Hypoxia-inducible factor 1alpha and 1beta proteins share common signaling pathways in human prostate cancer cells

Dysregulation of ferroptosis may participate in the mitigating effect of CoCl2 on contrast-induced nephropathy

BACKGROUND

Contrast agents can directly or indirectly induce renal tubular ischemia and hypoxic damage. Given that cobalt chloride (CoCl2) can protect renal tubules, the protective effect and potential mechanism of action of CoCl2 on contrast-induced nephropathy (CIN) warrant investigation.

METHODS

A CIN mouse model was established to determine the protective effect of CoCl2 on renal injury in vivo. Then, TMT-based proteomics was performed to determine the differentially expressed proteins (DEPs), following which, enrichment analyses of gene ontology and the KEGG pathway were performed. In vitro, a CIN model was constructed with renal tubular epithelial cells (HK-2) to determine the effect of CoCl2 on potential targets and the role of the key protein identified from the in vivo experiments.

RESULTS

CoCl2 treatment decreased the levels of BUN and serum creatinine (sCr), while increasing the levels of urea and creatinine (Cr) in the urine of mice after CIN injury. Damage to the renal tubules in the CoCl2 treatment group was significantly less than in the CIN model group. We identified 79 DEPs after treating the in vivo model with CoCl2, and frequently observed ferroptosis-related GO and KEGG pathway terms. Of these, Hp (haptoglobin) was selected and found to have a strong renoprotective effect, even though its expression level in kidney tissue decreased after CoCl2 treatment. In HK-2 cells, overexpression of Hp reduced the ferroptosis caused by erastin, while knocking down Hp negated the attenuation effect of CoCl2 on HK-2 cell ferroptosis.

CONCLUSION

CoCl2 attenuated kidney damage in the CIN model, and this effect was associated with the decrease in ferroptosis mediated by Hp.

Evolution of the HIF targeted therapy in clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most common type of kidney cancer, affecting hundreds of thousands of people worldwide and can affect people of any age. The pathogenesis of ccRCC is most commonly due to biallelic loss of the tumor suppressor gene VHL. VHL is the recognition subunit of an E3-ubiquitin-ligase-complex essential for degradation of the hypoxia-inducible factors (HIF) 1α and 2α. Dysfunctional degradation of HIF results in overaccumulation, which is particularly concerning with the HIF2α subunit. This leads to nuclear translocation, dimerization, and transactivation of numerous HIF-regulated genes responsible for cell survival and proliferation in ccRCC. FDA-approved therapies for RCC have primarily focused on targeting downstream effectors of HIF, then incorporated immunotherapeutics, and now, novel approaches are moving back to HIF with a focus on interfering with upstream targets. This review summarizes the role of HIF in the pathogenesis of ccRCC, novel HIF2α-focused therapeutic approaches, and opportunities for ccRCC treatment.

Regulation of CMGC kinases by hypoxia

Hypoxia, a widespread occurrence observed in various malignant tumors, results from rapid tumor growth that outpaces the oxygen supply. Tumor hypoxia precipitates several effects on tumor biology; these include activating angiogenesis, intensifying invasiveness, enhancing the survival of tumor cells, suppressing anti-tumor immunity, and fostering resistance to therapy. Aligned with the findings that correlate CMGC kinases with the regulation of Hypoxia-Inducible Factor (HIF), a pivotal modulator, reports also indicate that hypoxia governs the activity of CMGC kinases, including DYRK1 kinases. Prolyl hydroxylation of DYRK1 kinases by PHD1 constitutes a novel mechanism of kinase maturation and activation. This modification "primes" DYRK1 kinases for subsequent tyrosine autophosphorylation, a vital step in their activation cascade. This mechanism adds a layer of intricacy to comprehending the regulation of CMGC kinases, and underscores the complex interplay between distinct post-translational modifications in harmonizing precise kinase activity. Overall, hypoxia assumes a substantial role in cancer progression, influencing diverse aspects of tumor biology that include angiogenesis, invasiveness, cell survival, and resistance to treatment. CMGC kinases are deeply entwined in its regulation. To fathom the molecular mechanisms underpinning hypoxia's impact on cancer cells, comprehending how hypoxia and prolyl hydroxylation govern the activity of CMGC kinases, including DYRK1 kinases, becomes imperative. This insight may pave the way for pioneering therapeutic approaches that target the hypoxic tumor microenvironment and its associated challenges. [BMB Reports 2023; 56(11): 584-593].

Polymorphism, Expression, and Structure Analysis of a Key Gene ARNT in Sheep (Ovis aries)

Growth traits are influential factors that significantly affects the development of the sheep industry. A previous TMT proteomic analysis found that a key protein in the HIF signaling pathway, ARNT, may influence embryonic skeletal muscle growth and development in sheep. The purpose of this study was to better understand the association between the polymorphisms of ARNT and growth traits of sheep, and the potential function of ARNT. Real-time qPCR (qRT-PCR) of ARNT was carried out to compare its expression in different developmental stages of the muscle tissues and primary myoblasts in the Hu, Chinese merino, and Gangba sheep. The genetic variance of ARNT was detected using the Illumina Ovine SNP 50 K and 600 K BeadChip in the Hu and Ujimqin sheep populations, respectively. The CDS sequence of the ARNT gene was cloned in the Hu sheep using PCR technology. Finally, bioinformatic analytical methods were applied to characterize the genes and their hypothetical protein products. The qRT-PCR results showed that the ARNT gene was expressed significantly in the Chinese merino embryo after 85 gestation days (D85) (p < 0.05). Additionally, after the sheep were born, the expression of ARNT was significant at the weaning stage of the Hu sheep (p < 0.01). However, there was no difference in the Gangba sheep.In addition, six SNP loci were screened using 50 K and 600 K BeadChip. We found a significant association between rs413597480 A > G and the Hu sheep weight at weaning and backfat thickness in the 5-month-old sheep (p < 0.05), and four SNP loci (rs162298018 G > C, rs159644025 G > A, rs421351865 G > A, and rs401758103 A > G) were also associated with growth traits in the Ujimqin sheep (p < 0.05). Interestingly, we found that a G > C mutation at 1948 bp in the cloned ARNT CDS sequence of the Hu sheep was the same locus mutation as rs162298018 G > C identified using the 600 K BeadChip, which resulted in a nonconservative missense point mutation, leading to a change from proline to alanine and altering the number of DNA, protein-binding sites, and the α-helix of the ARNT protein. There was a strong linkage disequilibrium between rs162298018 G > C and rs159644025 G > A, and the ARNT protein was conserved among the goat, Hu sheep, and Texel sheep. And, we propose that a putative molecular marker for growth and development in sheep may be the G > C mutation at 1948 bp in the CDS region of the ARNT gene. Our study systematically analyzed the expression, structure, and function of the ARNT gene and its encoded proteins in sheep. This provides a basis for future studies of the regulatory mechanisms of the ARNT gene.

