Radicicol rescues yeast cell death triggered by expression of human α-synuclein and its A53T mutant, but not by human βA4 peptide and proapoptotic protein bax
Authors: Sunil K Deshmukh
Shreyans K Jain
Bhabatosh Chaudhuri
Asma Derf
Shilpa A Verekar
Sandip B Bharate
Journal: Bioorganic chemistry (2019)
Discipline: BIOLOGY & BIOCHEMISTRY
Keywords: Bax; Hsp90 inhibitor; Parkinson’s disease; Radicicol; α-synuclein.
Affiliations: Leicester School of Pharmacy, De Montfort University, Leicester LE1 9BH, UK., Piramal Life Sciences Limited, Goregaon (East), Mumbai 400 063, India., CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India., CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu 180001, India. Electronic address: ., Leicester School of Pharmacy, De Montfort University, Leicester LE1 9BH, UK. Electronic address: .

Abstract:  Aggregation/misfolding of α-synuclein and βA4 proteins cause neuronal cell death (NCD) associated with Parkinson's and Alzheimer's disease. It has been suggested that a heat shock protein-90 (Hsp90) inhibitor can prevent NCD by activating the heat shock transcription factor-1 which, in turn, upregulates molecular chaperones such as Hsp70 that targets aggregated/misfolded proteins for refolding/degradation. We have isolated radicicol, an Hsp90 inhibitor, from a fungus occurring in the crevices of marble rocks of Central India. Radicicol, which was found to be a strong antioxidant, was tested for its ability to rescue yeast cells from death induced by expression of wild-type α-synuclein, its more toxic A53T mutant, and βA4. It effectively overcomes wild-type/mutant α-synuclein mediated yeast cell death, concomitantly diminishes ROS levels, reverses mitochondrial dysfunction and prevents nuclear DNA-fragmentation, a hallmark of apoptosis. Surprisingly however, radicicol is unable to rescue yeast cells from death triggered by expression of secreted βA4. Moreover, although radicicol acts as an antioxidant it fails to prevent yeast cell death inflicted by the proapoptotic protein, Bax. Our results indicate that radicicol specifically targets aggregated/misfolded α-synuclein's toxicity and opens up the possibility of using multiple yeast assays to screen natural product libraries for compounds that would unambiguously target α-synuclein aggregation/misfolding. 

Retracted: No

PubPeer comments:
 Two images in figure 2G appear to be the same, with a vertical flip. *** ![file] , 
 #1 Fig 2D, G  (D) Nuclear DNA fragmentation, as observed using the TUNEL assay, in yeast cells expressing 2-copies of Invss-u03b2A4 in minimal SG medium (containing galactose), in the absence of any compound, (panel 1) and in the presence of radicicol (panel 2). ... (G) Nuclear DNA fragmentation, as observed using the TUNEL assay, in yeast cells expressing 1-copy of Bax in minimal SG medium containing galactose, in the absence of any compound, (panel 1) and in the presence of radicicol (panel 2). ![file] Purple and brown boxes indicate panels repeated (after horizontal vertical flips) between (D) and (G). Other colors indicate panels also appearing in Fig 1D of [Derf et al (2019)] :  (D) Levels of nuclear DNA fragmentation, a hallmark of apoptosis, in yeast cells25 (which express (i) 2-copies of u03b1-syn alone (row 4) and co-expressing ySec22p (row 5), and (ii) a copy of Bax alone (row 1) and co-expressing ySec22p (row 2) or hBcl-xL (row 3). ![] , 
 1F, G:  (F). 3-copy u03b1-syn bearing yeast cells grown, in the absence (panel 1) or presence of radicicol (panel 2), stained with Phloxine B. (G).3-copy u03b1-syn bearing yeast cells stained with Hoechst 33,342 dye. **Panels 1** and 2 are controls; panel 1 shows that only a small percentage of cells are alive in SG medium (containing galactose) because of u03b1-syn expression, whereas in panel 2, most cells are alive in glucose-containing SD medium (because there is no u03b1-syn expression). In the presence of radicicol (panel 3), cells grown in galactosecontaining SG medium are resistant to the toxic effects of u03b1-syn . ![] Panel 1G 1 also appears as panel 1 of Fig 3D of [Derf et al (2019)] : marked with red boxes. ![] Panel 1F 1 also appeared as panel 2 of the original 3D of the Aegeline paper - shown in green boxes - though fortunately this was amended in an Erratum. , 
 The comments pertaining to this publication are related to the biological experiments (microscopy) which were conducted by authors, Asma Derf and mentored by Prof. Bhabatosh Chaudhuri at DeMontfort University UK. My group only provided the natural product, radicicol to Prof. Bhabatosh Chaudhuriu2019s group for biological investigations and performed molecular modeling study (Fig. 3). Thus, there are no clarifications against these comments from my side. At my end, these authors have been contacted via email and they will address the raised queries. ,