Triiodothyronine stimulates the expression of sucrase-isomaltase in Caco-2 cells cultured in serum-free medium

The BAG-1 isoform BAG-1M regulates keratin-associated Hsp70 chaperoning of aPKC in intestinal cells during activation of inflammatory signaling

Atypical PKC (ι/λ and ζ; hereafter referred to as aPKC) is a key player in the acquisition of epithelial polarity and participates in other signaling cascades including the control of NF-κB signaling. This kinase is post-translationally regulated through Hsp70-mediated refolding. Previous work has shown that such a chaperoning activity is specifically localized to keratin intermediate filaments. Our work was performed with the goal of identifying the molecule(s) that block Hsp70 activity on keratin filaments during inflammation. A transcriptional screen allowed us to focus on BAG-1, a multi-functional protein that assists Hsp70 in nucleotide exchange but also blocks its activity at higher concentrations. We found the BAG-1 isoform BAG-1M upregulated threefold in human Caco-2 cells following stimulation with tumor necrosis factor receptor α (TNFα) to induce a pro-inflammatory response, and up to sixfold in mouse enterocytes following treatment with dextran sodium sulfate (DSS) to induce colitis. BAG-1M, but no other isoform, was found to co-purify with intermediate filaments and block Hsp70 activity in the keratin fraction but not in the soluble fraction within the range of concentrations found in epithelial cells cultured under control and inflammation conditions. Constitutive expression of BAG-1M decreased levels of phosphorylated aPKC. By contrast, knockdown of BAG-1, blocked the TNFα-induced decrease of phosphorylated aPKC. We conclude that BAG-1M mediates Hsp70 inhibition downstream of NF-κB.

β-Catenin regulates deiodinase levels and thyroid hormone signaling in colon cancer cells

BACKGROUND & AIMS

Activation of the β-catenin/T-cell factor (TCF) complex occurs in most colon tumors, and its actions correlate with the neoplastic phenotype of intestinal epithelial cells. Type 3 deiodinase (D3), the selenoenzyme that inactivates thyroid hormone (3,5,3' triiodothyronine [T3]), is frequently expressed by tumor cells, but little is known about its role in the regulation of T3 signaling in cancer cells.

METHODS

We measured D3 expression in 6 colon cancer cell lines and human tumors and correlated it with the activity of the β-catenin/TCF complex. We also determined the effects of D3 loss on local thyroid hormone signaling and colon tumorigenesis.

RESULTS

We show that D3 is a direct transcriptional target of the β-catenin/TCF complex; its expression was higher in human intestinal adenomas and carcinomas than in healthy intestinal tissue. Experimental attenuation of β-catenin reduced D3 levels and induced type 2 deiodinase (the D3 antagonist that converts 3,5,3',5' tetraiodothyronine into active T3) thereby increasing T3-dependent transcription. In the absence of D3, excess T3 reduced cell proliferation and promoted differentiation in cultured cells and in xenograft mouse models. This occurred via induction of E-cadherin, which sequestered β-catenin at the plasma membrane and promoted cell differentiation.

CONCLUSIONS

Deiodinases are at the interface between the β-catenin and the thyroid hormone pathways. Their synchronized regulation of intracellular T3 concentration is a hitherto unrecognized route by which the multiple effects of β-catenin are generated and may be targeted to reduce the oncogenic effects of β-catenin in intestinal cells.

Ethanol and polyphenolic free wine matrix stimulate the differentiation of human intestinal Caco-2 cells. Influence of their association with a procyanidin-rich grape seed extract

The effect of daily contact with ethanol on Caco-2 cell differentiation was investigated. Pure ethanol (1%) and a polyphenolic free wine matrix (polyphenol-free wine containing 1% ethanol) associated or not with a procyanidin-rich grape seed extract (GSE) were added to Caco-2 cells from confluency for 2 h a day after successive incubation in salivary, gastric, and pancreatic media. Treatment with 1% ethanol did not appear to be cytotoxic to cells, but it also stimulated Caco-2 cell differentiation, particularly in the first days following confluency, and this effect was more marked when associated with polyphenolic free wine matrix constituents. This activation resulted in an increase in microvillar density, organization, and elongation (+70%) and was associated with strong stimulation of sucrase-isomaltase (+780%) and a concomitant regular increase in cell protein content (+50-88%). While the presence of GSE in alcoholic solutions did not modify the morphological pattern observed in cells subjected to ethanol and polyphenolic free wine matrix alone, it had a clear reducing effect on their microvillus elongation (-30%). However, these stimulating effects of ethanol on morphological differentiation were attenuated from day 10 postconfluency, which could suggest cell cytoprotection against ethanol. These are the first results in support of the notion that moderate concentration of ethanol may stimulate the differentiation of Caco-2 cells, particularly when integrated with a polyphenolic free wine matrix.

Grape seed extract affects proliferation and differentiation of human intestinal Caco-2 cells

The effect of daily contact of a grape seed extract (GSE) on Caco-2 cell proliferation and differentiation was investigated. GSE at 400 mg/L was added to Caco-2 cells for 2 h a day after successive incubation in saliva, gastric, and pancreatic media. When applied at the beginning of the cell culture, GSE triggered inhibition of cell growth associated with a possible cytotoxic reaction. On the other hand, when the treatment was applied to confluent cells, treated cells displayed a higher protein content than control cells and a more developed brush border, with taller and denser microvilli. These observations were accompanied by stimulation of alkaline phosphatase activity, especially at day 5 postconfluency, with a 2.2-fold increase in comparison with the control. On the other hand, aminopeptidase N activity was inhibited throughout the differentiation period in GSE-treated cells to reach 28.8% of control cell activity on day 30. GSE did not affect either sucrase-isomaltase activity or cytoplasmic lactate dehydrogenase (LDH) activity, which otherwise appeared to be a good cellular marker. GSE treatment of Caco-2 cells thus inhibited their proliferation from seeding onward and stimulated both proliferation and differentiation after confluency.

Changes in growth and function of chick small intestine epithelium due to early thermal conditioning

The effect of exposure to heat at 3 d of age on small intestine functionality and development was assayed by measuring villus size, proliferating enterocytes, and brush-border membrane (BBM) enzyme expression and activity. Results showed that thermal conditioning caused an immediate effect characterized by lowered triiodothyronine (T3) level, reduced feed intake, and depressed enterocyte proliferation and BBM enzyme activity. A second series of effects, observed 48 h posttreatment, was characterized by elevated T3, increased feed intake, increased enterocyte proliferation, and higher expression and activity of BBM enzymes. The association between ambient temperature, feed intake, growth rate, and plasma T3 levels was reflected in the structure and function of the intestinal tract. The results suggest that thermal conditioning at an early age influences T3 concentrations, which in turn alter the intestinal capacity to proliferate, grow, and digest nutrients. However, these experiments were not able to discriminate between effects due to feed intake and those due to thermal conditioning. The treatments modulated changes in the intestinal tract following thermal treatment.

Increased vitamin D receptor level enhances 1,25-dihydroxyvitamin D3-mediated gene expression and calcium transport in Caco-2 cells

Altered vitamin D receptor (VDR) level has been proposed to explain differences in intestinal responsiveness to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. We tested whether the enterocyte VDR level influences 1,25(OH)2D3-mediated gene expression and transepithelial calcium (Ca) transport in the human intestinal cell line Caco-2. Cells were stably transfected with a human metallothionein (hMT) IIA promoter-human VDR (hVDR) complementary DNA (cDNA) transgene that overexpressed hVDR in response to heavy metals. In MTVDR clones, induction of 25-hyroxyvitamin D3-24-hydroxylase (24-OHase) messenger RNA (mRNA) expression by 1,25(OH)2D3 (10(-9) M, 4 h) was correlated to metal-induced changes in nuclear VDR level (r2 = 0.99). In MTVDR clones, basal VDR level was 2-fold greater and 1,25(OH)2D3-mediated Ca transport (10(-7) M, 24 h) was 43% higher than in parental Caco-2 cells. Treatment of MTVDR clones with Cd (1 microM, 28 h) increased VDR level by 68%, significantly enhanced 1,25(OH)2D3-mediated Ca transport by 24%, and increased accumulation of calbindin D9K mRNA by 76% relative to 1,25(OH)2D3 alone. These observations support the hypothesis that the enterocyte VDR level is an important modulator of intestinal responsiveness to 1,25(OH)2D3.

Convergent effects of growth factors, hormones, and fibronectin are necessary for the enterocyte differentiation of a colon adenocarcinoma cell line (HT29-D4)

The aim of this work was to show in serum-free medium a convergent effect of physiological factors and extracellular matrix proteins on the differentiation process of enterocytes by taking as a model the HT29-D4 clone that has the feature of differentiating when subcultured in fetal bovine serum glucose-free medium. We show that triiodothyronine (T3) as well as insulin promotes limited cell growth and differentiation, whereas fibronectin or bovine serum albumin (BSA) induces cell growth and a low level of differentiation. However, insulin, T3, fibronectin, and BSA together with epidermal growth factor and transferrin promoted satisfactory growth and enterocyte morphology with epithelial electrophysiological properties in HT29-D4 cells. With these factors adequate protein targeting was achieved since cells apically expressed the carcinoembryonic antigen, and basolaterally transferrin and insulin receptors, beta 1 and alpha v beta 6 integrins, talin, vinculin, and focal adhesion kinase (FAK). Talin, vinculin, FAK, and alpha v beta 6 integrin, the fibronectin receptor, were clustered in focal contacts, which agrees with a possible role of fibronectin in final cell growth, the latter process mediating the final phase of differentiation. This level of differentiation can be maintained for a long time. Thus HT29-D4 cells appear to be a suitable model to study the implication of integrins in the differentiation process of human enterocytes.

