Suppression of hypoxia-inducible factor 2alpha restores p53 activity via Hdm2 and reverses chemoresistance of renal carcinoma cells

HIF2 Inactivation and Tumor Suppression with a Tumor-Directed RNA-Silencing Drug in Mice and Humans

PURPOSE

HIF2α is a key driver of kidney cancer. Using a belzutifan analogue (PT2399), we previously showed in tumorgrafts (TG) that ∼50% of clear cell renal cell carcinomas (ccRCC) are HIF2α dependent. However, prolonged treatment induced resistance mutations, which we also identified in humans. Here, we evaluated a tumor-directed, systemically delivered, siRNA drug (siHIF2) active against wild-type and resistant-mutant HIF2α.

EXPERIMENTAL DESIGN

Using our credentialed TG platform, we performed pharmacokinetic and pharmacodynamic analyses evaluating uptake, HIF2α silencing, target gene inactivation, and antitumor activity. Orthogonal RNA-sequencing studies of siHIF2 and PT2399 were pursued to define the HIF2 transcriptome. Analyses were extended to a TG line generated from a study biopsy of a siHIF2 phase I clinical trial (NCT04169711) participant and the corresponding patient, an extensively pretreated individual with rapidly progressive ccRCC and paraneoplastic polycythemia likely evidencing a HIF2 dependency.

RESULTS

siHIF2 was taken up by ccRCC TGs, effectively depleted HIF2α, deactivated orthogonally defined effector pathways (including Myc and novel E2F pathways), downregulated cell cycle genes, and inhibited tumor growth. Effects on the study subject TG mimicked those in the patient, where HIF2α was silenced in tumor biopsies, circulating erythropoietin was downregulated, polycythemia was suppressed, and a partial response was induced.

CONCLUSIONS

To our knowledge, this is the first example of functional inactivation of an oncoprotein and tumor suppression with a systemic, tumor-directed, RNA-silencing drug. These studies provide a proof-of-principle of HIF2α inhibition by RNA-targeting drugs in ccRCC and establish a paradigm for tumor-directed RNA-based therapeutics in cancer.

Low expression of LncRNA-CAF attributed to the high expression of HIF1A in esophageal squamous cell carcinoma and gastric cancer patients

PURPOSE

Cancer-associated fibroblasts (CAFs) are major components of tumor microenvironment that stimulate ESCC and GC progression. The LncRNA-CAF, FLJ22447, is located in the vicinity of HIF1A, while their association remains unclear. This study aims to assess the FLJ22447 expression in the ESCC and GC patients and evaluate its association with the HIF1A gene.

METHODS

Fresh ESCC and GC tumor samples and their adjacent non-tumor tissues were collected from patients who underwent surgery in Imam Khomeini Hospital, Tehran, Iran. The expression of FLJ22447, HIF1A, and VEGF was evaluated using qRT-PCR test. The association of their expression with tumor clinicopathological features in ESCC patients was assessed. System biology tools were then applied for the possible biological subsequences of the FLJ22447.

RESULTS

A significant reduction in FLJ22447 expression was observed in ESCC and GC tissues than adjacent non-tumor tissues, while, the expression of HIF1A and VEGF were increased. Low expression of FLJ22447 was significantly correlated with HIF1A (P = 2.4e-73, R = 0.63) and VEGF (P = 0.00019, R = 0.15) expression. A significant relationship was detected between the high expression of HIF1A and tumor stages (I-II) and it was related to the reduced survival of ESCC patients. Conversely, increased VEGF expression was linked to the advanced stages (III-IV) and metastasis in ESCC. The analysis of FLJ22447-interacted proteins showed that MYC, JUN, SMRCA4, PPARG, AR, FOS, and CEBPA are the hub genes. These proteins were implicated in the cancer related pathways. Among them, SPI1, E2F1, TCF7L2, and STAT1 were significantly expressed in esophageal and gastric cancers that were functionally involved in the proliferation, apoptosis, and angiogenesis pathways in cancer.

CONCLUSION

The results suggested that FLJ22447 may have a regulatory function on the HIF1A expression. We identified the FLJ22447-interacted proteins and their molecular function in cancer pathogenesis. Further research emphasis is to realize the association of FLJ22447 with its protein partners in progression of cancer. These may provide an insight into the FLJ22447 activity that could introduce it as a potential value in tumor gene therapy.

Oxygen-sensing mechanisms in development and tissue repair

Under normoxia, hypoxia inducible factor (HIF) α subunits are hydroxylated by PHDs (prolyl hydroxylase domain proteins) and subsequently undergo polyubiquitylation and degradation. Normal embryogenesis occurs under hypoxia, which suppresses PHD activities and allows HIFα to stabilize and regulate development. In this Primer, we explain molecular mechanisms of the oxygen-sensing pathway, summarize HIF-regulated downstream events, discuss loss-of-function phenotypes primarily in mouse development, and highlight clinical relevance to angiogenesis and tissue repair.

Impact of Hypoxia over Human Viral Infections and Key Cellular Processes

Oxygen is essential for aerobic cells, and thus its sensing is critical for the optimal maintenance of vital cellular and tissue processes such as metabolism, pH homeostasis, and angiogenesis, among others. Hypoxia-inducible factors (HIFs) play central roles in oxygen sensing. Under hypoxic conditions, the α subunit of HIFs is stabilized and forms active heterodimers that translocate to the nucleus and regulate the expression of important sets of genes. This process, in turn, will induce several physiological changes intended to adapt to these new and adverse conditions. Over the last decades, numerous studies have reported a close relationship between viral infections and hypoxia. Interestingly, this relation is somewhat bidirectional, with some viruses inducing a hypoxic response to promote their replication, while others inhibit hypoxic cellular responses. Here, we review and discuss the cellular responses to hypoxia and discuss how HIFs can promote a wide range of physiological and transcriptional changes in the cell that modulate numerous human viral infections.

