Acetone Fraction of the Red Marine Alga Laurencia papillosa Reduces the Expression of Bcl-2 Anti-apoptotic Marker and Flotillin-2 Lipid Raft Marker in MCF-7 Breast Cancer Cells

Marine macroalgae have attracted much attention in recent years as a valuable source of bioactive metabolites. The cytotoxic potential of the Laurencia papillosa red alga collected from the Lebanese coast has been investigated on human breast cancer cells MCF-7. The crude extract of Laurencia papillosa (L. papillosa) was fractionated by column chromatography using a series of increasingly polar solvents (methylene chloride, acetone and methanol). Cytotoxicity of the crude extract and fractions was determined by MTT assay in MCF-7 cells. Apoptosis was detected by annexin V/propidium iodide assay and by measurement of Bcl-2 expression. Flotillin-2 expression was examined using RT-qPCR and Western blot. The crude extract, and the fractions of CH2Cl2 and acetone exhibited a dose-dependent cytotoxic effect on MCF-7 cells. Apoptosis was specifically induced by one of the acetone fractions having the highest cytotoxicity. It has been demonstrated by an increase in late phase apoptotic cell populations, and a decrease in Bcl-2 anti-apoptotic marker expression on mRNA and protein levels in a dose- and time- dependent manner. Furthermore, this active fraction decreased Flotillin-2 expression associated with cancer progression. Our data suggest that L. papillosa is an important source of cytotoxic metabolites. Further studies are needed for the chemical characterization of the metabolite associated with observed biological activities.

4-cholesten-3-one decreases breast cancer cell viability and alters membrane raft-localized EGFR expression by reducing lipogenesis and enhancing LXR-dependent cholesterol transporters

Background

The alteration of lipid metabolism in cancer cells is recognized as one of the most important metabolic hallmarks of cancer. Membrane rafts defined as plasma membrane microdomains enriched in cholesterol and sphingolipids serve as platforms for signaling regulation in cancer. The main purpose of this study was to evaluate the effect of the cholesterol metabolite, 4-cholesten-3-one, on lipid metabolism and membrane raft integrity in two breast cancer cell lines, MCF-7 and MDA-MB-231. Its ability to reduce cell viability and migration has also been investigated.

Methods

RT-qPCR was performed to evaluate the expression of enzymes involved in lipogenesis and cholesterol synthesis, and ABCG1 and ABCA1 transporters involved in cholesterol efflux. Its effect on cell viability and migration was studied using the MTT assay, the wound healing assay and the Transwell migration assay, respectively. The effect of 4-cholesten-3-one on membrane rafts integrity was investigated by studying the protein expression of flotillin-2, a membrane raft marker, and raft-enriched EGFR by western blot.

Results

Interestingly, we found that 4-cholesten-3-one treatment decreased mRNA expression of different enzymes including ACC1, FASN, SCD1 and HMGCR. We further demonstrated that 4-cholesten-3-one increased the expression of ABCG1 and ABCA1. We also found that 4-cholesten-3-one decreased the viability of MCF-7 and MDA-MB-231 cells. This effect was neutralized after treatment with LXR inverse agonist or after LXRβ knockdown by siRNA. As a result, we also demonstrated that 4-cholesten-3-one disrupts membrane rafts and cell migration capacity.

Conclusion

Our results show that 4-cholesten-3-one exerts promising antitumor activity by altering LXR-dependent lipid metabolism in breast cancer cells without increasing lipogenesis.

Lithocholic bile acid inhibits lipogenesis and induces apoptosis in breast cancer cells

BACKGROUND

It has amply been documented that mammary tumor cells may exhibit an increased lipogenesis. Biliary acids are currently recognized as signaling molecules in the intestine, in addition to their classical roles in the digestion and absorption of lipids. The aim of our study was to evaluate the impact of lithocholic acid (LCA) on the lipogenesis of breast cancer cells. The putative cytotoxic effects of LCA on these cells were also examined.

METHODS

The effects of LCA on breast cancer-derived MCF-7 and MDA-MB-231 cells were studied using MTT viability assays, Annexin-FITC and Akt phosphorylation assays to evaluate anti-proliferative and pro-apoptotic properties, qRT-PCR and Western blotting assays to assess the expression of the bile acid receptor TGR5 and the estrogen receptor ERα, and genes and proteins involved in apoptosis (Bax, Bcl-2, p53) and lipogenesis (SREBP-1c, FASN, ACACA). Intracellular lipid droplets were visualized using Oil Red O staining.

