Protein kinase C-mediated modulation of FIH-1 expression by the homeodomain protein CDP/Cut/Cux

The Asparagine Hydroxylase FIH: A Unique Oxygen Sensor

Significance: Limited oxygen availability (hypoxia) commonly occurs in a range of physiological and pathophysiological conditions, including embryonic development, physical exercise, inflammation, and ischemia. It is thus vital for cells and tissues to monitor their local oxygen availability to be able to adjust in case the oxygen supply is decreased. The cellular oxygen sensor factor inhibiting hypoxia-inducible factor (FIH) is the only known asparagine hydroxylase with hypoxia sensitivity. FIH uniquely combines oxygen and peroxide sensitivity, serving as an oxygen and oxidant sensor. Recent Advances: FIH was first discovered in the hypoxia-inducible factor (HIF) pathway as a modulator of HIF transactivation activity. Several other FIH substrates have now been identified outside the HIF pathway. Moreover, FIH enzymatic activity is highly promiscuous and not limited to asparagine hydroxylation. This includes the FIH-mediated catalysis of an oxygen-dependent stable (likely covalent) bond formation between FIH and selected substrate proteins (called oxomers [oxygen-dependent stable protein oligomers]). Critical Issues: The (patho-)physiological function of FIH is only beginning to be understood and appears to be complex. Selective pharmacologic inhibition of FIH over other oxygen sensors is possible, opening new avenues for therapeutic targeting of hypoxia-associated diseases, increasing the interest in its (patho-)physiological relevance. Future Directions: The contribution of FIH enzymatic activity to disease development and progression should be analyzed in more detail, including the assessment of underlying molecular mechanisms and relevant FIH substrate proteins. Also, the molecular mechanism(s) involved in the physiological functions of FIH remain(s) to be determined. Furthermore, the therapeutic potential of recently developed FIH-selective pharmacologic inhibitors will need detailed assessment. Antioxid. Redox Signal. 37, 913-935.

Redox-sensitive signaling pathways in renal cell carcinoma

Renal cell carcinoma (RCC) is one of the most lethal urological cancers, highly resistant to chemo and radiotherapy. Obesity and smoking are the best-known risk factors of RCC, both related to oxidative stress presence, suggesting a significant role in RCC development and maintenance. Surgical resection is the treatment of choice for localized RCC; however, this neoplasia is hardly diagnosable at its initial stages, occurring commonly in late phases and even when metastasis is already present. Systemic therapies are the option against RCC in these more advanced stages, such as cytokine therapy or a combination of tyrosine kinase inhibitors with immunotherapies; nevertheless, these strategies are still insufficient. A field poorly analyzed in this neoplasia is the status of cell signaling pathways sensible to the redox state, which have been associated with the development and maintenance of RCC. This review focuses on alterations reported in the following redox-sensitive molecules and signaling pathways in RCC: mitogen-activated protein kinases, protein kinase B (AKT)/tuberous sclerosis complex 2/mammalian target of rapamycin C1, AKT/glycogen synthase kinase 3/β-catenin, nuclear factor κB/inhibitor of κB/epidermal growth factor receptor, and protein kinase Cζ/cut-like homeodomain protein/factor inhibiting hypoxia-inducible factor (HIF)/HIF as potential targets for redox therapy.

Molecular Insights into the Oxygen-Sensing Pathway and Erythropoietin Expression Regulation in Erythropoiesis

Erythropoiesis is regulated by several factors, including the oxygen-sensing pathway as the main regulator of erythropoietin (EPO) synthesis in the kidney. The release of EPO from the kidney and its binding to the EPO receptor (EPOR) on erythrocyte progenitor cells in the bone marrow results in increased erythropoiesis. Any imbalance in these homeostatic mechanisms can lead to dysregulated erythropoiesis and hematological disorders. For example, mutations in genes encoding key players of oxygen-sensing pathway and regulation of EPO production (HIF-EPO pathway), namely VHL, EGLN, EPAS1 and EPO, are well known causative factors that contribute to the development of erythrocytosis. We aimed to investigate additional molecular mechanisms involved in the HIF-EPO pathway that correlate with erythropoiesis. To this end, we conducted an extensive literature search and used several in silico tools. We identified genes encoding transcription factors and proteins that control transcriptional activation or repression; genes encoding kinases, deacetylases, methyltransferases, conjugating enzymes, protein ligases, and proteases involved in post-translational modifications; and genes encoding nuclear transport receptors that regulate nuclear transport. All these genes may modulate the stability or activity of HIF2α and its partners in the HIF-EPO pathway, thus affecting EPO synthesis. The theoretical information we provide in this work can be a valuable tool for a better understanding of one of the most important regulatory pathways in the process of erythropoiesis. This knowledge is necessary to discover the causative factors that may contribute to the development of hematological diseases and improve current diagnostic and treatment solutions in this regard.

