CCAAT/Enhancer-binding Proteins β and δ Mediate the Repression of Gene Transcription of Cartilage-derived Retinoic Acid-sensitive Protein Induced by Interleukin-1β

Abstract

Cartilage-derived retinoic acid-sensitive protein (CD-RAP) is a secreted protein expressed by chondrocytes; the expression is repressed by interleukin 1␤ (IL-1␤). To investigate the transcriptional mechanism, by which CD-RAP expression is suppressed by IL-1␤, deletion constructs of the mouse CD-RAP promoter were transfected into rat chondrocytes treated with or without IL-1␤. The results revealed an IL-1␤-responsive element located between ؊2138 and ؊2068 bp. As this element contains a CAAT/enhancer-binding protein (C/EBP) motif, the function of C/EBP␤ and C/EBP␦ was examined. IL-1␤ stimulated the expression of C/EBP␤ and -␦, and the direct binding of C/EBP␤ to the C/EBP motif was confirmed. The ؊2251-bp CD-RAP promoter activity was down-regulated by co-transfection with C/EBP expression vectors. Mutation of the C/EBP motif abolished the inhibitory response to IL-1␤. Additionally, C/EBP expression vectors were found to down-regulate the construct containing the promoter and enhancer of the type II collagen gene. Finally, the enhancer factor, Sox9, was shown to bind adjacent to the C/EBP site competing with C/EBP binding. Taken together, these results suggest that C/EBP␤ and -␦ may play an important role in the IL-1␤-induced repression of cartilage-specific proteins and that expression of matrix proteins will be influenced by the availability of positive and negative trans-acting factors.

CCAAT/Enhancer-binding Protein β Regulates the Repression of Type II Collagen Expression during the Differentiation from Proliferative to Hypertrophic Chondrocytes

“…C/EBP␤ is known to be induced by pro-inflammatory cytokines such as IL-1␤, IL-6, and TNF-␣, and it is expressed in arthritic cartilage (15,20,22). It has been suggested that C/EBP␤ also plays a role in the repression of COL2A1 in response to inflammatory signals (20). Some other transcription factors including c-Fos, c-Jun, Jun B, and Egr-1, have been reported to be induced by FIGURE 6.…”

“…Among them, C/EBP␤ (encoded by CEBPB) was first identified as a nuclear protein that bound to the IL-1␤ response element in the IL-6 promoter region (15), and it has subsequently been reported to regulate various genes involved in cell differentiation, proliferation, survival, immune function, tumor invasiveness, and progression (16 -19). Previously, it was reported that C/EBP␤, in response to IL-1␤, down-regulated cartilage-derived retinoic acid-sensitive protein (Cd-rap), a small secreted protein expressed in cartilage throughout chondrogenesis and in mature chondrocytes (20). C/EBP␤ induced by pro-inflammatory cytokines such as IL-1␤ and TNF-␣ directly binds to the MMP13 and MMP3 promoter regions and stimulates their expression in chondrocytes, resulting in degradation of cartilage in arthritis (21,22).…”

CCAAT/ENHANCER binding protein β mediates expression of matrix metalloproteinase 13 in human articular chondrocytes in inflammatory arthritis

“…IL-1␤ treatment of chondrosarcoma cells increases C/EBP␤ expression, which in turn represses CD-RAP and Col2a1 gene transcription (14). Furthermore, it was recently reported that C/EBP␤ mediates the expression of MMP-1 in cartilage in response to IL-1␤ (25).…”

“…These pathways lead directly to the deterioration of cartilage matrix structures. IL-1␤ and TNF␣ treatment of chondrocytes induces many transcription factors related to inflammation, such as NF-B, IKK, activator protein 1 (AP-1) (11,12), early growth response 1 (13), and members of the CCAAT/enhancer binding protein (C/EBP) family (14).…”

“…C/EBP␤ has also been reported to regulate expression of a number of ECM proteins, including pro␣1(I) and pro␣2(I) type I collagen, osteocalcin, and cartilage-derived retinoic acid-sensitive protein (CD-RAP), in response to IL-1␤ or TNF␣ (14,23,24). IL-1␤ treatment of chondrosarcoma cells increases C/EBP␤ expression, which in turn represses CD-RAP and Col2a1 gene transcription (14).…”