Inhibitory role of alpha 6 beta 4-associated erbB-2 and phosphoinositide 3-kinase in keratinocyte haptotactic migration dependent on alpha 3 beta 1 integrin

Testing biological actions of medicinal plants from northern Vietnam on zebrafish embryos and larvae: Developmental, behavioral, and putative therapeutical effects

Evaluating the risks and benefits of using traditional medicinal plants is of utmost importance for a huge fraction of the human population, in particular in Northern Vietnam. Zebrafish are increasingly used as a simple vertebrate model for testing toxic and physiological effects of compounds, especially on development. Here, we tested 12 ethanolic extracts from popular medicinal plants collected in northern Vietnam for their effects on zebrafish survival and development during the first 4 days after fertilization. We characterized more in detail their effects on epiboly, hatching, growth, necrosis, body curvature, angiogenesis, skeletal development and mostly increased movement behavior. Finally, we confirm the effect on epiboly caused by the Mahonia bealei extract by staining the actin filaments and performing whole genome gene expression analysis. Further, we show that this extract also inhibits cell migration of mouse embryo fibroblasts. Finally, we analyzed the chemical composition of the Mahonia bealei extract and test the effects of its major components. In conclusion, we show that traditional medicinal plant extracts are able to affect zebrafish early life stage development to various degrees. In addition, we show that an extract causing delay in epiboly also inhibits mammalian cell migration, suggesting that this effect may serve as a preliminary test for identifying extracts that inhibit cancer metastasis.

Polymeric immunoglobulin receptor suppresses colorectal cancer through the AKT-FOXO3/4 axis by downregulating LAMB3 expression

Colorectal cancer (CRC) remains one of the most common malignancies worldwide and its mechanism is unclear. Polymeric immunoglobulin receptor (PIGR) which plays an important role in mucosal immunity is widely expressed in the mucosal epithelium and is dysregulated in different tumors. However, the role and underlying mechanisms of PIGR in CRC remain unclear. Here, we demonstrated that PIGR was hypermethylated and downregulated in our cohort (N = 272), and these features were associated with reduced overall survival in patients (HRmethylation 1.61, 95% CI [1.11-2.33]). These findings were validated by external TCGA and GEO data. Moreover, PIGR overexpression inhibits CRC cell malignant phenotypes in vitro and impedes CRC cells growth in male BALB/c nude mice. Mechanistically, PIGR physically associates with RE1 silencing transcription factor (REST) and blocks the transcription of laminin subunit beta 3 (LAMB3). Subsequently, the AKT-FOXO3/4 axis was suppressed by downregulated LAMB3. In the drug sensitive assay, PIGR-overexpressing cells were more sensitive to cisplatin and gemcitabine. Together, PIGR may serve as a powerful prognostic biomarker and putative tumor suppressor by suppressing the AKT-FOXO3/4 axis by downregulating LAMB3 in CRC. Our study may offer a novel therapeutic strategy for treating CRC patients who highly express PIGR with cisplatin and gemcitabine.

Protein Ligand Nanopattern Size Selects for Cellular Adhesion via Hemidesmosomes over Focal Adhesions

Hemidesmosomes (HDs) are multiprotein complexes that firmly anchor epidermal cells to the basement membrane of skin through the interconnection of the cytoplasmic intermediate filaments with extracellular laminin 332 (Ln332). Considerably less attention has been paid to HDs compared to focal complexes/focal adhesions (FC/FAs) in mechanistic single-cell structures due to the lack of suitable in vitro model systems. Here nanopatterns of Ln332 (100-1000 nm) are created to direct and study the formation of HD in adherent HaCaT cells. It is observed that HaCaT cells at Ln 332 nanopatterns adhere via hemidesmosomes, in stark contrast to cells at homogeneous Ln332 surfaces that adhere via FC/FAs. Clustering of α6 integrin is observed at nanopatterned Ln332 of 300 nm patches and larger. Cells at 500 nm diameter patterns show strong colocalization of α6 integrin with ColXVII or pan-cytokeratin compared to 300 nm/1000 nm indicating a threshold for HD initiation >100 nm but a pattern size selection for maturation of HDs. It is demonstrated that the pattern of Ln332 can determine the cellular selection of adhesion types with a size-dependent initiation and maturation of HDs. The protein nanopatterning approach that is presented provides a new in vitro route to study the role of HDs in cell signaling and function.

