Karyopherin α2 is a maternal effect gene required for early embryonic development and female fertility in mice.

The nuclear transport of proteins plays an important role in mediating the transition from egg to embryo and distinct karyopherins have been implicated in this process. Here, we studied the impact of KPNA2 deficiency on preimplantation embryo development in mice. Loss of KPNA2 results in complete arrest at the 2cell stage and embryos exhibit the inability to activate their embryonic genome as well as a severely disturbed nuclear translocation of Nucleoplasmin 2. Our findings define KPNA2 as a new maternal effect gene.

Distinguishing the impact of distinct obstructive sleep apnea syndrome (OSAS) and obesity related factors on human monocyte subsets.

Obstructive sleep apnea syndrome (OSAS) and obesity go hand in hand in the majority of patients and both are associated with a systemic inflammation, immune disturbance and comorbidities such as cardiovascular disease. However, the unambiguous impact of OSAS and obesity on the individual inflammatory microenvironment and the immunological consequences of human monocytes has not been distinguished yet. Therefore, aim of this study was to investigate the impact of OSAS and obesity related factors on the inflammatory microenvironment by performing flow cytometric whole blood measurements of CD14/CD16 monocyte subsets in normal weight OSAS patients, patients with obesity but without OSAS, and patients with OSAS and obesity, compared to healthy donors. Moreover, explicitly OSAS and obesity related plasma levels of inflammatory mediators adiponectin, leptin, lipocalin and metalloproteinase-9 were determined and the influence of different OSAS and obesity related factors on cytokine secretion and expression of different adhesion molecules by THP-1 monocytes was analysed. Our data revealed a significant redistribution of circulating classical and intermediate monocytes in all three patient cohorts, but differential effects in terms of monocytic adhesion molecules CD11a, CD11b, CD11c, CX3CR1, CD29, CD49d, and plasma cytokine levels. These data were reflected by differential effects of OSAS and obesity related factors leptin, TNFα and hypoxia on THP-1 cytokine secretion patterns and expression of adhesion molecules CD11b and CD49d. In summary, our data revealed differential effects of OSAS and obesity, which underlines the need for a customized therapeutic regimen with respect to the individual weighting of these overlapping diseases.

Characterization of the nuclear import of the human CHD4-NuRD complex.

Chromatin remodeling enzymes form large multiprotein complexes that play central roles in regulating access to the genome. Here, we characterize the nuclear import of the human CHD4 protein. We show that CHD4 enters the nucleus by means of several importin-α proteins (1, 5, 6 and 7), but independently of importin ß1. Importin α1 directly interacts with a monopartite 'KRKR'-motif in the N-terminus of CHD4 (amino acids 304-307). However, alanine mutagenesis of this motif only leads to an ∼50% reduction in nuclear localization of CHD4, implying that there are additional import mechanisms. Interestingly, we could show that CHD4 was already associated with the nucleosome remodeling deacetylase (NuRD) core subunits, such as MTA2, HDAC1 and RbAp46 (also known as RBBP7), in the cytoplasm, suggesting an assembly of the NuRD core complex before nuclear import. We propose that, in addition to the importin-α-dependent nuclear localization signal, CHD4 is dragged into the nucleus by a 'piggyback' mechanism using the import signals of the associated NuRD subunits.

miR663 Prevents Epo Inhibition Caused by TNF-Alpha in Normoxia and Hypoxia.

