Transcriptome analysis and prognosis of ALDH isoforms in human cancer

Mesenchymal Stem Cell-Derived Extracellular Vesicles Increase Human MCF7 Breast Cancer Cell Proliferation associated with OCT4 Expression and ALDH Activity

OBJECTIVE

The aim of this study was to investigate the effect of mesenchymal stem cells-derived extracellular vesicles (MSC-EVs) on the human MCF7 breast cancer cell proliferation that have been considered to contain limited CSC population and its association with the expression of OCT4 and ALDH1 stemness markers.

METHODS

EVs were successfully isolated from the conditioned medium of umbilical cord MSCs using size exclusion chromatography. The isolated EV fraction was verified under a transmission electron microscope (TEM). Five and ten percent (v/v) concentration of MSC-EVs were then co-cultured with MCF7 cells. To investigate MSC-EV uptake by MCF7 cells, we performed confocal microscopy analysis. Subsequently, the proliferation of co-cultured MCF7 cells was determined using trypan blue exclusion assay, while their mRNA and protein expression of OCT4 as well as ALDH activity as the marker of stemness properties were analyzed using quantitative reverse transcription polymerase chain reaction, Western Blot, and Aldefluor™ assays, respectively.

RESULT

MSC-EVs were detected as round-shaped, ~100 nm sized particles under TEM. We also demonstrate that MSC-EVs can be internalized by MCF7 cells. Notably, MSC-EVs of 5% concentration increased OCT4 mRNA expression and ALDH1 activity in MCF7 cells. At 10% concentration, MSC-EVs reduced the OCT4 expression and ALDH1 activity.

CONCLUSION

MSC-derived EVs modulate the stemness of MCF7 cells, either OCT4 expression or ALDH1 activity, in a concentration dependent manner along with the increase of cell proliferation.

ALDH1L2 regulation of formate, formyl-methionine, and ROS controls cancer cell migration and metastasis

Mitochondrial 10-formyltetrahydrofolate (10-formyl-THF) is utilized by three mitochondrial enzymes to produce formate for nucleotide synthesis, NADPH for antioxidant defense, and formyl-methionine (fMet) to initiate mitochondrial mRNA translation. One of these enzymes-aldehyde dehydrogenase 1 family member 2 (ALDH1L2)-produces NADPH by catabolizing 10-formyl-THF into CO2 and THF. Using breast cancer cell lines, we show that reduction of ALDH1L2 expression increases ROS levels and the production of both formate and fMet. Both depletion of ALDH1L2 and direct exposure to formate result in enhanced cancer cell migration that is dependent on the expression of the formyl-peptide receptor (FPR). In various tumor models, increased ALDH1L2 expression lowers formate and fMet accumulation and limits metastatic capacity, while human breast cancer samples show a consistent reduction of ALDH1L2 expression in metastases. Together, our data suggest that loss of ALDH1L2 can support metastatic progression by promoting formate and fMet production, resulting in enhanced FPR-dependent signaling.

Ethanol Metabolism and Melanoma

Malignant melanoma is the deadliest form of skin cancer. Despite significant efforts in sun protection education, melanoma incidence is still rising globally, drawing attention to other socioenvironmental risk factors for melanoma. Ethanol and acetaldehyde (AcAH) are ubiquitous in our diets, medicines, alcoholic beverages, and the environment. In the liver, ethanol is primarily oxidized to AcAH, a toxic intermediate capable of inducing tumors by forming adducts with proteins and DNA. Once in the blood, ethanol and AcAH can reach the skin. Although, like the liver, the skin has metabolic mechanisms to detoxify ethanol and AcAH, the risk of ethanol/AcAH-associated skin diseases increases when the metabolic enzymes become dysfunctional in the skin. This review highlights the evidence linking cutaneous ethanol metabolism and melanoma. We summarize various sources of skin ethanol and AcAH and describe how the reduced activity of each alcohol metabolizing enzyme affects the sensitivity threshold to ethanol/AcAH toxicity. Data from the Gene Expression Omnibus database also show that three ethanol metabolizing enzymes (alcohol dehydrogenase 1B, P450 2E1, and catalase) and an AcAH metabolizing enzyme (aldehyde dehydrogenase 2) are significantly reduced in melanoma tissues.

