Intestinal alkaline phosphatase deficiency increases the risk of diabetes

INTRODUCTION

Our previous case-control study demonstrated that a high level of intestinal alkaline phosphatase (IAP), an endotoxin-detoxifying anti-inflammatory enzyme secreted by villus-associated enterocytes and excreted with stool, plays a protective role against type 2 diabetes mellitus (T2DM) irrespective of obesity. In the current study, we investigated the long-term effect of IAP deficiency (IAPD) on the pathogenesis of T2DM.

RESEARCH DESIGN AND METHODS

A healthy cohort of participants without diabetes (30-60 years old), comprising 188 without IAPD (IAP level: ≥65 U/g stool) and 386 with IAPD (IAP level: <65 U/g stool), were followed up for 5 years. We measured stool IAP (STAP) and fasting plasma glucose, and calculated the risk ratio (RR) using log-binomial regression model.

RESULTS

T2DM incidence rates were 8.0%, 11.7%, 25.6%, and 33.3% in participants with 'persistent no IAPD' (IAP level: always ≥65 U/g stool), 'remittent IAPD' (IAP level: increased from <65 U/g stool to ≥65 U/g stool), 'persistent IAPD' (IAP level: always <65 U/g stool), and 'incident IAPD' (IAP level: decreased from ≥65 U/g stool to <65 U/g stool), respectively. Compared with 'persistent no IAPD' the risk of developing T2DM with 'incident IAPD' was 270% higher (RR: 3.69 (95% CI 1.76 to 7.71), χ² p<0.001). With 'persistent IAPD' the risk was 230% higher (RR: 3.27 (95% CI 1.64 to 6.50), p<0.001). 'Remittent IAPD' showed insignificant risk (RR: 2.24 (95% CI 0.99 to 5.11), p=0.0541). Sensitivity analyses of persistent IAP levels revealed that, compared with participants of the highest persistent IAP pentile (always >115 U/g stool), the rate of increase of fasting glycemia was double and the risk of developing T2DM was 1280% higher (RR: 13.80 (95% CI 1.87 to 101.3), p=0.0099) in participants of the lowest persistent IAP pentile (always <15 U/g stool). A diabetes pathogenesis model is presented.

CONCLUSIONS

IAPD increases the risk of developing T2DM, and regular STAP tests would predict individual vulnerability to T2DM. Oral IAP supplementation might prevent T2DM.

Phosphate Groups in the Lipid A Moiety Determine the Effects of LPS on Hepatic Stellate Cells: A Role for LPS-Dephosphorylating Activity in Liver Fibrosis

Alkaline phosphatase (AP) activity is highly upregulated in plasma during liver diseases. Previously, we demonstrated that AP is able to detoxify lipopolysaccharide (LPS) by dephosphorylating its lipid A moiety. Because a role of gut-derived LPS in liver fibrogenesis has become evident, we now examined the relevance of phosphate groups in the lipid A moiety in this process. The effects of mono-phosphoryl and di-phosphoryl lipid A (MPLA and DPLA, respectively) were studied in vitro and LPS-dephosphorylating activity was studied in normal and fibrotic mouse and human livers. The effects of intestinal AP were studied in mice with CCL4-induced liver fibrosis. DPLA strongly stimulated fibrogenic and inflammatory activities in primary rat hepatic stellate cells (rHSCs) and RAW264.7 macrophages with similar potency as full length LPS. However, MPLA did not affect any of the parameters. LPS-dephosphorylating activity was found in mouse and human livers and was strongly increased during fibrogenesis. Treatment of fibrotic mice with intravenous intestinal-AP significantly attenuated intrahepatic desmin+- and αSMA+ -HSC and CD68+- macrophage accumulation. In conclusion, the lack of biological activity of MPLA, contrasting with the profound activities of DPLA, shows the relevance of LPS-dephosphorylating activity. The upregulation of LPS-dephosphorylating activity in fibrotic livers and the protective effects of exogenous AP during fibrogenesis indicate an important physiological role of intestinal-derived AP during liver fibrosis.

Intestinal alkaline phosphatase targets the gut barrier to prevent aging

Gut barrier dysfunction and gut-derived chronic inflammation play crucial roles in human aging. The gut brush border enzyme intestinal alkaline phosphatase (IAP) functions to inhibit inflammatory mediators and also appears to be an important positive regulator of gut barrier function and microbial homeostasis. We hypothesized that this enzyme could play a critical role in regulating the aging process. We tested the role of several IAP functions for prevention of age-dependent alterations in intestinal homeostasis by employing different loss-of-function and supplementation approaches. In mice, there is an age-related increase in gut permeability that is accompanied by increases in gut-derived portal venous and systemic inflammation. All these phenotypes were significantly more pronounced in IAP-deficient animals. Oral IAP supplementation significantly decreased age-related gut permeability and gut-derived systemic inflammation, resulted in less frailty, and extended lifespan. Furthermore, IAP supplementation was associated with preserving the homeostasis of gut microbiota during aging. These effects of IAP were also evident in a second model system, Drosophilae melanogaster. IAP appears to preserve intestinal homeostasis in aging by targeting crucial intestinal alterations, including gut barrier dysfunction, dysbiosis, and endotoxemia. Oral IAP supplementation may represent a novel therapy to counteract the chronic inflammatory state leading to frailty and age-related diseases in humans.

Intestinal Alkaline Phosphatase Attenuates Alcohol-Induced Hepatosteatosis in Mice

BACKGROUND AND AIMS

Bacterially derived factors from the gut play a major role in the activation of inflammatory pathways in the liver and in the pathogenesis of alcoholic liver disease. The intestinal brush-border enzyme intestinal alkaline phosphatase (IAP) detoxifies a variety of bacterial pro-inflammatory factors and also functions to preserve gut barrier function. The aim of this study was to investigate whether oral IAP supplementation could protect against alcohol-induced liver disease.

