Increase in gene dosage is a mechanism of HIF-1alpha constitutive expression in head and neck squamous cell carcinomas

Differential HIF2α Protein Expression in Human Carotid Body and Adrenal Medulla under Physiologic and Tumorigenic Conditions

Hypoxia-inducible factors (HIF) 2α and 1α are the major oxygen-sensing molecules in eukaryotic cells. HIF2α has been pathogenically linked to paraganglioma and pheochromocytoma (PPGL) arising in sympathetic paraganglia or the adrenal medulla (AM), respectively. However, its involvement in the pathogenesis of paraganglioma arising in the carotid body (CB) or other parasympathetic ganglia in the head and neck (HNPGL) remains to be defined. Here, we retrospectively analyzed HIF2α by immunohistochemistry in 62 PPGL/HNPGL and human CB and AM, and comprehensively evaluated the HIF-related transcriptome of 202 published PPGL/HNPGL. We report that HIF2α is barely detected in the AM, but accumulates at high levels in PPGL, mostly (but not exclusively) in those with loss-of-function mutations in VHL and genes encoding components of the succinate dehydrogenase (SDH) complex. This is associated with upregulation of EPAS1 and the HIF2α-regulated genes COX4I2 and ADORA2A. In contrast, HIF2α and HIF2α-regulated genes are highly expressed in CB and HNPGL, irrespective of VHL and SDH dysfunctions. We also found that HIF2α and HIF1α protein expressions are not correlated in PPGL nor HNPGL. In addition, HIF1α-target genes are almost exclusively overexpressed in VHL-mutated HNPGL/PPGL. Collectively, the data suggest that involvement of HIF2α in the physiology and tumor pathology of human paraganglia is organ-of-origin-dependent and HIF1α-independent.

Low HIF-1α and low EGFR mRNA Expression Significantly Associate with Poor Survival in Soft Tissue Sarcoma Patients; the Proteins React Differently

In various tumors, the hypoxia inducible factor-1α (HIF-1α) and the epidermal growth factor-receptor (EGFR) have an impact on survival. Nevertheless, the prognostic impact of both markers for soft tissue sarcoma (STS) is not well studied. We examined 114 frozen tumor samples from adult soft tissue sarcoma patients and 19 frozen normal tissue samples. The mRNA levels of HIF-1α, EGFR, and the reference gene hypoxanthine phosphoribosyltransferase (HPRT) were quantified using a multiplex qPCR technique. In addition, levels of EGFR or HIF-1α protein were determined from 74 corresponding protein samples using ELISA techniques. Our analysis showed that a low level of HIF-1α or EGFR mRNA (respectively, relative risk (RR) = 2.8; p = 0.001 and RR = 1.9; p = 0.04; multivariate Cox´s regression analysis) is significantly associated with a poor prognosis in STS patients. The combination of both mRNAs in a multivariate Cox’s regression analysis resulted in an increased risk of early tumor-specific death of patients (RR = 3.1, p = 0.003) when both mRNA levels in the tumors were low. The EGFR protein level had no association with the survival of the patient’s cohort studied, and a higher level of HIF-1α protein associated only with a trend to significance (multivariate Cox’s regression analysis) to a poor prognosis in STS patients (RR = 1.9, p = 0.09). However, patients with low levels of HIF-1α protein and a high content of EGFR protein in the tumor had a three-fold better survival compared to patients without such constellation regarding the protein level of HIF-1α and EGFR. In a bivariate two-sided Spearman’s rank correlation, a significant correlation between the expression of HIF-1α mRNA and expression of EGFR mRNA (p < 0.001) or EGFR protein (p = 0.001) was found, additionally, EGFR mRNA correlated with EGFR protein level (p < 0.001). Our results show that low levels of HIF-1α mRNA or EGFR mRNA are negative independent prognostic markers for STS patients, especially after combination of both parameters. The protein levels showed a different effect on the prognosis. In addition, our analysis suggests a possible association between HIF-1α and EGFR expression in STS.

