Cytokine regulation of cartilage-derived retinoic acid-sensitive protein (CD-RAP) in primary articular chondrocytes: suppression by IL-1, bfGF, TGF beta and stimulation by IGF-1

Cartilage-derived retinoic acid-sensitive protein (CD-RAP) is a secreted pr otein identified in our laboratory by RT-PCR and differential display [U.H. Dietz, L.J. Sandell. Cloning of a retinoic acid-sensitive mDNA expressed i n cartilage and during chondrogenesis. J. Biol. Chem. 271 (1996) 3311-3316] . It is synthesized by chondrocytes throughout development and down-regulat ed by retinoic acid in coordination with type II collagen gene expression. To further explore the regulation CD-RAP in primary articular chondrocytes, we examined effects of selected cytokines on CD-RAP gene expression compar ed to their effects on type IT collagen expression. Northern blot analysis showed that expression of CD-RAP mRNA was suppressed by bFGF, IL-1 beta and retinoic acid in coordination with type 11 collagen mRNA. TGF-beta decreas ed CD-RAP expression while increasing type II collagen mRNA whereas both mR NAs were up-regulated by IGF-1. In chondrocytes dedifferentiated with retin oic acid, IGF-1 induced re-expression of both CD-RAP and type 11 collagen m RNAs. The mechanism of stimulation of CD-RAP by IGF-1 was further investiga ted. An mRNA stability assay revealed that IGF-1 had no effect on CD-RAP or type 11 collagen mRNA half life, suggesting that the enhancement by IGF-1 is due to increased gene transcription. To study the transcriptional mechan ism, we used the 5 ' -flanking region of the CD-RAP gene fused to a promote r-less reporter plasmid encoding luciferase. Deletion analysis of the CD-RA P promoter indicated that an IGF-1-responsive element is present between nu cleotides -475 and -458. These data indicate that CD-RAP expression can be regulated by cytokines known to influence chondrocyte metabolism and that I GF-1 up-regulates CD-RAI? gene expression through a transcriptional mechani sm. (C) 2001 Orthopaedic Research Society. Published by Elsevier Science Lt d. All rights reserved.