CDK6 is stimulated by hyperthermia and protects gastric cancer cells from hyperthermia-induced damage

Hyperthermia is one of the most widely employed adjuvant treatments for cancer, especially for hyperthermic intraperitoneal chemotherapy, and has few side effects. Gastric cancer has various hyperthermia sensitivities, but the exact molecular mechanisms remain to be elucidated. In the present study, western blotting was performed to detect differential expression of proteins that have been reported to be upregulated in gastric cancer. Following knockdown of these proteins, apoptosis was measured by Annexin V-FITC/propidium iodide (PI) double staining and hyperthermia treatment was applied. To evaluate the effect of cyclin-dependent kinase 6 (CDK6) on hyperthermia-induced apoptosis, CDK6 was knocked down or inhibited by the addition of a specific inhibitor and subsequent PI staining and cell proliferation, migration and invasion assays were performed. Hyperthermia-induced protein kinase B (AKT) expression and phosphorylation inhibition were detected. As demonstrated in the present study, the hyperthermia-induced proteins kinesin family member 11 (KIF11), cyclin-dependent kinase 6 (CDK6), stromal antigen 2, NIMA-related kinase 2 and karyopherin subunit α 4 were highly expressed in gastric cancer cells, including SH-10-TC and HGC-27 cells. Knockdown of KIF11 significantly increased apoptosis without hyperthermia treatment and CDK6 significantly increased hyperthermia-induced apoptosis, prompting the present study to focus on CDK6. It was further confirmed that CDK6 activity was critical for decreasing hyperthermia-induced apoptosis and for cell proliferation. Hyperthermia-induced AKT expression and phosphorylation inhibition is potentially the main cause of CDK6 transcriptional upregulation. Taken together, these findings demonstrated that CDK6 is upregulated via hyperthermia-induced AKT inhibition and subsequently protected gastric cancer cells from hyperthermia-induced apoptosis, indicating that it is a potential therapeutic target to sensitize gastric cancer cells to hyperthermia-based therapy.