sq-23377 and geldanamycin

Cellular levels of G protein-coupled receptor kinase (GRK)3 determine the sensitivity of the alpha(2A/B)-adrenoceptor (alpha(2)-AR) to agonist-induced down-regulation. Using human neuroblastoma BE(2)-C cells, this study examines how cellular GRK3 levels are affected by several mechanisms reported to influence stability and degradation of other GRKs. We first examined the interaction between the 90-kDa heat shock protein (Hsp90) and GRK3; Hsp90 reportedly affects the maturation and stability of GRK2. In unstimulated cells, GRK3 coimmunoprecipitates with Hsp90, suggesting a physical interaction. Moreover, when GRK3 protein expression was increased by 24-h epinephrine (EPI) treatment, Hsp90 protein expression increased with a similar but slightly delayed time course. To investigate the influence of Hsp90 on GRK3 protein stability, we determined the effect of the Hsp90 inhibitor geldanamycin (GA) on cellular GRK3 levels. GA eliminated the interaction between Hsp90 with GRK3 and produced a rapid, proteasome-mediated, 70% decrease in GRK3 levels within 24 h. To investigate the influence of Hsp90 on up-regulation of GRK3 expression, we examined the effect of GA on EPI-induced up-regulation. GA reduced the absolute increase in GRK3; however, the percentage of increase in GRK3 by EPI was not significantly different in the absence versus presence of GA (141 +/- 41 versus 94 +/- 12%). Finally, we examined the influence of Ca(2+)-activated proteases on cellular GRK3. Treatment with the calcium ionophore ionomycin produced a rapid decrease in GRK3 levels that was inhibited by the calpain inhibitor calpeptin. In conclusion, several mechanisms influence the degradation of GRK3 and therefore have the potential to affect GPCR signaling by regulating GRK3 levels in neurons.

Topics: Benzoquinones; beta-Adrenergic Receptor Kinases; Blotting, Western; Calpain; Cell Line, Tumor; Enzyme Stability; G-Protein-Coupled Receptor Kinase 3; HSP90 Heat-Shock Proteins; Humans; Immunoprecipitation; Ionomycin; Lactams, Macrocyclic; Neurons; Signal Transduction; Up-Regulation

Systemic injections of sodium tungstate, a protein-tyrosine phosphatase (PTPase) inhibitor, to pupae immediately after pupation have been shown to efficiently produce characteristic color-pattern modifications on the wings of many species of butterflies. Here we demonstrated that the tungstate-induced modification pattern was entirely different from other chemically-induced ones in a species of nymphalid butterfly Junonia (Precis) orithya. In this species, the systemic injections of tungstate produced characteristic expansion of black area and shrinkage of white area together with the move of parafocal elements toward the wing base. Overall, pattern boundaries became obscure. In contrast, an entirely different modification pattern, overall darkening of wings, was observed by the injections of stress-inducing chemicals, thapsigargin, ionomycin, or geldanamycin, to pupae under the rearing conditions for the adult summer form. On the ventral wings, this darkening was due to an increase of the proportion of peppered dark scales, which was reminiscent of the natural fall form of this species. Under the same rearing conditions, the injections of ecdysteroid, which is a well-known hormone being responsible for the seasonal polyphenism of nymphalid butterflies, yielded overall expansion of orange area especially around eyespots. Taken together, we conclude that the tungstate-induced modifications are clearly distinguishable from those of stress response and ecdysteroid effect. This conclusion then suggests that the putative PTPase signaling pathway that is sensitive to tungstate uniquely contributes to the wing-wide color-pattern development in butterflies.