Oxygen-Based Nanocarriers to Modulate Tumor Hypoxia for Ameliorated Anti-Tumor Therapy: Fabrications, Properties, and Future Directions

Over the past five years, oxygen-based nanocarriers (NCs) to boost anti-tumor therapy attracted tremendous attention from basic research and clinical practice. Indeed, tumor hypoxia, caused by elevated proliferative activity and dysfunctional vasculature, is directly responsible for the less effectiveness or ineffective of many conventional therapeutic modalities. Undeniably, oxygen-generating NCs and oxygen-carrying NCs can increase oxygen concentration in the hypoxic area of tumors and have also been shown to have the ability to decrease the expression of drug efflux pumps (e.g., P-gp); to increase uptake by tumor cells; to facilitate the generation of cytotoxic reactive oxide species (ROS); and to evoke systematic anti-tumor immune responses. However, there are still many challenges and limitations that need to be further improved. In this review, we first discussed the mechanisms of tumor hypoxia and how it severely restricts the therapeutic efficacy of clinical treatments. Then an up-to-date account of recent progress in the fabrications of oxygen-generating NCs and oxygen-carrying NCs are systematically introduced. The improved physicochemical and surface properties of hypoxia alleviating NCs for increasing the targeting ability to hypoxic cells are also elaborated with special attention to the latest nano-technologies. Finally, the future directions of these NCs, especially towards clinical translation, are proposed. Therefore, we expect to provide some valued enlightenments and proposals in engineering more effective oxygen-based NCs in this promising field in this comprehensive overview.

Hypoxia Dictates Metabolic Rewiring of Tumors: Implications for Chemoresistance

Hypoxia is a condition commonly observed in the core of solid tumors. The hypoxia-inducible factors (HIF) act as hypoxia sensors that orchestrate a coordinated response increasing the pro-survival and pro-invasive phenotype of cancer cells, and determine a broad metabolic rewiring. These events favor tumor progression and chemoresistance. The increase in glucose and amino acid uptake, glycolytic flux, and lactate production; the alterations in glutamine metabolism, tricarboxylic acid cycle, and oxidative phosphorylation; the high levels of mitochondrial reactive oxygen species; the modulation of both fatty acid synthesis and oxidation are hallmarks of the metabolic rewiring induced by hypoxia. This review discusses how metabolic-dependent factors (e.g., increased acidification of tumor microenvironment coupled with intracellular alkalinization, and reduced mitochondrial metabolism), and metabolic-independent factors (e.g., increased expression of drug efflux transporters, stemness maintenance, and epithelial-mesenchymal transition) cooperate in determining chemoresistance in hypoxia. Specific metabolic modifiers, however, can reverse the metabolic phenotype of hypoxic tumor areas that are more chemoresistant into the phenotype typical of chemosensitive cells. We propose these metabolic modifiers, able to reverse the hypoxia-induced metabolic rewiring, as potential chemosensitizer agents against hypoxic and refractory tumor cells.

NOX2-Derived Reactive Oxygen Species in Cancer

The formation of reactive oxygen species (ROS) by the myeloid cell NADPH oxidase NOX2 is critical for the destruction of engulfed microorganisms. However, recent studies imply that ROS, formed by NOX2⁺ myeloid cells in the malignant microenvironment, exert multiple actions of relevance to the growth and spread of neoplastic cells. By generating ROS, tumor-infiltrating myeloid cells and NOX2⁺ leukemic myeloid cells may thus (i) compromise the function and viability of adjacent cytotoxic lymphocytes, including natural killer (NK) cells and T cells, (ii) oxidize DNA to trigger cancer-promoting somatic mutations, and (iii) affect the redox balance in cancer cells to control their proliferation and survival. Here, we discuss the impact of NOX2-derived ROS for tumorigenesis, tumor progression, regulation of antitumor immunity, and metastasis. We propose that NOX2 may be a targetable immune checkpoint in cancer.

Oroxylin A reverses hypoxia-induced cisplatin resistance through inhibiting HIF-1α mediated XPC transcription

Hypoxia is a key concern during the treatment of non-small cell lung cancer (NSCLC), and hypoxia-inducible factor 1 alpha (HIF-1α) has been associated with increased tumor resistance to therapeutic modalities such as cisplatin. Compensatory activation of nucleotide excision repair (NER) pathway is the major mechanism that accounts for cisplatin resistance. In the present study, we suggest a novel strategy to improve the treatment of NSCLC and overcome the hypoxia-induced cisplatin resistance by cotreatment with Oroxylin A, one of the main bioactive flavonoids of Scutellariae radix. Based on the preliminary screening, we found that xeroderma pigmentosum group C (XPC), an important DNA damage recognition protein involved in NER, dramatically increased in hypoxic condition and contributed to hypoxia-induced cisplatin resistance. Further data suggested that Oroxylin A significantly reversed the hypoxia-induced cisplatin resistance through directly binding to HIF-1α bHLH-PAS domain and blocking its binding to HRE3 transcription factor binding sites on XPC promoter which is important to hypoxia-induced XPC transcription. Taken together, our findings not only demonstrate a crucial role of XPC dependent NER in hypoxia-induced cisplatin resistance, but also suggest a previously unrecognized tumor suppressive mechanism of Oroxylin A in NSCLC which through sensitization of cisplatin-mediated growth inhibition and apoptosis under hypoxia.

