Xueli Pang

ER stress induced by ionising radiation in IEC-6 cells

Purpose: Ionising radiation (IR) can evoke a series of biochemical events inside the cell. However, whether IR can directly induce endoplasmic reticulum (ER) stress is not clear. In our previous study, we found that there might be a causative link between IR and ER stress. In this study, we further characterised the type of ER stress induced by IR. Materials and methods: Rat intestinal epithelial cells IEC-6 were irradiated at a dose of 10 Gy, and total RNA and proteins were harvested at indicated time points. The mRNA and protein expression of immunoglobulin heavy chain binding protein (BiP) and glucose regulated protein 94 (GRP94) was detected along with proteins associated with ER stress signal pathways. Results: Our results indicated that IR induced up-regulation of ER stress marker including BiP and GRP94 at protein and mRNA levels in IEC-6 cells. Increased phosphorylation of eukaryotic translation initiation factor 2 (eIF2α) and induced mRNA splicing of X-box binding protein 1 (XBP1) suggested that PERK (interferon-induced double-stranded RNA-activated protein kinase (PRKR) -like endoplasmic reticulum kinase) and IRE1 (inositol requirement 1) signal transduction pathways were involved in this kind of ER stress. However, the active form of activating transcription factor 6 (ATF6) did not change significantly in irradiated cells, which suggested that the ATF6 pathway was not involved. Conclusions: Thus, we concluded that IR could induce moderate ER stress directly in IEC-6 cells.

Endoplasmic reticulum stress sensitizes human esophageal cancer cell to radiation

AIM To investigate the role of endoplasmic reticulum (ER) stress in cancer radiotherapy and its molecular mechanism. METHODS Tunicamycin (TM) was applied to induce ER stress in human esophageal cancer cell line EC109, and the radiosensitization effects were detected by acute cell death and clonogenic survival assay. Cell cycle arrest induced by TM was determined by flow cytometric analysis after the cellular DNA content was labeled with propidium iodide. Apoptosis of EC109 cells induced by TM was detected by annexin V staining and Western blotting of caspase-3 and its substrate poly ADP-ribose polymerase. Autophagic response was determined by acridine orange (AO) staining and Western blotting of microtubule-associated protein-1 light chain-3 (LC3) and autophagy related gene 5 (ATG5). In order to test the biological function of autophagy, specific inhibitor or Beclin-1 knockdown was used to inhibit autophagy, and its effect on cell apoptosis was thus detected. Additionally, involvement of the phosphatidylinositol-3 kinase (PI3K)/Akt/mammalian target of the rapamycin (mTOR) pathway was also detected by Western blotting. Finally, male nude mice inoculated subcutaneously with EC109 cells were used to confirm cell model observations. RESULTS Our results showed that TM treatment enhanced cell death and reduced the colony survival fraction induced by ionizing radiation (IR), which suggested an obvious radiosensitization effect of TM. Moreover, TM and IR combination treatment led to a significant increase of G2/M phase and apoptotic cells, compared with IR alone. We also observed an increase of AO positive cells, and the protein level of LC3-II and ATG5 was induced by TM treatment, which suggested an autophagic response in EC109 cells. However, inhibition of autophagy by using a chemical inhibitor or Beclin-1 silencing led to increased cell apoptosis and decreased cell viability, which suggested a cytoprotective role of autophagy in stressed EC109 cells. Furthermore, TM treatment also activated mTORC1, and in turn reduced Akt phosphorylation, which suggested the PI3K/Akt/mTOR signal pathway was involved in the TM-induced autophagic response in EC109 cells. Tumor xenograft results also showed synergistic retarded tumor growth by TM treatment and IR, as well as the involvement of the PI3K/Akt/mTOR pathway. CONCLUSION Our data showed that TM treatment sensitized human esophageal cancer cells to radiation via apoptosis and autophagy both in vitro and in vivo.

MCM-2 is a Therapeutic Target of Trichostatin A in Colon Cancer Cells

Histone deacetylase (HDAC) inhibitors have recently emerged as a new class of anti-cancer agents. Trichostatin A (TSA), a classical HDAC inhibitor, has been demonstrated to induce cell cycle arrest, promote cell apoptosis, and inhibit metastasis. However, the molecular mechanism underlying TSA function has not been fully elucidated. In the current study, we found that TSA treatment induced altered expression of cell cycle-associated genes in HCT116 cells by RT-PCR array. Among the 84 genes related to cell cycle control, 34 genes were significantly altered by TSA treatment, with 7 genes upregulated and 27 genes downregulated. Interestingly, gene expression of minichromosome maintenance protein-2 (MCM-2) was significantly downregulated by TSA treatment. This was confirmed by quantitative RT-PCR and Western blotting. Moreover, silencing of MCM-2 by siRNA led to cell cycle arrest and apoptosis in HCT116 cells. In addition, TSA caused an increase of phosphorylated JNK, which was involved in downregulation of MCM-2. Together, our results suggest that MCM-2 is a noval therapeutic target of TSA in colon cancer cells.