RESULTS

We found that LCA induces TGR5 expression and exhibits anti-proliferative and pro-apoptotic effects in MCF-7 and MDA-MB-231 cells. Also, an increase in pro-apoptotic p53 protein expression and a decrease in anti-apoptotic Bcl-2 protein expression were observed after LCA treatment of MCF-7 cells. In addition, we found that LCA reduced Akt phosphorylation in MCF-7 cells, but not in MDA-MB-231 cells. We also noted that LCA reduced the expression of SREBP-1c, FASN and ACACA in both breast cancer-derived cell lines and that cells treated with LCA contained low numbers of lipid droplets compared to untreated control cells. Finally, a decrease in ERα expression was observed in MCF-7 cells treated with LCA.

CONCLUSIONS

Our data suggest a potential therapeutic role of lithocholic acid in breast cancer cells through a reversion of lipid metabolism deregulation.

LXR Activation Down-regulates Lipid Raft Markers FLOT2 and DHHC5 in MCF-7 Breast Cancer Cells

BACKGROUND/AIM

Lipid rafts are cholesterol-enriched microdomains of the plasma membrane. Recent studies have underlined that their integrity is critical for cancer cell survival. Liver X receptor (LXR) has a central role in cellular cholesterol homeostasis and its stimulation inhibits proliferation of several cancer cell lines. This study investigated whether LXR could modulate lipid rafts integrity and consequently alter proliferation of the MCF-7 breast cancer cell line.

MATERIALS AND METHODS

Effect of LXR agonist T0901317 on integrity of MCF-7 lipid rafts was examined by studying the expression of rafts marker flotillin-2 (FLOT2) and DHHC5, which palmitoylates FLOT2, and by studying the expression of phospho-Akt.

RESULTS

We demonstrated that LXR stimulation decreases mRNA and protein expression of FLOT2 and DHHC5 in MCF-7 cells. LXR stimulation also reduces Akt phosphorylation and its localization at the plasma membrane.

CONCLUSION

We showed, for the first time, that LXR regulates transcription of specific proteins of lipid rafts in a breast cancer model.

Macrophage apolipoprotein E and proliferation of MCF-7 breast cancer cells: role of LXR

BACKGROUND

Apolipoprotein E (APOE), a lipid transport protein that has a key role in the lipoprotein metabolism, is expressed by macrophages under the control of the transcription factor Liver X Receptor (LXR), an oxysterol-activated transcriptional factor involved in cholesterol metabolism. Recent work has shown that LXR agonists may inhibit breast cancer cell proliferation in vitro. We hypothesized that LXR-activated macrophages, and in particular secreted macrophagic APOE, may potentiate the effect of LXR agonists. Our goal was to evaluate the effect of APOE, secreted by THP-1 macrophages under the control of LXR, on MCF-7 cell proliferation, a model of breast cancer.

MATERIALS AND METHODS

MCF-7 cells were incubated with supernatants from THP-1 cells previously treated with LXR agonists [T0901317 or 22(R)-hydroxycholestrol], or supernatants from THP-1 cells transfected with siRNA against APOE mRNA.

RESULTS

Viability assays and cell death quantification showed that media from LXR-activated macrophages reduced cell proliferation and increased apoptosis of MCF-7 cells. Interestingly, the opposite effects were observed when MCF-7 cells wre treated with media from the siRNA APOE-mediated knock-down model.

CONCLUSION

This study highlights the protective role of LXR-activated macrophages against breast cancer growth, and the implication of APOE protein in the anti-proliferative and pro-apoptotic effects observed.

