In mammals, two major Hsp90 isoforms (Hsp90 alpha. and Hsp90 beta) have been identified and found to be highly conserved among different species. However, the expression control of Hsp90 isoforms at both transcriptional and translational levels is largely unknown. Herein, we quantitatively investigate the changes in the total mRNA and inductive protein levels of Hsp90 alpha and Hsp90 beta in rat gliosarcoma cells treated with geldanamycin (GA). The stability of mRNA and protein was estimated. The translational efficiency of Hsp90 isoforms was measured employing in vitro translation techniques. It was found that Hsp90 alpha was more inducible than Hsp90 beta after GA treatment, whereas the hsp90 alpha mRNA level was lower than that of hsp90 beta. In addition, higher translational efficiency of hsp90 alpha mRNA was observed, suggesting that translational control played an important role. Taken together, our results indicate that differential expression between Hsp90 alpha, and Hsp90 beta is a consequence of both distinct mRNA profiles and differential translation processes. (c) 2006 Elsevier Inc. All rights reserved.