Intestinal epithelial cell differentiation involves activation of p38 mitogen-activated protein kinase that regulates the homeobox transcription factor CDX2

The role of CDX2 in intestinal homeostasis and inflammation

Many transcription factors are known to control transcription at several promoters, while others are only active at a few places. However, due to their importance in controlling cellular functions, aberrant transcription factor function and inappropriate gene regulation have been shown to play a causal role in a large number of diseases and developmental disorders. Inflammatory bowel disease (IBD) is characterized by a chronically inflamed mucosa caused by dysregulation of the intestinal immune homeostasis. The aetiology of IBD is thought to be a combination of genetic and environmental factors, including luminal bacteria. The Caudal-related homeobox transcription factor 2 (CDX2) is critical in early intestinal differentiation and has been implicated as a master regulator of the intestinal homeostasis and permeability in adults. When expressed, CDX2 modulates a diverse set of processes including cell proliferation, differentiation, cell adhesion, migration, and tumorigenesis. In addition to these critical cellular processes, there is increasing evidence for linking CDX2 to intestinal inflammation. The aim of the present paper was to review the current knowledge of CDX2 in regulation of the intestinal homeostasis and further to reveal its potential role in inflammation.

p38 maintains E-cadherin expression by modulating TAK1-NF-kappa B during epithelial-to-mesenchymal transition

Epithelial-to-mesenchymal transition (EMT) of peritoneal mesothelial cells is a pathological process that occurs during peritoneal dialysis. EMT leads to peritoneal fibrosis, ultrafiltration failure and eventually to the discontinuation of therapy. Signaling pathways involved in mesothelial EMT are thus of great interest, but are mostly unknown. We used primary mesothelial cells from human omentum to analyze the role of the p38 MAPK signaling pathway in the induction of EMT. The use of specific inhibitors, a dominant-negative p38 mutant and lentiviral silencing of p38α demonstrated that p38 promotes E-cadherin expression both in untreated cells and in cells co-stimulated with the EMT-inducing stimuli transforming growth factor (TGF)-β1 and interleukin (IL)-1β. p38 inhibition also led to disorganization and downregulation of cytokeratin filaments and zonula occludens (ZO)-1, whereas expression of vimentin was increased. Analysis of transcription factors that repress E-cadherin expression showed that p38 blockade inhibited expression of Snail1 while increasing expression of Twist. Nuclear translocation and transcriptional activity of p65 NF-κB, an important inducer of EMT, was increased by p38 inhibition. Moreover, p38 inhibition increased the phosphorylation of TGF-β-activated kinase 1 (TAK1), NF-κB and IκBα. The effect of p38 inhibition on E-cadherin expression was rescued by modulating the TAK1-NF-κB pathway. Our results demonstrate that p38 maintains E-cadherin expression by suppressing TAK1-NF-κB signaling, thus impeding the induction of EMT in human primary mesothelial cells. This represents a novel role of p38 as a brake or 'gatekeeper' of EMT induction by maintaining E-cadherin levels.

Genome-wide analysis of CDX2 binding in intestinal epithelial cells (Caco-2)

The CDX2 transcription factor is known to play a crucial role in inhibiting proliferation, promoting differentiation and the expression of intestinal specific genes in intestinal cells. The overall effect of CDX2 in intestinal cells has previously been investigated in conditional knock-out mice, revealing a critical role of CDX2 in the formation of the normal intestinal identity. The identification of direct targets of transcription factors is a key problem in the study of gene regulatory networks. The ChIP-seq technique combines chromatin immunoprecipitation (ChIP) with next generation sequencing resulting in a high throughput experimental method of identifying direct targets of specific transcription factors. The method was applied to CDX2, leading to the identification of the direct binding of CDX2 to several known and novel target genes in the intestinal cell. Examination of the transcript levels of selected genes verified the regulatory role of CDX2 binding. The results place CDX2 as a key node in a transcription factor network controlling the proliferation and differentiation of intestinal cells.

Cadmium-induced hormetic effect in differentiated Caco-2 cells: ERK and p38 activation without cell proliferation stimulation

Cadmium (Cd) is a toxic metal that enters the food chain. Following oral ingestion, the intestinal epithelium may in part protect against Cd toxicity but is also a target tissue. Using human enterocytic-like Caco-2 cells, we have previously shown differences in sensitivity to Cd according to the differentiation status. The present study focuses on Cd effects on differentiated cells. Concentration and time-dependent increases in MTT (3-[4,5-dimethyl-2-thiazol-2-yl]-2,5-diphenyltetrazolium bromide assay) activity were observed in post-confluent cultures exclusively, with a twofold maximal stimulation in 21-day-old cells exposed to 10 microM Cd for 24 h. No concomitant increase in [methyl-(3)H] thymidine incorporation was noted and Cd did not modify cell distribution in the cell-cycle phases. However, Cd-induced increase in MTT activity was inhibited by cycloheximine as well as by inhibitors of ERK1/2 and p38, but not by that of JNK. Consistently, Cd increased the levels of ERK1/2 and p38 phosphorylation. Inhibition of Ras-GTP or PI3K enhanced the stimulatory effect of Cd, whereas mTOR inhibition had no effect. Inhibition of G protein-phospholipase and PKC decreased MTT stimulation. These results show a hormesis-like stimulation of Cd on MTT activity in differentiated intestinal cells exclusively. This effect is not related to cell proliferation but more likely to increased protein synthesis which involves ERK1/2 and p38 cascades and possibly PLC-beta signaling pathways. Because growth-related differentiation of intestinal cells is linked to the selective and sequential activation of MAPKs, the impacts that these Cd-induced perturbations in signaling pathways may have on intestinal functions clearly deserve to be investigated.

Muc4/MUC4 functions and regulation in cancer

The membrane mucin MUC4 (human) is abundantly expressed in many epithelia, where it is proposed to play a protective role, and is overexpressed in some epithelial tumors. Studies on the rat homologue, Muc4, indicate that it acts through anti-adhesive or signaling mechanisms. In particular, Muc4/MUC4 can serve as a ligand/modulator of the receptor tyrosine kinase ErbB2, regulating its phosphorylation and the phosphorylation of its partner ErbB3, with or without the involvement of the ErbB3 ligand neuregulin. Muc4/MUC4 can also modulate cell apoptosis via multiple mechanisms, both ErbB2 dependent and independent. Muc4/MUC4 expression is regulated by multiple mechanisms, ranging from transcriptional to post-translational. The roles of MUC4 in tumors suggest that it may be valuable as a tumor marker or target for therapy.

Regulation of UGT1A1 and HNF1 transcription factor gene expression by DNA methylation in colon cancer cells

Background

UDP-glucuronosyltransferase 1A1 (UGT1A1) is a pivotal enzyme involved in metabolism of SN-38, the active metabolite of irinotecan commonly used to treat metastatic colorectal cancer. We previously demonstrated aberrant methylation of specific CpG dinucleotides in UGT1A1-negative cells, and revealed that methylation state of the UGT1A1 5'-flanking sequence is negatively correlated with gene transcription. Interestingly, one of these CpG dinucleotides (CpG -4) is found close to a HNF1 response element (HRE), known to be involved in activation of UGT1A1 gene expression, and within an upstream stimulating factor (USF) binding site.

Results

Gel retardation assays revealed that methylation of CpG-4 directly affect the interaction of USF1/2 with its cognate sequence without altering the binding for HNF1-alpha. Luciferase assays sustained a role for USF1/2 and HNF1-alpha in UGT1A1 regulation in colon cancer cells. Based on the differential expression profiles of HNF1A gene in colon cell lines, we also assessed whether methylation affects its expression. In agreement with the presence of CpG islands in the HNF1A promoter, treatments of UGT1A1-negative HCT116 colon cancer cells with a DNA methyltransferase inhibitor restore HNF1A gene expression, as observed for UGT1A1.

Conclusions

This study reveals that basal UGT1A1 expression in colon cells is positively regulated by HNF1-alpha and USF, and negatively regulated by DNA methylation. Besides, DNA methylation of HNF1A could also play an important role in regulating additional cellular drug metabolism and transporter pathways. This process may contribute to determine local inactivation of drugs such as the anticancer agent SN-38 by glucuronidation and define tumoral response.