OBJECTIVE: In chronic inflammatory diseases, proinflammatory cytokines such as TNF-α are present in high amounts in the circulation and are associated with anemia in most cases. Experimental studies have shown that TNF-α inhibits the synthesis of erythropoietin (Epo), the main stimulant of hematopoiesis. Our aim was to figure out which microRNAs are involved in the Epo repression by TNF-α. METHODS: First, we determined the dose of TNF-α in HepG2 cells that has no cytotoxic effect by using MTT assays and that inhibits Epo synthesis by qRT-PCR and ELISA. Then, we performed the microRNA array study with TNF-α (20 ng/ml)-treated cells, and the array results were confirmed by qRT-PCR. We transfected the miR663 group with the mimic-miR663 (30 pmol) for 24 hrs; other groups were treated with a transfection reagent followed by treatment of TNF-α for 24 hrs; miR663 groups were treated with TNF-α for 24 hrs; and the control group was incubated with normal medium. We analyzed Epo mRNA levels by qRT-PCR. If mimic-miR663 prevents the Epo repression by TNF-α, more Epo-dependent UT-7 cells would survive. Therefore, we cocultured HepG2 cells with UT-7 cells. The percentage of apoptotic UT-7 cells was determined by TUNEL assays. RESULTS: According to our array study, TNF-α significantly decreases miR663 expression. After transfection of miR663 mimics into HepG2 cells, TNF-alpha was unable to decrease Epo mRNA amounts. Furthermore, mimic-miR663 transfection resulted in a lower apoptosis rate of UT-7 cells in coculture experiments. CONCLUSIONS: miR663 is involved in Epo mRNA production and that is able to prevent or reverse the inhibitory effect of TNF-α. In our coculture study, transfecting HepG2 cells with miR663 mimics decreased the apoptosis of UT-7 cells.

Selinexor decreases HIF-1α via inhibition of CRM1 in human osteosarcoma and hepatoma cells associated with an increased radiosensitivity.

BACKGROUND: The nuclear pore complexes (NPCs) are built of about 30 different nucleoporins and act as key regulators of molecular traffic between the cytoplasm and the nucleus for sizeable proteins (> 40 kDa) which must enter the nucleus. Various nuclear transport receptors are involved in import and export processes of proteins through the nuclear pores. The most prominent nuclear export receptor is chromosome region maintenance 1 (CRM1), also known as exportin 1 (XPO1). One of its cargo proteins is the prolyl hydroxylase 2 (PHD2) which is involved in the initiation of the degradation of hypoxia-inducible factors (HIFs) under normoxia. HIFs are proteins that regulate the cellular adaptation under hypoxic conditions. They are involved in many aspects of cell viability and play an important role in the hypoxic microenvironment of cancer. In cancer, CRM1 is often overexpressed thus being a putative target for the development of new cancer therapies. The newly FDA-approved pharmaceutical Selinexor (KPT-330) selectively inhibits nuclear export via CRM1 and is currently tested in additional Phase-III clinical trials. In this study, we investigated the effect of CRM1 inhibition on the subcellular localization of HIF-1α and radiosensitivity. METHODS: Human hepatoma cells Hep3B and human osteosarcoma cells U2OS were treated with Selinexor. Intranuclear concentration of HIF-1α protein was measured using immunoblot analysis. Furthermore, cells were irradiated with 2-8 Gy after treatment with Selinexor compared to untreated controls. RESULTS: Selinexor significantly reduced the intranuclear level of HIF-1α protein in human hepatoma cells Hep3B and human osteosarcoma cells U2OS. Moreover, we demonstrated by clonogenic survival assays that Selinexor leads to dose-dependent radiosensitization in Hep3B-hepatoma and U2OS-osteosarcoma cells. CONCLUSION: Targeting the HIF pathway by Selinexor might be an attractive tool to overcome hypoxia-induced radioresistance.

The Nuclear Export Inhibitor Selinexor Inhibits Hypoxia Signaling Pathways And 3D Spheroid Growth Of Cancer Cells.