Identification, distribution, and tissular origin of the alpha5(IV) and alpha6(IV) collagen chains in the developing human intestine

The basement membrane type IV collagen is a family composed of six genetically distinct but structurally similar polypeptide chains, alpha1-alpha6. The alpha1(IV) and alpha2(IV) chains are ubiquitous components of all BMs whereas the other four have a restricted tissue distribution. In the present study, we have analyzed the expression, distribution, and cellular origin of the alpha5(IV) and alpha6(IV) chains in the developing and adult human small intestine and in well-characterized in vitro models by indirect immunofluorescence, Western blot, and RT-PCR. We have found that in the fetal small intestine, alpha(IV) and alpha6(IV) are present in the epithelial BM and, in contrast to alpha1(IV) and alpha2(IV), are produced by both epithelial and mesenchymal cells. A distinct tissular origin for the alpha1/alpha2(IV) and alpha5/alpha6(IV) chains suggests that alpha5(IV) and alpha6(IV) associate as a heterotrimer in this organ. We have also found that a particular situation of alpha5(IV)/alpha6(IV) chain expression occurs in the adult intestine. Indeed, as compared with the fetal intestine, alpha6(IV) chain production is maintained while the expression of the alpha5(IV) chain is substantially reduced. Altered expression of the alpha5(IV) chain was also observed in the differentiating enterocytic-like Caco-2/15 cells, suggesting that in the intestinal model, the alpha5(IV) chain is subject to a regulated expression. Taken together, these observations indicate that the human intestinal epithelial BM contains up to four type IV collagen chains: the classical alpha1(IV)/alpha2(IV) chains, which originate from mesenchymal cells, and the alpha5(IV)/alpha6(IV) chains, which are of both epithelial and mesenchymal origin and have their expression regulated throughout development.

Sucrase-isomaltase ontogeny: synergism between glucocorticoids and thyroxine reflects increased mRNA and no change in cell migration

During postnatal maturation of the rat small intestine, glucocorticoid hormones (GC) and thyroxine (T4) act synergistically to elicit a precocious increase of sucrase activity. The current work shows that the synergistic effect on sucrase activity is paralleled by increased steady-state levels of sucrase-isomaltase mRNA. The enhancing effects of T4 on dexamethasone (DEX)-induced sucrase activity was seen even after prolonged treatment (9 days). Moreover, when the location of sucrase-bearing cells was examined after 2 days of hormone treatment, there was distinctly stronger immunostaining of sucrase in the presence of T4, and the sucrase-bearing cells were located on the lower quarter of the intestinal villi regardless of whether the animals received DEX or T4 plus DEX. Thus, despite predictions from the literature, there was no evidence for increased migration in the presence of T4. Instead, we conclude that the synergism between the two hormones is due to greater accumulation of sucrase-isomaltase per epithelial cell.

Multilineage differentiation of cloned HRA-19 cells in serum-free medium: a model of human colorectal epithelial differentiation

Colorectal epithelium is composed of polarised absorptive enterocytes, mucus-producing goblet cells and enteroendocrine cells. All these cell lineages are thought to arise from multipotential stem cells located near the base of the crypt, but the mechanisms which control differentiation and commitment of cells to a particular lineage are poorly understood. We have used the human rectal adenocarcinoma cell line, HRA-19, to investigate the regulation of expression of lineage-specific markers. HRA-19 cells have multipotential characteristics, forming absorptive, mucous and endocrine cells when grown as xenografts. However, HRA-19 cells grown in vitro in culture medium containing 10% foetal calf serum show negligible expression of the differentiated phenotypes observed in vivo. These findings initially suggested that the absence of positive stimuli from extracellular matrix, stromal cells and/or soluble factors present in vivo resulted in the lack of differentiation in vitro. The subsequent demonstration of a marked inhibitory effect of foetal calf serum on differentiation provided an alternative explanation for the differences between in vivo and in vitro differentiation. In addition, the inhibition of differentiation differed widely between batches of foetal calf serum and limited the usefulness of the system for studying the regulation of differentiation. This manuscript describes the development of chemically defined culture conditions (Dulbecco's Eagles medium supplemented with insulin, transferrin and ascorbic acid) which reproducibly induced the multilineage differentiation of HRA-19 cells into absorptive, mucous and endocrine cells. Morphological characteristics and the expression of lineage-specific markers, as determined by immunocytochemistry, identified absorptive, goblet and endocrine cells in HRA-19 monolayers grown in this serum-free medium. Differentiation of cloned HRA-19 cells in to the three cell lineages proceeds in the absence of stromal cells and without exogenous extracellular matrix, although these factors may subsequently be shown to modulate the rate of cell differentiation. These chemically defined culture conditions will facilitate the study of differentiation in the HRA-19 cell line in the absence of the complex mixture of growth factors, hormones and differentiation inhibitory factor(s) present in foetal calf serum.