Feeling Things Out: Bidirectional Signaling of the Cell-ECM Interface, Implications in the Mechanobiology of Cell Spreading, Migration, Proliferation, and Differentiation

Biophysical cues stemming from the extracellular environment are rapidly transduced into discernible chemical messages (mechanotransduction) that direct cellular activities-placing the extracellular matrix (ECM) as a potent regulator of cell behavior. Dynamic reciprocity between the cell and its associated matrix is essential to the maintenance of tissue homeostasis and dysregulation of both ECM mechanical signaling, via pathological ECM turnover, and internal mechanotransduction pathways contribute to disease progression. This review covers the current understandings of the key modes of signaling used by both the cell and ECM to coregulate one another. By taking an outside-in approach, the inherent complexities and regulatory processes at each level of signaling (ECM, plasma membrane, focal adhesion, and cytoplasm) are captured to give a comprehensive picture of the internal and external mechanoregulatory environment. Specific emphasis is placed on the focal adhesion complex which acts as a central hub of mechanical signaling, regulating cell spreading, migration, proliferation, and differentiation. In addition, a wealth of available knowledge on mechanotransduction is curated to generate an integrated signaling network encompassing the central components of the focal adhesion, cytoplasm and nucleus that act in concert to promote durotaxis, proliferation, and differentiation in a stiffness-dependent manner.

Cancer Invasion: Watch Your Neighbourhood!

The critical event in neoplastic diseases is the invasion of surrounding tissue by cancer cells. This event greatly reduces treatment options, and makes cancer a lethal disease. Factors that initiate cancer invasion are not well understood, neither do we have mechanistic insights in the process itself. Recently, a new concept has emerged: the tissue surrounding tumor cells, ie, the tumor microenvironment, may play an important, if not decisive role in triggering invasion. This concept is based on data from many laboratories working on the cell biology of cancer invasion. In this review, we survey several components of the tumor microenvironment, including extracellular matrix macromolecules, metalloproteinases and soluble factors, and discuss their potential involvement in stimulating cancer cell motility. These novel views may have far-reaching consequences, since “normal” tissue microenvironment components, rather than the traditional tumor cells themselves, may eventually become targets for devising new treatments that prevent, inhibit or block cancer invasion and metastasis.

Muscle Stem Cells and Aging

Satellite cells (SCs) are a population of muscle-resident stem cells that are essential for efficient tissue repair. SCs reside in a relatively quiescent state during normal tissue turnover, but are activated in response to injury through the microenvironment and cell-intrinsic signals. During aging, SC dysfunction is a major contributor to the decline in regenerative potential of muscle tissue. Recent studies have demonstrated that both cell-intrinsic and cell-extrinsic factors are deregulated during aging. Interventions that reverse age-associated changes in SCs or the niche have shown to partially rejuvenate the regenerative capacity of aged muscle SCs. In this review, we discuss recent advances in SC biology as it pertains to the deleterious effects of aging. A better understanding of how age-dependent changes in the SC and its environment niche impact muscle regeneration could lead to interventions to ameliorate the effects of aging in humans.

In-vitro Wound Healing Effect of 15-Hydroxyprostaglandin Dehydrogenase Inhibitor from Plant

BACKGROUND

Prostaglandins (PGs) have short existence in vivo because they are rapidly metabolized by NAD⁺-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) to 15-ketoprostaglandins. Inhibition of 15-PGDH causes elevated level of PGE₂ in cellular system. It will be valuable for the therapeutic management of diseases requiring elevated PGE₂ levels, like wound healing.

OBJECTIVE

Ninety-eight plant samples were screened for the discovery of potent 15-PGDH inhibitor. Among them, top five plant extracts as potent 15-PGDH inhibitor were chosen to determine PGE₂ release from HaCaT (Keratinocyte cell line) cell line. Finally, top 15-PGDH inhibitor was selected to evaluate in vitro wound healing effect on HaCaT scratch model.

METHOD

The inhibitory activity for 15-PGDH inhibitors was evaluated using fluorescence spectrophotometer by measuring the formation of NADH at 468 nm following excitation at 340 nm. Cell viability assay and PGE₂ release was evaluated in HaCaT cell line after treatment of 15-PGDH inhibitors. Scratches were made using sterile 200 μL on HaCaT cell and wound-healing effect was evaluated after treatment of 15-PGDH inhibitor.