METHODS

Mice underwent acute binge or chronic ethanol exposure to induce alcoholic liver injury and steatosis ± IAP supplementation. Liver tissue was assessed for biochemical, inflammatory, and histopathological changes. An ex vivo co-culture system was used to examine the effects of alcohol and IAP treatment in regard to the activation of hepatic stellate cells and their role in the development of alcoholic liver disease.

RESULTS

Pretreatment with IAP resulted in significantly lower serum alanine aminotransferase compared to the ethanol alone group in the acute binge model. IAP treatment attenuated the development of alcohol-induced fatty liver, lowered hepatic pro-inflammatory cytokine and serum LPS levels, and prevented alcohol-induced gut barrier dysfunction. Finally, IAP ameliorated the activation of hepatic stellate cells and prevented their lipogenic effect on hepatocytes.

CONCLUSIONS

IAP treatment protected mice from alcohol-induced hepatotoxicity and steatosis. Oral IAP supplementation could represent a novel therapy to prevent alcoholic-related liver disease in humans.

A High Level of Intestinal Alkaline Phosphatase Is Protective Against Type 2 Diabetes Mellitus Irrespective of Obesity

Mice deficient in intestinal alkaline phosphatase (IAP) develop type 2 diabetes mellitus (T2DM). We hypothesized that a high level of IAP might be protective against T2DM in humans. We determined IAP levels in the stools of 202 diabetic patients and 445 healthy non-diabetic control people. We found that compared to controls, T2DM patients have approx. 50% less IAP (mean +/- SEM: 67.4 +/- 3.2 vs 35.3 +/- 2.5 U/g stool, respectively; p < 0.000001) indicating a protective role of IAP against T2DM. Multiple logistic regression analyses showed an independent association between the IAP level and diabetes status. With each 25 U/g decrease in stool IAP, there is a 35% increased risk of diabetes. The study revealed that obese people with high IAP (approx. 65 U/g stool) do not develop T2DM. Approx. 65% of the healthy population have < 65.0 U/g stool IAP, and predictably, these people might have 'the incipient metabolic syndrome', including 'incipient diabetes', and might develop T2DM and other metabolic disorders in the near future. In conclusion, high IAP levels appear to be protective against diabetes irrespective of obesity, and a 'temporal IAP profile' might be a valuable tool for predicting 'the incipient metabolic syndrome', including 'incipient diabetes'.

The intestinal epithelial cell differentiation marker intestinal alkaline phosphatase (ALPi) is selectively induced by histone deacetylase inhibitors (HDACi) in colon cancer cells in a Kruppel-like factor 5 (KLF5)-dependent manner

The histone deacetylase inhibitor (HDACi) sodium butyrate promotes differentiation of colon cancer cells as evidenced by induced expression and enzyme activity of the differentiation marker intestinal alkaline phosphatase (ALPi). Screening of a panel of 33 colon cancer cell lines identified cell lines sensitive (42%) and resistant (58%) to butyrate induction of ALP activity. This differential sensitivity was similarly evident following treatment with the structurally distinct HDACi, MS-275. Resistant cell lines were significantly enriched for those harboring the CpG island methylator phenotype (p = 0.036, Chi square test), and resistant cell lines harbored methylation of the ALPi promoter, particularly of a CpG site within a critical KLF/Sp regulatory element required for butyrate induction of ALPi promoter activity. However, butyrate induction of an exogenous ALPi promoter-reporter paralleled up-regulation of endogenous ALPi expression across the cell lines, suggesting the presence or absence of a key transcriptional regulator is the major determinant of ALPi induction. Through microarray profiling of sensitive and resistant cell lines, we identified KLF5 to be both basally more highly expressed as well as preferentially induced by butyrate in sensitive cell lines. KLF5 overexpression induced ALPi promoter-reporter activity in resistant cell lines, KLF5 knockdown attenuated butyrate induction of ALPi expression in sensitive lines, and butyrate selectively enhanced KLF5 binding to the ALPi promoter in sensitive cells. These findings demonstrate that butyrate induction of the cell differentiation marker ALPi is mediated through KLF5 and identifies subsets of colon cancer cell lines responsive and refractory to this effect.

Intestinal alkaline phosphatase promotes gut bacterial growth by reducing the concentration of luminal nucleotide triphosphates

The intestinal microbiota plays a pivotal role in maintaining human health and well-being. Previously, we have shown that mice deficient in the brush-border enzyme intestinal alkaline phosphatase (IAP) suffer from dysbiosis and that oral IAP supplementation normalizes the gut flora. Here we aimed to decipher the molecular mechanism by which IAP promotes bacterial growth. We used an isolated mouse intestinal loop model to directly examine the effect of exogenous IAP on the growth of specific intestinal bacterial species. We studied the effects of various IAP targets on the growth of stool aerobic and anaerobic bacteria as well as on a few specific gut organisms. We determined the effects of ATP and other nucleotides on bacterial growth. Furthermore, we examined the effects of IAP on reversing the inhibitory effects of nucleotides on bacterial growth. We have confirmed that local IAP bioactivity creates a luminal environment that promotes the growth of a wide range of commensal organisms. IAP promotes the growth of stool aerobic and anaerobic bacteria and appears to exert its growth promoting effects by inactivating (dephosphorylating) luminal ATP and other luminal nucleotide triphosphates. We observed that compared with wild-type mice, IAP-knockout mice have more ATP in their luminal contents, and exogenous IAP can reverse the ATP-mediated inhibition of bacterial growth in the isolated intestinal loop. In conclusion, IAP appears to promote the growth of intestinal commensal bacteria by inhibiting the concentration of luminal nucleotide triphosphates.

