Autophagy In Colon Cancer Cells Research Articles

Expression of Concern: ASF1A regulates H4Y72 phosphorylation and promotes autophagy in colon cancer cells via a kinase activity

This article refers to:ASF1A regulates H4Y72 phosphorylation and promotes autophagy in colon cancer cells via a kinase activity

Livin Regulates H2A.XY142 Phosphorylation and Promotes Autophagy in Colon Cancer Cells via a Novel Kinase Activity.

Objective: To investigate Livin-mediated regulation of H2A.XY142 phosphorylation via a novel kinase activity and its effect on autophagy in colon cancer cells.Methods: The interaction between Livin and H2A.X was tested by immunoprecipitation. H2A.X–/– HCT116 cells were transfected with human influenza hemagglutinin (HA)-tagged WT or Y142F phospho-dead mutantH2A.X plasmids. GST-tagged recombinant Livin protein was used to perform in vitro pull-down experiment and kinase assay. H2A.X–/–Livin+/+ SW480 cells were co-transfected with H2A.XWT/H2A.XY142F plasmid and LC3 EGFP-tagged plasmid to explore whether H2A.XY142F was involved in Livin-mediated autophagy induced by starvation in colon cancer cells.Results: Co-immunoprecipitation studies confirmed that Livin interacted with H2A.X and that it was phosphorylation dependent. In vitro kinase assay confirmed that Livin could phosphorylate H2A.X. Knockdown of Livin (Livin–/–) in SW480 cells or HCT116 cells canceled the starvation-induced autophagy in colon cancer cells; H2A.X–/–Livin+/+ SW480 cells transfected with H2A.XWT activated autophagy induced by starvation while cells transfected with H2A.XY142F had no significant difference; Livin-H2A.XY142F axis activated autophagy in colon cancer cells through transcriptionally regulating ATG5 and ATG7.Conclusion: Livin promotes autophagy in colon cancer cells via regulating the phosphorylation of H2A.XY142.

Shikonin regulates invasion and autophagy of cultured colon cancer cells by inhibiting yes-associated protein.

Colon cancer is a common malignancy, and its morbidity and mortality have been increasing in recent years in China. Shikonin (Shi), a naturally occurring naphthoquinone, exhibits anticancer activity. However, the mechanisms of action of Shi remain unclear. The aim of the present study was to investigate the antitumor mechanism of Shi in colon cancer cells. The effects of different Shi concentrations on the viability of colon cancer cells using MTT, colony formation and wound-healing assays were assessed. Western blot analysis was performed to detect the expression of LC3-II, p62. Shi effectively suppressed viability and cell migration, and induced autophagy in colon cancer cells. Yes-associated protein (YAP) increases cell viability, and inhibits cell apoptosis and cell contact. Expression of YAP is downregulated by Shi. The cytotoxic effects of Shi were further investigated on YAP overexpression and on YAP knockout cell lines. The findings revealed that Shi suppressed the viability and induced autophagy of colon cancer cells. Additionally, YAP expression reversed the effects of Shi. The results of the present study suggest that Shi may be a promising anticancer treatment for colon cancer, and YAP may be a potential diagnostic marker for colon cancer.

ASF1A regulates H4Y72 phosphorylation and promotes autophagy in colon cancer cells via a kinase activity

Colon cancer is one of the most malignant cancers. Histone modification is closely related to tumour development. Our study explored the functions of anti-silencing function 1A (ASF1A) on H4Y72ph in colon cancer cells. Colon cancer cell lines and clinical specimens were obtained and/or transfected with full length ASF1A or interference mRNA to mimic or silence of ASF1A expression. Immunoprecipitation and GST pull down was used to target targeting ASF1A or H4Y72ph. Cells were transfected with H4WT- or H4Y72F-expressing. An in vitro kinase activity assay was set to determine whether ASF1A could phosphorylate H4. The severity of autophagy was measured by detecting number of autophagosomes, number of EGFP-LC3, LC3-II/I, percentage of degradation and expression of autophagy associated gene (ATG). ASF1A positively regulated H4Y72ph; Immunoprecipitation assay and GST pull down results showed that ASF1A interacted directly with H4. In addition, ASF1A silence inhibited autophagosomes number, EGFP-LC3 number, LC3-II/I, percentage of degradation and ATG expression. Moreover, H4Y72F impaired the promoting autophagy effects of ASF1A. The ASF1A-H4Y72ph axis promoted colon cancer autophagy via transcriptional regulation of ATG genes. ASF1A regulated H4Y72ph and promotes autophagy in colon cancer cells via a kinase activity through regulation of ATG.

