Post-transcriptional regulation of Smad7 in the gut of patients with inflammatory bowel disease.
OBJECTIVE
Transforming growth factor (TGF)-beta1 is one of the most powerful endogenous negative regulators of inflammation. In patients with inflammatory bowel disease, despite abundant local TGF-beta1, there is a failure of TGF-beta-mediated negative regulation of nuclear factor kappaB activation and proinflammatory cytokine production because of increased intracellular expression of the endogenous inhibitor of TGF-beta1 signaling, Smad7. In this study, we examined the molecular mechanism underlying the induction of Smad7 in the human gut.


METHODS
Whole intestinal mucosal and lamina propria mononuclear cell samples were analyzed for Smad7 by real-time polymerase chain reaction and Western blotting. Smad7 ubiquitination and acetylation, and interaction of Smad7 with the intrinsic histone acetyltransferase, p300, were examined by immunoprecipitation and Western blotting. The effect of p300 silencing on Smad7 expression was determined in Crohn's disease lamina propria mononuclear cells.


RESULTS
We showed that Smad7 is not transcriptionally regulated in human gut but that its increase in patients with inflammatory bowel disease is due to posttranscriptional acetylation and stabilization by p300, which prevents Smad7 ubiquitination and degradation in the proteasome. Hence, Smad7 protein in cells from normal gut is ubiquitinated and rapidly degraded. In contrast, in inflamed gut, Smad7 is acetylated and not ubiquitinated, is not degraded, and can be decreased by short interfering RNA to p300.


CONCLUSIONS
These results identify posttranslational protein modification as of importance in chronic gut inflammation in humans.
Monteleone
Giovanni
G
Department of Internal Medicine and Centre of Excellence for Genomic Risk Assessment in Multifactorial and Complex Diseases, University of Tor Vergata, Rome, Italy. gi.monteleone@med.uniroma2.it
Del Vecchio Blanco
Giovanna
G
Monteleone
Ivan
I
Fina
Daniele
D
Caruso
Roberta
R
Gioia
Valentina
V
Ballerini
Sabrina
S
Federici
Giorgio
G
Bernardini
Sergio
S
Pallone
Francesco
F
MacDonald
Thomas T
TT
D000107:Acetylation; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002908:Chronic Disease; D003424:Crohn Disease / Q000235:genetics* / Q000276:immunology / Q000503:physiopathology*; D004751:Enteritis / Q000235:genetics* / Q000276:immunology / Q000503:physiopathology; D005786:Gene Expression Regulation / Q000276:immunology; D051548:Histone Acetyltransferases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D051906:Smad7 Protein / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000378:metabolism; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor
D018797:Cell Cycle Proteins; D051548:Histone Acetyltransferases; D046988:Proteasome Endopeptidase Complex; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D051906:Smad7 Protein; D014157:Transcription Factors; D025801:Ubiquitin; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor; C497806:SMAD7 protein, human