The role of drug-metabolizing enzymes in synthetic lethality of cancer

Drug-metabolizing enzymes (DMEs) have shown increasing importance in anticancer therapy. It is not only due to their effect on activation or deactivation of anticancer drugs, but also because of their extensive connections with pathological and biochemistry changes during tumorigenesis. Meanwhile, it has become more accessible to discovery anticancer drugs that selectively targeted cancer cells with the development of synthetic lethal screen technology. Synthetic lethal strategy makes use of unique genetic markers that different cancer cells from normal tissues to discovery anticancer agents. Dysregulation of DMEs has been found in various cancers, making them promising candidates for synthetic lethal strategy. In this review, we will systematically discuss about the role of DMEs in tumor progression, the application of synthetic lethality strategy in drug discovery, and a link between DMEs and synthetic lethal of cancer.

Alternative RNA splicing modulates ribosomal composition and determines the spatial phenotype of glioblastoma cells

Glioblastoma (GBM) is characterized by exceptionally high intratumoral heterogeneity. However, the molecular mechanisms underlying the origin of different GBM cell populations remain unclear. Here, we found that the compositions of ribosomes of GBM cells in the tumour core and edge differ due to alternative RNA splicing. The acidic pH in the core switches before messenger RNA splicing of the ribosomal gene RPL22L1 towards the RPL22L1b isoform. This allows cells to survive acidosis, increases stemness and correlates with worse patient outcome. Mechanistically, RPL22L1b promotes RNA splicing by interacting with lncMALAT1 in the nucleus and inducing its degradation. Contrarily, in the tumour edge region, RPL22L1a interacts with ribosomes in the cytoplasm and upregulates the translation of multiple messenger RNAs including TP53. We found that the RPL22L1 isoform switch is regulated by SRSF4 and identified a compound that inhibits this process and decreases tumour growth. These findings demonstrate how distinct GBM cell populations arise during tumour growth. Targeting this mechanism may decrease GBM heterogeneity and facilitate therapy.

Characterizing isoform switching events in esophageal adenocarcinoma

Isoform switching events with predicted functional consequences are common in many cancers, but characterization of switching events in esophageal adenocarcinoma (EAC) is lacking. Next-generation sequencing was used to detect levels of RNA transcripts and identify specific isoforms in treatment-naïve esophageal tissues ranging from premalignant Barrett’s esophagus (BE), BE with low- or high-grade dysplasia (BE.LGD, BE.HGD), and EAC. Samples were stratified by histopathology and TP53 mutation status, identifying significant isoform switching events with predicted functional consequences. Comparing BE.LGD with BE.HGD, a histopathology linked to cancer progression, isoform switching events were identified in 75 genes including KRAS, RNF128, and WRAP53. Stratification based on TP53 status increased the number of significant isoform switches to 135, suggesting switching events affect cellular functions based on TP53 mutation and tissue histopathology. Analysis of isoforms agnostic, exclusive, and shared with mutant TP53 revealed unique signatures including demethylation, lipid and retinoic acid metabolism, and glucuronidation, respectively. Nearly half of isoform switching events were identified without significant gene-level expression changes. Importantly, two TP53-interacting isoforms, RNF128 and WRAP53, were significantly linked to patient survival. Thus, analysis of isoform switching events may provide new insight for the identification of prognostic markers and inform new potential therapeutic targets for EAC.

Alcohol Consumption, ALDH2 Polymorphism as Risk Factors for Upper Aerodigestive Tract Cancer Progression and Prognosis

The upper aerodigestive tract (UADT) is highly susceptible to multiple primary cancers originated from squamous epithelia and constitutes a field of cancerization. Patients with head and neck cancer (head and neck squamous cell carcinoma, HNSCC) are at high risk of developing multiple cancers in the esophagus (esophageal squamous cell carcinoma, ESCC). Conversely, esophageal cancer patients are prone to develop multiple primary tumors in the head and neck region. The East Asian-specific dysfunctional ALDH2*2 missense mutation is a genetic risk factor for UADT cancer. It is not only associated with increased incidences of UADT cancer, but is also implicated in faster cancer progression and poorer prognosis. Alcohol use is a major lifestyle risk factor which causes UADT cancer among ALDH2*2 carriers. The accumulation of the immediate metabolite of alcohol, acetaldehyde, is likely the genotoxic agents that is involved in the process of tumorigenesis. This review summarizes recent publications on the risk and association of ALDH2*2 mutation, alcohol consumption in synchronous, metachronous UADT cancer. Possible molecular mechanisms involved in cancer initiation, progress and prognosis are discussed. The review also highlights a need for precision medicine-based preventive and therapeutic strategies by integrating lifestyle and genetic risk factors, such as alcohol consumption, genotypes of the alcohol metabolizing genes, ADH1B and ALDH2, into a risk assessment model for better screening, surveillance and treatment outcome.

