Cytoskeletal signaling by way of alpha-actinin-1 mediates ERK1/2 activation by repetitive deformation in human Caco2 intestinal epithelial cells

Schlafen 12 mediates the effects of butyrate and repetitive mechanical deformation on intestinal epithelial differentiation in human Caco-2 intestinal epithelial cells

Intestinal epithelial differentiation may be stimulated by diverse pathways including luminal short-chain fatty acids and repetitive mechanical deformation engendered by villous motility and peristalsis. Schlafen 12 (SLFN12) is a cytosolic protein that stimulates sucrase-isomaltase (SI) expression. We hypothesized that two disparate differentiating stimuli, butyrate and repetitive deformation, would each stimulate SLFN12 expression in human Caco-2 intestinal epithelial cells and that increased SLFN12 expression would contribute to the differentiating activity of the human Caco-2 intestinal epithelial cells. We stimulated Caco-2 cells with 1-2 mM butyrate or repetitive mechanical deformation at 10 cycles/min at an average 10% strain, and measured SLFN12 and SI expression by qRT-PCR. Sodium butyrate enhanced SLFN12 expression at both 1 mM and 2 mM although SI expression was only significantly increased at 2 mM. Repetitive deformation induced by cyclic mechanical strain also significantly increased both SLFN12 and SI gene expression. Reducing SLFN12 by siRNA decreased basal, deformation-stimulated, and butyrate-stimulated SLFN12 levels, compared to control cells treated with non-targeting siRNA, although both deformation and butyrate were still able to stimulate SLFN12 expression in siRNA-treated cells compared to control cells treated with the same siRNA. This attenuation of the increase in SLFN12 expression in response to mechanical strain or butyrate was accompanied by parallel attenuation of SI expression. Butyrate stimulated SI-promoter activity, and reducing SLFN12 by siRNA attenuated butyrate-induced SI-promoter activity. These data suggest that SLFN12 mediates at least in part the stimulation by both butyrate and repetitive mechanical deformation of sucrase-isomaltase, a late stage differentiation marker in human intestinal epithelial cells.

Physical and functional interactions between a glioma cation channel and integrin-β1 require α-actinin

Major plasma membrane components of the tumor cell, ion channels, and integrins play crucial roles in metastasis. Glioma cells express an amiloride-sensitive nonselective cation channel composed of acid-sensing ion channel (ASIC)-1 and epithelial Na(+) channel (ENaC) α- and γ-subunits. Inhibition of this channel is associated with reduced cell migration and proliferation. Using the ASIC-1 subunit as a reporter for the channel complex, we found a physical and functional interaction between this channel and integrin-β1. Short hairpin RNA knockdown of integrin-β1 attenuated the amiloride-sensitive current, which was due to loss of surface expression of ASIC-1. In contrast, upregulation of membrane expression of integrin-β1 increased the surface expression of ASIC-1. The link between the amiloride-sensitive channel and integrin-β1 was mediated by α-actinin. Downregulation of α-actinin-1 or -4 attenuated the amiloride-sensitive current. Mutation of the putative binding site for α-actinin on the COOH terminus of ASIC-1 reduced the membrane localization of ASIC-1 and also resulted in attenuation of the amiloride-sensitive current. Our data suggest a novel interaction between the amiloride-sensitive glioma cation channel and integrin-β1, mediated by α-actinin. This interaction may form a mechanism by which channel activity can regulate glioma cell proliferation and migration.

The impact of ATRA on shaping human myeloid cell responses to epithelial cell-derived stimuli and on T-lymphocyte polarization

