Temperature Sensitivity of Cyclic‐Adenosine‐3′:5′‐Monophosphate‐Binding Proteins, Activity of Protein Kinases and the Regulation of Cell Growth

A clone of neuroblastoma cells has been selected for its ability to survive and multiply at 40 °C. This temperature‐resistant clone, like clones of neuroblastoma cells selected for resistance to dibutyryl‐adenosine 3′:5′‐monophosphate (Bt 2 ‐Ado‐3′:5′‐ P ) showed an increased tumorogenicity in animals and an increased saturation density at 37 °C. The Ado‐3′:5′‐ P ‐binding proteins and Ado‐3′:5′‐ P ‐dependent protein kinases from the temperature‐resistant and non‐resistant cells have been partially purified by chromatography on a DEAE‐cellulose column. The Ado‐3′:5′‐ P ‐binding proteins from temperature‐resistant cells were more sensitive to temperature than the binding proteins from non‐resistant cells. After incubation of binding proteins from resistant cells at 37 °C, the specific activity of Ado‐3′:5′‐ P ‐binding to proteins was decreased about 50% and the apparent association constant ( K a ) for Ado‐3′:5′‐ P ‐binding was decreased from 7.4 × 10 7 M −1 to 4.4 × 10 7 M −1 . There was no such decrease with binding proteins from non‐resistant cells. A decrease in the activity of binding proteins from the temperature‐resistant cells, but not of those from non‐resistant cells, was also found when the proteins were stored at 2 °C. Treatment with 2‐mercaptoethanol made binding proteins from the resistant cells less temperature‐sensitive. In the absence of added Ado‐3′:5′‐ P the protein kinase activity from the temperature‐resistant cells was about 50% of the activity from non‐resistant cells. Kinase activity was increased by addition of Ado‐3′:5′‐ P and there was a greater increase with kinases from resistant cells. The maximum protein kinase activity was found in the presence of 10 μM Ado‐3′: 5′‐ P for the temperature‐resistant cells and 0.1 μM Ado‐3′: 5′‐ P for the non‐resistant cells. The results indicate that the temperature sensitivity of Ado‐3′: 5′‐ P ‐binding proteins, and the activity of protein kinase from cells selected for resistance to high temperature, are similar to those of cells selected for resistance to Bt 2 ‐Ado‐3′: 5′‐ P . It is suggested that the temperature sensitivity of Ado‐3′: 5′‐ P ‐binding proteins and the activity of Ado‐3′: 5′‐ P ‐dependent protein kinases are involved in the regulation of malignancy and of cell growth at different temperatures.