The catabolic and proinflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) produced in the joint tissues, not only contribute to the destruction of cartilage matrix in osteoarthntis and rheumatoid arthritis, but also decrease the synthesis of cartilage-specific matrix proteins, including type II collagen and aggrecan. We have shown in published and preliminary studies that IL-1beta suppresses expression of the type II collagen gene (COL2A1) in chondrocytes at the transcriptional level via multiple signaling pathways. Furthermore, we have found that a novel ETS factor, ESE-1, which is induced by ILi1beta and TNF-alpha, binds to the COL2A1 promoter and directly suppresses its activity, indicating a pivotal role for this transcription factor in regulating COL2A1 gene expression. Our hypothesis is that IL-1beta-induced suppression of COL2A1 gene expression is mediated by ESE-1 as the primary transcriptional regulator and involves multiple signaling pathways and transcription factors that interact directly or indirectly with ESE-1. For these studies, we have developed immortalized human chondrocyte cell lines, which retain chondrocyte-specific phenotype and responses to cytokines.
The Specific Aims will test the hypotheses that: (1) ESE-1 is the primary transcription factor involved in IL-1beta-mediated suppression of the COL2A 1 gene; (2) multiple signaling pathways involving p38 MAPK, JNK, Jak3, IKK/IkappaB and P13K/Akt kinase cascades transduce IL-1beta-induced suppression of COL2A1 gene expression, both directly and indirectly, via ESE-1; (3) ESE-1 serves its repressor function on COL2A1 expression via specific protein-DNA and protein-protein interactions involving other IL-1beta-induced transcription factors and constitutive factors; and (4) ESE-1 suppression of COL2A1 expression results in chondrocyte-dependent inhibition of cartilage matrix synthesis. These studies will permit dissection of the specific signaling pathways and molecular regulatory systems involved in transcriptional regulation of the COL2A1 gene by IL-1beta. These results may also lead to the development of more specific and effective therapeutic approaches for blocking the adverse effects of IL-1beta on cartilage matrix genes and their products in disorders such as OA and RA.
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