Identification of potential small-molecule protein-protein inhibitors of cancer metastasis by 3D epitope-based computational screening

In cancer cells exposed to extracellular pressure or shear stress, AKT1-FAK interaction drives focal adhesion kinase (FAK) phosphorylation, leading to force-activated cancer cell adhesion and metastasis. Blocking the AKT1-FAK interaction is therefore an attractive target for cancer therapy, avoiding the side effects of global FAK inhibition. Starting with our previous identification of a short FAK peptide that binds AKT1, we identified a series of small-molecule inhibitor candidates using a novel approach for inhibiting protein-protein interactions. Using a 3D structural fragment of the FAK peptide as the query, millions of drug-like, commercially available molecules were screened to identify a subset mimicking the volume and chemistry of the FAK fragment to test for their ability to block pressure-sensitive FAK phosphorylation by AKT1. Two compounds reduced the stimulation of FAK phosphorylation in response to extracellular pressure in human SW620 colon cancer cells without affecting basal FAK phosphorylation. Thus, using a 3D protein interaction epitope as a novel query for ligand-based virtual screening can successfully identify small-molecules that show promise in modulating cancer cell adhesion and metastasis.

Hierarchies of healing in gut mucosal injury

The mucosal response to injury can best be understood as a complex layering of different responses that may be invoked depending upon the size and nature of the injury, the persistence of the injurious stimulus, and the availability of various trophic host factors that stimulate repair. There is a hierarchy of responses that ranges from small rapid resealing of acute apical membrane or single cell wounds through the long term attempt to heal a giant peptic ulcer or respond to inflammatory bowel disease. Although much previous attention has been paid to the local factors that regulate these pathways and responses, there is increasing interest in systemic factors that may act either by the production of cytokines and trophic factors or by the direct migration of bone marrow derived stem cells into the mucosal wound.

The C-terminal region of the focal adhesion kinase F1 domain binds Akt1 and inhibits pressure-induced cell adhesion

Increased extracellular pressure or shear stress activate a complex signal pathway that stimulates integrin binding affinity and potentiates metastatic cell adhesion. Inhibiting either focal adhesion kinase (FAK) and Akt1 can block this pathway, but risks interfering with the diverse other functions of each kinase. However, the mechanotransduced signal pathway involves a novel Akt1-FAK interaction not required for most FAK or Akt1 function, so modeling and blocking this interaction seems a desirable target. Building upon previous work suggesting that FAK-Akt1 binding is mediated by the FAK F1 lobe, we demonstrated that independently expressing the F1 domain in human Caco-2 or murine CT-26 colon cancer cells by transient or stable inducible plasmid expression respectively prevents the stimulation of cancer cell adhesion by increased extracellular pressure. Serial further truncation of the FAK F1 lobe identified shorter regions capable of pulling down Akt1 on a glutathione S-transferase (GST) - conjugated column. Ultimately, we identified a 33 residue segment (residues 94-126) at the C-terminal of the F1 lobe as sufficient to pull down Akt1. These findings raise the possibility of developing a treatment modality around the disruption of the FAK-Akt1 interaction using peptides modeled from FAK.

Akt1 binds focal adhesion kinase via the Akt1 kinase domain independently of the pleckstrin homology domain

Akt1 and focal adhesion kinase (FAK) are protein kinases that play key roles in normal cell signaling. Individually, aberrant expression of these kinases has been linked to a variety of cancers. Together, Akt1/FAK interactions facilitate cancer metastasis by increasing cell adhesion under conditions of increased extracellular pressure. Pathological and iatrogenic sources of pressure arise from tumor growth against constraining stroma or direct perioperative manipulation. We previously reported that 15 mmHg increased extracellular pressure causes Akt1 to both directly interact with FAK and to phosphorylate and activate it. We investigated the nature of the Akt1/FAK binding by creating truncations of recombinant FAK, conjugated to glutathione S-transferase (GST), to pull down full-length Akt1. Western blots probing for Akt1 showed that FAK/Akt1 binding persisted in FAK truncations consisting of only amino acids 1-126, FAK(NT1), which contains the F1 subdomain of its band 4.1, ezrin, radixin, and moesin (FERM) domain. Using FAK(NT1) as bait, we then pulled down truncated versions of recombinant Akt1 conjugated to HA (human influenza hemagglutinin). Probes for GST-FAK(NT1) showed Akt1-FAK binding to occur in the absence of the both the Akt1 (N)-terminal pleckstrin homology (PH) domain and its adjacent hinge region. The Akt1 (C)-terminal regulatory domain was equally unnecessary for Akt1/FAK co-immunoprecipitation. Truncations involving the Akt1 catalytic domain showed that the domain by itself was enough to pull down FAK. Additionally, a fragment spanning from the PH domain to half way through the catalytic domain demonstrated increased FAK binding compared to full length Akt1. These results begin to delineate the Akt1/FAK interaction and can be used to manipulate their force-activated signal interactions. Furthermore, the finding that the N-terminal half of the Akt1 catalytic domain binds so strongly to FAK when cleaved from the rest of the protein may suggest a means for developing novel inhibitors that target this specific Akt1/FAK interaction.

Pressure activates colon cancer cell adhesion via paxillin phosphorylation, Crk, Cas, and Rac1

Physical forces can activate colon cancer cell adhesion, critical for metastasis. Paxillin is phosphorylated by FAK and required for pressure-stimulated adhesion. However, whether paxillin acts as an inert scaffolding protein or whether paxillin phosphorylation is required is unknown. Transfection with paxillin point-phosphorylation mutants demonstrated that phosphorylation at tyrosines 31 and 118 together is necessary for pressure-stimulated adhesion. We further evaluated potential paxillin partners. Reducing the adaptor protein Crk or the focal adhesion protein p130Cas blocked pressure-stimulated adhesion. Furthermore, Crk and p130Cas both displayed increased co-immunoprecipitation with paxillin in response to increased pressure, except in cells transfected with a Y31Y118 paxillin mutant. Inhibiting the small GTPase Rac1 also abolished pressure-stimulated adhesion, and reducing paxillin by siRNA blocked Rac1 phosphorylation by pressure. Thus, paxillin phosphorylation at tyrosines 31 and 118 together is necessary for pressure-induced adhesion. Paxillin, Crk and Cas form a trimeric complex that activates Rac1 and mediates this effect.

Mondor's disease mimicking a Spigelian hernia

Superficial thrombophlebitis of the thoracoepigastric veins (also known as Mondor's disease) is an uncommon disorder that typically affects middle-aged women and classically involves the chest wall including the breasts. Only one previously published, non-operative case of the disease, describes how the condition can resemble a strangulated Spigelian hernia. Herein we describe another similar case in which the diagnosis was made intra-operatively. The extremely unusual and similar clinical findings we observed demonstrate that Mondor's disease can occur in the Spigelian hernia belt and cause diagnostic confusion.

Subxiphoid incisional hernias after median sternotomy

BACKGROUND

Subxiphoid incisional hernias are notoriously difficult to repair and are prone to recurrence. The few reports on subxiphoid hernia published over the last two decades have not fully addressed the etiology, pathology, treatment, and outcome of this problem. This review was performed to analyze the published experience and increase the understanding of these difficult hernias.

METHODS

We reviewed the extensive literature, including the Medline and Current Contents computerized database searches, and searched the available bibliographies.

RESULTS

Seven retrospective studies of a total of 113 patients who had clinical subxiphoid hernias after median sternotomy were found. An additional surgical technique describing a modified median sternotomy preventing the hernia, and a single review article on selected technical considerations of subxiphoid ventral repair were also found.

CONCLUSIONS

The incidence of subxiphoid hernia after median sternotomy can be possibly reduced by paraxiphoid extension of the sternotomy, reinforcement near the xiphoid end of the incision, or by optimizing closure of the distal sternotomy and the linea alba. Abdominal wall reinforcement by open-mesh closure or laparoscopic transperitoneal prosthetic repair can effectively deal with the defect. Long-term outcome analyses are not yet available.

Extracellular pressure stimulates tumor cell adhesion in vitro by paxillin activation

Metastasizing colon cancer cells bind target tissues primarily via integrins. Extracellular pressure or shear stress stimulates integrin-mediated adhesion to matrix proteins or endothelial cells by activating the focal adhesion proteins FAK and Src. Because this effect is blocked by cytoskeletal perturbation and paxillin may link the cytoskeleton to the focal adhesion complex, we evaluated the role of paxillin in pressure-induced malignant colonocyte adhesion. We studied SW620 colon cancer cells and confirmed key results in Caco-2 colon cancer cells, primary human colon cancer cells, and a murine colonic adenocarcinoma. We evaluated adhesion to collagen at ambient and 15 mmHg increased pressure after 30 minutes, and paxillin, FAK, and Src phosphorylation in suspended cells prior to adhesion. Some cells were treated with siRNA to paxillin or FAK, or the Src inhibitor PP2. We also compared pressure-induced signals in suspended cells with adhesion-induced signals after adhesion to collagen. Pressure stimulated adhesion and paxillin phosphorylation in SW620 and Caco-2 cells and human primary colon cancer cells. Pressure also increased paxillin phosphorylation in murine carcinoma cells. SiRNA to paxillin decreased SW620 and Caco-2 paxillin without altering basal levels of phosphorylated paxillin. Paxillin reduction decreased basal adhesion to collagen, and inhibited pressure-stimulated adhesion, as well as paxillin, FAK397, FAK576, and Src476 phosphorylation. Neither PP2 nor siRNA to FAK inhibited induction of paxillin phosphorylation by pressure. In contrast, adhesion stimulated FAK, Src, and paxillin phosphorylation regardless of paxillin reduction. In summary, pressure induced paxillin phosphorylation in colon cancer cells. Paxillin reduction inhibited basal adhesion and blocked the pressure-mediated increase in adhesion, as well as pressure-induced FAK and Src signals, while adhesion-induced signals were preserved. Paxillin may be an upstream mediator of pressure-stimulated adhesion, important in metastasis.

Extracellular pressure stimulates colon cancer cell proliferation via a mechanism requiring PKC and tyrosine kinase signals

Pressure in colonic tumours may increase during constipation, obstruction or peri-operatively. Pressure enhances colonocyte adhesion by a c-Src- and actin-cytoskeleton-dependent PKC-independent pathway. We hypothesized that pressure activates mitogenic signals.

METHODS

Malignant colonocytes on a collagen I matrix were subjected to 15 mmHg pressure. ERK, p38, c-Src and Akt phosphorylation and PKCalpha redistribution were assessed by western blot after 30 min and PKC activation by ELISA. Cells were counted after 24 h and after inhibition of each signal, tyrosine phosphorylation or actin depolymerization.

RESULTS

Pressure time-dependently increased SW620 and HCT-116 cell counts on collagen or fibronectin (P < 0.01). Pressure increased the SW620 S-phase fraction from 28 +/- 1 to 47 +/- 1% (P = 0.0002). Pressure activated p38, ERK, and c-Src (P < 0.05 each) but not Akt/PKB. Pressure decreased cytosolic PKC activity, and translocated PKCalpha to a membrane fraction. Blockade of p38, ERK, c-Src or PI-3-K or actin depolymerization did not inhibit pressure-stimulated proliferation. However, global tyrosine kinase blockade (genistein) and PKC blockade (calphostin C) negated pressure-induced proliferation.

CONCLUSIONS

Extracellular pressure stimulates cell proliferation and activates several signals. However, the mitogenic effect of pressure requires only tyrosine kinase and PKCalpha activation. Pressure may modulate colon cancer growth and implantation by two distinct pathways, one stimulating proliferation and the other promoting adhesion.

In vitro evidence for matrix regulation of intestinal epithelial biology during mucosal healing

We now know that restitution is more than a process of dedifferentiation and random cell movement across a wound defect. In fact, it is an orderly and regulated process in which gut mucosal epithelial cells adopt a migratory phenotype involving alterations in the cytoskeleton and intracellular motors likely to be tightly regulated by integrin-associated signal proteins and downstream second messengers. The extracellular matrix influences restitution not only as a physical substrate but also by modulating the expression, organization, and activation of the relevant intracellular proteins, as well as by modulating the expression and organization of receptors for soluble factors in the extracellular environment which also influence cell motility. The additional potential avenue of mechanicochemical signaling initiated by cytoskeletal rearrangement awaits further investigation.

Short-chain fatty acids inhibit invasive human colon cancer by modulating uPA, TIMP-1, TIMP-2, mutant p53, Bcl-2, Bax, p21 and PCNA protein expression in an in vitro cell culture model

High intakes of dietary fiber or resistant starches have been associated with a lower incidence of colon cancers. Because short-chain fatty acids (SCFA) such as butyrate are produced in the colonic lumen by the bacterial fermentation of dietary fibers and resistant starches, we hypothesized that SCFA may inhibit the development of invasive human colon cancers. To test this hypothesis, primary human invasive colonocytes were isolated from fresh surgical specimens and treated with 0.01 mol/L acetate, propionate or butyrate; cell invasion, cell adhesion, F-actin polymerization, urokinase plasminogen activator (uPA), tissue inhibitor matrix metalloproteinase (TIMP)-1, TIMP-2 and mutant p53, Bcl-2, Bax, p21 and proliferating cell nuclear antigen (PCNA) protein expression levels were examined. Although each of the SCFA tested significantly reduced primary cell invasion, butyrate was the most potent, inhibiting primary invasive human colon cancer invasion by 54% (P < 0.0001). The effects of SCFA on primary cell invasion appeared to be independent of cell adhesion and F-actin polymerization but dependent on the inhibition of uPA (P < 0.05) and the stimulation of TIMP-1 and TIMP-2 activities (P < 0.05). Protein expression levels of mutant p53, p21, Bax, Bcl-2 and PCNA were significantly altered by each of the SCFA tested (P < 0.05). These data indicate that SCFA inhibit invasive human colon cancer by modulating proteolytic uPA and antiproteolytic TIMP-1 and TIMP-2 activities, but their mechanisms of action on tumor suppression, apoptosis and growth arrest may differ.

Differential dietary effects on colonic and small bowel neoplasia in C57BL/6J Apc Min/+ mice

The effects of fiber on colon cancer are controversial. Twenty 5-week old C57BL/6J Apc Min/+ mice were fed for 60 days with a commercial mouse diet (Teklad LM-485) and eight semidefined diets containing 5-10% various fibers and 20% soybean oil. Ten additional C57BL/6J congenic litter-mates were fed each diet to assay colonic SCFA. SCFA, stool bulk, and colonic tumor incidence differed only slightly among the semidefined diets despite variations in fiber content and source. However, food consumption, caloric intake, stool bulk, and SCFA were substantially increased by the Teklad diet compared with all other groups. The Teklad diet significantly increased the number of mice with colonic tumors, average number of tumors/mouse, total tumor burden, colonic atypical hyperplasia, and small bowel tumors. Mice fed high-fat, no-fiber diets had more small bowel tumors (29.8 +/- 3.1) than mice fed diets with fiber (8.2 +/- 2.1) or with low fat and no fiber (18.1 +/- 3.4) (P < 0.05 for each group). These studies suggest that fat predisposes to and fiber protects against small bowel tumors but not colon tumors in these mice. Thus, diets high in fiber or yielding high colonic luminal SCFA may not necessarily protect against colonic cancer. Furthermore, the effects of dietary fiber in Teklad appear overshadowed by some other biologically active factors in this animal model.

Environmental factors of temperature, humidity, serum accumulation, and cell seeding increase colon cancer cell adhesion in vitro, with partial characterization of the serum component responsible for pressure-stimulated adhesion

Physical characteristics of surgical wounds and viable tumor cells shed may differ between open and laparoscopic procedures. Because environmental factors may vary between the laparoscopic milieu and that of open surgical procedures, we sought to characterize the effect of these factors on tumor cell adhesion, an early step in the process of wound implantation. Human SW620 colon cancer cells were placed in matrix-precoated dishes for 30 min at concentrations of 90,000-540,000 cells/well, at 25-37 degrees C, in the native state of the matrix proteins and after drying for 60 min, and in 0-10% serum. As increased pressure has previously been reported to stimulate colon cancer cell adhesion synergistically with serum, we then further partially characterized the serum components responsible for this potentiating effect. The number of adherent cells varied linearly with cells seeded. Adhesion was temperature-dependent, and also was dependent on the matrix conformation. Less adhesion occurred to dry matrix proteins. Serum dose-dependently potentiated SW620 pressure-stimulated adhesion, with a maximal increase in adhesion compared with ambient pressure conditions at 5% serum concentration. Heat inactivating the serum at 60 degrees C for 30 min ablated the effect. Filtration to remove molecules over 10 kDa produced no change in adhesion relative to ambient conditions, but filtration to 100 kDa preserved the serum effect. When the serum was passed over a gelatin-Sepharose column, which binds numerous proteins including fibronectin, the serum effect was lost. Addition of fibronectin to serum-free media did not reconstitute the effect. The environmental factors of warm temperature, moisture, and serum accumulation may contribute to increased colon cancer cell adhesion. However, the most important determinant of malignant adhesion to surgical wounds, laparoscopic or open, is likely to be the size of the tumor cell inoculum. Pressure stimulation of colon cancer cell adhesion is potentiated by heat-labile serum components of molecular weight 10-100 kDa which bind gelatin-Sepharose, and is not fibronectin alone. Irrigating serum from surgical wounds may decrease tumor implantation.

Complications of endoscopy

BACKGROUND

Although most gastrointestinal endoscopic procedures are performed by gastroenterologists, surgeons often assist in the management of patients with complications. This review provides an introduction to the incidence, prevention, and treatment of complications that may occur after upper endoscopy, colonoscopy, percutaneous endoscopic gastrostomy, and endoscopic retrograde cholangiopancreatography.

METHODS

Systematic review of the literature.

RESULTS

Preprocedural complications include medication effects and adverse effects of bowel preparation. Major procedural complications consist primarily of perforation and hemorrhage. Percutaneous endoscopic gastrostomy tube placement may be complicated by fistula and obstruction. There is also a risk of infectious disease transmission, both to and from the patient.

CONCLUSIONS

Endoscopy, like all invasive procedures, carries significant potential risks for the patient. In practiced hands, and with awareness of the problems that may arise, many complications may be avoided and others successfully managed.

Effect of nabumetone and aspirin on colonic mucosal bleeding time

BACKGROUND

The management of patients taking aspirin or non-steroidal anti-inflammatory drugs (NSAIDs) who require colonoscopy remains controversial because of concerns over bleeding after biopsy or polypectomy.

AIM

To determine whether patients using the NSAID nabumetone, a non-acidic prodrug with mixed activity against cyclooxygenase-1 (COX-1) and COX-2, exhibited prolonged mucosal bleeding times and how this might compare with mucosal bleeding times in patients using aspirin.

METHODS

We assessed triplicate mucosal bleeding times in patients undergoing screening flexible sigmoidoscopy. We compared 90 patients who had taken no aspirin or NSAIDs within the previous 2 weeks, to 60 patients who had received nabumetone 1 g b.d. by mouth for the previous 2 weeks, and 30 patients who had taken 325 mg aspirin daily for the previous 2 weeks. In each case, the investigator performing the study was blinded to the patient's medication.

RESULTS

Mucosal bleeding times did not differ significantly among control or nabumetone-using patients. However, the patients receiving aspirin exhibited significant prolongation. Mucosal bleeding time correlated statistically significantly, but weakly, with skin bleeding time.

CONCLUSIONS

Nabumetone does not appear to prolong mucosal bleeding time after mucosal pinch biopsy, and skin bleeding time does not reliably screen for prolonged mucosal bleeding time.

Short chain fatty acids differentially modulate cellular phenotype and c-myc protein levels in primary human nonmalignant and malignant colonocytes

Short chain fatty acids may protect colonic mucosa against neoplastic transformation by modulating colonocyte phenotype, DNA synthesis, and c-myc levels. To test this hypothesis, nonmalignant and malignant human colonocytes were isolated from surgical specimens and treated with 10 mM acetate, propionate, or butyrate. Markers of cellular phenotype, DNA synthesis, and c-myc protein levels were assayed by alkaline phosphatase and dipeptidyl dipeptidase IV activities, [3H]thymidine labeling, and western blotting, respectively. Butyrate, in particular, exerted discordant effects on alkaline phosphatase (P < 0.05), and c-myc levels (P < 0.05, N > or = 6) in nonmalignant and malignant human colonocytes. DPDD was unaffected by any of the short chain fatty acids tested. [3H]Thymidine labeling was differentially stimulated by short chain fatty acids in both cell types and greater DNA synthesis rates were observed in malignant colonocytes (P < 0.005, N = 16). These data suggest that in vitro, butyrate, in particular, may differentially modulate phenotype, DNA synthesis, and c-myc in nonmalignant and malignant human colonocytes.

Integrin and FAK-mediated MAPK activation is required for cyclic strain mitogenic effects in Caco-2 cells

Rhythmic strain stimulates Caco-2 proliferation. We asked whether mitogen-activated protein kinase (MAPK) activation mediates strain mitogenicity and characterized upstream signals regulating MAPK. Caco-2 cells were subjected to strain on collagen I-precoated membranes or antibodies to integrin subunits. Twenty-four hours of cyclic strain increased cell numbers compared with static conditions. MAPK-extracellular signal-regulated kinase (ERK) kinase inhibition (20 microM PD-98059) blocked strain mitogenicity. p38 Inhibition (10 microM SB-202190) did not. Strain rapidly and time-dependently activated focal adhesion kinase (FAK), paxillin, ERK1 and 2, and p38 on collagen. c-Jun NH(2)-terminal kinase (JNK)1 and 2 exhibited delayed activation. Similar activation occurred when Caco-2 cells were subjected to strain on a substrate of functional antibody to the alpha2-, alpha3-, alpha6-, or beta1-integrin subunits but not on a substrate of functional antibody to the alpha5-subunit. FAK inhibition by FAK397 transfection blocked ERK2 and JNK1 activation by in vitro kinase assays, but pharmacological protein kinase C inhibition did not block ERK1 or 2 activation by strain. Strain-induced ERK signals mediate strain's mitogenic effects and may require integrins and FAK activation.

Collagen IV-dependent ERK activation in human Caco-2 intestinal epithelial cells requires focal adhesion kinase

Integrin-initiated extracellular signal-regulated kinase (ERK) activation by matrix adhesion may require focal adhesion kinase (FAK) or be FAK-independent via caveolin and Shc. This remains controversial for fibroblast and endothelial cell adhesion to fibronectin and is less understood for other matrix proteins and cells. We investigated Caco-2 intestinal epithelial cell ERK activation by collagen I and IV, laminin, and fibronectin. Collagens or laminin, but not fibronectin, stimulated tyrosine phosphorylation of FAK, paxillin, and p130(cas) and activated ERK1/2. Shc, tyrosine-phosphorylated by matrix adhesion in many cells, was not phosphorylated in Caco-2 cells in response to any matrix. Caveolin expression did not affect Caco-2 Shc phosphorylation in response to fibronectin. FAK, ERK, and p130(cas) tyrosine phosphorylation were activated after 10-min adhesion to collagen IV. FAK activity increased for 45 min after collagen IV adhesion and persisted for 2 h, while p130(cas) phosphorylation increased only slightly after 10 min. ERK activity peaked at 10 min, declined after 30 min, and returned to base line after 1 h. Transfection with FAK-related nonkinase, but not substrate domain deleted p130(cas), strongly inhibited ERK2 activation in response to collagen IV, indicating Caco-2 ERK activation is at least partly regulated by FAK.

Matrix-specific FAK and MAPK reorganization during Caco-2 cell motility

We have previously reported that Caco-2 cell motility redistributes FAK, paxillin, and activates p38. However, the subcellular organization of these intracellular signals during cell migration is unclear. We, therefore, investigated the organization of actin, FAK, paxillin, and activated ERK and activated p38 during Caco-2 motility across collagen I, fibronectin, laminin, and tissue culture treated glass. Differential density seeding generated homogeneous static and migrating populations. Expression of actin, FAK, paxillin, phospho-ERK, and phospho-p38 were examined by immunofluorescent staining in static and motile cells. Actin was concentrated toward the peri-nuclear central area of cells migrating on matrix proteins studied. Actin immunoreactivity was decreased in the leading edge of lamellipodia. FAK immunoreactivity was weaker in migrating cells than in static cells on the same matrix. FAK was expressed along cell-cell contacts of both cell populations, but absent in migrating lamellipodia of matrix-cultured cells. Paxillin staining was diffuse in static cells but organized toward migrating lamellipodia in a radial manner. Like FAK, phosphorylated ERK was expressed in the central region of migrating cells but was dramatically decreased at areas of cell-cell contact and free lamellipodia. Fibronectin exerted the greatest effect on ERK activation in all matrix proteins studied. In contrast, phosphorylated p38 staining was stronger in migrating cells on matrix than in static cells on the same matrix. Phosphorylated p38 was expressed in the nuclear of migrating cells and disappeared in the cell-cell contact side and free lamellipodia. Interestingly, the reorganization of these proteins was distinctly different on tissue culture treated glass without a physiologic matrix substrate. For instance, FAK staining increased rather than decreased in motile cells on plastic, and lamellipodial FAK staining could be discerned. Matrix may influence Caco-2 biology during migration not only by triggering intracellular phosphorylation events but also by reorganizing the cytoskeleton and the subcellular localization of these intracellular signals.

Matrix-specific FAK and MAPK reorganization during Caco-2 cell motility

We have previously reported that Caco-2 cell motility redistributes FAK, paxillin, and activates p38. However, the subcellular organization of these intracellular signals during cell migration is unclear. We, therefore, investigated the organization of actin, FAK, paxillin, and activated ERK and activated p38 during Caco-2 motility across collagen I, fibronectin, laminin, and tissue culture treated glass. Differential density seeding generated homogeneous static and migrating populations. Expression of actin, FAK, paxillin, phospho-ERK, and phospho-p38 were examined by immunofluorescent staining in static and motile cells. Actin was concentrated toward the peri-nuclear central area of cells migrating on matrix proteins studied. Actin immunoreactivity was decreased in the leading edge of lamellipodia. FAK immunoreactivity was weaker in migrating cells than in static cells on the same matrix. FAK was expressed along cell-cell contacts of both cell populations, but absent in migrating lamellipodia of matrix-cultured cells. Paxillin staining was diffuse in static cells but organized toward migrating lamellipodia in a radial manner. Like FAK, phosphorylated ERK was expressed in the central region of migrating cells but was dramatically decreased at areas of cell-cell contact and free lamellipodia. Fibronectin exerted the greatest effect on ERK activation in all matrix proteins studied. In contrast, phosphorylated p38 staining was stronger in migrating cells on matrix than in static cells on the same matrix. Phosphorylated p38 was expressed in the nuclear of migrating cells and disappeared in the cell-cell contact side and free lamellipodia. Interestingly, the reorganization of these proteins was distinctly different on tissue culture treated glass without a physiologic matrix substrate. For instance, FAK staining increased rather than decreased in motile cells on plastic, and lamellipodial FAK staining could be discerned. Matrix may influence Caco-2 biology during migration not only by triggering intracellular phosphorylation events but also by reorganizing the cytoskeleton and the subcellular localization of these intracellular signals.

Identification and comparative analysis of human colonocyte short-chain fatty acid response genes

Short-chain fatty acids (SCFAs) butyrate, propionate, and acetate produced during fiber fermentation promote colonic differentiation and can reverse or suppress neoplastic progression. We sought to identify candidate genes responsible for SCFA activity on colonocytes and to compare the relative activities of independent SCFAs. cDNA was generated from polyA+ mRNA isolated from control Caco-2 cells and cells treated with equimolar butyrate, propionate, and acetate. GeneCalling, a restriction-based differential RNA expression platform linked to a DNA sequence database lookup, was applied. A total of 30,000 individual genetic sequences were analyzed for differential expression among the three SCFAs. Differentially expressed peaks corresponding to cancer-related genes were isolated, sequenced, and cross-referenced to the GenBank human database. Gene identities were independently confirmed by oligonucleotide poisoning. More than 1000 gene fragments were identified as being substantially modulated in expression by butyrate. Butyrate tended to have the most pronounced effects and acetate the least. Five fragments selected for further study were fully sequenced and proved 100% homologous with human sequences for clusterin, amyloid precursor-like protein 2, and caudal homeobox 2 protein, not previously known to be modulated by SCFAs. In each case, a similar order of potency for the three SCFAs studied was observed. The common SCFAs appear to exert different effects. This study suggests the diversity of the SCFA response at the molecular level and facilitates identifying genes important in the biologic activity of dietary fiber.

Alpha integrin subunits regulate human (Caco-2) intestinal epithelial proliferation and phenotype

BACKGROUND/AIMS

Cell-matrix interactions influence intestinal epithelial biology, but the whether specific integrin heterodimers exert different effects is unclear.

METHODS

We used functional antibodies to investigate effects of the alpha2, alpha3, alpha5, and alpha6 integrin subunits on proliferation and differentiation of human intestinal Caco-2 cells on laminin. Cells seeded onto laminin-coated inserts in defibronectinized medium were treated with functional antibodies or normal IgG for 72 hrs and proliferation, alkaline phosphatase and dipeptidyl dipeptidase specific activity were measured.

RESULTS

Caco-2 adhesion to antibody to each alpha-integrin subunit stimulated tyrosine phosphorylation of Focal Adhesion Kinase and paxillin, suggesting that these antibodies intiate integrin-related tyrosine signalling. Proliferation was inhibited by anti-alpha2 and anti-alpha3, but stimulated by anti-alpha6. Alkaline phosphatase and dipeptidyl dipeptidase specific activity were promoted by alpha2 blockade but decreased after a6 blockade. Proliferative blockade using mitomycin C or hydroxyurea prevented the effects of alpha2 ligation on differentiation, but the decrease in alkaline phosphatase specific activity observed after a6 integrin subunit blockade was preserved even after proliferative blockade.

CONCLUSION

lntegrin heterodimers modulate human Caco-2 intestinal epithelial biology on laminin in an alpha-subunit specific manner. The different effects of anti-alpha2 and anti-alpha6 may reflect competitition by these antibodies with integrin subunit interactions with laminin as well as initiation of their own signals or different functions for the alpha6 integrin subunit

Effects of increased ambient pressure on colon cancer cell adhesion

Forces such as strain modulate intestinal epithelial biology. Shear and pressure influence other cells. The effects of pressure on human colon cancer cells are poorly understood. Increasing ambient pressure for 30 min by 15 mm Hg over atmospheric stimulated adhesion to matrix proteins of four human colon cancer cell lines and primary cells from three human colon cancers, but not bovine aortic smooth-muscle cells. This effect was energy dependent and cation dependent (blocked by azide and chelation), accompanied by tyrosine phosphorylation of intracellular proteins including focal adhesion kinase, and blocked by tyrosine kinase inhibition (genistein, tyrphostin, and erbstatin) and a functional antibody to the beta1 integrin subunit. Although pressure stimulated adhesion even in a balanced salt solution, baseline and pressure-stimulated adhesion were each substantially diminished in the absence of serum. These data suggest that relatively low levels of increased pressure may stimulate malignant colonocyte adhesion by a cation-dependent beta1-integrin-mediated mechanism, perhaps via focal adhesion kinase-related tyrosine phosphorylation. In addition to elucidating another aspect of physical force regulation of colonocyte biology, these findings may be relevant to the effects of increased pressure engendered by colonic peristalsis, surgical manipulation, or laparoscopic surgery on colon cancer cell adhesion.

Effects of glutamine isomers on human (Caco-2) intestinal epithelial proliferation, strain-responsiveness, and differentiation

Enteral feeding with small amounts to stimulate bowel motility, and glutamine supplementation, which provides nutrients selectively used by intestinal epithelial cells, might preserve the gut mucosa during fasting. We evaluated the effects of the interaction between mechanical strain and glutamine supplementation in human Caco-2 intestinal epithelial cells, and pursued the finding of equivalent effects of L- and D-glutamine in Caco-2, HT-29, and primary malignant human colonocytes. Caco-2 cells were subjected to repetitive strain in media containing 2 mmol/L of L-glutamine and media supplemented with L- or D-glutamine. Proliferation was determined by automated cell counting. Differentiation and cellular production of L-glutamine were determined spectroscopically. Rhythmic deformation stimulated Caco-2 proliferation in a frequency-dependent manner. Maximal stimulation occurred at 10 cpm, consistent with in vivo frequencies of peristalsis and villous motility. Deformation at 10 cpm and L-glutamine supplementation from 2 to 5 mmol/L concentrations independently stimulated Caco-2 proliferation; the combination further increased proliferation. D-Glutamine supplementation yielded similar results, although with lesser potency. Furthermore, both L- and D-glutamine equivalently reduced Caco-2 dipeptidyl dipeptidase activity. The effects of each isoform were blocked by 1 to 3 mmol/L acivicin, a selective antagonist of glutamine metabolism. Indeed Caco-2 and HT-29 cells and primary malignant colonocytes each metabolized D-glutamine to L-glutamine. Glutamine supplementation in fasting patients might prove synergistic with stimulation of bowel motility by non-nutritive feeding, whereas tissue-specific variations in D-glutamine metabolism might facilitate selective nutripharmaceutical targeting of the gut mucosa.

Human caco-2 motility redistributes FAK and paxillin and activates p38 MAPK in a matrix-dependent manner

The signals involved in restitution during mucosal healing are poorly understood. We compared focal adhesion kinase (FAK) and paxillin protein and phosphorylation, extracellular signal-regulated kinase (ERK) 1, ERK2, and p38 activation, as well as FAK and paxillin organization in static and migrating human intestinal Caco-2 cells on matrix proteins and anionically derivatized polystyrene dishes (tissue culture plastic). We also studied effects of FAK, ERK, and p38 blockade in a monolayer-wounding model. Compared with static cells, cells migrating across matrix proteins matrix-dependently decreased membrane/cytoskeletal FAK and paxillin and cytosolic FAK. Tyrosine phosphorylated FAK and paxillin changed proportionately to FAK and paxillin protein. Conversely, cells migrating on plastic increased FAK and paxillin protein and phosphorylation. Migration matrix-dependently activated p38 and inactivated ERK1 and ERK2. Total p38, ERK1, and ERK2 did not change. Caco-2 motility was inhibited by transfection of FRNK (the COOH-terminal region of FAK) and PD-98059, a mitogen-activated protein kinase-ERK kinase inhibitor, but not by SB-203580, a p38 inhibitor, suggesting that FAK and ERK modulate Caco-2 migration. In contrast to adhesion-induced phosphorylation, matrix may regulate motile intestinal epithelial cells by altering amounts and distribution of focal adhesion plaque proteins available for phosphorylation as well as by p38 activation and ERK inactivation. Motility across plastic differs from migration across matrix.

Effects of increased ambient pressure on colon cancer cell adhesion

Forces such as strain modulate intestinal epithelial biology. Shear and pressure influence other cells. The effects of pressure on human colon cancer cells are poorly understood. Increasing ambient pressure for 30 min by 15 mm Hg over atmospheric stimulated adhesion to matrix proteins of four human colon cancer cell lines and primary cells from three human colon cancers, but not bovine aortic smooth-muscle cells. This effect was energy dependent and cation dependent (blocked by azide and chelation), accompanied by tyrosine phosphorylation of intracellular proteins including focal adhesion kinase, and blocked by tyrosine kinase inhibition (genistein, tyrphostin, and erbstatin) and a functional antibody to the beta1 integrin subunit. Although pressure stimulated adhesion even in a balanced salt solution, baseline and pressure-stimulated adhesion were each substantially diminished in the absence of serum. These data suggest that relatively low levels of increased pressure may stimulate malignant colonocyte adhesion by a cation-dependent beta1-integrin-mediated mechanism, perhaps via focal adhesion kinase-related tyrosine phosphorylation. In addition to elucidating another aspect of physical force regulation of colonocyte biology, these findings may be relevant to the effects of increased pressure engendered by colonic peristalsis, surgical manipulation, or laparoscopic surgery on colon cancer cell adhesion.

Mitogen-activated protein phosphorylation in endothelial cells exposed to hyperosmolar conditions

The effect of hyperosmolarity on the induction of the mitogen-activated protein kinases (MAPK) was studied in bovine aortic endothelial cell (EC). Different types of agents were used to differentiate the effects of osmolarity from other variables. Hypertonic treatment with physiologically relevant levels of NaCl (350 mOsm/kg H(2)O) significantly increased the level of expression of p38 within 2 min, and ERK-1/2 and JNK after 10 min. The inductions peaked between 30 and 60 min and returned to baseline levels within 2 h. A similar pattern of induction occurred with ionic contrast agent. p38 induction by glucose and mannitol showed a similar pattern, although the level of ERK-1/2 phosphorylation was not as robust, and JNK was not induced by glucose. Urea did not affect the level of induction of the MAPK isoforms. It is concluded that MAPK plays an important role in hyperosmolality-induced signal transduction. Different osmotic agents induce MAPK expression differently. No MAPK induction with urea implies that cell shrinkage may be an important component of hyperosmolality-induced MAPK phosphorylation.

Loss of matrix-dependent cytoskeletal tyrosine kinase signals may regulate intestinal epithelial differentiation during mucosal healing

Intestinal epithelial restitution and the migratory phenotype appear regulated by the extracellular matrix. Since integrin-associated adhesion to matrix triggers tyrosine kinase activity, we hypothesized that matrix-specific tyrosine kinase signals might modulate the intestinal epithelial migratory phenotype, particularly via focal adhesion kinase. Caco-2 cells were seeded at two densities on collagen I, laminin, fibronectin, and tissue culture plastic. Four days later the first cells were confluent, whereas the second cells were not contact inhibited and expressed migratory lamellipodia. Cells were fractionated into membrane/cytoskeletal and cytosolic fractions. Cytoskeletal tyrosine kinase activity in static cells was matrix dependent and, unlike cytoscolic tyrosine kinase, correlated with adhesion, highest on collagen and lowest on plastic. Migrating cells exhibited matrix-dependent increases in cystosolic tyrosine kinase activity. Cytosolic changes in tyrosine kinase activity in motile cells exceeded membrane/cytoskeletal changes. However, matrix-dependent variations in increase in cytosolic tyrosine kinase activity correlated inversely with changes in cytoskeletal tyrosine kinase activity, suggesting cytoskeletal tyrosine kinase translocation to the cytosol during motility. Indeed cytoskeletal focal adhesion kinase activity decreased during migration on collagen. Tyrosine kinase inhibition by genistein both inhibited migration and stimulated expression of brush-border enzymes downregulated during motility. Although enterocyte-matrix interactions alter both cytosolic and cytoskeletal tyrosine kinase activity, matrix-dependent cytoskeletal events are likely to regulate adhesion and differentiation in static cells. Loss of matrix-dependent cytoskeletal tyrosine kinase signals such as focal adhesion kinase during restitution may trigger a phenotypic switch to the "dedifferentiated" migrating intestinal epithelial phenotype.

Mechanical strain rapidly redistributes tyrosine phosphorylated proteins in human intestinal Caco-2 cells

Repetitive strain stimulates proliferation and modulates differentiation in human Caco-2 intestinal epithelial cells via tyrosine kinase activity. We therefore sought to characterize strain modulation of tyrosine phosphorylation in Caco-2 cells. Immunoblotting for phosphotyrosine demonstrated that repetitive strain (10 cpm, 10% strain) rapidly increased tyrosine phosphorylation of 125-, 70-, 60-, and 50-kDa bands in the soluble fraction by 94+/-31, 145+/-21, 365+/-46, and 1240+/-240%, respectively (p<0.05, n=4). However, strain decreased tyrosine phosphorylated band intensity of the 125-, 70-, 60-, and 50-kDa proteins in the particulate fraction by 81+/-17, 70+/-23, 79+/-7, and 59+/-23%, respectively (p<0.05, n=4). The decreased band intensity in the particulate fraction was not due to decreased tyrosine kinase activity because strain equally increased tyrosine kinase activity in both soluble and particulate fractions. Cyclic strain at a physiologically relevant amplitude and frequency appears to modulate the subcellular distribution of tyrosine phosphorylated proteins in human Caco-2 intestinal cells.

Strain induces Caco-2 intestinal epithelial proliferation and differentiation via PKC and tyrosine kinase signals

Although the intestinal epithelium undergoes complex deformations during normal function, nutrient absorption, fasting, lactation, and disease, the effects of deformation on intestinal mucosal biology are poorly understood. We previously demonstrated that 24 h of cyclic deformation at an average 10% deformation every 6 s stimulates proliferation and modulates brush-border enzyme activity in human intestinal Caco-2 cell monolayers. In the present study we sought potential mechanisms for these effects. Protein kinase C (PKC) activity increased within 1 min after initiation of cyclic deformation, and the PKC-alpha and -zeta isoforms translocated from the soluble to the particulate fraction. Cyclic deformation also rapidly increased tyrosine kinase activity. Tyrosine phosphorylation of several proteins was increased in the soluble fraction but decreased in the particulate fraction by cyclic deformation for 30 min. Inhibition of PKC and tyrosine kinase signals by calphostin C, G-06967, and erbstatin attenuated or blocked cyclic deformation-mediated modulation of Caco-2 DNA synthesis and differentiation. These results suggest that cyclic deformation may modulate intestinal epithelial proliferation and brush-border enzyme activity by regulating PKC and tyrosine kinase signals.

Human Caco-2 intestinal epithelial motility is associated with tyrosine kinase and cytoskeletal focal adhesion kinase signals

Intestinal epithelial cells assume a specialized phenotype adapted to motility and mucosal healing during mucosal restitution. Since cell-matrix interactions initiate tyrosine kinase (TK) signals, we hypothesized that the regulation of the intestinal epithelial migratory phenotype may also involve TK signals, particularly via focal adhesion kinase (FAK). Caco-2 cells were seeded simultaneously at 26,000 and 6000 cells/cm2. After 4 days, the first cells were confluent, while cells in the second population were not contact-inhibited and expressed migrating lamellipodia. Cells were fractionated into Triton X-100-soluble (membrane/cytoskeletal) and -insoluble (cytosolic) fractions. TK activity in each fraction was assayed by ELISA using a synthetic substrate. FAK protein was assessed by immunoprecipitation with monoclonal anti-FAK and Western blotting. Because active FAK autophosphorylates, we also measured FAK tyrosine phosphorylation, immunoprecipitating with anti-FAK and then Western blotting for phosphotyrosine. TK activity was increased in both cytosolic and membrane/cytoskeletal fractions of migrating cells by 17.6 +/- 3.6 and 28.9 +/- 4.1%, respectively, compared to static cells (n = 11, P < 0.01). FAK protein increased in the cytosolic fraction by 90.4 +/- 20.0% (n = 5, P = 0.01), but did not change in the membrane/cytoskeletal fraction. Tyrosine phosphorylated FAK increased by 62.8 +/- 21.4% in the cytosolic fraction of migrating cells but also by 46.6 +/- 38.4% in the membrane/cytoskeletal fraction (n = 5, P < 0.05). These data suggest that intestinal epithelial cell migration is associated with increases in both cytosolic and cytoskeletal TK activity and upregulation of cytosolic FAK protein. The increase in cytoskeletal FAK phosphorylation without increased FAK protein suggests autophosphorylation and increased cytoskeletal FAK activity. The migrating intestinal epithelial phenotype may therefore be modulated by TK signals including cytoskeletal FAK activity.

Differential effects of mucosal pH on human (Caco-2) intestinal epithelial cell motility, proliferation, and differentiation

Mucosal pH abnormalities are associated with anastomotic dehiscence, ischemia, and malignancy. We postulated that intraluminal pH influences intestinal epithelial motility, proliferation, and differentiation and studied extracellular pHo (7.0-8.5) effects on human (Caco-2) intestinal epithelial motility, proliferation, and differentiation. Mucosal healing was modeled by sheet migration and differentiation by alkaline phosphatase and dipeptidyl dipeptidase specific activity. In parallel differentiation and motility studies, we inhibited proliferation with mitomycin to dissociate indirect mitogenic effects. Intracellular pHi was quantitated using BCECF/AM at varying extracellular pHo and in migrating cells. Motility was maximal at pHo 7.6 and proliferation at 7.2. Each decreased with acidity and alkalinity. By contrast, brush border enzyme activity was lowest at pHo 7.0 and highest at pHo 8.5. pHi was highest at pHo 8.5. Migrating cell pHi was higher than static cell pHi. Thus, extracellular pHo deviations perturb Caco-2 pHi homeostasis and motility. Alkalinity promotes differentiation while acidity induces proliferation and limits differentiation.

Effects of modulation of tyrosine phosphorylation on brush border enzyme activity in human Caco-2 intestinal epithelial cells

Intestinal epithelial cell differentiation is closely regulated during normal cell renewal, maturation, and malignant transformation. Since tyrosine phosphorylation influences differentiation in other cell types and has been reported to vary between crypt cells to differentiated villus tip cells, we investigated the influence of tyrosine phosphorylation in colonocyte differentiation, by using human colonic Caco-2 cells as a model and expression of the brush border enzymes alkaline phosphatase (AKP) and dipeptidyl peptidase (DPDD) as differentiation markers. We studied three tyrosine kinase inhibitors with different modes of action and specificities, viz., genistein, erbstatin analog (EA), and tyrphostin, and the tyrosine phosphatase inhibitor sodium orthovanadate. AKP- and DPDD-specific activities were assayed in protein-matched cell lysates by synthetic substrate digestion. We also correlated the effects of these agents on brush border enzyme activity with tyrosine phosphorylation of phosphoproteins by Western blotting. Genistein (5-75 mg/ml) dose-dependently stimulated AKP and DPDD with a maximal stimulation at 75 mg/ml by 158.6+/- 17.5% and 228.6+/-37.1% of control values, respectively (n=12, P<0.001). The inactive analog genistin had no effect. Tyrphostin (25 mM) similarly stimulated AKP and DPDD by 138. 6+/-6.6% and 131.8+/-1.5% of control values (n=12, P<0.001). Unexpectedly, EA (0.1-10 mM) had the opposite effect, inhibiting AKP- and DPDD-specific activity significantly at 10 mM with a maximal 14.8+/-6.4% and 26.5+/-2.5% of control values (n=12, each P<0.001). Sodium orthovanadate had a discordant effect on these two differentiation markers. Orthovanadate dose-dependently increased AKP to a maximal 188.5+/-16.1% of basal activity at 1.5 mM but decreased DPDD activity at 1.5 mM to 47.2+/-3.8% (n=9, P<0.001 each). The effects of each agent were preserved when proliferation was blocked with mitomycin C, suggesting that the modulation of phenotype by these agents was independent of any effects of proliferation. The tyrosine phosphorylation of several phosphoprotein bands was affected differently by these agents. In particular, the tyrosine phosphorylation of one 70-kDa to 71-kDa band was increased by genistein and tyrophostin but deceased by EA. The different effects of these modulators of tyrosine kinase activity raise the possibility that at least two independent enzymes or pathways regulating tyrosine phosphorylation modulate intestinal epithelial differentiation. Furthermore, tyrosine phosphorylation of the 70-kDa to 71-kDa phosphoprotein may be important in the intracellular signaling by which intestinal epithelial cell differentiation is controlled.