Associations between ALDH Genetic Variants, Alcohol Consumption, and the Risk of Nasopharyngeal Carcinoma in an East Asian Population

Nasopharyngeal carcinoma (NPC) and alcohol flush syndrome are thought to be strongly influenced by genetic factors and are highly prevalent amongst East Asians. Diminished activity of aldehyde dehydrogenase (ALDH), a major enzyme in the alcohol-metabolizing pathway, causes the flushing syndrome associated with alcoholic consumption. The genetic effect of ALDH isoforms on NPC is unknown. We therefore investigated the association between the genetic polymorphisms of all 19 ALDH isoforms and NPC among 458 patients with NPC and 1672 age- and gender-matched healthy controls in Taiwan. Single-nucleotide polymorphisms (SNPs) located between the 40,000 base pairs upstream and downstream of the 19 ALDH isoform coding regions were collected from two genome-wise association studies conducted in Taiwan and from the Taiwan Biobank. Thirteen SNPs located on ALDH4A1, ALDH18A1, ALDH3B2, ALDH1L2, ALDH1A2, and ALDH2 Glu487Lys (rs671) were associated with NPC susceptibility. Stratification by alcohol status revealed a cumulative risk effect for NPC amongst drinkers and non-drinkers, with odds ratios of 4.89 (95% confidence interval 2.15–11.08) and 3.57 (1.97–6.47), respectively. A synergistic effect was observed between SNPs and alcohol. This study is the first to report associations between genetic variants in 19 ALDH isoforms, their interaction with alcohol consumption and NPC in an East Asian population.

Uncovering cancer vulnerabilities by machine learning prediction of synthetic lethality

BACKGROUND

Synthetic lethality describes a genetic interaction between two perturbations, leading to cell death, whereas neither event alone has a significant effect on cell viability. This concept can be exploited to specifically target tumor cells. CRISPR viability screens have been widely employed to identify cancer vulnerabilities. However, an approach to systematically infer genetic interactions from viability screens is missing.

METHODS

Here we describe PAn-canceR Inferred Synthetic lethalities (PARIS), a machine learning approach to identify cancer vulnerabilities. PARIS predicts synthetic lethal (SL) interactions by combining CRISPR viability screens with genomics and transcriptomics data across hundreds of cancer cell lines profiled within the Cancer Dependency Map.

RESULTS

Using PARIS, we predicted 15 high confidence SL interactions within 549 DNA damage repair (DDR) genes. We show experimental validation of an SL interaction between the tumor suppressor CDKN2A, thymidine phosphorylase (TYMP) and the thymidylate synthase (TYMS), which may allow stratifying patients for treatment with TYMS inhibitors. Using genome-wide mapping of SL interactions for DDR genes, we unraveled a dependency between the aldehyde dehydrogenase ALDH2 and the BRCA-interacting protein BRIP1. Our results suggest BRIP1 as a potential therapeutic target in ~ 30% of all tumors, which express low levels of ALDH2.

CONCLUSIONS

PARIS is an unbiased, scalable and easy to adapt platform to identify SL interactions that should aid in improving cancer therapy with increased availability of cancer genomics data.

Aldehyde dehydrogenase 1A1 and 1A3 isoforms - mechanism of activation and regulation in cancer

In some types of human cancer, aldehyde dehydrogenases represent stemness markers and their expression is associated with advanced disease stages and poor prognosis. Although several biological functions are mediated by their product Retinoid acid, the molecular mechanism is tissue-dependent and only partially understood.

