SET overexpression decreases cell detoxification efficiency: ALDH2 and GSTP1 are downregulated, DDR is impaired and DNA damage accumulates

Thirty years of SET/TAF1β/I2PP2A: from the identification of the biological functions to its implications in cancer and Alzheimer's disease

The gene encoding for the protein SE translocation (SET) was identified for the first time 30 years ago as part of a chromosomal translocation in a patient affected by leukemia. Since then, accumulating evidence have linked overexpression of SET, aberrant SET splicing, and cellular localization to cancer progression and development of neurodegenerative tauopathies such as Alzheimer's disease. Molecular biology tools, such as targeted genetic deletion, and pharmacological approaches based on SET antagonist peptides, have contributed to unveil the molecular functions of SET and its implications in human pathogenesis. In this review, we provide an overview of the functions of SET as inhibitor of histone and non-histone protein acetylation and as a potent endogenous inhibitor of serine-threonine phosphatase PP2A. We discuss the role of SET in multiple cellular processes, including chromatin remodelling and gene transcription, DNA repair, oxidative stress, cell cycle, apoptosis cell migration and differentiation. We review the molecular mechanisms linking SET dysregulation to tumorigenesis and discuss how SET commits neurons to progressive cell death in Alzheimer's disease, highlighting the rationale of exploiting SET as a therapeutic target for cancer and neurodegenerative tauopathies.

SET improved oocyte maturation by serine/threonine protein phosphatase 2A and inhibited oocyte apoptosis in mouse oocytes

SET is a multifunctional protein involved in a variety of molecular processes such as cell apoptosis and cell-cycle regulation. In ovaries SET is predominantly expressed in theca cells and oocytes. In polycystic ovary syndrome (PCOS) patients the expression of SET was increased than healthy people. The current study was designed to determine whether SET plays a role in oocyte maturation and apoptosis, which may provide clues for the underlying pathological mechanism of follicular development in PCOS patients. Oocytes at germinal vesicle (GV) stage were collected from 6-week-old female ICR mice ovaries. The expression of SET was manipulated by AdCMV-SET and AdH1-SiRNA/SET adenoviruses. SET overexpression improved oocyte maturation whereas SET knockdown inhibited oocyte maturation. Moreover, SET negatively regulated serine/threonine protein phosphatase 2A (PP2A) activity in oocytes. Treatment with PP2A inhibitor okadaic acid (OA) promoted oocyte maturation. Furthermore, PP2A knockdown confirmed the role of PP2A in oocyte maturation, and OA was able to block the AdH1-SiRNA/SET-mediated inhibition on oocyte maturation. The central role of PP2A in SET-mediated regulation of oocyte maturation was confirmed by the finding that SET increased the expression of bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) and PP2A inhibited their expressions. Besides, SET inhibited oocyte apoptosis through decreasing the expression of caspase 3 and caspases 8, while PP2A had no effect on oocyte apoptosis. SET promoted oocyte maturation by inhibiting PP2A activity and inhibited oocyte apoptosis in mouse in-vitro cultured oocytes, which may provide a pathologic pathway leading to impaired oocyte developmental competence in PCOS.

Titanium with nanotopography attenuates the osteoclast-induced disruption of osteoblast differentiation by regulating histone methylation

