Apobec-1 protects intestine from radiation injury through posttranscriptional regulation of cyclooxygenase-2 expression.
OBJECTIVE
This study aimed to determine the role of the RNA binding protein apobec-1 in radioprotection of the intestine.


METHODS
Apobec-1-deleted mice (APOBEC-1(-/-)) and wild-type controls were treated with 12 Gy of whole-body gamma-irradiation in a cesium irradiator. The number of surviving intestinal crypts was assessed 3.5 days after irradiation by using a clonogenic assay. Cyclooxygenase-2 messenger RNA and protein expression were determined by real-time polymerase chain reaction and Western blot, respectively. RNA stability was studied by examining the turnover of a chimeric transcript containing the cyclooxygenase-2 3' untranslated region cloned downstream of luciferase complementary DNA. Apobec-1 binding to the cyclooxygenase-2 3' untranslated region was studied by electrophoretic mobility shift and UV crosslinking assays.


RESULTS
After gamma-irradiation, the survival of intestinal stem cells decreased significantly in APOBEC-1(-/-) mice. In wild-type mice treated with lipopolysaccharide before gamma-irradiation, intestinal stem cells were protected by marked increases in prostaglandin E 2 mediated by cyclooxygenase-2. No such effect was observed in the APOBEC-1(-/-) mice. The mechanism of this radioprotective effect involves the binding of apobec-1 to AU-rich sequences in the first 60 nucleotides of the 3' untranslated region of cyclooxygenase-2. Upon binding to the AU-rich sequences, apobec-1 stabilizes cyclooxygenase-2 messenger RNA. This stabilization process does not seem to be mediated by p38 mitogen-activated protein kinase pathways.


CONCLUSIONS
Lipopolysaccharide increases intestinal stem cell survival through apobec-1-mediated regulation of cyclooxygenase-2 messenger RNA stability.
Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA. sanant@im.wustl.edu
Shrikant
S
Anant
Nabendu
N
Murmu
Courtney W
CW
Houchen
Debnath
D
Mukhopadhyay
Terrence E
TE
Riehl
Stephen G
SG
Young
Aubrey R
AR
Morrison
William F
WF
Stenson
Nicholas O
NO
Davidson
D020413:3' Untranslated Regions; D000071479:APOBEC-1 Deaminase; D000818:Animals; D051546:Cyclooxygenase 2; D003564:Cytidine Deaminase / Q000502:physiology*; D005720:Gamma Rays; D015971:Gene Expression Regulation, Enzymologic; D007093:Imidazoles / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000528:radiation effects*; D007527:Isoenzymes / Q000235:genetics*; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics*; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D011832:Radiation Injuries / Q000517:prevention & control*; D013234:Stem Cells / Q000528:radiation effects; D048051:p38 Mitogen-Activated Protein Kinases
D020413:3' Untranslated Regions; D007093:Imidazoles; D007527:Isoenzymes; D008070:Lipopolysaccharides; D011725:Pyridines; D012333:RNA, Messenger; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000071479:APOBEC-1 Deaminase; C000605090:Apobec1 protein, mouse; D003564:Cytidine Deaminase; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole