Margaret M. Lotz

Intestinal Restitution: Progression of Actin Cytoskeleton Rearrangements and Integrin Function in a Model of Epithelial Wound Healing

Superficial injury involving the mucosa of the gastrointestinal tract heals by a process termed restitution that involves epithelial sheet movement into the damaged area. The forces that drive epithelial sheet movement are only partially understood, although it is known to involve changes in the morphology of cells bordering the damage, such as the formation of large, flat, cytoplasmic extensions termed lamellae. We investigated the mechanism of epithelial sheet movement by following the response of the actin cytoskeleton and specific integrins (alpha6beta4, alpha6beta1, and alpha3beta1) to wounding. To model this event in vitro, monolayers of T84 cells, well-differentiated colon carcinoma cells, were damaged by aspiration and the ensuing response was analyzed by a combination of time-lapse video microscopy, fluorescence confocal microscopy and antibody inhibition assays. We show that wound healing begins with retraction of the monolayer. alpha6beta4 integrin is localized on the basal surface in structures referred to as type II hemidesmosomes that persist throughout this early stage. We hypothesize that these structures adhere to the substrate and function to retard retraction. Once retraction ceases, the wound is contracted initially by actin purse strings and then lamellae. Purse strings and lamellae produce a pulling force on surrounding cells, inducing them to flatten into the wound. In the case of lamellae, we detected actin suspension cables that appear to transduce this pulling force. As marginal cells produce lamellae, their basal type II hemidesmosomes disappear and the alpha6 integrins appear evenly distributed over lamellae surfaces. Antibodies directed against the alpha6 subunit inhibit lamellae formation, indicating that redistribution of the alpha6 integrins may contribute to the protrusion of these structures. Antibodies directed against the alpha3beta1 integrin also reduce the size and number of lamellae. This integrins contribution to lamellae extension is most likely related to its localization at the leading edge of emerging protrusions. In summary, wounds in epithelial sheets initially retract, and then are contracted by first an actin purse string and then lamellae, both of which serve to pull the surrounding cells into the denuded area. The alpha6 integrins, particularly alpha6beta4, help contain retraction and both the alpha6 integrins and alpha3beta1 integrin contribute to lamellae formation.

Effects of substance P on human colonic mucosa in vitro.

Previous studies indicated that the peptide substance P (SP) causes Cl--dependent secretion in animal colonic mucosa. We investigated the effects of SP in human colonic mucosa mounted in Ussing chamber. Drugs for pharmacological characterization of SP-induced responses were applied 30 min before SP. Serosal, but not luminal, administration of SP (10-8 to 10-6 M) induced a rapid, monophasic concentration and Cl--dependent, bumetanide-sensitive short-circuit current ( I sc) increase, which was inhibited by the SP neurokinin 1 (NK1)-receptor antagonist CP-96345, the neuronal blocker TTX, the mast cell stabilizer lodoxamide, the histamine 1-receptor antagonist pyrilamine, and the PG synthesis inhibitor indomethacin. SP caused TTX- and lodoxamide-sensitive histamine release from colonic mucosa. Two-photon microscopy revealed NK1(SP)-receptor immunoreactivity on nerve cells. The tyrosine kinase inhibitor genistein concentration dependently blocked SP-induced I sc increase without impairing forskolin- and carbachol-mediated I sc increase. We conclude that SP stimulates Cl--dependent secretion in human colon by a pathway(s) involving mucosal nerves, mast cells, and the mast cell product histamine. Our results also indicate that tyrosine kinases may be involved in this SP-induced response.Previous studies indicated that the peptide substance P (SP) causes Cl--dependent secretion in animal colonic mucosa. We investigated the effects of SP in human colonic mucosa mounted in Ussing chamber. Drugs for pharmacological characterization of SP-induced responses were applied 30 min before SP. Serosal, but not luminal, administration of SP (10(-8) to 10(-6) M) induced a rapid, monophasic concentration and Cl--dependent, bumetanide-sensitive short-circuit current (Isc) increase, which was inhibited by the SP neurokinin 1 (NK1)-receptor antagonist CP-96345, the neuronal blocker TTX, the mast cell stabilizer lodoxamide, the histamine 1-receptor antagonist pyrilamine, and the PG synthesis inhibitor indomethacin. SP caused TTX- and lodoxamide-sensitive histamine release from colonic mucosa. Two-photon microscopy revealed NK1 (SP)-receptor immunoreactivity on nerve cells. The tyrosine kinase inhibitor genistein concentration dependently blocked SP-induced Isc increase without impairing forskolin- and carbachol-mediated Isc increase. We conclude that SP stimulates Cl--dependent secretion in human colon by a pathway(s) involving mucosal nerves, mast cells, and the mast cell product histamine. Our results also indicate that tyrosine kinases may be involved in this SP-induced response.