Intestinal alkaline phosphatase prevents metabolic syndrome in mice

Metabolic syndrome comprises a cluster of related disorders that includes obesity, glucose intolerance, insulin resistance, dyslipidemia, and fatty liver. Recently, gut-derived chronic endotoxemia has been identified as a primary mediator for triggering the low-grade inflammation responsible for the development of metabolic syndrome. In the present study we examined the role of the small intestinal brush-border enzyme, intestinal alkaline phosphatase (IAP), in preventing a high-fat-diet-induced metabolic syndrome in mice. We found that both endogenous and orally supplemented IAP inhibits absorption of endotoxin (lipopolysaccharides) that occurs with dietary fat, and oral IAP supplementation prevents as well as reverses metabolic syndrome. Furthermore, IAP supplementation improves the lipid profile in mice fed a standard, low-fat chow diet. These results point to a potentially unique therapy against metabolic syndrome in at-risk humans.

Intestinal alkaline phosphatase inhibits the proinflammatory nucleotide uridine diphosphate

Uridine diphosphate (UDP) is a proinflammatory nucleotide implicated in inflammatory bowel disease. Intestinal alkaline phosphatase (IAP) is a gut mucosal defense factor capable of inhibiting intestinal inflammation. We used the malachite green assay to show that IAP dephosphorylates UDP. To study the anti-inflammatory effect of IAP, UDP or other proinflammatory ligands (LPS, flagellin, Pam3Cys, or TNF-α) in the presence or absence of IAP were applied to cell cultures, and IL-8 was measured. UDP caused dose-dependent increase in IL-8 release by immune cells and two gut epithelial cell lines, and IAP treatment abrogated IL-8 release. Costimulation with UDP and other inflammatory ligands resulted in a synergistic increase in IL-8 release, which was prevented by IAP treatment. In vivo, UDP in the presence or absence of IAP was instilled into a small intestinal loop model in wild-type and IAP-knockout mice. Luminal contents were applied to cell culture, and cytokine levels were measured in culture supernatant and intestinal tissue. UDP-treated luminal contents induced more inflammation on target cells, with a greater inflammatory response to contents from IAP-KO mice treated with UDP than from WT mice. Additionally, UDP treatment increased TNF-α levels in intestinal tissue of IAP-KO mice, and cotreatment with IAP reduced inflammation to control levels. Taken together, these studies show that IAP prevents inflammation caused by UDP alone and in combination with other ligands, and the anti-inflammatory effect of IAP against UDP persists in mouse small intestine. The benefits of IAP in intestinal disease may be partly due to inhibition of the proinflammatory activity of UDP.

A role for intestinal alkaline phosphatase in the maintenance of local gut immunity

BACKGROUND AND AIMS

Intestinal alkaline phosphatase (IAP) is a gut mucosal defense factor known to dephosphorylate lipopolysaccharide (LPS); however, the role of IAP in the gut response to luminal bacteria remains poorly defined. We investigated immune responses of wild-type (WT) and IAP-knockout (IAP-KO) mice to LPS and Salmonella typhimurium challenges.

METHODS

Cryostat sectioning and standard indirect immunohistochemical staining for major histocompatibility complex (MHC) class II molecules were performed on liver tissue from WT and IAP-KO mice. WT and IAP-KO mice were orally gavaged with S. typhimurium; bacterial translocation to mesenteric nodes, liver, and spleen was determined by tissue homogenization and plating. In other experiments, WT and IAP-KO mice received intraperitoneal injections of LPS, with subsequent quantification of complete blood counts and serum interleukin (IL)-6 by enzyme-linked immunosorbent assay (ELISA). WT and IAP-KO whole blood were plated and stimulated with LPS and Pam-3-Cys, followed by cytokine assays.

RESULTS

Immunohistologic liver examinations showed increased expression of MHC class II molecules in IAP-KO mice. Following S. typhimurium challenge, WT mice appeared moribund compared with IAP-KO mice, with increased bacterial translocation. WT mice had >50% decrease (P<.005) in platelets and 1.8-fold (P<.05) increased serum IL-6 compared with IAP-KO mice in response to LPS injections. IAP-KO whole-blood stimulation with LPS and Pam-3-Cys resulted in increased IL-6 and tumor necrosis factor (TNF)-alpha secretion compared with WT.

CONCLUSIONS

IAP-KO mice exhibit characteristics consistent with local LPS tolerance. Whole-blood response of IAP-KO mice did not reflect systemic tolerance. These data suggest that IAP is a local immunomodulating factor, perhaps regulating LPS-toll-like receptor 4 (TLR4) interaction between commensal microflora and intestinal epithelium.

Intestinal alkaline phosphatase has beneficial effects in mouse models of chronic colitis

BACKGROUND

The brush border enzyme intestinal alkaline phosphatase (IAP) functions as a gut mucosal defense factor and is protective against dextran sulfate sodium (DSS)-induced acute injury in rats. The present study evaluated the potential therapeutic role for orally administered calf IAP (cIAP) in two independent mouse models of chronic colitis: 1) DSS-induced chronic colitis, and 2) chronic spontaneous colitis in Wiskott-Aldrich Syndrome protein (WASP)-deficient (knockout) mice that is accelerated by irradiation.