PURPOSE: The nucleocytoplasmic transport of macromolecules is critical for both cell physiology and pathophysiology. Exportin 1 (XPO1), the major nuclear export receptor, is involved in the cellular adaptation to reduced oxygen availability by controlling the nuclear activity of the hypoxia-inducible factors (HIFs). Recently, a specific inhibitor of XPO1, selinexor (KPT-330), has been identified that inhibits nuclear export of cargo proteins by binding to the XPO1 cargo-binding pocket. PATIENTS AND METHODS: We used different cancer cell lines from human tissues and evaluated the physiological activity of selinexor on the hypoxia response pathway in two-dimensional (2D) monolayer cell cultures in quantitative real-time (qRT)-PCR experiments and luciferase reporter gene assays. A three-dimensional (3D) tumor spheroid culture model of MCF-7 breast cancer cells was established to analyze the effect of selinexor on 3D tumor spheroid structure, formation and viability. RESULTS: Selinexor treatment reduces HIF-transcriptional activity and expression of the HIF-1 target gene solute carrier family 2 member 1 (SLC2A1). Moreover, 3D tumor spheroid structure, formation and viability are inhibited in response to selinexor-induced nuclear export inhibition. CONCLUSION: Here, we demonstrate the effect of specific XPO1-inhibition on the hypoxic response on the molecular level in 2D and 3D culture models of MCF-7 cells.

Septin 9 isoform 1 (SEPT9_i1) specifically interacts with importin-α7 to drive hypoxia-inducible factor (HIF)-1α nuclear translocation.

We have shown previously that septin 9 isoform 1 (SEPT9_i1) protein associates with hypoxia-inducible factor (HIF)-1α to augment HIF-1 transcriptional activity by driving its importin-α-mediated nuclear translocation. Using in vitro and in vivo binding assays we identified that HIF-1α interacts with importin-α5 and importin-α7 in prostate cancer cells but only importin-α7 interacts with SEPT9_i1. The interaction with importin-α7 was dependent on the first 25 amino acids of SEPT9_i1 that are unique compared to other members of the mammalian septin family. Depletion of endogenous importin-α7 reduced HIF-1α levels in the nucleus. Our results provide evidence that there are importin-α specificities in the cytosolic/nuclear translocation process of HIF-1α protein, which may act differently under certain pathophysiological circumstances where SEPT9_i1 is overexpressed.

1H-NMR spectroscopy shows cellular uptake of HEPES buffer by human cell lines-an effect to be considered in cell culture experiments.

HEPES is commonly used in cell culture media as a buffering substance. Compared to the bicarbonate/CO2 buffer system, it does not require a CO2 atmosphere, thereby ensuring stable pH values during handling of cell culture media outside of an incubator. Due to its intrinsic charge, HEPES is considered not to be taken up by cells, which was a prerequisite during buffer development for cell culture by Good and colleagues. However, during the last years, evidence has emerged that HEPES seems to be taken up into cells and that it has major effects on cellular functions. Investigating three different cell lines (MCF-7, U2OS, HeLa) showed that all of them accommodated HEPES-containing medium, i.e., they survive and proliferate in the presence of HEPES. Determination of intracellular metabolites revealed the presence of HEPES for all cell lines. Further analysis of MCF-7 cells showed that even 48 h after medium exchange from HEPES-containing medium to HEPES-free medium, intracellular HEPES could still be detected. Thus, contrary to the common view, HEPES is taken up by cells which should be taken into consideration for studies of specific cellular functions. Graphical abstract ᅟ.

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.

Hey1- and p53-dependent TrkC proapoptotic activity controls neuroblastoma growth.

