Role of caspase activation in butyrate-induced terminal differentiation of HT29 colon carcinoma cells

Exosomal MiRNA Transfer between Retinal Microglia and RPE

The retinal pigment epithelium (RPE), the outermost layer of the retina, provides essential support to both the neural retina and choroid. Additionally, the RPE is highly active in modulating functions of immune cells such as microglia, which migrate to the subretinal compartment during aging and age-related degeneration. Recently, studies have highlighted the important roles of microRNA (miRNA) in the coordination of general tissue maintenance as well as in chronic inflammatory conditions. In this study, we analyzed the miRNA profiles in extracellular vesicles (EVs) released by the RPE, and identified and validated miRNA species whose expression levels showed age-dependent changes in the EVs. Using co-culture of RPE and retinal microglia, we further demonstrated that miR-21 was transferred between the two types of cells, and the increased miR-21 in microglia influenced the expression of genes downstream of the p53 pathway. These findings suggest that exosome-mediated miRNA transfer is a signaling mechanism that contributes to the regulation of microglia function in the aging retina.

Three lysophosphatidic acids with a distinct long chain moiety differently affect cell differentiation of human colon epithelial cells to goblet cells

AIM

The intestinal mucus layer helps maintain intestinal homeostasis. In this study, we investigated the effects of lysophosphatidic acids (LPA) on differentiation of human colon carcinoma cell line, HT-29, to goblet cells with and without sodium butyrate, a known differentiation factor for intestinal cells.

MAIN METHODS

Number and average size of cells with goblet-like morphology in five photographs per dish were measured for assessment of differentiation of HT-29 cells to goblet cells as well as their relative portion of surface of to whole surface area of the photograph.

KEY FINDINGS

Our results revealed that 18:1 LPA enhanced butyrate-induced differentiation of HT-29 cells. Because increased mRNA expression of LPA₅ and decreased mRNA expression of LPA₆ were observed in HT-29 cells after treatment with butyrate, we explored the effects of alkyl LPA and 20:4 LPA, which show preferentially higher affinities to LPA₅ and LPA₆, respectively. As a result, the cell differentiation to goblet cell was increased by alkyl LPA but decreased by 20:4 LPA. Further, alkyl LPA and 18:1 LPA, but not 20:4 LPA, were found to reduce the numbers of cells surviving after incubation in a standard culture medium containing 10% fetal calf serum.

SIGNIFICANCE

We suggest that the three LPAs positively and negatively affect the differentiation of HT-29 cells to goblet cells, which may be associated with their reduced survival through the activation of distinct LPA receptor(s).

Suppression of Spleen Tyrosine Kinase (Syk) by Histone Deacetylation Promotes, Whereas BAY61-3606, a Synthetic Syk Inhibitor Abrogates Colonocyte Apoptosis by ERK Activation

Spleen tyrosine kinase (Syk), a non-receptor tyrosine kinase, regulates tumor progression, either negatively or positively, depending on the tissue lineage. Information about the role of Syk in colorectal cancers (CRC) is limited, and conflicting reports have been published. We studied Syk expression and its role in differentiation and apoptosis of the colonocytes. Here, we reported for the first time that expression of two transcript variants of Syk is suppressed in colonocytes during butyrate-induced differentiation, which mediates apoptosis of HT-29 cells. Despite being a known HDAC inhibitor, butyrate deacetylates histone3/4 around the transcription start site (TSS) of Syk. Histone deacetylation precludes the binding of RNA Polymerase II to the promoter and inhibits transcription. Since butyrate is a colonic metabolite derived from undigested fibers, our study offers a plausible explanation of the underlying mechanisms of the protective role of butyrate as well as the dietary fibers against CRC through the regulation of Syk. We also report that combined use of butyrate and highly specific Syk inhibitor BAY61-3606 does not enhance differentiation and apoptosis of colonocytes. Instead, BAY completely abolishes butyrate-induced differentiation and apoptosis in a Syk- and ERK1/2-dependent manner. While butyrate dephosphorylates ERK1/2 in HT-29 cells, BAY re-phosphorylates it, leading to its activation. This study describes a novel mechanism of butyrate action in CRC and explores the role of Syk in butyrate-induced differentiation and apoptosis. In addition, our study highlights those commercial small molecule inhibitors, although attractive drug candidates should be used with concern because of their frequent off-target effects. J. Cell. Biochem. 118: 191-203, 2017. © 2016 Wiley Periodicals, Inc.

