Extracellular high mobility group box 1 protein stimulates proliferation and mobility in human glioma cells

Human malignant gliomas, the most common primary brain tumors, are characterized by excessive proliferation and infiltrative growth. Although the molecular determinants of glioma properties are still unclear, a significant role for the altered regulation of modulators of glial growth and motility has been proposed. In the complex network of molecular signals involved in tumorigenesis, high mobility group box 1 protein (HMGB1) has recently emerged. This low molecular weight protein, previously considered solely as a chromatin-associated molecule, can be present extracellularly after passive release by necrotic cells or active secretion by some cell types. In the extracellular milieu, HMGB1 can act as a multifunctional paracrine/autocrine factor via its interaction with the receptor for advanced glycation end products (RAGE). Increasing evidence supports that HMGB1 plays an important role in tumors, promoting cancer cell growth, motility, and invasion. Although different human tumors overexpress both HMGB1 and RAGE, little is known on the involvement of HMGB1 in human gliomas. In the present study we addressed the question whether extracellular HMGB1 might determine changes in glioma cell proliferation and/or invasiveness. The human glioma cell lines CCF-STTG and T98G were used. After immunoblot with monoclonal anti-HMGB1 antibodies, our analyses demonstrated HMGB1 as well as RAGE expression in both cell lines. Moreover, in serum-starved cells, the administration of recombinant HMGB1 resulted in a rapid and transient ERK1/2 phosphorylation as well as in the stimulation of cell proliferation. Both HMGB1-induced effects were dose-dependent in the range 2-50 nmol/L, were inhibited by PD98059, the selective inhibitor of MEK, as well as by anti-RAGE antibodies. Thus, our data show that HMGB1 regulates the proliferation of glioma cells through RAGE/MEK/ERK signaling. Finally, using a scratch wound healing assay, we observed that HMGB1 treatment induced cells to extend membrane protrusion moving into the wounded areas, and increased the rate of cell migration. Taken together, our results suggest that HMGB1 may act as an extracellular signal in human gliomas, contributing to tumor growth and invasion. Grant support: MURST PRIN to LR