Translational Downregulation of HSP90 Expression by Iron Chelators in Neuroblastoma Cells

Abstract

Iron is an essential cellular nutrient, being a critical cofactor of several proteins involved in cell growth and replication. Compared with normal cells, neoplastic cells have been shown to require a greater amount of iron, thus laying the basis for the promising anticancer activity of iron chelators. In this work, we evaluated the effects of molecules with iron chelation activity on neuroblastoma (NB) cell lines. Of the 17 iron chelators tested, six reduced cell viability of two NB cell lines with an inhibition of growth of 50% below 10 mM; four of the six molecules-ciclopirox olamine (CPX), piroctone, 8-hydroxyquinoline, and deferasirox-were also shown to efficiently chelate intracellular iron within minutes after addition. Effects on cell viability of one of the compounds, CPX, were indeed dependent on chelation of intracellular iron and mediated by both G 0 /G 1 cell cycle block and induction of apoptosis. By combined transcriptome and translatome profiling we identified early translational downregulation of several members of the heat shock protein group as a specific effect of CPX treatment. We functionally confirmed iron-dependent depletion of HSP90 and its client proteins at pharmacologically achievable concentrations of CPX, and we extended this effect to piroctone, 8-hydroxyquinoline, and deferasirox. Given the documented sensitivity of NB cells to HSP90 inhibition, we propose CPX and other iron chelators as investigational antitumor agents in NB therapy.

MicroRNA-126 regulates Hypoxia-Inducible Factor-1α which inhibited migration, proliferation, and angiogenesis in replicative endothelial senescence

“…DFO also sustained HIF-1α levels in senescent HUVECs, but this finding could be explained by the well-known stabilizing effect of Hsp90 on HIF-1α. The translation of Hsp90 is downregulated for specific iron chelators—opposite to our observations—but this effect has not been demonstrated for DFO 54 . It is unknown whether HIF-1α degradation depends on O 2 /VHL (von Hippel Lindau), and the disruption of Hsp90 promotes HIF-1α degradation through an O 2 /VHL-independent pathway 51 , which might be the mechanism of degradation in our senescent HUVECs (e.g., Hsp90-regulated and O 2 /VHL-independent) because our cells were not grown under hypoxic conditions.…”

“…This result might be attributed to the advanced state of senescence in our model versus other paradigms. The rate of PD in HUVECs in our senescent model was 97 (PD > 96; passaged 27–38 times) compared with the current knowledge on replicative senescence in endothelial cells that reported rates of PD > 44 in endothelial cells (passage 13) 54,57 , PD between 49–50 (26 passages and onwards, late senescent HUVECs) 58 , and PD approximately 45 59,60 . Thus, the senescent endothelial state was irreversible, and DFO could not have affected the migration or proliferation (endothelial function) of senescent endothelial cells.…”

Ciclopirox inhibits cancer cell proliferation by suppression of Cdc25A

“…CPX induces autophagy by inducing reactive oxygen species and activating c-Jun N -terminal kinase cascade [14]. Of interest, CPX has been consistently found to inhibit cell proliferation by arresting cells in G 1 phase of cell proliferation in a concentration-dependent manner, the cell cycle [3, 7, 15], which is attributed to inhibition of cyclin dependent kinases (CDKs) [7]. Nevertheless, how CPX inhibits CDKs is not fully elucidated.…”

Thiosemicarbazones suppress expression of the c-Met oncogene by mechanisms involving lysosomal degradation and intracellular shedding

“…In these studies, NDRG1 mRNA levels were examined as a positive control for cellular iron depletion along with HSP90AA1. The expression of the latter was assessed as it was demonstrated by others that cellular iron chelation decreases HSP90AA1 mRNA expression (62). The HSP90AA1 mRNA translates to HSP90, which is known to act as a chaperone for c-Met protein (63).…”