| Summary: | 碩士 === 國立陽明大學 === 口腔生物研究所 === 93 === Insulin-like growth factor binding proteins is a family of protein that can bind IGF. They might exert inhibitory or enhancive effects on IGF-IGF receptor binding, that regulates cellular phenotypes. Previous studies have shown that IGFBP-5 is suppressive for tumor growth. Our previous study also indicated the profound down-regulation of IGFBP-5 mRNA and protein expression in oral carcinomas. Interestingly, IGFBP-5 is expressed in normal oral keratinocyte that is tightly associated with differentiation. Curcumin can up-regulate the IGFBP-5 mRNA and protein expression in SAS oral carcinoma cell line and normal oral keratinocyte. However, by what regulatory mechanisms that IGFBP-5 is down-regulated in OSCC and up-regulated by curcumin in oral epithelial cells are the main topics to be addressed in this study.
Using bi-sulfite modification and sequencing analysis, we identified that the intensity of CpG islands hypermethylation in exon 1 could underlies the silencing IGFBP-5 in OECM-1 oral carcinoma cell and HaCaT cells. Treatment with 5-aza-dC retrieved the IGFBP-5 mRNA expression in these cells. Such treatment also induced the promoter activity of IGFBP-5. It is hitherto unclear that the up-regulation of IGFBP-5 is mediated through a cis- or trans- activation. By promoter activity assay, we identified that curcumin can activate IGFBP-5 promoter in a dose-dependent manner. Deletion mapping further dissected that -84 ~ +23 in IGFBP-5 is the critical segment responsible for curcumin effects. Since this region encompassing multiple transcription factor binding sites, it will be served as a target to further elucidate the regulation of IGFBP-5 in oral epithelial cells.
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