Macrophage ABHD5 promotes colorectal cancer growth by suppressing spermidine production by SRM

Metabolic reprogramming in stromal cells plays an essential role in regulating tumour growth. The metabolic activities of tumour-associated macrophages (TAMs) in colorectal cancer (CRC) are incompletely characterized. Here, we identify TAM-derived factors and their roles in the development of CRC. We demonstrate that ABHD5, a lipolytic co-activator, is ectopically expressed in CRC-associated macrophages. We demonstrate in vitro and in mouse models that macrophage ABHD5 potentiates growth of CRC cells. Mechanistically, ABHD5 suppresses spermidine synthase (SRM)-dependent spermidine production in macrophages by inhibiting the reactive oxygen species-dependent expression of C/EBPɛ, which activates transcription of the srm gene. Notably, macrophage-specific ABHD5 transgene-induced CRC growth in mice can be prevented by an additional SRM transgene in macrophages. Altogether, our results show that the lipolytic factor ABHD5 suppresses SRM-dependent spermidine production in TAMs and potentiates the growth of CRC. The ABHD5/SRM/spermidine axis in TAMs might represent a potential target for therapy.

Inhibition of autophagy induced by TSA sensitizes colon cancer cell to radiation

Radiotherapy is one of the main treatments for clinical cancer therapy. However, its application was limited due to lack of radiosensitivity in some cancers. Trichostatin A (TSA) is a classic histone deacetylases inhibitor (HDACi) that specifically inhibits the biochemical functions of HDAC and is demonstrated to be an active anticancer drug. However, whether it could sensitize colon cancer to radiation is not clear. Our results showed that TSA enhanced the radiosensitivity of colon cancer cells as determined by CCK-8 and clonogenic survival assay. Moreover, apoptotic cell death induced by radiation was enhanced by TSA treatment. Additionally, TSA also induced autophagic response in colon cancer cells, while autophagy inhibition led to cell apoptosis and enhanced the radiosensitivity of colon cancer cells. Our data suggested that inhibition of cytoprotective autophagy sensitizes cancer cell to radiation, which might be further investigated for clinical cancer radiotherapy.

Melatonin regulates PARP1 to control the senescence‐associated secretory phenotype (SASP) in human fetal lung fibroblast cells

Cellular senescence is an important tumor‐suppressive mechanism. However, acquisition of a senescence‐associated secretory phenotype (SASP) in senescent cells has deleterious effects on the tissue microenvironment and, paradoxically, promotes tumor progression. In a drug screen, we identified melatonin as a novel SASP suppressor in human cells. Strikingly, melatonin blunts global SASP gene expression upon oncogene‐induced senescence (OIS). Moreover, poly(ADP‐ribose) polymerase‐1 (PARP‐1), a sensor of DNA damage, was identified as a new melatonin‐dependent regulator of SASP gene induction upon OIS. Here, we report two different but potentially coherent epigenetic strategies for melatonin regulation of SASP. The interaction between the telomeric repeat‐containing RNA (TERRA) and PARP‐1 stimulates the SASP, which was attenuated by 67.9% (illustrated by the case of IL8) by treatment with melatonin. Through binding to macroH2A1.1, PARP‐1 recruits CREB‐binding protein (CBP) to mediate acetylation of H2BK120, which positively regulates the expression of target SASP genes, and this process is interrupted by melatonin. Consequently, the findings provide novel insight into melatonins epigenetic role via modulating PARP‐1 in suppression of SASP gene expression in OIS‐induced senescent cells. Our studies identify melatonin as a novel anti‐SASP molecule, define PARP‐1 as a new target by which melatonin regulates SASP, and establish a new epigenetic paradigm for a pharmacological mechanism by which melatonin interrupts PARP‐1 interaction with the telomeric long noncoding RNA(lncRNA) or chromatin.

Enhanced radiosensitivity of EC109 cells by inhibition of HDAC1 expression.

Histone deacetylase (HDAC) activity plays the role of deacetylation of histone and non-histone proteins, which can alter gene expression patterns and cell behavior potentially associated with malignant transformation. Aberrant expression of HDAC1 has been found in various types of cancers, which indicated that it might be a target for cancer therapy. In this study, overexpression of HDAC1 was found in esophageal cancer samples by real-time RT-PCR, compared with adjacent non-cancerous tissues. To further verify the possibility of anticancer treatment by silencing the increased HDAC1 in esophageal carcinoma cells, HDAC1 expression was knockdown using plasmid-based RNA interference (RNAi). Results showed the HDAC1 expression was efficiently inhibited and the acetylation of histone H3 was significantly increased by RNAi in EC109 cells. Increased apoptotic cell death was observed when HDAC1 expression was knockdown, which indicated that cells were more sensitive to radiation. Moreover, the results also showed DNA was more easily broken by radiation in EC109 cells when HDAC1 expression was knockdown, as measured by γH2AX foci and single-cell electrophoresis. Our data suggested that targeting the increased HDAC1 expression might be feasible for esophageal cancer therapy.