Differential modulation of human (Caco-2) colon cancer cell line phenotype by short chain fatty acids

Fermentation of dietary fiber within the colonic lumen yields short chain fatty acids (SCFA) such as butyrate, which may modulate colonic mucosal biology and inhibit the development of a malignant phenotype. However, different fibers yield varying proportions of various SCFA. We studied the effects of the three most common SCFA, acetate, butyrate, and propionate, on the proliferation, adhesion, and motility of the human intestinal Caco-2 cell line, as well as the effects of these SCFA on alkaline phosphatase and dipeptidyl dipeptidase specific activity (common laboratory markers of differentiation). In addition, we examined the modulation of c-myc protein and the tyrosine phosphorylation of cellular proteins by these SCFA in order to determine whether the variations in the potency of these three SCFA for phenotypic change extended to variations in effects on intracellular signaling and protooncogene expression. All three SCFA tended to slow proliferation, promote brush border enzyme activity, and inhibit both adhesion to and motility across a type I collagen matrix substrate. However, we observed substantial differences in the potency of these three SCFA with regard to these effects. In particular, butyrate was uniformly more potent than an equimolar concentration of acetate whereas equimolar propionate achieved comparable effects with regard to proliferation and brush border enzyme activity but was intermediate between butyrate and acetate with regard to modulation of cell-matrix interactions. Similarly, the SCFA downregulated c-myc protein levels and modulated the phosphorylation of several intracellular tyrosine phosphoproteins, but the effects of the three SCFA varied substantially for these parameters. These results suggest that the common short chain fatty acids are not equipotent in their effects on human Caco-2 colon cancer cell biology. Such differences in potency could contribute to the observed differences in effects of different dietary fibers in vivo.

Short chain fatty acids inhibit human (SW1116) colon cancer cell invasion by reducing urokinase plasminogen activator activity and stimulating TIMP-1 and TIMP-2 activities, rather than via MMP modulation

BACKGROUND

Short chain fatty acids derived from dietary fiber may protect against invasive colon cancer by modulating degradative matrix metalloproteinases (MMPs) and protective tissue inhibitor matrix metalloproteinases (TIMPs). Since invasion depends on the MMP/TIMP ratio, we hypothesized that short chain fatty acids inhibit colon cancer invasion by inhibiting MMPs and stimulating TIMPs.

MATERIALS AND METHODS

SW1116 colon cancer cells were seeded onto Matrigel-coated Boyden chambers and treated with unsupplemented media or media containing 10 mM acetate, propionate, or butyrate. SW1116 invasion was quantitated by light microscopy and conditioned media were assayed by ELISA for MMP-1,2,3,9; TIMP-1,2; MMP/TIMP complex; and urokinase plasminogen activator (uPA). All data are expressed as mean percentage of control +/- SE (n > 6).

RESULTS

Although all three short chain fatty acids inhibited invasion, butyrate was more potent than either acetate or propionate, inhibiting SW1116 invasion by 35 +/- 1% of control (n = 18, P < .0001) vs. 18 +/- 9% (n = 7, P < .05) for acetate and 10 +/- 6% (n = 7, P < .05) for propionate. MMP-2 was not modulated by any of the short chain fatty acids while MMP-1 was modulated only by butyrate and MMP-3 by propionate. Acetate did not modulate MMPs, TIMP-1, or uPA, but stimulated TIMP-2. In contrast, propionate and butyrate stimulated MMP-9 and TIMP-2 by 119-233% and both inhibited uPA by 8-16%. TIMP-1 was stimulated only by butyrate and actually inhibited by propionate. Only butyrate stimulated both TIMP-1 and TIMP-2.

CONCLUSIONS

These data suggest that dietary fiber may protect against invasive colon cancer through stimulation of TIMP and inhibition of uPA activities, rather than through short chain fatty acids effects on the activities of the MMPs studied.

Role of integrins in enterocyte migration

1. Enterocyte motility depends critically on cell-matrix interactions. Although still incompletely understood, these appear critically dependent upon integrin-mediated cell adhesion. 2. In addition to providing a mechanism for cell adhesion and traction, the integrins are likely to serve as true receptors for the matrix across which cell motility occurs, initiating signals by both mechanical and chemical means that alter cell phenotype and proliferation as well as cell motility. 3. Sound rationale now exists to postulate that soluble growth factors within the extracellular milieu regulate intestinal mucosal healing not only directly but also indirectly by modulating integrin expression and organization.

Effects of short-chain fatty acids on human rectosigmoid mucosal colonocyte brush-border enzymes

Short-chain fatty acids produced by bacterial fermentation of dietary fiber may provide a tonic stimulus to colonocyte differentiation that contributes to the protective effect of fiber against colorectal malignancy. Since brush-border enzymes are common markers of colonocytic differentiation, we compared the effects of equimolar (10 mmol/L) concentrations of the three most common short-chain fatty acids, acetate, butyrate, and propionate, on the alkaline phosphatase and dipeptidyl dipeptidase specific activity of human colonic mucosal biopsies obtained from normal volunteers. Only butyrate significantly stimulated alkaline phosphatase specific activity (50.4% +/- 18.6%, P < .05). Short-chain fatty acid stimulation of dipeptidyl dipeptidase did not achieve statistical significance. Fibers yielding high colonic butyrate levels could have different effects on human colonic mucosal differentiation.

Coculture conditions alter endothelial modulation of TGF-beta 1 activation and smooth muscle growth morphology

We examined whether endothelial cells (ECs) inhibit smooth muscle cell (SMC) transforming growth factor-beta 1 (TGF-beta 1) activation in bilayer coculture. Western analysis showed that SMCs cocultured with ECs as a bilayer had lower amounts of active TGF-beta 1 protein compared with SMCs cultured alone and SMCs cocultured with ECs as a monolayer. EC inhibition of TGF-beta 1 activation could be blocked with plasminogen activator inhibitor-1 (PAI-1) antibody. Similarly, SMC hill-and-valley growth, a marker for TGF-beta 1 activity, was present in SMCs cultured alone and SMCs cocultured with ECs as a monolayer but was absent in SMCs cocultured as a bilayer. SMCs cocultured with ECs as a bilayer migrated at a greater rate than SMCs cultured either alone or cocultured as a monolayer. The EC effect on SMC migration was inhibited by the addition of 5 ng/ml TGF-beta 1. ECs had no effect on SMC RNA levels of TGF-beta 1. PAI-1 levels were increased in ECs and ECs cocultured with SMCs compared with SMCs cultured alone. ECs inhibit TGF-beta 1 activation in bilayer coculture. This appears to be mediated through an increase in EC PAI-1 release. Alterations in coculture conditions, in particular the degree of EC-SMC cell contact, have profound effects on this process.

Tyrosine kinase inhibitors reverse butyrate stimulation of human Caco-2 intestinal epithelial cell alkaline phosphatase but not butyrate promotion of dipeptidyl dipeptidase

Short chain fatty acids such as sodium butyrate are concentrated in the colonic lumen and may protect against colon carcinogenesis by maintaining colonocytic differentiation, but the mechanisms by which they act are not fully understood. It has recently been suggested that short chain fatty acids modulate cellular tyrosine kinase activity in addition to altering chromatin structure via regulation of histone acetylation and DNA methylation. Therefore, the authors evaluated the influence of tyrosine kinase inhibition on the effects of 10 mM butyrate on human Caco-2 intestinal epithelial differentiation, using alkaline phosphatase and dipeptidyl dipeptidase specific activity as markers of differentiation, and two tyrosine kinase inhibitors, of different mechanisms of action and different effects on Caco-2 brush border enzyme specific activity, to block tyrosine kinase activity. As expected, butyrate stimulated both alkaline phosphatase and dipeptidyl dipeptidase specific activity. The tyrosine kinase inhibitors prevented, and indeed one inhibitor reversed the effects of butyrate on alkaline phosphatase specific activity. However, tyrosine kinase inhibition did not prevent butyrate stimulation of dipeptidyl dipeptidase specific activity. Different pathways are likely to regulate the effects of butyrate on expression of these two brush border enzymes. Butyrate stimulation of alkaline phosphatase, but not dipeptidyl dipeptidase, may involve tyrosine phosphorylation signaling.