Renal Carcinogenesis, Tumor Heterogeneity, and Reactive Oxygen Species: Tactics Evolved

SIGNIFICANCE

The number of kidney cancers is growing 3-5% each year due to unknown etiologies. Intra- and inter-tumor mediators increase oxidative stress and drive tumor heterogeneity. Recent Advances: Technology advancement in state-of-the-art instrumentation and methodologies allows researchers to detect and characterize global landscaping modifications in genes, proteins, and pathophysiology patterns at the single-cell level.

CRITICAL ISSUES

We postulate that the sources of reactive oxygen species (ROS) and their activation within subcellular compartments will change over a timeline of tumor evolvement and contribute to tumor heterogeneity. Therefore, the complexity of intracellular changes within a tumor and ROS-induced tumor heterogeneity coupled to the advancement of detecting these events globally are limited at the level of data collection, organization, and interpretation using software algorithms and bioinformatics.

FUTURE DIRECTIONS

Integrative and collaborative research, combining the power of numbers with careful experimental design, protocol development, and data interpretation, will translate cancer biology and therapeutics to a heightened level or leave the abundant raw data as stagnant and underutilized. Antioxid. Redox Signal. 25, 685-701.

FIH-1-Mint3 axis does not control HIF-1 transcriptional activity in nucleus pulposus cells

The objective of this study was to determine the role of FIH-1 in regulating HIF-1 activity in the nucleus pulposus (NP) cells and the control of this regulation by binding and sequestration of FIH-1 by Mint3. FIH-1 and Mint3 were both expressed in the NP and were shown to strongly co-localize within the cell nucleus. Although both mRNA and protein expression of FIH-1 decreased in hypoxia, only Mint3 protein levels were hypoxiasensitive. Overexpression of FIH-1 was able to reduce HIF-1 function, as seen by changes in activities of hypoxia response element-luciferase reporter and HIF-1-C-TAD and HIF-2-TAD. Moreover, co-transfection of either full-length Mint3 or the N terminus of Mint3 abrogated FIH-1-dependent reduction in HIF-1 activity under both normoxia and hypoxia. Nuclear levels of FIH-1 and Mint3 decreased in hypoxia, and the use of specific nuclear import and export inhibitors clearly showed that cellular compartmentalization of overexpressed FIH-1 was critical for its regulation of HIF-1 activity in NP cells. Interestingly, microarray results after stable silencing of FIH-1 showed no significant changes in transcripts of classical HIF-1 target genes. However, expression of several other transcripts, including those of the Notch pathway, changed in FIH-1-silenced cells. Moreover, co-transfection of Notch-ICD could restore suppression of HIF-1-TAD activity by exogenous FIH-1. Taken together, these results suggest that, possibly due to low endogenous levels and/or preferential association with substrates such as Notch, FIH-1 activity does not represent a major mechanism by which NP cells control HIF-1-dependent transcription, a testament to their adaptation to a unique hypoxic niche.

The hypoxia-inducible miR-429 regulates hypoxia-inducible factor-1α expression in human endothelial cells through a negative feedback loop

Hypoxia-inducible factors (HIFs) 1 and 2 are dimeric α/β transcription factors that regulate cellular responses to low oxygen. HIF-1 is induced first, whereas HIF-2 is associated with chronic hypoxia. To determine how HIF1A mRNA, the inducible subunit of HIF-1, is regulated during hypoxia, we followed HIF1A mRNA levels in primary HUVECs over 24 hours using quantitative PCR. HIF1A and VEGF A (VEGFA) mRNA, a transcriptional target of HIF-1, increased ∼ 2.5- and 8-fold at 2-4 hours, respectively. To determine how the mRNAs were regulated, we identified a microRNA (miRNA), miR-429, that destabilized HIF1A message and decreased VEGFA mRNA by inhibiting HIF1A. Target protector analysis, which interferes with miRNA-mRNA complex formation, confirmed that miR-429 targeted HIF1A message. Desferoxamine treatment, which inhibits the hydroxylases that promote HIF-1α protein degradation, stabilized HIF-1 activity during normoxic conditions and elevated miR-429 levels, demonstrating that HIF-1 promotes miR-429 expression. RNA-sequencing-based transcriptome analysis indicated that inhibition of miRNA-429 in HUVECs up-regulated 209 mRNAs, a number of which regulate angiogenesis. The results demonstrate that HIF-1 is in a negative regulatory loop with miR-429, that miR-429 attenuates HIF-1 activity by decreasing HIF1A message during the early stages of hypoxia before HIF-2 is activated, and this regulatory network helps explain the HIF-1 transition to HIF-2 during chronic hypoxia in endothelial cells.

