Thermal sensitivity and resistance of insulin-receptor binding in thermotolerant cells

Cells may be made extremely resistant to elevated temperatures (thermotolerant) by a mild heat shock a few hours prior to more rigorous heating. In the present report, we show that a single cellular process - insulin binding to its receptor (in HA-1 Chinese hamster ovary cells) - may be made similarly heat-resistant. Heat resistance, whether expressed as cell survival or insulin binding, had similar dose-response characteristics, showing maximum resistance after 30 min at 43 degrees C. The processes had similar induction kinetics (2-6 h) and decayed over a similar time-course (100 h) after 43 degrees C, 30 min preheating. Thermal resistance of insulin binding was induced only when residual receptor loss (due to heating) occurred. Also, decay of resistance was closely correlated with recovery of insulin binding capacity. There thus appeared to be an inverse relationship between receptor number and the degree of heat resistance of both receptors and whole cells. (Scatchard analysis indicated that decreased insulin binding was due to receptor loss, not affinity decrease.) Whether the insulin receptor has a direct role in the mediation of cell killing or whether it passively reflects the state of the whole cell is not clear. However, identification of the receptor as an entity specifically protected in the thermotolerant cells may permit examination of the expression of thermotolerance at the molecular level.