[High mobility group box 1 is increased in children with acute lymphocytic leukemia and stimulates the release of tumor necrosis factor-alpha in leukemic cell].

Cytokine mediated cell immunity is the main mode of anti-tumor immunity in organism, and the disequilibrium of cytokine network is the main cause of tumor cells escaping immunologic surveillance. High mobility group box 1 (HMGB1), a nuclear protein, has recently been identified as an important mediator of local and systemic inflammatory diseases when released into the extracellular milieu. In the present study, the investigators explored the clinical significance of alteration in the serum levels of HMGB1 in childhood acute lymphocytic leukemia (ALL) and the mechanism of HMGB1-induced tumor necrosis factor (TNF)-alpha secretion in leukemic cells. The serum levels of HMGB1 in healthy children and childhood ALL were assayed by Western blotting. K562 leukemic cells were stimulated with recombinant HMGB1 protein in vitro, and the secretion of TNF-alpha was determined by using ELISA. The effects of HMGB1 on activation of p38, c-Jun amino-terminal kinase (JNK), and extracellular-signal regulated protein kinase (ERK) and mitogen-activated protein kinase (MAPK) in K562 cells were assayed by using Western blotting. The effects of inhibitors specific for the MAPK on HMGB1-induced TNF-alpha secretion were assayed by using ELISA. The serum levels of HMGB1 were significantly higher in ALL initial treatment group (n = 15, 43.78 +/- 4.62 microg/ml) than those in healthy control group (n = 15, 0.60 +/- 0.48 microg/ml, P < 0.01) and ALL complete remission group (n = 15, 0.89 +/- 0.62 microg/ml, P < 0.01). No significant difference was found between the healthy control group and ALL complete remission group in HMGB1 levels (P > 0.05). TNF-alpha started to become detectable at 2 h and was still increasing at 16 h after HMGB1 (1 microg/ml) treatment in K562 cell culture. TNF-alpha was also secreted from K562 cells in a dose-dependent manner after HMGB1 (1 ng/ml-1 microg/ml) exposure. HMGB1 induced the phosphorylation of p38, JNK and ERK in k562 cells. Inhibitors specific for the JNK (SP600125), MEK (PD98059), and p38 MAPK (SB203580), abrogated HMGB1-induced TNF-alpha secretion. The measurement of serum HMGB1 is helpful to evaluate the prognosis of the childhood ALL. HMGB1 stimulates leukemic cells to secrete TNF-alpha through a MAPK-dependent mechanism.