Overexpression of DICER1 induced by the upregulation of GATA1 contributes to the proliferation and apoptosis of leukemia cells

Dicer, a member of the RNase III family, is the key enzyme required for the biogenesis of microRNAs and small interfering RNAs. Recent evidence indicates that DICER1 expression levels vary among different solid tumors and decreased or increased DICER1 expression has been associated with aggressive cancers. In this study, we assessed DICER1 expression levels in acute myeloid leukemia (AML) and investigated its biological effects and transcriptional regulation in leukemia cell lines. We demonstrated that DICER1 was overexpressed in AML patients and leukemia cell lines by real-time quantitative PCR and western blot analysis. A functional assay demonstrated that the silencing of DICER1 inhibited cell proliferation and promoted apoptosis in leukemia cell lines. We also demonstrated that DICER1 was upregulated by the hematopoietic transcription factor, GATA1, through luciferase, electrophoretic mobility shift and chromatin immunoprecipitation assays. These data suggest that DICER1 plays an important role in AML and the finding that the upregulation of DICER1 is induced by GATA1 may provide a framework for the understanding of differential DICER1 expression levels in multiple types of cancer.

MYCT1-TV, a novel MYCT1 transcript, is regulated by c-Myc and may participate in laryngeal carcinogenesis

BACKGROUND

MYCT1, a putative target of c-Myc, is a novel candidate tumor suppressor gene cloned from laryngeal squamous cell carcinoma (LSCC). Its transcriptional regulation and biological effects on LSCC have not been clarified.

METHODOLOGY/PRINCIPAL FINDINGS

Using RACE assay, we cloned a 1106 bp transcript named Myc target 1 transcript variant 1 (MYCT1-TV) and confirmed its transcriptional start site was located at 140 bp upstream of the ATG start codon of MYCT1-TV. Luciferase, electrophoretic mobility shift and chromatin immunoprecipitation assays confirmed c-Myc could regulate the promoter activity of MYCT1-TV by specifically binding to the E-box elements within -886 to -655 bp region. These results were further verified by site-directed mutagenesis and RNA interference (RNAi) assays. MYCT1-TV and MYCT1 expressed lower in LSCC than those in paired adjacent normal laryngeal tissues, and overexpression of MYCT1-TV and MYCT1 could inhibit cell proliferation and invasion and promote apoptosis in LSCC cells.

CONCLUSIONS/SIGNIFICANCE

Our data indicate that MYCT1-TV, a novel MYCT1 transcript, is regulated by c-Myc and down-regulation of MYCT1-TV/MYCT1 could contribute to LSCC development and function.

High doses of TGF-β potently suppress type I collagen via the transcription factor CUX1

Uncontrolled expression of collagen often leads to tissue scarring and loss of organ function. In this study, we identify a molecular mechanism that may enable us to switch off collagen production when unnecessary (i.e., fibrosis). We conclude that CUX1, which is a CCAAT binding factor displacement protein, may serve as a therapeutic target in treating fibrosis.

Transforming growth factor-β (TGF-β) is an inducer of type I collagen, and uncontrolled collagen production leads to tissue scarring and organ failure. Here we hypothesize that uncovering a molecular mechanism that enables us to switch off type I collagen may prove beneficial in treating fibrosis. For the first time, to our knowledge, we provide evidence that CUX1 acts as a negative regulator of TGF-β and potent inhibitor of type I collagen transcription. We show that CUX1, a CCAAT displacement protein, is associated with reduced expression of type I collagen both in vivo and in vitro. We show that enhancing the expression of CUX1 results in effective suppression of type I collagen. We demonstrate that the mechanism by which CUX1 suppresses type I collagen is through interfering with gene transcription. In addition, using an in vivo murine model of aristolochic acid (AA)-induced interstitial fibrosis and human AA nephropathy, we observe that CUX1 expression was significantly reduced in fibrotic tissue when compared to control samples. Moreover, silencing of CUX1 in fibroblasts from kidneys of patients with renal fibrosis resulted in increased type I collagen expression. Furthermore, the abnormal CUX1 expression was restored by addition of TGF-β via the p38 mitogen-activated protein kinase pathway. Collectively, our study demonstrates that modifications of CUX1 expression lead to aberrant expression of type I collagen, which may provide a molecular basis for fibrogenesis.

