TGF-beta1 modulates focal adhesion kinase expression in rat intestinal epithelial IEC-6 cells via stimulatory and inhibitory Smad binding elements

Regulation of homeostasis and regeneration in the adult intestinal epithelium by the TGF-β superfamily

The delicate balance between the homeostatic maintenance and regenerative capacity of the intestine makes this a fascinating tissue of study. The intestinal epithelium undergoes continuous homeostatic renewal but is also exposed to a diverse array of stresses that can range from physiological processes such as digestion, to exposure to infectious agents, drugs, radiation therapy, and inflammatory stimuli. The intestinal epithelium has thus evolved to efficiently maintain and reinstate proper barrier function that is essential for intestinal integrity and function. Factors governing homeostatic epithelial turnover are well described, however, the dynamic regenerative mechanisms that occur following injury are the subject of intense ongoing investigations. The TGF-β superfamily is a key regulator of both homeostatic renewal and regenerative processes of the intestine. Here we review the roles of TGF-β and BMP on the adult intestinal epithelium during self-renewal and injury to provide a framework for understanding how this major family of morphogens can tip the scale between intestinal health and disease. This article is protected by copyright. All rights reserved.

Bovine Lactoferricin Induces Intestinal Epithelial Cell Activation through Phosphorylation of FAK and Paxillin and Prevents Rotavirus Infection

We investigated the effect of bovine lactoferricin (Lfcin-B), a peptide derived from bovine lactoferrin, on activation of intestinal epithelial cells in IEC-6 intestinal cell, and protection against in vivo rotavirus (RV) infection. Treatment with Lfcin-B significantly enhanced the growth of IEC-6 cells and increased their capacity for attachment and spreading in culture plates. Also, Lfcin-B synergistically augmented the binding of IEC-6 cells to laminin, a component of the extracellular matrix (ECM). In the analysis of the intracellular mechanism related to Lfcin-B-induced activation of IEC-6 cells, this peptide upregulated tyrosine-dependent phosphorylation of focal adhesion kinase (FAK) and paxillin, which are intracellular proteins associated with cell adhesion, spreading, and signal transduction during cell activation. An experiment using synthetic peptides with various sequences of amino acids revealed that a sequence of 9 amino acids (FKCRRWQWR) corresponding to 17-25 of the N-terminus of Lfcin-B is responsible for the epithelial cell activation. In an in vivo experiment, treatment with Lfcin-B one day before RV infection effectively prevented RV-induced diarrhea and significantly reduced RV titers in the bowels of infected mice. These results suggest that Lfcin-B plays meaningful roles in the maintenance and repair of intestinal mucosal tissues, as well as in protecting against intestinal infection by RV. Collectively, Lfcin-B is a promising candidate with potential applications in drugs or functional foods beneficial for intestinal health and mucosal immunity.

ZINC40099027 Promotes Gastric Mucosal Repair in Ongoing Aspirin-Associated Gastric Injury by Activating Focal Adhesion Kinase

Nonsteroidal anti-inflammatory drugs cause gastric ulcers and gastritis. No drug that treats GI injury directly stimulates mucosal healing. ZINC40099027 (ZN27) activates focal adhesion kinase (FAK) and heals acute indomethacin-induced small bowel injury. We investigated the efficacy of ZN27 in rat and human gastric epithelial cells and ongoing aspirin-associated gastric injury. ZN27 (10 nM) stimulated FAK activation and wound closure in rat and human gastric cell lines. C57BL/6J mice were treated with 300 mg/kg/day aspirin for five days to induce ongoing gastric injury. One day after the initial injury, mice received 900 µg/kg/6 h ZN27, 10 mg/kg/day omeprazole, or 900 µg/kg/6 h ZN27 plus 10 mg/kg/day omeprazole. Like omeprazole, ZN27 reduced gastric injury vs. vehicle controls. ZN27-treated mice displayed better gastric architecture, with thicker mucosa and less hyperemia, inflammation, and submucosal edema, and lost less weight than vehicle controls. Gastric pH, serum creatinine, serum alanine aminotransferase (ALT), and renal and hepatic histology were unaffected by ZN27. Blinded scoring of pFAK-Y-397 immunoreactivity at the edge of ZN27-treated lesions demonstrated increased FAK activation, compared to vehicle-treated lesions, confirming target activation in vivo. These results suggest that ZN27 ameliorates ongoing aspirin-associated gastric mucosal injury by a pathway involving FAK activation. ZN27-derivatives may be useful to promote gastric mucosal repair.