Protopine isolated from Nandina domestica induces apoptosis and autophagy in colon cancer cells by stabilizing p53.

The tumor suppressor p53 plays essential roles in cellular protection mechanisms against a variety of stress stimuli and its activation induces apoptosis or autophagy in certain cancer cells. Here, we identified protopine, an isoquinoline alkaloid isolated from Nandina domestica, as an activator of the p53 pathway from cell-based natural compound screening based on p53-responsive transcription. Protopine increased the p53-mediated transcriptional activity and promoted p53 phosphorylation at the Ser15 residue, resulting in stabilization of p53 protein. Moreover, protopine up-regulated the expression of p21WAF1/CIP1 and BAX, downstream genes of p53, and inhibited the proliferation of HCT116 colon cancer cells. Apoptosis was elicited by protopine as indicated by caspase-3/7 activation, poly ADP ribose polymerase cleavage, and increased population of Annexin V-FITC-positive cells. Furthermore, protopine induced the formation of microtubule-associated protein 1 light chain 3 (LC3) puncta and LC3-II turnover, typical biochemical markers of autophagy, in HCT116 cells. Our findings suggest that protopine exerts its antiproliferative activity by stimulating the p53 pathway and may have potential as a chemopreventive agent for human colon cancer.

RACK1 promotes tumorigenicity of colon cancer by inducing cell autophagy

RACK1 is upregulated in the various types of human cancers, and considered to play a role in the development and progression of human cancer. However, the role and mechanism of RACK in the colon cancer are poorly understood. In this study, we detected RACK1 expression in 63 normal colonic mucosa, 60 colonic inflammatory polyps, 60 colonic adenomas, 180 colon adenocarcinomas, and 40 lymph node metastases by immunohistochemistry, and observed that RACK1 expression was progressively elevated in the carcinogenic process of human colonic epithelium, and RACK1 expressional levels were positively correlated with the malignant degree and lymph node metastasis of colon cancers, and negatively correlated with the patient survival. With a combination of loss-of-function and gain-of-function approaches, we observed that RACK1 promoted colon cancer cell proliferation, inhibited colon cancer cell apoptosis, and enhanced the anchorage-independent and xenograft growth of colon cancer cells. Moreover, we found that RACK1-induced autophagy of colon cancer cells; RACK1-induced autophagy promoted colon cancer cell proliferation and inhibited colon cancer cell apoptosis. Our data suggest that RACK1 acts as an oncogene in colon cancer, and RACK1-induced autophagy promotes proliferation and survival of colon cancer, highlighting the therapeutic potential of autophagy inhibitor in the colon cancer with high RACK1 expression.

Activation of the p53 pathway with digiferrol isolated from Rubia philippinensis induces cell cycle arrest, apoptosis, and autophagy in colon cancer cells

Activation of the p53 pathway with digiferrol isolated from Rubia philippinensis induces cell cycle arrest, apoptosis, and autophagy in colon cancer cells

Knockdown of Beclin-1 impairs epithelial-mesenchymal transition of colon cancer cells.