The anti-proliferative and pro-apoptotic effects of the trans9, trans11 conjugated linoleic acid isomer on MCF-7 breast cancer cells are associated with LXR activation

Conjugated linoleic acids (CLA), naturally found in dairy products and ruminant meat, are positional and geometric isomers (trans: t or cis: c) of linoleic acid, and have been widely reported to possess anti-tumoral activity against breast cancer both in vitro and in vivo. CLA isomer t9,t11 was recently proposed as an agonist of the transcriptional factor LXR, which is known for inducing genes implicated in cholesterol efflux. In this study, the growth inhibitory effect of three CLA isomers (c9,t11-CLA, t9,t11-CLA and t10,c12-CLA) was investigated on MCF-7 breast cancer cells, as well as their effect on LXR target genes. Our results revealed that t9,t11-CLA was the most efficient isomer by decreasing MCF-7 proliferation, inhibiting migration, and inducing apoptosis after 24h of treatment. t9,t11-CLA treatment led to an increase in the mRNA levels of LXR target genes involved in cholesterol efflux (ABCG1 and ARL7), as well as an increase of HMG-CoA-reductase which is the rate-limiting step of cholesterol biosynthesis. Interestingly, confocal microscopy analysis showed that t9,t11-CLA treatment remarkably reduced the intracellular and membrane-associated cholesterol levels. LXR activation through t9,t11-CLA isomer could lead to cholesterol cell deprivation by stimulating its efflux, which results in the inhibition of cell proliferation and stimulation of apoptosis.

LXR agonists and ABCG1-dependent cholesterol efflux in MCF-7 breast cancer cells: relation to proliferation and apoptosis

BACKGROUND

Liver X receptor (LXR) plays a key role in reverse cholesterol transport by inducing the expression of the ATP-binding cassette (ABC) transporters, implicated in cholesterol efflux. Recent data showed that LXR agonists inhibit the proliferation of multiple types of human cancer cells. However, whether these effects are related to cholesterol efflux has not yet been elucidated.

MATERIALS AND METHODS

Effects of two LXR agonists (TO901317 and 22(R)-hydroxycholesterol [22(R)-HC]) on proliferation, apoptosis and cholesterol efflux were examined in MCF-7 breast cancer cells.

RESULTS

Treatment with LXR agonists (TO901317 at 20 μM and 22(R)-HC at 2 μg/ml) inhibited proliferation and induced apoptosis of MCF-7 cells. Furthermore, LXR activation resulted in an increase in gene and protein levels of ABCG1 transporters and in cholesterol efflux to isolated high-density lipoprotein (HDL), without affecting the ABCA1/APOA-I mediated efflux. Under these conditions, a remarkable reduction of intracellular and membrane-associated cholesterol levels was observed.

CONCLUSION

LXR activation in MCF-7 cells could deprive cells of cholesterol, required for their growth, by stimulating its efflux, resulting in the inhibition of cell proliferation and in stimulation of apoptosis.

Unusual sterolic mixture, and 24-isopropylcholesterol, from the sponge Ciocalypta sp. reduce cholesterol uptake and basolateral secretion in Caco-2 cells

An unusual sterolic mixture (82.3% of 24-isopropylated sterols) and its major component, 24-isopropylcholesterol, isolated from a marine sponge, Ciocalypta sp. (Halichondriidae), reduce cholesterol uptake, basolateral secretion and ACAT-2 mRNA expression and increase the expression of ABCA1 mRNA in Caco-2 cells. The decreases of cholesterol uptake and secretion induced by 24-isopropylcholesterol alone were more than that of both the sterolic mixture and beta-sitosterol. These data add a new sterol, 24-isopropylcholesterol, to sterols that may reduce intestinal cholesterol absorption.

Effect of LPS on basal and induced apo E secretion by 25-OH chol and 9cRA in differentiated CaCo-2

The infection and inflammation process is associated with disturbances in lipid and lipoprotein metabolism. The apolipoprotein E (apo E) plays an important role in the lipoprotein metabolism and has been linked to inflammatory disease such as atherosclerosis and Alzheimer disease. An anti-inflammatory effect has also been suggested. The heterodimer nuclear receptor Liver-X-Receptor(alpha)/Retinoid-X-Receptor (LXR(alpha)/RXR) is considered to be a transcription factor for apo E. The aim of this study was to determine whether lipopolysaccharide (LPS) (principal component of the outer membrane Gram-negative bacteria) has an effect on apo E secretion by intestinal mucosa cells, using the Caco-2 cell line. Differentiated Caco-2 cells grown on filter inserts were incubated apically with LPS and/or 25-hydroxycholesterol (25-OH chol) and 9 cis retinoic acid (9cRA), ligands of LXR and RXR, respectively. The apical and basolateral media were separately collected. Apo E was detected by specific antibodies after protein separation by Two-dimensional nondenaturing gradient gel electrophoresis and apo E secreted in the cell culture media was measured by enzyme linked immunosorbent assay (ELISA). Apo E mRNA was analyzed by reverse transcription-polymerase chain reaction (RT-PCR). LXR(alpha) and RXR mass was analyzed by Western Blot. We demonstrate here that CaCo-2 cells secrete apo E, by either apical or basolateral sides, associated with a high-density like lipoprotein, with a stoke's diameter comprised between 7.10 and 8.16 nm. We show that only apical secretion is decreased by LPS in a dose and time dependent manner. This is associated with a decrease in apo E gene expression contrasting with an increase of Il-8, a chemokine factor. Moreover, we demonstrate that only basolateral apo E secretion by CaCo-2 is significantly increased by 25-OH chol and 9cRA while apical secretion remains unchanged. LPS does not decrease the 25-OH chol and 9cRA mediated apo E secretion in basolateral compartment, while apical secretion is diminished under these circumstances. Our results provide evidence for the polarized secretion of apo E by intestinal epithelium. They also demonstrate that apo E secretion by CaCo-2 cell line is decreased by LPS through an LXR(alpha)/RXR independent signaling pathway.