Interaction between AhR and HIF-1 signaling pathways mediated by ARNT/HIF-1β

Background

The main causes of lung cancer are smoking, environmental pollution and genetic susceptibility. It is an indisputable fact that PAHs are related to lung cancer, and benzo(a) pyrene is a representative of PAHs. The purpose of the current investigation was to investigate the interaction between AhR and HIF-1 signaling pathways in A549 cells, which provide some experimental basis for scientists to find drugs that block AhR and HIF-1 signaling pathway to prevent and treat cancer.

Methods

This project adopts the CYP1A1 signaling pathways and the expression of CYP1B1 is expressed as a measure of AhR strength index. The expression of VEGF and CAIX volume as a measure of the strength of the signal path HIF-1 indicators. Through the construction of plasmid vector, fluorescence resonance energy transfer, real-time quantitative PCR, western blotting and immunoprecipitation, the interaction between AhR signaling pathway and HIF-1 signaling pathway was observed.

Results

BaP can enhance the binding ability of HIF-1α protein to HIF-1β/ARNT in a dose-dependent manner without CoCl₂. However, the binding ability of AhR protein to HIF-1β/ARNT is inhibited by HIF-1α signaling pathway in a dose-dependent manner with CoCl₂.

Conclusion

It is shown that activation of the AhR signaling pathway does not inhibit the HIF-1α signaling pathway, but activation of the HIF-1α signaling pathway inhibits the AhR signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00564-8.

Hypoxia-inducible factor-1β is essential for upregulation of the hypoxia-induced FLT1 gene in placental trophoblasts

Placental hypoxia and increased levels of maternal blood anti-angiogenic protein, soluble fms-like tyrosine kinase-1 (sFLT1), are associated with the pathogenesis of pre-eclampsia. We have demonstrated that hypoxia-inducible factor (HIF)-2α mediates the upregulation of the hypoxia-induced FLT1 gene in trophoblasts and their cell lines. Here, we investigated the involvement of HIF-1β, which acts as a dimerization partner for HIF-α, in the upregulation of the FLT1 gene via hypoxia. We confirmed the interactions between HIF-1β and HIF-2α in the nuclei of BeWo, JAR and JEG-3 cells under hypoxia via co-immunoprecipitation. We found that hypoxia-induced upregulation of the FLT1 gene in BeWo cells and secretion of sFLT1 in human primary trophoblasts were significantly reduced by siRNAs targeting HIF-1β. Moreover, the upregulation of the FLT1 gene in BeWo cells induced by dimethyloxaloylglycine (DMOG) was also inhibited by silencing either HIF-2α or HIF-1β mRNA. It was recently shown that DNA demethylation increases both basal and hypoxia-induced expression levels of the FLT1 gene in three trophoblast-derived cell lines. In the demethylated BeWo cells, siRNAs targeting HIF-2α and HIF-1β suppressed the further increase in the expression levels of the FLT1 gene due to hypoxia or treatment with DMOG. However, luciferase reporter assays and bisulfite sequencing revealed that a hypoxia response element (-966 to -962) of the FLT1 gene is not involved in hypoxia or DMOG-induced upregulation of the FLT1 gene. These findings suggest that HIF-1β is essential for the elevated production of sFLT1 in the hypoxic trophoblasts and that the HIF-2α/HIF-1β complex may be a crucial therapeutic target for pre-eclampsia.

Immunogenomic Profiling and Classification of Prostate Cancer Based on HIF-1 Signaling Pathway

The HIF-1 signaling pathway plays an important role in the pathogenesis of cancer. Many studies have explored the progression of prostate cancer (PCa) under hypoxic conditions based on transcriptome data; few have uncovered the immunogenomic profiling and prostate cancer classification based on the HIF-1 signaling pathway. This pathway may help to identify the optimal subset of PCa patients responsive to immunotherapy/chemotherapy. The immunogenomic PCa subsets were classified based on profiling of the HIF-1 signaling pathway, using four publicly available PCa datasets. Three PCa subtypes that named as HIF-1 High (HIF-1_H), HIF-1 Medium (HIF-1_M), and HIF-1 Low (HIF-1_L) were identified. Functional enrichment was analyzed in each subtype. Several cancer-associated and immune-related pathways were hyperactivated in the HIF-1_H subtypes. In contrast, HIF-1_L subtypes were enriched in cell cycle and cell repair. Compared with other subtypes, HIF-1_H subtypes have greater immune cell infiltration, anti-tumor immune activity, and better survival prognosis. The submap and TIDE algorithm were used to predict the clinical response to immune checkpoint blockade, and GDSC was employed to screen potential chemotherapeutic targets for the treatment of PCa. Several chemotherapy drugs were identified in the GDSC dataset, including ABT 888, Temsirolimus, and EHT 1864. Meanwhile, HIF-1_H was defined as an early PCa marker, which is more likely to respond to immunotherapy. The identification of immunogenomic PCa subtypes based on the HIF-1 signaling pathway has potential clinical implications for PCa treatment. Immunopositive PCa subtypes will help to explore the reasons for the poor response of PCa to immunotherapy, and it is expected that immunotherapy will guide the personalized treatment of PCa patients.

