| Summary: | 碩士 === 長庚大學 === 基礎醫學研究所 === 93 === Thyroid hormone (T3) regulates growth, development, and differentiation. These activities are mediated by the nuclear thyroid hormone receptors (TRs), which belong to the steroid/TR superfamily of ligand-dependent transcription factors. The effect of T3 treatment on target gene regulation was investigated in a TRα-overexpressing hepatoma cell line, by performing cDNA microarrays.
Approximately 201 of 7600 genes (2.6%) were positively regulated by T3. Among them are several transcription factors including p8. p8 is a stress-induced protein with multiple functions and bio-chemically related to the architectural factor HMG-I/Y. To confirm the microarray results, p8 was further investigated using quantitative RT-PCR. The T3-induction ratios observed by quantitative RT-PCR were 50-fold after 48 h of T3 treatment. Furthermore, using HepG2-TRα cell lines, revealed a 6.7-fold induction of p8 transcription after 48 h of T3 treatment (compared with 6h of T3 treatment). In addition, the expression level of p8 protein was increased 2.5- to 3.5-fold in HepG2-TRα cell after 3h of T3 treatment. The protein synthesis inhibitor, cycloheximide, inhibited the induction of p8 by T3, indicating that this regulation was indirect. Similar results were observed on the regulation of p8 by T3 using the thyroidectomized (TX) rats as an in vivo model. To search for the potential inducers regulating the expression of p8, several available transcription factors were used. The expression of USF1 and USF2 were up-regulated by T3 at mRNA. They also enhanced p8 promoter activity. Moreover, we found that TGFβ-1(5 ng/ml) resulted in activation of p8 mRNA expression. While simultaneously treated T3（100nM）and TGFβ（5ng/ml）in HepG2-TRα cells was synergistically up-regulated the expression of p8 mRNA by 4.5-Fold. Further study is required to understand the physiological significance of p8 up-regulation.
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