Importazole, a Small Molecule Inhibitor of the Transport Receptor Importin-β

Abstract

During interphase, the transport receptor importin-β carries cargoes into the nucleus, where RanGTP releases them. A similar mechanism operates in mitosis to generate a gradient of active spindle assembly factors around mitotic chromosomes. Importin-β and RanGTP have been implicated in additional cellular processes, but the precise roles of the Ran/importin-β pathway throughout the cell cycle remain poorly understood. We implemented a FRET-based, high-throughput small molecule screen for compounds that interfere with the interaction between RanGTP and importin-β and identified importazole, a 2,4-diaminoquinazoline. Importazole specifically blocks importin-β-mediated nuclear import both in Xenopus egg extracts and cultured cells, without disrupting transportin-mediated nuclear import or CRM1-mediated nuclear export. When added during mitosis, importazole impairs the release of an importin-β cargo FRET probe and causes both predicted and novel defects in spindle assembly. Together, these results indicate that importazole specifically inhibits the function of importin-β, likely by altering its interaction with RanGTP. Importazole is a valuable tool to evaluate the function of importin-β/RanGTP pathway at specific stages during the cell cycle.

In vivo loss-of-function screens identify KPNB1 as a new druggable oncogene in epithelial ovarian cancer

“…2 B-D). We then examined the antitumor effect of pharmacological inhibition of KPNB1 using importazole, a small molecule that specifically inhibits the importin β family (17). Consistent with our siRNA results, blockade of KPNB1 by importazole also significantly reduced cell proliferation/survival in a dosedependent manner (Fig.…”

Essential elements for translation: the germline factor Vasa functions broadly in somatic cells

“…6B) as well as Kpna2 itself, suggesting a physical interaction between Kpna2 and Vasa. Importazole (Soderholm et al, 2011), a specific functional inhibitor of Importin β, a partner of Kpna2, diminished the characteristic vasa mRNA and Vasa protein distribution, as well as other mRNA enrichment, both on the nuclear envelope and on the spindle (Fig. 6C, Importazole-Vasa IF; supplementary material Fig.…”

Targeting the Nuclear Import Receptor Kpnβ1 as an Anticancer Therapeutic

“…Its nuclear-cytoplasmic transport is regulated via calcium exposure (41), where NFAT is predominantly cytoplasmic; however, an increase in intracellular calcium levels leads to its nuclear accumulation. Soderholm and colleagues (2011) showed by fluorescence microscopy that inhibiting nuclear import via Kpnb1 prevented the nuclear accumulation of NFAT-GFP in response to stimulation with the calcium ionophore, ionomycin (16). We assayed for nuclear NFAT following cotreatment with ionomycin and the compounds identified in the in silico screen.…”

“…Ivermectin is a broadspectrum antiparasitic reagent recently found to inhibit Kpna/b, but it does not appear to block import mediated by Kpnb1 alone (14). Karyostatin 1A (15) and importazole (16) are the first novel small molecule inhibitors of Kpnb1 to be identified, which inhibit RanGTP binding to Kpnb1; however, their off-target effects have not yet been examined, nor have their anticancer effects. There thus remains a need for the identification of novel effective Kpnb1 inhibitors and for these to be tested for their effects on cancer cells.…”