Controlling the Gatekeeper: Therapeutic Targeting of Nuclear Transport.

Nuclear transport receptors of the karyopherin superfamily of proteins transport macromolecules from one compartment to the other and are critical for both cell physiology and pathophysiology. The nuclear transport machinery is tightly regulated and essential to a number of key cellular processes since the spatiotemporally expression of many proteins and the nuclear transporters themselves is crucial for cellular activities. Dysregulation of the nuclear transport machinery results in localization shifts of specific cargo proteins and associates with the pathogenesis of disease states such as cancer, inflammation, viral illness and neurodegenerative diseases. Therefore, inhibition of the nuclear transport system has future potential for therapeutic intervention and could contribute to the elucidation of disease mechanisms. In this review, we recapitulate clue findings in the pathophysiological significance of nuclear transport processes and describe the development of nuclear transport inhibitors. Finally, clinical implications and results of the first clinical trials are discussed for the most promising nuclear transport inhibitors.

The importin α/ß-specific inhibitor Ivermectin affects HIF-dependent hypoxia response pathways.

Hypoxia-inducible transcription factors (HIFs) regulate hundreds of genes involved in cellular adaptation to reduced oxygen availability. HIFs consist of an O2-labile α-subunit (primarily HIF-1α and HIF-2α) and a constitutive HIF-1ß subunit. In normoxia the HIF-α subunit is hydroxylated by members of a family of prolyl-4-hydroxylase domain (PHD) proteins, PHD1-3, resulting in recognition by von Hippel-Lindau protein, ubiquitination and proteasomal degradation. In contrast, reduced oxygen availability inhibits PHD activity resulting in HIF-1α stabilisation and nuclear accumulation. Nuclear import of HIF-1α mainly depends on classical nuclear localisation signals (NLS) and involves importin α/ß heterodimers. Recently, a specific inhibitor of nuclear import has been identified that inhibits importin α/ß-dependent import with no effects on a range of other nuclear transport pathways involving members of the importin protein family. In this study we evaluated the physiological activity of this importin α/ß-inhibitor (Ivermectin) in the hypoxia response pathway. Treatment with Ivermectin decreases binding activity of HIF-1α to the importin α/ß-heterodimer. Moreover, HIF-1α nuclear localisation, nuclear HIF-1α protein levels, HIF-target gene expression, as well as HIF-transcriptional activity are reduced upon Ivermectin treatment. For the first time, we demonstrate the effect of specific importin α/ß-inhibition on the hypoxic response on the molecular level.

Clinical spectrum of females with HCCS mutation: from no clinical signs to a neonatal lethal form of the microphthalmia with linear skin defects (MLS) syndrome.

BACKGROUND: Segmental Xp22.2 monosomy or a heterozygous HCCS mutation is associated with the microphthalmia with linear skin defects (MLS) or MIDAS (microphthalmia, dermal aplasia, and sclerocornea) syndrome, an X-linked disorder with male lethality. HCCS encodes the holocytochrome c-type synthase involved in mitochondrial oxidative phosphorylation (OXPHOS) and programmed cell death. METHODS: We characterized the X-chromosomal abnormality encompassing HCCS or an intragenic mutation in this gene in six new female patients with an MLS phenotype by cytogenetic analysis, fluorescence in situ hybridization, sequencing, and quantitative real-time PCR. The X chromosome inactivation (XCI) pattern was determined and clinical data of the patients were reviewed. RESULTS: Two terminal Xp deletions of ≥ 11.2 Mb, two submicroscopic copy number losses, one of ~850 kb and one of ≥ 3 Mb, all covering HCCS, 1 nonsense, and one mosaic 2-bp deletion in HCCS are reported. All females had a completely (>98:2) or slightly skewed (82:18) XCI pattern. The most consistent clinical features were microphthalmia/anophthalmia and sclerocornea/corneal opacity in all patients and congenital linear skin defects in 4/6. Additional manifestations included various ocular anomalies, cardiac defects, brain imaging abnormalities, microcephaly, postnatal growth retardation, and facial dysmorphism. However, no obvious clinical sign was observed in three female carriers who were relatives of one patient. CONCLUSION: Our findings showed a wide phenotypic spectrum ranging from asymptomatic females with an HCCS mutation to patients with a neonatal lethal MLS form. Somatic mosaicism and the different ability of embryonic cells to cope with an OXPHOS defect and/or enhanced cell death upon HCCS deficiency likely underlie the great variability in phenotypes.