Molecular cloning and characterization of two ARNT (ARNT-1 and ARNT-2) genes in Atlantic croaker and their expression during coexposure to hypoxia and PCB77

Aryl hydrocarbon receptor nuclear translocator (ARNT) is an important transcriptions factor that binds/coactivates drug-metabolizing genes in vertebrates. In this study, we report the cloning and characterization of two ARNT (ARNT-1 and ARNT-2) genes and their mRNA and protein expression in liver tissues of Atlantic croaker after co-exposure to hypoxia and 3,3',4,4'-tetrachlorobiphenyl (PCB77). The full-length croaker ARNT-1 and ARNT-2 genes encode proteins of 537 and 530 amino acids, respectively, and are highly homologous to ARNT-1 and ARNT-2 genes of other vertebrates. ARNT mRNAs are ubiquitously expressed in all tissues. Hypoxia (dissolved oxygen: 1.7 mg/L) exposure (1-4 weeks) did not affect hepatic ARNTs mRNA levels. Dietary PCB77 treatment (2 and 8 μg/g body weight/day for 4 weeks) caused marked increases in ARNTs mRNA and protein levels in normoxic fish. However, coexposure to hypoxia and PCB77 for 4 weeks significantly blunted the increase in ARNTs mRNA and protein levels in response to PCB77 exposure. These results suggest that ARNT activity and functions induced by exposure to PCB aryl hydrocarbon receptor (AhR) agonists could be compromised in croaker inhabiting hypoxic coastal regions.

Montelukast inhibits hypoxia inducible factor-1α translation in prostate cancer cells

Through regulating the expression of hundreds of genes, hypoxia-inducible factor -1(HIF-1) plays a critical role in hypoxic adaption of cancer cells and is considered as a target for cancer therapy. Here we show that montelukast, a clinical leukotriene receptor antagonist for the treatment of asthma, inhibits hypoxia or CoCl₂-induced HIF-1α activation and reduces its protein expression in prostate cancer cells. However, the other two leukotriene receptor antagonists, pranlukast and zafirlukast, cannot decrease HIF-1α protein, which indicates that montelukast-induced downregulation of HIF-1α is not mediated by leukotriene receptor. Neither proteasome inhibitor MG132 nor the lysosomal inhibitor chloroquine (CQ) can block montelukast-induced downregulation of HIF-1α protein. Interestingly, GSK2606414, a PKR-like endoplasmic reticulum kinase (PERK) inhibitor, abrogates montelukast-induced downregulation of HIF-1α under hypoxic conditions. However, montelukast increases phosphorylation of eIF-2α at Ser51. Moreover, montelukast inhibits the proliferation of prostate cancer cells, which can be reversed by overexpression of HIF-1α protein. In conclusion, we identify montelukast may be used as a novel agent for the treatment of prostate cancer by decreasing HIF-1α protein translation.

Loss of HIF-1α in macrophages attenuates AhR/ARNT-mediated tumorigenesis in a PAH-driven tumor model

Activation of hypoxia-inducible factor (HIF) and macrophage infiltration of solid tumors independently promote tumor progression. As little is known how myeloid HIF affects tumor development, we injected the polycyclic aromatic hydrocarbon (PAH) and procarcinogen 3-methylcholanthrene (MCA; 100 μg/100 μl) subcutaneously into myeloid-specific Hif-1α and Hif-2α knockout mice (C57BL/6J) to induce fibrosarcomas (n = 16). Deletion of Hif-1α but not Hif-2α in macrophages diminished tumor outgrowth in the MCA-model. While analysis of the tumor initiation phase showed comparable inflammation after MCA-injection, metabolism of MCA was impaired in the absence of Hif-1α. An ex vivo macrophage/fibroblast coculture recapitulated reduced DNA damage after MCA-stimulation in fibroblasts of cocultures with Hif-1α^LysM−/− macrophages compared to wild type macrophages. A loss of myeloid Hif-1α decreased RNA levels of arylhydrocarbon receptor (AhR)/arylhydrocarbon receptor nuclear translocator (ARNT) targets such as Cyp1a1 because of reduced Arnt but unchanged Ahr expression. Cocultures using Hif-1α^LysM−/− macrophages stimulated with the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA; 2 μg/ml) also attenuated a DNA damage response in fibroblasts, while the DNA damage-inducing metabolite DMBA-trans-3,4-dihydrodiol remained effective in the absence of Hif-1α. In chemical-induced carcinogenesis, HIF-1α in macrophages maintains ARNT expression to facilitate PAH-biotransformation. This implies a metabolic activation of PAHs in stromal cells, i.e. myeloid-derived cells, to be crucial for tumor initiation.

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.

Genome-wide copy number analysis reveals candidate gene loci that confer susceptibility to high-grade prostate cancer

BACKGROUND

Two key issues in prostate cancer (PCa) that demand attention currently are the need for a more precise and minimally invasive screening test owing to the inaccuracy of prostate-specific antigen and differential diagnosis to distinguish advanced vs. indolent cancers. This continues to pose a tremendous challenge in diagnosis and prognosis of PCa and could potentially lead to overdiagnosis and overtreatment complications. Copy number variations (CNVs) in the human genome have been linked to various carcinomas including PCa. Detection of these variants may improve clinical treatment as well as an understanding of the pathobiology underlying this complex disease.

METHODS

To this end, we undertook a pilot genome-wide CNV analysis approach in 36 subjects (18 patients with high-grade PCa and 18 controls that were matched by age and ethnicity) in search of more accurate biomarkers that could potentially explain susceptibility toward high-grade PCa. We conducted this study using the array comparative genomic hybridization technique. Array results were validated in 92 independent samples (46 high-grade PCa, 23 benign prostatic hyperplasia, and 23 healthy controls) using polymerase chain reaction-based copy number counting method.

RESULTS

A total of 314 CNV regions were found to be unique to PCa subjects in this cohort (P<0.05). A log₂ ratio-based copy number analysis revealed 5 putative rare or novel CNV loci or both associated with susceptibility to PCa. The CNV gain regions were 1q21.3, 15q15, 7p12.1, and a novel CNV in PCa 12q23.1, harboring ARNT, THBS1, SLC5A8, and DDC genes that are crucial in the p53 and cancer pathways. A CNV loss and deletion event was observed at 8p11.21, which contains the SFRP1 gene from the Wnt signaling pathway. Cross-comparison analysis with genes associated to PCa revealed significant CNVs involved in biological processes that elicit cancer pathogenesis via cytokine production and endothelial cell proliferation.