METHODS

The wildtype (WT) and IAP knockout (IAP-KO) mice received four cycles of 2% DSS ad libitum for 7 days. Each cycle was followed by a 7-day DSS-free interval during which mice received either cIAP or vehicle in the drinking water. The WASP-KO mice received either vehicle or cIAP for 6 weeks beginning on the day of irradiation.

RESULTS

Microscopic colitis scores of DSS-treated IAP-KO mice were higher than DSS-treated WT mice (52±3.8 versus 28.8±6.6, respectively, P<0.0001). cIAP treatment attenuated the disease in both groups (KO=30.7±6.01, WT=18.7±5.0, P<0.05). In irradiated WASP-KO mice cIAP also attenuated colitis compared to control groups (3.3±0.52 versus 6.2±0.34, respectively, P<0.001). Tissue myeloperoxidase activity and proinflammatory cytokines were significantly decreased by cIAP treatment.

CONCLUSIONS

Endogenous IAP appears to play a role in protecting the host against chronic colitis. Orally administered cIAP exerts a protective effect in two independent mouse models of chronic colitis and may represent a novel therapy for human IBD.

Intestinal alkaline phosphatase preserves the normal homeostasis of gut microbiota

BACKGROUND AND AIMS

The intestinal microbiota plays a critical role in maintaining human health; however, the mechanisms governing the normal homeostatic number and composition of these microbes are largely unknown. Previously it was shown that intestinal alkaline phosphatase (IAP), a small intestinal brush border enzyme, functions as a gut mucosal defence factor limiting the translocation of gut bacteria to mesenteric lymph nodes. In this study the role of IAP in the preservation of the normal homeostasis of the gut microbiota was investigated.

METHODS

Bacterial culture was performed in aerobic and anaerobic conditions to quantify the number of bacteria in the stools of wild-type (WT) and IAP knockout (IAP-KO) C57BL/6 mice. Terminal restriction fragment length polymorphism, phylogenetic analyses and quantitative real-time PCR of subphylum-specific bacterial 16S rRNA genes were used to determine the compositional profiles of microbiotas. Oral supplementation of calf IAP (cIAP) was used to determine its effects on the recovery of commensal gut microbiota after antibiotic treatment and also on the colonisation of pathogenic bacteria.

RESULTS

IAP-KO mice had dramatically fewer and also different types of aerobic and anaerobic microbes in their stools compared with WT mice. Oral supplementation of IAP favoured the growth of commensal bacteria, enhanced restoration of gut microbiota lost due to antibiotic treatment and inhibited the growth of a pathogenic bacterium (Salmonella typhimurium).

CONCLUSIONS

IAP is involved in the maintenance of normal gut microbial homeostasis and may have therapeutic potential against dysbiosis and pathogenic infections.

Identification of specific targets for the gut mucosal defense factor intestinal alkaline phosphatase

Intestinal alkaline phosphatase (IAP) is a small intestinal brush border enzyme that has been shown to function as a gut mucosal defense factor, but its precise mechanism of action remains unclear. We investigated the effects of IAP on specific bacteria and bacterial components to determine its molecular targets. Purulent fluid from a cecal ligation and puncture model, specific live and heat-killed bacteria (Escherichia coli, Salmonella typhimurium, and Listeria monocytogenes), and a variety of proinflammatory ligands (LPS, CpG DNA, Pam-3-Cys, flagellin, and TNF) were incubated with or without calf IAP (cIAP). Phosphate release was determined by using a malachite green assay. The various fluids were applied to target cells (THP-1, parent HT-29, and IAP-expressing HT-29 cells) and IL-8 secretion measured by ELISA. cIAP inhibited IL-8 induction by purulent fluid in THP-1 cells by >35% (P < 0.005). HT29-IAP cells had a reduced IL-8 response specifically to gram-negative bacteria; >90% reduction compared with parent cells (P < 0.005). cIAP had no effect on live bacteria but attenuated IL-8 induction by heat-killed bacteria by >40% (P < 0.005). cIAP exposure to LPS and CpG DNA caused phosphate release and reduced IL-8 in cell culture by >50% (P < 0.005). Flagellin exposure to cIAP also resulted in reduced IL-8 secretion by >40% (P < 0.005). In contrast, cIAP had no effect on TNF or Pam-3-Cys. The mechanism of IAP action appears to be through dephosphorylation of specific bacterial components, including LPS, CpG DNA, and flagellin, and not on live bacteria themselves. IAP likely targets these bacterially derived molecules in its role as a gut mucosal defense factor.

The pro-inflammatory cytokines, IL-1beta and TNF-alpha, inhibit intestinal alkaline phosphatase gene expression

High levels of the pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), are present in the gut mucosa of patients suffering form various diseases, most notably inflammatory bowel diseases (IBD). Since the inflammatory milieu can cause important alterations in epithelial cell function, we examined the cytokine effects on the expression of the enterocyte differentiation marker, intestinal alkaline phosphatase (IAP), a protein that detoxifies bacterial lipopolysaccharides (LPS) and limits fat absorption. Sodium butyrate (NaBu), a short-chain fatty acid and histone deacetylase (HDAC) inhibitor, was used to induce IAP expression in HT-29 cells and the cells were also treated +/- the cytokines. Northern blots confirmed IAP induction by NaBu, however, pretreatment (6 h) with either cytokine showed a dose-dependent inhibition of IAP expression. IAP Western analyses and alkaline phosphatase enzyme assays corroborated the Northern data and confirmed that the cytokines inhibit IAP induction. Transient transfections with a reporter plasmid carrying the human IAP promoter showed significant inhibition of NaBu-induced IAP gene activation by the cytokines (100 and 60% inhibition with IL-1beta and TNF-alpha, respectively). Western analyses showed that NaBu induced H4 and H3 histone acetylation, and pretreatment with IL-1beta or TNF-alpha did not change this global acetylation pattern. In contrast, chromatin immunoprecipitation showed that local histone acetylation of the IAP promoter region was specifically inhibited by either cytokine. We conclude that IL-1beta and TNF-alpha inhibit NaBu-induced IAP gene expression, likely by blocking the histone acetylation within its promoter. Cytokine-mediated IAP gene silencing may have important implications for gut epithelial function in the setting of intestinal inflammatory conditions.

