title: Ins(1,4,5)P3 receptor-mediated Ca2+ signaling and autophagy induction are interrelated.
abstract: The role of intracellular Ca2+ signaling in starvation-induced autophagy remains unclear. Here, we examined Ca2+ dynamics during starvation-induced autophagy and the underlying molecular mechanisms. Tightly correlating with autophagy stimulation, we observed a remodeling of the Ca2+ signalosome. First, short periods of starvation (1 to 3 h) caused a prominent increase of the ER Ca2+-store content and enhanced agonist-induced Ca2+ release. The mechanism involved the upregulation of intralumenal ER Ca2+-binding proteins, calreticulin and Grp78/BiP, which increased the ER Ca2+-buffering capacity and reduced the ER Ca2+ leak. Second, starvation led to Ins(1,4,5)P3R sensitization. Immunoprecipitation experiments showed that during starvation Beclin 1, released from Bcl-2, first bound with increasing efficiency to Ins(1,4,5)P3Rs; after reaching a maximal binding after 3 h, binding, however, decreased again. The interaction site of Beclin 1 was determined to be present in the N-terminal Ins(1,4,5)P3-binding domain of the Ins(1,4,5)P3R. The starvation-induced Ins(1,4,5)P3R sensitization was abolished in cells treated with BECN1 siRNA, but not with ATG5 siRNA, pointing toward an essential role of Beclin 1 in this process. Moreover, recombinant Beclin 1 sensitized Ins(1,4,5)P3Rs in 45Ca2+-flux assays, indicating a direct regulation of Ins(1,4,5)P3R activity by Beclin 1. Finally, we found that Ins(1,4,5)P3R-mediated Ca2+ signaling was critical for starvation-induced autophagy stimulation, since the Ca2+ chelator BAPTA-AM as well as the Ins(1,4,5)P3R inhibitor xestospongin B abolished the increase in LC3 lipidation and GFP-LC3-puncta formation. Hence, our results indicate a tight and essential interrelation between intracellular Ca2+ signaling and autophagy stimulation as a proximal event in response to starvation.
authors.affiliation: Laboratory of Molecular and Cellular Signaling, Department Molecular Cell Biology, K.U. Leuven, Campus Gasthuisberg, Leuven, Belgium.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Decuypere
authors.forename: Kirsten
authors.initials: K
authors.lastname: Welkenhuyzen
authors.forename: Tomas
authors.initials: T
authors.lastname: Luyten
authors.forename: Raf
authors.initials: R
authors.lastname: Ponsaerts
authors.forename: Michael
authors.initials: M
authors.lastname: Dewaele
authors.forename: Jordi
authors.initials: J
authors.lastname: Molgó
authors.forename: Patrizia
authors.initials: P
authors.lastname: Agostinis
authors.forename: Ludwig
authors.initials: L
authors.lastname: Missiaen
authors.forename: Humbert
authors.initials: H
authors.lastname: De Smedt
authors.forename: Jan B
authors.initials: JB
authors.lastname: Parys
authors.forename: Geert
authors.initials: G
authors.lastname: Bultynck
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002135:Calcium-Binding Proteins / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D055785:Gene Knockdown Techniques; D006367:HeLa Cells; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000737:chemistry / Q000378:metabolism*; D042541:Intracellular Space / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008954:Models, Biological; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism
chemical_list: C502778:ATG5 protein, human; D051017:Apoptosis Regulatory Proteins; D000071187:Autophagy-Related Protein 5; C491997:BECN1 protein, human; D000071186:Beclin-1; D002135:Calcium-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium
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