Hsp90-mediated inhibition of FKBP38 regulates apoptosis in neuroblastoma cells

2-Methoxyestradiol and Hydrogen Peroxide as Promising Biomarkers in Parkinson's Disease

Estrogens function in numerous physiological processes including controlling brain cell growth and differentiation. 2-Methoxestradiol (2-ME2), a 17β-estradiol (E2) metabolite, is known for its anticancer effects as observed both in vivo and in vitro. 2-ME2 affects all actively dividing cells, including neurons. The study aimed to determine whether 2-ME2 is a potentially cancer-protective or rather neurodegenerative agent in a specific tissue culture model as well as a clinical setup. In this study, 2-ME2 activity was determined in a Parkinson's disease (PD) in vitro model based on the neuroblastoma SH-SY5Y cell line. The obtained results suggest that 2-ME2 generates nitro-oxidative stress and controls heat shock proteins (HSP), resulting in DNA strand breakage and apoptosis. On the one hand, it may affect intensely dividing cells preventing cancer development; however, on the other hand, this kind of activity within the central nervous system may promote neurodegenerative diseases like PD. Thus, the translational value of 2-ME2's neurotoxic activity in a PD in vitro model was also investigated. LC-MS/MS technique was used to evaluate estrogens and their derivatives, namely, hydroxy and methoxyestrogens, in PD patients' blood, whereas the stopped-flow method was used to assess hydrogen peroxide (H2O2) levels. Methoxyestrogens and H2O2 levels were increased in patients' blood as compared to control subjects, but hydoxyestrogens were simultaneously decreased. From the above, we suggest that the determination of plasma levels of methoxyestrogens and H2O2 may be a novel PD biomarker. The presented research is the subject of the pending patent application "The use of hydrogen peroxide and 17β-estradiol and its metabolites as biomarkers in the diagnosis of neurodegenerative diseases," no. P.441360.

The structure of FKBP38 in complex with the MEEVD tetratricopeptide binding-motif of Hsp90

Tetratricopeptide (TPR) domains are known protein interaction domains. We show that the TPR domain of FKBP8 selectively binds Hsp90, and interactions upstream of the conserved MEEVD motif are critical for tight binding. In contrast FKBP8 failed to bind intact Hsp70. The PPIase domain was not essential for the interaction with Hsp90 and binding was completely encompassed by the TPR domain alone. The conformation adopted by Hsp90 peptides, containing the conserved MEEVD motif, in the crystal structure were similar to that seen for the TPR domains of CHIP, AIP and Tah1. The carboxylate clamp interactions with bound Hsp90 peptide were a critical component of the interaction and mutation of Lys 307, involved in the carboxylate clamp, completely disrupted the interaction with Hsp90. FKBP8 binding to Hsp90 did not substantially influence its ATPase activity.

FKBP38-Bcl-2 interaction: a novel link to chemoresistance

FKBP38, a noncanonical member of the immunosuppressive drug FK506 binding protein (FKBP) family members, possesses an inducible rotamase. FKBP38 interacts with several proteins and regulates multiple signaling pathways such as cell survival, apoptosis, proliferation, and metastasis. Deregulation of apoptosis is associated with chemoresistance and tumor relapse. The antiapoptotic protein Bcl-2 is a key player for increasing the apoptotic threshold in response to various cytotoxic drugs. The molecular interaction of Bcl-2 with FKBP38 potentiates the biological function of Bcl-2 and contributes to tumorigenesis and chemoresistance. Here, we discuss recent advances in the role of FKBP38 in connection with Bcl-2 and its possible link to chemotherapeutic resistance.

FKBP family proteins as promising new biomarkers for cancer

FK506-binding proteins (FKBPs) belong to the immunophilin family and bind immunosuppressive drugs, such as FK506 and rapamycin. These proteins, through interactions with steroid hormone receptors, kinases, or other cellular factors, play important roles in various physiological processes and, more interestingly, in pathological processes in mammals. Accumulating evidence has implicated some FKBP members in a variety of processes, such as the cell cycle and survival and apoptotic signaling pathways, particularly in cancers. After the deregulation of their expression was observed in cancer tissues, it became increasingly clear that FKBP members played an important role in tumorigenesis and the response to chemotherapies and radiotherapies and that FKBP members could act as oncogenes or tumor suppressors depending on the tissue type. A wealth of data from in vitro and clinical studies is paving the way for novel, promising roles of FKBPs as diagnostic, prognostic or therapy-monitoring cancer biomarkers.

From cell death to viral replication: the diverse functions of the membrane-associated FKBP38

FKBP38 is in many ways an exceptional member of the FK506-binding proteins. The calmodulin-regulated activity of FKBP38 for instance is unique within this protein family. The activated FKBP38 participates in apoptosis signaling by inhibiting the anti-apoptotic Bcl-2. Beyond this role in programmed cell death, FKBP38 seems to be involved in very different cellular processes that do not necessarily depend on the FKBP domain. These functions involve regulation of the kinase mTOR, regulation of neural tube formation, regulation of cellular hypoxia response, but also Hepatitis C virus replication. Pharmacological targeting of FKBP38 might therefore prove a successful strategy for intervention in different FKBP38-dependent processes, including programmed cell death in cancer or neurodegenerative diseases.

