Alteration of microtubule physiology in hepatocytes by insulin

Incubation of primary cultures of rat hepatocytes with insulin caused an alteration in several parameters of microtubule physiology. There was a transient decrease in total cellular tubulin levels and, at the same time, an apparent stabilization of microtubule polymers which was also transient. The level of microtubule polymer, however, was not altered, which indicated that an insulin-inducible decrease in the level of nonpolymerized tubulin was responsible for the decrease in total cellular tubulin. These changes were followed by an increase in tubulin mRNA levels and, shortly thereafter, by an increase in tubulin protein synthesis. This study demonstrates that microtubule physiology in hepatocytes is modulated by insulin and, further, suggests a model by which insulin-induced changes in microtubule physiology may play a role in regulating other insulin responses.