CONCLUSION

In conclusion, we postulated that the CNVs identified in this study could provide an insight into the development of advanced PCa.

Obesity promotes aerobic glycolysis in prostate cancer cells

Obesity is the leading preventable comorbidity associated with increased prostate cancer-related recurrence and mortality. Epidemiological and clinical studies indicate that a body mass index >30 is associated with increased oxidative DNA damage within the prostate gland and increased prostate cancer-related mortality. Here we provide evidence that obesity promotes worse clinical outcome through induction of metabolic abnormalities known to promote genotoxic stress. We have previously reported that blood serum derived from obese mice may enhance the proliferative and invasive potential of human prostate cancer cell lines ex vivo. Here we show that a 1-h exposure of LNCaP or PacMetUT1 prostate cancer cell lines and nonmalignant RWPE-1 prostate epithelial cells to 2% serum from obese mice induces markers of aerobic glycolysis relative to those exposed to serum from nonobese mice. This metabolic change was correlated with accumulation of reactive oxygen species (ROS) and increased frequency of DNA double-strand breaks. Interestingly, N-tert-Butylhydroxylamine, an antioxidant, significantly suppressed markers of aerobic glycolysis in the cells exposed to the blood serum of obese mice, suggesting that ROS contributes to a metabolic shift toward aerobic glycolysis. Here we describe obesity-induced changes in key metabolic markers that impact prostate cancer cell progression and explore the role of antioxidants in ameliorating these effects.

Hypoxia-inducible aryl hydrocarbon receptor nuclear translocator (ARNT) (HIF-1β): is it a rare exception?

The aryl hydrocarbon receptor nuclear translocator (ARNT), also designated as hypoxia-inducible factor (HIF)-1β, plays a pivotal role in the adaptive responses to (micro-)environmental stresses such as dioxin exposure and oxygen deprivation (hypoxia). ARNT belongs to the group of basic helix-loop-helix (bHLH)-Per-ARNT-Sim (PAS) transcription factors, which act as heterodimers. ARNT serves as a common binding partner for the aryl hydrocarbon receptor (AhR) as well as HIF-α subunits. HIF-α proteins are regulated in an oxygen-dependent manner, whereas ARNT is generally regarded as constitutively expressed, meaning that neither the arnt mRNA nor the protein level is influenced by hypoxia (despite the name HIF-1β). However, there is emerging evidence that tumor cells derived from different entities are able to upregulate ARNT, especially under low oxygen tension in a cell-specific manner. The objective of this review is therefore to highlight and summarize current knowledge regarding the hypoxia-dependent upregulation of ARNT, which is in sharp contrast to the general point of view described in the literature. Elucidating the mechanism behind this rare cellular attribute will help us to gain new insights into HIF biology and might provide new strategies for anti-cancer therapeutics. In conclusion, putative treatment effects on ARNT should be taken into account while studying the HIF pathway. This step is of great importance when ARNT is intended to serve as a loading control or as a reference.

Clinical activity of mammalian target of rapamycin inhibitors in solid tumors

The phosphatidylinositol 3-kinase (PI3K)-Akt-mammalian target of rapamycin (mTOR) pathway is vital for cell metabolism, growth, and proliferation. mTOR is frequently upregulated in many tumor types and hence has become an important target in cancer treatment. Sirolimus and its derivatives (rapalogs) interact with the intracellular receptor FK506 binding protein 12 (FKBP12), forming a complex with high affinity for mTOR and thus disrupting its activity. Rapalogs are being evaluated extensively in cancer patients with different formulations and schedules. Significant clinical activity has led to their approval for the treatment of kidney cancer, mantle cell lymphoma, and subependymal giant cell astrocytoma; however, despite increasing knowledge about cancer cell biology, their activity in other malignancies is unclear. Further research is needed to identify optimal dosage, administration and targeted combination as well as the subset of patients likely to respond to mTOR/PI3K inhibition. This review focuses on a discussion of the pathway, its implications in cancer biology and results of clinical trials of rapalogs alone or in combination, organizing them by common malignancy type.

mTOR signaling and drug development in cancer

Mammalian target of rapamycin (mTOR) is a protein kinase of the PI3K/Akt signaling pathway. Activation of mTOR in response to growth, nutrient and energy signals leads to an increase in protein synthesis, which is required for tumor development. This feature makes mTOR an attractive target for cancer therapy. First-generation mTOR inhibitors are sirolimus derivatives (rapalogs), which have been evaluated extensively in cancer patients. Everolimus and temsirolimus are already approved for the treatment of renal-cell carcinoma. Temsirolimus is also approved for the treatment of mantle-cell lymphoma. These drugs, in addition to ridaforolimus (formerly deforolimus) and sirolimus, are currently being evaluated in clinical trials of various cancers. Second-generation mTOR inhibitors are small molecules that target the kinase domain, and have also entered clinical development. Clinical trials are underway to identify additional malignancies that respond to mTOR inhibitors, either alone or in combination with other therapies. Future research should evaluate the optimal drug regimens, schedules, patient populations, and combination strategies for this novel class of agents.

