Grbovic OM, Basso AD, Sawai A, Ye Q, Friedlander P, Solit D et al.. V600E B-Raf requires the Hsp90 chaperone for stability and is degraded in response to Hsp90 inhibitors. Proc Natl Acad Sci USA 103: 57-62

Program in Molecular Pharmacology and Chemistry and Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 02/2006; 103(1):57-62. DOI: 10.1073/pnas.0609973103
Source: PubMed


The Raf family includes three members, of which B-Raf is frequently mutated in melanoma and other tumors. We show that Raf-1 and A-Raf require Hsp90 for stability, whereas B-Raf does not. In contrast, mutated, activated B-Raf binds to an Hsp90-cdc37 complex, which is required for its stability and function. Exposure of melanoma cells and tumors to the Hsp90 inhibitor 17-allylamino-17-demethoxygeldanamycin results in the degradation of mutant B-Raf, inhibition of mitogen-activated protein kinase activation and cell proliferation, induction of apoptosis, and antitumor activity. These data suggest that activated mutated B-Raf proteins are incompetent for folding in the absence of Hsp90, thus suggesting that the chaperone is required for the clonal evolution of melanomas and other tumors that depend on this mutation. Hsp90 inhibition represents a therapeutic strategy for the treatment of melanoma.

Download full-text


Available from: Neal Rosen, Apr 22, 2014
  • Source
    • "Increased levels of chaperones, DNA repair proteins, and RNA helicases in poor prognosis patients Cytosolic heat-shock protein 90 kDa, beta (HSP90AB1), its ER paralogue, tumor rejection antigen gp96 (HSP90B1), and heat-shock cognate 71 kDa protein (HSPA8), are found at higher levels in poor prognosis patients (Tables 1, S3 and S7). Many proteins required for melanoma initiation and progression, including mutated BRAF, CRAF, IGF1R, cyclin D1, CDK4, and AKT, are known clients of HSP90 (Grbovic et al., 2006). HSP90 was identified as a progression marker in primary melanomas , with high levels associated with higher Clark levels and increased Breslow thickness (McCarthy et al., 2008). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Outcomes for melanoma patients with stage III disease, differ widely even within the same sub-category. Molecular signatures that more accurately predict prognosis are needed to stratify patients according to risk. Proteomic analyses were used to identify differentially abundant proteins in extracts of surgically excised samples from patients with stage IIIc melanoma lymph node metastases. Analysis of samples from patients with poor (n = 14, < 1 year) and good (n = 19, > 4 years) survival outcomes identified 84 proteins that were differentially abundant between prognostic groups. Subsequent selected reaction monitoring analysis verified 21 proteins as potential biomarkers for survival. Poor prognosis patients are characterized by increased levels of proteins involved in protein metabolism, nucleic acid metabolism, angiogenesis, deregulation of cellular energetics and methylation processes, and decreased levels of proteins involved in apoptosis and immune response. These proteins are able to classify stage IIIc patients into prognostic sub-groups (p < 0.02). This is the first report of potential prognostic markers from stage III melanoma using proteomic analyses. Validation of these protein markers in larger patient cohorts should define protein signatures that enable better stratification of stage III melanoma patients.This article is protected by copyright. All rights reserved.
    Full-text · Article · Jul 2014 · Pigment Cell & Melanoma Research
  • Source
    • "However, the structural basis for HSP90-kinase interaction is not fully elucidated [2]. Interestingly, many mutant oncoproteins are HSP90 clients while their cellular counterparts are not [3]. It has been speculated that a shift from an inactive to an active conformation leads to an association of kinases with the HSP90 chaperone [2], [4]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The role of HSP90 in stabilization of oncogenic tyrosine kinases made it an attractive therapeutic target for treating cancer but the molecular basis underlying the interaction between the HSP90 chaperone and client kinases is not elucidated yet. Using kinase inhibitors we show that the inactive conformation of ERBB2 does not interact with HSP90 chaperone and is thus not amenable to degradation upon HSP90 inhibitor treatment, while active ERBB2 kinase conformation promotes interaction with the HSP90 machinery and thus is degraded upon HSP90 inhibitor treatment. Interestingly, the kinase-chaperone interaction is disrupted in case of BCR-ABL and FLT3-ITD when bound to inhibitors irrespective of whether they block the kinase in an active or inactive conformation and thus our results indicate that the stability of the active kinase conformation varies between different kinases.
    Full-text · Article · Jul 2013 · PLoS ONE
  • Source
    • "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 [29] and mutated PDGFRA [30] 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. Trial registration NCT00687934
    Full-text · Article · Mar 2013 · BMC Cancer
Show more