The neurotrophin-3 (NT-3) receptor tropomyosin receptor kinase C (TrkC/NTRK3) has been described as a dependence receptor and, as such, triggers apoptosis in the absence of its ligand NT-3. This proapoptotic activity has been proposed to confer a tumor suppressor activity to this classic tyrosine kinase receptor (RTK). By investigating interacting partners that might facilitate TrkC-induced cell death, we have identified the basic helix-loop-helix (bHLH) transcription factor Hey1 and importin-α3 (karyopherin alpha 4 [KPNA4]) as direct interactors of TrkC intracellular domain, and we show that Hey1 is required for TrkC-induced apoptosis. We propose here that the cleaved proapoptotic portion of TrkC intracellular domain (called TrkC killer-fragment [TrkC-KF]) is translocated to the nucleus by importins and interacts there with Hey1. We also demonstrate that Hey1 and TrkC-KF transcriptionally silence mouse double minute 2 homolog (MDM2), thus contributing to p53 stabilization. p53 transcriptionally regulates the expression of TrkC-KF cytoplasmic and mitochondrial interactors cofactor of breast cancer 1 (COBRA1) and B cell lymphoma 2-associated X (BAX), which will subsequently trigger the intrinsic pathway of apoptosis. Of interest, TrkC was proposed to constrain tumor progression in neuroblastoma (NB), and we demonstrate in an avian model that TrkC tumor suppressor activity requires Hey1 and p53.

Karyopherin α-3 is a key protein in the pathogenesis of spinocerebellar ataxia type 3 controlling the nuclear localization of ataxin-3.

Spinocerebellar ataxia type 3 (SCA3) is a neurodegenerative disorder caused by a CAG expansion in the ATXN3 gene leading to a polyglutamine expansion in the ataxin-3 protein. The nuclear presence and aggregation of expanded ataxin-3 are critical steps in disease pathogenesis. To identify novel therapeutic targets, we investigated the nucleocytoplasmic transport system by screening a collection of importins and exportins that potentially modulate this nuclear localization. Using cell, Drosophila, and mouse models, we focused on three transport proteins, namely, CRM1, IPO13, KPNA3, and their respective Drosophila orthologs Emb, Cdm, and Kap-α3. While overexpression of CRM1/Emb demonstrated positive effects in Drosophila, KPNA3/Kap-α3 emerged as the most promising target, as knockdown via multiple RNAi lines demonstrated its ability to shuttle both truncated and full-length expanded ataxin-3, rescue neurodegeneration, restore photoreceptor formation, and reduce aggregation. Furthermore, KPNA3 knockout in SCA3 mice resulted in an amelioration of molecular and behavioral disturbances such as total activity, anxiety, and gait. Since KPNA3 is known to function as an import protein and recognize nuclear localization signals (NLSs), this work unites ataxin-3 structure to the nuclear pore machinery and provides a link between karyopherins, NLS signals, and polyglutamine disease, as well as demonstrates that KPNA3 is a key player in the pathogenesis of SCA3.

Interplay between environmentally modulated feedback loops - hypoxia and circadian rhythms - two sides of the same coin?

Sensing of environmental parameters is critically important for cells of metazoan organisms. Members of the superfamily of bHLH-PAS transcription factors, involved in oxygen sensing and circadian rhythm generation, are important players in such molecular pathways. The interplay between both networks includes a so far unknown factor, connecting PER2 (circadian clocks) to hypoxia sensing (HIF-1 α) to result in a more adapted state of homeostasis at the right time.

ARNT is a potential direct HIF-1 target gene in human Hep3B hepatocellular carcinoma cells.

BACKGROUND: The transcription factor aryl hydrocarbon receptor nuclear translocator (ARNT) participates in the hypoxia-inducible factor (HIF) pathway which senses a decline in cellular oxygen tension. In hypoxia, HIF-1α and ARNT form the transcriptional active complex HIF-1 followed by the expression of target genes. ARNT is considered as constitutively expressed and unaffected by hypoxia. However, certain tumour cell lines derived from different entities are capable to elevate ARNT expression under hypoxic conditions which implies a survival benefit. It was demonstrated that high ARNT protein levels mediate radioresistance in tumour cells. Furthermore, a HIF-1α-driven feed-forward loop leading to augmented HIF signalling was discovered in Hep3B cells. Herein HIF-1α elevates the mRNA and protein expression of its binding partner ARNT in hypoxia. However, the detailed mechanism remained unclear. The objective of this study was to test whether HIF-1α might directly regulate ARNT expression by recruitment to the ARNT promoter. METHODS: Chromatin immunoprecipitation (ChIP), CRISPR/Cas9 genome editing, Western blotting, quantitative RT-PCR and reporter gene assays were applied. The unpaired t test was used for statistical analysis. RESULTS: ChIP assays revealed the binding of both HIF-1α and ARNT to the ARNT promoter in hypoxia. The relevance of this particular region for hypoxic ARNT induction was confirmed by CRISPR/Cas9 genome editing. ARNT normoxic basal expression and hypoxic inducibility was reduced in genome-edited Hep3B cells. This phenotype was accompanied with impaired HIF signalling and was rescued by ARNT overexpression. CONCLUSIONS: The results indicate ARNT to be a putative HIF-1 target gene and a limiting factor in this model.

