ARTHRITIS & RHEUMATISM
Vol. 48, No. 6, June 2003, pp 1569–1581
DOI 10.1002/art.11020
© 2003, American College of Rheumatology
Mediation of Interleukin-1–Induced
Transforming Growth Factor 1 Expression
by Activator Protein 4 Transcription Factor in
Primary Cultures of Bovine Articular Chondrocytes
Possible Cooperation With Activator Protein 1
R. Andriamanalijaona,
1
N. Felisaz,
1
S.-J. Kim,
2
K. King-Jones,
3
M. Lehmann,
3
J.-P. Pujol,
1
and K. Boumediene
1
Objective. Interleukin-1 (IL-1) and transforming
growth factor 1 (TGF1) play major roles in osteoar-
ticular diseases, exerting opposite effects on both the
catabolism and anabolism of cartilage matrix. Previous
findings suggest that IL-1 and TGF1 could function in
a feedback interaction. However, the effect exerted by
IL-1 on expression of TGF by articular chondrocytes
is, so far, poorly understood. The present study was
carried out to determine the influence of IL-1 on the
expression of TGF1 by bovine articular chondrocytes
(BACs) in primary culture.
Methods. BAC primary cultures were treated with
IL-1, and TGF1 messenger RNA (mRNA) steady-
state levels and protein expression were measured by
real-time reverse transcription–polymerase chain reac-
tion and enzyme-linked immunosorbent assay, respec-
tively. Transient transfection of TGF1 gene promoter
constructs was performed to delineate the DNA se-
quences that mediate the IL-1 effect. Electrophoretic
mobility shift assays (EMSAs) and supershift analysis
were used to characterize the transcription factors
binding to these sequences.
Results. Cultured BACs responded to IL-1 ex-
posure by exhibiting an increase of TGF1 expression at
both the mRNA and protein levels. The effect was found
to be mediated by a major 80-bp sequence located
between 732 and 652 upstream of the transcription
initiation site. EMSA and supershift analysis revealed
that the transcription factors activator protein 4 (AP-4)
and AP-1 specifically bound to the 720/696 part of
this sequence under IL-1 treatment. Overexpression of
AP-4 in the BAC cultures resulted in stimulation of the
transcriptional activity of the 732/11 TGF1 pro-
moter construct through the same IL-1–responsive
element.
Conclusion. IL-1 induces an increase of TGF1
in articular chondrocytes through activation of AP-4
and AP-1 binding to the TGF1 gene promoter. These
findings may help us understand the role of IL-1 in the
disease process. Notwithstanding its deleterious effect
on cartilage, IL-1 could initiate the repair response
displayed by injured cartilage in the early stages of
osteoarthritis through its ability to enhance TGF1
expression by local chondrocytes.
Osteoarthritis (OA) is a progressively destructive
joint disease that is characterized by erosive deteriora-
tion of the articular cartilage. Interleukin-1 (IL-1) has
long been implicated in this pathologic mechanism, since
it is a cytokine capable of stimulating the expression of
several metalloproteases by joint cells, including chon-
drocytes (1,2). The lesions appearing in the cartilage fail
to heal spontaneously and undergo inexorable enlarge-
ment with time, leading to the debilitating disease that
Supported by the Regional Council of Normandy, and UCB
Pharma (Belgium).
1
R. Andriamanalijaona, PhD, N. Felisaz, PhD, J.-P. Pujol,
PhD, K. Boumediene, PhD: Laboratory of Connective Tissue Bio-
chemistry, Caen, France;
2
S.-J. Kim, PhD: National Cancer Institute,
Bethesda, Maryland;
3
K. King-Jones, PhD, M. Lehmann, PhD: Institut
fu ¨r Genetik der Freien Universita ¨t Berlin, Berlin, Germany.
Address correspondence and reprint requests to J.-P. Pujol,
PhD, Laboratory of Connective Tissue Biochemistry, Faculty of
Medecine, 14032 Caen Cedex, France. E-mail: pujol@ibba.unicaen.fr.
Submitted for publication August 5, 2002; accepted in revised
form February 14, 2003.
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