The bone remodeling process is crucial for titanium (Ti) osseointegration and involves the crosstalk between osteoclasts and osteoblasts. Considering the high osteogenic potential of Ti with nanotopography (Ti Nano) and that osteoclasts inhibit osteoblast differentiation, we hypothesized that nanotopography attenuate the osteoclast-induced disruption of osteoblast differentiation. Osteoblasts were co-cultured with osteoclasts on Ti Nano and Ti Control and non-co-cultured osteoblasts were used as control. Gene expression analysis using RNAseq showed that osteoclasts downregulated the expression of osteoblast marker genes and upregulated genes related to histone modification and chromatin organization in osteoblasts grown on both Ti surfaces. Osteoclasts also inhibited the mRNA and protein expression of osteoblast markers, and such effect was attenuated by Ti Nano. Also, osteoclasts increased the protein expression of H3K9me2, H3K27me3 and EZH2 in osteoblasts grown on both Ti surfaces. ChIP assay revealed that osteoclasts increased accumulation of H3K27me3 that represses the promoter regions of Runx2 and Alpl in osteoblasts grown on Ti Control, which was reduced by Ti Nano. In conclusion, these data show that despite osteoclast inhibition of osteoblasts grown on both Ti Control and Ti Nano, the nanotopography attenuates the osteoclast-induced disruption of osteoblast differentiation by preventing the increase of H3K27me3 accumulation that represses the promoter regions of some key osteoblast marker genes. These findings highlight the epigenetic mechanisms triggered by nanotopography to protect osteoblasts from the deleterious effects of osteoclasts, which modulate the process of bone remodeling and may benefit the osseointegration of Ti implants.

Crosstalk between hnRNP K and SET in ATRA-induced differentiation in acute promyelocytic leukemia

HnRNP K protein is a heterogeneous nuclear ribonucleoprotein which has been proposed to be involved in the leukemogenesis of acute promyelocytic leukemia (APL), as well as in differentiation induced by all‐trans retinoic acid (ATRA). We previously demonstrated a connection between SET and hnRNP K function in head and neck squamous cell carcinoma (HNSCC) cells related to splicing processing. The objective of this study was to characterize the participation of hnRNP K and SET proteins in ATRA‐induced differentiation in APL. We observed higher (5‐ to 40‐fold) levels of hnRNP K and SET mRNA in APL patients at the diagnosis phase compared with induction and maintenance phases. hnRNP K knockdown using short‐hairpin RNA led to cell death in ATRA‐sensitive NB4 and resistant NB4‐R2 cells by apoptosis with SET cleavage. In addition, hnRNP K knockdown increased granulocytic differentiation in APL cells, mainly in NB4‐R2 with ATRA. hnRNP K knockdown had an effect similar to that of treatment with U0126 (an meiosis‐specific serine/threonine protein kinase/ERK inhibitor), mainly in NB4‐R2 cells. SET knockdown in APL cells revealed that apoptosis induction in cells with hnRNP K knockdown occurred by SET cleavage rather than by reduction in SET protein. Transplantation of NB4‐R2 cells into nude mice confirmed that arsenic trioxide (ATO) combined with U0126 has higher potential against tumor progression when compared to ATO. Therefore, hnRNP K/SET and ERK are potential therapeutic targets for both antineoplastic leukemia therapy and relapsed APL patients with ATRA resistance.

The role of ALDH2 in tumorigenesis and tumor progression: Targeting ALDH2 as a potential cancer treatment

A major mitochondrial enzyme for protecting cells from acetaldehyde toxicity is aldehyde dehydrogenase 2 (ALDH2). The correlation between ALDH2 dysfunction and tumorigenesis/growth/metastasis has been widely reported. Either low or high ALDH2 expression contributes to tumor progression and varies among different tumor types. Furthermore, the ALDH2∗2 polymorphism (rs671) is the most common single nucleotide polymorphism (SNP) in Asia. Epidemiological studies associate ALDH2∗2 with tumorigenesis and progression. This study summarizes the essential functions and potential ALDH2 mechanisms in the occurrence, progression, and treatment of tumors in various types of cancer. Our study indicates that ALDH2 is a potential therapeutic target for cancer therapy.

SET protein modulates H4 histone methylation status and regulates miR-137 level in oral squamous cell carcinoma

Aim: Histone acetylation and methylation control gene expression. We investigated the impact of SET knockdown on histone methylation status and the consequences for the miRNAs levels in oral squamous cell carcinoma (OSCC). Methods: OSCC cells with and without SET knockdown were analyzed by quantitative real-time PCR to determine miRNA levels, and by immunoreactions to histone modifications. Results: The knockdown of SET increased the levels of histone H4K20me2 and miR-137. Still, SET protein binds to the miR-137 promoter region. The transfection of miR-137 mimic reduced the KI67 and Rb proteins and proliferation of OSCC cells. Conclusion: Our results show for the first time a relationship between SET and histone methylation associated with the control of miRNA expression and KI67 and Rb as targets of miR-137 in OSCC.

