| Budget Amount *help |
¥12,200,000 (Direct Cost: ¥12,200,000)
Fiscal Year 2004: ¥5,800,000 (Direct Cost: ¥5,800,000)
Fiscal Year 2003: ¥6,400,000 (Direct Cost: ¥6,400,000)
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| Research Abstract |
Objective. Forced expression of cyclin-dependent kinase inhibitor (CDKI) gene, p16INK4a or p21Cip1 in the synovial tissues was effective in treating animal models of rheumatoid arthritis (RA). Although the primary function of CDKIs is halting cell cycle progression, their anti-proliferative effect accompanied suppression of inflammation in the treated joints. Subsequently, we and others found that p21 Cip1 does not only inhibit activitity of CDKs but downmodulates c-Jun N-terminal kinase (JNK) and other intracellular signaling pathways. Despite lack of solid evidence for interaction of p16INK4a with other molecules, p16INK4a suppressed specific inflammatory molecules produced by rheumatoid synovial fibroblasts (RSF). Since, some of these molecules were shared by the effects of p16INK4a and p21 Cip1, direct effects of CDK4/6 activity on their production were studied. Methods. Genes for CDKIs, p16INK4a and p18INK4c, a constitutively active, hypophosphorylated form of retinoblastoma gene
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product (Rb), cyclin D1 and CDK4 were transferred into RSF with adenoviruses to modulate CDK4/6 activity. A synthetic CDK4/6 inhibitor was used to inhibit CDK4/6. Cell cycle was studied with 3H-thymidine incorporation and flow cytometry. Expression levels of matrix metalloproteinase (MMP)-3, monocyte chemoattaractant protein (MCP)-1 or type I interleukin 1 receptor (IL-1R1) was determined with Northern blot analyses, real-time polymerase chain reaction, and/or ELISAs. CDKIs were immunoprecipitated to reveal their association with JNK. Results. Gene transfer of p16INK4a as well as p18INK4c inhibited cell cycle progression and suppressed MMP-3 and MCP-1 production. Unlike p21Cip1, neither molecules inhibit IL-1 R1 expression or bind to JNK. Inhibition of CDK4/6 by a synthetic CDK4/6 inhibitor also downregulated these inflammatory mediators. They were upregulated when CDK4 activity was augmented. This regulation functioned at the mRNA level for MMP-3, but not for MCP-1. Transfer of active Rb, which mimicked inhibition of CDK-dependent Rb phosphorylation, suppressed production of both without changing their mRNA levels. Conclusions. Inhibition of CDK4/6 in RSF downregulated MCP-1 and MMP-3 production, which was upregulated by augmented CDK4 activity. MMP-3 production was primarily regulated by the kinase activity at the mRNA level in an Rb-independent manner, while MCP-1 production was controlled posttranscriptionally by Rb. Less
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