Fibroblast expression of the coactivator p300 governs the intensity of profibrotic response to transforming growth factor beta.
OBJECTIVE
Transforming growth factor beta (TGFbeta) induces profibrotic responses in normal fibroblasts, and plays a fundamental role in the pathogenesis of fibrosis in scleroderma (systemic sclerosis [SSc]). The intensity of cellular responses elicited by cytokines is modulated by transcriptional coactivators such as the histone acetylase p300. The objective of these studies was to delineate the physiologic role of p300 in Smad-dependent profibrotic responses elicited by TGFbeta.


METHODS
Ectopic p300 was transiently expressed in normal dermal fibroblasts. Cellular p300 levels were suppressed using p300-specific ribozymes. The regulation of gene expression was examined by transient transfection assays, Northern blotting, and immunoblot analysis. The expression of p300 in normal and scleroderma fibroblasts was evaluated by confocal microscopy and immunoblotting, and p300 levels in skin from mice with experimental scleroderma were assessed by immunohistochemistry.


RESULTS
In normal fibroblasts, TGFbeta induced an increase in the levels of p300. Forced expression of ectopic p300 in these cells dramatically enhanced the magnitude of TGFbeta responses, whereas selective depletion of p300 using ribozyme resulted in abrogation of TGFbeta-induced collagen synthesis and promoter activity. Furthermore, TGFbeta lost its ability to induce Smad-dependent transcription in p300-depleted fibroblasts. These responses could be fully rescued with ectopic p300. Abrogation of Smad-mediated TGFbeta signaling was not due to alterations in the levels or the ligand-dependent phosphorylation or intracellular trafficking of endogenous Smads. Immunohistochemical analysis demonstrated substantially increased p300 expression in lesional skin from mice with chronic graft-versus-host disease, an animal model of scleroderma. Furthermore, levels of p300 were 2-3-fold higher in cultured fibroblasts derived from SSc patients than in fibroblasts from matched normal controls.


CONCLUSIONS
These results establish, for the first time, that the coactivator histone acetylase p300, itself a target of TGFbeta regulation, is an essential component of the cellular TGFbeta signal transduction pathways mediating stimulation of collagen synthesis in fibroblasts. Since the cellular abundance of p300 appears to govern the intensity of profibrotic responses elicited by TGFbeta, elevated p300 expression in lesional tissue may contribute to the progression of skin fibrosis in scleroderma.
Bhattacharyya
Swati
S
Northwestern University, Chicago, Illinois.
Ghosh
Asish K
AK
Pannu
Jaspreet
J
Mori
Yasuji
Y
Takagawa
Shinsuke
S
Chen
Guofen
G
Trojanowska
Maria
M
Gilliam
Anita C
AC
Varga
John
J
D000123:Acetyltransferases / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004195:Disease Models, Animal; D005260:Female; D005347:Fibroblasts / Q000201:enzymology* / Q000473:pathology; D005355:Fibrosis / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D006086:Graft vs Host Disease / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D051548:Histone Acetyltransferases; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008875:Middle Aged; D016337:RNA, Catalytic; D012595:Scleroderma, Systemic / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D012867:Skin / Q000201:enzymology / Q000473:pathology; D051900:Smad3 Protein; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor
D000123:Acetyltransferases; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D051548:Histone Acetyltransferases; D016337:RNA, Catalytic; D051900:Smad3 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor; C497790:SMAD3 protein, human; C497791:Smad3 protein, mouse