RESULTS

15-PGDH inhibitors elevated PGE₂ levels in concentration-dependent manner. Ethanol extract of Artocarpus heterophyllus (EEAH), the most potent 15-PGDH inhibitor (IC₅₀ = 0.62 µg/mL) with least cytotoxicity (IC₅₀ = 670 µg/ml), elevated both intracellular and extracellular PGE₂ levels. EEAH facilitated in-vitro wound healing in a HaCaT (Keratinocyte cell line) scratch model.

CONCLUSION

EEAH might apply to treat dermal wounds by elevating PGE₂ levels via COX-1 induction and 15-PGDH inhibition.

SUMMARY

Biological inactivation of 15-PGDH causes elevated level of PGE₂ which will be useful for the management of disease that requires elevated level of PGE₂. Abbreviations used: 15-PGDH: 15-hydroxyprostaglandin dehydrogenase, COX: Cyclooxygenase, DTT: Dithiothreitol, DMEM: Dulbecco's modified Eagle's media, EEAH: Ethanol extract of Artocarpus heterophyllus, MRP4: Multidrug resistance 4, PGs: Prostaglandins, PGT: Prostaglandin transporter, SDS: Sodium dodecylsulfate.

Reversal of Aged Muscle Stem Cell Dysfunction

The loss of muscle stem cell (MuSC) numbers and function in the elderly results in a dramatic delay or incomplete repair of muscle following injury or surgery. Prolonged immobility can exacerbate the loss of muscle mass with increased morbidity of affected patients. Stem cells and their niche cooperate to regulate the activation, self-renewal, differentiation, and return to quiescence of MuSCs. Extracellular matrix fibronectin (FN) and MuSC β1-integrin have been identified as critical factors in the dysfunction of aging muscle. Reduced amounts and/or function of β1-integrin and fibronectin are critical factors in the decline in MuSC regeneration and homeostasis with aging. Replacement of fibronectin and/or stimulation of β1-integrin may provide a novel means to augment the decline in MuSC function with age.

Targeting β1-integrin signaling enhances regeneration in aged and dystrophic muscle in mice

Interactions between stem cells and their microenvironment, or niche, are essential for stem cell maintenance and function. Our knowledge of the niche for the skeletal muscle stem cell, i.e., the satellite cell (SC), is incomplete. Here we show that β1-integrin is an essential niche molecule that maintains SC homeostasis, and sustains the expansion and self-renewal of this stem cell pool during regeneration. We further show that β1-integrin cooperates with fibroblast growth factor 2 (Fgf2), a potent growth factor for SCs, to synergistically activate their common downstream effectors, the mitogen-activated protein (MAP) kinase Erk and protein kinase B (Akt). Notably, SCs in aged mice show altered β1-integrin activity and insensitivity to Fgf2. Augmenting β1-integrin activity with a monoclonal antibody restores Fgf2 sensitivity and improves regeneration after experimentally induced muscle injury. The same treatment also enhances regeneration and function of dystrophic muscles in mdx mice, a model for Duchenne muscular dystrophy. Therefore, β1-integrin senses the SC niche to maintain responsiveness to Fgf2, and this integrin represents a potential therapeutic target for pathological conditions of the muscle in which the stem cell niche is compromised.

Circulatory shear flow alters the viability and proliferation of circulating colon cancer cells

During cancer metastasis, circulating tumor cells constantly experience hemodynamic shear stress in the circulation. Cellular responses to shear stress including cell viability and proliferation thus play critical roles in cancer metastasis. Here, we developed a microfluidic approach to establish a circulatory microenvironment and studied circulating human colon cancer HCT116 cells in response to a variety of magnitude of shear stress and circulating time. Our results showed that cell viability decreased with the increase of circulating time, but increased with the magnitude of wall shear stress. Proliferation of cells survived from circulation could be maintained when physiologically relevant wall shear stresses were applied. High wall shear stress (60.5 dyne/cm(2)), however, led to decreased cell proliferation at long circulating time (1 h). We further showed that the expression levels of β-catenin and c-myc, proliferation regulators, were significantly enhanced by increasing wall shear stress. The presented study provides a new insight to the roles of circulatory shear stress in cellular responses of circulating tumor cells in a physiologically relevant model, and thus will be of interest for the study of cancer cell mechanosensing and cancer metastasis.