Intestinal cell kinase, a MAP kinase-related kinase, regulates proliferation and G1 cell cycle progression of intestinal epithelial cells

Intestinal cell kinase (ICK), originally cloned from the intestine and expressed in the intestinal crypt epithelium, is a highly conserved serine/threonine protein kinase that is similar to mitogen-activated protein kinases (MAPKs) in the catalytic domain and requires dual phosphorylation within a MAPK-like TDY motif for full activation. Despite these similarities to MAPKs, the biological functions of ICK remain unknown. In this study, we report that suppression of ICK expression in cultured intestinal epithelial cells by short hairpin RNA (shRNA) interference significantly impaired cellular proliferation and induced features of gene expression characteristic of colonic or enterocytic differentiation. Downregulation of ICK altered expression of cell cycle regulators (cyclin D1, c-Myc, and p21(Cip1/WAF1)) of G(1)-S transition, consistent with the G(1) cell cycle delay induced by ICK shRNA. ICK deficiency also led to a significant decrease in the expression and/or activity of p70 ribosomal protein S6 kinase (S6K1) and eukaryotic initiation factor 4E (eIF4E), concomitant with reduced expression of their upstream regulators, the mammalian target of rapamycin (mTOR) and the regulatory associated protein of mTOR (Raptor). Furthermore, ICK interacts with the mTOR/Raptor complex in vivo and phosphorylates Raptor in vitro. These results suggest that disrupting ICK function may downregulate protein translation of specific downstream targets of eIF4E and S6K1 such as cyclin D1 and c-Myc through the mTOR/Raptor signaling pathway. Taken together, our findings demonstrate an important role for ICK in proliferation and differentiation of intestinal epithelial cells.

Mitogen activated protein kinases: a role in inflammatory bowel disease?

Since their discovery more than 15 years ago, the mitogen activated protein kinases (MAPK) have been implicated in an ever-increasingly diverse array of pathways, including inflammatory signalling cascades. Inflammatory bowel diseases (IBD), such as ulcerative colitis and Crohn's disease, are characterized by the perpetual production of inflammatory mediators. Research into the transduction pathway behind this over-production has highlighted the potential mediating role for the MAPKs and their related signalling components. This review highlights some of the research into the role for the MAPKs and their related signalling proteins in influencing the progression of IBD.

Selective activation of tumor growth-promoting Ca2+ channel MS4A12 in colon cancer by caudal type homeobox transcription factor CDX2

Colon cancer-associated MS4A12 is a novel colon-specific component of store-operated Ca²⁺ (SOC) entry sensitizing cells for epidermal growth factor (EGF)-mediated effects on proliferation and chemotaxis. In the present study, we investigated regulation of the MS4A12 promoter to understand the mechanisms responsible for strict transcriptional restriction of this gene to the colonic epithelial cell lineage. DNA-binding assays and luciferase reporter assays showed that MS4A12 promoter activity is governed by a single CDX homeobox transcription factor binding element. RNA interference (RNAi)-mediated silencing of intestine-specific transcription factors CDX1 and CDX2 and chromatin immunoprecipitation (ChIP) in LoVo and SW48 colon cancer cells revealed that MS4A12 transcript and protein expression is essentially dependent on the presence of endogenous CDX2. In summary, our findings provide a rationale for colon-specific expression of MS4A12. Moreover, this is the first report establishing CDX2 as transactivator of tumor growth-promoting gene expression in colon cancer, adding to untangle the complex and conflicting biological functions of CDX2 in colon cancer and supporting MS4A12 as important factor for normal colonic development as well as for the biology and treatment of colon cancer.

Down-regulation of Cdx2 in colorectal carcinoma cells by the Raf-MEK-ERK 1/2 pathway

Cdx2 is a homeodomain transcription factor that regulates normal intestinal cell differentiation. Cdx2 is frequently lost during progression of colorectal cancer (CRC) and is widely viewed as a colorectal tumour suppressor. A previous study suggested that activation of protein kinase C (PKC) may be responsible for Cdx2 down-regulation in CRC cells. Here we show that activation of PKC does indeed promote down-regulation of Cdx2 at both the mRNA and protein levels. However, PKC-dependent loss of Cdx2 is dependent upon activation of the Raf-MEK-ERK1/2 pathway. Indeed, specific activation of the ERK1/2 pathway using the conditional kinase DeltaRaf-1:ER is sufficient to inhibit Cdx2 transcription. The Raf-MEK-ERK1/2 pathway is hyper-activated in a large fraction of colorectal cancers due to mutations in K-Ras and we show that treatment of CRC cell lines with MEK inhibitors causes an increase in Cdx2 expression. Furthermore, activation of the ERK1/2 pathway promotes the phosphorylation and proteasome-dependent degradation of the Cdx2 protein. The inhibitory effect of ERK1/2 upon Cdx2 in CRC cells is in sharp contrast to its stimulatory effect upon Cdx2 expression in trophectoderm and trophoblast stem cells. These results provide important new insights into the regulation of the Cdx2 tumour suppressor by linking it to ERK1/2, a pathway which is frequently activated in CRC.

Inhibition of nucleostemin upregulates CDX2 expression in HT29 cells in response to bile acid exposure: implications in the pathogenesis of Barrett's esophagus

BACKGROUND

Barrett's esophagus (BE), a squamous-to-columnar metaplasia, may originate from growth-promoting mutations in metaplastic stem cells. Nucleostemin is a protein highly expressed in undifferentiated embryonic stem cells. The objectives of this study were to explore the potential role of nucleostemin in the pathogenesis of BE METHODS: The expression profiles of 30,968 genes were compared between BE and normal esophageal tissues (n = 6 in each group) by using oligo microarray. Three siRNA plasmid expression vectors against nucleostemin, pRNAi-1, pRNAi-2, and pRNAi-3, were constructed and transfected into HT29 cells. In addition, HT29 cells were exposed to 100-1,000 microM chenodeoxycholic acid (CDC), a bile acid, for 2, 12, and 24 h, and then messenger RNA and protein expressions of nucleostemin and CDX2 were determined by reverse-transcriptase polymerase chain reaction and Western blotting.

RESULTS

Four hundred and twenty-six differentially expressed genes were detected in BE; 142 were upregulated and 284 downregulated. Nucleostemin was downregulated while CDX2 was upregulated. In vitro, all the recombinant plasmids inhibited the nucleostemin expression in transfected HT29 cells, with pRNAi-1 being the most effective. CDX2 expression was significantly increased in pRNAi-1-transfected HT29 cells, compared with that in the empty plasmid (pRNAT-U6.1/Neo) transfected or untransfected HT29 cells. In addition, CDX2 expression was increased whereas nucleostemin expression was decreased in a dose- and time-dependent manner in HT29 cells treated with CDC.

CONCLUSION

These findings suggest that the inhibition of nucleostemin expression in "esophageal stem cells" in response to bile acid exposure may be involved in the pathogenesis of BE through upregulating CDX2 expression.

Nuclear receptor co-repressor is required to maintain proliferation of normal intestinal epithelial cells in culture and down-modulates the expression of pigment epithelium-derived factor

Stem cells of the gut epithelium constantly produce precursors that progressively undergo a succession of molecular changes resulting in growth arrest and commitment to a specific differentiation program. Few transcriptional repressors have been identified that maintain the normal intestinal epithelial cell (IEC) proliferation state. Herein, we show that the nuclear receptor co-repressor (NCoR1) is differentially expressed during the proliferation-to-differentiation IEC transition. Silencing of NCoR1 expression in proliferating cells of crypt origin resulted in a rapid growth arrest without associated cell death. A genechip profiling analysis identified several candidate genes to be up-regulated in NCoR1-deficient IEC. Pigment epithelium-derived factor (PEDF, also known as serpinf1), a suspected tumor suppressor gene that plays a key role in the inhibition of epithelial tissue growth, was significantly up-regulated in these cells. Chromatin immunoprecipitation experiments showed that the PEDF gene promoter was occupied by NCoR1 in proliferating epithelial cells. Multiple retinoid X receptor (RXR) heterodimers interacting sites of the PEDF promoter were confirmed to interact with RXR and retinoid acid receptor (RAR). Cotransfection assays showed that RXR and RAR were able to transactivate the PEDF promoter and that NCoR1 was repressing this effect. Finally, forced expression of PEDF in IEC resulted in a slower rate of proliferation. These observations suggest that NCoR1 expression is required to maintain IEC in a proliferative state and identify PEDF as a novel transcriptional target for NCoR1 repressive action.