Inhibition of HIF-1 alpha and VEGF expression by the chemopreventive bioflavonoid apigenin is accompanied by Akt inhibition in human prostate carcinoma PC3-M cells

Progression of cancer leads to hypoxic solid tumors that mount specific cell signaling responses to low oxygen conditions. An important objective of anti-cancer therapy is the development of new drugs that suppress hypoxic responses in solid tumors. Apigenin is a natural flavone that has been shown to have chemopreventive and/or anti-cancer properties against a number of tumor types. However, the mechanisms underlying apigenin's chemopreventive properties are not yet completely understood. In this study, we have investigated the effects of apigenin on expression of hypoxia-inducible factor-1 (HIF-1) in human metastatic prostate PC3-M cancer cells. We found that hypoxia induced a time-dependent increase in the level of HIF-1alpha subunit protein in PC3-M cells, and treatment with apigenin markedly decreased HIF-1alpha expression under both normoxic and hypoxic conditions. Further, apigenin prevented the activation of the HIF-1 downstream target gene vascular endothelial growth factor (VEGF). We then showed that apigenin inhibited expression of HIF-1alpha by reducing stability of the protein as well as by reducing the level of HIF-1alpha mRNA. We also found that apigenin inhibited Akt and GSK-3beta phosphorylation in PC3-M cells. Further experiments demonstrated that constitutively active Akt blunted the effect of apigenin on HIF-1alpha expression. Taken together, our results identify apigenin as a bioflavonoid that inhibits hypoxia-activated pathways linked to cancer progression in human prostate cancer, in particular the PI3K/Akt/GSK-3 pathway. Further studies on the mechanism of action of apigenin will likely provide new insight into its applicability for pharmacologic targeting of HIF-1alpha for cancer therapeutic or chemopreventive purposes.

Regulation of the Warburg effect in early-passage breast cancer cells

Malignancy in cancer is associated with aerobic glycolysis (Warburg effect) evidenced by increased trapping of [(18)F]deoxyglucose (FdG) in patients imaged by positron emission tomography (PET). [(18)F]deoxyglucose uptake correlates with glucose transporter (GLUT-1) expression, which can be regulated by hypoxia-inducible factor 1 alpha (HIF-1alpha). We have previously reported in established breast lines that HIF-1alpha levels in the presence of oxygen leads to the Warburg effect. However, glycolysis and GLUT-1 can also be induced independent of HIF-1alpha by other factors, such as c-Myc and phosphorylated Akt (pAkt). This study investigates HIF-1alpha, c-Myc, pAkt, and aerobic glycolysis in low-passage breast cancer cells under the assumption that these represent the in vivo condition better than established lines. Similar to in vivo FdG-PET or primary breast cancers, rates of glycolysis were diverse, being higher in cells expressing both c-Myc and HIF-1alpha and lower in cell lines low or negative in both transcription factors. No correlations were observed between glycolytic rates and pAkt levels. Two of 12 cell lines formed xenografts in mice. Both were positive for HIF-1alpha and phosphorylated c-Myc, and only one was positive for pAkt. Glycolysis was affected by pharmacological regulation of c-Myc and HIF-1alpha. These findings suggest that c-Myc and/or HIF-1alpha activities are both involved in the regulation of glycolysis in breast cancers.

Chrysin inhibits expression of hypoxia-inducible factor-1α through reducing hypoxia-inducible factor-1α stability and inhibiting its protein synthesis

Chrysin is a natural flavonoid and has been shown recently to have anticancer effects. However, the mechanisms that chrysin inhibits cancers are not well known. In this study, we investigated the effects of chrysin on expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor in human prostate cancer DU145 cells. Chrysin inhibited insulin-induced expression of HIF-1alpha by reducing its stability. Chrysin increases ubiquitination and degradation of HIF-1alpha by increasing its prolyl hydroxylation. In addition, chrysin interfered with interaction between HIF-1alpha and heat shock protein 90. Chrysin was also found to inhibit HIF-1alpha expression through AKT signaling. Inhibition of HIF-1alpha by chrysin resulted in abrogation of vascular endothelial growth factor expression. Finally, we showed that chrysin inhibited DU145 xenograft-induced angiogenesis in nude mice. Taken together, these results suggest that chrysin is a potent inhibitor of HIF-1alpha and provide a new sight into the mechanisms of chrysin against cancers.

YC-1 inhibits HIF-1 expression in prostate cancer cells: contribution of Akt/NF-kappaB signaling to HIF-1alpha accumulation during hypoxia

Hypoxia-inducible factor 1 (HIF-1), a transcription factor that is critical for tumor adaptation to microenvironmental stimuli, represents an attractive chemotherapeutic target. YC-1 is a novel antitumor agent that inhibits HIF-1 through previously unexplained mechanisms. In the present study, YC-1 was found to prevent HIF-1alpha and HIF-1beta accumulation in response to hypoxia or mitogen treatment in PC-3 prostate cancer cells. Neither HIF-1alpha protein half-life nor mRNA level was affected by YC-1. However, YC-1 was found to suppress the PI3K/Akt/mTOR/4E-BP pathway, which serves to regulate HIF-1alpha expression at the translational step. We demonstrated that YC-1 also inhibited hypoxia-induced activation of nuclear factor (NF)-kappaB, a downstream target of Akt. Two modulators of the Akt/NF-kappaB pathway, caffeic acid phenethyl ester and evodiamine, were observed to decrease HIF-1alpha expression. Additionally, overexpression of NF-kappaB partly reversed the ability of wortmannin to inhibit HIF-1alpha-dependent transcriptional activity, suggesting that NF-kappaB contributes to Akt-mediated HIF-1alpha accumulation during hypoxia. Overall, we identify a potential molecular mechanism whereby YC-1 serves to reduce HIF-1 expression.

Molecular markers in the diagnosis of prostate cancer

The genetic alterations leading to prostate cancer are gradually being discovered. A wide variety of genes have been associated with prostate cancer development as well as tumor progression. Knowledge of gene polymorphisms associated with disease aid in the understanding of important pathways involved in this process and may result in the near future in clinical applications. Urinary molecular markers will soon be available to aid in the decision of repeat prostate biopsies. Recent findings suggest the importance of androgen signaling in disease development and progression. The further understanding of interaction of inflammation, diet, and genetic predisposition will improve risk stratification in the near future.

