Tài liệu Báo cáo khoa học: The cartilage-specific transcription factor Sox9 regulates AP-2e

The cartilage-specific transcription factor Sox9 regulates

AP-2e expression in chondrocytes

Ann-Kathrin Wenke1

, Susanne Gra¨ ssel2

, Markus Moser3 and Anja K. Bosserhoff1

1 Institute of Pathology, University Regensburg, Germany

2 Department of Orthopedics, University Regensburg, Germany

3 Max-Planck-Institute of Biochemistry, Martinsried, Germany

The family of activating enhancer-binding protein

(AP)-2 transcription factors regulate their target genes

through binding to the palindromic recognition

sequence 5¢-GCCN3GGC-3¢ or variations of this

GC-rich sequence within multiple gene promoters [1].

Both in vitro and in vivo data from AP-2 knockout

mice have shown their importance in numerous physi￾ological processes during development, cell cycle regu￾lation, and cell survival [1,2]. The AP-2 family consists

of five members: AP-2a, AP-2b, AP-2c, AP-2d and

AP-2e [3–8]. They all share a conserved basic-helix–

span–helix DNA-binding and dimerization domain

at their C-terminus, and a less conserved proline and

glutamine-rich transactivation domain at their N-ter￾minus [9–11].

So far, the most recently identified AP-2 transcrip￾tion factor, AP-2e, has been only poorly characterized

[4,12]. Expression of AP-2e was first described in the

olfactory system [4], in skin, and in in vitro-cultured

keratinocytes [12]. Previously, we demonstrated that

AP-2e is also expressed in chondrocytes, where it regu￾lates the expression of integrin a10, the predominant

collagen-binding integrin during cartilage development

[13].

The axial skeleton is formed by a process named

endochondral bone formation. This complex process

Keywords

AP-2e; cartilage; differentiation;

osteoarthritis; transcriptional regulation

Correspondence

A.-K. Bosserhoff, Institute of Pathology,

University of Regensburg, Franz-Josef￾Strauss-Allee 11, D-93053 Regensburg,

Germany

Fax: +49 941 944 6602

Tel: +49 941 944 6705

E-mail: anja.bosserhoff@klinik.

uni-regensburg.de

(Received 14 January 2009, revised 13

February 2009, accepted 18 February 2009)

doi:10.1111/j.1742-4658.2009.06973.x

Activating enhancer-binding protein (AP)-2e was previously described as a

new regulator of integrin a10 expression in cartilage. In this study, we ana￾lyzed the expression of AP-2e in differentiated chondrocytes and in human

mesenchymal stem cells (HMSCs), which have been differentiated into

chondrocytes in vitro. AP-2e is predominantly expressed during the late

stages of chondrocyte differentiation, mainly in early hypertrophic carti￾lage, consistent with immunohistochemical stainings of mouse embryo

sections. Furthermore, osteoarthritic chondrocytes, resembling a hyper￾trophic phenotype, have high AP-2e levels. The AP-2e promoter harbors

binding sites for the transcription factors AP-2a and Sox9. Both transcrip￾tion factors strongly activate AP-2e expression in a cooperative manner in

the chondrosarcoma cell line SW1353. The inhibition of Sox9 expression

by small interfering RNA resulted in decreased AP-2e expression. In

addition, direct interaction of Sox9 with the AP-2e promoter could be con￾firmed by chromatin immunoprecipitation and electromobility shift assays.

This is the first study to prove the direct regulation of AP-2e by the

transcription factor Sox9, and to indicate that AP-2e potentially has an

important role as a modulator of hypertrophic cartilage.

Abbreviations

AP, activating enhancer-binding protein; CD-RAP, cartilage-derived retinoic acid-sensitive protein; ChIP, chromatin immunoprecipitation; ECM,

extracellular matrix; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HMSC, human mesenchymal stem cell; OA, osteoarthritis; SEM,

standard error of the mean; siRNA, small interfering RNA.

2494 FEBS Journal 276 (2009) 2494–2504 ª 2009 The Authors Journal compilation ª 2009 FEBS