Julie C. Carrier

The PTEN Phosphatase Controls Intestinal Epithelial Cell Polarity and Barrier Function: Role in Colorectal Cancer Progression

Background The PTEN phosphatase acts on phosphatidylinositol 3,4,5-triphosphates resulting from phosphatidylinositol 3-kinase (PI3K) activation. PTEN expression has been shown to be decreased in colorectal cancer. Little is known however as to the specific cellular role of PTEN in human intestinal epithelial cells. The aim of this study was to investigate the role of PTEN in human colorectal cancer cells. Methodology/Principal Findings Caco-2/15, HCT116 and CT26 cells were infected with recombinant lentiviruses expressing a shRNA specifically designed to knock-down PTEN. The impact of PTEN downregulation was analyzed on cell polarization and differentiation, intercellular junction integrity (expression of cell-cell adhesion proteins, barrier function), migration (wound assay), invasion (matrigel-coated transwells) and on tumor and metastasis formation in mice. Electron microscopy analysis showed that lentiviral infection of PTEN shRNA significantly inhibited Caco-2/15 cell polarization, functional differentiation and brush border development. A strong reduction in claudin 1, 3, 4 and 8 was also observed as well as a decrease in transepithelial resistance. Loss of PTEN expression increased the spreading, migration and invasion capacities of colorectal cancer cells in vitro. PTEN downregulation also increased tumor size following subcutaneous injection of colorectal cancer cells in nude mice. Finally, loss of PTEN expression in HCT116 and CT26, but not in Caco-2/15, led to an increase in their metastatic potential following tail-vein injections in mice. Conclusions/Significance Altogether, these results indicate that PTEN controls cellular polarity, establishment of cell-cell junctions, paracellular permeability, migration and tumorigenic/metastatic potential of human colorectal cancer cells.

Estrogen receptor β deficiency enhances small intestinal tumorigenesis in ApcMin/+ mice

Clinical evidence suggests that estradiol replacement therapy reduces colon cancer risk in ‘post’menopausal women. In colon epithelial cells, the estrogen receptor β (ERβ) is the predominant ER subtype and is thought to mediate the genomic effect of estrogens. The first aim of this study was to investigate the consequence of ERβ deficiency on intestinal tumorigenesis in the ApcMin/+ mouse model. Furthermore, to explore the biological mechanisms by which estrogens may influence the pathogenesis of colorectal cancer, we performed gene expression profiles in colonocytes from ovariectomized wild‐type (WT) vs. ERβ−/− mice, treated with estradiol (E2) or vehicle. Specifically in female, ERβ deficiency was found to be associated with higher adenoma multiplicity in the small intestine, but not in the colon. Furthermore, tumors from ERβ−/−ApcMin/+ female mice were on average significantly larger than those from control ApcMin/+ mice. Higher steady‐state proliferation in epithelial cells of the jejunum and colon from ERβ−/−ApcMin/+ vs. ApcMin/+ female mice was confirmed by BrdU incorporation assay. Interestingly, functional categorization of microarray results revealed the TGFβ signaling pathway to be modulated in colonocytes, especially for the WT + E2 vs. WT + Vehicle and the ERβ−/− + E2 vs. WT + E2 comparisons. Using quantitative PCR analysis, we observed transcripts from ligands of the TGFβ pathway to be upregulated in colonocytes from E2‐treated WT and ERβ−/− mice and downregulated in ERβ‐deficient mice, mostly in an E2‐independent manner. Therefore, our results demonstrate that ERβ deficiency enhances small intestinal tumorigenesis and suggest that modulation of the TGFβ signaling pathway could contribute to the protective role of estrogens on intestinal tumorigenesis.