Cellular pathways affected by carbon nanopowder-benzo(α)pyrene complex in human skin fibroblasts identified by proteomics

One of the crucial and unsolved problems of the airborne carbon nanoparticles is the role played by the adsorbed environmental pollutants on their toxicological effect. Indeed, in the urban areas, the carbon nanoparticles usually adsorb some atmospheric contaminants, whose one of the leading representatives is the benzo(α)pyrene. Herein, we used the proteomics to investigate the alteration of toxicological pathways due to the carbon nanopowder-benzo(α)pyrene complex in comparison with the two contaminants administered alone on human skin-derived fibroblasts (hSDFs) exposed for 8 days in semi-static conditions. The preliminary confocal microscopy observations highlighted that carbon-nanopowder was able to pass through the cell membranes and accumulate into the cytoplasm both when administered alone and with the adsorbed benzo(α)pyrene. Proteomics revealed that the effect of carbon nanopowder-benzo(α)pyrene complex seems to be related to a new toxicological behavior instead of simple additive or synergistic effects. In detail, the cellular pathways modulated by the complex were mainly related to energy shift (glycolysis and pentose phosphate pathway), apoptosis, stress response and cellular trafficking.

SET oncoprotein accumulation regulates transcription through DNA demethylation and histone hypoacetylation

Epigenetic modifications are essential in the control of normal cellular processes and cancer development. DNA methylation and histone acetylation are major epigenetic modifications involved in gene transcription and abnormal events driving the oncogenic process. SET protein accumulates in many cancer types, including head and neck squamous cell carcinoma (HNSCC); SET is a member of the INHAT complex that inhibits gene transcription associating with histones and preventing their acetylation. We explored how SET protein accumulation impacts on the regulation of gene expression, focusing on DNA methylation and histone acetylation. DNA methylation profile of 24 tumour suppressors evidenced that SET accumulation decreased DNA methylation in association with loss of 5-methylcytidine, formation of 5-hydroxymethylcytosine and increased TET1 levels, indicating an active DNA demethylation mechanism. However, the expression of some suppressor genes was lowered in cells with high SET levels, suggesting that loss of methylation is not the main mechanism modulating gene expression. SET accumulation also downregulated the expression of 32 genes of a panel of 84 transcription factors, and SET directly interacted with chromatin at the promoter of the downregulated genes, decreasing histone acetylation. Gene expression analysis after cell treatment with 5-aza-2′-deoxycytidine (5-AZA) and Trichostatin A (TSA) revealed that histone acetylation reversed transcription repression promoted by SET. These results suggest a new function for SET in the regulation of chromatin dynamics. In addition, TSA diminished both SET protein levels and SET capability to bind to gene promoter, suggesting that administration of epigenetic modifier agents could be efficient to reverse SET phenotype in cancer.

Directional Migration in Esophageal Squamous Cell Carcinoma (ESCC) is Epigenetically Regulated by SET Nuclear Oncogene, a Member of the Inhibitor of Histone Acetyltransferase Complex