Intestinal alkaline phosphatase gene expression is activated by ZBP-89

Intestinal alkaline phosphatase (IAP) is an enterocyte differentiation marker that functions to limit fat absorption. Zinc finger binding protein-89 (ZBP-89) is a Kruppel-type transcription factor that appears to promote a differentiated phenotype in the intestinal epithelium. The purpose of this study was to investigate the regulation of IAP gene expression by ZBP-89. RT-PCR, quantitative real-time RT-PCR, Western blot analyses, and reporter assays were used to determine the regulation of IAP by ZBP-89 in HT-29 and Caco-2 colon cancer cells. ZBP-89 knockdown was achieved by specific short interfering (si)RNA. EMSA and chromatin immunoprecipitation (ChIP) were performed to examine the binding of ZBP-89 to the IAP promoter. The results of RT-PCR, quantitative real-time PCR, and Western blot analyses showed that ZBP-89 was expressed at low levels in Caco-2 and HT-29 cells, whereas IAP was minimally expressed and absent in these cells, respectively. Transfection with ZBP-89 expression plamid increased IAP mRNA and protein levels in both cell lines, whereas knockdown of endogenous ZBP-89 by siRNA reduced basal levels of IAP gene expression in Caco-2 cells. IAP-luciferase reporter assays, EMSA, and ChIP established that ZBP-89 activated the IAP gene through a response element (ZBP-89 response element: 5'-CCTCCTCCC-3') located between -1018 and -1010 bp upstream of the AUG start codon. We conclude that ZBP-89 is a direct transcriptional activator of the enterocyte differentiation marker IAP. These findings are consistent with the role that this transcription factor is thought to play as a tumor suppressor and suggests its possible function in the physiology of fat absorption.

A 'Swinging Cradle' model for in vitro classification of different types of response elements of a nuclear receptor

Nuclear receptors are hormone-activated transcription factors that bind to specific target sequences termed hormone-response element (HRE). A HRE usually consists of two half-sites (5'-AGGTCA-3' consensus sequence) arranged as a direct, everted or inverted repeat with variable spacer region. Assignment of a HRE as a direct, everted or inverted repeat is based on its homology to the consensus half-site, but minor variations can make such an assignment confusing. We hypothesize a 'Swinging Cradle' model for HRE classification, whereby the core HRE functions as the "sitting platform" for the NR, and the extra nucleotides at either end act as the "sling" of the Cradle. We show that in vitro binding of the thyroid hormone receptor and 9-cis retinoic acid receptor heterodimer to an everted repeat TRE follows the 'Swinging Cradle' model, whereas the other TREs do not. We also show that among these TREs, the everted repeat mediates the highest biological activity.

Differential regulation of intestinal alkaline phosphatase gene expression by Cdx1 and Cdx2

We have examined the role that the caudal-related homeobox transcription factors Cdx1 and Cdx2 play in activating the enterocyte differentiation marker gene intestinal alkaline phosphatase (IAP). Human colon cancer Caco-2 cells were transiently transfected with Cdx1 and/or Cdx2, and semiquantitative RT-PCR was used to study the effects on IAP mRNA expression. Transfections with a variety of IAP-luciferase reporter constructs were used to identify a Cdx response element located within the human IAP gene promoter. Protein-DNA interactions were examined by EMSA. Results showed that Cdx1 markedly induced IAP mRNA expression, whereas Cdx2 did not, and, in fact, inhibited the Cdx1 effects. Functional analysis revealed that Cdx1 transactivates (fourfold, P < 0.05) the IAP promoter through a novel Cdx response element (GTTTAGA) located between -2369 and -2375 upstream of the translational start site. EMSA showed that both Cdx1 and Cdx2 could bind to the cis element, but in cotransfection experiments, Cdx2 inhibited the Cdx1 effects by approximately 50%. Thus we have identified a previously unrecognized interaction between two important gut transcription factors, Cdx1 and Cdx2, in the context of IAP gene regulation. Cdx1 activates the IAP gene via a novel cis element, whereas Cdx2 inhibits the Cdx1 effects.

Thyroid hormone positively regulates the enterocyte differentiation marker intestinal alkaline phosphatase gene via an atypical response element

Thyroid hormone (T3) is a critical regulator of intestinal epithelial development and homeostasis, but its mechanism of action within the gut is not well understood. We have examined the molecular mechanisms underlying the T3 activation of the enterocyte differentiation marker intestinal alkaline phosphatase (IAP) gene. RT-PCR and Western blotting showed that thyroid hormone receptors TRalpha1 and TRbeta1 were expressed in human colorectal adenocarcinoma Caco-2 cells. Northern blotting detected expression of two IAP transcripts, which were increased approximately 3-fold in response to T3. Transient transfection studies with luciferase reporter plasmids carrying various internal and 5' deletion mutations of the IAP promoter localized a putative thyroid hormone response element (TRE) to a region approximately 620 nucleotides upstream (-620) of the ATG start codon. EMSAs using TRalpha1-retinoid X receptor alpha (RXRalpha) on sequential 5' and 3' single nucleotide deletions defined the TRE between -632 and -612 (5'-TTGAACTCAgccTGAGGTTAC-3'). Compared with the consensus TRE, the IAP-TRE is novel in that it contains an everted repeat of two nonamers (not hexamers) separated by three nucleotides. Neither TRalpha1 nor RXRalpha binds to the IAP-TRE; however, TRbeta1 binds to this TRE with minimal affinity. In the presence of TR and RXRalpha, only the TR-RXRalpha heterodimer binds to the IAP-TRE. Mutagenesis of either nonamer abolishes the biological activity of IAP promoter. We have thus identified a novel response element that appears to mediate the T3-induced activation of the enterocyte differentiation marker, intestinal alkaline phosphatase.