In this review, we summarize the current knowledge about the role of ALDH in solid tumours, especially ALDH1A1 and ALDH1A3 isoforms, regarding the molecular mechanism of their transcription and regulation, and their crosstalk with main molecular pathways resulting in the excessive proliferation, chemoresistance, stem cells properties and invasiveness. The recent knowledge of the regulatory effect of lnRNA on ALDH1A1 and ALDH1A3 is discussed too.

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Aldehyde dehydrogenases are important stem cell markers in many human cancer types.

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ALDH1A1 or ALDH1A3 activation participates in tumour progression, chemoresistance, stem-cell properties and invasiveness.

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ALDH1A1 interacts with oncogenic pathways Notch, NRF, CXCR4, Polycomb, MDR, and HOX.

Biochemical Mechanisms Associating Alcohol Use Disorders with Cancers

Simple Summary

Of all yearly deaths attributable to alcohol consumption globally, approximately 12% are due to cancers, representing approximately 0.4 million deceased individuals. Ethanol metabolism disturbs cell biochemistry by targeting the structure and function of essential biomolecules (proteins, nucleic acids, and lipids) and by provoking alterations in cell programming that lead to cancer development and cancer malignancy. A better understanding of the metabolic and cell signaling realm affected by ethanol is paramount to designing effective treatments and preventive actions tailored to specific neoplasias.

Abstract

The World Health Organization identifies alcohol as a cause of several neoplasias of the oropharynx cavity, esophagus, gastrointestinal tract, larynx, liver, or female breast. We review ethanol’s nonoxidative and oxidative metabolism and one-carbon metabolism that encompasses both redox and transfer reactions that influence crucial cell proliferation machinery. Ethanol favors the uncontrolled production and action of free radicals, which interfere with the maintenance of essential cellular functions. We focus on the generation of protein, DNA, and lipid adducts that interfere with the cellular processes related to growth and differentiation. Ethanol’s effects on stem cells, which are responsible for building and repairing tissues, are reviewed. Cancer stem cells (CSCs) of different origins suffer disturbances related to the expression of cell surface markers, enzymes, and transcription factors after ethanol exposure with the consequent dysregulation of mechanisms related to cancer metastasis or resistance to treatments. Our analysis aims to underline and discuss potential targets that show more sensitivity to ethanol’s action and identify specific metabolic routes and metabolic realms that may be corrected to recover metabolic homeostasis after pharmacological intervention. Specifically, research should pay attention to re-establishing metabolic fluxes by fine-tuning the functioning of specific pathways related to one-carbon metabolism and antioxidant processes.

Bioinformatic analysis of differentially expressed genes as prognostic markers in pheochromocytoma and paraganglioma tumors

The pathogenesis of pheochromocytoma and paraganglioma (PCPG) catecholamine-producing tumors is exceedingly complicated. Here, we sought to identify important genes affecting the prognosis and survival rate of patients suffering from PCPG. We analyzed 95 samples obtained from two microarray data series, GSE19422 and GSE60459, from the Gene Expression Omnibus (GEO) repository. First, differentially expressed genes (DEGs) were identified by comparing 87 PCPG tumor samples and eight normal adrenal tissue samples using R language. The GEO2R tool and Venn diagram software were applied to the Database for Annotation, Visualization and Integrated Discovery (DAVID) to analyze Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene Ontology (GO). We further employed Cytoscape with the Molecular Complex Detection (MCODE) tool to make protein-protein interactions visible for the Search Tool for Retrieval of Interacting Genes (STRING). These procedures resulted in 30 candidate DEGs, which were subjected to Kaplan-Meier analysis and validated by Gene Expression Profiling Interactive Analysis (GEPIA) to determine their influence on overall survival rate. Finally, we identified ALDH3A2 and AKR1B1, two genes in the glycerolipid metabolism pathway, as being particularly enriched in PCPG tumors and correlated with T and B tumor-infiltrating immune cells. Our results suggest that these two DEGs are closely associated with the prognosis of malignant PCPG tumors.

ALDH1A3 Coordinates Metabolism With Gene Regulation in Pulmonary Arterial Hypertension

BACKGROUND

Metabolic alterations provide substrates that influence chromatin structure to regulate gene expression that determines cell function in health and disease. Heightened proliferation of smooth muscle cells (SMC) leading to the formation of a neointima is a feature of pulmonary arterial hypertension (PAH) and systemic vascular disease. Increased glycolysis is linked to the proliferative phenotype of these SMC.

