7-Hydroxystaurosporine (UCN-01) Inhibition of Akt Thr308 but not Ser473 Phosphorylation

• Published in: Clinical cancer research 2004-11, Vol.10 (21), p.7192-7198
• Main Authors: Kondapaka, Sudhir B., Zarnowski, MaryJane, Yver, Dena R., Sausville, Edward A., Cushman, Samuel W.
• Format: Article
• Language: English
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.CCR-04-0772

7-Hydroxystaurosporine (UCN-01) infused for 72 hours by continuous i.v. infusion induced insulin resistance during phase I clinical trials. To understand the mechanism for this observation, we examined the effect of UCN-01 on insulin-stimulated glucose transport activity with 3- O -methylglucose in isolated rat adipose cells. UCN-01 inhibits glucose transport activity in a dose-dependent manner at all insulin concentrations. At the clinically relevant concentration of 0.25 μmol/L UCN-01, glucose transport is inhibited 66, 29, and 26% at insulin concentrations of 10, 50, and 100,000 (100K) microunits/mL respectively, thus shifting the dose-response curve to the right. Increasing concentrations of UCN-01 up to 2.5 μmol/L progressively shift the insulin dose-response curve even further. As Akt is known to mediate in part action initiated at the insulin receptor, we also studied the effect of UCN-01 on Akt activation in whole-cell homogenates of these cells. Decreased glucose transport activity directly parallels decreased Akt Thr 308 phosphorylation in both an insulin and UCN-01 dose-dependent manner, whereas Akt Ser 473 phosphorylation is inhibited only at the lowest insulin concentration, and then, only modestly. UCN-01 also inhibits insulin-induced Thr 308 but not Ser 473 phosphorylation of Akt associated with the plasma membranes and low-density microsomes and inhibits translocation of GLUT4 from low-density microsomes to plasma membranes as expected from the glucose transport activity measurements. These data suggest that UCN-01 induces clinical insulin resistance by blocking Akt activation and subsequent GLUT4 translocation in response to insulin, and this effect appears to occur by inhibiting Thr 308 phosphorylation even in the face of almost completely unaffected Ser 473 phosphorylation.