Promotion of cell migration by neural cell adhesion molecule (NCAM) is enhanced by PSA in a polysialyltransferase-specific manner

Neural cell adhesion molecule 140 (NCAM-140) is a glycoprotein and always highly polysialylated in cancer. Functions of polysialic acid (PSA) that binds to N-glycan termini on NCAM remain unclear. ldlD-14 cells, a CHO cell mutant deficient in UDP-Gal 4-epimerase, are useful for structural and functional studies of Gal-containing glycoproteins because their abnormal glycosylation can be converted to normal status by exogenous addition of galactose (Gal). We cloned the genes for NCAM-140 and for polysialyltransferases STX and PST (responsible for PSA synthesis) from normal murine mammary gland epithelial (NMuMG) cells and transfected them into ldlD-14 and human breast cancer cells MCF-7. The effect of PSA on NCAM-mediated cell proliferation, motility, migration and adhesion was studied. We found that NCAM-140 significantly promoted cell proliferation, motility and migration, while polysialylation of NCAM-140 catalyzed by STX, but not by PST, enhanced NCAM-mediated cell migration, but not cell proliferation or motility. In addition, PSA catalyzed by different polysialyltransferases affected the adhesion of NCAM to different extracellular matrix (ECM) components.

The role of phosphoinositide 3-kinase in adhesion of oral epithelial cells to titanium

BACKGROUND

Oral epithelial cells (OECs) adhesion to titanium may improve the success rate of implant restoration.

PURPOSE

We investigated the mechanism by which OECs adhere to titanium dental implants.

MATERIALS AND METHODS

(1) After culturing rat OECs on titanium plates (Ti) or culture dishes in the presence or absence of a phosphoinositide 3-kinase (PI3K) activator or inhibitors and/or growth factors, and OEC morphology under these conditions were analyzed. (2) Right maxillary first molars were extracted and replaced with experimental implants. The rats were treated with or without growth factors.

RESULTS

(1) Cell adherence was lower of OECs on Ti than in those on culture dishes, as were the levels of integrin β4 and the continuity of F-actin structures. After PI3K inhibition, markedly reducing adherence to both substrates. In contrast, PI3K activation with activator or insulin-like growth factor restored the OEC adherence and the expression of adhesion molecules on Ti to the levels seen in OECs cultured on dishes. Cell migration was inhibited by PI3K activation. (2) High expression of integrin β4 was observed in the peri-implant epithelia of PI3K-activated rats.

CONCLUSION

These findings suggest that PI3K plays an important role in the adhesion of OECs to Ti.

The metastasis-associated molecule C4.4A promotes tissue invasion and anchorage independence by associating with the alpha6beta4 integrin

C4.4A is a metastasis-associated molecule that functions appear to rely on associated alph6beta4 integrin. To corroborate the impact of the C4.4A-alpha6beta4 integrin association on metastasis formation, C4.4A was knocked-down in a highly metastatic rat pancreatic adenocarcinoma (ASML, ASML-C4.4Akd). Metastasis formation by ASML-C4.4Akd cells after intrafootpad application was strongly retarded in draining nodes and lung colonization was rare. Furthermore, cisplatin treatment significantly prolonged the survival time only of ASML-C4.4Akd-bearing rats. ASML-C4.4Akd cells display reduced migratory activity and impaired matrix protein degradation due to inefficient MMP14 activation; loss of drug-resistance is due to mitigated PI3K/Akt pathway activation. These losses of function rely on the laminin receptor C4.4A recruiting activated alpha6beta4 integrin into rafts, where C4.4A cooperates with alpha6beta4 and via alpha6beta4 with MMP14. Within this raft-located complex, MMP14 provokes focalized matrix degradation and mostly alpha6beta4 integrin promotes BAD phosphorylation and upregulated Bcl2 and BclXl expression. Thus, metastasis-promoting activities of C4.4A are not genuine characteristics of C4.4A. Instead, the raft-located laminin receptor C4.4A recruits alpha6beta4 integrin and supports via the alpha6beta4 integrin MMP14 activation. Thereby C4.4A acts as a linker to facilitate several steps in the metastatic cascade. Taking the restricted C4.4A expression in non-transformed tissue, this knowledge should pave the way toward the use of C4.4A as a therapeutic target.

