Our study sought to determine how HMGB1, a proinflammatory cytokine, affects tumor invasion and metastasis induced by hypoxia. We found that hypoxia induces selleck chemical casapse-1 activation in HCC cells. For the first time, we report that
HMGB1 is essential for hypoxia-induced caspase-1 activation in HCC cells. HMGB1 translocates from the nucleus to the cytoplasm in hypoxic HCC cells and inhibiting its release prevents hypoxia-induced caspase-1 activation. Furthermore, treatment with rhHMGB1 or overexpression of HMGB1 in HCC cells induces caspase-1 activation, even in normoxic cell culture. HMGB1 is recognized as the prototypical DAMP.23 Initially identified as a chromatin-binding protein, HMGB1 can be released by both passive24 and active25 pathways. The passive pathway requires loss of cell-membrane integrity, as observed in necrosis. The active pathway appears to involve HMGB1 hyperacetylation and packaging into secretory vesicles. Our previous studies showed that HMGB1 release from cultured hepatocytes is an active process regulated by reactive oxygen species in the setting of hypoxia.17 In cancer cells, HMGB1 is actively released
after anticancer agent treatment and promotes cell survival.26 We postulated that HMGB1 release in HCC cells would be an active process under hypoxic conditions. Indeed, hypoxia did not promote the expression of HMGB1, but induced the nuclear to cytoplasmic translocation of HMGB1 and release of HMGB1 into the extracellular space in two HCC cell lines, indicating that HMGB1 release selleck inhibitor in this setting may affect the biologic behavior of tumors. Tumor CX-4945 cost development and progression is associated with caspase activation, which regulates apoptosis and inflammation.27 One hallmark of tumor cells is the intrinsic or acquired resistance to apoptosis. Surprisingly, recent studies demonstrate that apoptosis promotes early tumorigenesis.19 Apoptosis-related caspases (caspase-3 and -9) were activated in hypoxic HCC
cells (data not shown). In our study, cell invasiveness was increased after inhibiting caspase-3 in hypoxic HCC cells, which suggests that apoptosis seems to inhibit hypoxia-induced invasion (data not shown). Studies have implicated caspase-1, an inflammation-related caspase, in a variety of responses, including the host response to microbial pathogens, inflammatory diseases, and metabolic and autoimmune disorders.28 Recent studies have also shown that caspase-1 is involved in tumorigenesis and tumor progression.29 Caspase-1 activation, regulated by the inflammasome, promotes the maturation of proinflammatory cytokines, such as IL-1β and -18, and induces inflammatory responses. Caspase-1 is activated not only in immune cells, but also in epithelial and mesenchymal cells in conditions such as tissue repair.30 Recently, Okamoto et al.16 found that fresh melanoma biopsies constitutively express activated caspase-1 and secrete IL-1β.
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