Abstract
Xylosyltransferase I (XT-I) is an essential enzyme of proteoglycan (PG) biosynthesis pathway catalyzing the initial and rate-limiting step in glycosaminoglycan chain assembly. It plays a critical role in the regulation of PG synthesis in cartilage; however, little is known about underlying mechanism. Here, we provide evidence that, in human primary chondrocytes, IL-1β regulates XT-I gene expression into an early phase of induction and a late phase of down-regulation. Based on promoter deletions, the region up to -850 bp was defined as a major element of XT-I gene displaying both constitutive and IL-1β-regulated promoter activity. Point mutation and signaling analyses revealed that IL-1β-induced promoter activity is achieved through AP-1 response elements and mediated by SAP/JNK and p38 signaling pathways. Transactivation and chromatin immunoprecipitation assays indicated that AP-1 is a potent transactivator of XT-I promoter and that IL-1β-induced activity is mediated through increased recruitment of AP-1 to the promoter. Finally, we show that Sp3 is a repressor of XT-I promoter and bring evidence that the repressive effect of IL-1β during the late phase is mediated through Sp3 recruitment to the promoter. This suggests that modulation of Sp3 in cartilage could prevent IL-1β inhibition of PG synthesis and limit tissue degradation.
Highlights
Xylosyltransferase I plays a critical role in proteoglycan synthesis
Xylosyltransferase I (XT-I) Gene Expression Is Regulated by IL-1 in Human Primary Chondrocyte Cells—Accumulating evidence indicates that XT-I catalyzes a rate-limiting step in PG synthesis pathway and plays a central role in the regulation of the PG synthesis process both in physiological and physiopathological conditions [18, 21, 26, 27]
The results revealed that treatment of chondrocytes with IL-1 for 6 and 12 h increased by 1.8- and 3-fold, respectively, the mRNA expression level of XT-I gene, whereas a decrease of 50% was produced by the cytokine when the cells were treated for 24 h (Fig. 1A), indicating that IL-1 regulates the expression of XT-I into an early phase of induction and a late phase of down-regulation
Summary
Xylosyltransferase I plays a critical role in proteoglycan synthesis. Results: IL-1 cytokine regulates xylosyltranserase I expression into an early phase of induction and a late phase of repression through AP-1 and Sp3, respectively. Xylosyltransferase I (XT-I) is an essential enzyme of proteoglycan (PG) biosynthesis pathway catalyzing the initial and rate-limiting step in glycosaminoglycan chain assembly It plays a critical role in the regulation of PG synthesis in cartilage; little is known about underlying mechanism. We show that Sp3 is a repressor of XT-I promoter and bring evidence that the repressive effect of IL-1 during the late phase is mediated through Sp3 recruitment to the promoter This suggests that modulation of Sp3 in cartilage could prevent IL-1 inhibition of PG synthesis and limit tissue degradation. In addition to genetic disorders, strong evidence supports the involvement of GAG defects in the pathogenesis of several diseases, including arthropathies [10], atherosclerosis [11], Alzheimer disease [12], and cancer [13, 14] In these pathological conditions, biosynthesis of GAGs is markedly affected as a result of the altered function and/or regulation of synthetic enzymes. We show that Sp3 transcription factor is a repressor of XT-I promoter and provide evidence that the repressive effect of IL-1 during the late phase results from recruitment of Sp3 to a critical Sp1 binding site
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