Natural product-derived small molecule activators of hypoxia-inducible factor-1 (HIF-1)

Hypoxia-inducible factor-1 (HIF-1) is a key mediator of oxygen homeostasis that was first identified as a transcription factor that is induced and activated by decreased oxygen tension. Upon activation, HIF-1 upregulates the transcription of genes that promote adaptation and survival under hypoxic conditions. HIF-1 is a heterodimer composed of an oxygen-regulated subunit known as HIF-1alpha and a constitutively expressed HIF-1beta subunit. In general, the availability and activity of the HIF-1alpha subunit determines the activity of HIF-1. Subsequent studies have revealed that HIF-1 is also activated by environmental and physiological stimuli that range from iron chelators to hormones. Preclinical studies suggest that HIF-1 activation may be a valuable therapeutic approach to treat tissue ischemia and other ischemia/hypoxia-related disorders. The focus of this review is natural product-derived small molecule HIF-1 activators. Natural products, relatively low molecular weight organic compounds produced by plants, animals, and microbes, have been and continue to be a major source of new drugs and molecular probes. The majority of known natural product-derived HIF-1 activators were discovered through the pharmacological evaluation of specifically selected individual compounds. On the other hand, the combination of natural products chemistry with appropriate high-throughput screening bioassays may yield novel natural product-derived HIF-1 activators. Potent natural product-derived HIF-1 activators that exhibit a low level of toxicity and side effects hold promise as new treatment options for diseases such as myocardial and peripheral ischemia, and as chemopreventative agents that could be used to reduce the level of ischemia/reperfusion injury following heart attack and stroke.

Ascorbate depletion mediates up-regulation of hypoxia-associated proteins by cell density and nickel

Exposure of human lung cells to carcinogenic nickel compounds in the presence of oxygen up-regulated carbonic anhydrase IX (CA IX) and NDRG1/Cap43, both known as intrinsic hypoxia markers and cancer-associated genes. This suggests that factors other than a shortage of oxygen may be involved in this induction. Both proteins can also be induced in the presence of oxygen by culturing these cells to a high density without medium change. The intracellular ascorbate measurements revealed its rapid depletion in both metal- and density-exposed cells. Nickel exposure caused strong activation of HIF-1alpha and HIF-2alpha proteins, underscoring activation of HIF-1-dependent transcription. In contrast, cell density-dependent transcription was characterized by minor induction of HIF-1alpha or HIF-2alpha. Moreover, the up-regulation of NDRG1/Cap43 in HIF-1alpha deficient fibroblasts suggested the involvement of different transcription factor(s). The repletion of intracellular ascorbate reversed the induction of CA IX and NDRG1/Cap43 caused by cell density or nickel exposure. Thus, the loss of intracellular ascorbate triggered the induction of both tumor markers by two different conditions in the presence of oxygen. Ascorbate is delivered to lung cells via the SVCT2 ascorbate transporter, which was found to be sensitive to nickel or cell density. Collectively these findings establish the importance of intracellular ascorbate levels for the regulation of expression of CA IX and NDRG1/Cap43. We suggest, that, in addition to low oxygenation, insufficient supply of ascorbate or its excessive oxidation in tumors, can contribute to the induction of hypoxia-associated proteins via both HIF-dependent and independent mechanisms.

Ocular oxygenation and the treatment of diabetic retinopathy

Retinal photocoagulation and vitrectomy both reduce diabetic macular edema and neovascularization in diabetic retinopathy. We suggest that this clinical effect is based on the effect these treatment modalities have on retinal oxygenation, and we present a theory to explain why retinal photocoagulation and vitrectomy influence edema and neovascularization in diabetic and other ischemic retinopathies.

Hypoxia-induced IL-6 production is associated with activation of MAP kinase, HIF-1, and NF-kappaB on HEI-OC1 cells

In the present study, we investigated the signal transduction pathways of expression of IL-6 in the desferrioxamine (DFX)-stimulated cochlear auditory cell line, HEI-OC1 cells. DFX increased the expression of HIF-1alpha and NF-kappaB in HEI-OC1 cells. DFX significantly increased the production of IL-6 (P<0.05) and expression of IL-6 mRNA but did not affect TNF-alpha production. DFX also induced the activation of mitogen-activated protein kinase (MAPK) including p38, ERK, and JNK on HEI-OC1. Increased IL-6 by DFX was significantly inhibited by p38 inhibitor, SB203580 (about 72% inhibition, P=0.027) but not ERK inhibitor, PD98059 or JNK inhibitor, SP600125. SB203580 inhibited the expression of IL-6 mRNA. Increased IL-6 production was partially inhibited by treatment of iron (HIF-1 inhibitor) or pyrriolidine-dithiocarbamate (PDTC, NF-kappaB inhibitor). DFX also induced IL-6 production and HIF-1alpha expression in the inner ear. We demonstrated the regulatory effects of MAPK, HIF-1alpha, and NF-kappaB on DFX-induced IL-6 production in a HEI-OC1 for the first time. In conclusion, these data indicate that regulation of inflammatory cytokine IL-6 by DFX, through mimicking hypoxic conditions, might explain its beneficial effect in the treatment of hypoxia-induced inner ear diseases.

Reversible inactivation of HIF-1 prolyl hydroxylases allows cell metabolism to control basal HIF-1

Continuous hydroxylation of the HIF-1 transcription factor alpha subunit by oxygen and 2-oxoglutarate-dependent dioxygenases promotes decay of this protein and thus prevents the transcriptional activation of many genes involved in energy metabolism, angiogenesis, cell survival, and matrix modification. Hypoxia blocks HIF-1alpha hydroxylation and thus activates HIF-1alpha-mediated gene expression. Several nonhypoxic stimuli can also activate HIF-1, although the mechanisms involved are not well known. Here we show that the glucose metabolites pyruvate and oxaloacetate inactivate HIF-1alpha decay in a manner selectively reversible by ascorbate, cysteine, histidine, and ferrous iron but not by 2-oxoglutarate or oxygen. Pyruvate and oxaloacetate bind to the 2-oxoglutarate site of HIF-1alpha prolyl hydroxylases, but their effects on HIF-1 are not mimicked by other Krebs cycle intermediates, including succinate and fumarate. We show that inactivation of HIF-1 hydroxylation by glucose-derived 2-oxoacids underlies the prominent basal HIF-1 activity commonly seen in many highly glycolytic cancer cells. Since HIF-1 itself promotes glycolytic metabolism, enhancement of HIF-1 by glucose metabolites may constitute a novel feed-forward signaling mechanism involved in malignant progression.

