FIG. 5.

Effects of hsp90 inhibition. FRAPs at MMTV arrays are faster after treatment with 2.5 μg of geldanamycin/ml (a) or 5 μg of radicicol/ml (c) than in control cells, but the speed-up is detectable immediately in corticosterone (e) while it appears only after 30 to 60 min in dexamethasone (a). (b) These changes are not caused by a generic effect on protein mobility, as cells transfected with GFP-HP1α show no effect on FRAPs after geldanamycin treatment. (Note that the GFP-HP1α recoveries are not fit by effective diffusion [data not shown], so a t test to compute a P value cannot be performed.) (d) Hormone withdrawal experiments demonstrate that, compared to dexamethasone, corticosterone exchanges much more rapidly with GR. Shown are the average transcriptional levels measured from 35 cells by RNA FISH. Cells were induced by 100 nM corticosterone (CORT) or dexamethasone (DEX) for 15 min and then washed three times over a 5-min period in hormone-free medium and left in that medium for 45 min. With corticosterone as a ligand, transcription is abolished after a 5-min wash, indicating complete exchange of the ligand with GR during the wash time. In the same wash period, a significant amount of dexamethasone remains bound, since transcription drops by only 50%. (f) Treatment with geldanamycin induces a progressive loss of GFP-GR from the array and a decrease in size, and this is accompanied by a loss of chaperones. Shown is the loss of p23 from the array following geldanamycin (GELD) treatment with dexamethasone as a ligand. Scale bar, 5 μm.