Faecal pharmacokinetics of orally administered vancomycin in patients with suspected Clostridium difficile infection

BackgroundOral vancomycin (125 mg qid) is recommended as treatment of severe Clostridium difficile infection (CDI). Higher doses (250 or 500 mg qid) are sometimes recommended for patients with very severe CDI, without supporting clinical evidence. We wished to determine to what extent faecal levels of vancomycin vary according to diarrhoea severity and dosage, and whether it is rational to administer high-dose vancomycin to selected patients.MethodsWe recruited hospitalized adults suspected to have CDI for whom oral vancomycin (125, 250 or 500 mg qid) had been initiated. Faeces were collected up to 3 times/day and levels were measured with the AxSYM fluorescence polarization immunoassay.ResultsFifteen patients (9 with confirmed CDI) were treated with oral vancomycin. Patients with ≥4 stools daily presented lower faecal vancomycin levels than those with a lower frequency. Higher doses of oral vancomycin (250 mg or 500 mg qid) led to consistently higher faecal levels (> 2000 mg/L), which were 3 orders of magnitude higher than the MIC90 of vancomycin against C. difficile. One patient receiving 125 mg qid had levels below 50 mg/L during the first day of treatment.ConclusionsFaecal levels of vancomycin are proportional to the dosage administered and, even in patients with increased stool frequency, much higher than the MIC90. Patients given the standard 125 mg qid dosage might have low faecal levels during the first day of treatment. A loading dose of 250 mg or 500 mg qid during the first 24-48 hours followed by the standard dosage should be evaluated in larger studies, since it might be less disruptive to the colonic flora and save unnecessary costs.

Oncogenic KRAS signalling promotes the Wnt/β-catenin pathway through LRP6 in colorectal cancer

Aberrant regulation of the Wnt/β-catenin signaling pathway is one of the major causes of colorectal cancer (CRC). Loss-of-function mutations in APC are commonly found in CRC, leading to inappropriate activation of canonical Wnt signaling. Conversely, gain-of-function mutations in KRAS and BRAF genes are detected in up to 60% of CRCs. Whereas KRAS/mitogen-activated protein kinase (MAPK) and canonical Wnt/β-catenin pathways are critical for intestinal tumorigenesis, mechanisms integrating these two important signaling pathways during CRC development are unknown. Results herein demonstrate that transformation of normal intestinal epithelial cells (IECs) by oncogenic forms of KRAS, BRAF or MEK1 was associated with a marked increase in β-catenin/TCF4 and c-MYC promoter transcriptional activities and mRNA levels of c-Myc, Axin2 and Lef1. Notably, expression of a dominant-negative mutant of T-Cell Factor 4 (ΔNTCF4) severely attenuated IEC transformation induced by oncogenic MEK1 and markedly reduced their tumorigenic and metastatic potential in immunocompromised mice. Interestingly, the Frizzled co-receptor LRP6 was phosphorylated in a MEK-dependent manner in transformed IECs and in human CRC cell lines. Expression of LRP6 mutant in which serine/threonine residues in each particular ProlineProlineProlineSerine/ThreonineProline motif were mutated to alanines (LRP6-5A) significantly reduced β-catenin/TCF4 transcriptional activity. Accordingly, MEK inhibition in human CRC cells significantly diminished β-catenin/TCF4 transcriptional activity and c-MYC mRNA and protein levels without affecting β-catenin expression or stability. Lastly, LRP6 phosphorylation was also increased in human colorectal tumors, including adenomas, in comparison with healthy adjacent normal tissues. Our data indicate that oncogenic activation of KRAS/BRAF/MEK signaling stimulates the canonical Wnt/β-catenin pathway, which in turn promotes intestinal tumor growth and invasion. Moreover, LRP6 phosphorylation by ERK1/2 may provide a unique point of convergence between KRAS/MAPK and Wnt/β-catenin signalings during oncogenesis.

Endogenous pain modulation during the formalin test in estrogen receptor beta knockout mice.

The involvement of estrogen in pain has been investigated in many ways. However the specific role played by estrogen receptors remains elusive. Estrogen receptors alpha and beta mediate different physiological functions. For example, estrogen receptor beta is more closely related to non-reproductive effects than the alpha subtype is. To verify the involvement of estrogen receptor beta on acute and persistent pain as well as on endogenous pain inhibitory mechanisms, hotplate and formalin tests were carried out in wild type (WT) and estrogen receptor beta knockout (ERbeta KO) mice of both sexes. Ovariectomies followed by estrogen and progesterone replacement were performed in female groups to insure comparable sex hormone levels. We found that nociceptive responses are lower in ERbeta KO female than in WT female mice during the interphase and early tonic phase II of the formalin test but not during acute and late tonic phases. Moreover, behavioral and spinal (c-Fos) differences were only observed in females. ERbeta KO females had lower c-Fos expression in laminae I-II and IV-V of the spinal cord than WT females. These results suggest that estrogen, through its actions on ERbeta, dampens the efficacy of endogenous pain modulation mechanisms during the interphase and/or inflammation process in the early phase II, triggering an increase in spinal nociceptive neuronal activity. This confirms our previous observations that estrogen specifically influences nociceptive responses during the interphase of the formalin test and demonstrates a role for ERbeta on endogenous pain modulation systems.

E2F4 expression is required for cell cycle progression of normal intestinal crypt cells and colorectal cancer cells.

The generation of knock‐out mice for E2F4 gene expression has suggested a role for this transcription factor in establishing and/or maintaining the intestinal crypt compartment. Having previously demonstrated that E2F4 is cytoplasmic in quiescent‐differentiated cells but nuclear in growth factor‐stimulated proliferative cells, the present study was aimed at determining the role of E2F4 in the control of human intestinal epithelial proliferation. Results herein demonstrate that lentiviral infection of an shRNA which specifically knocked‐down E2F4 expression slowed down G1/S phase transition and the proliferation rate of normal human intestinal epithelial cells (HIEC) and of colon cancer cells. Protein expression of Cdk2, cyclins D1 and A, Cdc25A and c‐myc was markedly down‐regulated in shE2F4‐expressing cells; by contrast, expression of the cell cycle inhibitors p21Cip/Waf and p27Kip1 was increased. In addition, the expression of many genes involved in DNA synthesis was down‐regulated in shE2F4‐expressing cells, whereas no modulation in E2F1 expression was observed. A decrease in E2F4 in colon cancer cell lines also resulted in a reduction in soft‐agar growth capacity. Immunofluorescence experiments in human fetal intestine revealed that cells expressing high nuclear levels of E2F4 also expressed cyclin A protein. Lastly, E2F4 and its target cyclin A were up‐regulated and mostly nuclear in human colorectal tumor cells in comparison to the corresponding benign epithelium. These results indicate that nuclear E2F4 may be determinant in the promotion of proliferation of human intestinal epithelial crypt cells and colorectal cancer cells. J. Cell. Physiol. 221: 350–358, 2009.

Hepatocyte Nuclear Factor-4α Promotes Gut Neoplasia in Mice and Protects against the Production of Reactive Oxygen Species

Hepatocyte nuclear factor-4α (Hnf4α) is a transcription factor that controls epithelial cell polarity and morphogenesis. Hnf4α conditional deletion during postnatal development has minor effects on intestinal epithelium integrity but promotes activation of the Wnt/β-catenin pathway without causing tumorigenesis. Here, we show that Hnf4α does not act as a tumor-suppressor gene but is crucial in promoting gut tumorigenesis in mice. Polyp multiplicity in ApcMin mice lacking Hnf4α is suppressed compared with littermate ApcMin controls. Analysis of microarray gene expression profiles from mice lacking Hnf4α in the intestinal epithelium identifies novel functions of this transcription factor in targeting oxidoreductase-related genes involved in the regulation of reactive oxygen species (ROS) levels. This role is supported with the demonstration that HNF4α is functionally involved in the protection against spontaneous and 5-fluorouracil chemotherapy-induced production of ROS in colorectal cancer cell lines. Analysis of a colorectal cancer patient cohort establishes that HNF4α is significantly upregulated compared with adjacent normal epithelial resections. Several genes involved in ROS neutralization are also induced in correlation with HNF4A expression. Altogether, the findings point to the nuclear receptor HNF4α as a potential therapeutic target to eradicate aberrant epithelial cell resistance to ROS production during intestinal tumorigenesis.

Polycomb repressive complex 2 impedes intestinal cell terminal differentiation

Summary The crypt–villus axis constitutes the functional unit of the small intestine, where mature absorptive cells are confined to the villi, and stem cells and transit amplifying and differentiating cells are restricted to the crypts. The polycomb group (PcG) proteins repress differentiation and promote self-renewal in embryonic stem cells. PcGs prevent transcriptional activity by catalysing epigenetic modifications, such as the covalent addition of methyl groups on histone tails, through the action of the polycomb repressive complex 2 (PRC2). Although a role for PcGs in the preservation of stemness characteristics is now well established, recent evidence suggests that they may also be involved in the regulation of differentiation. Using intestinal epithelial cell models that recapitulate the enterocytic differentiation programme, we generated a RNAi-mediated stable knockdown of SUZ12, which constitutes a cornerstone for PRC2 assembly and functionality, in order to analyse intestinal cell proliferation and differentiation. Expression of SUZ12 was also investigated in human intestinal tissues, revealing the presence of SUZ12 in most proliferative epithelial cells of the crypt and an increase in its expression in colorectal cancers. Moreover, PRC2 disruption led to a significant precocious expression of a number of terminal differentiation markers in intestinal cell models. Taken together, our data identified a mechanism whereby PcG proteins participate in the repression of the enterocytic differentiation program, and suggest that a similar mechanism exists in situ to slow down terminal differentiation in the transit amplifying cell population.

Cathepsin B promotes colorectal tumorigenesis, cell invasion, and metastasis

Cathepsin B is a cysteine proteinase that primarily functions as an endopeptidase within endolysosomal compartments in normal cells. However, during tumoral expansion, the regulation of cathepsin B can be altered at multiple levels, thereby resulting in its overexpression and export outside of the cell. This may suggest a possible role of cathepsin B in alterations leading to cancer progression. The aim of this study was to determine the contribution of intracellular and extracellular cathepsin B in growth, tumorigenesis, and invasion of colorectal cancer (CRC) cells. Results show that mRNA and activated levels of cathepsin B were both increased in human adenomas and in CRCs of all stages. Treatment of CRC cells with the highly selective and non‐permeant cathepsin B inhibitor Ca074 revealed that extracellular cathepsin B actively contributed to the invasiveness of human CRC cells while not essential for their growth in soft agar. Cathepsin B silencing by RNAi in human CRC cells inhibited their growth in soft agar, as well as their invasion capacity, tumoral expansion, and metastatic spread in immunodeficient mice. Higher levels of the cell cycle inhibitor p27Kip1 were observed in cathepsin B‐deficient tumors as well as an increase in cyclin B1. Finally, cathepsin B colocalized with p27Kip1 within the lysosomes and efficiently degraded the inhibitor. In conclusion, the present data demonstrate that cathepsin B is a significant factor in colorectal tumor development, invasion, and metastatic spreading and may, therefore, represent a potential pharmacological target for colorectal tumor therapy.

ERRα metabolic nuclear receptor controls growth of colon cancer cells

The estrogen-related receptor alpha (ERRα) is a nuclear receptor that acts primarily as a regulator of metabolic processes, particularly in tissues subjected to high-energy demand. In addition to its control of energy metabolism and mitochondrial biogenesis, ERRα has recently been associated with cancer progression. Notably, increased expression of ERRα has been shown in several cancerous tissues, including breast, ovary and colon. However, additional studies are required to gain insight into the action of ERRα in cancer biology, particularly in non-endocrine-related cancers. Therefore, using a short hairpin RNA-mediated approach, we investigated whether ERRα is required for the rapid growth of colon cancer cells and to maintain their neoplastic metabolic state. Results show that silencing ERRα significantly impaired colon cancer cell proliferation and colony formation in vitro as well as their in vivo tumorigenic capacity. A pronounced delay in G1-to-S cell cycle phase transition was observed in ERRα-depleted cells in association with reduced cyclin-dependent kinase 2 activity and hyperphosphorylated state of the retinoblastoma protein along with disturbed expression of several cell cycle regulators, including p15 and p27. Interestingly, ERRα-depleted HCT116 cells also displayed significant reduction in expression of a large set of key genes to glycolysis, tricarboxylic acid cycle and lipid synthesis. Furthermore, using (14)C isotope tracer analysis, ERRα depletion in colon cancer cells resulted in reduced glucose incorporation and glucose-mediated lipogenesis in these cells. These findings suggest that ERRα coordinates colon cancer cell proliferation and tumorigenic capacity with energy metabolism. Thus, ERRα could represent a promising therapeutic target in colon cancer.