Heat shock protein 90 protects rat mesenchymal stem cells against hypoxia and serum deprivation-induced apoptosis via the PI3K/Akt and ERK1/2 pathways

Mesenchymal stem cell (MSC) transplantation has shown a therapeutic potential to repair the ischemic and infracted myocardium, but the effects are limited by the apoptosis and loss of donor cells in host cardiac microenvironment. The aim of this study is to explore the cytoprotection of heat shock protein 90 (Hsp90) against hypoxia and serum deprivation-induced apoptosis and the possible mechanisms in rat MSCs. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was assessed by Hoechst 33258 nuclear staining and flow cytometric analysis with annexin V/PI staining. The gene expression of Toll-like receptor-4 (TLR-4) and V-erb-b2 erythroblastic leukemia viral oncogene homolog 2 (ErbB2) was detected by real-time polymerase chain reaction (PCR). The protein levels of cleaved caspase-3, Bcl-2, Bcl-xL, Bax, total-ERK, phospho-ERK, total-Akt, phospho-Akt, and Hsp90 were detected by Western blot. The production of nitric oxide was measured by spectrophotometric assay. Hsp90 improves MSC viability and protects MSCs against apoptosis induced by serum deprivation and hypoxia. The protective role of Hsp90 not only elevates Bcl-2/Bax and Bcl-xL/Bax expression and attenuates cleaved caspase-3 expression via down-regulating membrane TLR-4 and ErbB2 receptors and then activating their downstream PI3K/Akt and ERK1/2 pathways, but also enhances the paracrine effect of MSCs. These findings demonstrated a novel and effective treatment strategy against MSC apoptosis in cell transplantation.

The neuroblastoma tumour-suppressor TrkAI and its oncogenic alternative TrkAIII splice variant exhibit geldanamycin-sensitive interactions with Hsp90 in human neuroblastoma cells

Hsp90 chaperones stabilize many tyrosine kinases including several oncogenes, which are inhibited or induced to degrade by the Hsp90 inhibitor geldanamycin (GA). As a consequence, GA has been developed for future chemotherapeutic use in several tumour types including neuroblastoma (NB). Alternative splicing of the neurotrophin receptor tyrosine kinase TrkA may have a pivotal function in regulating NB behaviour, with reports suggesting that tumour-suppressing signals from TrkA may be converted to oncogenic signals by stress-regulated alternative TrkAIII splicing. Within this context, it is important to know whether Hsp90 interacts with TrkA variants in NB cells and how GA influences this. Here, we report that both TrkAI and TrkAIII are Hsp90 clients in human NB cells. TrkAI exhibits GA-sensitive interaction with Hsp90 required for receptor endoplasmic reticulum export, maturation, cell surface stabilization and ligand-mediated activation, whereas TrkAIII exhibits GA-sensitive interactions with Hsp90 required for spontaneous activity and to a lesser extent stability. We show that GA inhibits proliferation and induces apoptosis of TrkAI expressing NB cells, whereas TrkAIII reduces the sensitivity of NB cells to GA-induced elimination. Our data suggest that GA-sensitive interactions with Hsp90 are critical for both TrkAI tumour suppressor and TrkAIII oncogenic function in NB and that TrkAIII expression exerts a negative impact on GA-induced NB cell eradication, which can be counteracted by a novel TrkAIII-specific peptide nucleic acid inhibitor.

Re-evaluating the roles of proposed modulators of mammalian target of rapamycin complex 1 (mTORC1) signaling

Signaling through mammalian target of rapamycin complex 1 (mTORC1) is stimulated by amino acids and insulin. Insulin inactivates TSC1/2, the GTPase-activator complex for Rheb, and Rheb.GTP activates mTORC1. It is not clear how amino acids regulate mTORC1. FKBP38 (immunophilin FK506-binding protein, 38 kDa), was recently reported to exert a negative effect on mTORC1 function that is relieved by its binding to Rheb.GTP. We confirm that Rheb binds wild type FKBP38, but inactive Rheb mutants showed contrasting abilities to bind FKBP38. We were unable to observe any regulation of FKBP38/mTOR binding by amino acids or insulin. Furthermore, FKBP38 did not inhibit mTORC1 signaling. The translationally controlled tumor protein (TCTP) in Drosophila was recently reported to act as the guanine nucleotide-exchange factor for Rheb. We have studied the role of TCTP in mammalian TORC1 signaling and its control by amino acids. Reducing TCTP levels did not reproducibly affect mTORC1 signaling in amino acid-replete/insulin-stimulated cells. Moreover, overexpressing TCTP did not rescue mTORC1 signaling in amino acid-starved cells. In addition, we were unable to see any stable interaction between TCTP and Rheb or mTORC1. Accumulation of uncharged tRNA has been previously proposed to be involved in the inhibition of mTORC1 signaling during amino acid starvation. To test this hypothesis, we used a Chinese hamster ovary cell line containing a temperature-sensitive mutation in leucyl-tRNA synthetase. Leucine deprivation markedly inhibited mTORC1 signaling in these cells, but shifting the cells to the nonpermissive temperature for the synthetase did not. These data indicate that uncharged tRNA(Leu) does not switch off mTORC1 signaling and suggest that mTORC1 is controlled by a distinct pathway that senses the availability of amino acids. Our data also indicate that, in the mammalian cell lines tested here, neither TCTP nor FKBP38 regulates mTORC1 signaling.