NLRP3 inflammasome is expressed and regulated in human islets

NRLP3 inflammasome is a protein complex involved in the maturation of IL1β. In the onset of type 1 diabetes as well as in islet transplantation, IL-1β is one of the cytokines involved in the recruitment of immune cells in islets and eventually in islet destruction. Whether IL-1β is produced by islet cells is still under debate and NLRP3 inflammasome-dependent IL-1β production has not been yet determined in human islets. The aim of this study was to determine the expression and the regulation of the NRLP3 inflammasome in human islets. Human islets were stimulated with LPS and successively with ATP (LPS + ATP) in the presence or absence of the inflammasome inhibitor glyburide. Islets were also incubated in hypoxic or normoxic conditions for 24 h in the presence or absence of glyburide. Then, IL1B and NLRP3 expression was studied by real time PCR, protein expression by western blot, protein localization by immunofluorescence and protein secretion by ELISA. LPS + ATP increased gene expression of NRLP3 and IL1B. Glyburide partially prevented this effect. IL-1β protein was localized in β and non-β cells. Moreover, LPS + ATP increased IL-1β protein expression and production, which were prevented by glyburide. Hypoxia increased gene expression of NRLP3 and IL1B and induced IL-1β and caspase-1 production. Finally, hypoxia-induced cell death which was not prevented by inhibition of NLRP3 inflammasome. NRLP3 inflammasome is expressed and plays a role in IL-1β production by human islets. By contrast, NRLP3 inflammasome activation is not involved in islet cell death induced by hypoxia.

The von Hippel–Lindau Tumor Suppressor Protein

The von Hippel–Lindau (VHL) gene is a two-hit tumor suppressor gene and is linked to the development of the most common form of kidney cancer, clear cell renal carcinoma; blood vessel tumors of the retina, cerebellum, and spinal cord called hemangioblastomas; and tumors of the sympathoadrenal nervous system called paragangliomas. The VHL gene product, pVHL, is the substrate recognition subunit of a cullin-dependent ubiquitin ligase that targets the α subunits of hypoxia-inducible factor (HIF) for destruction when oxygen is plentiful. Mounting evidence implicates HIF2 in the pathogenesis of pVHL-defective tumors and has provided a conceptual foundation for the development of drugs to treat them that inhibit HIF2-responsive gene products such as VEGF and, more recently, HIF2 itself. pVHL has additional, noncanonical functions that are cancer relevant, including roles related to the primary cilium, chromosome stability, extracellular matrix formation, and survival signaling.

VHL deficiency augments anthracycline sensitivity of clear cell renal cell carcinomas by down-regulating ALDH2

The von Hippel-Lindau (VHL) is deficient in ∼70% of clear-cell renal cell carcinomas (ccRCC), which contributes to the carcinogenesis and drug resistance of ccRCC. Here we show that VHL-deficient ccRCC cells present enhanced cytotoxicity of anthracyclines in a hypoxia-inducible factor-independent manner. By subtractive proteomic analysis coupling with RNAi or overexpression verification, aldehyde dehydrogenase 2 (ALDH2) is found to be transcriptionally regulated by VHL and contributes to enhanced anthracyclines cytotoxicity in ccRCC cells. Furthermore, VHL regulates ALDH2 expression by directly binding the promoter of -130 bp to -160 bp to activate the transcription of hepatocyte nuclear factor 4 alpha (HNF-4α). In addition, a positive correlation is found among the protein expressions of VHL, HNF-4α and ALDH2 in ccRCC samples. These findings will deepen our understanding of VHL function and shed light on precise treatment for ccRCC patients.

Hypoxia: A Double-Edged Sword in Cancer Therapy

Hypoxia is a common feature of malignant tumors. There is an interactive connection between hypoxia and chemoresistance, radioresistance, invasiveness, and angiogenesis. Therefore, tumor hypoxia has been considered as a validated target for treating cancer. This review focuses on the role of hypoxia on chemoresistance and radioresistance. In addition, we address several approaches targeting tumor hypoxia, known as hypoxia-targeted therapy.

The role of hypoxia in cancer progression, angiogenesis, metastasis, and resistance to therapy

Hypoxia is a non-physiological level of oxygen tension, a phenomenon common in a majority of malignant tumors. Tumor-hypoxia leads to advanced but dysfunctional vascularization and acquisition of epithelial-to-mesenchymal transition phenotype resulting in cell mobility and metastasis. Hypoxia alters cancer cell metabolism and contributes to therapy resistance by inducing cell quiescence. Hypoxia stimulates a complex cell signaling network in cancer cells, including the HIF, PI3K, MAPK, and NFĸB pathways, which interact with each other causing positive and negative feedback loops and enhancing or diminishing hypoxic effects. This review provides background knowledge on the role of tumor hypoxia and the role of the HIF cell signaling involved in tumor blood vessel formation, metastasis, and development of the resistance to therapy. Better understanding of the role of hypoxia in cancer progression will open new windows for the discovery of new therapeutics targeting hypoxic tumor cells and hypoxic microenvironment.

On-target efficacy of a HIF-2α antagonist in preclinical kidney cancer models

Clear cell renal cell carcinoma, the most common form of kidney cancer, is usually linked to inactivation of the pVHL tumour suppressor protein and consequent accumulation of the HIF-2α transcription factor (also known as EPAS1). Here we show that a small molecule (PT2399) that directly inhibits HIF-2α causes tumour regression in preclinical mouse models of primary and metastatic pVHL-defective clear cell renal cell carcinoma in an on-target fashion. pVHL-defective clear cell renal cell carcinoma cell lines display unexpectedly variable sensitivity to PT2399, however, suggesting the need for predictive biomarkers to be developed to use this approach optimally in the clinic.