The P-loop region of Schlafen 3 acts within the cytosol to induce differentiation of human Caco-2 intestinal epithelial cells

Schlafen 3 (Slfn3) mediates rodent enterocyte differentiation in vitro and in vivo, required for intestinal function. Little is known about Schlafen protein structure-function relationships. To define the Slfn3 domain that promotes differentiation, we studied villin and sucrase isomaltase (SI) promoter activity in Slfn3-null human Caco-2BBE cells transfected with full-length rat Slfn3 DNA or truncated constructs. Confocal microscopy and Western blots showed that Slfn3 is predominantly cytosolic. Villin promoter activity, increased by wild type Slfn3, was further enhanced by adding a nuclear exclusion sequence, suggesting that Slfn3 does not affect transcription by direct nuclear action. We therefore sought to dissect the region in Slfn3 stimulating promoter activity. Since examination of the Slfn3 N-terminal region revealed sequences similar to both an aminopeptidase (App) and a divergent P-loop resembling those in NTPases, we initially divided Slfn3 into an N-terminal domain containing the App and P-loop regions, and a C-terminal region. Only the N-terminal construct stimulated promoter activity. Further truncation indicated that both the App and the smaller P-loop constructs enhanced promoter activity similarly to the N-terminal sequence. Point mutations within the N-terminal region (R128L, altering a critical active site residue in the App domain, and L212D, conserved in Schlafens but variable in P-loop proteins) did not affect activity. These results show that Slfn3 acts in the cytosol to trigger a secondary signal cascade that elicits differentiation marker expression and narrows the active domain to the third of the Slfn3 sequence homologous to P-loop NTPases, a first step in understanding its mechanism of action.

Mucosal healing in ulcerative colitis: pathophysiology and pharmacology

Ulcerative colitis (UC) is a colonic inflammatory condition with a substantial impact on the quality of life of affected persons. The disease carries a cumulative risk of need of colectomy of 20-30% and an estimated cumulative risk of colorectal cancer of 18% after 30 years of disease duration. With the introduction of the tumor necrosis factor-alpha inhibitors for the treatment of UC, it has become increasingly evident that the disease course is influenced by whether or not the patient achieves mucosal healing. Thus, patients with mucosal healing have fewer flare-ups, a decreased risk of colectomy, and a lower probability of developing colorectal cancer. Understanding the mechanisms of mucosal wound formation and wound healing in UC, and how they are affected therapeutically is therefore of importance for obtaining efficient treatment strategies holding the potential of changing the disease course of UC. This review is focused on the pathophysiological mechanism of mucosal wound formation in UC as well as the known mechanisms of intestinal wound healing. Regarding the latter topic, pathways of both wound healing intrinsic to epithelial cells and the wound-healing mechanisms involving interaction between epithelial cells and other cells of the mucosa are discussed. The biochemistry of wound healing in UC provides the basis for the subsequent description of how these pathways are affected by the current medications, and what can be learnt on how to design future treatment regimens for UC based on targeting mucosal healing.

Loss of MLK3 signaling impedes ulcer healing by modulating MAPK signaling in mouse intestinal mucosa

Mixed-lineage kinase 3 (MLK3) activates multiple MAPK pathways and can initiate apoptosis, proliferation, migration, or differentiation in different cell types. However, whether MLK3 signaling regulates intestinal epithelial cell sheet migration in vivo is not known. We sought to investigate whether MLK3 signaling is important in intestinal mucosal healing and epithelial cell motility in vivo and in vitro. In vivo, we compared the healing of jejunal mucosal ulcers induced in MLK3 knockout (KO) mice with healing in wild-type (WT) mice. Ulcer healing was 20.8% less at day 3 (P < 0.05) and 18.9% less at day 5 (P < 0.05) in MLK3 KO than WT mice. Within the intestinal mucosa of MLK3 KO mice, ERK and JNK signaling were reduced, phosphatase and tensin homolog deleted on chromosome 10 (PTEN) level was increased, and p38 signaling was unchanged. Parallel in vitro studies using an MLK inhibitor assessed the role of MLK signaling in human Caco-2 intestinal epithelial migration across collagen substrates. The MLK inhibitor reduced closure of circular wounds in Caco-2 monolayers. MLK inhibition reduced ERK and JNK, but not p38, signaling in Caco-2 cells. Although PTEN is increased after MLK inhibition, it does not influence MLK-mediated cell migration. These findings indicate that disruption of MLK3 signaling impairs ulcer healing by suppressing ERK and JNK signaling in vitro and in mouse intestinal mucosa in vivo. These results reveal a novel role for MLK3 signaling in the regulation of intestinal epithelial migration in vivo and suggest that MLK3 may be an important target for the regulation of intestinal mucosal healing.