Butyrate induces cell apoptosis through activation of JNK MAP kinase pathway in human colon cancer RKO cells

Butyrate has been shown to display anti-cancer activity through the induction of apoptosis in various cancer cells. However, the underlying mechanism involved in butyrate-induced apoptosis is still not fully understood. Here, we investigated the cytotoxicity mechanism of butyrate in human colon cancer RKO cells. The results showed that butyrate induced a strong growth inhibitory effect against RKO cells. Butyrate also effectively induced apoptosis in RKO cells, which was characterized by DNA fragmentation, nuclear staining of DAPI, and the activation of caspase-9 and caspase-3. The expression of anti-apoptotic protein Bcl-2 decreased, whereas the apoptotic protein Bax increased in a dose-dependent manner during butyrate-induced apoptosis. Moreover, treatment of RKO cells with butyrate induced a sustained activation of the phosphorylation of c-jun N-terminal kinase (JNK) in a dose- and time-dependent manner, and the pharmacological inhibition of JNK MAPK by SP600125 significantly abolished the butyrate-induced apoptosis in RKO cells. These results suggest that butyrate acts on RKO cells via the JNK but not the p38 pathway. Butyrate triggered the caspase apoptotic pathway, indicated by an enhanced Bax-to-Bcl-2 expression ratio and caspase cascade reaction, which was blocked by SP600125. Taken together, our data indicate that butyrate induces apoptosis through JNK MAPK activation in colon cancer RKO cells.

IGF-I activates caspases 3/7, 8 and 9 but does not induce cell death in colorectal cancer cells

BACKGROUND

Colorectal cancer is the third most common cancer in the western world. Chemotherapy is often ineffective to treat the advanced colorectal cancers due to the chemo-resistance. A major contributor to chemo-resistance is tumour-derived inhibition or avoidance of apoptosis. Insulin-like growth factor I (IGF-I) has been known to play a prominent role in colorectal cancer development and progression. The role of IGF-I in cancer cell apoptosis is not completely understood.

METHODS

Using three colorectal cancer cell lines and one muscle cell line, associations between IGF-I and activities of caspase 3/7, 8 and 9 have been examined; the role of insulin-like growth factor I receptor (IGF-IR) in the caspase activation has been investigated.

RESULTS

The results show that exogenous IGF-I significantly increases activity of caspases 3/7, 8 and 9 in all cell lines used; blocking IGF-I receptor reduce IGF-I-induced caspase activation. Further studies demonstrate that IGF-I induced caspase activation does not result in cell death. This is the first report to show that while IGF-I activates caspases 3/7, 8 and 9 it does not cause colorectal cancer cell death.

CONCLUSION

The study suggests that caspase activation is not synonymous with apoptosis and that activation of caspases may not necessarily induce cell death.

Side populations of gastrointestinal cancers are not enriched in stem cells

The side population (SP) phenotype, defined as the reserpine-blockable ability to efflux the nucleic acid dye Hoechst 33342, has been claimed to be enriched for stem cells in several human normal tissues, cancers and cell lines, and thus may be useful for the identification and isolation of cancer stem cells. We demonstrated the presence of SP fractions in all of seven tested gastrointestinal cancer cell lines. Four cell lines were selected (HT29, HGT101, Caco2 and HRA19a1.1) for detailed phenotypic and behavioural analysis with respect to stem cell characteristics. Cell surface marker analysis showed that, contrary to non-SP cells, the SPs entirely lack the expression of CD34. This difference, however, disappeared when the cells were cultured, rendering both populations CD34-positive. Expression of other putative stem cell markers (CD133, CD44, Hes-1, beta-catenin, Musashi-1, Oct-4 and CD117) was identical on SP and non-SPs before and after culturing. Sorted SP and non-SP cells were similarly clonogenic in vitro, tumourigenic in vivo, and displayed similar multipotential differentiation potential in vitro and in vivo. Additionally, culturing cytometrically-sorted SP and non-SP cells showed that the populations are interconvertible, each giving rise to the other. Expression of ABCG2 and Mdr-1, two membrane transporter proteins that have been suggested to be responsible for the drug-effluxing capacities of SP cells, including Hoechst 33342, was identical in non-SP and SP cells, indicating that there may be additional factors responsible for the Hoechst effluxing property in gastrointestinal cancer SP cells. Here, we show that the SP and non-SP fractions, albeit phenotypically distinct populations, do not differ with respect to stem cell-like cell number or behaviour. We thus conclude that the concept of the SP phenotype as a universal marker for stem cells does not apply to gastrointestinal cancer cells. These findings stand in contrast to the observations made in many other tissues and harbour important implications for the future search for intestinal cancer stem cell markers.