Therapeutic targeting of hypoxia and hypoxia-inducible factors in cancer

Insufficient tissue oxygenation, or hypoxia, contributes to tumor aggressiveness and has a profound impact on clinical outcomes in cancer patients. At decreased oxygen tensions, hypoxia-inducible factors (HIFs) 1 and 2 are stabilized and mediate a hypoxic response, primarily by acting as transcription factors. HIFs exert differential effects on tumor growth and affect important cancer hallmarks including cell proliferation, apoptosis, differentiation, vascularization/angiogenesis, genetic instability, tumor metabolism, tumor immune responses, and invasion and metastasis. As a consequence, HIFs mediate resistance to chemo- and radiotherapy and are associated with poor prognosis in cancer patients. Intriguingly, perivascular tumor cells can also express HIF-2α, thereby forming a "pseudohypoxic" phenotype that further contributes to tumor aggressiveness. Therefore, therapeutic targeting of HIFs in cancer has the potential to improve treatment efficacy. Different strategies to target hypoxic cancer cells and/or HIFs include hypoxia-activated prodrugs and inhibition of HIF dimerization, mRNA or protein expression, DNA binding capacity, and transcriptional activity. Here we review the functions of HIFs in the progression and treatment of malignant solid tumors. We also highlight how HIFs may be targeted to improve the management of patients with therapy-resistant and metastatic cancer.

Homozygous G/G variant of SNP309 in the human MDM2 gene is associated with earlier tumor onset in Caucasian female renal cell carcinoma patients

Human mouse double minute 2 (Mdm2) plays an essential role in the regulation of the tumor suppressor p53. The G/G variant of SNP309 was shown to increase Mdm2 mRNA/protein expression and to be associated with an increased risk and earlier onset of different cancers in Asian populations. However, the frequency and impact of these G/G variants have not been studied in Caucasian renal cell carcinoma (RCC) patients. Therefore, we analyzed an unselected German cohort of 197 consecutive RCC patients and detected the G/G variant in 18 (9.1%) patients, the G/T variant in 116 (58.9%) patients and the T/T variant in 63 (32.0%) patients. Studying the association between age at tumor onset and SNP309 genotypes, no correlation was detected in the entire RCC cohort or among the male RCC patients. However, the female G/G patients (median age 59.5 years) were diagnosed 13.5 years earlier than the T/T females (median age 73 years). When separating all females into two groups at their median age (68 years), 7 and 1 patients with the G/G variant and 9 and 13 patients with the T/T variant were noted in these age groups (P=0.024). To study the age dependency of tumor onset further, a second, age-selected cohort of 205 RCC patients was investigated, which comprised especially young and old patients. Interestingly, the G/G type occurred more often at lower tumor stages and tumor grades compared with higher stages (P=0.039 and 0.004, respectively). In females, the percentage of the G/G variant was only slightly higher in the younger age group, whereas in males, the percentage of the G/G variant was remarkably higher in the younger age group (19.4% vs 8.0%). In summary, female Caucasian RCC patients with the MDM2 SNP309 G/G genotype showed significantly earlier tumor onset than patients with the wild-type T/T genotype.

Metabolic Modulation of Clear-cell Renal Cell Carcinoma with Dichloroacetate, an Inhibitor of Pyruvate Dehydrogenase Kinase

BACKGROUND

Clear-cell renal cell carcinoma (ccRCC) exhibits suppressed mitochondrial function and preferential use of glycolysis even in normoxia, promoting proliferation and suppressing apoptosis. ccRCC resistance to therapy is driven by constitutive hypoxia-inducible factor (HIF) expression due to genetic loss of von Hippel-Lindau factor. In addition to promoting angiogenesis, HIF suppresses mitochondrial function by inducing pyruvate dehydrogenase kinase (PDK), a gatekeeping enzyme for mitochondrial glucose oxidation.

OBJECTIVE

To reverse mitochondrial suppression of ccRCC using the PDK inhibitor dichloroacetate (DCA).

DESIGN, SETTING, AND PARTICIPANTS

Radical nephrectomy specimens from patients with ccRCC were assessed for PDK expression. The 786-O ccRCC line and two animal models (chicken in ovo and murine xenografts) were used for mechanistic studies.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Mitochondrial function, proliferation, apoptosis, HIF transcriptional activity, angiogenesis, and tumor size were measured in vitro and in vivo. Independent-sample t-tests and analysis of variance were used for statistical analyses.

RESULTS

PDK was elevated in 786-O cells and in ccRCC compared to normal kidney tissue from the same patient. DCA reactivated mitochondrial function (increased respiration, Krebs cycle metabolites such as α-ketoglutarate [cofactor of factor inhibiting HIF], and mitochondrial reactive oxygen species), increased p53 activity and apoptosis, and decreased proliferation in 786-O cells. DCA reduced HIF transcriptional activity in an FIH-dependent manner, inhibiting angiogenesis in vitro. DCA reduced tumor size and angiogenesis in vivo in both animal models.

CONCLUSIONS

DCA can reverse the mitochondrial suppression of ccRCC and decrease HIF transcriptional activity, bypassing its constitutive expression. Its previous clinical use in humans makes it an attractive candidate for translation to ccRCC patients.

PATIENT SUMMARY

We show that an energy-boosting drug decreases tumor growth and tumor blood vessels in animals carrying human kidney cancer cells. This generic drug has been used in patients for other conditions and thus could be tested in kidney cancer that remains incurable.