Collagen VII plays a dual role in wound healing

Although a host of intracellular signals is known to contribute to wound healing, the role of the cell microenvironment in tissue repair remains elusive. Here we employed 2 different mouse models of genetic skin fragility to assess the role of the basement membrane protein collagen VII (COL7A1) in wound healing. COL7A1 secures the attachment of the epidermis to the dermis, and its mutations cause a human skin fragility disorder coined recessive dystrophic epidermolysis bullosa (RDEB) that is associated with a constant wound burden. We show that COL7A1 is instrumental for skin wound closure by 2 interconnected mechanisms. First, COL7A1 was required for re-epithelialization through organization of laminin-332 at the dermal-epidermal junction. Its loss perturbs laminin-332 organization during wound healing, which in turn abrogates strictly polarized expression of integrin α6β4 in basal keratinocytes and negatively impacts the laminin-332/integrin α6β4 signaling axis guiding keratinocyte migration. Second, COL7A1 supported dermal fibroblast migration and regulates their cytokine production in the granulation tissue. These findings, which were validated in human wounds, identify COL7A1 as a critical player in physiological wound healing in humans and mice and may facilitate development of therapeutic strategies not only for RDEB, but also for other chronic wounds.

Promotive effect of insulin-like growth factor-1 for epithelial sealing to titanium implants

Improvement of oral epithelial adhesion to titanium (Ti) may significantly enhance the efficacy of dental implants. Here, we investigated whether insulin-like growth factor-1 (IGF-1) improved the sealing of the peri-implant epithelium (PIE) around the implant. Right maxillary first molars were extracted from rats and replaced with experimental implants. After 4 weeks of IGF-1 treatment, the implant-PIE interface exhibited a band of immunoreactive laminin-332 (Ln-5), similar to the tooth-junctional epithelium interface, that was partially absent in the untreated group. Immunoelectron microscopy showed a characteristic Ln-5-positive band including hemidesmosomes at both the apical and upper portions of the implant-PIE interface in the IGF-1-treated group. We also investigated the effects of IGF-1/PI3K inhibitors on the dynamics of rat oral epithelial cells (OECs) grown on Ti plates. In OECs cultured with IGF-1, adhesion protein expression increased, cell adherence to Ti plates was higher, and proliferation was faster, whereas migration and apoptosis were induced in the absence of IGF-1 or in the presence of both IGF-1 and a PI3K inhibitor. These data suggest that PI3K mediates the promotive effects of IGF-1, and that IGF-1 is effective at enhancing epithelial integration around Ti implants.

The role of integrins in the development and homeostasis of the epidermis and skin appendages

Integrins play a critical role in the regulation of adhesion, migration, proliferation, and differentiation of cells. Because of the variety of the functions they play in the cell, they are necessary for the formation and maintenance of tissue structure integrity. The trove of data accumulated by researchers suggests that integrins participate in the morphogenesis of the epidermis and its appendages. The development of mice with tissue-specific integrin genes knockout and determination of the genetic basis for a number of skin diseases in humans showed the significance of integrins in the biology, physiology, and morphogenesis of the epidermis and hair follicles. This review discusses the data on the role of different classes of integrin receptors in the biology of epidermal cells, as well as the development of the epidermis and hair follicles.

N-glycosylation of ß4 integrin controls the adhesion and motility of keratinocytes

α6ß4 integrin is an essential component of hemidesmosomes and modulates cell migration in wound healing and cancer invasion. To elucidate the role of N-glycosylation on ß4 integrin, we investigated keratinocyte adhesion and migration through the re-expression of wild-type or N-glycosylation-defective ß4 integrin (ΔNß4) in ß4 integrin null keratinocytes. N-glycosylation of ß4 integrin was not essential for the heterodimer formation of ß4 integrin with α6 integrin and its expression on a cell surface, but N-glycosylation was required for integrin-mediated cell adhesion and migration. Concomitantly with the reduction of ß4 integrin in the membrane microdomain, the intracellular signals of Akt and ERK activation were decreased in cells expressing ΔNß4 integrin. Forced cross-linking of ß4 integrin rescued the decreased ERK activation in ΔNß4 integrin-expressing cells to a similar extent in wild-type ß4 integrin-expressing cells. Surprisingly, compared with cells expressing wild-type ß4 integrin, an alternation in N-glycan structures expressed on epidermal growth factor receptor (EGFR), and the induction of a stronger association between EGFR and ß4 integrin were observed in ΔNß4 integrin-expressing cells. These results clearly demonstrated that N-glycosylation on ß4 integrin plays an essential role in keratinocyte cellular function by allowing the appropriate complex formation on cell surfaces.

