title: Neuroprotectin D1 induces dephosphorylation of Bcl-xL in a PP2A-dependent manner during oxidative stress and promotes retinal pigment epithelial cell survival.
abstract: Retinal pigment epithelial (RPE) cell integrity is critical for the survival of photoreceptor cells. Bcl-x(L) is a major anti-apoptotic Bcl-2 protein required for RPE cell survival, and phosphorylation of Bcl-x(L) at residue Ser-62 renders this protein pro-apoptotic. In this study, we identify serine/threonine protein phosphatase 2A (PP2A) as a key regulator of Bcl-x(L) phosphorylation at residue Ser-62 in ARPE-19 cells, a spontaneously arising RPE cell line in which Bcl-x(L) is highly expressed. We found that either PP2A inhibitor okadaic acid or depletion of catalytic subunit alpha of PP2A (PP2A/Calpha) by small interfering RNA enhanced Bcl-x(L) phosphorylation when activated with hydrogen peroxide and tumor necrosis factor alpha-induced oxidative stress. Disruption of PP2A/Calpha exacerbated oxidative stress-induced apoptosis. PP2A/Calpha colocalized and interacted with S62Bcl-x(L) in cells stressed with H(2)O(2)/tumor necrosis factor alpha. By contrast, the omega-3 fatty acid docosahexaenoic acid derivative, neuroprotectin D1 (NPD1), a potent activator of survival signaling, down-regulated oxidative stress-induced phosphorylation of Bcl-x(L) by increasing protein phosphatase activity. NPD1 also attenuated the oxidative stress-induced apoptosis by knockdown of PP2A/Calpha and increased the association of PP2A/Calpha with S62Bcl-x(L) as well as total Bcl-x(L). NPD1 also enhanced the heterodimerization of Bcl-x(L) with its counterpart, pro-apoptotic protein Bax. Thus, NPD1 modulates the activation of this Bcl-2 family protein by dephosphorylating in a PP2A-dependent manner, suggesting a coordinated, NPD1-mediated regulation of cell survival in response to oxidative stress.
authors.affiliation: Neuroscience Center of Excellence, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.
authors.forename: Rajee
authors.initials: R
authors.lastname: Antony
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Lukiw
authors.forename: Nicolas G
authors.initials: NG
authors.lastname: Bazan
mesh_terms: D017209:Apoptosis; D002460:Cell Line; D002470:Cell Survival; D019281:Dimerization; D004281:Docosahexaenoic Acids / Q000378:metabolism*; D006801:Humans; D018384:Oxidative Stress; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism*
chemical_list: C494826:BAX protein, human; C494811:BCL2L1 protein, human; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C487679:protectin D1; D004281:Docosahexaenoic Acids; D012694:Serine