Bcl-2 regulates HIF-1alpha protein stabilization in hypoxic melanoma cells via the molecular chaperone HSP90
Authors: Elio Ziparo
Daniela Trisciuoglio
Chiara Gabellini
Marianna Desideri
Gabriella Zupi
Donatella Del Bufalo
Journal: PLoS ONE (2010)
Discipline: Multidisciplinary
Keywords: Hypoxia-Inducible Factor 1 (HIF-1); bcl-2; tumour angiogenesis; metastasis; therapeutic resistance
Affiliations: Experimental Chemotherapy Laboratory, Regina Elena Cancer Institute, Rome, Italy.

Abstract:  Background: Hypoxia-Inducible Factor 1 (HIF-1) is a transcription factor that is a critical mediator of the cellular response to hypoxia. Enhanced levels of HIF-1alpha, the oxygen-regulated subunit of HIF-1, is often associated with increased tumour angiogenesis, metastasis, therapeutic resistance and poor prognosis. It is in this context that we previously demonstrated that under hypoxia, bcl-2 protein promotes HIF-1/Vascular Endothelial Growth Factor (VEGF)-mediated tumour angiogenesis. Methodology/principal findings: By using human melanoma cell lines and their stable or transient derivative bcl-2 overexpressing cells, the current study identified HIF-1alpha protein stabilization as a key regulator for the induction of HIF-1 by bcl-2 under hypoxia. We also demonstrated that bcl-2-induced accumulation of HIF-1alpha protein during hypoxia was not due to an increased gene transcription or protein synthesis. In fact, it was related to a modulation of HIF-1alpha protein expression at a post-translational level, indeed its degradation rate was faster in the control lines than in bcl-2 transfectants. The bcl-2-induced HIF-1alpha stabilization in response to low oxygen tension conditions was achieved through the impairment of ubiquitin-dependent HIF-1alpha degradation involving the molecular chaperone HSP90, but it was not dependent on the prolyl hydroxylation of HIF-1alpha protein. We also showed that bcl-2, HIF-1alpha and HSP90 proteins form a tri-complex that may contribute to enhancing the stability of the HIF-1alpha protein in bcl-2 overexpressing clones under hypoxic conditions. Finally, by using genetic and pharmacological approaches we proved that HSP90 is involved in bcl-2-dependent stabilization of HIF-1alpha protein during hypoxia, and in particular the isoform HSP90beta is the main player in this phenomenon. Conclusions/significance: We identified the stabilization of HIF-1alpha protein as a mechanism through which bcl-2 induces the activation of HIF-1 in hypoxic tumour cells involving the beta isoform of molecular chaperone HSP90. 

Retracted: Yes

PubPeer comments:
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 Figure 2C. Much more similar than expected. ![file] , 
 Retraction: Bcl-2 Regulates HIF-1u03b1 Protein Stabilization in Hypoxic Melanoma Cells via the Molecular Chaperone HSP90 https: journals.plos.org plosone article?id=10.1371 journal.pone.0268235 After publication of this article [1], concerns were raised about the following results: Fig 1B: Similarities were noted between the u03b2-actin panels for the  dense and  4 days experiments. Fig 1D: There appear to be vertical discontinuities in background between lanes 1 2 and between lanes 2 3 in the HIF1u03b1 2 ml panel. Fig 1E: Similarities were noted between the Bcl2 5 and Bcl2 37 bands in the HIF-1u03b1 Insulin panel. Fig 2C: When aspect ratios are adjusted, the u03b2-actin panels for puro and Bcl2 5 appear more similar than would be expected for different experimental results. Fig 3B: There is an irregularity after lane 1 of the left bcl-2 blot, suggestive of possible image splicing. Fig 6A: The u03b2-actin data in lane 3 of the Bcl2 5 panel and in lane 1 of the Bcl2 37 panel appear similar. The authors noted that the original primary data supporting Fig 1B, 1D and 1E, and several other figures in the article are no longer available. They provided data from replication experiments to support the Fig 1B and E results, but the replication data did not fully resolve the concerns about the published figures. In light of the above issues, the PLOS ONE Editors retract this article. DT, CB, and DDB agreed with retraction but stand by the articleu2019s findings. EZ did not reply or could not be reached. The corresponding author noted that MD and GZ are deceased. ,