1. ¹Department of Pathology, Yonsei University College of Medicine, Seoul, Korea
2. ²Brain Korea 21 Project for Medical Sciences, Yonsei University College of Medicine, Seoul, Korea
3. ³Department of Microbiology, Yonsei University College of Medicine, Seoul, Korea
4. ⁴Division of Instrument Development, Korea Basic Science Institute, Daejeon, Republic of Korea
5. ⁵Yonsei Proteome Research Center, Department of Biochemistry and Bioproducts Research Center, Yonsei University, Seoul, Korea

Correspondence: Professor H Kim, MD, Department of Pathology, Yonsei University College of Medicine, CPO Box 8044, Seoul, Korea 120-1752. E-mail: hkyonsei@yuhs.ac

^*These two authors contributed equally to this work.

Received 19 September 2008; Revised 2 April 2009; Accepted 28 April 2009; Published online 8 June 2009.

Abstract

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.