Activation of autophagy significantly affects cancer cell behaviors, such as proliferation, differentiation, and invasiveness. Epithelial-to-mesenchymal transition (EMT) as an initial step of malignant transformation of cancer cells was linked to the activation of autophagy, but the detailed molecular mechanisms are still unknown. The present study investigates the effects of Beclin-1, a key molecule involved in activation of autophagy, on EMT of colon cancer cells. The normal colon epithelia cell line of CCD-18Co and six colon cancer cell lines with different expression levels of Beclin-1 were used in this study. The activation of autophagy and EMT markers of cancer cells were monitored by Western blotting and quantitative real-time PCR assay in the presence or absence of rapamycin (autophagy activator) and 3-MA (autophagy inhibitor). The expression of Beclin-1 in selected cell lines was modulated using small interfering RNA, and consequentially EMT markers, and cancer cell behaviors including migration and invasion, were also explored. Activation or inhibition of autophagy in colon cancer cells had positive or negative impacts on the expression of EMT markers and malignant behaviors such as cell migration and invasion. Knockdown of beclin-1 by siRNA apparently inhibited the activation of autophagy induced by rapamycin, consequentially resulted in suppression of EMT and attenuation of invasiveness of colon cancer cells. The results in this study demonstrated an association between activation of autophagy and EMT in colon cancer cells. The results showed suppression of Beclin-1 expression significantly reduced EMT and invasive behaviors in colon cancer cells.

Activation of the SphK1/ERK/p-ERK pathway promotes autophagy in colon cancer cells.

Sphingosine kinase 1 (SphK1) is a master kinase that catalyzes the synthesis of sphingosine 1 phosphate and participates in the regulation of cell proliferation and autophagy. The present study aimed to assess the effects of the activation of the SphK1/extracellular signal-regulated kinase (ERK)/phosphorylated (p-)ERK pathway in the regulation of autophagy in colon cancer (HT-29) cells. Inverted fluorescence microscopy was used to detect the expression of green fluorescent protein (GFP) in the SphK1-overexpressing HT-29 cells [SphK1(+)-HT-29] and the negative control HT-29 cells (NC-HT-29). Western blotting was used to detect the protein expression levels of SphK1, ERK1/2, p-ERK1/2, as well as those of the autophagy-associated markers LC3A, ATG5, and ULK1. Protein localization and expression of the LC3A antibody were detected by immunofluorescence. The results demonstrated that GFP was similarly expressed in SphK1(+)-HT-29 and NC-HT-29 cells. However, significantly increased SphK1 mRNA and protein expression levels were detected in SphK1(+)-HT-29 cells compared with in NC-HT-29 cells, which resulted in upregulated ERK/p-ERK. Furthermore, the protein expression levels of the three autophagy-associated markers increased. LC3A protein was localized in the cytoplasm of SphK1(+)-HT-29 cells, indicating autophagy. In summary, the findings of the present study suggested that activation of the SphK1/ERK/p-ERK pathway promotes autophagy in colon cancer HT-29 cells.

Wogonoside inhibits cell growth and induces mitochondrial-mediated autophagy-related apoptosis in human colon cancer cells through the PI3K/AKT/mTOR/p70S6K signaling pathway.

Wogonoside, the main effective constituent of traditional Chinese medicine Scutellaria, belongs to the glucuronide family, with various functions, including detoxification, anti-inflammation and nourishing gallbladder, lowering blood pressure, diuresis and anti-allergic reactions. However, the effects of wogonoside on human colon cancer cells remain unclear. The present study aimed to investigate the anticancer effect of wogonoside on human colon cancer cells in vitro and its anticancer mechanisms. The results demonstrated that wogonoside significantly inhibited cell growth, induced apoptosis and mitochondrial-mediated autophagy of colon cancer cells. Furthermore, the results revealed that wogonoside significantly increased caspase-3 and caspase-9 expression levels, induced apoptosis regulator Bax/Bcl-2 and microtubule-associated protein 1A/1B-light chain 3 protein expression, suppressed the phosphatidylinositol 3 kinase (PI3K)/RAC-α serine/threonine-protein kinase (Akt)/mechanistic target of rapamycin (mTOR)/p70 S6 kinase (p70S6K) signaling pathway and induced p62 protein expression in colon cancer cells. In conclusion, these results demonstrated that wogonoside inhibits cell growth and induces mitochondrial mediated autophagy-related apoptosis in human colon cancer cells through modulation of the PI3K/Akt/mTOR/p70S6K signaling pathway.

