title: cGMP Signaling Increases Antioxidant Gene Expression by Activating Forkhead Box O3A in the Colon Epithelium.
abstract: Signaling through cGMP has therapeutic potential in the colon, where it has been implicated in the suppression of colitis and colon cancer. In this study, we tested the ability of cGMP and type 2 cGMP-dependent protein kinase (PKG2) to activate forkhead box O (FoxO) in colon cancer cells and in the colon epithelium of mice. We show that activation of PKG2 in colon cancer cells inhibited cell proliferation, inhibited AKT, and activated FoxO. Treatment of colon explants with 8Br-cGMP also activated FoxO target gene expression at both RNA and protein levels, and reduced epithelial reduction-oxidation (redox) stress. FoxO3a was the most prominent isoform in the distal colon epithelium, with prominent luminal staining. FoxO3a levels were reduced in Prkg2-/-animals, and FoxO target genes were unaffected by 8Br-cGMP challenge in vitro. Treatment of mice with the phosphodiesterase-5 inhibitor vardenafil (Levitra) mobilized FoxO3a to the nucleus of luminal epithelial cells, which corresponded to increased FoxO target gene expression, reduced redox stress, and increased epithelial barrier integrity. Treatment of human colonic biopsy specimens with 8Br-cGMP also activated catalase and manganese superoxide dismutase expression, indicating that this pathway is conserved in humans. Taken together, these results identify a novel signaling pathway in the colon epithelium, where FoxO tumor suppressors could provide protection from redox stress. Moreover, this pathway is regulated by endogenous cGMP/PKG2 signaling, and can be targeted using phosphodiesterase-5 inhibitors.
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Bianca N
authors.initials: BN
authors.lastname: Islam
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Allison
authors.initials: A
authors.lastname: Bridges
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Sharman
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Muhan
authors.initials: M
authors.lastname: Hu
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Yali
authors.initials: Y
authors.lastname: Hou
authors.affiliation: Clinical and Experimental Therapeutics, University of Georgia and Charlie Norwood VA Medical Center, Augusta, Georgia.
authors.forename: Payaningal R
authors.initials: PR
authors.lastname: Somanath
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Laine
authors.initials: L
authors.lastname: Venable
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Nagendra
authors.initials: N
authors.lastname: Singh
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia.
authors.forename: Sangmi
authors.initials: S
authors.lastname: Kim
authors.affiliation: Section of Gastroenterology and Hepatology, Department of Medicine, Augusta University, Augusta, Georgia.
authors.forename: Subbaramiah
authors.initials: S
authors.lastname: Sridhar
authors.affiliation: Institute of Pharmacology and Toxicology, Technical University of Munich, Munich, Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Hofmann
authors.affiliation: Department of Biochemistry and Molecular Biology, Cancer Research Center, Augusta University, Augusta, Georgia. Electronic address: dbrowning@augusta.edu.
authors.forename: Darren D
authors.initials: DD
authors.lastname: Browning
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism; D000071316:Forkhead Box Protein O3 / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018384:Oxidative Stress / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D059467:Transcriptome
chemical_list: D000975:Antioxidants; D000071316:Forkhead Box Protein O3; D006152:Cyclic GMP