The heat shock protein antagonist 17-AAG potentiates the activity of enzastaurin against malignant human glioma cells

Jane, Esther P.; Pollack, Ian F.

doi:10.1016/j.canlet.2008.03.039

Cited by 18 publications

(19 citation statements)

References 38 publications

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“…AEB071 inhibited Erk1/2 phosphorylation in GNAQ mutated but not GNAQ wild type UM cells, and had minimal impact on Akt phophorylation. Similarly, we have recently found that PKC inhibitor enzastaurin inhibits phosphorylation of Erk1/2 but not Akt in GNAQ mutated cell lines (17), although enzastaurin has been reported to inhibit Akt phosphorylation but not Erk1/2 phosphorylation in other types of cancer cells (24, 26, 40). The inhibition of Erk1/2 phosphorylation is therefore likely a common mechanism for the anti-proliferative action of PKC inhibitors in GNAQ mutated UM cells.…”

Section: Discussionmentioning

confidence: 72%

“…It has been previously reported that PKC can activate the PI3K/Akt and MAPK pathways as well as GSK3β Ser9 phosphorylation. The PKC inhibitor enzastaurin inhibits Akt and GSK3β Ser9 phosphorylation in some types of cancer cells (21–26). Similarly, AEB071 decreased GSK3β Ser9 phsophorylation in all UM cell lines studied here (Supplemental Figure S2).…”

Section: Resultsmentioning

confidence: 99%

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Protein Kinase C Inhibitor AEB071 Targets Ocular Melanoma Harboring GNAQ Mutations via Effects on the PKC/Erk1/2 and PKC/NF-κB Pathways

Zhu

et al. 2012

Molecular Cancer Therapeutics

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Somatic GNAQ mutations at codon 209 have been identified in approximately 50% of uveal melanomas (UM) and have been reported to be oncogenic through activating PLCβ-PKC-Erk1/2 pathways. We hypothesized that PKC may provide new opportunities for therapeutic targeting of UM carrying GNAQ mutations. To test this hypothesis, UM cells harboring wild type or mutant GNAQ were treated with the PKC inhibitor AEB071 (sotrastaurin) or infected with lentivirus expressing shRNAs targeting PKC isoforms. Notably, AEB071 at low micromolar concentrations significantly inhibited the growth of UM cells harboring GNAQ mutations through induction of G1 arrest and apoptosis. However, AEB071 had little effect on UM cells carrying wild type GNAQ. AEB071-mediated cell inhibition in the GNAQ mutated UM was accompanied by inhibition of Erk1/2 phosphorylation, NF-κB, decreased expression of cyclin D1, survivin, Bcl-xL and XIAP, and increased expression of cyclin-dependent kinase inhibitor p27Kip1. AEB071 suppressed the expression of PKC α, β, δ, ε and θ in GNAQ mutated UM cells. Our findings from shRNA-mediated knockdown studies revealed that these PKC isoforms are functionally important for UM cells harboring GNAQ mutations. Furthermore, inhibitors of Erk1/2 and NF-κB pathways reduced viability of UM cells. Together, our findings demonstrate that AEB071 exerts antitumor action on UM cells carrying GNAQ mutations via targeting PKC/Erk1/2 and PKC/NF-κB pathways. Targeted PKC inhibition with drugs such as AEB071 offers novel therapeutic potential for UM harboring GNAQ mutations.

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Section: Discussionmentioning

confidence: 72%

Section: Resultsmentioning

confidence: 99%

Protein Kinase C Inhibitor AEB071 Targets Ocular Melanoma Harboring GNAQ Mutations via Effects on the PKC/Erk1/2 and PKC/NF-κB Pathways

Zhu

et al. 2012

Molecular Cancer Therapeutics

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Section: Discussionmentioning

confidence: 99%

“…A recent study showed that the Hsp90 inhibitor 17-AAG potentiated the activity of the PKC ␤II-specific inhibitor, enzastaurin, in malignant glioma (62). Although Akt activity is up-regulated in this cancer pathway (62), the efficacy of these two inhibitors could also be explained by Hsp90 regulation of PKC. The identification of PKC as a client of the Hsp90-Cdc37 chaperone complex suggests that Hsp90 and PKC inhibitors could serve as potential therapeutics in treating pathologies that have associated PKC mutations or elevated levels of PKC.…”

Section: Discussionmentioning

confidence: 99%

The Chaperones Hsp90 and Cdc37 Mediate the Maturation and Stabilization of Protein Kinase C through a Conserved PXXP Motif in the C-terminal Tail*