Transcriptional control of cell cycle-dependent kinase 4 by Smad proteins--implications for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by deregulation of neuronal cell cycle and differentiation control eventually resulting in cell death. During brain development, neuronal differentiation is regulated by Smad proteins, which are elements of the canonical transforming growth factor β (TGF-β) signaling pathway, linking receptor activation to gene expression. In the normal adult brain, Smad proteins are constitutively phosphorylated and predominantly localized in neuronal nuclei. Under neurodegenerative conditions such as AD, the subcellular localization of their phosphorylated forms is heavily disturbed, raising the question of whether a nuclear Smad deficiency in neurons might contribute to a loss of neuronal differentiation control and subsequent cell cycle re-entry. Here, we show by luciferase reporter assays, electromobility shift, and RNA interference (RNAi) technique a direct binding of Smad proteins to the CDK4 promoter inducing transcriptional inhibition of cell cycle-dependent kinase 4 (Cdk4). Mimicking the neuronal deficiency of Smad proteins observed in AD in cell culture by RNAi results in elevation of Cdk4 and retardation of neurite outgrowth. The results identify Smad proteins as direct transcriptional regulators of Cdk4 and add further evidence to a Smad-dependent deregulation of Cdk4 in AD, giving rise to neuronal dedifferentiation and cell death.

The role of focal adhesion kinase in the TGF-β-induced myofibroblast transdifferentiation of human Tenon's fibroblasts

Purpose

To investigate the role of focal adhesion kinase (FAK) in transforming growth factor (TGF)-β-induced myofibroblast transdifferentiation of human Tenon's fibroblasts.

Methods

Primary cultured human Tenon's fibroblasts were exposed to TGF-β1 for up to 48 hours. The mRNA levels of FAK, α smooth muscle actin (αSMA), and β-actin were determined by quantitative real time reverse transcription polymerase chain reaction. The protein levels of collagen type I, FAK, phospho-FAK, αSMA, and β-actin were determined by Western immunoblots. After the small interfering RNA targeting FAK (siRNA_FAK) molecules were delivered into the cells, the expressions of αSMA proteins were determined by Western immunoblots.

Results

In human Tenon's fibroblasts, TGF-β1 significantly increased the mRNA and protein expressions of αSMA. However, when the action of FAK was inhibited using siRNA_FAK, the TGF-β1-induced expression of αSMA was attenuated.

Conclusions

Our data suggest that FAK may be associated with the TGF-β1-induced transdifferentiation of human Tenon's fibroblasts to myofibroblasts, which is the essential step of subconjunctival fibrosis.

Effects of Ganoderma lucidum polysaccharides on IEC-6 cell proliferation, migration and morphology of differentiation benefiting intestinal epithelium healing in vitro

OBJECTIVES

Restoration of epithelial continuity in the intestinal surface after extensive destruction is important since intestinal epithelial cells stand as a boundary between the body's internal and external environment. Polysaccharides from Ganoderma lucidum (Gl-PS) may benefit intestinal epithelial wound healing in different aspects, which awaits clarification. To identify potential effects, a non-transformed small-intestinal epithelial cell line, IEC-6 cells, was used.

METHODS

Effects on epithelial cell proliferation, migration, morphology of differentiation and transforming growth factor beta (TGF-β) protein expression, as well as the cellular ornithine decarboxylase (ODC) mRNA and c-Myc mRNA expression, were assessed, respectively, by MTT assay, wound model in vitro, observation under a microscope after hematoxylin and eosin staining, enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction assays.

