RT Journal Article SR Electronic T1 A Small Molecule Pyrazolo[3,4-d]Pyrimidinone Inhibitor of Zipper-Interacting Protein Kinase Suppresses Calcium Sensitization of Vascular Smooth Muscle JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 105 OP 117 DO 10.1124/mol.115.100529 VO 89 IS 1 A1 Justin A. MacDonald A1 Cindy Sutherland A1 David A. Carlson A1 Sabreena Bhaidani A1 Abdulhameed Al-Ghabkari A1 Karl Swärd A1 Timothy A. J. Haystead A1 Michael P. Walsh YR 2016 UL http://molpharm.aspetjournals.org/content/89/1/105.abstract AB A novel inhibitor of zipper-interacting protein kinase (ZIPK) was used to examine the involvement of ZIPK in the regulation of smooth muscle contraction. Pretreatment of de-endothelialized rat caudal arterial smooth muscle strips with the pyrazolo[3,4-d]pyrimidinone inhibitor 2-((1-(3-chlorophenyl)-4-oxo-4,5-dihydro-1H-pyrazolo [3,4-d]-pyrimidin-6-yl)thio)propanamide (HS38) decreased the velocity of contraction (time to reach half-maximal force) induced by the phosphatase inhibitor calyculin A in the presence of Ca2+ without affecting maximal force development. This effect was reversed following washout of HS38 and correlated with a reduction in the rate of phosphorylation of myosin 20-kDa regulatory light chains (LC20) but not of protein kinase C-potentiated inhibitory protein for myosin phosphatase of 17 kDa (CPI-17), prostate apoptosis response-4, or myosin phosphatase-targeting subunit 1 (MYPT1), all of which have been implicated in the regulation of vascular contractility. A structural analog of HS38, with inhibitory activity toward proviral integrations of Moloney (PIM) virus 3 kinase but not ZIPK, had no effect on calyculin A–induced contraction or protein phosphorylations. We conclude that a pool of constitutively active ZIPK is involved in regulation of vascular smooth muscle contraction through direct phosphorylation of LC20 upon inhibition of myosin light chain phosphatase activity. HS38 also significantly attenuated both phasic and tonic contractile responses elicited by phenylephrine, angiotensin II, endothelin-1, U46619, and K+-induced membrane depolarization in the presence of Ca2+, which correlated with inhibition of phosphorylation of LC20, MYPT1, and CPI-17. These effects of HS38 suggest that ZIPK also lies downstream from G protein–coupled receptors that signal through both Gα12/13 and Gαq/11.