Urinary Metalloproteinases: Noninvasive Biomarkers for Breast Cancer Risk Assessment

Matrix metalloproteinases (MMP) and a disintegrin and metalloprotease 12 (ADAM 12) can be detected in the urine of breast cancer patients and provide independent prediction of disease status. To evaluate the potential of urinary metalloproteinases as biomarkers to predict breast cancer risk status, urine samples from women with known risk marker lesions, atypical hyperplasia and lobular carcinoma in situ (LCIS), were analyzed. Urine samples were obtained from 148 women: 44 women with atypical hyperplasia, 24 women with LCIS, and 80 healthy controls. MMP analysis was done using gelatin zymography and ADAM 12 analysis was done via immunoblotting with monospecific antibodies and subsequent densitometric measurement. Positive urinary MMP-9 levels indicated a 5-fold risk of atypical hyperplasia and >13-fold risk of LCIS compared with normal controls. Urinary ADAM 12 levels were significantly elevated in women with atypical hyperplasia and LCIS from normal controls, with receiver operating characteristic curve analysis showing an area under the curve of 0.914 and 0.950, respectively. To assess clinical applicability, a predictive index was developed using ADAM 12 in conjunction with Gail risk scores for women with atypia. Scores above 2.8 on this ADAM 12-Gail risk prediction index score are predictive of atypical hyperplasia (sensitivity, 0.976; specificity, 0.977). Our data suggest that the noninvasive detection and analysis of urinary ADAM 12 and MMP-9 provide important clinical information for use as biomarkers in the identification of women at increased risk of developing breast cancer. (Cancer Epidemiol Biomarkers Prev 2008;17(5):1034–12)

A Novel Structural Variant of the Human β4 Integrin cDNA

The ability of the alpha 6 beta 4 integrin to function as a laminin receptor appears to be cell-type dependent. We reported that this integrin functions as a laminin receptor on clone A cells, a colon carcinoma cell line (Lee et al., J. Cell Biol., 117:671-678), but this integrin may not function as a laminin receptor on all cell types in which it is expressed. One potential mode of alpha 6 beta 4 regulation resides in the beta 4 cytoplasmic domain because structural variants of this domain exist. We isolated beta 4 clones from a clone A cDNA library and identified a 21 bp (7aa), in-frame deletion not previously reported. This 7aa variant is located within a region that exhibits a relatively high degree of homology (42%) with the 70aa insert previously reported by Tamura et al. (J. Cell Biol., 111:1593-1604). One major difference between these two regions is that the region we have highlighted does not contain the four potential serine/threonine phosphorylation sites that are present in the 210 bp (70aa) insert. PCR analysis revealed that the 7aa variant is also expressed in RNA obtained from normal colon and placenta.

Bacteroides fragilis toxin 2 damages human colonic mucosa in vitro

BACKGROUND Strains ofBacteroides fragilis producing a 20 kDa protein toxin (B fragilis toxin (BFT) or fragilysin) are associated with diarrhoea in animals and humans. Although in vitro results indicate that BFT damages intestinal epithelial cells in culture, the effects of BFT on native human colon are not known. AIMS To examine the electrophysiological and morphological effects of purified BFT-2 on human colonic mucosa in vitro. METHODS For resistance (R) measurements, colonic mucosa mounted in Ussing chambers was exposed to luminal or serosal BFT-2 (1.25–10 nM) and after four hours morphological damage was measured on haematoxylin and eosin stained sections using morphometry. F actin distribution was assessed using confocal microscopy. RESULTS Serosal BFT-2 for four hours was four-, two-, seven-, and threefold more potent than luminal BFT-2 in decreasing resistance, increasing epithelial3H-mannitol permeability, and damaging crypt and surface colonocytes, respectively (p<0.05). Confocal microscopy showed reduced colonocyte F actin staining intensity after exposure to BFT-2. CONCLUSIONS BFT-2 increases human colonic permeability and damages human colonic epithelial cells in vitro. These effects may be important in the development of diarrhoea and intestinal inflammation caused by B fragilis in vivo.