Vitamin A plays an essential role in the maintenance of gut homeostasis but its interplay with chemokines has not been explored so far. Using an in vitro model system we studied the effects of human colonic epithelial cells (Caco2, HT-29, and HCT116) derived inflammatory stimuli on monocyte-derived dendritic cells and macrophages. Unstimulated Caco2 and HT-29 cells secreted CCL19, CCL21, and CCL22 chemokines, which could attract dendritic cells and macrophages and induced CCR7 receptor up-regulation by retinoic-acid resulting in dendritic cell migration. The chemokines Mk, CXCL16, and CXCL7 were secreted by all the 3 cell lines tested, and upon stimulation by IL-1β or TNF-α this effect was inhibited by ATRA but had no impact on CXCL1, CXCL8, and CCL20 secretion in response to IL-1β. In the presence of ATRA the supernatants of these cells induced CD103 expression on monocyte-derived dendritic cells and when conditioned by ATRA and cocultured with CD4⁺ T-lymphocytes they reduced the proportion of Th17 T-cells. However, in the macrophage-T-cell cocultures the number of these effector T-cells was increased. Thus cytokine-activated colonic epithelial cells trigger the secretion of distinct combinations of chemokines depending on the proinflammatory stimulus and are controlled by retinoic acid, which also governs dendritic cell and macrophage responses.

Increased extracellular pressure stimulates tumor proliferation by a mechanosensitive calcium channel and PKC-β

Large tumors exhibit high interstitial pressure heightened by growth against the constraining stroma. Such pressures could stimulate tumor proliferation via a mechanosensitive ion channel. We studied the effects of 0-80 mmHg increased extracellular pressure for 24 h on proliferation of SW620, Caco-2, and CT-26 colon; MCF-7 breast; and MLL and PC3 prostate cancer cells, and delineated its mechanism in SW620 cells with specific inhibitors and siRNA. Finally, we compared NF-kB, phospho-IkB and cyclin D1 immunoreactivity in the high pressure centers and low pressure peripheries of human tumors. Pressure-stimulated proliferation in all cells. Pressure-driven SW620 proliferation required calcium influx via the T-type Ca(2+) channel Cav3.3, which stimulated PKC-β to invoke the IKK-IkB-NF-kB pathway to increase proliferation and S-phase fraction. The mitotic index and immunoreactivity of NF-kB, phospho-IkB, and cyclin D1 in the center of 28 large human colon, lung, and head and neck tumors exceeded that in tumor peripheries. Extracellular pressure increases [Ca(2+)]i via Cav3.3, driving a PKC-β- IKK- IkB-NF-kB pathway that stimulates cancer cell proliferation. Rapid proliferation in large stiff tumors may increase intratumoral pressure, activating this pathway to stimulate further proliferation in a feedback cycle that potentiates tumor growth. Targeting this pathway may inhibit proliferation in large unresectable tumors.

The non-muscle functions of actinins: an update

α-Actinins are a major class of actin filament cross-linking proteins expressed in virtually all cells. In muscle, actinins cross-link thin filaments from adjacent sarcomeres. In non-muscle cells, different actinin isoforms play analogous roles in cross-linking actin filaments and anchoring them to structures such as cell-cell and cell-matrix junctions. Although actinins have long been known to play roles in cytokinesis, cell adhesion and cell migration, recent studies have provided further mechanistic insights into these functions. Roles for actinins in synaptic plasticity and membrane trafficking events have emerged more recently, as has a 'non-canonical' function for actinins in transcriptional regulation in the nucleus. In the present paper we review recent advances in our understanding of these diverse cell biological functions of actinins in non-muscle cells, as well as their roles in cancer and in genetic disorders affecting platelet and kidney physiology. We also make two proposals with regard to the actinin nomenclature. First, we argue that naming actinin isoforms according to their expression patterns is problematic and we suggest a more precise nomenclature system. Secondly, we suggest that the α in α-actinin is superfluous and can be omitted.

Influence of defunctionalization and mechanical forces on intestinal epithelial wound healing

