Hyperthermia maintains death receptor expression and promotes TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand activates apoptotic pathways and could potentially be used in anticancer treatments. However, oral squamous cell carcinoma cells are known to be resistant to tumor necrosis factor-related apoptosis-inducing ligand-induced cell death. It has been previously reported that hyperthermia upregulates tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in other cancers. As such, we evaluated whether hyperthermia upregulates tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis in a tumor necrosis factor-related apoptosis-inducing ligand-resistant oral squamous cell carcinoma cell line.

The oral squamous cell carcinoma cell line HSC3 was cultured and divided into hyperthermia and control groups. We investigated the antitumor effects of recombinant human tumor necrosis factor-related apoptosis-inducing ligand using cell proliferation and apoptosis assays. Additionally, we measured death receptor 4 and 5 levels, and determined death receptor ubiquitination status, as well as E3 ubiquitin ligase targeting of death receptor in both hyperthermia and control groups before recombinant human tumor necrosis factor-related apoptosis-inducing ligand administration.

Treatment with recombinant human tumor necrosis factor-related apoptosis-inducing ligand produced greater inhibitory effects in the hyperthermia group than in the control group. Moreover, death receptor protein expression in the hyperthermia group was upregulated on the cell surface (and overall), although death receptor mRNA was downregulated. The half-life of death receptor was several hours longer in the hyperthermia group; concomitantly, E3 ubiquitin ligase expression and death receptor ubiquitination were downregulated in this group.

Our findings suggested that hyperthermia enhances apoptotic signaling by tumor necrosis factor-related apoptosis-inducing ligand via the suppression of death receptor ubiquitination, which upregulates death receptor expression. These data suggest that the combination of hyperthermia and tumor necrosis factor-related apoptosis-inducing ligand has implications in developing a novel treatment strategy for oral squamous cell carcinoma.