Invasion potential of H22 hepatocarcinoma cells is increased by HMGB1-induced tumor NF-κB signaling via initiation of HSP70

The functional relationship and cross-regulation between damage-associated molecular patterns and NF-kappa B in the tumor microenvironment remains unclear. In the present study, high-mobility group protein B1 (HMGB1) was secreted in response to feed second phase of NF-kappa B activation from heat shock protein (HSP) 70 that may result in a higher invasion potential of hepatocarcinoma cells. HSP70 promoted the proliferation of H22 hepatocarcinoma cells through Toll-like receptor (TLR) 2 and TLR4 signaling and induced the early phosphorylation of NF-kappa B, which reached maximum levels within 30 min. However, HSP70 promoted the upregulation of Beclin-1 expression via Jun N-terminal kinase (JNK) activation in tumor cells and the release of HMGB1 from tumor cells. Inhibition of Beclin-1/c-JNK production prevented the second, but not the first, phase of NF-kappa B phosphorylation, implicating Beclin-1/c-JNK in the second phase of phosphorylation. HSP70 induced Beclin-1-derived HMGB1 production at 4 h, which occurred before the rise in the second phosphorylation that occurred at 6 h. Exogenous HMGB1 also induced the rapid phosphorylation of NF-kappa B and upregulated the expression of MMP-9, inhibited the rapid phosphorylation of NF-kappa B and reduced MMP-9 by receptor for advanced glycation end products (RAGE) inhibitor that prevented HMGB1-induced cell invasion in vitro, which demonstrated that the biological significance of HMGB1/RAGE is key to the second, but not the first, phase of NF-kappa B phosphorylation in tumor cells. HSP70 triggered a positive feedback loop of NF-kappa B activation in H22 cells. The second phase of NF-kappa B phosphorylation mediated by HSP70 is implicated in the increase of tumor cell malignant invasion.