The heat shock protein HSP90 serves as a chaperone for receptor protein kinases, steroid receptors, and other intracellular signaling molecules. Targeting HSP90 with ansamycin antibiotics disrupts the normal processing of clients of the HSP90 complex. The platelet-derived growth factor receptor alpha (PDGFRalpha) is a tyrosine kinase receptor up-regulated and activated in several malignancies. Here we show that the PDGFRalpha forms a complex with HSP90 and the co-chaperone cdc37 in ovarian, glioblastoma, and lung cancer cells. Treatment of cancer cell lines expressing the PDGFRalpha with the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG) promotes degradation of the receptor. Likewise, phospho-Akt, a downstream target, is degraded after treatment with 17-AAG. In contrast, PDGFRalpha expression is not affected by 17-AAG in normal human smooth muscle cells or 3T3 fibroblasts. PDGFRalpha degradation by 17-AAG is inhibited by the proteasome inhibitor MG132. High molecular weight, ubiquitinated forms of the receptor are detected in cells treated with 17-AAG and MG132. Degradation of the receptor is also inhibited by a specific neutralizing antibody to the PDGFRalpha but not by a neutralizing antibody to PDGF or by imatinib mesylate (Gleevec). Ultimately, PDGFRalpha-mediated cell proliferation is inhibited by 17-AAG. These results show that 17-AAG promotes PDGFRalpha degradation selectively in transformed cells. Thus, not only mutated tyrosine kinases but also overexpressed receptors in cancer cells can be targeted by 17-AAG.
" CCRP Retains CAR and PXR in the cytoplasm associated to microtubules  UNC-45 Favors assembly of myosin and myogenesis  Tom70 Facilitates mitochondrial import of proteins  CHIP Remodels Hsp90-client proteins targeting them to proteosomal degradation  SGT1 Required for kinetochore complex assembly and innate immunity in plants and animals   Kinases pp60-vSrc Required for Src-mediated cell transformation  Raf1 Essential for Raf-kinase activity and ternary assembly with Cdc37  eEF2-K Prevents aggregation and activates kinase activity  p210 Bcr-Abl Stabilizes de complex preventing its proteosomal degradation  Akt Essential for kinase activity and stability of complexes with Cdc37  Chk1 Favors kinase activity  ErB2 Stabilizes and restrains ErbB2 from interacting with other ErbBs in the absence of ligand   PDK Stabilizes PDK without affecting the intrinsic enzymatic activity of kinase  IκB kinase (IKK) Favors assembly, translocation, and activation of IKKs  IGF1R Permits the transduction of the signaling cascade of the receptor  Insulin R Receptor trafficking to cytosol. Mobility in the endoplasmic reticulum during maturation   VEGFR Favors the development of focal contacts at the receptor site via FAK activation  PDGFR Required for receptor maturation and oligomerization with cdc37   TrkA Favors the localization of the receptor in the cell surface  Cdk1 Forms complexes with cdc37  JAK Forms complexes with cdc37  p38 Forms complexes with cdc37 attenuating p38 autophosphorylation  PKC Required for phosphorylation, stability, mitochondrial and nuclear import    DNA-PK Proapoptotic response  PARK Possible enhancer of Akt-dependent actions  CMDKs Required for fungus transformation  Cdk4 Stabilizes complexes with cdc37  MEKK (o MAP3k) Stabilizes complexes and favors kinase activity  EPHA7-R Required for kinase activity  GSK3 Required for autophosphorylation and stability   Structural proteins Histones Induces chromatin condensation  Actin Modulates microfilaments assembly  Myosin Favors myofilaments assembly and myogenesis  Tubulin Protects against thermal denaturation and preserves microtubule polymerization  Lamin A/C Possible post-translational modifications  Vimentin Prevents cleavage by caspases  Keratins Enables protein unfolding and translocation to lysosomes  Neurofilaments Prevents protein aggregation and axonal degeneration  Nup62 Favors interaction of the GR with the nuclear pore complex and its nuclear translocation  Others p23 Client protein stabilization/maturation. Prostaglandin E2 synthase activity is enhanced   Hsp70 Regulates client protein function, trafficking and turnover. "
[Show abstract][Hide abstract] ABSTRACT: The term molecular chaperone was first used to describe the ability of nucleoplasmin to prevent the aggregation of histones with DNA during the assembly of nucleosomes. Subsequently, the name was extended to proteins that mediate the post-translational assembly of oligomeric complexes protecting them from denaturation and/or aggregation. Hsp90 is a 90-kDa molecular chaperone that represents the major soluble protein of the cell. In contrast to most conventional chaperones, Hsp90 functions as a refined sensor of protein function and its principal role in the cell is to facilitate biological activity to properly folded client proteins that already have a preserved tertiary structure. Consequently, Hsp90 is related to basic cell functions such as cytoplasmic transport of soluble proteins, translocation of client proteins to organelles, and regulation of the biological activity of key signalling factors such as protein kinases, ubiquitin ligases, steroid receptors, cell cycle regulators, transcription factors. A growing amount of evidence links the protective action of this molecular chaperone to mechanisms related to posttranslational modifications of soluble nuclear factors as well as histones. In this article, we discuss some aspects of the regulatory action of Hsp90 on transcriptional regulation and how this effect could have impacted genetic assimilation mechanism in some organisms.