Insulin-like growth factor and epidermal growth factor treatment: new approaches to protecting steatotic livers against ischemia-reperfusion injury

Hepatic steatosis is a major risk factor in ischemia-reperfusion (I/R). IGF-binding proteins (IGFBPs) modulate IGF-I action by transporting circulating IGF-I to its sites of action. Epidermal growth factor (EGF) stimulates IGF-I synthesis in vitro. We examined the effect of IGF-I and EGF treatment, separately or in combination, on the vulnerability of steatotic livers to I/R. Our results indicated that I/R impaired IGF-I synthesis only in steatotic livers. Only when a high dose of IGF-I (400 microg/kg) was given to obese animals did they show high circulating IGF-I:IGFBP levels, increased hepatic IGF-I levels, and protection against damage. In lean animals, a dose of 100 microg/kg IGF-I protected nonsteatotic livers. Our results indicated that the combined administration of IGF-I and EGF resulted in hepatic injury parameters in both liver types similar to that obtained by IGF-I and EGF separately. IGF-I increased egf expression in both liver types. The beneficial role of EGF on hepatic I/R injury may be attributable to p38 inhibition in nonsteatotic livers and to PPAR gamma overexpression in steatotic livers. In conclusion, IGF-I and EGF may constitute new pharmacological strategies to reduce the inherent susceptibility of steatotic livers to I/R injury.

The role of the calcium-sensing receptor in the development and progression of cancer

The calcium-sensing receptor (CaR) is responsive to changes in the extracellular Ca(2+) (Ca(2+)(o)) concentration. It is a member of the largest family of cell surface receptors, the G protein-coupled receptors, and it has been shown to be involved in Ca(2+)(o) homeostasis. Apart from its primary role in Ca(2+)(o) homeostasis, the CaR may be involved in phenomena that allow for the development of many types of benign or malignant tumors, from parathyroid adenomas to breast, prostate, and colon cancers. For example, whereas the CaR is expressed in both normal and malignant breast tissue, increased CaR levels have been reported in highly metastatic primary breast cancer cells and breast cancer cell lines, possibly contributing to their malignancy and associated alterations in their biological properties. In these settings the CaR exhibits oncogenic properties. Enhanced CaR expression and altered proliferation of prostate cancer cells in response to increased Ca(2+)(o) have also been described. In contrast, colon and parathyroid cancers often present with reduced or absent CaR expression, and activation of this receptor decreases cell proliferation, suggesting a role for the CaR as a tumor suppressor gene. Thus, the CaR may play an important role in the development of many types of neoplasia. Herein, we review the role of the CaR in various benign and malignant tumors in further detail, describing its contribution to parathyroid tumors, breast, prostate, and colon cancers, and we evaluate how pharmacological manipulations of this receptor may be of interest for the treatment of certain cancers in the future.

CaSR stimulates secretion of Wnt5a from colonic myofibroblasts to stimulate CDX2 and sucrase-isomaltase using Ror2 on intestinal epithelia

To understand whether extracellular calcium-sensing receptor (CaSR) expression on colonic myofibroblast cells (18Co) contributed to epithelial homeostasis, we activated the CaSR with 5 mM Ca(2+), screened by RT-PCR Wnt family members, and measured their secretion. Transcripts for Wnt 1, 2, 2b, 3a, 4, and 7a were either absent or unchanged whereas Wnt3 decreased and Wnt5a increased. We assessed Wnt5a secretion by Western blot. High Ca(2+) (5 mM) substantially increased Wnt5a secretion; small interfering RNA (siRNA) against the CaSR reduced this to constitutive amounts. Expression of Wnt5a plasmid but not Wnt1 or Wnt3a increased caudal homeodomain factor CDX2 transcripts and protein in HT-29 adenocarcinoma cells. Wnt5a increased activity of a sucrase-isomaltase (SI) promoter in Caco-2BBE cells. Wnt5a protein stimulation of CDX2 transcripts and protein and SI reporter were increased by overexpression of wild-type Ror2, a Wnt5a receptor, and reduced with siRNA against Ror2. CaSR activation of HT-29 cells increased Ror2 protein expression. Ror2 protein was expressed in mouse jejunum from crypt base to villus tip and in the colon on surface epithelia. Our results show that activation of a G protein-coupled receptor, the CaSR, stimulates secretion of Wnt5a from myofibroblasts. Stimulation of epithelia by the CaSR increased the expression of a receptor for Wnt5a, the tyrosine kinase Ror2, suggesting existence of a unique paracrine relationship for CDX2 homoeostasis in the intestine and revealing new contributions of CaSR-activated myofibroblasts to intestinal stem cell niche microenvironments.

Regulation of C/EBPdelta-dependent transactivation by histone deacetylases in intestinal epithelial cells

The C/EBPdelta transcription factor is involved in the positive regulation of the intestinal epithelial cell acute phase response. C/EBPdelta regulation by histone deacetylases (HDACs) during the course of inflammation remains to be determined. Our aim was to examine the effect of HDACs on C/EBPdelta-dependent regulation of haptoglobin, an acute phase protein induced in intestinal epithelial cells in response to pro-inflammatory cytokines. HDAC1, HDAC3, and HDAC4 were expressed in intestinal epithelial cells, as determined by Western blot. GST pull-down assays showed specific HDAC1 interactions with the transcriptional activation and the b-ZIP C/EBPdelta domains, while the co-repressor mSin3A interacts with the C-terminal domain. Immunoprecipitation assays confirmed the interaction between HDAC1 and the N-terminal C/EBPdelta amino acid 36-164 domain. HDAC1 overexpression decreased C/EBPdelta transcriptional activity of the haptoglobin promoter, as assessed by transient transfection and luciferase assays. Chromatin immunoprecipitation analysis showed a displacement of HDAC1 from the haptoglobin promoter in response to inflammatory stimuli and an increased acetylation of histone H3 and H4. HDAC1 silencing by shRNA expression increased both basal and IL-1beta-induced haptoglobin mRNA levels in epithelial intestinal cells. Our results suggest that interactions between C/EBPs and HDAC1 negatively regulate C/EBPdelta-dependent haptoglobin expression in intestinal epithelial cells.

Biology of intestinal metaplasia in 2008: more than a simple phenotypic alteration

This review concentrates on one main aspect of cancerization in the oesophagus and stomach: principally, intestinal metaplasia. There are at least two other important pathways that lead to cancer and do not need such a morphological transformation. One is the gastric type of carcinoma on the Lauren classification, which arises directly from the stem cell zone and is the signet ring form of cancer, while the other is spasmolytic polypeptide-expressing metaplasia (SPEM)--spasmolytic polypeptide (TFF2) expressing metaplasia, where the gastric glands become filled with TFF2-expressing cells and may also lead to gastric dysplasia and cancer. The development of intestinal metaplasia is complex. Here, we examine intestinal metaplasia in molecular terms, noting the over-expression of Cdx1, Cdx2, Pdx1, Oct1, TFF3 and the downregulation of Hedgehog signalling; Runx3 is deactivated by epigenetic silencing, and pathways such as Wnt and MARK/ERK are involved. These changes start to explain the principles of the development of intestinal metaplasia and suggest that the regulation of these genes is of importance in the development of gastric cancer.

Intrinsically disordered human C/EBP homologous protein regulates biological activity of colon cancer cells during calcium stress

Intrinsically disordered proteins are emerging as substantial functional constituents of mammalian proteomes. Although the abundance of these proteins has been established by bioinformatics approaches, the vast majority have not been characterized structurally or functionally. The C/EBP homologous protein (CHOP) is a proto-oncogene, traditionally shown as a dominant-negative inhibitor of C/EBPs and a transcriptional activator of activating protein-1. We report here the in vitro characterization of CHOP, where our computational analyses and experimental evidences show for the first time that CHOP is an intrinsically disordered protein. Intrinsic fluorescence, NMR spectroscopy, and analytical size-exclusion chromatography studies indicate that CHOP contains extensive disordered regions and self-associate in solution. Interestingly, the disordered N-terminal region has a key role in the oligomerization of CHOP and is vital for its biological activity. We report a novel mechanistic role of CHOP in the inhibition of Wnt/TCF signaling and stimulation of c-Jun and sucrase-isomaltase reporter activity in intestinal colon cancer cells. These findings are discussed in the context of oligomerization of intrinsically disordered proteins as one of the mechanisms through which they exert their biological function.