Enterocyte differentiation marker intestinal alkaline phosphatase is a target gene of the gut-enriched Kruppel-like factor

We have examined the role that the transcription factor gut-enriched Krüppel-like factor (KLF4 or GKLF) plays in activating the enterocyte differentiation marker gene intestinal alkaline phosphatase (IAP). A yeast one-hybrid screen was used to identify proteins interacting with a previously identified cis-element (IF-III) located within the human IAP gene promoter. DNA-protein interactions were determined by using EMSA. Northern blot analysis was used to study RNA expression in human colon cancer RKO cells engineered to overexpress KLF4. Transient transfections with IAP-luciferase reporter constructs were used to characterize the mechanisms by which KLF4 activates IAP transcription. The yeast one-hybrid screen and EMSA identified KLF4 as binding to IF-III. RKO cells induced to overexpress KLF4 demonstrated a corresponding dose-dependent increase in IAP expression, and EMSA with nuclear extract from these cells confirmed that KLF4 binds to the IF-III element. Transient transfections revealed that KLF4 transactivated the IAP gene largely via a critical segment in the IAP promoter that includes the IF-III cis-element. Mutant KLF4 constructs failed to fully activate IAP. We have identified the enterocyte differentiation marker IAP as a KLF4 target gene. IAP transactivation by KLF4 is likely mediated through a critical region located within the proximal IAP promoter region.

Convergence of the thyroid hormone and gut-enriched Krüppel-like factor pathways in the context of enterocyte differentiation

The gut-enriched Krüppel-like factor (KLF4) and the ligand-bound thyroid hormone receptor (TR) have each been shown to play a critical role in mammalian gut development and differentiation. We investigated an interrelationship between these two presumably independent pathways using the differentiation marker gene, intestinal alkaline phosphatase (IAP). Transient transfections were performed in Cos-7 cells using luciferase reporter plasmids containing a 2.5 kb segment of the proximal human IAP 5' regulatory region, as well as multiple deletions. Cells were cotransfected with TR and/or KLF4 expression vectors and treated+/-100 nmol/L thyroid hormone (T3). IAP reporter gene transactivation was increased independently by KLF4 (ninefold) and ligand-bound TR beta 1 (sevenfold). Cells cotransfected with KLF4 and TR beta 1 in the presence of T3 showed synergistic activation (70-fold). A similar pattern was seen with the other T3 receptor isoform, TR alpha 1. The synergistic effect was lost with deletions of the T3 and KLF4 response elements in the IAP promoter and was completely or partially abolished in the case of mutant KLF4 expression vectors. The thyroid hormone receptor complex and KLF4 synergistically activate the enterocyte differentiation marker gene IAP, suggesting a previously unrecognized interrelationship between these two transcription factor pathways.

Positive selection vectors for high-fidelity PCR cloning

The power of PCR cloning of a target DNA fragment is limited by polymerase-induced mutations. While high-fidelity PCR products can be achieved by reducing the number of PCR cycles, the cloning of the very small amount of DNA thus amplified should give only a few recombinant clones (carrying an insert), which would be very difficult to screen from thousands of background false-positive clones generated by all the currently available vectors, including the positive selection vectors. False-positive clones are mostly generated by the recircularization of linearized vectors that have lost some bases at their ends due to digestion with contaminating exonuclease activities present in restriction enzymes, ligases, polymerases, and other reagents. To overcome this problem, two positive selection vectors, pRGR1Ap and pREM5Tc, have been developed, based on the principles of reporter gene reconstruction and regulatory element modulation, respectively. A PCR primer carrying a vector-specific sequence at its 5' end is used in PCR. When the resultant PCR products are ligated to the specific vector, an antibiotic resistance gene is expressed, thus donating positive selection capability to the harboring cells in a specific selection medium. These vectors cloned PCR fragments generated from less than a femtomole quantity of Escherichia coli genomic DNA after only three cycles of PCR amplification, thus greatly reducing the number of recombinant clones containing polymerase-induced mutations.

Transcriptional activation of the enterocyte differentiation marker intestinal alkaline phosphatase is associated with changes in the acetylation state of histone H3 at a specific site within its promoter region in vitro