Sodium butyrate induced keratinocyte apoptosis

Apoptosis of keratinocytes is a key mechanism required for epidermal homeostasis and the renewal of damaged cells. Its dysregulation has been implicated in many skin diseases including cancer and hyperproliferative disorders. In the present study, the effect of sodium butyrate, a histone deacetylase inhibitor, on keratinocyte apoptosis was investigated using the HaCaT human keratinocyte cell line. Sodium butyrate induced morphological changes associated with apoptosis and nuclear fragmentation of HaCaTs. Annexin V staining demonstrated that sodium butyrate induced apoptosis in a dose and time-dependent manner with 50% of HaCaTs apoptotic after exposure to 0.8 mg/ml sodium butyrate for 24 h. Apoptosis was associated with upregulation of cell surface expression of the death receptor Fas and activation of the extrinsic caspase pathway, with induction of caspase 8 activity peaking after 8 h. Caspase 3 activity peaked after 24 h and was associated with cleavage of the caspase 3 substrate, poly (ADP-ribose) polymerase (PARP). The intrinsic caspase pathway was not activated as caspase 9 activity was not detected, and there was no change in the expression of terminal differentiation markers keratin 10 and involucrin following sodium butyrate treatment. Together these results indicate that sodium butyrate is a potent inducer of Fas associated apoptosis via caspase activation in HaCaT keratinocytes, an effect that is independent of the induction of terminal differentiation.

Overexpression of heat shock factor 1 inhibits butyrate-induced differentiation in colon cancer cells

Produced by dietary fiber, butyrate is a potential chemopreventive agent against colon cancer. It stimulates proliferation of normal colonic epithelial cells but induces growth inhibition, differentiation, apoptosis, or a combination of effects in colon carcinoma cells. In this study, we used cDNA membrane arrays and real-time reverse transcriptase-polymerase chain reaction to identify stress genes that were differentially regulated by sodium butyrate (NaB) in HT 29 human colon carcinoma cells. The results indicated that a group of heat shock protein (hsp) genes were upregulated by 3 mM NaB within the first 24 hours of exposure. Because the transcription of hsp genes is under the control of heat shock factors (HSFs), we measured the effects of overexpressed HSF-1 on the responses of HT 29 cells to NaB. Overexpression of HSF-1 inhibited NaB-induced differentiation as measured by alkaline phosphatase activity and carcinoembryonic antigen expression. These results suggest that increased expression of HSFs and Hsps might render colon carcinoma cells resistant to the chemopreventive effects of butyrate.

Chemical Modification of Santonin into a Diacetoxy Acetal Form Confers the Ability to Induce Differentiation of Human Promyelocytic Leukemia Cells via the Down-regulation of NF-κB DNA Binding Activity

Many sesquiterpene lactone compounds either induce or enhance the cell differentiation of human leukemia cells. However, we reported in a previous study that santonin, a eudesmanolide sesquiterpene lactone, exerts no effects on the differentiation of leukemia cells. In this report, to evaluate the possibility of chemically modifying santonin into its derivatives with differentiation inducing activity, we synthesized a series of santonin derivatives, and determined their effects on cellular differentiation in the human promyelocytic leukemia HL-60 cell system. A diacetoxy acetal derivative of santonin (DAAS) was found to induce significant HL-60 cell differentiation in a dose-dependent manner, whereas santonin in its original form did not. The HL-60 cells were differentiated into a granulocytic lineage when exposed to DAAS. In addition, the observed induction in cell differentiation closely correlated with the levels of NF-kappaB DNA binding activity inhibited by DAAS. Both Western blot analyses and kinase inhibitor studies determined that protein kinase C, ERK, and phosphatidylinositol 3-kinase were upstream components of the DAAS-mediated inhibition of NF-kappaB binding activity in HL-60 leukemia cells. The results of this study indicate that santonin can, indeed, be chemically modified into a derivative with differentiation inducing abilities, and suggest that DAAS might prove useful in the treatment of neoplastic diseases.

Inhibition of Single Minded 2 gene expression mediates tumor-selective apoptosis and differentiation in human colon cancer cells