Air exposure induced squamous metaplasia of human limbal epithelium

PURPOSE

Squamous metaplasia is a pathologic process that frequently occurs in nonkeratinized stratified ocular surface epithelia. The mechanism for this occurrence is largely unknown except for vitamin A deficiency.

METHODS

Human limbal explants were cultured under airlift with or without p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 or in a submerged manner for different durations up to 2 weeks. Epithelial cell proliferation, differentiation, limbal stem cell maintenance, and expansion were studied using certain markers such as Ki67, p63, K10 and K12 keratins, filaggrin, Pax6, ABCG-2, and Musashi-1. Expression of phospho-p38 MAPK and its downstream transcription factors, C/EBPalpha and C/EBPbeta, were studied by immunohistochemistry. Epithelial cells harvested from explants after 2 weeks of culturing under different conditions were seeded onto 3T3 feeder layers and cultured for 12 days. The differentiation of clonal epithelial cells was investigated by double staining to K12 and K10 keratins.

RESULTS

The squamous metaplasia model was successfully created by culturing human limbal explants at an air-liquid interface (airlift) for 2 weeks. Increased stratification and hyperproliferation only happened in the limbal, but not the corneal, epithelium in airlift, but not submerged, cultures. Epithelial proliferation was associated with a transient increase of limbal epithelial stem cells. Abnormal epidermal differentiation-evidenced by positive expression of K10 keratin in suprabasal cells and filaggrin in superficial cells-ensued. Clones generated from epithelial cells harvested from airlift culture only expressed K12 keratin without K10. As early as 2 days in airlift cultures, p38 expression emerged in limbal basal epithelial cells and gradually extended to the cytoplasm and nuclei. Furthermore, addition of the p38 inhibitor SB203580 abolished abnormal epidermal differentiation without affecting limbal epithelial proliferation. Expression of C/EBPalpha and C/EBPbeta, downstream of the p38 MAPK signaling pathway, was strongly induced by airlift culture and partially was inhibited by SB203580.

CONCLUSIONS

Dryness resulting from exposure activates p38 MAPK signaling coupled with abnormal epidermal differentiation without intrinsic alteration of stem cells in the limbus. On the ocular surface, p38 inhibitors may have the potential to revert the pathologic process of squamous metaplasia induced by dryness.

Epithelial: lamina propria lymphocyte interactions promote epithelial cell differentiation

BACKGROUND & AIMS

Intestinal lymphoepithelial interactions occur in the epithelium and the subepithelial space. We asked whether normal, Crohn's disease (CD), or ulcerative colitis (UC) lamina propria lymphocytes (LPL) could promote intestinal epithelial cell (IEC) growth and differentiation.

METHODS

T84 cells were cocultured with isolated LPL. IECs were then lysed and subjected to measurement of intestinal alkaline phosphatase (IAP) activity; Western blot analysis for MAPK and Akt activation; and real-time polymerase chain reaction to assess caudal-related homeoprotein 2 (CDX2) messenger RNA (mRNA) levels. Tissue sections were immunostained for evidence of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K) activation, CDX2, and IAP; and CDX2 mRNA expression was assessed in human colonic biopsy specimens.

RESULTS

IAP activity was increased in T84 cells cocultured for 8 days with normal LPL (P < .05) and even greater with CD LPL (P < .001). Crypt IECs in active CD mucosa expressed IAP ex vivo. Phospho-MAPK (extracellular signal-regulated kinase 1/2, p38, and c-Jun-N-terminal kinase) and phospho-Akt were seen as early as 30 minutes after coculture. MAPK activation was greatest in T84 cells cocultured with CD LPL. There was a specific increase in Phospho-p38 MAPK and Phospho-Akt staining in the nuclei of crypt IECs in active vs inactive CD, normal mucosa, and UC mucosa. CDX2 mRNA expression was increased in CD LPL cocultured T84 cells, which did not correlate with CDX2 protein localization ex vivo.

CONCLUSIONS

There is cross talk between LPL and IECs, which leads to IEC differentiation. The differentiation is accelerated in CD mucosa.

Effect of retinoic acid on cell proliferation and differentiation as well as on lipid synthesis, lipoprotein secretion, and apolipoprotein biogenesis

Dietary vitamin A and its active metabolites are essential nutrients for many functions as well as potent regulators of gene transcription and growth. Although the epithelium of the small intestine is characterized by rapid and constant renewal and enterocytes play a central role in the absorption and metabolism of alimentary retinol, very little is known about the function of retinoids in the human gastrointestinal epithelium and mechanisms by which programs engage the cell cycle are poorly understood. We have assessed the effects of 10 microM 9- and 13-cis-retinoic acid (RA) on proliferation and differentiation processes, lipid esterification, apolipoprotein (apo) biogenesis and lipoprotein secretion along with nuclear factor gene transcription. Treatment of Caco-2 cells with RA at different concentrations and incubation periods revealed the reduction of thymidine incorporation in 60% preconfluent or 100% confluent cells. Concomitantly, RA 1) modulated D-type cyclins by reducing the mitogen-sensitive cyclin D1 and upregulating cyclin D3 expressions and 2) caused a trend of increase in p38 MAPK, which triggers CDX2, a central protein in cell differentiation. RA remained without effect on lipoprotein output and apo synthesis, even for apo A-I that possesses RARE in its promoter. RA, in combination with 22-hydroxycholesterol, could induce apo A-I gene expression without any impact on apo A-I mass. Only the gene expression of peroxisome proliferator-activated receptor (PPAR)beta, retinoic receptor (RAR)beta, and RARgamma was augmented and no alteration was noted in PPARalpha, PPARgamma, liver X receptor (LXR)alpha, LXRbeta, and retinoid X receptors. Taken together, these data highlight RA-induced cell differentiation via specific signaling without a significant impact on apo A-I synthesis.

p38 MAP-kinases pathway regulation, function and role in human diseases

Mammalian p38 mitogen-activated protein kinases (MAPKs) are activated by a wide range of cellular stresses as well as in response to inflammatory cytokines. There are four members of the p38MAPK family (p38alpha, p38beta, p38gamma and p38delta) which are about 60% identical in their amino acid sequence but differ in their expression patterns, substrate specificities and sensitivities to chemical inhibitors such as SB203580. A large body of evidences indicates that p38MAPK activity is critical for normal immune and inflammatory response. The p38MAPK pathway is a key regulator of pro-inflammatory cytokines biosynthesis at the transcriptional and translational levels, which makes different components of this pathway potential targets for the treatment of autoimmune and inflammatory diseases. However, recent studies have shed light on the broad effect of p38MAPK activation in the control of many other aspects of the physiology of the cell, such as control of cell cycle or cytoskeleton remodelling. Here we focus on these emergent roles of p38MAPKs and their implication in different pathologies.

A novel cell type-specific role of p38alpha in the control of autophagy and cell death in colorectal cancer cells

Cancer develops when molecular pathways that control the fine balance between proliferation, differentiation, autophagy and cell death undergo genetic deregulation. The prospects for further substantial advances in the management of colorectal cancer reside in a systematic genetic and functional dissection of these pathways in tumor cells. In an effort to evaluate the impact of p38 signaling on colorectal cancer cell fate, we treated HT29, Caco2, Hct116, LS174T and SW480 cell lines with the inhibitor SB202190 specific for p38alpha/beta kinases. We report that p38alpha is required for colorectal cancer cell homeostasis as the inhibition of its kinase function by pharmacological blockade or genetic inactivation causes cell cycle arrest, autophagy and cell death in a cell type-specific manner. Deficiency of p38alpha activity induces a tissue-restricted upregulation of the GABARAP gene, an essential component of autophagic vacuoles and autophagosomes, whereas simultaneous inhibition of autophagy significantly increases cell death by triggering apoptosis. These data identify p38alpha as a central mediator of colorectal cancer cell homeostasis and establish a rationale for the evaluation of the pharmacological manipulation of the p38alpha pathway in the treatment of colorectal cancer.

Does CDX2 expression predict Barrett's metaplasia in oesophageal columnar epithelium without goblet cells?