Adenovirus-mediated gene transfer into isolated mouse adult pancreatic islets: normal beta-cell function despite induction of an anti-adenovirus immune response

The in vitro purification of pancreatic islets offers an opportunity for their modification by ex vivo gene transfer. We investigated the efficiency and functional consequences of adenovirus-mediated gene transfer into adult murine pancreatic islets with a recombinant adenovirus encoding for the beta-galactosidase (beta-Gal) reporter gene. At 10(6) pfu/islet, almost all of the islets were transduced, but maximal transduction was obtained at 10(7) pfu/islet. Histochemical analysis of frozen islet sections showed that transduced cells were only located at the periphery of islets. Transduced islets showed normal insulin secretion in vitro, and were able to normalize in vivo the glycemia of streptozotocin-induced diabetes in syngeneic and allogeneic mice. beta-Gal expression in transduced islets was observed for at least 6 weeks in naive normal recipients and in immunodeficient mice, but was shortened in mice preimmunized to adenovirus. Nevertheless, islets maintained normal control of glycemia in all mice. An early leukocyte infiltrate was observed in syngeneic grafts of transduced islets, but no acceleration in rejection of fully MHC-incompatible islet grafts occurred. In summary, adenovirus-mediated gene transfer in adult mouse islets, although sparing most of the beta-cells, was highly efficient and did not impair insulin secretion by islets. The immune response to the adenovirus and/or to the transgene might be only partially responsible for the decreased expression over time of the transduced gene. Accordingly, adenovirus-mediated gene transfer might allow efficient expression of vectorized sequences with potential immunosuppressive effects in the islet microenvironment.

Intact pig pancreatic islet function in the presence of human xenoreactive natural antibody binding and complement activation

BACKGROUND

The expression of xenogeneic epitopes and the activation of human complement by adult pig islets after prolonged culture have hitherto not been described.

MATERIALS AND METHODS

Freshly isolated and cultured islets were analyzed by fluorescence-activated cell sorter analysis, fluorescence microscopy, and immunohistology for expression of Gal(alpha1,3)Gal epitopes, binding of human xenoreactive natural antibodies (XNA), and complement deposition.

RESULTS

Freshly isolated and cultured islets showed detectable Gal(alpha1,3)Gal expression and human XNA binding limited to intraislet capillary endothelial cells. No significant modification in Gal(alpha1,3)Gal expression and human XNA binding levels was detected in adult pig islets cultured for up to 4 days compared with freshly isolated islets. Incubation of pig islets with human serum demonstrated the deposition of C3, C4, and membrane attack complex, but not factor B with a similar pattern to XNA. However C3 and C4 showed a more widespread deposition. Despite complement activation, no cytotoxic effect on islets was detected after 4 hr of incubation with human serum capable of killing porcine endothelial cells. Even after 4 days of culture in 50% intact human serum, pig islets retained both their normal morphology and a normal insulin response to glucose stimulation.

CONCLUSIONS

Neither islet cell lysis nor, more importantly, any alteration in beta cell function occurred, which suggests that adult pig islets may not be directly damaged by serum after xenotransplantation in humans. Nevertheless, complement activation in vivo could trigger rapid cellular rejection mechanisms through islet cell opsonization and release of bioactive fragments.