[show abstract][hide abstract] ABSTRACT: Ire1 (Ern1) is an unusual transmembrane protein kinase essential for the endoplasmic reticulum (ER) unfolded protein response (UPR). Activation of Ire1 by association of its N-terminal ER luminal domains promotes autophosphorylation by its cytoplasmic kinase domain, leading to activation of the C-terminal ribonuclease domain, which splices Xbp1 mRNA generating an active Xbp1s transcriptional activator. We have determined the crystal structure of the cytoplasmic portion of dephosphorylated human Ire1α bound to ADP, revealing the 'phosphoryl-transfer' competent dimeric face-to-face complex, which precedes and is distinct from the back-to-back RNase 'active' conformation described for yeast Ire1. We show that the Xbp1-specific ribonuclease activity depends on autophosphorylation, and that ATP-competitive inhibitors staurosporin and sunitinib, which inhibit autophosphorylation in vitro, also inhibit Xbp1 splicing in vivo. Furthermore, we demonstrate that activated Ire1α is a competent protein kinase, able to phosphorylate a heterologous peptide substrate. These studies identify human Ire1α as a target for development of ATP-competitive inhibitors that will modulate the UPR in human cells, which has particular relevance for myeloma and other secretory malignancies.
The EMBO Journal 02/2011; 30(5):894-905. · 9.82 Impact Factor
[show abstract][hide abstract] ABSTRACT: Immunoglobulin production by myeloma plasma cells depends on the unfolded protein response for protein production and folding. Recent studies have highlighted the importance of IRE1alpha and X box binding protein 1 (XBP1), key members of this pathway, in normal B-plasma cell development. We have determined the gene expression levels of IRE1alpha, XBP1, XBP1UNSPLICED (XBP1u), and XBP1SPLICED (XBP1s) in a series of patients with myeloma and correlated findings with clinical outcome. We show that IRE1alpha and XBP1 are highly expressed and that patients with low XBP1s/u ratios have a significantly better overall survival. XBP1s is an independent prognostic marker and can be used with beta2 microglobulin and t(4;14) to identify a group of patients with a poor outcome. Furthermore, we show the beneficial therapeutic effects of thalidomide in patients with low XBP1s/u ratios. This study highlights the importance of XBP1 in myeloma and its significance as an independent prognostic marker and as a predictor of thalidomide response.
[show abstract][hide abstract] ABSTRACT: Myeloma cells are highly dependent on the unfolded protein response to assemble folded immunoglobulins correctly. Therefore, targeting protein handling within a myeloma cell by inhibiting the aminopeptidase enzyme system, which catalyses the hydrolysis of amino acids from the proteins NH2 terminus, represents a therapeutic approach. CHR-2797, a novel aminopeptidase inhibitor, is able to inhibit proliferation and induce growth arrest and apoptosis in myeloma cells, including cells resistant to conventional chemotherapeutics. It causes minimal inhibition of bone marrow stromal cell (BMSC) proliferation but is able to overcome the microenvironmental protective effects, inhibiting the proliferation of myeloma cells bound to BMSCs and the increase in vascular endothelial growth factor levels seen when myeloma cells and BMSCs are bound together. Additive and synergistic effects are seen with bortezomib, melphalan, and dexamethasone. Apoptosis occurs via both caspase-dependent and non-caspase-dependent pathways with an increase in Noxa, cleavage of Mcl-1, and activation of the unfolded protein response. Autophagy is also seen. CHR-2797 causes an up-regulation of genes involved in the proteasome/ubiquitin pathway, as well as aminopeptidases, and amino acid deprivation response genes. In conclusion, inhibiting protein turnover using the aminopeptidase inhibitor CHR-2797 results in myeloma cell apoptosis and represents a novel therapeutic approach that warrants further investigation in the clinical setting.
Molecular Cancer Therapeutics 05/2009; 8(4):762-70. · 5.60 Impact Factor
[show abstract][hide abstract] ABSTRACT: Resistance to current cancer therapies has forced scientists to investigate new avenues of therapy distinct from those aimed at single targets, to strategies based on targeting families of proteins, on which cancers rely for their ability to survive stress. Two such protein families are the heat shock proteins (HSP), especially the HSP90 family, and proteins involved in mediating the unfolded protein response (UPR). HSP90 stabilises key survival factors in cancer cells including AKT, ERB2 and HIF1alpha, which alone makes HSP90 inhibitors extremely interesting as potential therapies. In addition targeting HSP90 can destabilise the UPR inducing cell death. A broad range of cancer-types rely on the UPR to correctly fold key signalling proteins properly, as well as to allow the cell to cope with the hypoxic environment associated with tumour development. These associations suggest that a range of tumours may be targeted using HSP90 inhibitors and that the development of specific inhibitors of the UPR may be of interest. In this article, based on work in multiple myeloma, we highlight the importance of targeting multiple signalling pathways simultaneously, using the UPR and heat shock proteins as examples, as a means of effectively killing cancer cells.
[show abstract][hide abstract] ABSTRACT: We have used global protein expression analysis to characterize the pathways of dexamethasone-mediated apoptosis and resistance in myeloma. Analysis of MM.1S cells by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) identified a series of proteins that were up- and downregulated following dexamethasone treatment. Downregulated proteins included proteins involved in cell survival and proliferation, whereas upregulated proteins were involved in post-translational modification, protein folding and trafficking. A comparison with published gene expression studies identified FK binding protein 5 (FKBP5) (also known as FKBP51), a key regulatory component of the Hsp90-steroid-receptor complex to be increased at the mRNA and protein level postdexamethasone exposure. Quantitative real time polymerase chain reaction and 2D-PAGE analysis of the dexamethasone resistant cell line MM.1R demonstrated no increase in FKBP5, consistent with its association with dexamethasone-mediated apoptosis. Western blot analysis of FKBP5 and other members of the Hsp90-receptor complex showed an increase in FKBP5 whilst FKBP4 (also known as FKBP52) and Hsp90 expression remained constant. No changes were observed in MM.1R. In conclusion, we demonstrated that following steroid receptor signalling, the cell carries out a number of adaptive responses prior to cell death. Interfering with these adaptive responses may enhance the myeloma killing effect of dexamethasone.
British Journal of Haematology 12/2007; 139(4):559-67. · 4.94 Impact Factor
[show abstract][hide abstract] ABSTRACT: Plasma cells producing high levels of paraprotein are dependent on the unfolded protein response (UPR) and chaperone proteins to ensure correct protein folding and cell survival. We hypothesized that disrupting client-chaperone interactions using heat shock protein 90 (Hsp90) inhibitors would result in an inability to handle immunoglobulin production with the induction of the UPR and myeloma cell death. To study this, myeloma cells were treated with Hsp90 inhibitors as well as known endoplasmic reticulum stress inducers and proteasome inhibitors. Treatment with thapsigargin and tunicamycin led to the activation of all 3 branches of the UPR, with early splicing of XBP1 indicative of IRE1 activation, upregulation of CHOP consistent with ER resident kinase (PERK) activation, and activating transcription factor 6 (ATF6) splicing. 17-AAG and radicicol also induced splicing of XBP1, with the induction of CHOP and activation of ATF6, whereas bortezomib resulted in the induction of CHOP and activation of ATF6 with minimal effects on XBP1. After treatment with all drugs, expression levels of the molecular chaperones BiP and GRP94 were increased. All drugs inhibited proliferation and induced cell death with activation of JNK and caspase cleavage. In conclusion, Hsp90 inhibitors induce myeloma cell death at least in part via endoplasmic reticulum stress and the UPR death pathway.