BACKGROUND

Intestinal metaplasia (Barrett's oesophagus), but not cardiac-type mucosa in columnar-lined oesophagus, is regarded as premalignant. As intestinal metaplasia and cardiac-type mucosa are endoscopically indiscernible, it is difficult to take targeted samples from columnar-lined oesophagus with consequently a risk of having undetected intestinal metaplasia.

AIM

To investigate whether the intestinal markers CDX2, MUC2 and villin can predict the presence of undetected intestinal metaplasia in columnar-lined oesophagus. Methods Presence of intestinal metaplasia or cardiac-type mucosa was identified in 122 biopsy sets of columnar-lined oesophagus from 61 patients, collected at two subsequent follow-up upper endoscopies. CDX2, MUC2 and villin expression were determined by immunohistochemistry.

RESULTS

All intestinal metaplasia samples (55) were positive for CDX2 and MUC2 and 32 of 55 for villin. CDX2 expression was detected in 23 of 67 (34%) samples with only cardiac-type mucosa. Detection of CDX2 in cardiac-type mucosa increased the likelihood of finding intestinal metaplasia in another biopsy set of columnar-lined oesophagus (odds ratio 3.5, 95% CI = 1.2-10, P = 0.02). MUC2 was positive in 13 of 23 (57%) of CDX2-positive cardiac-type mucosa samples, whereas villin was detected in seven of 23 (30%).

CONCLUSIONS

CDX2 expression in cardiac-type mucosa might be able to predict the presence of undetected intestinal metaplasia in columnar-lined oesophagus, and thus may be a putative marker for the presence of intestinal metaplasia in the absence of goblet cells.

MNK1 and MNK2 regulation in HER2-overexpressing breast cancer lines

MAPK-interacting protein kinases 1 and 2 (MNK1 and MNK2) function downstream of p38 and ERK MAPK, but there are large gaps in our knowledge of how MNKs are regulated and function. As proteins activated in the HER2/Ras/Raf/ERK pathway, the MNKs are of potential interest in HER2-overexpressing cancers. We utilized a panel of breast cell lines (HCC1419, AU565, SKBR3, MCF7, and MCF10A), three of which overexpress HER2, to characterize the amounts and activation status of MNKs and other pathway enzymes (ERKs and RSKs) in these cells. We generated a phosphospecific antibody to Thr(P)-214 in the T-loop of MNKs and found that phosphorylations of both Thr-209 and Thr-214 in human MNK1 are required for activation. Increased phosphorylation and activity of the MNKs correlate with HER2 overexpression, and inhibition of the MNKs reduces colony formation in soft agar. Our work identifies the MNKs as potential therapeutic targets for breast cancer treatments.

PTH regulation of c-Jun terminal kinase and p38 MAPK cascades in intestinal cells from young and aged rats

In the present study, we examined the role of Parathyroid hormone (PTH) on the c-Jun N-terminal kinase (JNK) 1/2 and p38 mitogen-activated protein kinase (MAPK) members of the MAPK family as it relates to ageing by measuring hormone-induced changes in their activity in enterocytes isolated from young (3 month old) and aged (24 month old) rats. Our results show that PTH induces a transient activation of JNK 1/2, peaking at 1 min (+threefold). The hormone also stimulates JNK 1/2 tyrosine phosphorylation, in a dose-dependent fashion, this effect being maximal at 10 nM. PTH-induced JNK 1/2 phosphorylation was suppressed by its selective inhibitor SP600125. Moreover, hormone-dependent activation of JNK 1/2 was dependent on calcium, since pretreatment of cells with BAPTA-AM or EGTA blocked PTH effects. With ageing, the response to PTH was significantly reduced. JNK basal protein expression was not different in the enterocytes from young and aged rats, however, basal protein phosphorylation increased with ageing. PTH did not stimulate, within 1-10 min, the basal activity and phosphorylation of p38 MAPK in rat intestinal cells. The hormone increased enterocyte DNA synthesis; the response was dose-dependent and decreased (-40%) with ageing. In agreement with the mitogenic role of the MAPK cascades, this effect was blocked by specific inhibitors of extracellular signal-regulated protein kinase (ERK) 1/2 and JNK 1/2. The results obtained in this work expand our knowledge on the mechanism of action of PTH in duodenal cells.

The centrosome and cell proliferation

Centrosomes are frequently amplified in cancer cells. Increased numbers of centrosomes can give rise to multipolar spindles in mitosis, and thereby lead to the formation of aneuploid daughter cells. However, whether centrosome amplification is a cause or a consequence of cancer is unclear. In contrast, loss of a functional centrosome has been shown to lead to cell cycle arrest. In this review, the potential mechanisms underlying centrosome amplification and centrosome-dependent cell cycle regulation are discussed.

Oxidative stress-induced intestinal epithelial cell apoptosis is mediated by p38 MAPK

Free oxygen radicals are involved in the pathogenesis of necrotizing enterocolitis (NEC) in premature infants. The stress-activated p38 mitogen-activated protein kinase (MAPK) has been implicated in gut injury. Here, we found that phosphorylated p38 was detected primarily in the villus tips of normal intestine, whereas it was expressed in the entire mucosa in NEC. H(2)O(2) treatment resulted in a rapid phosphorylation of p38 MAPK and subsequent apoptosis of rat intestinal epithelial (RIE)-1 cells; this induction was attenuated by treatment with SB203580, a selective p38 MAPK inhibitor, or transfection with p38alpha siRNA. Moreover, SB203580 also blocked H(2)O(2)-induced PKC activation. In contrast, the PKC inhibitor (GF109203x) did not affect p38 activation, indicating that p38 MAPK activation occurs upstream of PKC activation in H(2)O(2)-induced apoptosis. H(2)O(2) treatment also decreased mitochondrial membrane potential; pretreatment with SB203580 attenuated this response. Our study demonstrates that the p38 MAPK/PKC pathway plays an important role as a pro-apoptotic cellular signaling during oxidative stress-induced intestinal epithelial cell injury.

Muc4-ErbB2 complex formation and signaling in polarized CACO-2 epithelial cells indicate that Muc4 acts as an unorthodox ligand for ErbB2

Muc4 serves as an intramembrane ligand for the receptor tyrosine kinase ErbB2. The time to complex formation and the stoichiometry of the complex were determined to be <15 min and 1:1 by analyses of Muc4 and ErbB2 coexpressed in insect cells and A375 tumor cells. In polarized CACO-2 cells, Muc4 expression causes relocalization of ErbB2, but not its heterodimerization partner ErbB3, to the apical cell surface, effectively segregating the two receptors. The apically located ErbB2 is phosphorylated on tyrosines 1139 and 1248. The phosphorylated ErbB2 in CACO-2 cells recruits the cytoplasmic adaptor protein Grb2, consistent with previous studies showing phosphotyrosine 1139 to be a Grb2 binding site. To address the issue of downstream signaling from apical ErbB2, we analyzed the three MAPK pathways of mammalian cells, Erk, p38, and JNK. Consistent with the more differentiated phenotype of the CACO-2 cells, p38 phosphorylation was robustly increased by Muc4 expression, with a consequent activation of Akt. In contrast, Erk and JNK phosphorylation was not changed. The ability of Muc4 to segregate ErbB2 and other ErbB receptors and to alter downstream signaling cascades in polarized epithelial cells suggests that it has a role in regulating ErbB2 in differentiated epithelia.

E-cadherin-dependent Transcriptional Control of Apolipoprotein A-IV Gene Expression in Intestinal Epithelial Cells

Cell-matrix and cell-cell adhesion play a central role in the control of cell proliferation, differentiation, and gene expression. Integrins and E-cadherin are the key components involved in these processes in epithelial cells. We recently showed that integrin-dependent adhesion to the extracellular matrix reinforces the formation of E-cadherin-actin complexes inducing the polarization of Caco-2 enterocytes and increases the expression of a marker of enterocyte differentiation, the apolipoprotein A-IV (apoA-IV) gene. By impairing or enhancing E-cadherin-dependent cell adhesion, we demonstrate in the present study its involvement in the transcriptional activation of the apoA-IV gene in Caco-2 cells. This control requires the regulatory sequence that we have previously identified as necessary and sufficient to drive and restrict apoA-IV gene expression in enterocytes in vivo. Furthermore, using chimeric E-cadherin-Fc homophilic ligand-coated surfaces, we show that a direct activation of E-cadherin triggers the transcriptional activation of the apoA-IV promoter. Finally, E-cadherin-dependent cell-cell adhesion controls the nuclear abundance of the transcription factor hepatic nuclear factor 4alpha, which is involved in the enterocyte-specific expression of apoA-IV gene. Altogether, our results suggest that E-cadherin controls enterocyte-specific expression of genes, such as the apoA-IV gene, through the control of hepatic nuclear factor 4alpha nuclear abundance.

