| Summary: | 博士 === 長庚大學 === 生物醫學研究所 === 100 === The thyroid hormone, 3, 3,5-triiodo-L-thyronine (T3), regulates cell growth, development, differentiation, and metabolism via interactions with thyroid hormone receptors (TRs). However, the secreted proteins that are regulated by T3 are yet to be characterized. In this study, we used the quantitative proteomic approach of stable isotope labeling with amino acids in cell culture (SILAC) coupled with nano-LC-MS/MS performed on a LTQ-Orbitrap instrument to identify and characterize the T3-regulated proteins secreted in human hepatocellular carcinoma cell lines overexpressing TRα1 (HepG2-TRα1). In total, 1742 and 1714 proteins were identified and quantified, respectively, in three independent experiments. Among these, 61 upregulated two-fold and 11 downregulated two-fold proteins were identified. Eight proteins displaying increased expression and one with decreased expression in conditioned media were validated using Western blotting. Real-time quantitative RT-PCR further disclosed induction of plasminogen activator inhibitor-1 (PAI-1), a T3 target, in a time-course and dose-dependent manner. Serial deletions of the PAI-1 promoter region and subsequent chromatin immunoprecipitation assays revealed that the thyroid hormone response element on the promoter is localized at positions -327/-312. PAI-1 overexpression enhanced tumor growth and migration in a manner similar to what was seen when T3 induced PAI-1 expression in J7-TRα1 cells, both in vitro and in vivo. An in vitro neutralizing assay further supported a crucial role of secreted PAI-1 in T3/TR-regulated cell migration. To our knowledge, these results demonstrate for the first time that proteins involved in the urokinase plasminogen activator system, including PAI-1, uPAR and BSSP4, are augmented in the extra- and intracellular space of T3-treated HepG2-TRα1 cells. The T3-regulated secretome generated in the current study may provide an opportunity to establish the mechanisms underlying T3-associated tumor progression and prognosis.
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