METHODS

RNA sequencing was applied to pulmonary arterial SMC (PASMC) from PAH patients with and without a BMPR2 (bone morphogenetic receptor 2) mutation versus control PASMC to uncover genes required for their heightened proliferation and glycolytic metabolism. Assessment of differentially expressed genes established metabolism as a major pathway, and the most highly upregulated metabolic gene in PAH PASMC was aldehyde dehydrogenase family 1 member 3 (ALDH1A3), an enzyme previously linked to glycolysis and proliferation in cancer cells and systemic vascular SMC. We determined if these functions are ALDH1A3-dependent in PAH PASMC, and if ALDH1A3 is required for the development of pulmonary hypertension in a transgenic mouse. Nuclear localization of ALDH1A3 in PAH PASMC led us to determine whether and how this enzyme coordinately regulates gene expression and metabolism in PAH PASMC.

RESULTS

ALDH1A3 mRNA and protein were increased in PAH versus control PASMC, and ALDH1A3 was required for their highly proliferative and glycolytic properties. Mice with Aldh1a3 deleted in SMC did not develop hypoxia-induced pulmonary arterial muscularization or pulmonary hypertension. Nuclear ALDH1A3 converted acetaldehyde to acetate to produce acetyl coenzyme A to acetylate H3K27, marking active enhancers. This allowed for chromatin modification at NFYA (nuclear transcription factor Y subunit α) binding sites via the acetyltransferase KAT2B (lysine acetyltransferase 2B) and permitted NFY-mediated transcription of cell cycle and metabolic genes that is required for ALDH1A3-dependent proliferation and glycolysis. Loss of BMPR2 in PAH SMC with or without a mutation upregulated ALDH1A3, and transcription of NFYA and ALDH1A3 in PAH PASMC was β-catenin dependent.

CONCLUSIONS

Our studies have uncovered a metabolic-transcriptional axis explaining how dividing cells use ALDH1A3 to coordinate their energy needs with the epigenetic and transcriptional regulation of genes required for SMC proliferation. They suggest that selectively disrupting the pivotal role of ALDH1A3 in PAH SMC, but not endothelial cells, is an important therapeutic consideration.

Endogenous aldehyde accumulation generates genotoxicity and exhaled biomarkers in esophageal adenocarcinoma

Volatile aldehydes are enriched in esophageal adenocarcinoma (EAC) patients' breath and could improve early diagnosis, however the mechanisms of their production are unknown. Here, we show that weak aldehyde detoxification characterizes EAC, which is sufficient to cause endogenous aldehyde accumulation in vitro. Two aldehyde groups are significantly enriched in EAC biopsies and adjacent tissue: (i) short-chain alkanals, and (ii) medium-chain alkanals, including decanal. The short-chain alkanals form DNA-adducts, which demonstrates genotoxicity and confirms inadequate detoxification. Metformin, a putative aldehyde scavenger, reduces this toxicity. Tissue and breath concentrations of the medium-chain alkanal decanal are correlated, and increased decanal is linked to reduced ALDH3A2 expression, TP53 deletion, and adverse clinical features. Thus, we present a model for increased exhaled aldehydes based on endogenous accumulation from reduced detoxification, which also causes therapeutically actionable genotoxicity. These results support EAC early diagnosis trials using exhaled aldehyde analysis.

Immunohistochemically Characterized Intratumoral Heterogeneity Is a Prognostic Marker in Human Glioblastoma

Simple Summary

Intratumoral heterogeneity is believed to contribute to the immense therapy resistance and recurrence rate of glioblastoma. The aim of this retrospective study was to analyze the heterogeneity of 36 human glioblastoma samples on a morphological level by immunohistochemistry. We confirmed that this method is valid for heterogeneity detection. 115 Areas of Interest were labelled. By cluster analysis, we defined two subtypes (“classical” and “mesenchymal”). The results of epigenomic analyses corroborated the findings. Interestingly, patients with tumors that consisted of both subtypes (“subtype-heterogeneous”) showed a shorter overall survival compared to patients with tumor that were dominated by one subtype (“subtype-dominant”). Furthermore, the analysis of 21 corresponding pairs of primary and recurrent glioblastoma demonstrated that, additionally to an intratumoral heterogeneity, there is also a chronological heterogeneity with dominance of the mesenchymal subtype in recurrent tumors. Our study confirms the prognostic impact of intratumoral heterogeneity in glioblastoma and makes this hallmark assessable by routine diagnostics.