Laminin 511 partners with laminin 332 to mediate directional migration of Madin-Darby canine kidney epithelial cells

Sustained directional migration of epithelial cells is essential for regeneration of injured epithelia. Front-rear polarity of migrating cells is determined by local activation of a signaling network involving Cdc42 and other factors in response to spatial cues from the environment, the nature of which are obscure. We examined the roles of laminin (LM)-511 and LM-332, two structurally different laminin isoforms, in the migration of Madin-Darby canine kidney cells by suppressing expression of their α subunits using RNA interference. We determined that knockdown of LM-511 inhibits directional migration and destabilizes cell-cell contacts, in part by disturbing the localization and activity of the polarization machinery. Suppression of integrin α3, a laminin receptor subunit, in cells synthesizing normal amounts of both laminins has a similar effect as knockdown of LM-511. Surprisingly, simultaneous suppression of both laminin α5 and laminin α3 restores directional migration and cell-cell contact stability, suggesting that cells recognize a haptotactic gradient formed by a combination of laminins.

The role of ECM proteins and protein fragments in guiding cell behavior in regenerative medicine

The promise of biomaterials design for regenerative medicine tissue engineering is predicated on the fundamental ability to direct or guide specific and highly coordinated cellular behaviors that culminate in the creation of physiologically functional tissues and organs. To date, our efforts have focused primarily on the grafting and presentation of short synthetic peptides with just cause. Short peptides are capable of high levels of control, can be manufactured relatively easily in a highly reproducible manner under GMP guidelines and are readily modified to enable their integration with numerous current and emerging chemistries for biomaterials grafting. However, while extracellular matrix (ECM)-derived peptides have demonstrated their initial purpose of promoting cell adhesion, their general lack of specificity and significantly decreased receptor binding affinities have proven detrimental in attempts to regulate highly specific and integrated processes necessary for tissue regeneration. Unlike adhesion peptides, the natural ECM displays a complex interplay with cells by supporting environmentally sensitive and cell dependent integrin specificity and binding affinity. Furthermore, the adhesion ligands on ECM proteins display a finely tuned and evolutionarily directed spatial periodicity, of which is dynamically controlled through both mechanical and chemical modifications. These and other emerging concepts from matrix biology require our attention if biomaterials design is to fulfill its promise. Here, we are charged with debating the statement 'The use of short synthetic adhesion peptides, like RGD, is the best approach in the design of biomaterials that guide cell behavior for regenerative medicine tissue engineering'. In this Leading Opinion Paper I will focus on aspects of natural ECM proteins and protein fragments that have proven difficult, if not impossible to date, to recapitulate in peptide-based systems. While this represents an argument against the use of peptides per se, it might also be viewed as outlining the challenges and opportunities for the biomaterials field.

Collagen XXIII, novel ligand for integrin alpha2beta1 in the epidermis

Cellular receptors for collagens belong to the family of β(1) integrins. In the epidermis, integrin α(2)β(1) is the only collagen-binding integrin present. Its expression is restricted to basal keratinocytes with uniform distribution on the cell surface of those cells. Although α(2)β(1) receptors localized at the basal surface interact with basement membrane proteins collagen IV and laminin 111 and 332, no interaction partners have been reported for these integrin molecules at the lateral and apical membranes of basal keratinocytes. Solid phase binding and surface plasmon resonance spectroscopy demonstrate that collagen XXIII, a member of the transmembrane collagens, directly interacts with integrin α(2)β(1) in an ion- and conformation-dependent manner. The two proteins co-localize on the surface of basal keratinocytes. Furthermore, collagen XXIII is sufficient to induce adhesion and spreading of keratinocytes, a process that is significantly reduced in the absence of functional integrin α(2)β(1).