Blue light-emitting diodes induce autophagy in colon cancer cells by Opsin 3.

BackgroundLight emitting‐diodes (LED) have various effects on living organisms and recent studies have shown the efficacy of visible light irradiation from LED for anticancer therapies. However, the mechanism of LED's effects on cancer cells remains unclear. The aim of the present study was to investigate the effects of LED on colon cancer cell lines and the role of photoreceptor Opsin 3 (Opn3) on LED irradiation in vitro.MethodsHuman colon cancer cells (HT‐29 or HCT‐116) were seeded onto laboratory dishes and irradiated with 465‐nm LED at 30 mW/cm2 for 30 minutes. Cell Counting Kit‐8 was used to measure cell viability, and apoptosis and caspase 3/8 expression were evaluated by AnnexinV/PI and reverse transcription‐polymerase chain reaction (RT‐PCR), respectively. Autophagy and expression of LC‐3 and beclin‐1 were also evaluated by autophagy assays, RT‐PCR and Western blotting. We further tested Opn3 knockdown by Opn3 siRNA and the Gi/o G‐protein inhibitor NF023 in these assays.ResultsViability of HT‐29 and HCT‐116 cells was lower in 465‐nm LED‐irradiated cultures than in control cultures. LC‐3 and beclin‐1 expressions were significantly higher in LED‐irradiated cultures, and autophagosomes were detected in irradiated cells. The reductive effect of cancer cell viability following blue LED irradiation was reversed by Opn3 knockdown or NF023 treatment. Furthermore, increased LC‐3 and beclin‐1 expression that resulted from blue LED irradiation was suppressed by Opn3 knockdown or NF023 treatment.ConclusionBlue LED irradiation suppressed the growth of colon cancer cells and Opn3 may play an important role as a photoreceptor.

Apatinib has anti-tumor effects and induces autophagy in colon cancer cells.

Objective(s):Apatinib recently has been used to treat patients with gastric cancer, but the function of apatinib in colon cancer remains unclear. This study was conducted to investigate the impacts of apatinib on the biological function and its potential mechanism of colon cancer cells in vitro.Materials and Methods:The effect of apatinib in colon cancer cells were detected by assessing cell viability, migration and invasion capabilities. Apoptosis cells and the cell cycle distribution of colon cancer cells were analyzed by flow cytometry. The potential mechanism was investigated via autophagy related proteins and pathways in vitro.Results:The proliferation, migration and invasion of colon cancer cells were inhibited when they were treated with different concentration of apatinib (20, 40 μM). When HCT116 and SW480 cells were treated with apatinib at the concentration of 20 μM, the apoptosis percentage were 3.7% and 5.8% respectively. As the drug concentration increased to 40μΜ, the the apoptosis percentage increased to 11.9% and 13.5%. Meanwhile, cell cycle was also altered. Furthermore, apatinib inhibited the expression of AKT-mTOR signaling pathway and increased the expression of LC3-II.Conclusion:Apatinib can significantly inhibit the malignant phenotype of colon cancer cells, and it was involved in regulation of autophagy.

Mir-30d suppresses cell proliferation of colon cancer cells by inhibiting cell autophagy and promoting cell apoptosis.