Abstract

Tumor heterogeneity is considered to be a hallmark of glioblastoma (GBM). Only more recently, it has become apparent that GBM is not only heterogeneous between patients (intertumoral heterogeneity) but more importantly, also within individual patients (intratumoral heterogeneity). In this study, we focused on assessing intratumoral heterogeneity. For this purpose, the heterogeneity of 38 treatment-naïve GBM was characterized by immunohistochemistry. Perceptible areas were rated for ALDH1A3, EGFR, GFAP, Iba1, Olig2, p53, and Mib1. By clustering methods, two distinct groups similar to subtypes described in literature were detected. The classical subtype featured a strong EGFR and Olig2 positivity, whereas the mesenchymal subtype displayed a strong ALDH1A3 expression and a high fraction of Iba1-positive microglia. 18 tumors exhibited both subtypes and were classified as “subtype-heterogeneous”, whereas the areas of the other tumors were all assigned to the same cluster and named “subtype-dominant”. Results of epigenomic analyses corroborated these findings. Strikingly, the subtype-heterogeneous tumors showed a clearly shorter overall survival compared to subtype-dominant tumors. Furthermore, 21 corresponding pairs of primary and recurrent GBM were compared, showing a dominance of the mesenchymal subtype in the recurrent tumors. Our study confirms the prognostic impact of intratumoral heterogeneity in GBM, and more importantly, makes this hallmark assessable by routine diagnostics.

A Regulatory Cysteine Residue Mediates Reversible Inactivation of NAD+-Dependent Aldehyde Dehydrogenases to Promote Oxidative Stress Response

Aldehyde dehydrogenases (ALDHs) are a large family of enzymes that oxidize aldehydes into carboxylic acids. All ALDHs have a conserved catalytic cysteine residue but different cofactor preferences for NAD⁺ or NADP⁺. We discovered a CC motif composed of the catalytic and an adjacent cysteine, which are prone to disulfide bond formation under oxidative stress. This facilitates rapid detection of and response to oxidants, as well as protects the catalytic cysteine from overoxidation into irreversible products. In ALDHs, the CC motif only exists in NAD⁺-dependent ones, which leads to selective inhibition of NAD⁺-dependent ALDHs under oxidative stress, diverting carbon sources to the NADPH producing ALDHs. This alleviates the oxidative stress and promotes cell survival. Our findings revealed a novel regulatory mechanism for ALDHs that functions in the oxidative stress response. Many enzymes with catalytic cysteine residues have proximal cysteine, suggesting that such a regulatory mechanism may be general.

Detection of ALDH3B2 in Human Placenta

Aldehyde dehydrogenase 3B2 (ALDH3B2) gene contains a premature termination codon, which can be skipped or suppressed resulting in full-length protein expression. Alternatively, the longest putative open reading frame starting with the second in-frame start codon would encode short isoform. No unequivocal evidence of ALDH3B2 expression in healthy human tissues is available. The aim of this study was to confirm its expression in human placenta characterized by the highest ALDH3B2 mRNA abundance. ALDH3B2 DNA and mRNA were sequenced. The expression was investigated using western blot. The identity of the protein was confirmed using mass spectrometry (MS). The predicted tertiary and quaternary structures, subcellular localization, and phosphorylation sites were assessed using bioinformatic analyses. All DNA and mRNA isolates contained the premature stop codon. In western blot analyses, bands corresponding to the mass of full-length protein were detected. MS analysis led to the identification of two unique peptides, one of which is encoded by the nucleotide sequence located upstream the second start codon. Bioinformatic analyses suggest cytoplasmic localization and several phosphorylation sites. Despite premature stop codon in DNA and mRNA sequences, full-length ALDH3B2 was found. It can be formed as a result of premature stop codon readthrough, complex phenomenon enabling stop codon circumvention.