Knockdown of Rad9A enhanced DNA damage induced by trichostatin A in esophageal cancer cells

Histone deacetylase (HDAC) inhibitors have recently emerged as a new class of anticancer agents. As a classical HDAC inhibitor, trichostatin A (TSA) has been shown to possess many anticancer activities such as induction of cell cycle arrest, promotion of cell death, and enhancement of radiosensitity. In our previous work, we found that TSA treatment induced Rad9 gene expression, which suggested that Rad9 might play a role in TSA-induced biological effects. As Rad9 is involved in maintaining genomic integrity, we further analyzed the DNA damage induced by TSA and combined with Rad9 knockdown in esophageal cancer cells (ESCCs). Our results showed that TSA treatment alone induced significantly DNA damage in ESCC cells. Simultaneously, TSA also induced Rad9 gene expression both at transcriptional and translational levels in EC109 cells, but not in KYSE150 cells. Further, the induction of Rad9 by TSA was accompanied with increased level of histone H3K9 acetylation in Rad9 promoter region. To understand the role of Rad9 in TSA-induced DNA damage, Rad9 gene expression was efficiently knocked down by small interfering RNA (siRNA), which led to enhanced DNA damage and cell death induced by TSA. Our data suggested that Rad9 plays an important role in DNA damage, which is related to the biological effects of TSA.

Lentivirus-mediated Knockdown of HDAC1 Uncovers Its Role in Esophageal Cancer Metastasis and Chemosensitivity.

Histone deacetylationase 1 (HDAC1) is ubiquitously expressed in various cell lines and tissues and play an important role of regulation gene expression. Overexpression of HDAC1 has been observed in various types of cancers, which indicated that it might be a target for cancer therapy. To test HDAC1 inhibition for cancer treatment, the gene expression of HDAC1 was knockdown mediated by a lentivirus system. Our data showed the gene expression of HDAC1 could be efficiently knockdown by RNAi mediated by lentivirus in esophageal carcinoma EC109 cells. Knockdown of HDAC1 led to significant decrease of cell growth and altered cell cycle distribution. The result of transwell assay showed that the numbers of cells travelled through the micropore membrane was significantly decreased as HDAC1 expression was knockdown. Moreover, HDAC1 knockdown inhibited the migration of EC109 cells as determining by scratch test. Additionally, enhancement of cisplatin-stimulated apoptosis was detected by HDAC1 knockdown. Our data suggested inhibition of HDAC1 expression by lentivirus mediated shRNA might be further applied for esophageal cancer chemotherapy.

Functional Analysis of SNPs in the ERCC5 Promoter in Advanced Colorectal Cancer Patients Treated With Oxaliplatin-Based Chemotherapy.

AbstractThe promoter is the center for regulation of gene transcription due to containing numerous transcription factor binding sites. The aim of the study was to determine whether genetic variations at excision repair cross complementation group 5 (ERCC5) promoter could affect transcription factor binding and whether such single nucleotide polymorphism (SNP)-dependent binding could affect gene expression, drug response, and clinical outcome.A total of 170 patients who were cytologically or histologically confirmed with advanced colorectal cancer (CRC), at least 1 measurable lesion, and underwent oxaliplatin-based chemotherapy were studied. The polymerase chain reaction–ligation detection reaction (PCR-LDR) was used to analyze SNPs. The reporter gene assay system and electrophoretic mobility shift assays (EMSA) were performed to investigate the effect of SNPs on the ERCC5 promoter activity and DNA-binding activity, respectively. The mRNA and protein expression of ERCC5 in tumor tissues of colorectal cancer patients with different genotypes were detected by real-time PCR and western blot, respectively.Both −763A and −763G allele had nuclear protein-binding ability. +25A allele did not show any nuclear protein-binding ability, whereas +25G allele did. The relative luciferase activity of the −763A/+25G haplotype was significantly higher than other 3 haplotypes (P < 0.05). The expression level of ERCC5 mRNA and protein was significantly higher in tumor tissues with −763AA+25GG genotype combination than that with −763GG+25AA genotype combination (P < 0.05, respectively). Allelic variants (−763AA vs −763AG or –763GG, +25GG versus +25AG or +25AA) were significantly associated with shorter progression-free survival (PFS) and overall survival (OS) (P < 0.05, respectively). At multivariate analysis, patients with risk genotypes (−763AA or +25GG genotype) demonstrated a significantly increasing risk of progression (P = 0.01) or worse OS (P = 0.001).The ERCC5 promoter polymorphisms at −763 and +25 may be important functional variants and predictors of clinical outcome of CRC patients who received oxaliplatin chemotherapy.