Implications of Oxygen Homeostasis for Tumor Biology and Treatment

Tumors serve as a prototype system to study the role of the hypoxic microenvironment and gain insight in the regulation oxygen homeostasis. A series of biochemical and cell biological studies have significantly extended our knowledge of how tumor cells activate key regulatory mechanisms of oxygen homeostasis not only to adapt to the hostile tumor microenvironment but also to acquire a more aggressive tumor phenotype. Reduced oxygen levels and tumor-specific genetic alterations synergistically drive tumor progression by activating a key transcriptional system, the hypoxia inducible factors (HIFs). HIFs trigger a set of adaptive responses commonly associated with tumor malignancy including tumor angiogenesis, a shift in metabolism, proliferation, invasion, and metastasis. We and others could demonstrate that cancer stem cells are controlled by HIFs within a hypoxic niche, establishing an intriguing link between the well known function of hypoxia in tumor growth and stem cell biology. Additionally, HIF activation potentially conveys resistance to current tumor therapies including the evasive resistance phenotype observed after anti-angiogenic treatment. Together, these findings provide strong evidence that activation of the HIF system is a decisive step in cancer progression that critically shapes therapy response and clinical outcome. Recent insight into the precise mechanisms of oxygen sensing and signalling has offered new promising and potentially selective strategies to counteract this crucial pathway.

The role of hypoxia in cancer progression, angiogenesis, metastasis, and resistance to therapy

Hypoxia is a non-physiological level of oxygen tension, a phenomenon common in a majority of malignant tumors. Tumor-hypoxia leads to advanced but dysfunctional vascularization and acquisition of epithelial-to-mesenchymal transition phenotype resulting in cell mobility and metastasis. Hypoxia alters cancer cell metabolism and contributes to therapy resistance by inducing cell quiescence. Hypoxia stimulates a complex cell signaling network in cancer cells, including the HIF, PI3K, MAPK, and NFĸB pathways, which interact with each other causing positive and negative feedback loops and enhancing or diminishing hypoxic effects. This review provides background knowledge on the role of tumor hypoxia and the role of the HIF cell signaling involved in tumor blood vessel formation, metastasis, and development of the resistance to therapy. Better understanding of the role of hypoxia in cancer progression will open new windows for the discovery of new therapeutics targeting hypoxic tumor cells and hypoxic microenvironment.

Examining the connectivity between different cellular processes in the Barrett tissue microenvironment

In Barrett associated tumorigenesis, oxidative phosphorylation and glycolysis are reprogrammed early in the disease sequence and act mutually to promote disease progression. However, the link between energy metabolism and its connection with other central cellular processes within the Barrett microenvironment is unknown. The aim of this study was to examine the relationship between metabolism (ATP5B/GAPDH), hypoxia (HIF1α), inflammation (IL1β/SERPINA3), p53 and obesity status using in-vivo and ex-vivo models of Barrett oesophagus. At the protein level, ATP5B (r = 0.71, P < 0.0001) and p53 (r = 0.455, P = 0.015) were found to be strongly associated with hypoxia. In addition, levels of ATP5B (r = 0.53, P = 0.0031) and GAPDH (r = -0.39, P = 0.0357) were positively associated with p53 expression. Moreover, we demonstrate that ATP5B (r = 0.8, P < 0.0001) and GAPDH (r = 0.43, P = 0.022) were positively associated with IL1β expression. Interestingly, obesity was negatively associated with oxidative phosphorylation (r = -0.6016, P = 0.0177) but positively associated with glycolysis (r = 0.743, P = 0.0015). Comparable correlations were exhibited in the ex-vivo explant tissue between metabolism, p53, hypoxia, inflammation and angiogenesis (P < 0.05). We have shown that metabolism is closely linked with many cellular processes in the Barrett tissue microenvironment.

TRIM8 anti-proliferative action against chemo-resistant renal cell carcinoma

In some tumours, despite a wild-type p53 gene, the p53 pathway is inactivated by alterations in its regulators or by unknown mechanisms, leading to resistance to cytotoxic therapies. Understanding the mechanisms of functional inactivation of wild-type p53 in these tumours may help to define prospective targets for treating cancer by restoring p53 activity.

Recently, we identified TRIM8 as a new p53 modulator, which stabilizes p53 impairing its association with MDM2 and inducing the reduction of cell proliferation.

In this paper we demonstrated that TRIM8 deficit dramatically impairs p53-mediated cellular responses to chemotherapeutic drugs and that TRIM8 is down regulated in patients affected by clear cell Renal Cell Carcinoma (ccRCC), an aggressive drug-resistant cancer showing wild-type p53. These results suggest that down regulation of TRIM8 might be an alternative way to suppress p53 activity in RCC. Interestingly, we show that TRIM8 expression recovery in RCC cell lines renders these cells sensitive to chemotherapeutic treatments following p53 pathway re-activation.

These findings provide the first mechanistic link between TRIM8 and the drug resistance of ccRCC and suggest more generally that TRIM8 could be used as enhancer of the chemotherapy efficacy in cancers where p53 is wild-type and its pathway is defective.

RING finger protein 31 promotes p53 degradation in breast cancer cells

The atypical E3 ubiquitin ligase RNF31 is highly expressed in human breast cancer, the most frequent neoplastic lethality among women. Here, RNF31 depletion in breast cancer cells in combination with global gene expression profiling revealed p53 (TP53) signaling as a potential RNF31 target. Interestingly, RNF31 decreased p53 stability, whereas depletion of RNF31 in breast cancer cells caused cell cycle arrest and cisplatin-induced apoptosis in a p53-dependent manner. Furthermore, RNF31 associated with the p53/MDM2 complex and facilitated p53 polyubiquitination and degradation by stabilizing MDM2, suggesting a molecular mechanism by which RNF31 regulates cell death. Analysis of publically available clinical data sets displayed a negative correlation between RNF31 and p53 target genes, including IGFBP3 and BTG1, consistent with RNF31 regulating p53 function in vivo as well. Together, our findings suggest RNF31 as a potential therapeutic target to restore p53 function in breast cancer.