Hypoxia inducible factor pathways as targets for functional foods

The etiology of most chronic angiogenic diseases such as rheumatoid arthritis, atherosclerosis, diabetes complications, and cancer includes the presence of pockets of hypoxic cells growing behind aerobic cells and away from blood vessels. Hypoxic cells are the result of uncontrolled growth and insufficient vascularization and have undergone a shift from aerobic to anaerobic metabolism. Cells respond to hypoxia by stimulating the expression of hypoxia inducible factor (HIF), which is critical for survival under hypoxic conditions and in embryogenesis. HIF is a heterodimer consisting of the O2-regulated subunit, HIF-1alpha, and the constitutively expressed aryl hydrocarbon receptor nuclear translocator, HIF-1beta. Under hypoxic conditions, HIF-1alpha is stable, accumulates, and migrates to the nucleus where it binds to HIF-1beta to form the complex (HIF-1alpha + HIF-1beta). Transcription is initiated by the binding of the complex (HIF-1alpha + HIF-1beta) to hypoxia responsive elements (HREs). The complex [(HIF-1alpha + HIF-1beta) + HREs] stimulates the expression of genes involved in angiogenesis, anaerobic metabolism, vascular permeability, and inflammation. Experimental and clinical evidence show that these hypoxic cells are the most aggressive and difficult angiogenic disease cells to treat and are a major reason for antiangiogenic and conventional treatment failure. Hypoxia occurs in early stages of disease development (before metastasis), activates angiogenesis, and stimulates vascular remodeling. HIF-1alpha has also been identified under aerobic conditions in certain types of cancer. This review summarizes the role of hypoxia in some chronic degenerative angiogenic diseases and discusses potential functional foods to target the HIF-1alpha pathways under hypoxic and normoxic conditions. It is reported that dietary quinones, semiquinones, phenolics, vitamins, amino acids, isoprenoids, and vasoactive compounds can down-regulate the HIF-1 pathways and therefore the expression of several proangiogenic factors. Considering the lack of efficiency or the side effects of synthetic antiangiogenic drugs at clinical trials, down-regulation of hypoxia-induced angiogenesis by use of naturally occurring functional foods may provide an effective means of prevention.

Vascular endothelial growth factor is regulated by hypoxic stress via MAPK and HIF-1 alpha in the inner ear

Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis. The iron-chelator desferrioxamine (DFX) increased the expression of hypoxia-inducible factor (HIF)-1alpha in the hair cell line, HEI-OC1. The increased VEGF production by DFX was inhibited by iron. DFX also induced the activation of mitogen-activated protein kinase (MAPK) on HEI-OC1. The increased VEGF production by DFX was inhibited by a specific inhibitor of MAPK. In addition, DFX induced the VEGF production and HIF-1alpha stabilization in vivo. These results indicate that VEGF production is regulated via MAPK and HIF-1alpha under hypoxic condition in the inner ear.

Inhibitors of the mammalian target of rapamycin

The mammalian target of rapamycin (mTOR) is a downstream protein kinase of the phosphatidylinositol 3'-kinase-Akt signalling pathway. As a result of its position within this pathway and its central role in controlling cellular growth, mTOR is viewed as an important target for anticancer therapeutics development. Currently, the mTOR inhibitor rapamycin (sirolimus, Wyeth) and its derivatives temsirolimus (CCI-779, Wyeth), everolimus (RAD-001, Novartis Pharma AG) and AP-23573 (Ariad Pharmaceuticals) are being evaluated in cancer clinical trials. Preclinical studies suggest that sensitivity to mTOR inhibition may correlate with aberrant activation of the phosphatidylinositol 3'-kinase pathway and/or with aberrant expression of cell-cycle regulatory or antiapoptotic proteins. Clinical trial results show that mTOR inhibitors are generally well tolerated and may induce prolonged stable disease and even tumour regressions in a subset of patients. Questions remain regarding optimal dose, schedule, patient selection and combination strategies for this novel class of agents.

Expression of proinflammatory cytokines via HIF-1alpha and NF-kappaB activation on desferrioxamine-stimulated HMC-1 cells

We investigated the expression and the role of hypoxia-inducible factor 1alpha (HIF-1alpha) on the desferrioxamine (DFX)-induced cytokine production in human mast cells, HMC-1 cells. HIF-1alpha mRNA was constitutively expressed in mast cell lines including the P815, RBL-2H3, and HMC-1. DFX (100 microM) resulted in a great increase in protein levels of HIF-1alpha in HMC-1 cells, but it did not affect HIF-1alpha mRNA expression. Iron (HIF-1 inhibitor) inhibited increase of HIF-1alpha and NF-kappaB protein levels. Pyrriolidine-dithiocarbamate (PDTC, NF-kappaB inhibitor) inhibited increase of NF-kappaB protein levels, but it slightly increased HIF-1alpha protein levels. In addition, DFX significantly increased the production of IL-6, IL-8, and TNF-alpha in HMC-1 (P<0.05). These increased cytokine levels were significantly inhibited by treatment of iron or PDTC in a dose-dependent manner (P<0.05). We demonstrated the regulatory effects of HIF-1alpha on the DFX-induced proinflammatory cytokine production in human mast cells for the first time. These data indicate that inflammatory cytokines seem to be under HIF-1alpha or NF-kappaB transcriptional regulation in the hypoxic conditions on mast cells.

Dibenzoylmethane, a natural dietary compound, induces HIF-1 alpha and increases expression of VEGF

Hypoxia-inducible factor 1 (HIF-1) is the major transcription factor activated during hypoxia. It is composed of HIF-1 alpha and HIF-1 beta subunits. While HIF-1 beta is constitutively expressed, HIF-1 alpha is targeted to proteasome degradation under normoxic conditions. Under hypoxia, HIF-1 alpha is stabilized and heterodimerizes with HIF-1 beta. Iron chelators have also been reported to stabilize HIF-1 alpha protein and activate HIF-1. In this study, we investigated the effects of dibenzoylmethane (DBM), a natural dietary compound and an iron chelator, on HIF-1 pathway. We found that DBM increases HIF-1 alpha protein levels in a dose- and time-dependent manner. This induction was accompanied with activation of HIF-1, measured by reporter gene assay and increased production of its downstream target, the vascular endothelial growth factor. Mechanistically, HIF-1 alpha was stabilized by DBM at a step prior to ubiquitination. The effect of DBM on HIF-1 and its low toxicity profile might be therapeutically beneficial in ischemic diseases.

