Uterine estrogen receptor in vivo: phosphorylation of nuclear specific forms on serine residues

We have characterized further the heterogeneous nuclear-specific doublet forms of the mouse uterine estrogen receptor (ER). Estrogen treatment produced the multiple nuclear ER forms of 65 and 66.5 kDa, which were isolated and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Soluble ER preparations exhibited only a single 65-kDa form. Isolation of the individual nuclear ER forms and reanalysis demonstrated that formation of the multiple bands was not due to artifacts of nuclear sample preparation or the presence of contaminating proteins. Analysis of individual uterine cell types (epithelial and stromal/myometrium) indicated that both ER forms were present in both cell fractions. Fractionation of nuclear components with low salt showed that both ER forms were found in the salt-resistant fraction. Extraction of nuclei with high salt (0.6 M KCl) solubilized both ER forms. Phosphorylation was studied as a protein modification to account for the multiple forms. Incorporation of 32P into uterine protein both in vivo and in intact tissue incubation indicated 32P labeling of uterine nuclear ER after hormone treatment. Both nuclear ER forms are labeled, although the 66.5-kDa form appears to be more heavily labeled. Phosphoamino acid analysis of the immunopurified 32P-labeled ER from intact uterine tissue indicated phosphoserine as the only phospholabeled residue. These data suggest that phosphorylation is associated with the physiological functioning of the ER in response to hormone and produces the heterogeneous ER forms in the nucleus.     

HSP60/10 chaperonin systems are inhibited by a variety of approved drugs,natural products,and known bioactive molecules

All living organisms contain a unique class of molecular chaperones called 60?kDa heat shock proteins (HSP60 – also known as GroEL in bacteria). While some organisms contain more than one HSP60 or GroEL isoform, at least one isoform has always proven to be essential. Because of this, we have been investigating targeting HSP60 and GroEL chaperonin systems as an antibiotic strategy. Our initial studies focused on applying this antibiotic strategy for treating African sleeping sickness (caused by Trypanosoma brucei parasites) and drug-resistant bacterial infections (in particular Methicillin-resistant Staphylococcus aureus – MRSA). Intriguingly, during our studies we found that three known antibiotics – suramin, closantel, and rafoxanide – were potent inhibitors of bacterial GroEL and human HSP60 chaperonin systems. These findings prompted us to explore what other approved drugs, natural products, and known bioactive molecules might also inhibit HSP60 and GroEL chaperonin systems. Initial high-throughput screening of 3680 approved drugs, natural products, and known bioactives identified 161 hit inhibitors of the Escherichia coli GroEL chaperonin system (4.3% hit rate). From a purchased subset of 60 hits, 29 compounds (48%) re-confirmed as selective GroEL inhibitors in our assays, all of which were nearly equipotent against human HSP60. These findings illuminate the notion that targeting chaperonin systems might be a more common occurrence than we previously appreciated. Future studies are needed to determine if the in vivo modes of action of these approved drugs, natural products, and known bioactive molecules are related to GroEL and HSP60 inhibition.