The emerging role of hypoxia-inducible factor-2 involved in chemo/radioresistance in solid tumors

The hypoxic condition is a common feature that negatively impacts the efficacy of radio- and chemotherapy in solid tumors. Hypoxia-inducible factors (HIF-1, 2, 3) predominantly regulate the adaptation to hypoxia at the cellular or organismal level. HIF-2 is one of the three known alpha subunits of HIF transcription factors. Previous studies have shown that HIF-1 is associated with chemotherapy failure. Accumulating evidence in recent years suggests that HIF-2 also contributes to chemo/radioresistance in solid tumors. Despite sharing similar structures, HIF-1α and HIF-2α had highly divergent and even opposing roles in solid tumors under hypoxic conditions. Recent studies have also implied that HIF-2α had a role in chemo/radioresistance through different mechanisms, at least partly, compared to HIF-1α. The present paper summarizes the function of HIF-2 in chemo/radioresistance in solid tumors as well as some of its novel mechanisms that contributed to this pathological process.

Low expression of phosphatase and tensin homolog in clear‑cell renal cell carcinoma contributes to chemoresistance through activating the Akt/HDM2 signaling pathway

Clear-cell renal cell carcinoma (CCRCC) is the most frequent primary malignancy in the adult kidney. Most patients with advanced CCRCC have poor prognosis as CCRCC remains resistant to chemotherapy. The present study explored the possible mechanism underlying CCRCC resistance to chemotherapy and found that loss of PTEN in CCRCC may be involved. Knockdown of PTEN in the CCRCC cell line ACHN blocked etoposide-induced apoptosis and etoposide-impaired cell proliferation was also inhibited. It has been demonstrated that most chemotherapy drugs exert their anti-cancer effects via p53-mediated apoptosis, and in accordance, with this, the present study showed that treatment with etoposide significantly increased p53 levels. Silencing of PTEN in ACHN inhibited the Akt/HDM2 signaling cascade and depressed p53 expression, and the interaction between HDM2 and p53 was also enhanced. This was further verified in CCRCC tissue specimens from patients The results of the present study suggested that loss of PTEN, which deactivated Akt/HDM2 signaling followed by degradation of p53, may contribute to the development of etoposide resistance in CCRCC.

Apoptotic cell death under hypoxia

Eukaryotic life depends largely on molecular oxygen. During evolution, ingenious mechanisms have evolved that allow organisms to adapt when oxygen levels decrease. Many of these adaptional responses to low oxygen are orchestrated by the heterodimeric transcription factor hypoxia-inducible factor (HIF). Here, we review the link between HIF and apoptosis.

VHL, the story of a tumour suppressor gene

Since the Von Hippel-Lindau (VHL) disease tumour suppressor gene VHL was identified in 1993 as the genetic basis for a rare disorder, it has proved to be of wide medical and scientific interest. VHL tumour suppressor protein (pVHL) plays a key part in cellular oxygen sensing by targeting hypoxia-inducible factors for ubiquitylation and proteasomal degradation. Early inactivation of VHL is commonly seen in clear-cell renal cell carcinoma (ccRCC), and insights gained from the functional analysis of pVHL have provided the foundation for the routine treatment of advanced-stage ccRCC with novel targeted therapies. However, recent sequencing studies have identified additional driver genes that are involved in the pathogenesis of ccRCC. As our understanding of the importance of VHL matures, it is timely to review progress from its initial description to current knowledge of VHL biology, as well as future prospects for novel medical treatments for VHL disease and ccRCC.

Loss of VHL promotes progerin expression, leading to impaired p14/ARF function and suppression of p53 activity

Renal cell carcinomas (RCCs) are frequently occurring genitourinary malignancies in the aged population. A morphological characteristic of RCCs is an irregular nuclear shape, which is used to index cancer grades. Other features of RCCs include the genetic inactivation of the von Hippel-Lindau gene, VHL, and p53 genetic-independent inactivation. An aberrant nuclear shape or p53 suppression has not yet been demonstrated. We examined the effect of progerin (an altered splicing product of the LMNA gene linked to Hutchinson Gilford progeria syndrome; HGPS) on the nuclear deformation of RCCs in comparison to that of HGPS cells. In this study, we showed that progerin was suppressed by pVHL and was responsible for nuclear irregularities as well as p53 inactivation. Thus, progerin suppression can ameliorate nuclear abnormalities and reactivate p53 in response to genotoxic addition. Furthermore, we found that progerin was a target of pVHL E3 ligase and suppressed p53 activity by p14/ARF inhibition. Our findings indicate that the elevated expression of progerin in RCCs results from the loss of pVHL and leads to p53 inactivation through p14/ARF suppression. Interestingly, we showed that progerin was expressed in human leukemia and primary cell lines, raising the possibility that the expression of this LMNA variant may be a common event in age-related cancer progression.

The multifaceted von Hippel-Lindau tumour suppressor protein

Loss of von Hippel-Lindau protein (pVHL) is known to contribute to the initiation and progression of tumours associated with VHL disease as well as certain sporadic tumours including clear cell renal cell carcinoma (ccRCC). The VHL gene was first identified and cloned over 20 years ago and our understanding of its functions and effects has significantly increased since then. The best-known function of pVHL is its role in promoting the degradation of hypoxia-inducible factor α subunit (HIFα) as part of an E3 ubiquitin ligase complex. HIF stabilisation and transcriptional activation are also associated with various epigenetic alterations, indicating a potential role for VHL loss with changes in the epigenome. This review will highlight current knowledge regarding pVHL as well as discuss potentially novel roles of pVHL and how these may impact on cancer progression.

