Human eosinophils have an intact Smad signaling pathway leading to a major transforming growth factor-beta target gene expression.
BACKGROUND
There is a paradoxical finding that eosinophils are frequently accumulated at the sites of allergic inflammation where transforming growth factor (TGF)-beta, a negative regulator of eosinophil survival, is upregulated; however, eosinophil accumulation is persistent. We thus hypothesized that eosinophils might have aberrant TGF-beta signaling and be unresponsive to TGF-beta. To test the hypothesis, we examined the expression and function of Smad proteins, which are central mediators for TGF-beta signaling, in human eosinophils.


METHODS
Eosinophils were isolated from the peripheral blood of normal donors, and the expression and activation of endogenous Smad proteins were examined by reverse transcription polymerase chain reaction and Western blotting. The Smad function in the transcription of the major TGF-beta target gene Smad7 was investigated using a dominant negative form of Smad3. The effect of TGF-beta on eosinophil survival was then evaluated by a cell viability assay using normal and asthmatic eosinophils.


RESULTS
Human eosinophils expressed mRNAs and proteins of TGF-beta typeI and type II receptors, Smad2, Smad3 and Smad4. TGF-beta induced the phosphorylation of Smad2 in eosinophils, which was blocked by SB431542, an inhibitor of TGF-beta type I receptor kinase. A dominant negative Smad3 protein suppressed TGF-beta-induced Smad7 mRNA expression in eosinophils. Finally, TGF-beta prevented granulocyte macrophage colony-stimulating factor- or interferon-gamma-mediated survival of eosinophils obtained from asthmatic patients as well as normal subjects.


CONCLUSIONS
Human eosinophils have an intact Smad signaling pathway leading to a major TGF-beta target gene expression. Thus, eosinophils might become resistant to TGF-beta only in in vivo circumstances.
Kanzaki
Mirei
M
Department of Immunology, Faculty of Medicine, University of Yamanashi, Chuo, Yamanashi, Japan.
Shibagaki
Naotaka
N
Hatsushika
Kyosuke
K
Mitsui
Hiroshi
H
Inozume
Takashi
T
Okamoto
Atsushi
A
Dobashi
Yoh
Y
Ogawa
Hideoki
H
Shimada
Shinji
S
Nakao
Atsuhito
A
D030201:Activin Receptors, Type I / Q000378:metabolism; D001249:Asthma / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004804:Eosinophils / Q000187:drug effects* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D051899:Smad2 Protein / Q000378:metabolism*; D051900:Smad3 Protein / Q000378:metabolism*; D051901:Smad4 Protein / Q000378:metabolism*; D051906:Smad7 Protein / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; C497806:SMAD7 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D051906:Smad7 Protein; D016212:Transforming Growth Factor beta; D007371:Interferon-gamma; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II