Silencing transcription factor FOXM1 represses proliferation, migration, and invasion while inducing apoptosis of liver cancer stem cells by regulating the expression of ALDH2

OBJECTIVE

This study is performed to explore the role of transcription factor FOXM1 in promoting the self-renewal and proliferation of liver cancer stem cells (LCSCs) by regulating the expression of acetaldehyde dehydrogenase-2 (ALDH2).

METHODS

CD133⁺ CD24⁺ LCSCs were sorted and identified. A series of experiments were carried out to determine the proliferation, colony formation rate, migration, invasion, and apoptosis of LCSCs after interfering with FOXM1. Proliferation-, epithelial-mesenchymal transition (EMT)-, apoptosis-, and stemness-related factors were then detected by western blot analysis. Tumor xenograft in nude mice was used to figure out the role of FOXM1 in tumorigenesis in vivo by regulating ALDH2 expression. Luciferase activity assay was conducted to determine whether FOXM1 could target ALDH2 promoter region and thereby affecting ALDH2 expression.

RESULTS

The sorted CD133⁺ CD24⁺ Huh-7 cells had the characteristic of stem cells. FOXM1 was highly expressed in CD133⁺ CD24⁺ Huh-7 cells. Silencing FOXM1 inhibited the proliferation and colony formation of LCSCs and decreased the expression of proliferating cell nuclear antigen and Ki-67 protein; inhibited the migration, invasion, and EMT of LCSCs while promoting the apoptosis of LCSCs, as well as promoted the expression of Bax and cleaved-caspase-3, and inhibited the expression of Bcl-2. Silencing FOXM1 inhibited the expression of Nanog, Oct4, and Sox2 in LCSCs by decreasing the expression of ALDH2. in vivo experiment, silencing FOXM1 suppressed tumorigenesis of LCSCs by decreasing the expression of ALDH2.

CONCLUSION

Our study provides evidence that silencing FOXM1 inhibits stemness of LCSCs by decreasing the expression of ALDH2, and represses the proliferation, migration, invasion, and tumorigenesis while inducing the apoptosis of LCSCs.

p53 and Cell Fate: Sensitizing Head and Neck Cancer Stem Cells to Chemotherapy

Head and neck cancers are deadly diseases that are diagnosed annually in approximately half a million individuals worldwide. Growing evidence supporting a role for cancer stem cells (CSCs) in the pathobiology of head and neck cancers has led to increasing interest in identifying therapeutics to target these cells. Apart from the canonical tumor-suppressor functions of p53, emerging research supports a significant role for this protein in physiological stem cell and CSC maintenance and reprogramming. Therefore, p53 has become a promising target to sensitize head and neck CSCs to chemotherapy. In this review, we highlight the role of p53 in stem cell maintenance and discuss potential implications of targeting p53 to treat patients with head and neck cancers.

Identification of cancer-type specific expression patterns for active aldehyde dehydrogenase (ALDH) isoforms in ALDEFLUOR assay

Aldehyde dehydrogenases (ALDHs) defend intracellular homeostasis by catalyzing the conversion of toxic aldehydes into non-toxic carboxylic acids, which is of particular importance to the self-renewal of stem cells and cancer stem cells. The widely used ALDEFLUOR assay was initially designed to indicate the activity of ALDH1A1 in leukemia and has been demonstrated to detect the enzyme activity of several other ALDH isoforms in various cancer types in recent years. However, it is still elusive which isoforms, among the 19 ALDH isoforms in human genome, are the potential contributors in catalyzing ALDEFLUOR assay in different cancers. In the current study, we performed a screening via overexpressing each ALDH isoform to assess their ability of catalyzing ALDEFLUOR assay. Our results demonstrate that nine isoforms are active in ALDEFLUOR assay, whose overexpression significantly increases ALDH-positive (ALDH⁺) population. Further analysis of the expression of these active isoforms in various cancers reveals cancer-type specific expression patterns, suggesting that different cancer types may exhibit ALDEFLUOR activity through expression of specific active ALDH isoforms. This study strongly indicates that a detailed elucidation of the functions for each active ALDH isoform in CSCs is necessary and important for a profound understanding of the underlying mechanisms of ALDH-associated stemness.