The apoptosis repressor with a CARD domain (ARC) gene is a direct hypoxia-inducible factor 1 target gene and promotes survival and proliferation of VHL-deficient renal cancer cells

The induction of hypoxia-inducible factors (HIFs) is essential for the adaptation of tumor cells to a low-oxygen environment. We found that the expression of the apoptosis inhibitor ARC (apoptosis repressor with a CARD domain) was induced by hypoxia in a variety of cancer cell types, and its induction is primarily HIF1 dependent. Chromatin immunoprecipitation (ChIP) and reporter assays also indicate that the ARC gene is regulated by direct binding of HIF1 to a hypoxia response element (HRE) located at bp -190 upstream of the transcription start site. HIFs play an essential role in the pathogenesis of renal cell carcinoma (RCC) under normoxic conditions, through the loss of the Von Hippel-Lindau gene (VHL). Accordingly, our results show that ARC is not expressed in normal renal tissue but is highly expressed in 65% of RCC tumors, which also express high levels of carbonic anhydrase IX (CAIX), a HIF1-dependent protein. Compared to controls, ARC-deficient RCCs exhibited decreased colony formation and increased apoptosis in vitro. In addition, loss of ARC resulted in a dramatic reduction of RCC tumor growth in SCID mice in vivo. Thus, HIF-mediated increased expression of ARC in RCC can explain how loss of VHL can promote survival early in tumor formation.

Chemotherapy-mediated p53-dependent DNA damage response in clear cell renal cell carcinoma: role of the mTORC1/2 and hypoxia-inducible factor pathways

The DNA-damaging agent camptothecin (CPT) and its analogs demonstrate clinical utility for the treatment of advanced solid tumors, and CPT-based nanopharmaceuticals are currently in clinical trials for advanced kidney cancer; however, little is known regarding the effects of CPT on hypoxia-inducible factor-2α (HIF-2α) accumulation and activity in clear cell renal cell carcinoma (ccRCC). Here we assessed the effects of CPT on the HIF/p53 pathway. CPT demonstrated striking inhibition of both HIF-1α and HIF-2α accumulation in von Hippel–Lindau (VHL)-defective ccRCC cells, but surprisingly failed to inhibit protein levels of HIF-2α-dependent target genes (VEGF, PAI-1, ET-1, cyclin D1). Instead, CPT induced DNA damage-dependent apoptosis that was augmented in the presence of pVHL. Further analysis revealed CPT regulated endothelin-1 (ET-1) in a p53-dependent manner: CPT increased ET-1 mRNA abundance in VHL-defective ccRCC cell lines that was significantly augmented in their VHL-expressing counterparts that displayed increased phosphorylation and accumulation of p53; p53 siRNA suppressed CPT-induced increase in ET-1 mRNA, as did an inhibitor of ataxia telangiectasia mutated (ATM) signaling, suggesting a role for ATM-dependent phosphorylation of p53 in the induction of ET-1. Finally, we demonstrate that p53 phosphorylation and accumulation is partially dependent on mTOR activity in ccRCC. Consistent with this result, pharmacological inhibition of mTORC1/2 kinase inhibited CPT-mediated ET-1 upregulation, and p53-dependent responses in ccRCC. Collectively, these data provide mechanistic insight into the action of CPT in ccRCC, identify ET-1 as a p53-regulated gene and demonstrate a requirement of mTOR for p53-mediated responses in this tumor type.

HIF isoforms in the skin differentially regulate systemic arterial pressure

Vascular flow through tissues is regulated via a number of homeostatic mechanisms. Localized control of tissue blood flow, or autoregulation, is a key factor in regulating tissue perfusion and oxygenation. We show here that the net balance between two hypoxia-inducible factor (HIF) transcription factor isoforms, HIF-1α and HIF-2α, is an essential mechanism regulating both local and systemic blood flow in the skin of mice. We also show that balance of HIF isoforms in keratinocyte-specific mutant mice affects thermal adaptation, exercise capacity, and systemic arterial pressure. The two primary HIF isoforms achieve these effects in opposing ways that are associated with HIF isoform regulation of nitric oxide production. We also show that a correlation exists between altered levels of HIF isoforms in the skin and the degree of idiopathic hypertension in human subjects. Thus, the balance between HIF-1α and HIF-2α expression in keratinocytes is a control element of both tissue perfusion and systemic arterial pressure, with potential implications in human hypertension.

The human melanoma side population displays molecular and functional characteristics of enriched chemoresistance and tumorigenesis

Melanoma remains the most lethal skin cancer, mainly because of high resistance to therapy. Side population (SP) cells are found in many types of cancer and are usually enriched in therapy-resistant as well as tumorigenic cells. Here, we identified a Hoechst dye-effluxing SP in a large series of human melanoma samples representing different progression phases. The SP size did not change with disease stage but was correlated with the prognostic “Breslow’s depth” in the primary (cutaneous) tumors. When injected into immunodeficient mice, the SP generated larger tumors than the bulk “main population” (MP) melanoma cells in two consecutive generations, and showed tumorigenic capacity at lower cell numbers than the MP. In addition, the SP reconstituted the heterogeneous composition of the human A375 melanoma cell line, and its clonogenic activity was 2.5-fold higher than that of the MP. Gene-expression analysis revealed upregulated expression in the melanoma SP (versus the MP) of genes associated with chemoresistance and anti-apoptosis. Consistent with these molecular characteristics, the SP increased in proportion when A375 cells were exposed to the melanoma standard chemotherapeutic agent dacarbazine, and to the aggravating condition of hypoxia. In addition, the SP showed enhanced expression of genes related to cell invasion and migration, as well as to putative (melanoma) cancer stem cells (CSC) including ABCB1 and JARID1B. ABCB1 immunoreactivity was detected in a number of tumor cells in human melanomas, and in particular in clusters at the invasive front of the primary tumors. Together, our findings support that the human melanoma SP is enriched in tumorigenic and chemoresistant capacity, considered key characteristics of CSC. The melanoma SP may therefore represent an interesting therapeutic target.