Enterocyte differentiation is thought to occur through the transcriptional regulation of a small subset of specific genes. A recent growing body of evidence indicates that post-translational modifications of chromatin proteins (histones) play an important role in the control of gene transcription. Previous work has demonstrated that one such modification, histone acetylation, occurs in an in vitro model of enterocyte differentiation, butyrate-treated HT-29 cells. In the present work, we sought to determine if the epigenetic signal of histone acetylation occurs in an identifiable pattern in association with the transcriptional activation of the enterocyte differentiation marker gene intestinal alkaline phosphatase (IAP). HT-29 cells were maintained under standard culture conditions and differentiated with sodium butyrate. The chromatin immunoprecipitation (ChIP) assay was used to compare the acetylation state of histones associated with specific regions of the IAP promoter in the two cell populations (undifferentiated vs. differentiated). Chromatin was extracted from cells and cleaved by sonication or enzymatic digestion to obtain fragments of approximately 200 to 600 base-pairs, as confirmed by polymerase chain reaction using primers designed to amplify the IAP segments of interest. The ChIP assay selects DNA sequences that are associated with acetylated histones by immunoprecipitation. Unbound segments represent DNA sequences whose histones are not acetylated. After immunoprecipitation, sequences were detected by radiolabeled polymerase chain reaction, and the relative intensity of the bands was quantified by densitometry. The relative acetylation state of histones at specific sites was determined by comparing the ratios of bound/unbound segments. We determined that in a segment of the IAP promoter between -378 and -303 base-pairs upstream from the transcriptional start site, the acetylation state of histone H3 increased twofold in the differentiated, IAP expressing cells, whereas that of histone H4 remained essentially constant. Additionally, at a distant site, between -1378 and -1303 base-pairs, the acetylation state of H3 and H4 did not change appreciably between the undifferentiated and differentiated cells. We conclude that butyrate-induced differentiation is associated with specific and localized changes in the histone acetylation state within the IAP promoter. These changes within the endogenous IAP gene may underlie its transcriptional activation in the context of the enterocyte differentiation program.

Irreversible inhibition of epidermal growth factor receptor tyrosine kinase with in vivo activity by N-[4-[(3-bromophenyl)amino]-6-quinazolinyl]-2-butynamide (CL-387,785)

It has been shown previously that 4-anilino quinazolines compete with the ability of ATP to bind the epidermal growth factor receptor (EGF-R), inhibit EGF-stimulated autophosphorylation of tyrosine residues in EGF-R, and block EGF-mediated growth. Since millimolar concentrations of ATP in cells could reduce the efficacy of 4-anilino quinazolines in cells and the activity of these compounds would not be sustained once they were removed from the body, we reasoned that irreversible inhibitors of EGF-R might improve the activity of this series of compounds in animals. Molecular modeling of the EGF-R kinase domain was used to design irreversible inhibitors. We herein describe one such inhibitor: N-[4-[(3-bromophenyl)amino]-6-quinazolinyl]2-butynamide, known as CL-387,785. This compound covalently bound to EGF-R. It also specifically inhibited kinase activity of the protein (IC50 = 370+/-120 pM), blocked EGF-stimulated autophosphorylation of the receptor in cells (ic50 approximately 5 nM), inhibited cell proliferation (IC50 = 31-125 nM) primarily in a cytostatic manner in cell lines that overexpress EGF-R or c-erbB-2, and profoundly blocked the growth of a tumor that overexpresses EGF-R in nude mice (when given orally at 80 mg/kg/day for 10 days, daily). We conclude that CL-387,785 is useful for studying the interaction of small molecules with EGF-R and may have clinical utility.

Gene assignment by polymerase chain reaction: localization of the human potassium channel IsK gene to the Down's syndrome region of chromosome 21q22.1-q22.2

Gene mapping, using the polymerase chain reaction (PCR) on DNA obtained from a human/rodent hybrid cell line carrying only the human chromosome 21, permitted the assignment of the human IsK gene, encoding a slowly activating potassium channel, to chromosome 21. PCR analysis of two complete panels of human/rodent hybrid DNA mapped IsK to chromosome 21 with 100% concordance. By performing PCR on DNA of a human chromosome 21 regional mapping panel the gene was sublocalized to chromosome 21q22.1-q22.2, which also contains the putative Down's syndrome (trisomy 21) region. The PCR product obtained from the hybrid cell line DNA carrying only human chromosome 21 was sequenced, thus confirming that the PCR product was derived from human IsK.

Targeted gene walking by low stringency polymerase chain reaction: assignment of a putative human brain sodium channel gene (SCN3A) to chromosome 2q24-31

We have developed a low stringency polymerase chain reaction (LSPCR) to isolate the unknown neighboring region around a known DNA sequence, thus allowing efficient targeted gene walking. The method involves the polymerase chain reaction (PCR) with a single primer under conditions of low stringency for primer annealing (40 degrees C) for the first few cycles followed by more cycles at high stringency (55 degrees C). This enables the amplification of a targeted DNA fragment along with other nontargeted fragments. High stringency (55 degrees C) nested PCRs with end-labeled primers are then used to generate a ladder of radioactive bands, which accurately identifies the targeted fragment(s). We performed LSPCR on human placental DNA using a highly conserved sodium channel-specific primer for 5 cycles at 40 degrees C followed by 27 cycles at 55 degrees C for primer annealing. Subsequently, using higher stringency (55 degrees C) PCR with radiolabeled nested primers for 8 cycles, we have isolated a 0.66-kb fragment of a putative human sodium channel gene. Partial sequence (325 bp) of this fragment revealed a 270-bp region (exon) with homology to the rat brain sodium channel III alpha (RBIII) gene at the nucleotide (87%) and amino acid (92%) levels. Therefore, we putatively assign this sequence as a part of a gene coding the alpha-subunit of a human brain type III sodium channel (SCN3A). Using PCR on two human/rodent somatic cell hybrid panels with primers specific to this putative SCN3A gene, we have localized this gene to chromosome 2. Fluorescence in situ hybridization to human metaphase chromosomes was used to sublocalize the SCN3A gene to chromosome at 2q24-31. In conclusion, LSPCR is an efficient and sensitive method for targeted gene walking and is also useful for the isolation of homologous genes in related species.

