The high mobility group box 1 (HMGB1) protein, a non-histone nuclear factor, is overexpressed and localizes to the cytoplasm in some cancer cells. However, the mechanism of cytoplasmic HMGB1 transport, extracellular secretion, and its role in cancer progression is not clear. To simulate the activated state of HMGB1, we mutated serine residues of nuclear localization signals (NLSs) to glutamic acid and performed transfection assays. We carried out a kinase inhibitor study and evaluated the cell migration by invasion assay. We showed that phosphorylated HMGB1 localizes in the cytoplasm of colon cancer cells and also showed the interaction of PKC and HMGB1 by immunoprecipitation analysis. Concurrent mutations at six serine residues (35, 39, 42, 46, 53, and 181) to glutamic acid induced the nuclear to cytoplasmic transport of HMGB1, which was detected in the culture medium. We also observed that the secretion of HMGB1 correlated with increased cancer cell invasiveness. Our results suggest that phosphorylated HMGB1 is transported to the cytoplasm, is subsequently secreted from the cell, and has a role in tumor progression through the activation of genes related to cell migration.
Bibliographical noteFunding Information:
Eight colorectal carcinomas and matched normal mucosa were included in this study. All cases were identified in the Department of Pathology at the Yonsei University Medical Center between September 1995 and November 2000. Some of the fresh specimens were supported by the Liver Cancer Specimen Bank from the National Research Resource Bank Program of the Korea Science and Engineering Foundation of the Ministry of Science and Technology. Authorization for the use of these tissues for research purposes was obtained from the Institutional Review Board of the Yonsei University College of Medicine. To enrich the tumor cell population, areas with more than 90% tumor cells were selected from hematoxylin–eosin-stained slides using the cryostat microdissection technique.
This study was supported by a grant of the Korea Health 21 R&D Project (Ministry of Health & Welfare (03-PJ10-PG6-GP01-0002)) and FPR08A2-100 of the 21C Frontier Functional Proteomics Project from the Korean Ministry of Science & Technology.
All Science Journal Classification (ASJC) codes
- Pathology and Forensic Medicine
- Molecular Biology
- Cell Biology