Effect of laminin-1 on intestinal cell differentiation involves inhibition of nuclear nucleolin

Intestinal epithelial cells are characterized by continuous renewal and differentiation events, which may be influenced by the basement membrane, and in particular laminins, which are major components of this specialized extracellular matrix. The function and signaling pathways of laminins in these processes are still poorly documented. In this study, we investigated the possible role and the subcellular localization of nucleolin, a nuclear shuttling protein, in relation to differentiation of human intestinal epithelial Caco2/TC7 cells triggered by exogenous laminin-1. Immunofluorescence and Western blot analysis indicated that laminin-1 induced early differentiation of the cells concomitantly to a decrease in nuclear nucleolin and its a cell surface location. We also showed that both effects of laminin-1 on Caco2/TC7 cells--induction of the differentiation marker sucrase-isomaltase and redistribution of nucleolin--could be mediated by a beta1-integrin dependent cascade that implicated activation of the p38 MAPK pathway. In addition, knock-down of nucleolin expression by the small interfering RNA strategy mimicked the effect of laminin-1 as it resulted in the induction of cell polarization and differentiation. Thus, our study suggests that changes in the subcellular distribution and expression level of nucleolin play an important role in intestinal cell differentiation and relay the signaling pathway induced by laminin-1.

The CDX2 transcription factor regulates furin expression during intestinal epithelial cell differentiation

CDX2, a member of the caudal family of transcription factors, is involved in enterocyte lineage specification. CDX2 activates many intestine-specific genes, such as sucrase-isomaltase and lactase-phlorizin hydrolase (LPH), and adhesion proteins, namely, LI-cadherin and claudin-2. In this study, we show that the proprotein convertase furin, involved in proteolytic maturation of proprotein substrates including LPH and cell surface proteins, is a CDX2 target. Indeed, expression of the rat furin homolog was induced 1.5-fold, as determined by microarray experiments that compared control with CDX2-expressing intestinal epithelial cells (IEC-6). As determined by transient transfection assays in Caco-2/15 cells, the furin P1 promoter 1.3-kb fragment between SacI and NheI was essential for CDX2 transcriptional activation. Electrophoretic mobility shift/supershift assays followed by site-specific mutagenesis and chromatin immunoprecipitation identified the CDX DNA-binding site (CBS)2 sequence from nt -1827 to -1821 as the major CBS involved in furin P1 promoter activation. Increased furin mRNA and protein expression correlated with both CDX2 expression and intestinal epithelial cell differentiation. In addition, furin mRNAs were detected predominantly in differentiated epithelial cells of the villus, as determined by in situ hybridization. Treatment of Caco-2/15 cells with a furin inhibitor led to inhibition of LPH activity. Morphological differentiation of enterocyte-like features in Caco-2/15 such as epithelial cell polarity and brush-border formation were strongly attenuated by furin inhibition. These results suggest that CDX2 regulates furin expression in intestinal epithelial cells. Furin may be important in modulating the maturation and/or activation of key factors involved in enterocyte differentiation.

1α,25(OH)2-Vitamin D3 stimulates intestinal cell p38 MAPK activity and increases c-Fos expression

In intestinal cells, as in other target cells, the steroid hormone 1alpha,25(OH)(2)-Vitamin D(3) (1alpha,25(OH)(2)D(3)) regulates gene expression via the specific intracellular Vitamin D receptor and induces fast non-transcriptional responses involving stimulation of transmembrane signal transduction pathways. We have previously shown that the hormone activates the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2 in rat intestinal cells. In the present study, we have demonstrated that 1alpha,25(OH)(2)D(3) also induces the phosphorylation and activation of p38 MAPK in these cells. The hormone effects were time and dose-dependent, with maximal stimulation at 2min (+3-fold) and 1nM. 1alpha,25(OH)(2)D(3)-dependent p38 phosphorylation was suppressed by SB 203580, a selective inhibitor of p38 MAPK. Ca(2+) chelation with EGTA, inhibition of the c-Src-tyrosine kinase family with PP1 or protein kinase A (PKA) with Rp-cAMP, attenuated hormone activation of p38 MAPK. The physiological significance of 1alpha,25(OH)(2)D(3)-dependent activation of ERK1/2 and p38 MAP kinases was addressed by monitoring c-Fos expression. Incubation of intestinal cells with the hormone was followed by a rapid induction of c-Fos expression which was blocked by SB 203580 and partially suppressed by the ERK1/2 inhibitor PD 98059. Our results suggest that 1alpha,25(OH)(2)D(3) activates p38 MAPK, involving Ca(2+), c-Src and PKA as upstream regulators, and that p38 MAPK has a central role in hormone-induction of the oncoprotein c-Fos in rat intestinal cells.

Phosphorylation of the homeotic tumor suppressor Cdx2 mediates its ubiquitin-dependent proteasome degradation

The Caudal-related homeodomain transcription factor Cdx2 plays a key role in intestinal cell fate determination. Reduction of Cdx2 expression is a feature of many human colon carcinomas and inactivation of one cdx2 allele facilitates the development of invasive adenocarcinoma in the murine colon. Here, we investigated the post-translational regulation of Cdx2. We showed that various forms of Cdx2 coexist in the intestine and colon cancer cell lines, some of them being phosphorylated forms. We found that cyclin-dependent kinase 2 phosphorylated Cdx2 in vitro and in vivo. Using site-specific mutagenesis, we identified serine 281 as a new key residue for Cdx2 phosphorylation. Intriguingly, serine 281 belongs to a conserved motif of four evenly spaced serines (the 4S motif) similar to the one controlling beta-catenin degradation by the proteasome pathway. A nonphosphorylated mutant Cdx2 lacking the 4S motif (4S>A) exhibited reduced polyubiquitination upon proteasome inhibition and increased stability compared to wild-type Cdx2. In addition, we found that this mutant was less efficient to suppress colony formation than wild-type Cdx2. Thus, our data highlight a novel post-translational mechanism controlling Cdx2 degradation via phosphorylation and polyubiquitination, which may be of importance for intestinal development and cancer.

Regeneration of the rat neonatal intestine in transplantation

OBJECTIVE

Based on development of stem cell technology, newborn tissue, even undergoing cryopreservation, possesses promising potential as a donor source in the field of organ transplantation. However, the precise regeneration processes remains unclear. This study was designed to investigate the regenerative potential of newborn intestine with or without cryopreservation in the transplantation.

METHODS

Newborn rat intestines with or without cryopreservation were transplanted subcutaneously into the syngeneic host, and specimens were evaluated by histology, multiple immunostaining, and comprehensive gene expression analysis.

RESULTS

We determined that newborn rat intestine possessed regenerative potential in the syngeneic host even after cryopreservation, where angiogenesis was induced early in the submucosa with subsequent maturation in the crypts. Furthermore, newborn intestinal graft could facilitate the survival of maturation-incompetent 10-day-old graft that lacked regenerating activity (P < 0.01, n = 13). Tissue aggregates from the maturation-incompetent graft underwent reconstitution of their histologic configuration in the presence of newborn intestinal aggregates. Comprehensive gene expression analysis showed that 37 genes were preferentially up-regulated, while 19 genes were down-regulated in the regenerating 10-day-old graft (supported by the newborn graft).

CONCLUSIONS

Regeneration of newborn intestine is implicated in neo-angiogenesis in the host, and the newborn intestinal graft is capable of mediating the survival of the maturation-incompetent 10-day-old graft. Notwithstanding ethical and legal limitations in the clinic, these results may provide new insights into the regenerative role of newborn grafts.