Expression of divIB of Bacillus subtilis during vegetative growth

Expression of the division initiation gene, divIB, of Bacillus subtilis vegetative growth was examined. lacZ fusion studies and transcription start point mapping have established that a sigma A promoter proximal to divIB is utilized in vivo. The -10 region of this promoter, which is located 93 bp upstream of the start codon, has been defined precisely by site-directed mutagenesis that destroys the promoter. Examination of transcripts by Northern (RNA) blotting has shown that there are at least two transcripts for divIB. The established proximal promoter was found to give rise to a very minor transcript which could not be convincingly demonstrated in wild-type cells but which became apparent upon insertion of a plasmid into the chromosome just upstream of this promoter. The major transcript for divIB originated from a site several kb upstream of the gene and is probably the same as the long polycistronic message also traversing the murD-spoVE-murG genes that was identified previously by others (A.D. Henriques, H. de Lencastre, and P.J. Piggot, Biochimie 74:735-748, 1992). Transcription from the proximal promoter alone, in an upstream-deletion mutant strain, provided sufficient DivIB for normal growth and division as well as sporulation.

Localization of a putative human brain sodium channel gene (SCN1A) to chromosome band 2q24

We have identified four putative human sodium channel gene sequences, 55 bp each, using the polymerase chain reaction (PCR) on total human placental DNA with primers specific for the cDNA sequence of the rat brain sodium channel I alpha (Scn1a) gene. One of these sequences was extended bidirectionally by genomic inverse-PCR to obtain a 1.6-kb fragment. Sequencing of this 1,556-bp fragment showed a 282-bp complete exon, which has 95% and 94% homology at the nucleotide and amino acid levels, respectively, with the rat Scn1a gene. We putatively assign this sequence as belonging to the gene coding the alpha-subunit of a human brain type I sodium channel (SCN1A). PCR on human x rodent somatic cell hybrids with primers derived from SCN1A localized this gene to chromosome 2. Fluorescence in situ hybridization to human metaphase chromosomes sublocalized the gene to chromosome band 2q24.

Autoregulation of the gene encoding the replication terminator protein of Bacillus subtilis

One of two putative sigma A promoters identified previously in the region immediately upstream from the rtp gene (encoding the replication terminator protein) [Smith and Wake, J. Bacteriol. 170 (1988) 4083-4090] has been shown by transcription start point (tsp) mapping to be the functional rtp promoter. In these tsp mapping experiments, it was observed that the level of mRNA from this promoter, Prtp, was increased by a factor of 30 in the absence of the replication terminator protein (RTP), consistent with the autoregulation of rtp at the level of transcription. In vitro transcription from Prtp by sigma A RNA polymerase has been shown to be specifically repressed by RTP. A Prtp-spoVG-lacZ fusion was inserted into the chromosome of a strain in which RTP production was inducible by IPTG. Addition of IPTG to cultures of the new strain lowered beta Gal production by a factor of at least four. It is concluded that rtp is autoregulated in vivo at the level of transcription.

A rapid and efficient method for transcript mapping

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Promoter elements and regulation of expression of the cysD gene of Escherichia coli K-12

The cysD gene, involved in cysteine biosynthesis in Escherichia coli and Salmonella typhimurium, is positively regulated by the CysB regulatory protein. The cysD promoter of E. coli K-12 in a 492-bp PstI-Eco RI fragment was sequenced. The in vivo transcription start point (tsp) for the cysD gene was determined by the methods of T4 DNA polymerase mapping and mung-bean nuclease mapping. The -10 region of the cysD promoter (TATAGT) is closely homologous to the -10 consensus sequence (TATAAT) for E. coli promoters. The -35 region of this promoter (TTCATT) is less closely related to the -35 consensus sequence (TTGACA). Several mutants were obtained by using a chain-termination method for generating unidirectional deletions. Evidence is presented for a possible CysB protein binding site around -89, thought to be involved in regulation of expression of the cysD gene.

Promoter-detection vectors for Escherichia coli with multiple useful features

Two promoter-detection vectors have been constructed which enable the cloning and characterization of promoters recognized by the RNA polymerase of Escherichia coli K-12. The intergenic region of phage M13 DNA, present in opposite orientations in the two vectors, permits the preparation of single-stranded DNA of either strand of the insert thus facilitating oligodeoxyribonucleotide heteroduplex mutagenesis and sequencing of both strands by the dideoxy method of chain termination. After mutagenesis, isolates can be screened for changed function by replica-plating colonies to plates containing XGal. Selected isolates can be characterized by nucleotide sequence analysis, to determine the change in structure, and by beta-galactosidase assays, thus measuring the effect of mutagenesis on promoter function. The vectors could also be used like other protein-fusion vectors.

Lambda transducing phage and clones carrying genes of the cysJIHDC gene cluster of Escherichia coli K12

DNA from each of two specialized transducing lambda phage, lambda dcysJIHD and lambda cysJ, has been analysed by heteroduplex mapping. The segment of the Escherichia coli chromosome carried by lambda dcysJIHD was shown to be large, approximately 18 kb in length, and to replace a large length of lambda DNA, approximately 11 kb, which includes the genes for integration and recombination. Thus lambda dcysJIHD is a bio-type transducing phage. lambda cysJ was shown to have lost very little lambda DNA and to carry about 8 kb of bacterial DNA. Sites for several restriction endonucleases were mapped in the DNA from each phage and cloning experiments located some of the genes of the cluster in relation to the restriction map. Cysteine regulation of the cloned cysJ and cysD genes was shown as well as cysteine regulation of beta-galactosidase in some constructs. The direction of transcription of the cysD gene was established, and from physical evidence the size of the 'silent section' between the cysH and cysD genes was estimated to be at least 11 kb.