title: Requirement of phosphatidylinositol 3-kinase/Akt signaling pathway for regulation of tissue inhibitor of metalloproteinases-3 gene expression by TGF-beta in human chondrocytes.
abstract: Transforming growth factor beta (TGF-beta1) induces cartilage extracellular matrix synthesis and tissue inhibitor of metalloproteinases-3 (TIMP-3), an important natural inhibitor of matrix metalloproteinases, aggrecanases and TNF-alpha-converting enzyme, which are implicated in cartilage degradation and joint inflammation. This study tested the hypothesis that Akt/protein kinase B signaling pathway could mediate TGF-beta1 induction of TIMP-3 in human articular chondrocytes. TGF-beta activated phosphorylation of Akt in a delayed and sustained fashion that correlated with TIMP-3 mRNA induction. Phosphatidylinositol kinase (PI3K) inhibitors, Wortmannin and LY294002 and Akt inhibitor (NL-71-101) significantly inhibited TGF-beta-induced Akt phosphorylation, TIMP-3 expression, TIMP-3 promoter (-940 to +376)-driven luciferase activity and Sp1 transcription factor binding. PI3K p85, Akt and Sp1 small interfering RNA (siRNA)-driven knockdown of the respective gene products significantly suppressed TGF-beta-induced TIMP-3 gene expression. TGF-beta-stimulated phosphorylation of p70S6 Kinase and TIMP-3 protein induction was inhibited by rapamycin. Thus TGF-beta induces TIMP-3 gene expression in human chondrocytes partly through PI3K/Akt pathway and Sp1 transcription factor and by translational mechanisms via mammalian target of rapamycin (mTOR) signaling. TGF-beta induction of pro-survival Akt cascade and TIMP-3 may be related to strengthening of cartilage extracellular matrix, increased chondrocyte viability and maintenance of joint tissue integrity.
authors: Department of Medicine and Research Centre of Centre Hospitalier de l'Université de Montréal (CRCHUM), Montreal, Quebec, Canada H2L 4M1.
authors: Hamid Yaqoob
authors: HY
authors: Qureshi
authors: Rasheed
authors: R
authors: Ahmad
authors: Judith
authors: J
authors: Sylvester
authors: Muhammad
authors: M
authors: Zafarullah
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D002358:Cartilage, Articular / Q000166:cytology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D051058:Oncogene Protein v-akt / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010766:Phosphorylation; D015398:Signal Transduction; D019717:Tissue Inhibitor of Metalloproteinase-3 / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D019717:Tissue Inhibitor of Metalloproteinase-3; D016212:Transforming Growth Factor beta; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D019869:Phosphatidylinositol 3-Kinases; D051058:Oncogene Protein v-akt; D000077191:Wortmannin