In-depth Characterization of the Homodimerization Domain of the Transcription Factor THAP1 and Dystonia-Causing Mutations Therein.

Mutations in the THAP1 gene encoding the transcription factor THAP1 have been shown to cause DYT6 dystonia. THAP1 contains a highly conserved THAP zinc finger at its N-terminal region which allows specific binding to its target sequences as well as a coiled-coil domain (amino acids 139-190) towards its C-terminus postulated as a protein-protein-binding motif. While several DYT6-causing mutations within the THAP domain were shown to decrease THAP1 activity in transcriptional regulation and DNA-binding, the role of mutations within the coiled-coil domain is rather unknown. Therefore, assigning a function to this domain may enable functional testing of mutations in this region. Notably, THAP1 and other THAP proteins form homodimers; however, the responsible domain has not been elucidated in detail. We show that the region of amino acids 139-185 is involved in formation of THAP1 homodimers by using yeast-two-hybrid, GST pull-down, and cross-linking assays. Surprisingly, all nine reported DYT6-causing missense mutations within this region had no effect on dimerization of THAP1 in GST pull-down and formaldehyde cross-linking assays. In conclusion, we demonstrated that a region of 47 amino acids is involved in THAP1 homodimerization but mutations in this region seem not to impair this mechanism.

Impact of hypoxia inducible factors on estrogen receptor expression in breast cancer cells.

In women breast cancer is still the most commonly diagnosed cancer. This type of cancer is classified as a hormone-dependent tumor. Estrogen receptor (ER) expression and functional status contribute to breast cancer development and progression. Another important factor associated with cancer is hypoxia which is defined as the state of reduced oxygen availability in tissues. Intratumoral hypoxia results in the activation of the hypoxia inducible factors (HIFs). HIFs are heterodimeric transcription factors involved in the regulation of many cellular processes, such as angiogenesis, anaerobic metabolism, cell proliferation/survival, and promotion of metastasis. In this study we evaluated the interplay between hypoxia, HIF stabilization and the ER-α/ß-ratio in several ER-positive breast cancer cell lines. Hypoxia was shown to inhibit ER expression in ER-positive breast cancer cells. Further experiments using the hypoxia mimetic CoCl2 and HIF-1α knockdown cells indicated that the influence of hypoxia on breast cancer cells involves other pathways than the molecular oxygen sensing pathway. Moreover, we demonstrated that MCF-7 cells in long-term culture lost part of their ability to respond to hypoxic incubation. Understanding the relationships between HIF, ER-α and ER-ß expression holds the promise of the development of new therapeutic agents and may provide future advances in prognosis.

Targeting hypoxia to overcome radiation resistance in head & neck cancers: real challenge or clinical fairytale?