The influence on mucosal healing of luminal nutrient flow and the forces it creates are poorly understood. We hypothesized that altered deformation and extracellular pressure mediate, in part, the effects of defunctionalization on mucosal healing. We created patent or partially obstructing defunctionalizing jejunal Roux-en-Y anastomoses in rats to investigate mucosal healing in the absence or presence of luminal nutrient flow and measured luminal pressures to document partial obstruction. We used serosal acetic acid to induce ulcers in the proximal, distal, and defunctionalized intestinal segments. After 3 days, we assessed ulcer area, proliferation, and phosphorylated ERK. In vitro, we measured proliferation and migration in Caco-2 and IEC-6 intestinal epithelial cells subjected to cyclic strain, increased extracellular pressure, or strain and pressure together. Defunctionalization of intestine without obstruction reduced phosphorylated ERK, slowed ulcer healing, and inhibited mucosal proliferation. This outcome was blocked by PD-98059. Partial obstruction delayed ulcer healing but stimulated proliferation independently of ERK. In vitro, strain increased Caco-2 and IEC-6 proliferation and reduced migration across collagen but reduced proliferation and increased migration across fibronectin. In contrast, increased pressure and the combination of pressure and strain increased proliferation and reduced migration independently of substrate. PD-98059 reduced basal migration but increased migration under pressure. These results suggest that loss of the repetitive distension may decrease mucosal healing in defunctionalized bowel, while increased luminal pressure above anastomoses or in spastic bowel disease could further inhibit mucosal healing, despite peristaltic repetitive strain. ERK may mediate the effects of repetitive deformation but not the effects of pressure.

Changes in morphology and function in small intestinal mucosa after Roux-en-Y surgery in a rat model

BACKGROUND

Currently there is no an appropriate model to study intestinal mucosal atrophy in vivo that preserves the nutritional status of the organism.

MATERIALS AND METHODS

We created a defunctionalized segment of jejunum via a dead-end Roux-en-Y anastomosis in rats. We compared tissue morphometric parameters in the intestinal mucosa of the defunctionalized bowel with that of the mucosa proximal and distal to the anastomosis. We further measured extracellular signal-regulated kinase (ERK) activation within the mucosa as well as sucrase-isomaltase and dipeptidyl peptidase-4 levels as markers of intestinal mucosal differentiation by Western blotting of mucosal scrapings.

RESULTS

Three days after anastomosis, the defunctionalized bowel exhibited decreased diameter and thickness of both the mucosa and the fibromuscular layer compared with adjacent bowel in continuity for luminal nutrient flow or with bowel from control animals. Sucrase-isomaltase and dipeptidyl peptidase-4 levels also were decreased. Furthermore, mucosal ERK activation, assessed as the ratio of phosphorylated to total ERK, also was reduced. Animal weights did not differ between bypassed and control animals.

CONCLUSIONS

Deprivation of nutrient flow in a segment of bowel by defunctionalizing Roux-en-anastomosis produces mucosal atrophy as indicated by altered histology, differentiation marker expression, and ERK signaling, in animals that are otherwise able to maintain enteral nutrition.

Role of RhoA and its effectors ROCK and mDia1 in the modulation of deformation-induced FAK, ERK, p38, and MLC motogenic signals in human Caco-2 intestinal epithelial cells

Repetitive deformation enhances intestinal epithelial migration across tissue fibronectin. We evaluated the contribution of RhoA and its effectors Rho-associated kinase (ROK/ROCK) and mammalian diaphanous formins (mDia1) to deformation-induced intestinal epithelial motility across fibronectin and the responsible focal adhesion kinase (FAK), extracellular signal-regulated kinase (ERK), p38, and myosin light chain (MLC) signaling. We reduced RhoA, ROCK1, ROCK2, and mDia1 by smart-pool double-stranded short-interfering RNAs (siRNA) and pharmacologically inhibited RhoA, ROCK, and FAK in human Caco-2 intestinal epithelial monolayers on fibronectin-coated membranes subjected to 10% repetitive deformation at 10 cycles/min. Migration was measured by wound closure. Stimulation of migration by deformation was prevented by exoenzyme C3, Y27632, or selective RhoA, ROCK1, and ROCK2 or mDia1 siRNAs. RhoA, ROCK inhibition, or RhoA, ROCK1, ROCK2, mDia1, and FAK reduction by siRNA blocked deformation-induced nuclear ERK phosphorylation without preventing ERK phosphorylation in the cytoplasmic protein fraction. Furthermore, RhoA, ROCK inhibition or RhoA, ROCK1, ROCK2, and mDia1 reduction by siRNA also blocked strain-induced FAK-Tyr(925), p38, and MLC phosphorylation. These results suggest that RhoA, ROCK, mDia1, FAK, ERK, p38, and MLC all mediate the stimulation of intestinal epithelial migration by repetitive deformation. This pathway may be an important target for interventions to promote mechanotransduced mucosal healing during inflammation.