Factor inhibiting HIF (FIH-1) promotes renal cancer cell survival by protecting cells from HIF-1α-mediated apoptosis

Background:

Clear cell renal cell carcinoma (CCRCC) is the commonest form of kidney cancer. Up to 91% have biallelic inactivation of VHL, resulting in stabilisation of HIF-α subunits. Factor inhibiting HIF-1 is an enzyme that hydroxylates HIF-α subunits and prevents recruitment of the co-activator CBP/P300. An important question is whether FIH-1 controls HIF activity in CCRCC.

Methods:

Human VHL defective CCRCC lines RCC10, RCC4 and 786–O were used to determine the role of FIH-1 in modulating HIF activity, using small interfering RNA knockdown, retroviral gene expression, quantitative RT–PCR, western blot analysis, Annexin V and propidium iodide labelling.

Results:

Although it was previously suggested that FIH-1 is suppressed in CCRCC, we found that FIH-1 mRNA and protein are actually present at similar levels in CCRCC and normal kidney. The FIH-1 inhibition or knockdown in the VHL defective CCRCC lines RCC10 and RCC4 (which express both HIF-1α and HIF-2α) resulted in increased expression of HIF target genes. In the 786-O CCRCC cell line, which expresses only HIF-2α, FIH-1 attenuation showed no significant effect on expression of these genes; introduction of HIF-1α resulted in sensitivity of HIF targets to FIH-1 knockdown. In RCC4 and RCC10, knockdown of FIH-1 increased apoptosis. Suppressing HIF-1α expression in RCC10 prevented FIH-1 knockdown from increasing apoptosis.

Conclusion:

Our results support a unifying model in which HIF-1α has a tumour suppressor action in CCRCC, held in check by FIH-1. Inhibiting FIH-1 in CCRCC could be used to bias the HIF response towards HIF-1α and decrease tumour cell viability.

Nuclear localization of factor inhibitor hypoxia-inducible factor in prostate cancer is associated with poor prognosis

PURPOSE

We determined the role of factor inhibiting hypoxia-inducible factor-1 in prostate cancer specimens.

MATERIALS AND METHODS

A tissue microarray of 152 prostate cancers was constructed and stained for factor inhibiting hypoxia-inducible factor-1, hypoxia-inducible factor-1α and 2α, and glucose transporter 1 as a prototypical downstream target of hypoxia-inducible factor-1α. Correlation analysis was done between these variables, and between factor inhibiting hypoxia-inducible factor-1, and clinical and pathological variables, including prostate specific antigen as a surrogate of recurrence.

RESULTS

Factor inhibiting hypoxia-inducible factor-1 was expressed in the cytoplasm and/or the nucleus in 86.5% of tumors, including exclusive cytoplasmic expression in 51.3% and exclusive nuclear expression in 5.3%. Any nuclear and exclusive expression of factor inhibiting hypoxia-inducible factor was associated with poor prognosis on univariate analysis (p = 0.007 and 0.042, respectively). On multivariate analysis men with nuclear expression in tumors were twice as likely to experience recurrence (p = 0.034).

CONCLUSIONS

Factor inhibiting hypoxia-inducible factor-1 is widely expressed in prostate tumors. Its differential subcellular expression suggests that regulation of its expression is an important factor in the activity of the hypoxia-inducible factor pathway. Its modulation may help treat hypoxia-inducible factor driven aggressive prostate cancer.

Turn me on: regulating HIF transcriptional activity

The hypoxia-inducible factors (HIFs) are critical for cellular adaptation to limiting oxygen and regulate a wide array of genes when cued by cellular oxygen-sensing mechanisms. HIF is able to direct transcription from either of two transactivation domains, each of which is regulated by distinct mechanisms. The oxygen-dependent asparaginyl hydroxylase factor-inhibiting HIF-1alpha (FIH-1) is a key regulator of the HIF C-terminal transactivation domain, and provides a direct link between oxygen sensation and HIF-mediated transcription. Additionally, there are phosphorylation and nitrosylation events reported to modulate HIF transcriptional activity, as well as numerous transcriptional coactivators and other interacting proteins that together provide cell and tissue specificity of HIF target gene regulation.