Directional cell migration is of fundamental importance to a variety of biological events, including metastasis of malignant cells. Herein, we specifically investigated SET oncoprotein, a subunit of the recently identified inhibitor of acetyltransferases (INHAT) complex and identified its role in the establishment of front-rear cell polarity and directional migration in Esophageal Squamous Cell Carcinoma (ESCC). We further define the molecular circuits that govern these processes by showing that SET modulated DOCK7/RAC1 and cofilin signaling events. Moreover, a detailed analysis of the spatial distribution of RAC1 and cofilin allowed us to decipher the synergistical contributions of the two in coordinating the advancing dynamics by measuring architectures, polarities, and cytoskeletal organizations of the lamellipodia leading edges. In further investigations in vivo, we identified their unique role at multiple levels of the invasive cascade for SET cell and indicate the necessity for their functional balance to enable efficient invasion as well. Additionally, SET epigenetically repressed miR-30c expression by deacetylating histones H2B and H4 on its promoter, which was functionally important for the biological effects of SET in our cell-context. Finally, we corroborated our findings in vivo by evaluating the clinical relevance of SET signaling in the metastatic burden in mice and a large series of patients with ESCC at diagnosis, observing it's significance in predicting metastasis formation. Our findings uncovered a novel signaling network initiated by SET that epigenetically modulated ESCC properties and suggest that targeting the regulatory axis might be a promising strategy to inhibit migration and metastasis.

Aldehyde dehydrogenase 2*2 knock-in mice show increased reactive oxygen species production in response to cisplatin treatment

Background

The aldehyde dehydrogenase (ALDH) enzyme family metabolizes and detoxifies both exogenous and endogenous aldehydes. Since chemotherapeutic agents, such as cisplatin, generate cytotoxic aldehydes and oxidative stress, and chemoresistant cancer cells express high levels of ALDH enzymes, we hypothesized that different ALDH expression within cells may show different chemosensitivity. ALDH2 has the lowest Km for acetaldehyde among ALDH isozymes and detoxifies acetaldehydes in addition to other reactive aldehydes, such as 4-hydroxy-nonenal, malondialdehyde and acrolein produced from lipid peroxidation by reactive oxygen species (ROS). Thus, cells with an ALDH2 variant may sensitize them to these ROS-inducing chemotherapy drugs.

Methods

Here, we used wild type C57BL/6 mice and ALDH2*2 knock-in mutant mice and compared the basal level of ROS in different tissues. Then, we treated the mice with cisplatin, isolated cells from organs and fractionated them into lysates containing mitochondrial and cytosolic fractions, treated with cisplatin again in vitro, and compared the level of ROS generated.

Results

We show that overall ROS production increases with cisplatin treatment in cells with ALDH2 mutation. The treatment of cisplatin in the wild type mice did not change the level of ROS compared to PBS treated controls. In contrast, ALDH2*2 knock-in mutant mice showed a significantly increased level of ROS compared to wild type mice in tongue, lung, kidney and brain tissues without any treatment. ALDH2*2 mutant mice showed 20% of the ALDH2 activity in the kidney compared to wild type mice. Treatment of ALDH2*2 mutant mice with cisplatin showed increased ROS levels in the mitochondrial fraction of kidney. In the cytosolic fraction, treatment of mutant mice with cisplatin increased ROS levels in lung and brain compared to PBS treated controls. Furthermore, ALDH2*2 mutant mice treated with cisplatin showed increased cytotoxicity in the kidney cells compared to PBS treated mutant controls.

Conclusions

These data indicate that deficiency in ALDH2 activity may contribute to increased cisplatin sensitivity and cytotoxicity by producing more ROS by the treatment. Based on these data, the amount of cisplatin used in patients may need to be adjusted based on their ALDH2 variant profile.

Targeting acetaldehyde dehydrogenase 2 (ALDH2) in heart failure-Recent insights and perspectives

Heart failure is one of the major causes of the ever-rising mortality globally. ALDH2 rs671 polymorphism is proven to be closely related to the prevalence of CAD, hypertension, diabetes mellitus and alcoholism, which are etiological factors of heart failure. In addition, growing evidence supports a possible role for ALDH2 in different forms of heart failure. In this mini-review, we will review the recent insights regarding the effects of ALDH2 polymorphism on etiological factors of heart failure and underlying mechanisms involved. In addition, we will also discuss the booming epigenetic information in this field which will greatly improve our understanding of the cardiovascular effect of ALDH2. This article is part of a Special Issue entitled: Genetic and epigenetic control of heart failure edited by Dr. Jun Ren & Yingmei Zhang.

