Tacrolimus reduces nitric oxide synthase function by binding to FKBP rather than by its calcineurin effect.
abstract: Hypertension develops in many patients receiving the immunosuppressive drug tacrolimus (FK506). One possible mechanism for hypertension is a reduction in vasodilatory nitric oxide. We found that tacrolimus and a calcineurin autoinhibitory peptide significantly decreased vascular calcineurin activity; however, only tacrolimus altered intracellular calcium release in mouse aortic endothelial cells. In mouse aortas, incubation with tacrolimus increased protein kinase C activity and basal endothelial nitric oxide synthase phosphorylation at threonine 495 but reduced basal and agonist-induced endothelial nitric oxide synthase phosphorylation at serine 1177, a mechanism known to inhibit synthase activity. While this decreased nitric oxide production and endothelial function, the calcineurin autoinhibitory peptide had no such effects. Inhibition of ryanodine receptor opening or protein kinase C blocked the effects of tacrolimus. Since it is known that the FK506 binding protein (FKBP12/12.6) interacts with the ryanodine receptor to regulate calcium release, we propose this as the mechanism by which tacrolimus alters intracellular calcium and endothelial nitric oxide synthase rather than by its effect on calcineurin. Our study shows that prevention of the tacrolimus-induced intracellular calcium leak may attenuate endothelial dysfunction and the consequent hypertension.
authors.affiliation: Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas, USA.
authors.forename: Leslie G
authors.initials: LG
authors.lastname: Cook
authors.forename: Valorie L
authors.initials: VL
authors.lastname: Chiasson
authors.forename: Cheng
authors.initials: C
authors.lastname: Long
authors.forename: Gang-Yi
authors.initials: GY
authors.lastname: Wu
authors.forename: Brett M
authors.initials: BM
authors.lastname: Mitchell
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001011:Aorta / Q000166:cytology; D019703:Calcineurin; D002118:Calcium / Q000378:metabolism; D042783:Endothelial Cells; D006973:Hypertension / Q000139:chemically induced; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010750:Phosphoproteins; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel; D016559:Tacrolimus / Q000494:pharmacology*; D022021:Tacrolimus Binding Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C113151:Cabin1 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D019837:Ryanodine Receptor Calcium Release Channel; D052250:Nitric Oxide Synthase Type III; D011493:Protein Kinase C; D019703:Calcineurin; D022021:Tacrolimus Binding Proteins; D002118:Calcium; D016559:Tacrolimus