A Down's syndrome associated gene, Single Minded 2 gene short form (SIM2-s), is specifically expressed in colon tumors but not in the normal colon. Antisense inhibition of SIM2-s in a RKO-derived colon carcinoma cell line causes growth inhibition, apoptosis, and inhibition of tumor growth in a nude mouse tumoriginicity model. The mechanism of cell death in tumor cells is unclear. In the present study, we investigated the pathways underlying apoptosis. Apoptosis was seen in a tumor cell-specific manner in RKO cells but not in normal renal epithelial cells, despite inhibition of SIM2-s expression in both of these cells by the antisense. Apoptosis was depended on WT p53 status and was caspase-dependent; it was inhibited by a pharmacological inhibitor of mitogen-activated protein kinase activity. Expression of a key stress response gene, growth arrest and DNA damage gene (GADD)45alpha, was up-regulated in antisense-treated tumor cells but not in normal cells. In an isogenic RKO cell line expressing stable antisense RNA to GADD45alpha, a significant protection of the antisense-induced apoptosis was seen. Whereas antisense-treated RKO cells did not undergo cell cycle arrest, several markers of differentiation were deregulated, including alkaline phosphatase activity, a marker of terminal differentiation. Protection of apoptosis and block of differentiation showed a correlation in the RKO model. Our results support the tumor cell-selective nature of SIM2-s gene function, provide a direct link between SIM2-s and differentiation, and may provide a model to identify SIM2-s targets.

Vital functions for lethal caspases

Caspases are a family of cysteine proteases expressed as inactive zymogens in virtually all animal cells. These enzymes play a central role in most cell death pathways leading to apoptosis but growing evidences implicate caspases also in nonapoptotic functions. Several of these enzymes, activated in molecular platforms referred to as inflammasomes, play a role in innate immune response by processing some of the cytokines involved in inflammatory response. Caspases are requested for terminal differentiation of specific cell types, whether this differentiation process leads to enucleation or not. These enzymes play also a role in T and B lymphocyte proliferation and, in some circumstances, appear to be cytoprotective rather than cytotoxic. These pleiotropic functions implicate caspases in the control of life and death but the fine regulation of their dual effect remains poorly understood. The nonapoptotic functions of caspases implicate that cells can restrict the proteolytic activity of these enzymes to selected substrates. Deregulation of the pathways in which caspases exert these nonapoptotic functions is suspected to play a role in the pathophysiology of several human diseases.

Expression of PGE2, Bcl-2 and Bax in carcinogenesis of colorectal mucosa

AIM: To investigate the expression of PGE₂, Bcl-2 and Bax in the carcinogenesis of colorectal mucosa and the relationship between them.

METHODS: The expression of PGE₂, Bcl-2 and Bax were detected in 15 normal colorectal mucous membrane (NCM), 20 chronic colonitis (CHC), 30 colorectal adenoma (CAA), 50 colorectal cancer (CC)and 50 cancer adjacent (CAT) tissues by DAB immunohistochemical staining. The correlations among PGE₂, Bcl-2 and Bax expression as well as the clinical and pathological characteristics were analyzed.

RESULTS: The rates of PGE₂ expression in NCM, CHC, CAT, CAA and CC tissues were 6.67%, 10%, 40%, 56.7% and 90% respectively and manifested an ascending trend. The rates of Bcl-2 expression in the five groups were 6.67%, 10%, 38%, 46.7%, and 76% respectively and also showed an ascending trend. The rates of Bax expression in the five groups was 86.67%, 75%, 78%, 76.7% and 82% respectively and there was no significant difference among the five groups (P>0.05). However, the positive degree in NCM, CA and CC group exhibited a descending trend (P<0.05). The expressions of PGE₂, Bcl-2 and Bax in human CC were not associated with sex, age and the size of tumor (P>0.05). A positive correlation was noted between expression of PGE₂ and Bcl-2 in CC tissue (r = 0.532, P<0.05). The same correlation also existed between Bax and Bcl-2 (r = 0.653, P<0.05). The rates of PGE₂, Bcl-2 and Bax expression in highly and moderately differentiated CC were significantly higher than those in lowly differentiated one (100%, 88.9%, 85.2% vs 79.3%, 60.9%, 78.3%; P<0.05). The expression of Bcl-2 was significantly higher in Duke's A, B stage than that in Duke's C, D (90%, 77.8% vs 60%, 57.2%; P<0.05).

CONCLUSION: The expression of PGE₂ and Bcl-2 increases while that of Bax decreases with the occurrence and development of CC, which indicates that PGE₂ and Bcl-2 play important roles in the carcinogenesis and development of CC. At the same time, there is a positive relationship between PGE₂ and Bcl-2.