Deregulation of LIMD1-VHL-HIF-1α-VEGF pathway is associated with different stages of cervical cancer

To understand the mechanism of cellular stress in basal-parabasal layers of normal cervical epithelium and during different stages of cervical carcinoma, we analyzed the alterations (expression/methylation/copy number variation/mutation) of HIF-1α and its associated genes LIMD1, VHL and VEGF in disease-free normal cervix (n = 9), adjacent normal cervix of tumors (n = 70), cervical intraepithelial neoplasia (CIN; n = 32), cancer of uterine cervix (CACX; n = 174) samples and two CACX cell lines. In basal-parabasal layers of normal cervical epithelium, LIMD1 showed high protein expression, while low protein expression of VHL was concordant with high expression of HIF-1α and VEGF irrespective of HPV-16 (human papillomavirus 16) infection. This was in concordance with the low promoter methylation of LIMD1 and high in VHL in the basal-parabasal layers of normal cervix. LIMD1 expression was significantly reduced while VHL expression was unchanged during different stages of cervical carcinoma. This was in concordance with their frequent methylation during different stages of this tumor. In different stages of cervical carcinoma, the expression pattern of HIF-1α and VEGF was high as seen in basal-parabasal layers and inversely correlated with the expression of LIMD1 and VHL. This was validated by demethylation experiments using 5-aza-2'-deoxycytidine in CACX cell lines. Additional deletion of LIMD1 and VHL in CIN/CACX provided an additional growth advantage during cervical carcinogenesis through reduced expression of genes and associated with poor prognosis of patients. Our data showed that overexpression of HIF-1α and its target gene VEGF in the basal-parabasal layers of normal cervix was due to frequent inactivation of VHL by its promoter methylation. This profile was maintained during different stages of cervical carcinoma with additional methylation/deletion of VHL and LIMD1.

Role of VHL, HIF1A and SDH on the expression of miR-210: Implications for tumoral pseudo-hypoxic fate

The hypoxia-inducible factor 1α (HIF-1α) and its microRNA target, miR-210, are candidate tumor-drivers of metabolic reprogramming in cancer. Neuroendocrine neoplasms such as paragangliomas (PGLs) are particularly appealing for understanding the cancer metabolic adjustments because of their associations with deregulations of metabolic enzymes, such as succinate dehydrogenase (SDH), and the von Hippel Lindau (VHL) gene involved in HIF-1α stabilization. However, the role of miR-210 in the pathogenesis of SDH-related tumors remains an unmet challenge. Herein is described an in vivo genetic analysis of the role of VHL, HIF1A and SDH on miR-210 by using knockout murine models, siRNA gene silencing, and analyses of human tumors. HIF-1α knockout abolished hypoxia-induced miR-210 expression in vivo but did not alter its constitutive expression in paraganglia. Normoxic miR-210 levels substantially increased by complete, but not partial, VHL silencing in paraganglia of knockout VHL-mice and by over-expression of p76del-mutated pVHL. Similarly, VHL-mutated PGLs, not those with decreased VHL-gene/mRNA dosage, over-expressed miR-210 and accumulate HIF-1α in most tumor cells. Ablation of SDH activity in SDHD-null cell lines or reduction of the SDHD or SDHB protein levels elicited by siRNA-induced gene silencing did not induce miR-210 whereas the presence of SDH mutations in PGLs and tumor-derived cell lines was associated with mild increase of miR-210 and the presence of a heterogeneous, HIF-1α-positive and HIF-1α-negative, tumor cell population. Thus, activation of HIF-1α is likely an early event in VHL-defective PGLs directly linked to VHL mutations, but it is a late event favored but not directly triggered by SDHx mutations. This combined analysis provides insights into the mechanisms of HIF-1α/miR-210 regulation in normal and tumor tissues potentially useful for understanding the pathogenesis of cancer and other diseases sharing similar underpinnings.

Clinically relevant HIF-1α-dependent metabolic reprogramming in oropharyngeal squamous cell carcinomas includes coordinated activation of CAIX and the miR-210/ISCU signaling axis, but not MCT1 and MCT4 upregulation

Metabolic reprogramming is a very heterogeneous phenomenon in cancer. It mostly consists on increased glycolysis, lactic acid formation and extracellular acidification. These events have been associated to increased activity of the hypoxia inducible factor, HIF-1α. This study aimed at defining the metabolic program activated by HIF-1α in oropharyngeal squamous cell carcinomas (SCC) and assessing its clinical impact. Global gene/miRNA expression was analyzed in SCC-derived cells exposed to hypoxia. Expression of HIF-1α, the carbonic anhydrase CAIX, and the lactate/H⁺ transporters MCT1 and MCT4 were analyzed by immunohistochemistry in 246 SCCs. Cell-based analysis revealed that HIF-1α-driven metabolic program includes over-expression of glycolytic enzymes and the microRNA miR-210 coupled to down-regulation of its target, the iron-sulfur cluster assembly protein, ISCU. pH-regulator program entailed over-expression of CAIX, but not MCT1 or MCT4. Accordingly, significant overlapping exists between over-expression of HIF-1α and CAIX, but not HIF-1α and MCT1 or MCT4, in tumor cells. Increased miR-210 and concomitant decreased ISCU RNA levels were found in ~40% of tumors and this was significantly associated with HIF-1α and CAIX, but not MCT1 or MCT4, over-expression. HIF-1α and/or CAIX over-expression was associated with high recurrence rate and low overall survival of surgically treated patients. By contrast, clinically significant correlations were not found in tumors with MCT1 or MCT4 over-expression. This is the first study that provides in vivo evidences of coordinated activation of HIF-1α, CAIX, miR-210 and ISCU in carcinoma and association with poor prognosis, a finding with important implications for the development of metabolic-targeting therapies against hypoxia.

East Urals Radioactive Trace: Dose-dependent functional-metabolic effects in the myocardium of the pygmy wood mouse (Apodemus uralensis) taking into account population size

The population dynamics, radiometric data and biochemical parameters (concentrations of total lipids, proteins, DNA and RNA, activity of succinate dehydrogenase, glucose phosphate isomerase and catalase, as well as lipid peroxidation level) in the myocardium of the pygmy wood mouse (Apodemus uralensis Pall., 1811) inhabiting the area of the East Urals Radioactive Trace (EURT) were analyzed. The functional-metabolic radiation effects as a result external and internal exposure to ¹³⁷Cs and ⁹⁰Sr (unweighted total dose rate 0.04-0.5 mGy/day) are characterized by a reduction in lipid catabolism, mitochondrial oxidation and antioxidant defense, as well as the activation of anaerobic glycolysis as well as the protein-synthesizing and genetic apparatus. The data indicate the low efficiency of cell energy production and allow us to state that compensatory myocardial hypertrophy can improve myocardial contractile function. The level of the functional-metabolic response in pygmy wood mice in the EURT area increased with increasing whole-body radiation dose rate and was more pronounced with a large pygmy wood mouse population size. The harmful effects (cardiac decompensation stage) of synergies resulting from non-radiation and radiation factors manifest after population abundance above 30 ind./100 trap-day and a radiation burden above 0.1 mGy/day.

In vitro study of normoxic epidermal growth factor receptor-induced hypoxia-inducible factor-1-alpha, vascular endothelial growth factor, and BNIP3 expression in head and neck squamous cell carcinoma cell lines: Implications for anti-epidermal growth factor receptor therapy

BACKGROUND

We previously showed that activation of epidermal growth factor receptor (EGFR) induces hypoxia inducible factor-1α (HIF-1α) in head and neck squamous cell carcinoma (HNSCC) cells. In this study, we have furthered this by investigating the mechanism of HIF-1α activation by epidermal growth factor (EGF) and its association with the sensitivity to gefitinib.

METHODS

EGFR/HIF-1α signaling was tested by immunoblot, polymerase chain reaction (PCR), cell proliferation, and apoptosis assays.

RESULTS

HIF-1α accumulated in cells overexpressing EGF and phosphorylated epidermal growth factor receptor (pEGFR), phosphatidylinositol-3-kinase (pPI3K), and mitogen-activated protein kinase (pMAPK). EGF-induced expression of HIF-1α and its targets, vascular endothelial growth factor (VEGF) and BNIP3, were blocked by gefitinib and PI3K-inhibitors and MAPK-inhibitors. HIF-1α-siRNAs abrogated EGF-induced BNIP3 but not VEGF expression. Gefitinib inhibited cell proliferation and induced apoptosis more strongly in cells with constitutively active EGFR/HIF-1α signaling than in cells lacking activation of these pathways. HIF-1α-siRNA treatment reduced sensitivity to gefitinib.

CONCLUSION

The search for molecular predictors of sensitivity to gefitinib in HNSCC should be extended to the activation status of EGFR-downstream pathways, phosphorylated protein kinase B, pMAPK, and HIF-1α.

Identification of TRPC6 as a possible candidate target gene within an amplicon at 11q21-q22.2 for migratory capacity in head and neck squamous cell carcinomas

BACKGROUND

Cytogenetic and gene expression analyses in head and neck squamous cell carcinomas (HNSCC) have allowed identification of genomic aberrations that may contribute to cancer pathophysiology. Nevertheless, the molecular consequences of numerous genetic alterations still remain unclear.

METHODS

To identify novel genes implicated in HNSCC pathogenesis, we analyzed the genomic alterations present in five HNSCC-derived cell lines by array CGH, and compared high level focal gene amplifications with gene expression levels to identify genes whose expression is directly impacted by these genetic events. Next, we knocked down TRPC6, one of the most highly amplified and over-expressed genes, to characterize the biological roles of TRPC6 in carcinogenesis. Finally, real time PCR was performed to determine TRPC6 gene dosage and mRNA levels in normal mucosa and human HNSCC tissues.

RESULTS

The data showed that the HNSCC-derived cell lines carry most of the recurrent genomic abnormalities previously described in primary tumors. High-level genomic amplifications were found at four chromosomal sites (11q21-q22.2, 18p11.31-p11.21, 19p13.2-p13.13, and 21q11) with associated gene expression changes in selective candidate genes suggesting that they may play an important role in the malignant behavior of HNSCC. One of the most dramatic alterations of gene transcription involved the TRPC6 gene (located at 11q21-q22.2) which has been recently implicated in tumour invasiveness. siRNA-induced knockdown of TRPC6 expression in HNSCC-derived cells dramatically inhibited HNSCC-cell invasion but did not significantly alter cell proliferation. Importantly, amplification and concomitant overexpression of TRPC6 was also found in HNSCC tumour samples.

CONCLUSIONS

Altogether, these data show that TRPC6 is likely to be a target for 11q21-22.2 amplification that confers enhanced invasive behavior to HNSCC cells. Therefore, TRPC6 may be a promising therapeutic target in the treatment of HNSCC.

Polymorphisms in HIF-1alpha affect presence of lymph node metastasis and can influence tumor size in squamous-cell carcinoma of the glottic larynx

BACKGROUND

HIF-1alpha plays a key role in the development and progression of cancer. Its polymorphic variants C1772T and G1790A have been associated with greater susceptibility to cancer and increased tumor progression.

METHODS

We determined the distribution of these polymorphisms among 121 patients with glottic cancer and 154 healthy volunteers by PCR-RFLP. We also analyzed the relationship between the presence of these polymorphisms and various clinicopathologic variables.

RESULTS

Advanced tumors (T3-T4) were associated with the TT variant (p = 0.036), which was present in 75 % of T4 tumors (p = 0.008). Among patients with nodal metastasis (N+), 41.7 and 22 % were carrying the TT and GA variants, respectively, compared with 9.4 and 2 % of the patients with no metastasis (N0), (p = 0.006 and p = 0.032).

CONCLUSIONS

The presence of the TT and GA variants were associated with lymph node metastasis, while the presence of the TT variant can be associated with larger tumor size.

Reactive oxygen species-generating mitochondrial DNA mutation up-regulates hypoxia-inducible factor-1alpha gene transcription via phosphatidylinositol 3-kinase-Akt/protein kinase C/histone deacetylase pathway

Lewis lung carcinoma-derived high metastatic A11 cells constitutively overexpress hypoxia-inducible factor (HIF)-1alpha mRNA compared with low metastatic P29 cells. Because A11 cells exclusively possess a G13997A mutation in the mitochondrial NADH dehydrogenase subunit 6 (ND6) gene, we addressed here a causal relationship between the ND6 mutation and the activation of HIF-1alpha transcription, and we investigated the potential mechanism. Using trans-mitochondrial cybrids between A11 and P29 cells, we found that the ND6 mutation was directly involved in HIF-1alpha mRNA overexpression. Stimulation of HIF-1alpha transcription by the ND6 mutation was mediated by overproduction of reactive oxygen species (ROS) and subsequent activation of phosphatidylinositol 3-kinase (PI3K)-Akt and protein kinase C (PKC) signaling pathways. The up-regulation of HIF-1alpha transcription was abolished by mithramycin A, an Sp1 inhibitor, but luciferase reporter and chromatin immunoprecipitation assays indicated that Sp1 was necessary but not sufficient for HIF-1alpha mRNA overexpression in A11 cells. On the other hand, trichostatin A, a histone deacetylase (HDAC) inhibitor, markedly suppressed HIF-1alpha transcription in A11 cells. In accordance with this, HDAC activity was high in A11 cells but low in P29 cells and in A11 cells treated with the ROS scavenger ebselene, the PI3K inhibitor LY294002, and the PKC inhibitor Ro31-8220. These results suggest that the ROS-generating ND6 mutation increases HIF-1alpha transcription via the PI3K-Akt/PKC/HDAC pathway, leading to HIF-1alpha protein accumulation in hypoxic tumor cells.