title: Regulation of autophagy in cardiomyocytes by Ins(1,4,5)P(3) and IP(3)-receptors.
abstract: Autophagy is a process that removes damaged proteins and organelles and is of particular importance in terminally differentiated cells such as cardiomyocytes, where it has primarily a protective role. We investigated the involvement of inositol(1,4,5)trisphosphate (Ins(1,4,5)P(3)) and its receptors in autophagic responses in neonatal rat ventricular myocytes (NRVM). Treatment with the IP(3)-receptor (IP(3)-R) antagonist 2-aminoethoxydiphenyl borate (2-APB) at 5 or 20 μmol/L resulted in an increase in autophagosome content, defined as puncta labeled by antibody to microtubule associated light chain 3 (LC3). 2-APB also increased autophagic flux, indicated by heightened LC3II accumulation, which was further enhanced by bafilomycin (10nmol/L). Expression of Ins(1,4,5)P(3) 5-phosphatase (IP(3)-5-Pase) to deplete Ins(1,4,5)P(3) also increased LC3-labeled puncta and LC3II content, suggesting that Ins(1,4,5)P(3) inhibits autophagy. The IP(3)-R can act as an inhibitory scaffold sequestering the autophagic effector, beclin-1 to its ligand binding domain (LBD). Expression of GFP-IP(3)-R-LBD inhibited autophagic signaling and furthermore, beclin-1 co-immunoprecipitated with the IP(3)-R-LBD. A mutant GFP-IP(3)-R-LBD with reduced ability to bind Ins(1,4,5)P(3) bound beclin-1 and inhibited autophagy similarly to the wild type sequence. These data provide evidence that Ins(1,4,5)P(3) and IP(3)-R act as inhibitors of autophagic responses in cardiomyocytes. By suppressing autophagy, IP(3)-R may contribute to cardiac pathology.
authors.affiliation: Molecular Cardiology Laboratory, Baker IDI Heart and Diabetes Institute, 75 Commercial Road, Melbourne, Victoria 3004, Australia.
authors.forename: Albert
authors.initials: A
authors.lastname: Wong
authors.forename: David R
authors.initials: DR
authors.lastname: Grubb
authors.forename: Nicola
authors.initials: N
authors.lastname: Cooley
authors.forename: Jieting
authors.initials: J
authors.lastname: Luo
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Woodcock
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy; D000071186:Beclin-1; D001665:Binding Sites; D001896:Boron Compounds / Q000494:pharmacology; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism; D051858:Forkhead Transcription Factors / Q000378:metabolism; D006352:Heart Ventricles / Q000166:cytology; D006360:Heat-Shock Proteins / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010588:Phagosomes / Q000378:metabolism; D010714:Phosphatidylethanolamines / Q000502:physiology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D000071456:Sequestosome-1 Protein; D015398:Signal Transduction; D000071161:Forkhead Box Protein O1
chemical_list: D051017:Apoptosis Regulatory Proteins; D000071186:Beclin-1; D001896:Boron Compounds; D051858:Forkhead Transcription Factors; D006360:Heat-Shock Proteins; D015544:Inositol 1,4,5-Trisphosphate; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins; D010714:Phosphatidylethanolamines; D000071456:Sequestosome-1 Protein; C512829:Becn1 protein, rat; C526109:Anxa3 protein, rat; C491079:Sqstm1 protein, rat; C074639:Foxo1 protein, rat; D000071161:Forkhead Box Protein O1; C483858:phosphatidylethanolamine; C109986:2-aminoethoxydiphenyl borate