Synergy between deacetylase inhibitors and IL-1beta in activation of the serum amyloid A2 gene promoter

Butyrate (NaBu) regulates intestinal inflammatory gene expression in part through inhibition of deacetylase activity, but the exact mechanisms involved remain to be determined. In this study, we showed by Northern blot a synergistic induction of the acute phase protein gene SAA2 with a combination of deacetylase inhibitors (Trichostatin A or NaBu) and IL-1beta in the colon carcinoma cell line Caco-2. While the NF-kappa B DNA-binding site was essential for SAA2 regulation by IL-1beta and deacetylase inhibitors, the C/EBP DNA-binding site modulated SAA2 expression levels, as assessed by transient transfection assays and mutagenesis studies. NaBu was sufficient to induce SAA2 expression after transient treatment with IL-1beta and, conversely, IL-1beta induced SAA2 after transient treatment with NaBu. These data suggest that pretreatment with either NaBu or IL-1beta predisposes the SAA2 promoter to further stimulation. Indeed, both NaBu and IL-1beta led to increased recruitment of NF-kappa B p65, C/EBPbeta, and C/EBP delta, and decreased NF-kappa B p50 and C/EBP alpha DNA-binding to the proximal SAA2 promoter, as assessed by chromatin immunoprecipitation assays. Interestingly, while IL-1beta, in contrast to NaBu, induced histone H4 acetylation, addition of IL-1beta and NaBu increased histone H4 acetylation and both C/EBPbeta and NF-kappa B p65 DNA-binding. Therefore, these results suggest that NaBu and IL- 1beta mediate SAA2 synergistic induction by establishing and maintaining similar and complementary chromatin modifications and transcription factor recruitment as well. In addition to global effects, NaBu specifically regulate gene expression, as exemplified by SAA2.

IL-1 beta-dependent regulation of C/EBP delta transcriptional activity

We have previously shown that the transcription factor C/EBP delta is involved in the intestinal inflammatory response. C/EBP delta regulates several inflammatory response genes, such as haptoglobin, in the rat intestinal epithelial cell line IEC-6 in response to IL-1. However, the different C/EBP delta domains involved in IL-1 beta-mediated transcriptional activation and the kinases implicated have not been properly defined. To address this, we determined the role of the p38 MAP kinase in the regulation of C/EBP delta transcriptional activity. The IL-1-dependent induction of the acute phase protein gene haptoglobin in IEC-6 cells was decreased in response to the p38 MAP kinase inhibitor SB203580, as determined by Northern blot. Transcriptional activity of C/EBP delta was repressed by the specific inhibitor of the p38 MAP kinase, as assessed by transient transfection assays. Mutagenesis studies and transient transfection assays revealed an important domain for transcriptional activation between amino acids 70 and 108. This domain overlapped with a docking site for the p38 MAP kinase, between amino acids 75 and 85, necessary to insure C/EBP delta phosphorylation. Deletion of this domain led to a decrease in basal transcriptional activity of C/EBP delta and in p300-dependent transactivation, as assessed by transient transfection assays, and in IL-1-dependent haptoglobin induction. This unusual arrangement of a kinase docking site within a transactivation domain may functionally be important for the regulation of C/EBP delta transcriptional activity.

MAP kinases as structural adaptors and enzymatic activators in transcription complexes

Mitogen-activated protein kinase (MAPK) pathways regulate eukaryotic gene expression in response to extracellular stimuli. MAPKs and their downstream kinases phosphorylate transcription factors, co-regulators and chromatin proteins to initiate transcriptional changes. However, the spatial context in which the MAPKs operate in transcription complexes is poorly understood. Recent findings in budding yeast show that MAPKs can form integral components of transcription complexes and have novel structural functions in addition to phosphorylating local substrates. Hog1p MAPK is stably recruited to target promoters by specific transcription factors in response to osmotic stress, and acts as both a structural adaptor and enzymatic activator driving the assembly and activation of the transcription complex. We review the evidence that suggests a similar bifunctional role for MAPKs in mammalian transcription complexes.

Differential growth factor induction and modulation of human gastric epithelial regeneration

While several autocrine/paracrine growth factors (GFs) can all stimulate epithelial regeneration in experimentally wounded primary gastric cultures, clinical relevance for their non-redundant cooperative actions in human gastric ulcer healing is suggested by the sequential pattern of GF gene induction in vivo. Using new HGE cell lines able to form a coherent monolayer with tight junctions as well as using primary human gastric epithelial cultures, we show that EGF, TGFalpha, HGF and IGFs accelerate epithelial restitution upon wounding, independently of the TGFbeta pathway (as opposed to intestinal cells). However, they differently modulate cell behavior: TGFalpha exerts strong effects (even more than EGF) on cytoplasmic spreading and non-oriented protruding activity of bordering cells whereas HGF preferentially coordinates single lamella formation, cell elongation and migration into the wound. IGF-I and IGF-II rather induce the alignment of bordering cells and maintain a compact monolayer front. The number of mitotic cells maximally increases with EGF, followed by TGFalpha and IGF-I,-II. The current study demonstrates that GFs differentially regulate the regeneration of human gastric epithelial cells through specific modulation of cell shape adaptation, migration and proliferation, further stressing that a coordination of GF activities would be necessary for the normal progression of post-wounding epithelial repair.

Cdk2-dependent phosphorylation of homeobox transcription factor CDX2 regulates its nuclear translocation and proteasome-mediated degradation in human intestinal epithelial cells

By having demonstrated previously that p27(Kip1), a potent inhibitor of G(1) cyclin-cyclin-dependent kinases complexes, increases markedly during intestinal epithelial cell differentiation, we examined the effect of p27(Kip1) on the activity of the transcription factor CDX2. The present results revealed the following. 1) p27(Kip1) interacts with the CDX2 transcription factor. 2) In contrast to CDX2 mRNA levels, CDX2 protein expression levels significantly increased as soon as Caco-2/15 cells reached confluence, slowed their proliferation, and began their differentiation. The mechanism of CDX2 regulation is primarily related to protein stability, because inhibition of proteasome activity increased CDX2 levels. The half-life of CDX2 protein was significantly enhanced in differentiated versus undifferentiated proliferative intestinal epithelial cells. 3) Cdk2 interacted with CDX2 and phosphorylated CDX2, as determined by pull-down glutathione S-transferase and immunoprecipitation experiments with proliferating undifferentiated Caco-2/15 cell extracts. 4) Treatment of Caco-2/15 cells with MG132 (a proteasome inhibitor) and (R)-roscovitine (a specific Cdk2 inhibitor) induced an increase in CDX2 protein levels. 5) Conversely, ectopic expression of Cdk2 resulted in decreased expression of CDX2 protein. 6) Of note, treatment of proliferative Caco-2/15 cells with (R)-roscovitine or leptomycin (an inhibitor of nuclear export through CRM1) led to an accumulation of CDX2 into the nucleus. These data suggest that CDX2 undergoes CRM1-dependent nuclear export and cytoplasmic degradation in cells in which Cdk2 is activated, such as in proliferative intestinal epithelial cells. The targeted degradation of CDX2 following its phosphorylation by Cdk2 identifies a new mechanism through which CDX2 activity can be regulated in coordination with the cell cycle machinery.

Adult-type hypolactasia and regulation of lactase expression

A common genetically determined polymorphism in the human population leads to two distinct phenotypes in adults, lactase persistence and adult-type hypolactasia (lactase non-persistence). All healthy newborn children express high levels of lactase and are able to digest large quantities of lactose, the main carbohydrate in milk. Individuals with adult-type hypolactasia lose their lactase expression before adulthood and consequently often become lactose intolerant with associated digestive problems (e.g. diarrhoea). In contrast, lactase persistent individuals have a lifelong lactase expression and are able to digest lactose as adults. Lactase persistence can be regarded as the mutant phenotype since other mammals down-regulate their lactase expression after weaning (the postweaning decline). This phenomenon does not occur in lactase persistent individuals. The regulation of lactase expression is mainly transcriptional and it is well established that adult-type hypolactasia is inherited in an autosomal recessive manner, whereas persistence is dominant. The recent findings of single nucleotide polymorphisms associated with lactase persistence have made it possible to study the potential mechanisms underlying adult-type hypolactasia. This work has led to the identification of gene-regulatory sequences located far from the lactase gene (LCT). The present review describes the recent advances in the understanding of the regulation of lactase expression and the possible mechanisms behind adult-type hypolactasia.