MiR-30 family plays an important role in the tumorigenesis of human cancers. The aim of the study is to investigate the role of miR-30d in human colon cancer cell lines and explore the molecular mechanism in the proliferation of colon cancer cells. The expression of miR-30d was determined by real-time polymerase chain reaction assay in colon cancer cell lines (HCT15, HCT116, HT-29, DLD-1, and SW480) and the results demonstrated that miR-30d level was significantly decreased in human colon cancer cell lines, compared with normal colon epithelial cell line. Transfection with miR-30d mimics inhibited cell proliferation, and transfection with miR-30d inhibitors significantly promoted cell viability of colon cancer cells. Furthermore, TargetScan analysis predicted that miR-30d interacted with messenger RNA on its 3' untranslated region of ATG5, phosphoinositide 3-kinase, and Beclin1 to negatively regulate cell autophagy in colon cancer cells. Moreover, transfection with miR-30d induced cell arrest at G2/M phase of HT-29 cells. Overexpression of miR-30d mimics inhibited cell viability probably due to the inhibition of cell autophagy and promotion of cell apoptosis. Thus, MiR-30d inhibited cell autophagy by directly targeting messenger RNA of ATG5, phosphoinositide 3-kinase, and Beclin1 and promoted cell apoptosis of human colon cancer cells. It is helpful to clarify the function of miR-30d in tumorigenesis of human cancers.

Combination of Fe/Cu -chelators and docosahexaenoic acid: an exploration for the treatment of colorectal cancer.

Colorectal cancer (CRC) is one of the major causes of cancer deaths in the world. 5-fluorouracil (5-FU) -based chemotherapy is a common choice for patients with CRC; unfortunately, the benefit is rather limited due to the acquisition of drug resistance. Therefore, the alternative therapeutic strategies are required. The activation of autophagic mechanism was considered as the main cause of the acquisition of drug resistance in 5-FU treatment. Docosahexaenoic acid (DHA), a fatty acid, has been regarded as an efficient anticancer agent and can improve the drug resistance in conventional cancer therapy by a low basal level of autophagy in colon cancer cells. Moreover, removal of iron or copper by metal chelators could cause ROS levels increase and mediate cancer cell cytotoxicity led by autophagy. In the present study, we constructed a combination of 5-FU, 1:1 mixture of metal chelators di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone hydrochloride (DpC) and N, N, N’, N’-tetrakis-[2-pyridylmethyl]-ethylenediamine (TPEN) named DTN, and DHA to evaluate the anticancer effect of this combination, compared to the traditional 5-FU-based chemotherapy; further we investigated the underlying mechanism. Through inducing ROS-mediated degradation of Mcl-1 ubiquitination, the triple combination of 5-FU, DTN and DHA resulted in the elevated apoptosis in CRC cells, thus to reduce the tumor size and weight. Taken together, this study suggests the triple combination of 5-FU+DTN+DHA exhibits an effective anticancer activity of overcoming drug resistance in colorectal cancer, mechanism as the elevated apoptosis mediated by an increase of ROS and Mcl-1 ubiquitination, may be a novel strategy for clinical colon cancer treatment.

Adipocytes activate mitochondrial fatty acid oxidation and autophagy to promote tumor growth in colon cancer

Obesity has been associated with increased incidence and mortality of a wide variety of human cancers including colorectal cancer. However, the molecular mechanism by which adipocytes regulate the metabolism of colon cancer cells remains elusive. In this study, we showed that adipocytes isolated from adipose tissues of colon cancer patients have an important role in modulating cellular metabolism to support tumor growth and survival. Abundant adipocytes were found in close association with invasive tumor cells in colon cancer patients. Co-culture of adipocytes with colon cancer cells led to a transfer of free fatty acids that released from the adipocytes to the cancer cells. Uptake of fatty acids allowed the cancer cells to survive nutrient deprivation conditions by upregulating mitochondrial fatty acid β-oxidation. Mechanistically, co-culture of adipocytes or treating cells with fatty acids induced autophagy in colon cancer cells as a result of AMPK activation. Inhibition of autophagy attenuated the ability of cancer cells to utilize fatty acids and blocked the growth-promoting effect of adipocytes. In addition, we found that adipocytes stimulated the expression of genes associated with cancer stem cells and downregulated genes associated with intestinal epithelial cell differentiation in primary colon cancer cells and mouse tumor organoids. Importantly, the presence of adipocytes promoted the growth of xenograft tumors in vivo. Taken together, our results show that adipocytes in the tumor microenvironment serve as an energy provider and a metabolic regulator to promote the growth and survival of colon cancer cells.