Intestinal glutathione: determinant of mucosal peroxide transport, metabolism, and oxidative susceptibility

The intestine is a primary site of nutrient absorption and a critical defense barrier against dietary-derived mutagens, carcinogens, and oxidants. Accumulation of oxidants like peroxidized lipids in the gut lumen can contribute to impairment of mucosal metabolic pathways, enterocyte dysfunction independent of cell injury, and development of gut pathologies, such as inflammation and cancer. Despite this recognition, we know little of the pathways of intestinal transport, metabolism, and luminal disposition of dietary peroxides in vivo or of the underlying mechanisms of lipid peroxide-induced genesis of intestinal disease processes. This chapter summarizes our current understanding of the determinants of intestinal absorption and metabolism of peroxidized lipids. I will review experimental evidence from our laboratory and others (Table 1) supporting the pivotal role that glutathione (GSH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) play in mucosal transport and metabolism of lipid hydroperoxides and how reductant availability can be compromised under chronic stress such as hypoxia, and the influence of GSH on oxidative susceptibility, and redox contribution to genesis of gut disorders. The discussion is pertinent to understanding dietary lipid peroxides and GSH redox balance in intestinal physiology and pathophysiology and the significance of luminal GSH in preserving the integrity of the intestinal epithelium.

Effects of resistant starch fermentation on physiological changes of colon in rats

AIM: To evaluate the effects of resistant starch (RS) fermentation on colon health-related indexes, including bowel functions, luminal short-chain fatty acid production and toxic compounds excretion.

METHODS: Fifty-seven healthy male SD rats were randomly divided into 5 groups based on body weight, and given basal diets with 0%, 6% and 12% RS, or high-protein diets (36% casein, HP) with 6% or 12% RS, respectively. After fed for 3 wk, gut transit time (GTT) for rats in each group was examined; at 5 wk three day feces samples were collected and their contents were assessed; at 7 wk all rats were killed. The morphological and histological characteristics of caecum were observed and the caecal function was evaluated by determination of the weight of caecal wall and caecal digesta, detection of caecal short chain fatty acid (SCFA), ammonia, phenol concentration and pH value.

RESULTS: In comparison with those in rats fed with 0% RS diet, shortened GTT was significantly shortened (601 ± 49 min vs 700 ± 58 min, P < 0.001), stool bulk was increased with more moisture (1.04 ± 0.22 g vs 0.37 ± 0.12 g, P < 0.001), and weight of caecal wall and caecal digesta was also increased (1.12 ± 0.14 g vs 0.73 ± 0.13 g, P < 0.001; 4.78 ± 1.44 g vs 3.00 ± 1.12 g, P = 0.004 < 0.01) in rats fed with 12% RS diet; the concentration of SCFA in caecum was two- to three-fold enhanced by 12% RS (35.5 ± 11.4 μmol/g vs 13.9 ± 6.7 μmol/g, P = 0.003 < 0.01), while the concentration of ammonia in both feces and caecum and phenol in caecum decreased (0.26 ± 0.13 mg/g vs 0.59 ± 0.15 mg/g, 0.35 ± 0.13 mg/g vs 0.63 ± 0.13 mg/g, 2.03 ± 0.42 mg/g vs 3.15 ± 0.55 mg/g, P < 0.001, respectively); caecal and fecal pH value dropped significantly (6.26 ± 0.36 vs 7.46 ± 0.28; 5.67 ± 0.31 vs 7.24 ± 0.31, P < 0.001), and the variation of pH in feces was greater than that in caecum (P < 0.001), suggesting extended fermentation in distal colon. Rats in 6% RS group had similar but intermediate variances in fecal ammonia, caecal phenol and intestinal pH value (P < 0.05). All indexes mentioned above were dose-dependent (P < 0.01). For rats fed with HP, GTT was prolonged. Fecal bulk and caecal SCFA level dropped in HP+12% RS group (659 ± 47 min, P = 0.009 < 0.01; 0.80 ± 0.29 g, P = 0.005 < 0.01, 24.6 ± 13.6 μmol/g, P = 0.043 < 0.05), compared with 12% RS group. The concentrations of caecal phenol in HP+6% RS and HP+12% RS group were 3.20 ± 0.49 mg/g and 2.71 ± 0.55 mg/g respectively, significantly higher than that in 6% and 12% RS groups (P < 0.001); fecal and caecal pH value elevated as well. However, as RS intake increased (12%), these negative changes above were attenuated (P < 0.05). There was a significant interaction between RS and casein on fecal dry matter and caecal pH value (P < 0.01). Histological observation showed no abnormal changes in caecum tissues of rats fed with RS.

CONCLUSION: RS is beneficial to sustain intestinal health-related indexes and has potential protective effects on bowel functions. Adequate RS intake could attenuate the negative effects of high casein on colon by improving bowel habit, acidifying intestinal tract, promoting SCFA production and decreasing intestinal inner noxious phenol.

Effect of wound infections on head and neck cancer

There seems to be a consensus in the surgical literature that wound infections after surgery for cancer have a favorable effect on the course of certain malignant diseases. In a review of laryngeal cancer during a 10-year period, the recurrence rate was statistically lower in the group that suffered wound infections than in the group that did not have a wound infection.