Topics: Animals; Benzoquinones; Butterflies; Color; Dimethyl Sulfoxide; Ecdysteroids; Ionomycin; Lactams, Macrocyclic; Phenotype; Protein Tyrosine Phosphatases; Quinones; Thapsigargin; Tungsten Compounds; Wings, Animal

Inhibition of CD28 signalling after an immune response impedes T cell activation and can lead to immunosuppression. To identify inhibitors of anti-CD28 induced IL-2 production, a library of fungal metabolites was screened in a cell-based, high throughput assay. A reduced novel benzofluoranthene, tentatively named as (6bS, 7R, 8S)-7-methoxy-4, 8, 9-trihydroxy-1, 6b, 7, 8-tetrahydro-2H-benzo[j] fluoranthen-3-one (XR774), from Cladosporium cf. cladosporioides, was isolated. XR774 inhibited IL-2 mRNA and protein expression induced by anti-CD28 and anti-CD3 but had no effect on IL-2 induction by PMA and ionomycin. Moreover, XR774 inhibited the activity of the tyrosine kinases, Fyn, Lck, Abl and epidermal growth factor receptor (EGFR) with nanomolar activity, whereas micromolar concentrations of XR774 were ineffective on the serine-threonine kinase, PKA. Kinetic analysis of Fyn kinase inhibition was consistent with XR774 as a competitive inhibitor with respect to ATP. In peripheral blood, mononuclear cells (PBMC), XR774 inhibited anti-CD3 and anti-CD28 induced IL-2 and IL-2R alpha chain (CD25) expression but was consistently less active for inhibition of IFN-gamma production. On stimulation with PMA and anti-CD28, XR774 inhibited IL-2 production but had no effect on CD25 expression and enhanced IFN-gamma production. In contrast, the ansamycin, geldanamycin, inhibited both IL-2 and IFN-gamma production induced by anti-CD3 and anti-CD28 or PMA and anti-CD28. No significant associated cytotoxicity or inhibition of protein synthesis was observed at concentrations up to 14 microM. Thus, XR774 represents a novel class of pharmacological agent with selective biological activities that distinguish it from other natural product inhibitors, such as the ansamycins.

Topics: Benzoquinones; CD28 Antigens; CD3 Complex; Cladosporium; Cyclosporine; Drug Evaluation, Preclinical; Enzyme Inhibitors; Fluorenes; Humans; Interferon-gamma; Interleukin-2; Ionomycin; Jurkat Cells; Lactams, Macrocyclic; Protein-Tyrosine Kinases; Quinones; T-Lymphocytes; Tetradecanoylphorbol Acetate

The 90-kDa heat shock protein (Hsp90) is the most abundant molecular chaperone of eukaryotic cells. Its chaperone function in folding nascent proteins seems to be restricted to a subset of proteins including major components of signal transduction pathways (eg, nuclear hormone receptors, transcription factors, and protein kinases). Improper function of these proteins can be induced by selective disruption of their complexes with Hsp90 using the benzoquinonoid ansamycin geldanamycin. In this study, we demonstrate that geldanamycin treatment blocks interleukin (IL)-2 secretion, IL-2 receptor expression, and proliferation of stimulated T-lymphocytes. Moreover, geldanamycin decreases the amount and phosphorylation of Lck and Raf-1 kinases and prevents activation of the extracellular signal regulated kinase (ERK)-2 kinase. Geldanamycin also disrupts the T-cell receptor-mediated activation of nuclear factor of activated T-cells (NF-AT). Treatment with geldanamycin, however, does not affect the activation of lysophosphatide acyltransferase, which is a plasma membrane enzyme coupled to the T-cell receptor after T-cell stimulation. Through demonstrating the selective inhibition of kinase-related T-lymphocyte responses by geldanamycin, our results emphasize the substantial role of Hsp90-kinase complexes in T-cell activation.

Topics: Acyltransferases; Benzoquinones; Cell Division; DNA-Binding Proteins; Enzyme Inhibitors; Genes, Reporter; HSP90 Heat-Shock Proteins; Humans; Interleukin-2; Ionomycin; Jurkat Cells; Lactams, Macrocyclic; Lymphocyte Activation; Lymphocyte Specific Protein Tyrosine Kinase p56(lck); MAP Kinase Signaling System; Mitogen-Activated Protein Kinase 1; Muromonab-CD3; Neoplasm Proteins; NFATC Transcription Factors; Nuclear Proteins; Proto-Oncogene Proteins c-raf; Quinones; Receptors, Interleukin-2; Recombinant Fusion Proteins; Signal Transduction; T-Lymphocytes; Tetradecanoylphorbol Acetate; Transcription Factors