6-C-(E-phenylethenyl)naringenin induces cell growth inhibition and cytoprotective autophagy in colon cancer cells

6-C-(E-phenylethenyl)naringenin (6-CEPN) is a small molecule found in naringenin fortified fried beef. It has been shown to suppress colon cancer cell proliferation, but the underlying mechanisms are not fully understood. Here we demonstrate that 6-CEPN suppresses tumour cell proliferation through cell cycle arrest in G1 phase, induces necrotic cell death and autophagy in colon cancer cells. Blockade of autophagy by knockdown of the essential autophagy proteins, Atg7 or beclin-1, resulted in aggravated cell death in response to 6-CEPN treatment. In addition, genome-wide transcriptome expression profiling by RNA-sequencing revealed that 6-CEPN-mediated gene expression pattern was extremely similar to the transcriptome response induced by a RAS inhibitor salirasib (farnesylthiosalicylic acid [FTS; salirasib]). Subsequent molecular biological and biochemical experiments demonstrated that 6-CEPN indeed strongly inhibited RAS activation, leading to the inhibition of the downstream effector pathways c-Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase kinase and phosphoinositide 3-kinase/AKT/mammalian target of rapamycin. More importantly, our computational molecular docking data showed that 6-CEPN could bind to the active site of isoprenylcysteine carboxyl methyltransferase (Icmt), a critical enzyme for the activation of RAS. Icmt activity assay showed that 6-CEPN inhibited its activity significantly. Knockdown of Icmt by siRNA attenuated 6-CEPN-mediated autophagy and cell death. The present study demonstrates that 6-CEPN induces cell growth inhibition and cytoprotective autophagy in colon cancer cells, at least in part, though inhibition of the Icmt/RAS signalling pathways.

Abstract 4088: Adipocytes-mediated autophagy activation and metabolic reprogramming promotes colon cancer survival

Abstract Obesity has been associated with increased incidence and mortality of a wide variety of human cancers including colorectal cancer. However, the molecular mechanism underlying the functional interaction between obesity and cancer remains elusive. Here, we demonstrated that adipocytes isolated from adipose tissues of colon cancer patients play an important role in promoting tumor cell survival and progression by altering cellular metabolism. In stage IV colon cancer cases, abundant adipocytes were found in close association with invasive colon cancer cells. Co-culture of adipocytes with colon cancer cells led to direct transfer of free fatty acids (FAs) released by the adipocytes to colon cancer cells. Uptake of FAs allowed the cancer cells to survive nutrient deprivation conditions by upregulating mitochondrial fatty acid β-oxidation, suggesting that FAs from adipocytes were used as an energy source by the cancer cells. In addition, we found that co-culture of adipocytes or treating cells with fatty acids induced autophagy in colon cancer cells as a result of AMPK activation. Inhibition of autophagy attenuated the ability of cancer cells to utilize FAs and blocked the growth promoting effect of adipocytes. Furthermore, we found that adipocytes induced dedifferentiation of tumor cells in primary colon cancer cells and mouse tumor organoids. Taken together, these results identify adipocytes as active contributors to the tumor microenvironment that promote tumor growth and survival by serving as an energy provider and a metabolic regulator for the embedded colon cancer cells. Citation Format: Yang-an Wen, Xiaopeng Xiong, Jennifer Harris, Yekaterina Zaytseva1, Tianyan Gao. Adipocytes-mediated autophagy activation and metabolic reprogramming promotes colon cancer survival. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4088.

