Ins(1,4,5)P3 receptor-mediated Ca2+ signaling and autophagy induction are interrelated.
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.
Mesh Terms:
Apoptosis Regulatory Proteins, Autophagy, Autophagy-Related Protein 5, Beclin-1, Binding Sites, Calcium, Calcium Signaling, Calcium-Binding Proteins, Cytosol, Endoplasmic Reticulum, Gene Knockdown Techniques, HeLa Cells, Humans, Inositol 1,4,5-Trisphosphate, Inositol 1,4,5-Trisphosphate Receptors, Intracellular Space, Membrane Proteins, Microtubule-Associated Proteins, Models, Biological, Protein Binding, Protein Structure, Tertiary, Proto-Oncogene Proteins c-bcl-2, RNA, Small Interfering
Apoptosis Regulatory Proteins, Autophagy, Autophagy-Related Protein 5, Beclin-1, Binding Sites, Calcium, Calcium Signaling, Calcium-Binding Proteins, Cytosol, Endoplasmic Reticulum, Gene Knockdown Techniques, HeLa Cells, Humans, Inositol 1,4,5-Trisphosphate, Inositol 1,4,5-Trisphosphate Receptors, Intracellular Space, Membrane Proteins, Microtubule-Associated Proteins, Models, Biological, Protein Binding, Protein Structure, Tertiary, Proto-Oncogene Proteins c-bcl-2, RNA, Small Interfering
Autophagy
Date: Dec. 01, 2011
PubMed ID: 22082873
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