Effects of Sesquiterpenes Isolated From Largehead Atractylodes Rhizome on Growth, Migration, and Differentiation of B16 Melanoma Cells

The aims of this study were to isolate sesquiterpene compounds from the largehead atractylodes rhizome (LAR) and to investigate their effects on B16 cancer cells. A total of 8 sesquiterpenes from LAR were identified, of which eudesm-4 (15), 7-diene-9α, 11-diol (7) was isolated for the first time. All 8 compounds inhibited growth of B16 cells, and atractylenolide I (AT-I), atractylenolide II (AT-II), and atractylenolactam (ATR) were the most potent, with IC50 values of 76.46, 84.02, and 54.88 μΜ, respectively. Monomer lactone or lactam structures in the 8 compounds appeared to be critical for their antiproliferative activities. In addition, AT-I, AT-II, and ATR could induce cell differentiation and inhibit cell migration. Western blot analysis indicated that 2 of the compounds, AT-I and AT-II, could inactivate ERK, where all 3 inhibited AKT activation, suggesting that Ras/ERK and PI3K/AKT signaling pathways are involved in the action mechanisms of the LAR sesquiterpene compounds.

Transcriptome analysis of human cancer reveals a functional role of heme oxygenase-1 in tumor cell adhesion

Background

Heme Oxygenase-1 (HO-1) is expressed in many cancers and promotes growth and survival of neoplastic cells. Recently, HO-1 has been implicated in tumor cell invasion and metastasis. However, the molecular mechanisms underlying these biologic effects of HO-1 remain largely unknown. To identify a common mechanism of action of HO-1 in cancer, we determined the global effect of HO-1 on the transcriptome of multiple tumor entities and identified a universal HO-1-associated gene expression signature.

Results

Genome-wide expression profiling of Heme Oxygenase-1 expressing versus HO-1 silenced BeWo choriocarcinoma cells as well as a comparative meta-profiling of the preexisting expression database of 190 human tumors of 14 independent cancer types led to the identification of 14 genes, the expression of which correlated strongly and universally with that of HO-1 (P = 0.00002). These genes included regulators of cell plasticity and extracellular matrix (ECM) remodeling (MMP2, ADAM8, TGFB1, BGN, COL21A1, PXDN), signaling (CRIP2, MICB), amino acid transport and glycosylation (SLC7A1 and ST3GAL2), estrogen and phospholipid biosynthesis (AGPAT2 and HSD17B1), protein stabilization (IFI30), and phosphorylation (ALPPL2). We selected PXDN, an adhesion molecule involved in ECM formation, for further analysis and functional characterization. Immunofluorescence and Western blotting confirmed the positive correlation of expression of PXDN and HO-1 in BeWo cancer cells as well as co-localization of these two proteins in invasive extravillous trophoblast cells. Modulation of HO-1 expression in both loss-of and gain-of function cell models (BeWo and 607B melanoma cells, respectively) demonstrated a direct relationship of HO-1 expression with cell adhesion to Fibronectin and Laminin coated wells. The adhesion-promoting effects of HO-1 were dependent on PXDN expression, as loss of PXDN in HO-1 expressing BeWo and 607B cells led to reduced cell attachment to Laminin and Fibronectin coated wells.

Conclusions

Collectively, our results show that HO-1 expression determines a distinct 'molecular signature' in cancer cells, which is enriched in genes associated with tumorigenesis. The protein network downstream of HO-1 modulates adhesion, signaling, transport, and other critical cellular functions of neoplastic cells and thus promotes tumor cell growth and dissemination.

CD151 modulates expression of matrix metalloproteinase 9 and promotes neoangiogenesis and progression of hepatocellular carcinoma

