Characterization of p50(cdc37), the Kinase-Specific Component of the HSP90 Chaperone Machinery

Abstract

Molecular chaperones are proteins that assist the assembly of other proteins and protein oligomers by binding to hydrophobic regions that are transiently exposed during various cellular processes thereby inhibiting nonproductive interactions that may otherwise produce non�functional structures. Hsp90 has been tenned the "signal transduction chaperone" based on its interactions with steroid honnone receptors and tyrosine kinases involved in signal transduction pathways. Steroid hormone receptors require hsp90 chaperone machinery to maintain a confonnation capable of honnone binding while some tyrosine kinases require hsp90 for maturation. CDC37 is a widely expressed protein that participates in cell processes controlled by kinases. CDC37 homologues are found in yeast, Drosophila, and mammalian cells. Studies in mammalian cells have found a CDC37 homologue protein, p50cdc37 to be important in kinase activity, specifically pp60v - src, CDK4, and raf. The role of p50cdc37 and hsp90 in kinase maturation is not certain and is complicated by the fact that hsp90 can bind to p50cdc37 in the absence of a kinase. In my thesis, 1attempted to illuminate the roles and mechanisms underlying p50cdc37 function by analyzing its interaction with hsp90. The first step in this process is to determine the stability of the p50cdc37/hsp90 complex in the absence ofa kinase. Treatment ofthe p50cdc37/hsp90 complex with geldanamycin and molybdate would help detennine how p50cdc37 interacts with hsp90. The final step in understanding the interaction between p50cdc37 and hsp90 is to determine if p50cdc37 acts in concert with hsp90 cohorts as part of the hsp90 chaperone machinery. My data allow me to draw three significant conclusions. The first is that p50cdc37 and hsp90 are weakly associated in the absence of a kinase. Additionally, the interaction between p50cdc37 and hsp90 is not dependent on phosphorylation events nor does ATP binding to hsp90 effect the interaction. I have also shown that p50cdc37 is found in hsp90 complexes along with other hsp90 cohorts.