Overexpression of pp60c-src elicits invasive behavior in rat colon epithelial cells

BACKGROUND & AIMS Src activation is reported as an early event found in preneoplastic colonic adenomas and in 70% of colon carcinomas. The aim of this study was to identify the biological consequences of c-src overexpression in rat colon epithelial cells. METHODS Introduction and overexpression of c-src in an immortalized rat colon epithelial cell line was achieved using lipofection. Transfectants were tested for changes in growth and cell behavior using different in vitro assay systems. RESULTS Colon epithelial cells overexpressing c-src showed the ability to form microcolonies in soft agar without acquiring tumorigenic potential. In in vitro assays, c-src transfectants displayed a gain of invasive potential through Matrigel without an accompanying change in migrational ability. No discernible qualitative changes were observed in the phosphotyrosyl protein profile between c-src and v-src transfectants. Assessment of the cadherin/catenin status in these cells revealed an intact, functional complex with no detectable tyrosine phosphorylation of different components of the complex. CONCLUSIONS Overexpression of c-src in an immortalized rat colon epithelial cell line does not elicit full neoplastic transformation but enhances anchorage-independent growth and confers invasion capability. Increased invasion through Matrigel was not linked to inactivation of the cadherin complex in c-src transfectants.

K+ channel inhibition accelerates intestinal epithelial cell wound healing

Restitution is the process by which superficial interruptions in the gastrointestinal mucosa are repaired by the flattening and spreading of epithelial cells surrounding the damage. During this process, mucosal epithelial cells undergo extensive reshaping and cytoskeletal remodeling. K+ channels, located primarily on the basolateral surface of gut epithelial cells, are central to both actin polymerization, via their control of membrane potential, and cell volume regulation. We questioned whether K+ channels are involved in restitution using an in vitro model of intestinal epithelium, monolayers of the human colon carcinoma cell line T84. We report that pharmacologic K+ channel inhibition accelerates wound healing in T84 cell monolayers. Both Ca++‐dependent and constitutively active channels are involved, as indicated by the sensitivity to clotrimazole, charybdotoxin, and barium. The ability of clotrimazole to accelerate wound resealing was also observed in Caco‐2 cell sheets. Pharmacologic stimulation of K+ channel activity had no effect on the repair rate. Analysis of the resealing process by time lapse and confocal microscopy revealed that K+ channel inhibitors abolished the initial wound retraction, briefly accelerated the repair rate, and altered the shape of the cell sheet abutting the injury during the early phase of resealing. We hypothesize that K+ channel inactivation interrupts the coregulation of f‐actin polymerization and volume control that is initiated by the healing process.

Protein kinase C activation downregulates the expression and function of the basolateral Na+/K+/2Cl− cotransporter

The basolateral Na+/K+/2Cl− cotransporter (NKCC1) has been shown to be an independent regulatory site for electrogenic Cl− secretion. The proinflammatory phorbol ester, phorbol 12‐myristate 13‐acetate (PMA), which activates protein kinase C (PKC), inhibits basal and cyclic adenosine monophosphate (cAMP)‐stimulated NKCC1 activity in T84 intestinal epithelial cells and decreases the steady state levels of NKCC1 mRNA in a time‐ and dose‐dependent manner. The levels of NKCC1 protein also fall in accordance with the NKCC1 mRNA transcript and these levels are unaffected by 4α‐phorbol, which does not activate PKC. Inhibition of maximal (cAMP‐stimulated) NKCC1 functional activity by PMA was first detected by 1 h, whereas decreases in the steady state levels of NKCC1 mRNA were not detectable until 4 h. NKCC1 mRNA expression recovers toward control levels with extended treatment of cells with PMA suggesting that the PMA effects on NKCC1 expression are mediated through activation of PKC. Although NKCC1 mRNA and protein levels return to control values after extended PMA exposure, NKCC1 functional activity does not recover. Immunofluorescence imaging suggest that the absence of functional recovery is due to failure of newly synthesized NKKC1 protein to reach the cell surface. We conclude that NKCC1 has the capacity to be regulated at the level of de novo expression by PKC, although decreased NKCC1 expression alone cannot account for either early or late loss of NKCC1 function. J. Cell. Physiol. 181:489–498, 1999.