"However clinical effect may be linked to the biological profile of the tumor since two patients, who presented with NSCLC and GIST and achieved SD, had tumors harboring BRAF G469A and PDGFRAD842V exon 18 mutations, respectively. Interestingly, activated BRAF  and mutated PDGFRA  are known client proteins requiring Hsp90, and these oncogenes can be effectively degraded by Hsp90 inhibitors [30-32]. Ongoing clinical trials are currently focusing on identifying the predictors of response to ganetespib treatment, based on molecular characterization of tumor tissues. "
[Show abstract][Hide abstract] ABSTRACT: This phase I study investigated the maximum tolerated dose (MTD), safety, pharmacokinetics and antitumor activity of ganetespib in patients with solid malignancies.
Patients were enrolled in cohorts of escalating ganetespib doses, given as 1 hour IV infusion, once weekly for 3 weeks, followed by a 1-week rest until disease progression or unacceptable toxicity. Endpoints included safety, pharmacokinetic and pharmacodynamic parameters and preliminary clinical activity.
Fifty-three patients were treated at doses escalating from 7 to 259 mg/m2. The most common adverse events were Grade 1 and 2 diarrhea, fatigue, nausea or vomiting. Dose-limiting toxicities (DLT) observed were: one Grade 3 amylase elevation (150 mg/m2), one Grade 3 diarrhea and one Grade 3 and one Grade 4 asthenia (259 mg/m2). The MTD was 216 mg/m2 and the recommended phase 2 dose was established at 200 mg/m2 given IV at Days 1, 8, and 15 every 4 weeks. There was a linear relationship between dose and exposure. Plasma HSP70 protein levels remained elevated for over a week post treatment. Disease control rate (objective response and stable disease at ≥ 16 weeks) was 24.4%.
Ganetespib is well tolerated as a weekly infusion for 3 of every 4 weeks cycle. The recommended phase II dose is 200 mg/m2, and is associated with an acceptable tolerability profile.
BMC Cancer 03/2013; 13(1):152. DOI:10.1186/1471-2407-13-152 · 3.36 Impact Factor
"More recently it has been shown that Cdc37 is essential for maintaining prostate tumor cell growth . Additionally, the platelet-derived growth factor receptor alpha which is up-regulated and activated in several malignancies forms a complex with HSP90 and the co-chaperone Cdc37 in ovarian, glioblastoma, and lung cancer cells . Together, these results support the targeting of Cdc37 for cancer therapy. "
[Show abstract][Hide abstract] ABSTRACT: Cdc37 is a 50 kDa molecular chaperone which targets intrinsically unstable protein kinases to the molecular chaperone HSP90. It is also an over-expressed oncoprotein that mediates carcinogenesis and maintenance of the malignant phenotype by stabilizing the compromised structures of mutant and/or over-expressed oncogenic kinases. Here we report that Cdc37 is not restricted intracellularly but instead it is also present on the surface of MDA-MB-453 and MDA-MB-231 human breast cancer cells, where it is shown to participate in cancer cell motility processes. Furthermore, we demonstrate using an anti-Cdc37 cell impermeable antibody, that similarly to its intracellular counterpart, this surface pool of Cdc37 specifically interacts with HSP90 as well as the kinase receptors HER2 and EGFR on the cell surface, probably acting as a co-factor in HSP90's extracellular chaperoning activities. Finally, we show that functional inhibition of surface HSP90 using mAb 4C5, a cell impermeable monoclonal antibody against this protein, leads not only to disruption of the Cdc37/HSP90 complex but also to inhibition of the Cdc37/ErbB receptors complexes. These results support an essential role for surface Cdc37 in concert with HSP90 on the cell surface during cancer cell invasion processes and strengthen the therapeutic potential of mAb 4C5 for the treatment of cancer.
PLoS ONE 08/2012; 7(8):e42722. DOI:10.1371/journal.pone.0042722 · 3.23 Impact Factor
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