INTRODUCTION: Tumor hypoxia is a major cause for failure of therapy in patients with inoperable head and neck cancers. AREAS COVERED: Various anti-hypoxic treatment strategies (e.g. hyperbaric oxygenation, hypoxic cell sensitizers) have been tested in clinical trials in head and neck cancer over the past 30 years and have shown modest improvements in combination with radiotherapy in meta-analyses. Anemia worsens tumor hypoxia, but anemia correction had no significant effect. New approaches (e.g. anti-HIF-directed molecular therapies) have just entered early clinical studies and data are lacking. Expert commentary: A new attractive and promising approach derives from recent advances in imaging and radiotherapy delivery. Progress in imaging of hypoxia (e.g. by positron emission tomography) can select patients for specific therapies and may, in particular, facilitate anti-hypoxia-directed radiotherapy which has become feasible with advanced radiotherapy techniques (IMRT with 'dose-painting'). The combination of both methods may offer a powerful tool for effective targeting of hypoxia in the near future.

Prolyl-4-Hydroxylase 2 Potentially Contributes to Hepatocellular Carcinoma-Associated Erythrocytosis by Maintaining Hepatocyte Nuclear Factor-4α Expression.

BACKGROUND: Increased red blood cell count (Erythrocytosis) is an important paraneoplastic syndrome of hepatocellular carcinoma (HCC) and is a significant risk factor for lethal lung artery thromboembolism. HCC-associated erythrocytosis is partially caused by the ability of several HCC cells to produce erythropoietin (EPO). Prolyl-4-hydroxylase 2 (PHD2) is an enzyme encoded by the gene EGLN1. The best-known function of PHD2 is to mediate the oxygen-dependent degradation of the labile α-subunit of hypoxia-inducible factor (HIF). However, there is increasing evidence that PHD2 also regulates HIF-independent pathways by interacting with other substrates. METHODS: In the EPO-producing human HCC cell line HepG2, the expression of PHD2 gene was silenced with siRNA. EPO production was estimated using quantitative PCR and ELISA. RESULTS: In HepG2 cells, PHD2 suppresses the activity of TGF-ß1 pathway and consequently maintains the expression of hepatocyte nuclear factor-4α (HNF-4α), an important transcription factor promoting the EPO expression in hepatocytes. PHD2 knockdown caused a marked reduction of EPO production. HIF seemed not to be involved in this biology. CONCLUSION: Our findings show that PHD2 represents a potential contributing factor for HCC-associated erythrocytosis. Selective inhibition of PHD2 in HCC cells might be considered as a new way to manage erythrocytosis in HCC patients.

The expression level of the transcription factor Aryl hydrocarbon receptor nuclear translocator (ARNT) determines cellular survival after radiation treatment.

BACKGROUND: Tumour hypoxia promotes radioresistance and is associated with poor prognosis. The transcription factor Aryl hydrocarbon receptor nuclear translocator (ARNT), also designated as Hypoxia-inducible factor (HIF)-1ß, is part of the HIF pathway which mediates cellular adaptations to oxygen deprivation and facilitates tumour progression. The subunits HIF-1α and ARNT are key players within this pathway. HIF-1α is regulated in an oxygen-dependent manner whereas ARNT is considered to be constitutively expressed. However, there is mounting evidence that certain tumour cells are capable to elevate ARNT in hypoxia which suggests a survival benefit. Therefore the objective of this study was to elucidate effects of an altered ARNT expression level on the cellular response to radiation. METHODS: Different human cell lines (Hep3B, MCF-7, 786-Owt, 786-Ovhl, RCC4wt and RCC4vhl) originating from various tumour entities (Hepatocellular carcinoma, breast cancer and renal cell carcinoma respectively) were X-irradiated using a conventional linear accelerator. Knockdown of ARNT expression was achieved by transient siRNA transfection. Complementary experiments were performed by forced ARNT overexpression using appropriate plasmids. Presence/absence of ARNT protein was confirmed by Western blot analysis. Clonogenic survival assays were performed in order to determine cellular survival post irradiation. Statistical comparison of two groups was achieved by the unpaired t-test. RESULTS: The results of this study indicate that ARNT depletion renders tumour cells susceptible to radiation whereas overexpression of this transcription factor confers radioresistance. CONCLUSIONS: These findings provide evidence to consider ARNT as a drug target and as a predictive marker in clinical applications concerning the response to radiation.

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.