The Expression and Function of Nuclear Insulin-like Growth Factor Binding Protein-5 (IGFBP-5) in an Oral Cancer Cell Line

• Main Authors: Shun-Min Chang, 張舜閔
• Other Authors: Shu-Chun Lin
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/37923759242190323513

碩士 === 國立陽明大學 === 口腔生物研究所 === 93 === Insulin-like growth factor binding protein 5 (IGFBP-5) is an important IGF binding protein. It can exert regulatory functions when binding with IGF. It also has IGF-independent function in regulating cell mobility. Recent studies have indicated that IGFBP-5 can enter nucleus with unclear function. N-terminal sequence of IGFBP-5 was postulated have transcription-activating function, but the target genes are unknown. In our laboratory, we have identified that IGFBP-5 was down-regulated in the vast majority of oral squamous cell carcinoma (OSCC) and OSCC cell lines. Treatment with recombinant IGFBP-5 remarkably inhibited the growth of OSCC cells without IGFBP-5 expression. Down-regulation of IGFBP-5 seems to be contributive for OSCC growth. Matrix metalloproteinases (MMPs) is a group of preoteinases associated with tumor invasion, that are frequently overexpressed in cancers. Our previous study has specified the presence of MMP-13 in cell nuclei of OSCC. This study established stable cells line transfected with plasmid expressing IGFBP-5-EGFP fusion protein. Both immunofluoresence resolved by confocal microscopy and immunocytochemistry showed eminent nuclear-localization of IGFBP-5-EGFP in these cells. Abundant mRNA and protein expression was detected in nuclear extract and whole cell lysate. Besides, this fusion protein can be detected in supernatant. This fusion protein exhibits binding affinity to IGF-1. These stable cells had extended population-doubling time 5 h longer than parental cells. They also exhibited increase in cellular mobility. In enzyme digestion experiments, we identified for the first time that MMP-7 and MMP-13 can cleave recombinant IGFBP-5 in a time-dependent manner. MMP inhibitor drastically hindered such cleavage. Interestingly, IGFBP-5-EGFP fusion protein is also a substrate of MMP-7 and MMP-13. This study established an overexpression system that can be used to approach the phenotypic impacts of IGFBP-5 on OSCC.