title: Protein kinase g positively regulates proteasome-mediated degradation of misfolded proteins.
abstract: BACKGROUND
  Proteasome functional insufficiency is implicated in a large subset of cardiovascular diseases and may play an important role in their pathogenesis. The regulation of proteasome function is poorly understood, hindering the development of effective strategies to improve proteasome function.
  
  
  RESULTS
  Protein kinase G (PKG) was manipulated genetically and pharmacologically in cultured cardiomyocytes. Activation of PKG increased proteasome peptidase activities, facilitated proteasome-mediated degradation of surrogate (enhanced green fluorescence protein modified by carboxyl fusion of degron CL1) and bona fide (CryAB(R120G)) misfolded proteins, and attenuated CryAB(R120G) overexpression-induced accumulation of ubiquitinated proteins and cellular injury. PKG inhibition elicited the opposite responses. Differences in the abundance of the key 26S proteasome subunits Rpt6 and β5 between the PKG-manipulated and control groups were not statistically significant, but the isoelectric points were shifted by PKG activation. In transgenic mice expressing a surrogate substrate (GFPdgn), PKG activation by sildenafil increased myocardial proteasome activities and significantly decreased myocardial GFPdgn protein levels. Sildenafil treatment significantly increased myocardial PKG activity and significantly reduced myocardial accumulation of CryAB(R120G), ubiquitin conjugates, and aberrant protein aggregates in mice with CryAB(R120G)-based desmin-related cardiomyopathy. No discernible effect on bona fide native substrates of the ubiquitin-proteasome system was observed from PKG manipulation in vitro or in vivo.
  
  
  CONCLUSIONS
  PKG positively regulates proteasome activities and proteasome-mediated degradation of misfolded proteins, likely through posttranslational modifications to proteasome subunits. This may be a new mechanism underlying the benefit of PKG stimulation in treating cardiac diseases. Stimulation of PKG by measures such as sildenafil administration is potentially a new therapeutic strategy to treat cardiac proteinopathies.
authors.affiliation: Division of Basic Biomedical Sciences, University of South Dakota, 414 E Clark St, Vermillion, SD 57069, USA.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Ranek
authors.forename: Erin J M
authors.initials: EJ
authors.lastname: Terpstra
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: David A
authors.initials: DA
authors.lastname: Kass
authors.forename: Xuejun
authors.initials: X
authors.lastname: Wang
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D002318:Cardiovascular Diseases / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D062965:Cyclic GMP-Dependent Protein Kinase Type I / Q000235:genetics / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000235:genetics* / Q000378:metabolism*; D003893:Desmin / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D032383:Myocytes, Cardiac / Q000166:cytology / Q000201:enzymology*; D058986:Phosphodiesterase 5 Inhibitors / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000502:physiology; D057165:Proteostasis Deficiencies / Q000235:genetics* / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology
chemical_list: D003893:Desmin; D058986:Phosphodiesterase 5 Inhibitors; D010879:Piperazines; D011687:Purines; D034741:RNA, Small Interfering; D013450:Sulfones; D049452:Green Fluorescent Proteins; D000068677:Sildenafil Citrate; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases; C569718:PRKG1 protein, human; C569720:Prkg1 protein, mouse; C569721:Prkg1 protein, rat; D046988:Proteasome Endopeptidase Complex
keywords: cardiomyopathies; cyclic GMP-dependent protein kinase; desmin; proteasome inhibitors; proteins