Gould

Kannan

Taylor

et al. 2009

Journal of Biological Chemistry

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The life cycle of protein kinase C (PKC) is tightly controlled by mechanisms that mature the enzyme, sustain the activationcompetent enzyme, and degrade the enzyme. Here we show that a conserved PXXP motif (Kannan, N., Haste, N., Taylor, S. S., and Neuwald, A. F. (2007) Proc. Natl. Acad. Sci. U. S. A. 104, 1272-1277), in the C-terminal tail of AGC (c-AMP-dependent protein kinase/protein kinase G/protein kinase C) kinases, controls the processing phosphorylation of conventional and novel PKC isozymes, a required step in the maturation of the enzyme into a signaling-competent species. Mutation of both Pro-616 and Pro-619 to Ala in the conventional PKC ␤II abolishes the phosphorylation and activity of the kinase. Co-immunoprecipitation studies reveal that conventional and novel, but not atypical, PKC isozymes bind the chaperones Hsp90 and Cdc37 through a PXXP-dependent mechanism. Inhibitors of Hsp90 and Cdc37 significantly reduce the rate of processing phosphorylation of PKC. Of the two C-terminal sites processed by phosphorylation, the hydrophobic motif, but not the turn motif, is regulated by Hsp90. Overlay of purified Hsp90 onto a peptide array containing peptides covering the catalytic domain of PKC ␤II identified regions surrounding the PXXP segment, but not the PXXP motif itself, as major binding determinants for Hsp90. These Hsp90-binding regions, however, are tethered to the C-terminal tail via a "molecular clamp" formed between the PXXP motif and a conserved Tyr (Tyr-446) in the ␣E-helix. Disruption of the clamp by mutation of the Tyr to Ala recapitulates the phosphorylation defect of mutating the PXXP motif. These data are consistent with a model in which a molecular clamp created by the PXXP motif in the C-terminal tail and determinants in the ␣E-helix of the catalytic domain allows the chaperones Hsp90 and Cdc37 to bind newly synthesized PKC, a required event in the processing of PKC by phosphorylation.Protein kinases, which comprise ϳ2% of the human genome, are key signal transducers that regulate a wide variety of cellular processes, such as growth, proliferation, and metabolism, through catalysis of specific phosphorylation events (1). By integrating signals from extracellular stimuli and transmitting them to targeted downstream substrates, protein kinases serve as a pivotal point of regulation within the cell. Deregulation and mutation of protein kinases play a causal role in human pathology, notably cancer, poising kinases as important targets for the design of therapeutics (2-5). Therefore, understanding the mechanisms that regulate protein kinases, such as those important for maturation and processing, would be critical for designing therapeutics that would maintain the correct functioning of signal transduction pathways.Heat shock proteins (Hsp), 3 such as Hsp90, are ubiquitously expressed molecular chaperones that facilitate protein folding, regulate quality control, and guide protein turnover in an effort to maintain cellular homeostasis (6 -8). Unlike other chaperones such as Hsp70, which non...

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“…Many of these client proteins are mutated or overexpressed in GBM [1] and therefore, inhibiting Hsp90 protein or its inducible component Hsp90α, could disrupt the oncogenic signalling pathways. Hsp90 silencing can be achieved using the benzoquinone antibiotic 17-allylamino-17-demethoxygeldanamycin (17-AAG) which is an Hsp90 inhibitor [9] and RNA interference (RNAi) using small interfering RNA (siRNA) [10]. …”

Section: Introductionmentioning

confidence: 99%

A Novel Therapeutic Strategy for the Treatment of Glioma, Combining Chemical and Molecular Targeting of Hsp90a

Mehta

Shervington

Munje

et al. 2011

Cancers

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Hsp90α's vital role in tumour survival and progression, together with its highly inducible expression profile in gliomas and its absence in normal tissue and cell lines validates it as a therapeutic target for glioma. Hsp90α was downregulated using the post-transcriptional RNAi strategy (sihsp90α) and a post-translational inhibitor, the benzoquinone antibiotic 17-AAG. Glioblastoma U87-MG and normal human astrocyte SVGp12 were treated with sihsp90α, 17-AAG and concurrent sihsp90α/17-AAG (combined treatment). Both Hsp90α gene silencing and the protein inhibitor approaches resulted in a dramatic reduction in cell viability. Results showed that sihsp90α, 17-AAG and a combination of sihsp90α/17-AAG, reduced cell viability by 27%, 75% and 88% (p < 0.001), respectively, after 72 h. hsp90α mRNA copy numbers were downregulated by 65%, 90% and 99% after 72 h treatment with sihsp90α, 17-AAG and sihsp90α/17-AAG, respectively. The relationship between Hsp90α protein expression and its client Akt kinase activity levels were monitored following treatment with sihsp90α, 17-AAG and sihsp90α/17-AAG. Akt kinase activity was downregulated as a direct consequence of Hsp90α inhibition. Both Hsp90α and Akt kinase levels were significantly downregulated after 72 h. Although, 17-AAG when used as a single agent reduces the Hsp90α protein and the Akt kinase levels, the efficacy demonstrated by combinatorial treatment was found to be far more effective. Combination treatment reduced the Hsp90α protein and Akt kinase levels to 4.3% and 43%, respectively, after 72 h. hsp90α mRNA expression detected in SVGp12 was negligible compared to U87-MG, also, the combination treatment did not compromise the normal cell viability. Taking into account the role of Hsp90α in tumour progression and the involvement of Akt kinase in cell signalling and the anti-apoptotic pathways in tumours, this double targets treatment infers a novel therapeutic strategy.

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The heat shock protein antagonist 17-AAG potentiates the activity of enzastaurin against malignant human glioma cells

Cited by 18 publications

References 38 publications

Protein Kinase C Inhibitor AEB071 Targets Ocular Melanoma Harboring GNAQ Mutations via Effects on the PKC/Erk1/2 and PKC/NF-κB Pathways

Protein Kinase C Inhibitor AEB071 Targets Ocular Melanoma Harboring GNAQ Mutations via Effects on the PKC/Erk1/2 and PKC/NF-κB Pathways

The Chaperones Hsp90 and Cdc37 Mediate the Maturation and Stabilization of Protein Kinase C through a Conserved PXXP Motif in the C-terminal Tail*

A Novel Therapeutic Strategy for the Treatment of Glioma, Combining Chemical and Molecular Targeting of Hsp90a

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