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Misoprostol‐Induced Activation of NF‐kB Functions to Repress the Bnip3 Cell Death Pathway in Neonatal Hypoxia
Author(s) -
Martens Matthew D.,
Field Jared,
Hai Yan,
Mughal Wajihah,
Silva Rosa Simone,
Blaney Caitlin,
Ivanco Tammy,
DiehlJones William,
Gordon Joseph W.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.774.17
Subject(s) - hypoxia (environmental) , programmed cell death , microbiology and biotechnology , misoprostol , protein kinase a , biology , intracellular , signal transduction , pharmacology , endocrinology , kinase , medicine , chemistry , apoptosis , biochemistry , genetics , oxygen , organic chemistry , abortion , pregnancy
Neonatal hypoxia affects more than 50% of preterm infants and is implicated in a number of diseases of prematurity. The exact mechanism for hypoxic injury remains unclear, although it appears that the genetically conserved, pro‐death Bnip3 pathway may play a central role. Previous work has suggested that a transcription factor known as NF‐kB may bind to the Bnip3 promoter region and repress its expression, thereby preventing the induction of cell death. Additionally, our laboratory has shown that misoprostol, a prostaglandin E2 receptor agonist, mitigates the effects of Bnip3 in enterocytes. On this basis, we hypothesize that misoprostol induces the nuclear translocation of NF‐kB through the protein kinase‐A (PKA)/cAMP signaling pathway, resulting in Bnip3 repression and prevention of cell death. To test this, both environmental hypoxia (10% oxygen) and drug treatments were applied to a neonatal rat model to assess the effect of misoprostol and hypoxia on hippocampal, cardiac, and intestinal Bnip3. In the animal study we observed that hypoxia induced a several‐fold increase in Bnip3 protein expression in the intestine, hippocampus and heart. However, when misoprostol was administered to hypoxic rat pups, Bnip3 protein was repressed by more than 87%. In parallel cell culture studies (HCT‐116 cells), expression of Bnip3 increased cell death by 3.8‐fold coupled with a 56.2% decrease in mitochondrial membrane potential compared to empty vector treated cells. Both of these effects were rescued by misoprostol. Additionally, misoprostol induced a 3‐fold increase in intracellular PKA activation, assessed through a fluorescent PKA biosensor, and a nearly 20% increase in nuclear localization of NF‐kB. Further study revealed that expression of wild‐type NF‐kB causes reductions in endogenous Bnip3 protein expression; however, when NF‐kB phosphorylation was inhibited with a neutral alanine mutation (NF‐kB S276A), Bnip3 expression was unchanged. Taken together, both in vivo and in vitro data suggests that misoprostol activates PKA, resulting in nuclear accumulation of NF‐kB which represses Bnip3 protein expression, and ultimately prevents cell death.