The Hsp90 Inhibitor Geldanamycin Abrogates Colocalization of eIF4E and eIF4E-Transporter into Stress Granules and Association of eIF4E with eIF4G

Abstract

The eukaryotic translation initiation factor eIF4E plays a critical role in the control of translation initiation through binding to the mRNA 5 cap structure. eIF4E is also a component of processing bodies and stress granules, which are two types of cytoplasmic RNA granule in which translationally inactivated mRNAs accumulate. We found that treatment with the Hsp90 inhibitor geldanamycin leads to a substantial reduction in the number of HeLa cells that contain processing bodies. In contrast, stress granules are not disrupted but seem to be only partially affected by the inhibition of Hsp90. However, it is striking that eIF4E as well as its binding partner eIF4E transporter (4E-T), which mediates the import of eIF4E into the nucleus, are obviously lost from stress granules. Furthermore, the amount of eIF4G that is associated with the cap via eIF4E is reduced by geldanamycin treatment. Thus, the chaperone activity of Hsp90 probably contributes to the correct localization of eIF4E and 4E-T to stress granules and also to the interaction between eIF4E and eIF4G, both of which may be needed for eIF4E to acquire the physiological functionality that underlies the mechanism of translation initiation.

Dynamic Impacts of the Inhibition of the Molecular Chaperone Hsp90 on the T-Cell Proteome Have Implications for Anti-Cancer Therapy

“…In addition, components of the R2TP-Hsp90 complex, which has a role in assembling multi-molecular protein complexes involved in gene expression, were confirmed as Hsp90 clients [61]. These observations, as well as a slow and sustained mild decrease of proteins identified in our stSILAC analysis as taking part in post-transcriptional control processes, attest to an Hsp90-mediated regulatory role in the control of gene expression [58], [60], [62], [63].…”

Iruka Eliminates Dysfunctional Argonaute by Selective Ubiquitination of Its Empty State

“…We found that Ago1 was destabilized upon RNAi-mediated knockdown (KD) of the miRNA biogenesis factor Drosha in Drosophila S2 cells compared with mock (LacZ) KD ( Figures 1A and S1), consistent with previous work (Smibert et al, 2013). In addition, we blocked miRNA loading into Ago1 by treating S2 cells with the Hsp90 chaperone inhibitor 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) Schulte and Neckers, 1998) and observed Ago1 destabilization ( Figure 1B), as reported previously in mammals (Johnston et al, 2010;Suzuki et al, 2009).…”

“…Depletion of Drosha or Dcr-1 induces degradation of Ago1 in Drosophila (Smibert et al, 2013). Moreover, treatment with Hsp90 inhibitors, which block the loading of miRNA/miRNA* duplexes into AGO , destabilizes mammalian AGO (Johnston et al, 2010;Suzuki et al, 2009). Thus, selective degradation of empty AGO is evolutionarily conserved, strongly implying that it is significant for miRNA function.…”

Label-Free LC–MS/MS Proteomic Analysis of Cerebrospinal Fluid Identifies Protein/Pathway Alterations and Candidate Biomarkers for Amyotrophic Lateral Sclerosis

“…We showed previously that RBM45, an RNA binding protein whose levels are increased in the CSF of ALS patients 72 , forms cytoplasmic inclusions in motor neurons and glia of ALS patients. Similarly, we now show that increased levels of the stress-granule associated 74 eIF4E transporter protein (4e-T) in the CSF of sALS patients correlate with its presence in p62-positive nuclear granules and cytoplasmic inclusions (Figure S-2). Intranuclear inclusions are a pathological feature of sALS 99,100 and we demonstrate the presence of a transport protein, 4e-T, in these inclusions.…”