KEY FINDINGS

It was shown that Gl-PS stimulated IEC-6 cell proliferation and migration significantly in a dose-dependent manner; 10 µg/ml Gl-PS improved the morphology of differentiation in IEC-6 cells. Inefficacy in expression of TGF-β in IEC-6 cells indicated a possible TGF-β independent action of Gl-PS. However, Gl-PS increased ODC mRNA and c-Myc mRNA expression in a dose-dependent manner, indicating, at least partially possible involvement of ODC and c-Myc gene expression in improvement of intestinal wound healing.

CONCLUSIONS

These results suggest the potential usefulness of Gl-PS to cure intestinal disorders characterized by injury and ineffective repair of the intestinal mucosa.

Non-Smad transforming growth factor-β signaling regulated by focal adhesion kinase binding the p85 subunit of phosphatidylinositol 3-kinase

TGF-β modulates numerous diverse cellular phenotypes including growth arrest in epithelial cells and proliferation in fibroblasts. Although the Smad pathway is fundamental for the majority of these responses, recent evidence indicates that non-Smad pathways may also have a critical role. Here we report a novel mechanism whereby the nonreceptor tyrosine focal adhesion kinase (FAK) functions as an adaptor necessary for cell type-specific responses to TGF-β. We show that in contrast to Smad actions, non-Smad pathways, including c-Abl, PAK2, and Akt, display an obligate requirement for FAK. Interestingly, this occurs in Src null SYF cells and is independent of FAK tyrosine phosphorylation, kinase activity, and/or proline-rich sequences in the C-terminal FAT domain. FAK binds the phosphatidylinositol 3-kinase (PI3K) p85 regulatory subunit following TGF-β treatment in a subset of fibroblasts but not epithelial cells and has an obligate role in TGF-β-stimulated anchorage-independent growth and migration. Together, these results uncover a new scaffolding role for FAK as the most upstream component regulating the profibrogenic action of TGF-β and suggest that inhibiting this interaction may be useful in treating a number of fibrotic diseases.

Progress in researches about focal adhesion kinase in gastrointestinal tract

Focal adhesion kinase (FAK) is a 125-kDa non-receptor protein tyrosine. Growth factors or the clustering of integrins facilitate the rapid phosphorylation of FAK at Tyr-397 and this in turn recruits Src-family protein tyrosine kinases, resulting in the phosphorylation of Tyr-576 and Tyr-577 in the FAK activation loop and full catalytic FAK activation. FAK plays a critical role in the biological processes of normal and cancer cells including the gastrointestinal tract. FAK also plays an important role in the restitution, cell survival and apoptosis and carcinogenesis of the gastrointestinal tract. FAK is over-expressed in cancer cells and its over-expression and elevated activities are associated with motility and invasion of cancer cells. FAK has been proposed as a potential target in cancer therapy. Small molecule inhibitors effectively inhibit the kinase activity of FAK and show a potent inhibitory effect for the proliferation and migration of tumor cells, indicating a high potential for application in cancer therapy.

Role of ERK/mTOR signaling in TGFbeta-modulated focal adhesion kinase mRNA stability and protein synthesis in cultured rat IEC-6 intestinal epithelial cells

Increasing evidence is available showing the importance of the FAK (focal adhesion kinase) protein level in the migration and homeostasis of intestinal cells. TGFbeta (transforming growth factor beta) modulates FAK protein expression in a complex fashion not only by inducing the activation of p38 and Smad signaling resulting in increased fak promoter activity and increased FAK protein levels, but also by activating ERK (extracellular signal regulated kinases), p38, and the Smad pathway. We show that the blockade of ERK signaling by a specific MEK (MAPK kinase) inhibitor attenuates TGFbeta-induced FAK mRNA stability and reduces FAK protein levels in rat IEC-6 intestinal epithelial cells. The mTOR (mammalian target of rapamycin)-specific inhibitor rapamycin and small interfering RNAs for mTOR and p70(S6) kinase also block TGFbeta-induced FAK protein synthesis. Furthermore, we have found that a TGFbeta-induced increase in wound closures in monolayers of these cells is abolished in the presence ERK or mTOR inhibition. Thus, TGFbeta also modulates FAK protein levels in cultured rat IEC-6 intestinal epithelial cells via ERK activation, acting at the transcriptional level to complement Smad signaling and at on the translational level via the mTOR pathway downstream of ERK, which in turn promotes intestinal epithelial cell migration.