PML Regulates Apoptosis at Endoplasmic Reticulum by Modulating Calcium Release

Abstract

The promyelocytic leukemia (PML) tumor suppressor is a pleiotropic modulator of apoptosis. However, the molecular basis for such a diverse proapoptotic role is currently unknown. We show that extranuclear Pml was specifically enriched at the endoplasmic reticulum (ER) and at the mitochondria-associated membranes, signaling domains involved in ER-to-mitochondria calcium ion (Ca 2+ ) transport and in induction of apoptosis. We found Pml in complexes of large molecular size with the inositol 1,4,5-trisphosphate receptor (IP 3 R), protein kinase Akt, and protein phosphatase 2a (PP2a). Pml was essential for Akt-and PP2a-dependent modulation of IP 3 R phosphorylation and in turn for IP 3 R-mediated Ca 2+ release from ER. Our findings provide a mechanistic explanation for the pleiotropic role of Pml in apoptosis and identify a pharmacological target for the modulation of Ca 2+ signals.The promyelocytic leukemia gene (PML)was originally identified at the breakpoint of the t(15;17) translocation of acute promyelocytic leukemia (APL), and function of the PML protein is frequently lost or aberrant in human solid tumors and hematopoietic malignancies

Identification of PTEN at the ER and MAMs and its regulation of Ca2+ signaling and apoptosis in a protein phosphatase-dependent manner

“…24,30 We performed co-immunoprecipitation experiments of proteins extracted from the ER fraction in basal condition or after ArA treatment, and found that PTEN co-immunoprecipitated with IP3R3, together with Akt, a known iteractor and modulator of IP3R-mediated Ca 2 þ release from the ER. 19 Akt-dependent inhibition of Ca 2 þ transfer from the ER to mitochondria, through IP3R3 phosphorylation, protects from Ca 2 þ -mediated apoptosis. 24 The increased ER localization of PTEN in ArA-treated cells resulted in a greater amount of PTEN coimmunoprecipitating with IP3R3, but strikingly we observed a reduction of co-precipitated Akt.…”

“…Akt was found in the same fractions. 19 To further discriminate whether PTEN associates with the outer mitochondrial membrane (OMM) or resides within these organelles, purified mitochondria were treated with proteinase K (PK). PTEN was almost completely degraded by PK treatment, indicating that it can associate with the OMM but not localize within mitochondria (Figure 1c).…”

“…Akt can phosphorylate all IP3R isoforms, 36,37 and a specific activity of Akt on IP3R3 leads to diminished ER-to-mitochondria Ca 2 þ transfer and protection from apoptosis. 19,24 The functional importance of PTEN interaction with IP3R3 is highlighted by the demonstration that, during apoptotic stimulation, the enhanced ER localization of PTEN positively correlated with an increased interaction with IP3R3, whereas Akt amount and phosphorylation levels as well as IP3R3 phosphorylation were reduced. The modulation of Akt-dependent phosphorylation of IP3Rs exerted by ER-localized PTEN could reveal a further level of PTEN-mediated inhibition of Akt activity, beyond its plasma membrane lipid phosphatase activity.…”

“…21 For constructing ER-PTEN, a sequence from UBC6 19 was subcloned (KpnI/BamHI) to the N-terminus of human PTEN cloned (EcoRI/EcoRI) into pcDNA3.1. AKAP-PTEN was constructed by fusing the mouse AKAP1 sequence (from OMM-IP3R-LBD, 4 amplified as BglII-HindIII and then subcloned HindIII/HindIII) to the N-terminus of human PTEN.…”

Role of the c subunit of the FOATP synthase in mitochondrial permeability transition

“…23,[58][59][60] The molecular mechanisms that trigger the opening of the PTPC in these settings share a prominent oxidative component and the cytosolic accumulation of Ca 2+ ions, which de facto are tightly linked to each other. 61 During the last decades, several proteins have been suggested to constitute core components of the PTPC, including various isoforms of VDAC and ANT as well as CYPD, yet only the latter appears to be truly required for MPT in vivo. 21,22,[24][25][26] Here, we demonstrate that the c subunit of the F O ATP synthase is also necessary for MPT and its functional consequences, i.e., MOMP and cell death.…”