HMGB1 (High-Mobility Group Box 1) protein is a nuclear protein which is located mainly in nucleus of most of cells with binding to chromosomes. At first, it is known to maintain a structure of chromatin and control of transcription, but several reports have found that HMGB1 is translocated to cytoplasm and secreted to extracellular region in some cases such as activated immune cells or cells undergoing necrosis. However, there was no evidence not only on the mechanism of translocation and secretion of HMGB1 but also on its function out of nuclear in cancer cells. Therefore, we constructed an expression vector which contains HMGB1 and 3X FLAG sequence therein and transfected it to the HCT116 cell lines. Then, we collected the cell lines, extracting proteins of nuclear, cytoplasm, plasma membrane and culture media to show the location of HMGB1 and therefore we confirmed that HMGB1 is located in all cellular locations. We also performed immunoprecipitation and mass spectrometry analysis to identify binding partners of HMGB1 in each cellular location and, therefore, identified 38 proteins are bound to HMGB1. Among them, we further analyzed several targets whose functions are related to protein transportation to make clues for translocation and secretion of HMGB1. In addition to we found that HMGB1 was more secreted in HCT116 colon cancer cell media than in normal colon fibroblast cell line CCD18Co and that the secretion level of HMGB1 in culture media was variable between cell lines. We demonstrated that HMGB1 was significantly secreted to the cell media in colon and liver cancer cell lines but was not significantly secreted in gastric cancer cell lines after we tested several other cancer cell lines. Our findings indicate that HMGB1 is abnormally translocated and secreted in cancer cell lines and the secreted HMGB1 may be used for the diagnostic test of colon and liver cancer patients.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4488.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO