Molecular and metabolic features of oncocytomas: Seeking the blueprints of indolent cancers

Molecular testing in salivary gland cytopathology: A practical overview in conjunction with the Milan system

Recently, significant advances in the molecular characterization of salivary gland neoplasms have facilitated the classification and diagnosis of specific diagnostic entities. In the highly challenging diagnostic scenario of salivary malignancies, molecular testing is increasingly being adopted in routine practice to refine the cytological diagnosis of salivary lesions. Here, we reviewed the most recent evidence in the field of salivary glands molecular cytopathology.

Respiratory Complex I dysfunction in cancer: from a maze of cellular adaptive responses to potential therapeutic strategies

Mitochondria act as key organelles in cellular bioenergetics and biosynthetic processes producing signals that regulate different molecular networks for proliferation and cell death. This ability is also preserved in pathologic contexts such as tumorigenesis, during which bioenergetic changes and metabolic reprogramming confer flexibility favoring cancer cell survival in a hostile microenvironment. Although different studies epitomize mitochondrial dysfunction as a protumorigenic hit, genetic ablation or pharmacological inhibition of respiratory complex I causing a severe impairment is associated with a low-proliferative phenotype. In this scenario, it must be considered that despite the initial delay in growth, cancer cells may become able to resume proliferation exploiting molecular mechanisms to overcome growth arrest. Here, we highlight the current knowledge on molecular responses activated by complex I-defective cancer cells to bypass physiological control systems and to re-adapt their fitness during microenvironment changes. Such adaptive mechanisms could reveal possible novel molecular players in synthetic lethality with complex I impairment, thus providing new synergistic strategies for mitochondrial-based anticancer therapy.

Identification of RCC Subtype-Specific microRNAs-Meta-Analysis of High-Throughput RCC Tumor microRNA Expression Data

Renal cell carcinoma (RCC) is one of the most common cancers worldwide with a nearly non-symptomatic course until the advanced stages of the disease. RCC can be distinguished into three subtypes: papillary (pRCC), chromophobe (chRCC) and clear cell renal cell carcinoma (ccRCC) representing up to 75% of all RCC cases. Detection and RCC monitoring tools are limited to standard imaging techniques, in combination with non-RCC specific morphological and biochemical read-outs. RCC subtype identification relays mainly on results of pathological examination of tumor slides. Molecular, clinically applicable and ideally non-invasive tools aiding RCC management are still non-existent, although molecular characterization of RCC is relatively advanced. Hence, many research efforts concentrate on the identification of molecular markers that will assist with RCC sub-classification and monitoring. Due to stability and tissue-specificity miRNAs are promising candidates for such biomarkers. Here, we performed a meta-analysis study, utilized seven NGS and seven microarray RCC studies in order to identify subtype-specific expression of miRNAs. We concentrated on potentially oncocytoma-specific miRNAs (miRNA-424-5p, miRNA-146b-5p, miRNA-183-5p, miRNA-218-5p), pRCC-specific (miRNA-127-3p, miRNA-139-5p) and ccRCC-specific miRNAs (miRNA-200c-3p, miRNA-362-5p, miRNA-363-3p and miRNA-204-5p, 21-5p, miRNA-224-5p, miRNA-155-5p, miRNA-210-3p) and validated their expression in an independent sample set. Additionally, we found ccRCC-specific miRNAs to be differentially expressed in ccRCC tumor according to Fuhrman grades and identified alterations in their isoform composition in tumor tissue. Our results revealed that changes in the expression of selected miRNA might be potentially utilized as a tool aiding ccRCC subclass discrimination and we propose a miRNA panel aiding RCC subtype distinction.

Targeting Metabolic Plasticity and Flexibility Dynamics for Cancer Therapy

Cancer cells continuously rewire their metabolism to fulfill their need for rapid growth and survival while subject to changes in environmental cues. Thus, a vital component of a cancer cell lies in its metabolic adaptability. The constant demand for metabolic alterations requires flexibility, that is, the ability to utilize different metabolic substrates; as well as plasticity, that is, the ability to process metabolic substrates in different ways. In this review, we discuss how dynamic changes in cancer metabolism affect tumor progression and the consequential implications for cancer therapy. SIGNIFICANCE: Recognizing cancer dynamic metabolic adaptability as an entity can lead to targeted therapy that is expected to decrease drug resistance.

Decreased prolyl hydroxylase 3 mRNA expression in oncocytomas compared with clear cell renal cell carcinoma

INTRODUCTION

Hypoxia inducible factors (HIF) and prolyl hydroxylase domain (PHD) enzymes play a central role in tumor progression in clear cell renal cell carcinoma (ccRCC). However, there are currently no data regarding the behavior of this pathway (HIF/PHD) in a large number of benign renal tumors, the oncocytomas. The aim of the present study was to compare the expression levels of these factors between ccRCC and oncocytoma tumors.

MATERIAL AND METHODS

A total of 56 fresh frozen specimens from patients with ccRCC and 14 oncocytoma specimens were analyzed via reverse transcription-quantitative polymerase chain reaction in order to assess the expression levels of HIF-1α, HIF-2α, PHD1, PHD2, and PHD3. The analysis involved both fresh frozen tumor samples as well as adjacent normal kidney tissues.

RESULTS

In ccRCC, HIF-1α and HIF-2α levels were upregulated in 65.5% and 71.4% of cases, respectively. PHD3 was downregulated only in 15.4% of the ccRCC cases, in contrast with oncocytoma cases, which exhibited low expression levels in the majority. The upregulation of PHD3 messenger RNA (mRNA) levels in ccRCC when compared with oncocytoma was statistically significant (P<0.001). No other comparisons (HIF-1α, HIF-2α, PHD1, and PHD2) were significantly different. HIF-2α and PHD3 mRNA expression levels were negatively correlated with Fuhrman Grade (P=0.029 and P=0.026, respectively) in ccRCC.

CONCLUSION

To the best of our knowledge, this is the first time that the HIF/PHD pathway was compared between ccRCC and a common benign tumor, identifying the upregulation of PHD3 as the possible underlying factor guiding the difference in the behavior of ccRCC.

mRNA overexpression of prolyl hydroxylase PHD3 is inversely related to nuclear grade in renal cell carcinoma

The aim of the present study was to evaluate the relative mRNA expression levels of genes involved in the hypoxia inducible factor (HIF) signalling pathway in renal cell carcinoma (RCC) and to analyse their associations with clinicopathological parameters and survival outcomes. Reverse transcription-quantitative PCR was used to quantify the mRNA expression levels of HIF-1α, HIF-2α, prolyl hydroxylase (PHD)1, PHD2 and PHD3 in formalin-fixed paraffin-embedded (FFPE) tumour tissue samples from 41 patients with RCC, including 33 cases of clear cell RCC (ccRCC). FFPE samples of corresponding adjacent normal kidney tissues were used as a comparison. mRNA expression levels were analysed in regard to clinical parameters, histological type, stage, nuclear grade, cancer specific survival and overall survival. Compared with adjacent normal kidney tissue, HIF-1α levels were lower in 16/33 ccRCC samples (48.48%), while HIF-2α, PHD1 and PHD2 levels did not exhibit a specific expression pattern. By contrast, the PHD3 mRNA level was higher in 29/33 (87.87%) of the tumour samples. HIF-1α was positively associated with HIF-2α, PHD1 and PHD2. HIF-2α levels were associated with PHD1, PHD2 and PHD3, while PHD3 was strongly associated with PHD2. PHD3 mRNA levels were inversely associated with nuclear grade (P=0.015). However, in univariate analysis, PHD3 was not associated with cancer-specific or overall survival rates. The present findings suggest an important involvement of PHD3 in ccRCC, since PHD3 mRNA expression was inversely associated with nuclear grade. However, PHD3 mRNA levels did not have an independent prognostic value. Further studies are required to investigate whether PHD3 could be used as either a therapeutic target or prognostic marker.

Mitochondrial Involvement in Migration, Invasion and Metastasis

Mitochondria in addition to be a main cellular power station, are involved in the regulation of many physiological processes, such as generation of reactive oxygen species, metabolite production and the maintenance of the intracellular Ca²⁺ homeostasis. Almost 100 years ago Otto Warburg presented evidence for the role of mitochondria in the development of cancer. During the past 20 years mitochondrial involvement in programmed cell death regulation has been clarified. Moreover, it has been shown that mitochondria may act as a switchboard between various cell death modalities. Recently, accumulated data have pointed to the role of mitochondria in the metastatic dissemination of cancer cells. Here we summarize the modern knowledge concerning the contribution of mitochondria to the invasion and dissemination of tumor cells and the possible mechanisms behind that and attempts to target metastatic cancers involving mitochondria.

EGFR and KRAS mutations in Chinese patients with sinonasal inverted papilloma and oncocytic papilloma

AIMS

Sinonasal inverted papilloma (SIP) and sinonasal oncocytic papilloma (SOP) are uncommon, benign epithelial neoplasms located in the sinonasal region, that have the potential for malignant transformation. A recent study reported that EGFR and KRAS mutations occurred in the majority of Western patients with SIP and SOP, respectively. The aims of this study were to investigate the prevalence of KRAS and EGFR mutations in Chinese SIP and SOP patients, and to study the association between molecular alterations and their clinical features.

METHODS AND RESULTS

We retrospectively collected 80 sinonasal papilloma specimens, including 44 cases with SIP, 33 cases with SOP, and three cases with mixed sinonasal papilloma, which harboured elements of both inverted and oncocytic types. Formalin-fixed paraffin-embedded tissues were used to extract genomic DNA, and EGFR and KRAS mutations were evaluated with direct Sanger sequencing. Thirty-five (78%) SIP patients harboured EGFR mutations, and all mutations were exon 20 insertions, whereas no KRAS mutations were detected. In contrast, KRAS mutations were detected in 82% of SOP patients, but no EGFR mutations were detected. Among the three mixed-type cases, two harboured both EGFR exon 20 insertions and KRAS mutations. Another case harboured a KRAS mutation, but no EGFR mutation was detected.

CONCLUSION

SIP and SOP are two clinical entities with different genetic mutational patterns of EGFR and KRAS. Mixed types with elements of both SIP and SOP may harbour both EGFR and KRAS mutations.

Metabolic Plasticity of Tumor Cell Mitochondria

Mitochondria are dynamic organelles that exchange a multiplicity of signals with other cell compartments, in order to finely adjust key biological routines to the fluctuating metabolic needs of the cell. During neoplastic transformation, cells must provide an adequate supply of the anabolic building blocks required to meet a relentless proliferation pressure. This can occur in conditions of inconstant blood perfusion leading to variations in oxygen and nutrient levels. Mitochondria afford the bioenergetic plasticity that allows tumor cells to adapt and thrive in this ever changing and often unfavorable environment. Here we analyse how mitochondria orchestrate the profound metabolic rewiring required for neoplastic growth.

The Oncojanus Paradigm of Respiratory Complex I

Mitochondrial respiratory function is now recognized as a pivotal player in all the aspects of cancer biology, from tumorigenesis to aggressiveness and chemotherapy resistance. Among the enzymes that compose the respiratory chain, by contributing to energy production, redox equilibrium and oxidative stress, complex I assumes a central role. Complex I defects may arise from mutations in mitochondrial or nuclear DNA, in both structural genes or assembly factors, from alteration of the expression levels of its subunits, or from drug exposure. Since cancer cells have a high-energy demand and require macromolecules for proliferation, it is not surprising that severe complex I defects, caused either by mutations or treatment with specific inhibitors, prevent tumor progression, while contributing to resistance to certain chemotherapeutic agents. On the other hand, enhanced oxidative stress due to mild complex I dysfunction drives an opposite phenotype, as it stimulates cancer cell proliferation and invasiveness. We here review the current knowledge on the contribution of respiratory complex I to cancer biology, highlighting the double-edged role of this metabolic enzyme in tumor progression, metastasis formation, and response to chemotherapy.

PGC1α: Friend or Foe in Cancer?

The PGC1 family (Peroxisome proliferator-activated receptor γ (PPARγ) coactivators) of transcriptional coactivators are considered master regulators of mitochondrial biogenesis and function. The PGC1α isoform is expressed especially in metabolically active tissues, such as the liver, kidneys and brain, and responds to energy-demanding situations. Given the altered and highly adaptable metabolism of tumor cells, it is of interest to investigate PGC1α in cancer. Both high and low levels of PGC1α expression have been reported to be associated with cancer and worse prognosis, and PGC1α has been attributed with oncogenic as well as tumor suppressive features. Early in carcinogenesis PGC1α may be downregulated due to a protective anticancer role, and low levels likely reflect a glycolytic phenotype. We suggest mechanisms of PGC1α downregulation and how these might be connected to the increased cancer risk that obesity is now known to entail. Later in tumor progression PGC1α is often upregulated and is reported to contribute to increased lipid and fatty acid metabolism and/or a tumor cell phenotype with an overall metabolic plasticity that likely supports drug resistance as well as metastasis. We conclude that in cancer PGC1α is neither friend nor foe, but rather the obedient servant reacting to metabolic and environmental cues to benefit the tumor cell.

Mitochondrial Dysfunction: A Novel Potential Driver of Epithelial-to-Mesenchymal Transition in Cancer

Epithelial-to-mesenchymal transition (EMT) allows epithelial cancer cells to assume mesenchymal features, endowing them with enhanced motility and invasiveness, thus enabling cancer dissemination and metastatic spread. The induction of EMT is orchestrated by EMT-inducing transcription factors that switch on the expression of “mesenchymal” genes and switch off the expression of “epithelial” genes. Mitochondrial dysfunction is a hallmark of cancer and has been associated with progression to a metastatic and drug-resistant phenotype. The mechanistic link between metastasis and mitochondrial dysfunction is gradually emerging. The discovery that mitochondrial dysfunction owing to deregulated mitophagy, depletion of the mitochondrial genome (mitochondrial DNA) or mutations in Krebs’ cycle enzymes, such as succinate dehydrogenase, fumarate hydratase, and isocitrate dehydrogenase, activate the EMT gene signature has provided evidence that mitochondrial dysfunction and EMT are interconnected. In this review, we provide an overview of the current knowledge on the role of different types of mitochondrial dysfunction in inducing EMT in cancer cells. We place emphasis on recent advances in the identification of signaling components in the mito-nuclear communication network initiated by dysfunctional mitochondria that promote cellular remodeling and EMT activation in cancer cells.

Etiopathogenesis of oncocytomas

Oncocytomas are distinct tumors characterized by an abnormal accumulation of defective and (most probably) dysfunctional mitochondria in cell cytoplasm of such tumors. This particular phenotype has been studied for the last decades and the clarification of the etiopathogenic causes are still needed. Several mechanisms involved in the formation and maintenance of oncocytomas are accepted as reasonable causes, but the relevance and contribution of each one for oncocytic transformation may depend on different cancer etiopathogenic contexts. In this review, we describe the current knowledge of the etiopathogenic events that may lead to oncocytic transformation and discuss their contribution for tumor progression and mitochondrial accumulation.