Peptide YY selectively stimulates expression of the colonocytic phenotype

Peptide YY (PYY) is produced by colonic mucosal endocrine cells and modulates gastrointestinal endocrine activity through specific Y-receptors. The direct effects of PYY on intestinal mucosal growth and differentiation remain uncharacterized. The abundance of PYY in colonic mucosa suggests that PYY acts locally to maintain colonocytic differentiation. We tested this hypothesis in human Caco-2 intestinal epithelial cells, which express alkaline phosphatase (AP) and dipeptidyl dipeptidase (DP), brush-border enzymes differentially concentrated in large and small intestinal mucosa, respectively. The effects of PYY on enzyme specific activity were compared with those of pancreatic polypeptide, neuropeptide-Y, vasoactive intestinal peptide, pentagastrin, bombesin, and selective Y1- and Y2-receptor agonists. Brush-border enzyme activity was assessed by AP and DP specific activity in cell lysates quantitated spectrophotometrically following synthetic substrate digestion. PYY, neuropeptide-Y, pancreatic polypeptide, and vasoactive intestinal peptide (10(-7) mol/L) stimulated AP activity. PYY brought about the greatest increase (38.0%+/-11.0%, n=48). Only PYY decreased DP specific activity (7.9%+/-2.2%, n=48). The Y2-agonist but not the Y1-agonist mimicked these PYY effects (increasing AP 28.3%+/-3.5% and decreasing DP 10.4%+/-3.6%). These data suggest that PYY promotes differentiation toward a colonocytic phenotype in Caco-2 intestinal epithelial cells and that this effect may be mediated through the Y2-receptor subtype.

Basal nutrition promotes human intestinal epithelial (Caco-2) proliferation, brush border enzyme activity, and motility

OBJECTIVES

Provision of nutrients to the apical membrane of intestinal epithelial cells by the enteral route is critical for normal gut mucosal function and for the sheet migration required for mucosal healing. The present work attempts to determine whether supplemental nutrient delivery to the basal epithelial surface is important for intestinal epithelial biology. Since attempts to regulate intestinal epithelial cell biology by manipulation of parenteral nutrition solutions have met with some success, we hypothesized that basally delivered nutrients might also be important for intestinal epithelial biology.

DESIGN

To test this hypothesis, we compared the brush border enzyme activity, proliferation, and motility of human intestinal epithelial (Caco-2) cells cultured on a type I collagen substrate either on cell culture dishes with culture medium above the apical side of the cell monolayer or in culture inserts on 0.45-mu semipermeable membranes with culture medium beneath the monolayers as well as above them. Proliferation was assessed by serial hematocytometric counts over 13-day period. Doubling times were calculated by logarithmic transformation of cell counts 48 hrs apart. The specific activity of the brush border enzymes, dipeptidyl dipeptidase and alkaline phosphatase, was assayed by the digestion of synthetic chromogenic substrates in protein-matched aliquots of cell lysates. Sheet migration was quantitated by the expansion of Caco-2 monolayers across collagen. Motility was dissociated from the proliferative component of monolayer expansion by blocking proliferation with mitomycin C.

SETTING

Laboratory for gastrointestinal mucosal biology.

SUBJECTS

A well-differentiated subclone of cells derived from the established human Caco-2 colonic epithelial cell line.

MEASUREMENTS AND MAIN RESULTS

Basal nutrient delivery promoted Caco-2 proliferation, brush border enzyme activity, monolayer expansion, and cell motility. Proliferation was actually increased by 694 +/- 9.89% (n = 90, p < .0001) in cells nourished apically and basally compared with a 314 +/- 3.31% increase (n = 90, p < .0001) in those cells receiving only apical nutrition. The addition of basal nutrient delivery to the cell culture system augmented both alkaline phosphatase and dipeptidyl dipeptidase specific activity by 116 +/- 5.4% and 256 +/- 14.0%, respectively (p < .0001, n = 6 for each group). The effects of basal nutrient delivery were maintained after mitomycin blockade of proliferation for both alkaline phosphatase (392 +/- 89.8% of control, n = 3, p < .0005) and dipeptidyl dipeptidase (374 +/- 79.1% of control, n = 3, p < .005), suggesting that the increased digestive enzyme-specific activity reflected differentiation rather than indirect effects of slowing of proliferation. Epithelial sheet migration increased by 389 +/- 8.8% and proliferation-blocked cell motility also increased by 76.5 +/- 1.56% (p < .0005, n = 12 for each) compared with apical nutrient delivery only.

CONCLUSIONS

These results suggest that although apical nutrition may be critical for intestinal epithelial cell biology, nutrient delivery to the basal surface of intestinal epithelial cell membranes may also promote intestinal epithelial differentiation, proliferation, and mucosal healing.

Sucralfate impedes intestinal epithelial sheet migration in a Caco-2 cell culture model

Sucralfate, which binds to the matrix of the ulcer bed, is theoretically advantageous for duodenal ulcer therapy, but has not fulfilled its promise clinically. We examined the effects of sucralfate and related compounds in a human intestinal epithelial (Caco-2) cell culture model of restitution on sheet migration across and adhesion to collagen I. Migration was quantitated across a collagen I matrix treated with sucralfate or related compounds and correlated with cell adhesion. Caco-2 motility was significantly and dose-responsively inhibited by sucralfate at therapeutic luminal concentrations. Sucrose octaacetate, the sucralfate backbone, and lactose octaacetate exhibited similar effects while the beta-bonded disaccharide maltose octaacetate had little effect. Sucrose itself slightly stimulated motility. Adhesion effects paralleled motility. Thus, sucralfate may inhibit intestinal epithelial motility by sterically interfering with adhesion to collagen I. A sucralfate analog with a lactose octaacetate backbone might retain growth factor binding without inhibiting enterocyte motility, perhaps improving its clinical efficacy.

Regulation of human colonic cell line proliferation and phenotype by sodium butyrate

Colonic butyrate may maintain mucosal differentiation and oppose carcinogenesis. We characterized butyrate effects on differentiation, proliferation, and matrix interactions in Caco-2 and SW620 human colonic cells. Differentiation was assessed by brush border enzyme activity and doubling time by serial cell counts. Motility across matrix proteins was quantitated by monolayer expansion and correlated with adhesiveness to matrix. Integrin subunit surface pools were measured by immunoprecipitation. Butyrate-stimulated differentiation inhibited proliferation and was significantly more potent than acetate in this regard. Butyrate also inhibited motility across collagen I, collagen IV, and laminin, as well as decreasing adhesiveness to these matrices and beta 1, alpha 1, and alpha 2 integrin subunit surface expression. Butyrate acts in cultured cells at clinically relevant concentrations to oppose classical malignant behavior, inhibiting proliferation and motility while promoting differentiation. Since butyrate is derived from fermentation of dietary fiber, such mechanisms may contribute to the apparent protective action of fiber against colon carcinogenesis.

Amplitude-dependent modulation of brush border enzymes and proliferation by cyclic strain in human intestinal Caco-2 monolayers

Little is known about the effects of repetitive deformation during peristaltic distension and contraction or repetitive villus shortening on the proliferation and differentiation of the intestinal epithelium. We sought to characterize the effects of repetitive deformation of a physiologically relevant magnitude and frequency on the proliferation and differentiation of human intestinal epithelial Caco-2 cells, a common cell culture model for intestinal epithelial biology. Human intestinal epithelial Caco-2 cells were cultured on collagen-coated membranes deformed by -20 kPa vacuum at 10 cycles/minute, producing an average 10% strain on the adherent cells. Proliferation was assessed by cell counting and 3H-thymidine incorporation. Alkaline phosphatase and dipeptidyl dipeptidase specific activity were measured in cell lysates. Since cells at the membrane periphery experience higher strain than cells in the center, the topography of brush border enzyme histochemical and immunohistochemical staining was analyzed for strain-dependence. Cyclic strain stimulated proliferation compared to static cells. Proliferation was highest in the membrane periphery where strain was maximal. Strain also modulated differentiation independently of its mitogenic effects, selectively stimulating dipeptidyl dipeptidase while inhibiting alkaline phosphatase. Strain-associated enzyme changes were also maximal in areas of greatest strain. The PKC inhibitors staurosporine and calphostin C ablated strain mitogenic effects while intracellular PKC activity was increased by strain. The strain-associated brush border enzyme changes were attenuated but not blocked by PKC inhibition. Thus, strain of a physiologically relevant frequency and magnitude promotes proliferation and modulates the differentiation of a well-differentiated human intestinal epithelial cell line in an amplitude-dependent fashion. PKC may be involved in coupling strain to increased proliferation.