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: Jean-Paul Decuypere, Kirsten Welkenhuyzen, Tomas Luyten, Raf Ponsaerts, Michael Dewaele, Jordi Molgó, Patrizia Agostinis, Ludwig Missiaen, Humbert De Smedt, Jan B Parys, Geert Bultynck
• Journal: Autophagy (Autophagy) Vol. 7 Issue 12 Pg. 1472-89 (Dec 2011) ISSN: 1554-8635 [Electronic] United States
• PMID: 22082873 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• ATG5 protein, human
• Apoptosis Regulatory Proteins
• Autophagy-Related Protein 5
• BECN1 protein, human
• Beclin-1
• Calcium-Binding Proteins
• Endoplasmic Reticulum Chaperone BiP
• HSPA5 protein, human
• Inositol 1,4,5-Trisphosphate Receptors
• MAP1LC3A protein, human
• Membrane Proteins
• Microtubule-Associated Proteins
• Proto-Oncogene Proteins c-bcl-2
• RNA, Small Interfering
• Inositol 1,4,5-Trisphosphate
• Calcium

Topics

• Apoptosis Regulatory Proteins (metabolism)
• Autophagy
• Autophagy-Related Protein 5
• Beclin-1
• Binding Sites
• Calcium (metabolism)
• Calcium Signaling
• Calcium-Binding Proteins (metabolism)
• Cytosol (metabolism)
• Endoplasmic Reticulum (metabolism)
• Endoplasmic Reticulum Chaperone BiP
• Gene Knockdown Techniques
• HeLa Cells
• Humans
• Inositol 1,4,5-Trisphosphate (metabolism)
• Inositol 1,4,5-Trisphosphate Receptors (chemistry, metabolism)
• Intracellular Space (metabolism)
• Membrane Proteins (metabolism)
• Microtubule-Associated Proteins (metabolism)
• Models, Biological
• Protein Binding
• Protein Structure, Tertiary
• Proto-Oncogene Proteins c-bcl-2 (metabolism)
• RNA, Small Interfering (metabolism)