Immunochemical characterization of the ATP-stimulated glucocorticoid-receptor-translocation promoter from various organs of rat

Disruption of glycerol metabolism by RNAi targeting of genes encoding glycerol kinase results in a range of phenotype severity in Drosophila

In Drosophila, RNAi targeting of either dGyk or dGK can result in two alternative phenotypes: adult glycerol hypersensitivity or larval lethality. Here we compare these two phenotypes at the level of glycerol kinase (GK) phosphorylation activity, dGyk and dGK-RNA expression, and glycerol levels. We found both phenotypes exhibit reduced but similar levels of GK phosphorylation activity. Reduced RNA expression levels of dGyk and dGK corresponded with RNAi progeny that developed into glycerol hypersensitive adult flies. However, quantification of dGyk/dGK expression levels for the larval lethality phenotype revealed unexpected levels possibly due to a compensatory mechanism between dGyk and dGK or RNAi inhibition. The enzymatic role of glycerol kinase converts glycerol to glycerol 3-phosphate. As expected, elevated glycerol levels were observed in larvae that went on to develop into glycerol hypersensitive adults. Interestingly, larvae that died before eclosion revealed extremely low glycerol levels. Further characterization identified a wing phenotype that is enhanced by a dGpdh null mutation, indicating disrupted glycerol metabolism underlies the wing phenotype. In humans, glycerol kinase deficiency (GKD) exhibits a wide range of phenotypic variation with no obvious genotype-phenotype correlations. Additionally, disease severity often does not correlate with GK phosphorylation activity. It is intriguing that both human GKD patients and our GKD Drosophila model show a range of phenotype severity. Additionally, the lack of correlation between GK phosphorylation and dGyk/dGK-RNA expression with phenotypic severity suggests further study including understanding the alternative functions of the GK protein, could provide insights into the complex pathogenic mechanism observed in human GKD patients.

Glycerol hypersensitivity in a Drosophila model for glycerol kinase deficiency is affected by mutations in eye pigmentation genes

Glycerol kinase plays a critical role in metabolism by converting glycerol to glycerol 3-phosphate in an ATP dependent reaction. In humans, glycerol kinase deficiency results in a wide range of phenotypic variability; patients can have severe metabolic and CNS abnormalities, while others possess hyperglycerolemia and glyceroluria with no other apparent phenotype. In an effort to help understand the pathogenic mechanisms underlying the phenotypic variation, we have created a Drosophila model for glycerol kinase deficiency by RNAi targeting of dGyk (CG18374) and dGK (CG7995). As expected, RNAi flies have reduced glycerol kinase RNA expression, reduced phosphorylation activity and elevated glycerol levels. Further investigation revealed these flies to be hypersensitive to fly food supplemented with glycerol. Due to the hygroscopic nature of glycerol, we predict glycerol hypersensitivity is a result of greater susceptibility to desiccation, suggesting glycerol kinase to play an important role in desiccation resistance in insects. To evaluate a role for genetic modifier loci in determining severity of the glycerol hypersensitivity observed in knockdown flies, we performed a preliminary screen of lethal transposon insertion mutant flies using a glycerol hypersensitive survivorship assay. We demonstrate that this type of screen can identify both enhancer and suppressor genetic loci of glycerol hypersensitivity. Furthermore, we found that the glycerol hypersensitivity phenotype can be enhanced or suppressed by null mutations in eye pigmentation genes. Taken together, our data suggest proteins encoded by eye pigmentation genes play an important role in desiccation resistance and that eye pigmentation genes are strong modifiers of the glycerol hypersensitive phenotype identified in our Drosophila model for glycerol kinase deficiency.

Conserved family of glycerol kinase loci in Drosophila melanogaster

Glycerol kinase (GK) is an enzyme that catalyzes the formation of glycerol 3-phosphate from ATP and glycerol, the rate-limiting step in glycerol utilization. We analyzed the genome of the model organism Drosophila melanogaster and identified five GK orthologs, including two loci with sequence homology to the mammalian Xp21 GK protein. Using a combination of sequence analysis and evolutionary comparisons of orthologs between species, we characterized functional domains in the protein required for GK activity. Our findings include additional conserved domains that suggest novel nuclear and mitochondrial functions for glycerol kinase in apoptosis and transcriptional regulation. Investigation of GK function in Drosophila will inform us about the role of this enzyme in development and will provide us with a tool to examine genetic modifiers of human metabolic disorders.

New purification method for glucocorticoid receptors

In this report, we describe a new purification method for activated recombinant glucocorticoid receptor (GR) utilizing a cation-exchanger (Mono S) at pH8.4. This method is based upon a new finding that activated GR binds to both Mono Q and Mono S columns at the same pH. This method enables us to purify recombinant GR within 3 h. The purified GR represents more than 97% of the eluted proteins. Purified recombinant GR is able to bind specifically to a DNA fragment containing the glucocorticoid response element. Recombinant GR has no tag sequence that can be utilized for purification. Thus, this separation method is also applicable to purification of native GR.

Novel and simple two-step purification of a full-length rat glucocorticoid-receptor expressed in a baculovirus system

We purified the activated recombinant glucicorticoid receptor (GR) overexpressed in insect cells by sequential chromatographies using Mono Q and Mono S columns. This procedure was based upon a new finding that the activated GR binds both to a Mono Q column and to a Mono S column at the same pH (pH 8.4). The entire chromatographies took about 3 h and GR represented 97% of the purified protein sample. The purified GR was able to bind specifically to a DNA fragment containing the glucocorticoid response element. This purification protocol will be applicable to the purification of native GR, point-mutated recombinant GR and other nuclear receptors.