title: Autophagy induced by calcium phosphate precipitates involves endoplasmic reticulum membranes in autophagosome biogenesis.
abstract: Calcium can play an important role in the regulation of autophagy. We previously reported that exogenously introduced calcium in the form of calcium phosphate precipitates (CPP) induces autophagy. Here we showed that CPP-induced autophagy required the classical autophagic machinery, including the autophagosome initiating molecules FIP200 and Beclin 1, as well as molecules involved in the autophagosome membrane extension, Atg4, Atg5 and Atg3. On the other hand, Atg9 seemed to place a restriction on CPP-induced autophagy. Loss of Atg9 led to enhanced LC3 punctation and enhanced p62 degradation. CPP-induced autophagy was independent of mTOR and reactive oxygen species. It also did not affect MAP kinase activation and ER stress. DFCP1 is an ER-resident molecule that binds to phosphatidylinositol 3-phosphate. CPP activated DFCP1 punctation in a class III phosphatidylinositol-3-kinase and calcium dependent manner, and caused the association of DFCP1 puncta with the autophagosomes. Consistently, ER membranes, but not Golgi or mitochondrial membranes, colocalized with CPP-induced LC3 positive autophagosomes. These data suggest that CPP-induced autophagosome formation involves the interaction with the ER membrane.
authors.affiliation: Department of Pathology and Laboratory Medicine, Indiana University School of Medicine, Indianapolis, Indiana, USA.
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Daohong
authors.initials: D
authors.lastname: Chen
authors.forename: Wentao
authors.initials: W
authors.lastname: Gao
authors.forename: Jun-Lin
authors.initials: JL
authors.lastname: Guan
authors.forename: Massaki
authors.initials: M
authors.lastname: Komatsu
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Yin
mesh_terms: D001343:Autophagy / Q000187:drug effects*; D002130:Calcium Phosphates / Q000494:pharmacology*; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D010588:Phagosomes / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D002130:Calcium Phosphates; C020243:calcium phosphate