Propofol's effects on phagocytosis, proliferation, nitrate production, and cytokine secretion in pressure-stimulated microglial cells

BACKGROUND

Intracranial hypertension complicates severe traumatic brain injury frequently and might be associated with poor outcomes. Traumatic brain injury induces a neuroinflammatory response by microglial activation and upregulation of proinflammatory cytokines, such as interleukin-1β, tumor necrosis factor alpha, and interleukin-6. To elucidate the effect of increased intracranial pressure on microglial function, we studied the effects of increased extracellular pressure on primary human microglial cell phagocytosis, proliferation, cytokine secretion, and total nitrate production. In addition, because many patients receive propofol during anesthesia or intensive care unit sedation, we evaluated whether propofol alters the effects of pressure.

METHODS

Human microglial cells were pretreated with (2.5-20 μg/mL) propofol or Intralipid as a vehicle control were incubated at ambient atmospheric pressure or at 15 or 30 mm Hg increased pressure for 2 h for phagocytosis assays or 24 h for proliferation, cytokine secretion, and total nitrate production studies. Phagocytosis was determined by incorporation of intracellular fluorescent latex beads. Tumor necrosis factor alpha, interleukin-1β, and interleukin-6 were assayed by sandwich enzyme-linked immunosorbent assay and total nitrate by Greiss reagent.

RESULTS

Increased extracellular pressure stimulated phagocytosis versus untreated microglial cells or cells treated with an Intralipid vehicle control. Propofol also stimulated microglial phagocytosis at ambient pressure. Increased pressure, however, decreased phagocytosis in the presence of propofol. Pressure also increased microglial tumor necrosis factor-α and interleukin-1β secretion and propofol pretreatment blocked the pressure-stimulated effect. Interleukin-6 production was not altered either by pressure or by propofol. Pressure also induced total nitrate secretion, and propofol pretreatment decreased basal as well as pressure-induced microglial nitrate production.

CONCLUSION

Extracellular pressures consistent with increased intracranial pressure after a head injury activate inflammatory signals in human primary microglial cells in vitro, stimulating phagocytosis, proliferation, tumor necrosis factor-α, interleukin-1β, and total nitrate secretion but not affecting interleukin-6. Such inflammatory events may contribute to the worsened prognosis of traumatic brain injury after increased intracranial pressure. Because propofol alleviated these potentially proinflammatory effects, these results suggest that the inflammatory cascade activated by intracranial pressure might be targeted by propofol in patients with increased intracranial pressure after traumatic brain injury.

Identification of an FHL1 protein complex containing ACTN1, ACTN4, and PDLIM1 using affinity purifications and MS-based protein-protein interaction analysis

INTRODUCTION

Four and a half LIM domains protein 1 (FHL1) is the most widely expressed member of the FHL family of proteins, consisting of four and a half highly conserved LIM domains. A multifunctional and integral role for FHL1 has been implicated in muscle development, structural maintenance, and signaling. To date, 27 FHL1 mutations have been identified that result in at least six different X-linked myopathies, with patients often presenting with cardiovascular complications. Since proteins assemble into dynamic complexes within the cell, FHL1 likely mediates its biological functions in conjunction with other proteins. Delineation of FHL1 interactions could provide insight into its regulatory functions.

METHODS

We performed tandem affinity purification from human embryonic kidney 293 (HEK-293) cells to purify FHL1 and interacting proteins. To identify the potential interactors of FHL1 we performed a total of 9 different purifications from HEK-293 cells which included 3 experimental replicates for each biological condition: FHL1, tag control (DPYSL3), and negative control (empty vector). Purified samples were analyzed by liquid chromatography mass spectrometry (LC-MS). Potential interactors were then verified by immunoprecipitation from mouse heart ventricles and interactions visualized in adult cardiomyocytes using 3D fluorescence microscopy.