Vitamin E metabolite 13′-carboxychromanols inhibit pro-inflammatory enzymes, induce apoptosis and autophagy in human cancer cells by modulating sphingolipids and suppress colon tumor development in mice

Vitamin E forms are substantially metabolized to various carboxychromanols including 13′-carboxychromanols (13′-COOHs) that are found at high levels in feces. However, there is limited knowledge about functions of these metabolites. Here we studied δT-13′-COOH and δTE-13′-COOH, which are metabolites of δ-tocopherol and δ-tocotrienol, respectively. δTE-13′-COOH is also a natural constituent of a traditional medicine Garcinia Kola. Both 13′-COOHs are much stronger than tocopherols in inhibition of pro-inflammatory and cancer promoting cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX), and in induction of apoptosis and autophagy in colon cancer cells. The anticancer effects by 13′-COOHs appeared to be partially independent of inhibition of COX-2/5-LOX. Using liquid chromatography tandem mass spectrometry, we found that 13′-COOHs increased intracellular dihydrosphingosine and dihydroceramides after short-time incubation in HCT-116 cells, and enhanced ceramides while decreased sphingomyelins during prolonged treatment. Modulation of sphingolipids by 13′-COOHs was observed prior to or coinciding with biochemical manifestation of cell death. Pharmaceutically blocking the increase of these sphingolipids partially counteracted 13′-COOH-induced cell death. Further, 13′-COOH inhibited dihydroceramide desaturase without affecting the protein expression. In agreement with these mechanistic findings, δTE-13′-COOH significantly suppressed the growth and multiplicity of colon tumor in mice. Our study demonstrates that 13′-COOHs have anti-inflammatory and anticancer activities, may contribute to in vivo anticancer effect of vitamin E forms and are promising novel cancer prevention agents.

Abstract B19: Short chain fatty acids suppress mTOR activation in colon cancer cells via the long noncoding RNA rhabdomyosarcoma 2 associated transcript

Abstract Short chain fatty acids (SCFAs), derived from dietary fiber bacterial fermentation in the colon, exert multiple effects on colonic functions including tumor suppressing activities. Our previous studies found that SCFAs can induce autophagy in colon cancer cells via suppressing mTOR activities, but the mechanism involved is not well understood. Herein we identify rhabdomyosarcoma 2 associated transcript (RMST), a long non-coding RNA, and protein tyrosine phosphatase non-receptor type 7(PTPN7) as key mediators for SCFAs to suppress mTOR signaling. SCFAs induce the expression of RMST in colon cancer cells. RMST by itself is sufficient to suppress mTOR signaling and sensitize colon cancer cells to SCFAs induction of autophagy. Through profiling, PTPN7 was identified as an effector for both RMST and SCFAs to suppress mTOR signaling. RMST increases the expression of PTPN7 by recruiting RNAPII to its promoter region. The data delineate a novel RMST-PTPN7 cellular pathway, enlisted by SCFAs, to modulate mTOR activities. Citation Format: Jiuhui Wang, Daotai Nie. Short chain fatty acids suppress mTOR activation in colon cancer cells via the long noncoding RNA rhabdomyosarcoma 2 associated transcript. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr B19.

Nicotine-induced cellular stresses and autophagy in human cancer colon cells: A supportive effect on cell homeostasis via up-regulation of Cox-2 and PGE2 production

Nicotine, one of the active components in cigarette smoke, has been described to contribute to the protective effect of smoking in ulcerative colitis (UC) patients. Furthermore, the nicotinic acetylcholine receptor α7 subunit (α7nAChR) expressed on immune cells, is an essential regulator of inflammation. As intestinal epithelial cells also express α7nAChR, we investigated how nicotine could participate in the homeostasis of intestinal epithelial cells. First, using the human adenocarcinoma cell line HT-29, we revealed that nicotine, which triggers an influx of extracellular Ca2+ following α7nAChR stimulation, induces mitochondrial reactive oxygen species (ROS) production associated with a disruption of the mitochondrial membrane potential and endoplasmic reticulum stress. This results in caspase-3 activation, which in turn induces apoptosis. Additionally, we have shown that nicotine induces a PI3-K dependent up-regulation of cyclooxygenase-2 (Cox-2) expression and prostaglandin E2 (PGE2) production. In this context, we suggest that this key mediator participates in the cytoprotective effects of nicotine against apoptosis by stimulating autophagy in colon cancer cells. Our results provide new insight into one potential mechanism by which nicotine could protect from UC and suggest an anti-inflammatory role for the cholinergic pathway at the epithelial cell level.