Control of differentiation-induced calbindin-D9k gene expression in Caco-2 cells by cdx-2 and HNF-1alpha

Calbindin D9k (CaBP) is critical for intestinal calcium absorption; its in vivo expression is restricted to differentiated enterocytes of the small intestine. Our goal was to identify factors controlling the transcriptional regulation of this gene in the human intestine. Both the natural gene and a 4600-bp promoter construct were strongly regulated by differentiation (>100-fold) but not by treatment with 1,25(OH)2 vitamin D (<2-fold) in the Caco-2 clone TC7. Deletion-mutation studies revealed that conserved promoter sequences for cdx-2 (at -3158 bp) and hepatocyte nuclear factor (HNF)-1 (at -3131 and at -98 bp) combined to control CaBP expression during differentiation. Other putative response elements were not important for CaBP regulation in TC7 cells (CCAAT enhancer binding protein, pancreatic duodenal homebox-1 (pdx-1), a proximal cdx-2 element). Mutation of the distal HNF-1 site had the greatest impact on CaBP gene expression through disruption of HNF-1alpha binding; both basal and differentiation-mediated CaBP expression was reduced by 80%. In contrast, mutation of the distal cdx-2 element reduced only basal CaBP expression. Whereas a 60% reduction of CaBP mRNA in the duodenum of HNF-1alpha null mice confirmed the physiological importance of HNF-1alpha for CaBP gene regulation, additional studies showed that maximal CaBP expression requires the presence of both HNF-1alpha and cdx-2. Our data suggest that cdx-2 is a permissive factor that influences basal CaBP expression in enterocytes and that HNF-1alpha modulates CaBP gene expression during cellular differentiation.

The nucleocytoplasmic shuttling of E2F4 is involved in the regulation of human intestinal epithelial cell proliferation and differentiation

The specific mechanisms controlling the transition from proliferation to terminal differentiation in human intestinal epithelial cells (HIEC) remain largely undefined. Herein, we analyzed the expression and localization of Rb and E2F proteins in well-established normal intestinal epithelial cell models which allow for the re-enactment of the crypt-villus axis in vitro as well as in intact epithelium and in colon cancer cells. We report that (1) expression of E2F1 is down-regulated while E2F4 protein is sequestered in the cytoplasm during G(0) arrest associated with serum deprivation, confluency, and terminal differentiation of intestinal cells; (2) concurrently, there is an accumulation of the hypophosphorylated form of the pocket proteins into the nucleus with an increased association of E2F4 with pRb and p130; (3) cells which expressed high levels of nuclear E2F4 are all positive for Ki67 staining in human fetal intestine; (4) activation of HIEC crypt cells by growth factors leads to an increase in the nuclear localization of E2F4 which may be attributable to a decrease in the serine/threonine phosphorylation of this transcription factor; (5) inhibition of p38 MAP kinase with alpha/beta inhibitor SB203580 induces E2F4 translocation into the nucleus and its transcriptional activity. In conclusion, our data suggest a key role for E2F4 in proliferation of human intestinal crypt cells and that its cytoplasmic retention as well as its sequestration by Rb proteins may represent a critical step in initiating cell-cycle exit.

Down-regulation of MEK/ERK signaling by E-cadherin-dependent PI3K/Akt pathway in differentiating intestinal epithelial cells

In vitro experiments have shown that the establishment of cell-cell contacts in intestinal epithelial cell cultures is a critical step in initiating ERK inhibition, cell cycle arrest, and induction of the differentiation process. Herein, we determined the mechanisms through which E-cadherin-mediated cell-cell contacts modulate the ERK pathway in intestinal epithelial cells. We report that: (1) removal of calcium from the culture medium of newly confluent Caco-2/15 cells (30 min, 4 mM EGTA) results in the disruption of both adherens and tight junctions and clearly decreases Akt phosphorylation while increasing MEK and ERK activities. Akt, MEK, and ERK activation levels return to control levels 60 min after calcium restoration; (2) the use of E-cadherin blocking antibodies efficiently prevents Akt phosphorylation and MEK-ERK inhibition after 70 min of calcium restoration; (3) using the PI3K inhibitor LY294002 (15 microM) in calcium switch experiments, we demonstrate that the assembly of adherens junctions activates Akt activity and triggers the inhibition of ERK1/2 activities in a PI3K-dependent manner; (4) adenoviral infection of confluent Caco-2/15 cells with a constitutively active mutant of Akt1 strongly represses ERK1/2 activities; (5) inhibition of PI3K abolishes Akt activity but leads to a rapid and sustained activation of the MEK-ERK1/2 in confluent differentiating Caco-2/15 cells, but not in undifferentiated growing Caco-2/15 cells. Our data suggest that E-cadherin engagement leads to MEK/ERK inhibition in a PI3K/Akt-dependent pathway. This mechanism may account for the role of E-cadherin in proliferation/differentiation transition along the crypt-villus axis of the human intestinal epithelium.

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Ectopic expression of the homeobox gene Cdx2 is the transforming event in a mouse model of t(12;13)(p13;q12) acute myeloid leukemia

Creation of fusion genes by balanced chromosomal translocations is one of the hallmarks of acute myeloid leukemia (AML) and is considered one of the key leukemogenic events in this disease. In t(12;13)(p13;q12) AML, ectopic expression of the homeobox gene CDX2 was detected in addition to expression of the ETV6-CDX2 fusion gene, generated by the chromosomal translocation. Here we show in a murine model of t(12;13)(p13;q12) AML that myeloid leukemogenesis is induced by the ectopic expression of CDX2 and not by the ETV6-CDX2 chimeric gene. Mice transplanted with bone marrow cells retrovirally engineered to express Cdx2 rapidly succumbed to fatal and transplantable AML. The transforming capacity of Cdx2 depended on an intact homeodomain and the N-terminal transactivation domain. Transplantation of bone marrow cells expressing ETV6-CDX2 failed to induce leukemia. Furthermore, coexpression of ETV6-CDX2 and Cdx2 in bone marrow cells did not accelerate the course of disease in transplanted mice compared to Cdx2 alone. These data demonstrate that activation of a protooncogene by a balanced chromosomal translocation can be the pivotal leukemogenic event in AML, characterized by the expression of a leukemia-specific fusion gene. Furthermore, these findings link protooncogene activation to myeloid leukemogenesis, an oncogenic mechanism so far associated mainly with lymphoid leukemias and lymphomas.

Human homolog of disc-large is required for adherens junction assembly and differentiation of human intestinal epithelial cells

We and others have shown that phosphatidylinositol 3-kinase (PI3K) is recruited to and activated by E-cadherin engagement. This PI3K activation is essential for adherens junction integrity and intestinal epithelial cell differentiation. Here we provide evidence that hDlg, the homolog of disc-large tumor suppressor, is another key regulator of adherens junction integrity and differentiation in mammalian epithelial cells. We report the following. 1) hDlg co-localizes with E-cadherin, but not with ZO-1, at the sites of cell-cell contact in intestinal epithelial cells. 2) Reduction of hDlg expression levels by RNA(i) in intestinal cells not only severely alters adherens junction integrity but also prevents the recruitment of p85/PI3K to E-cadherin-mediated cell-cell contact and inhibits sucrase-isomaltase gene expression. 3) PI3K and hDlg are associated with E-cadherin in a common macromolecular complex in living differentiating intestinal cells. 4) This interaction requires the association of hDlg with E-cadherin and with Src homology domain 2 domains of the p85/PI3K subunit. 5) Phosphorylation of hDlg on serine and threonine residues prevents its interaction with the p85 Src homology domain 2 in subconfluent cells, whereas phosphorylation of hDlg on tyrosine residues is essential. We conclude that hDlg may be a determinant in E-cadherin-mediated adhesion and signaling in mammalian epithelial cells.

Transcriptional regulation by the MAP kinase signaling cascades

A major function of the mitogen-activated protein kinase (MAPK) pathways is to control eukaryotic gene expression programmes in response to extracellular signals. MAPKs directly control gene expression by phosphorylating transcription factors. However, it is becoming clear that transcriptional regulation in response to MAPK signaling is more complex. MAPKs can also target coactivators and corepressors and affect nucleosomal structure by inducing histone modifications. Furthermore, multiple inputs into individual promoters can be elicited by MAPKs by targeting different components of the same coregulatory complex or by triggering different events on the same transcription factor. "Postgenomic approaches" are beginning to impact on our understanding of these gene regulatory networks. In this review, we summarise the current knowledge of MAPK-mediated gene regulation, and focus on how complexities in signaling outcomes are achieved and how this relates to physiological processes.