Protein Phosphorylation and Kinase Activities in Tumour Cells after Hyperthermia

Summary

Phosphorylation of various proteins and the activities of specific kinases were studied in tumour cells after hyperthermia. P388 lymphoid tumour cells were treated at 40–45°C for 1 h in vitro. Immediately after heat treatment, particulate and cytosol cell fractions were isolated, phosphorylated proteins separated and various kinase activities were measured. Hyperthermic treatment of the cells caused a significant decrease in protein kinase C activity while the activity of calcium-ion and phospholipid-independent protein kinases increased. Phosphorylation of cytosol proteins of 120, 80, 33, 25 and 14 kDa increased significantly after hyperthermia, and protein kinase C selectively phosphorylated the last three of these proteins. The phosphorylation of three heat shock proteins (44, 70 and 85 kDa) was not changed after hyperthermic treatment. Four tyrosine kinase activities were separated. The protein tyrosine kinase activity decreased to one-tenth of the control value after 45°C for 1 h hyperthermia. The changes in kinase activities and protein phosphorylation induced by hyperthermia proved to be temperature- and time-dependent.