RESULTS

We identified a total of 310 different proteins from all 9 purifications and by applying stringent filtering criteria we eliminated all proteins found in any of the controls and only allowed those that were detected in two or more bait purification. We identified 34 high confidence potential binding partners of FHL1. We then showed that FHL1 exists as part of a complex that binds with PDLIM1, GSN and ACTN1.

Isoform-specific contributions of alpha-actinin to glioma cell mechanobiology

Glioblastoma Multiforme (GBM) is a malignant astrocytic tumor associated with low survival rates because of aggressive infiltration of tumor cells into the brain parenchyma. Expression of the actin binding protein alpha-actinin has been strongly correlated with the invasive phenotype of GBM in vivo. To probe the cellular basis of this correlation, we have suppressed expression of the nonmuscle isoforms alpha-actinin-1 and alpha-actinin-4 and examined the contribution of each isoform to the structure, mechanics, and motility of human glioma tumor cells in culture. While subcellular localization of each isoform is distinct, suppression of either isoform yields a phenotype that includes dramatically reduced motility, compensatory upregulation and redistribution of vinculin, reduced cortical elasticity, and reduced ability to adapt to changes in the elasticity of the extracellular matrix (ECM). Mechanistic studies reveal a relationship between alpha-actinin and non-muscle myosin II in which depletion of either alpha-actinin isoform reduces myosin expression and maximal cell-ECM tractional forces. Our results demonstrate that both alpha-actinin-1 and alpha-actinin-4 make critical and distinct contributions to cytoskeletal organization, rigidity-sensing, and motility of glioma cells, thereby yielding mechanistic insight into the observed correlation between alpha-actinin expression and GBM invasiveness in vivo.

The effects of mechanical forces on intestinal physiology and pathology

The epithelial and non-epithelial cells of the intestinal wall experience a myriad of physical forces including strain, shear, and villous motility during normal gut function. Pathologic conditions alter these forces, leading to changes in the biology of these cells. The responses of intestinal epithelial cells to forces vary with both the applied force and the extracellular matrix proteins with which the cells interact, with differing effects on proliferation, differentiation, and motility, and the regulation of these effects involves similar but distinctly different signal transduction mechanisms. Although normal epithelial cells respond to mechanical forces, malignant gastrointestinal epithelial cells also respond to forces, most notably by increased cell adhesion, a critical step in tumor metastasis. This review will focus on the phenomenon of mechanical forces influencing cell biology and the mechanisms by which the gut responds these forces in both the normal as well as pathophysiologic states when forces are altered. Although more is known about epithelial responses to force, information regarding mechanosensitivity of vascular, neural, and endocrine cells within the gut wall will also be discussed, as will, the mechanism by which forces can regulate epithelial tumor cell adhesion.

Supraphysiologic extracellular pressure inhibits intestinal epithelial wound healing independently of luminal nutrient flow

BACKGROUND

Luminal pressure may injure the gut mucosa in obstruction, ileus, or inflammatory bowel disease.

METHODS

We formed Roux-en-Y anastomoses in 19 mice, creating proximal and defunctionalized partially obstructed limbs and a distal limb to vary luminal pressure and flow. We induced mucosal ulcers by serosal acetic acid, and assessed proliferation (proliferating cell nuclear antigen) and ERK (immunoblotting). Parallel studies compared Caco-2 enterocyte migration and proliferation after pressure and/or ERK blockade.

RESULTS

At 3 days, anastomoses were probe-patent, proximal and distal limbs contained chyme, and defunctionalized limbs were empty. The proximal and defunctionalized limbs showed increased pressure and slower healing despite increased proliferation, ERK protein, and ERK activation. In vitro, pressure decreased Caco-2 migration across collagen or fibronectin, stimulated proliferation, and activated ERK. However, ERK blockade did not prevent pressure effects.

CONCLUSIONS

Luminal pressure during obstruction or ileus may impair mucosal healing independently of luminal flow despite increased mitosis and ERK activation.

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.