casein-kinase-ii and tanespimycin

Many types of cancer express high levels of heat shock proteins (HSPs) that are molecular chaperones regulating protein folding and stability ensuring protection of cells from potentially lethal stress. HSPs in cancer cells promote survival, growth and spreading even in situations of growth factors deprivation by associating with oncogenic proteins responsible for cell transformation. Hence, it is not surprising that the identification of potent inhibitors of HSPs, notably HSP90, has been the primary research focus, in recent years. Exposure of cancer cells to HSP90 inhibitors, including 17-AAG, has been shown to cause resistance to chemotherapeutic treatment mostly attributable to induction of the heat shock response and increased cellular levels of pro-survival chaperones. In this study, we show that treatment of glioblastoma cells with 17-AAG leads to HSP90 inhibition indicated by loss of stability of the EGFR client protein, and significant increase in HSP70 expression. Conversely, co-treatment with the small-molecule kinase inhibitor D11 leads to suppression of the heat shock response and inhibition of HSF1 transcriptional activity. Beside HSP70, Western blot and differential mRNA expression analysis reveal that combination treatment causes strong down-regulation of the small chaperone protein HSP27. Finally, we demonstrate that incubation of cells with both agents leads to enhanced cytotoxicity and significantly high levels of LC3-II suggesting autophagy induction. Taken together, results reported here support the notion that including D11 in future treatment regimens based on HSP90 inhibition can potentially overcome acquired resistance induced by the heat shock response in brain cancer cells.

Topics: Benzoquinones; Brain Neoplasms; Casein Kinase II; Cell Line, Tumor; DNA-Binding Proteins; Down-Regulation; Drug Interactions; Drug Resistance, Neoplasm; Glioblastoma; Glucosides; Heat Shock Transcription Factors; HSP70 Heat-Shock Proteins; HSP90 Heat-Shock Proteins; Humans; Lactams, Macrocyclic; Lignans; Protein Kinase Inhibitors; Transcription Factors; Transcription, Genetic; Transcriptome; Up-Regulation

Protein kinase CK2 promotes multiple myeloma cell growth by regulating critical signaling pathways. CK2 also modulates proper HSP90-dependent client protein folding and maturation by phosphorylating its co-chaperone CDC37. Because the endoplasmic reticulum (ER) stress/unfolded protein response (UPR) is central in myeloma pathogenesis, we tested the hypothesis that the CK2/CDC37/HSP90 axis could be involved in UPR in myeloma cells.. We analyzed CK2 activity upon ER stress, the effects of its inactivation on the UPR pathways and on ER stress-induced apoptosis. The consequences of CK2 plus HSP90 inhibition on myeloma cell growth in vitro and in vivo and CK2 regulation of HSP90-triggered UPR were determined.. CK2 partly localized to the ER and ER stress triggered its kinase activity. CK2 inhibition reduced the levels of the ER stress sensors IRE1α and BIP/GRP78, increased phosphorylation of PERK and EIF2α, and enhanced ER stress-induced apoptosis. Simultaneous inactivation of CK2 and HSP90 resulted in a synergic anti-myeloma effect (combination index = 0.291) and in much stronger alterations of the UPR pathways as compared with the single inhibition of the two molecules. Cytotoxicity from HSP90 and CK2 targeting was present in a myeloma microenvironment model, on plasma cells from patients with myeloma and in an in vivo mouse xenograft model. Mechanistically, CK2 inhibition led to a reduction of IRE1α/HSP90/CDC37 complexes in multiple myeloma cells.. Our results place CK2 as a novel regulator of the ER stress/UPR cascades and HSP90 function in myeloma cells and offer the groundwork to design novel combination treatments for this disease.

Topics: Animals; Apoptosis; Benzoquinones; Blotting, Western; Casein Kinase II; Cell Line, Tumor; Cells, Cultured; Endoplasmic Reticulum Chaperone BiP; Endoplasmic Reticulum Stress; Enzyme Inhibitors; Gene Expression Regulation, Neoplastic; HSP90 Heat-Shock Proteins; Humans; Lactams, Macrocyclic; Mice; Mice, SCID; Microscopy, Confocal; Multiple Myeloma; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; Signal Transduction; Thapsigargin; Unfolded Protein Response; Xenograft Model Antitumor Assays