Hypoxia-induced cytotoxic drug resistance in osteosarcoma is independent of HIF-1Alpha

Survival rates from childhood cancer have improved dramatically in the last 40 years, such that over 80% of children are now cured. However in certain subgroups, including metastatic osteosarcoma, survival has remained stubbornly poor, despite dose intensive multi-agent chemotherapy regimens, and new therapeutic approaches are needed. Hypoxia is common in adult solid tumours and is associated with treatment resistance and poorer outcome. Hypoxia induces chemotherapy resistance in paediatric tumours including neuroblastoma, rhabdomyosarcoma and Ewing’s sarcoma, in vitro, and this drug resistance is dependent on the oxygen-regulated transcription factor hypoxia inducible factor-1 (HIF-1). In this study the effects of hypoxia on the response of the osteosarcoma cell lines 791T, HOS and U2OS to the clinically relevant cytotoxics cisplatin, doxorubicin and etoposide were evaluated. Significant hypoxia-induced resistance to all three agents was seen in all three cell lines and hypoxia significantly reduced drug-induced apoptosis. Hypoxia also attenuated drug-induced activation of p53 in the p53 wild-type U2OS osteosarcoma cells. Drug resistance was not induced by HIF-1α stabilisation in normoxia by cobalt chloride nor reversed by the suppression of HIF-1α in hypoxia by shRNAi, siRNA, dominant negative HIF or inhibition with the small molecule NSC-134754, strongly suggesting that hypoxia-induced drug resistance in osteosarcoma cells is independent of HIF-1α. Inhibition of the phosphoinositide 3-kinase (PI3K) pathway using the inhibitor PI-103 did not reverse hypoxia-induced drug resistance, suggesting the hypoxic activation of Akt in osteosarcoma cells does not play a significant role in hypoxia-induced drug resistance. Targeting hypoxia is an exciting prospect to improve current anti-cancer therapy and combat drug resistance. Significant hypoxia-induced drug resistance in osteosarcoma cells highlights the potential importance of hypoxia as a target to reverse drug resistance in paediatric osteosarcoma. The novel finding of HIF-1α independent drug resistance suggests however other hypoxia related targets may be more relevant in paediatric osteosarcoma.

Hypoxia influences stem cell-like properties in multidrug resistant K562 leukemic cells

OBJECTIVES

The present study investigates the potential role of hypoxia in maintaining stem cell-like properties and therapeutic resistance in K562 leukemic cell.

METHODS

Western blot, flow cytometry and cell viability assays were used to investigate the effects of hypoxia (1% O2) on cell proliferation, drug resistance and expression of the hypoxia inducible factor-2α (HIF-2α), the octamer-binding transcription factor 4 (Oct4), CD133, CD34 and the ATP-binding cassette sub-family G member 2 (ABCG2) as well as Smad2 phosphorylation in the drug resistant cell line K562/DOX and its parental cell line.

RESULTS

Hypoxia induced growth inhibition and significantly upregulated HIF-2α, CD133, Oct4, CD34 and ABCG2 expression in the wild type K562 cells (p<0.05). The IC50 of doxorubicin was also enhanced about 2.5-fold in hypoxia. In contrast, the K562/DOX cells, which showed significantly higher ABCG2 expression and IC50 for various drugs, no significant difference in cell proliferation was observed between hypoxia and normoxia. The hypoxia-induced upregulation of HIF-2α, CD133, Oct4, CD34 and ABCG2 expression was significantly lower than in the wild type cells (p<0.05). Moreover, hypoxia induced the phosphorylation of Smad2 and additional treatment with SD-208, an inhibitor of the TGF-β receptor I kinase, resulted in a dose-dependent downregulation of CD133 and Oct4 in the K562/DOX cells.

CONCLUSIONS

Hypoxia plays an important role in enhancing the stem cell-like properties and to induce multidrug resistance of leukemia cells. The activation of the TGF-β/Smad2 signaling pathway may be involved in the regulation of this pathophysiological process.

Combined mutation of Vhl and Trp53 causes renal cysts and tumours in mice

The combinations of genetic alterations that cooperate with von Hippel–Lindau (VHL) mutation to cause clear cell renal cell carcinoma (ccRCC) remain poorly understood. We show that the TP53 tumour suppressor gene is mutated in approximately 9% of human ccRCCs. Combined deletion of Vhl and Trp53 in primary mouse embryo fibroblasts causes proliferative dysregulation and high rates of aneuploidy. Deletion of these genes in the epithelium of the kidney induces the formation of simple cysts, atypical cysts and neoplasms, and deletion in the epithelia of the genital urinary tract leads to dysplasia and tumour formation. Kidney cysts display a reduced frequency of primary cilia and atypical cysts and neoplasms exhibit a pro-proliferative signature including activation of mTORC1 and high expression of Myc, mimicking several cellular and molecular alterations seen in human ccRCC and its precursor lesions. As the majority of ccRCC is associated with functional inactivation of VHL, our findings suggest that for a subset of ccRCC, loss of p53 function represents a critical event in tumour development.

The impact of hypoxia on cell death pathways

Hypoxia is a frequently encountered feature of the cellular microenvironment in a number of pathophysiological processes in which programmed cell death (apoptosis) affects disease progression including, but not limited to, cancer, chronic inflammation, myocardial infarction, stroke and ischaemic acute kidney injury. In these diseases, the presence of hypoxia can significantly affect the rate of cell death and thus may make a significant contribution to disease progression. In the present review, we discuss the complex relationship that exists between the presence of hypoxia and the regulation of cell death pathways.