Mitochondrial aldehyde dehydrogenase 2 protects gastric mucosa cells against DNA damage caused by oxidative stress

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is a member of the aldehyde dehydrogenase superfamily and is involved with the metabolic processing of aldehydes. ALDH2 plays a cytoprotective role by removing aldehydes produced during normal metabolism. We examined the cytoprotective role of ALDH2 specifically in gastric mucosa cells. Overexpression of ALDH2 increased the viability of gastric mucosa cells treated with H2O2, while knockdown of ALDH2 had an opposite effect. Moreover, overexpression of ALDH2 protected gastric mucosa cells against oxidative stress-induced apoptosis as determined by flow cytometry, Hoechst 33342, and TUNEL assays. Consistently, ALDH2 knockdown had an opposite effect. Additionally, DNA damage was ameliorated in ALDH2-overexpressing gastric mucosa cells treated with H2O2. We further identified that this cytoprotective role of ALDH2 was mediated by metabolism of 4-hydroxynonenal (4-HNE). Consistently, 4-HNE mimicked the oxidative stress induced by H2O2 in gastric mucosa cells. Treatment with 4-HNE increased levels of DNA damage in ALDH2-knockdown GES-1 cells, while overexpression of ALDH2 decreased 4-HNE-induced DNA damage. These findings suggest that ALDH2 can protect gastric mucosa cells against DNA damage caused by oxidative stress by reducing levels of 4-HNE.

Paclitaxel resistance in MCF-7/PTX cells is reversed by paeonol through suppression of the SET/phosphatidylinositol 3-kinase/Akt pathway

Breast cancer is one of the most prevalent types of malignant tumor. Paclitaxel is widely used in the treatment of breast cancer; however, the major problem contributing to the failure of chemotherapy in breast cancer is the development of drug resistance. Therefore, it is necessary to identify novel therapeutic targets and reversal agents for breast cancer. In the present study, the protein expression levels of SET, protein phosphatase 2A (PP2A) and phosphatidylinositol 3-kinase (PI3K)/Akt pathway were determined in MCF-7/PTX human breast carcinoma paclitaxel-resistant cells using western blot analysis. Small interference RNAs (siRNAs) were used to knock down the gene expression of SET in MCF-7/PTX cells and the cell viability was assessed following treatment with paclitaxel, using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assays and flow cytometry. In addition, western blot analysis was used to determined PI3K/Akt pathway activity following SET knockdown. Furthermore, the reversal effects of paeonol on paclitaxel, and its underlying mechanisms of action, were investigated using western blot analysis and reverse transcription-quantitative polymerase chain reaction. The results demonstrated that increased levels of SET and PI3K/Akt pathway proteins were present in the MCF-7/PTX cells, compared with normal MCF-7 cells. Knockdown of SET significantly sensitized MCF-7/PTX cells to paclitaxel and induced cell apoptosis. In addition, the expression levels of the adenosine triphosphate binding cassette (ABC) transporter proteins were significantly reduced in the MCF-7/PTX cells compared with the normal MCF-7 cells. SET-induced paclitaxel resistance was found to be associated with the activation of the PI3K/Akt pathway. Paeonol significantly reduced the mRNA and protein expression levels of SET in the MCF-7/PTX cells. Furthermore, paeonol significantly sensitized the MCF-7/PTX to paclitaxel via regulation of ABC transporters, B cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein. In addition, paeonol inhibited SET-mediated paclitaxel resistance by attenuating PI3K/Akt pathway activity in the MCF-7/PTX cells. In conclusion, the results of the present study demonstrated that SET was associated with paclitaxel resistance in MCF-7/PTX cells, and that paeonol reversed paclitaxel resistance in MCF-7/PTX cells by downregulating the activity of the SET/PP2A/Akt pathway.

Stable SET knockdown in head and neck squamous cell carcinoma promotes cell invasion and the mesenchymal-like phenotype in vitro, as well as necrosis, cisplatin sensitivity and lymph node metastasis in xenograft tumor models

BACKGROUND

SET/I2PP2A is a multifunctional protein that is up-regulated in head and neck squamous cell carcinoma (HNSCC). The action of SET in HNSCC tumorigenicity is unknown.