Expression and significance of PTEN, hypoxia-inducible factor-1 alpha in colorectal adenoma and adenocarcinoma

AIM: To investigate the expression and significance of PTEN, hypoxia-inducible factor-1 alpha (HIF-1α), and targeting gene VEGF during colorectal carciogenesis.

METHODS: Total 71 cases colorectal neoplasms (9 cases of colorectal adenoma and 62 colorectal adenocarcinoma) were formalin fixed and paraffin-embedded, and all specimens were evaluated for PTEN mRNA, HIF-1α mRNA and VEGF protein expression. PTEN mRNA, HIF-1α mRNA were detected by in situ hybridization. VEGF protein was identified by citrate-microwave SP immunohistochemical method.

RESULTS: There were significant differences in PTEN, HIF-1α and VEGF expression between colorectal adenomas and colorectal adenocarcinoma (P < 0.05). The level of PTEN expression decreased as the pathologic stage increased. Conversely, HIF-1α and VEGF expression increased with the Dukes stage as follows: stage A (0.1029 ± 0.0457: 0.1207 ± 0.0436), stage B (0.1656 ± 0.0329: 0.1572 ± 0.0514), and stage C + D (0.2335 ± 0.0748: 0.2219 ± 0.0803). For PTEN expression, there was a significant difference among Dukes stage A, B, and C + D, and the level of PTEN expression was found to be significant higher in Dukes stage A or B than that of Dukes stage C or D. For HIF-1α expression, there was a significant difference between Dukes stage A and B, and the level of HIF-1α expression was found to be significantly higher in Dukes stage C+D than that of Dukes stage A or B. The VEGF expression had similar results as HIF-1α expression. In colorectal adenocarcinoma, decreased levels of PTEN were significantly associated with increased expression of HIF-1α mRNA (r = -0.36, P < 0.05) and VEGF protein (r = -0.48, P < 0.05) respectively. The levels of HIF-1 were positively correlated with VEGF expression (r = 0.71, P < 0.01).

CONCLUSION: Loss of PTEN expression and increased levels of HIF-1α and VEGF may play an important role in carcinogenesis and progression of colorectal adenocarcinoma.

Hypoxia-inducible factor induction by tumour necrosis factor in normoxic cells requires receptor-interacting protein-dependent nuclear factor kappa B activation

Tumour necrosis factor alpha (TNF-alpha) binds to its receptor (TNFR1) and activates both death- and inflammation/survival-related signalling pathways. The inflammation and survival-related signalling cascade results in the activation of the transcription factor, nuclear factor kappa B (NF-kappa B) and requires recruitment of receptor-interacting protein (RIP) to TNFR1. The indispensable role of RIP in TNF-induced NF-kappa B activation has been demonstrated in RIP(-/-) mice and in cell lines derived from such mice. In the present study, we show that the TNF-alpha-induced accumulation of hypoxia-inducible factor 1 alpha (HIF-1 alpha) protein in normoxic cells is RIP-dependent. Exposing fibroblasts derived from RIP(-/-) mice to either cobalt or PMA resulted in an equivalent HIF-1 alpha induction to that seen in RIP(+/+) fibroblasts. In contrast, RIP(-/-) cells were unable to induce HIF-1 alpha in response to TNF-alpha. Further, transient transfection of NIH 3T3 cells with an NF-kappa B super-repressor plasmid (an inhibitor of NF-kappa B activation) also prevented HIF-1 alpha induction by TNF-alpha. Surprisingly, although HIF-1 alpha mRNA levels remained unchanged after induction by TNF, induction of HIF-1 alpha protein by the cytokine was completely blocked by pretreatment with the transcription inhibitors actinomycin D and 5,6-dichlorobenzimidazole riboside. Finally, TNF failed to induce both HIF-1 alpha, made resistant to von Hippel-Lindau (VHL), and wild-type HIF-1 alpha transfected into VHL(-/-) cells. These results indicate that HIF-1 alpha induction by TNF-alpha in normoxic cells is mediated by protein stabilization but is nonetheless uniquely dependent on NF-kappa B-driven transcription. Thus the results describe a novel mechanism of HIF-1 alpha up-regulation and they identify HIF-1 alpha as a unique component of the NF-kappa B-mediated inflammatory/survival response.

Cellular adaptation to hypoxia: O2-sensing protein hydroxylases, hypoxia-inducible transcription factors, and O2-regulated gene expression

Although it was known for a long time that oxygen deprivation leads to the transcriptional induction of the gene encoding erythropoietin, the molecular mechanisms behind this process remained enigmatic. The cloning of the hypoxia-inducible factors (HIFs), the finding that HIF-1 regulates the expression of many more genes apart from erythropoietin, and the elucidation of the oxygen-dependent mechanisms degrading the HIF alpha subunits recently led to the spectacular discovery of the molecular principles of oxygen sensing. This review aims to summarize our current knowledge of oxygen-regulated gene expression..

The pathogenesis of diabetic retinopathy: old concepts and new questions

Hyperglycaemia appears to be a critical factor in the aetiology of diabetic retinopathy and initiates downstream events including: basement membrane thickening, pericyte drop out and retinal capillary non-perfusion. More recently, focus has been directed to the molecular basis of the disease process in diabetic retinopathy. Of particular importance in the development and progression of diabetic retinopathy is the role of growth factors (eg vascular endothelial growth factor, placenta growth factor and pigment epithelium-derived factor) together with specific receptors and obligate components of the signal transduction pathway needed to support them. Despite these advances there are still a number of important questions that remain to be answered before we can confidently target pathological signals. How does hyperglycaemia regulate retinal vessels? Which growth factors are most important and at what stage of retinopathy do they operate? What is the preferred point in the growth factor signalling cascade for therapeutic intervention? Answers to these questions will provide the basis for new therapeutic interventions in a debilitating ocular condition.