The rapid expression of myocardial Hsp 70 mRNA and the heat shock 70 kDa protein can be achieved after only a brief period of retrograde hyperthermic perfusion

The induction of heat shock proteins in the myocardium has been suggested as a possible intervention to allow for enhanced cardioprotection. We have postulated that a brief period of retrograde hyperthermic perfusion would be sufficient to induce Hsp 70 mRNA and protein accumulation. To investigate this hypothesis, rat hearts (n = 45) were perfused at 37 degrees C for 30 min, then perfused for 15 min at 42 degrees C, and allowed to recover at 37 degrees C for 120 min. Control hearts (n = 23) were perfused at 37 degrees C continuously. Northern analysis indicated that in hearts treated with a brief period of retrograde hyperthermic perfusion Hsp 70 mRNA levels were increased 2.85 +/- 0.02-fold (P < 0.01) by 10 min, 4.88 +/- 0.94-fold (P < 0.01) by 15 min, 9.19 +/- 0.62-fold (P < 0.001) by 30 min, 9.4 +/- 0.52-fold (P < 0.001) by 60 min, 9.45 +/- 0.57-fold (P < 0.001) by 90 min and 9.66 +/- 0.99-fold (P < 0.001) by 120 min of normothermic recovery as compared to control hearts. Western analysis revealed that the heat inducible Hsp 72 kDa protein was increased 2.37 +/- 0.45-fold (P < 0.01) at 60 min, 2.53 +/- 0.25-fold (P < 0.01) at 90 min, and 2.7 +/- 0.6&-fold (P < 0.01) at 120 min when compared to control hearts. Our results indicate that the induction of the heat shock protein Hsp 70 can be rapidly achieved through retrograde hyperthermic perfusion of the myocardium.

Epidermal Growth Factor Stimulation Can Substitute for c-Src Overexpression in Promoting Breast Carcinoma Invasion

BACKGROUND AND AIMS Cancer progression is in large part dependent on the complex process of cell invasion, involving adhesion, motility, and enzymatic proteolysis. Overexpression of the Src proto-oncogene (c-Src), a nonreceptor tyrosine kinase, has been implicated in the progression of both colon and breast cancer. Our group has previously reported that overexpression of c-Src leads to a significant gain in invasive cell behavior in vitro. In this study, we sought to assess the relative importance of epidermal growth factor (EGF) stimulation and c-Src overexpression in conferring an invasive phenotype. METHODS Breast carcinoma cells and colon epithelial cells which naturally express low levels of c-Src were used for these studies. The cells were transfected so that they overexpressed c-Src; the mock-transfected parent lines were used as controls. Transfectants were tested for changes in invasion patterns after Src inhibition and EGF stimulation. RESULTS Invasion assays in both cell systems confirmed the importance of c-Src in determining invasive potential. A significant correlation was shown between c-Src kinase protein and cell invasion. Furthermore, Src inhibition significantly inhibited invasion in a dose-dependent manner. To clarify the relative contribution of EGF and c-Src to cell invasion, the ability of cells to invade through growth-factor-reduced matrigel, with or without EGF added, was compared to invasion through intact matrigel. The breast and colon cell lines behave quite differently in this regard. In the colon model, overexpressed c-Src is critical for cell invasion and stimulation with EGF is synergistic with c-Src overexpression. Conversely, the breast carcinoma cells transfected with c-Src were unable to invade without EGF stimulation and did not demonstrate the same synergistic relationship between c-Src and EGF. Instead, our results indicate that in BT474 breast carcinoma cells, EGF can substitute for c-Src in promoting breast cancer cell invasion. CONCLUSIONS Because most breast carcinomas overexpress c-Src, it behooves one to question the extent to which reducing the amount of EGF and consequent EGFR activity will decrease invasion. In this study, the effects of EGF on cell invasion were determined in light of a single alteration in c-Src expression. Our results show that EGF enhances the impact of c-Src overexpression on invasion. In breast cancer cells, EGF is capable of inducing invasion to the same extent as c-Src overexpression. This suggests that anti-EGFR therapies will be efficacious in retarding breast carcinoma invasion and metastasis.