METHODS

Stable SET knockdown by shRNA (shSET) was established in three HNSCC cell lines: HN12, HN13, and Cal27. Protein expression and phosphorylated protein levels were determined by Western blotting and immunofluorescence, cell migration and invasion were measured by functional analysis, and PP2A activity was determined using a serine/threonine phosphatase assay. A real-time PCR array was used to quantify 84 genes associated with cell motility. Metalloproteinase (MMP) activity was assessed by zymographic and fluorometric assays. HN12shSET xenograft tumors (flank and tongue models) were established in Balb/c nude mice; the xenograft characteristics and cisplatin sensitivity were demonstrated by macroscopic, immunohistochemical, and histological analyses, as well as lymph node metastasis by histology.

RESULTS

The HN12shSET cells displayed reduced ERK1/2 and p53 phosphorylation compared with control. ShSET reduced HN12 cell proliferation and increased the sub-G1 population of HN12 and Cal27 cells. Increased PP2A activity was also associated with shSET. The PCR array indicated up-regulation of three mRNAs in HN12 cells: vimentin, matrix metalloproteinase-9 (MMP9) and non-muscle myosin heavy chain IIB. Reduced E-cadherin and pan-cytokeratin, as well as increased vimentin, were also demonstrated as the result of SET knockdown. These changes were accompanied by an increase in MMP-9 and MMP-2 activities, migration and invasion. The HN12shSET subcutaneous xenograft tumors presented a poorly differentiated phenotype, reduced cell proliferation, and cisplatin sensitivity. An orthotopic xenograft tumor model using the HN12shSET cells displayed increased metastatic potential.

CONCLUSIONS

SET accumulation has important actions in HNSCC. As an oncogene, SET promotes cell proliferation, survival, and resistance to cell death by cisplatin in vivo. As a metastasis suppressor, SET regulates invasion, the epithelial mesenchymal transition, and metastasis.

Accumulated SET protein up-regulates and interacts with hnRNPK, increasing its binding to nucleic acids, the Bcl-xS repression, and cellular proliferation

SET and hnRNPK are proteins involved in gene expression and regulation of cellular signaling. We previously demonstrated that SET accumulates in head and neck squamous cell carcinoma (HNSCC); hnRNPK is a prognostic marker in cancer. Here, we postulate that SET and hnRNPK proteins interact to promote tumorigenesis. We performed studies in HEK293 and HNSCC (HN6, HN12, and HN13) cell lines with SET/hnRNPK overexpression and knockdown, respectively. We found that SET and/or hnRNPK protein accumulation increased cellular proliferation. SET accumulation up-regulated hnRNPK mRNA and total/phosphorylated protein, promoted hnRNPK nuclear location, and reduced Bcl-x mRNA levels. SET protein directly interacted with hnRNPK, increasing both its binding to nucleic acids and Bcl-xS repression. We propose that hnRNPK should be a new target of SET and that SET-hnRNPK interaction, in turn, has potential implications in cell survival and malignant transformation.

Expression of set is downregulated by rapamycin in human colorectal cancer cells

The purpose of this study was to determine the mechanism through which rapamycin treatment affects the expression of the set gene in human colorectal adenocarcinoma cells. The effect of rapamycin treatment on set expression was evaluated by assessing the mRNA and protein expression of set in the SW480 and LoVo human colon carcinoma cell lines following treatment with rapamycin by quantitative polymerase chain reaction (qPCR) and western blot analysis, respectively. Our results demonstrated that the mRNA and protein levels of set were significantly decreased subsequent to rapamycin treatment in the two cell lines, indicating that set expression may be downregulated by rapamycin in human colorectal adenocarcinoma cells. Our findings suggested that the mammalian target of rapamycin signaling pathway may play a role in tumorigenesis through the regulation of the set gene.