Tetraspanin CD151 is involved in several pathological activities associated with tumor progression, including neoangiogenesis. However, the role and molecular mechanism of CD151 in the neoangiogenesis of hepatocellular carcinoma (HCC) remain enigmatic. We found that the level of expression of matrix metalloproteinase 9 (MMP9) was positively associated with CD151 expression in HCC cells. We developed a zone-by-zone blockade and demonstrated that overexpression of CD151 in HCC cells facilitated MMP9 expression through a phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt)/glycogen synthase kinase 3beta (GSK-3beta)/Snail signaling pathway. In contrast, down-regulation of CD151 expression impaired the ability of HCC cells to form microvessels in vitro and reduced their in vivo metastatic potential. In a clinical setting, a significant correlation of the expression of CD151 with MMP9 expression and with microvessel density (MVD) was revealed by Pearson correlation analysis of HCC patients. The postoperative 3-, 5-, and 7-year overall survival rates of HCC patients with CD151(high)/MMP9(high)/MVD(high) were significantly lower than those of the CD151(low)/MMP9(low)/MVD(low) group or groups in which only one or two of CD151, MMP9, and MVD were highly expressed. Cumulative recurrence rates were also highest in HCC patients with CD151(high)/MMP9(high)/MVD(high) in comparison with the other groups. Multivariate Cox proportional hazards analysis showed that the concomitant overexpression of CD151, MMP9, and MVD was an independent marker for predicting poor prognosis of HCC.

CONCLUSION

Overexpression of CD151 up-regulated the expression of MMP9 through the PI3K/Akt/GSK-3beta/Snail pathway. CD151-dependent neoangiogenesis appeared to promote the progression of HCC, and this suggests that CD151 may be useful as a high-priority therapeutic target for antiangiogenesis in HCC.

Disruption of laminin-integrin-CD151-focal adhesion kinase axis sensitizes breast cancer cells to ErbB2 antagonists

Resistance to anti-ErbB2 agents is a significant problem in the treatment of human ErbB2+ breast cancers. We show here that adhesion of human ErbB2+ breast cancer cells to basement membrane laminin-5 provides substantial resistance to trastuzumab and lapatinib, agents that respectively target the extracellular and kinase domains of ErbB2. Knockdown of laminin-binding integrins (alpha6beta4, alpha3beta1) or associated tetraspanin protein CD151 reversed laminin-5 resistance and sensitized ErbB2+ cells to trastuzumab and lapatinib. CD151 knockdown, together with trastuzumab treatment, inhibited ErbB2 activation and downstream signaling through Akt, Erk1/2, and focal adhesion kinase (FAK). Hence, ErbB2 function in mammary tumor cells is promoted by integrin-mediated adhesion to laminin-5, with strong support by CD151, leading to signaling through FAK. Consequently, removal or inhibition of any of these components (laminin-5, integrin, CD151, FAK) markedly sensitizes cells to anti-ErbB2 agents. These new insights should be useful when devising strategies for overcoming drug resistance in ErbB2+ cancers.

Laminin-binding integrins and their tetraspanin partners as potential antimetastatic targets

Within the integrin family of cell adhesion receptors, integrins alpha3beta1, alpha6beta1, alpha6beta4 and alpha7beta1 make up a laminin-binding subfamily. The literature is divided on the role of these laminin-binding integrins in metastasis, with different studies indicating either pro- or antimetastatic functions. The opposing roles of the laminin-binding integrins in different settings might derive in part from their unusually robust associations with tetraspanin proteins. Tetraspanins organise integrins into multiprotein complexes within discrete plasma membrane domains termed tetraspanin-enriched microdomains (TEMs). TEM association is crucial to the strikingly rapid cell migration mediated by some of the laminin-binding integrins. However, emerging data suggest that laminin-binding integrins also promote the stability of E-cadherin-based cell-cell junctions, and that tetraspanins are essential for this function as well. Thus, TEM association endows the laminin-binding integrins with both pro-invasive functions (rapid migration) and anti-invasive functions (stable cell junctions), and the composition of TEMs in different cell types might help determine the balance between these opposing activities. Unravelling the tetraspanin control mechanisms that regulate laminin-binding integrins will help to define the settings where inhibiting the function of these integrins would be helpful rather than harmful, and may create opportunities to modulate integrin activity in more sophisticated ways than simple functional blockade.

Transdominant regulation of integrin function: mechanisms of crosstalk

Transdominant inhibition of integrins or integrin-integrin crosstalk is an important regulator of integrin ligand binding and subsequent signaling events that control a variety of cell functions in many tissues. Here we discuss examples of integrin crosstalk and detail our current understanding of the molecular mechanisms that are involved in this receptor phenomenon. The cytoskeleton associated protein talin is a key regulator of integrin crosstalk. We describe how the interaction of talin and the cytoplasmic tail of beta integrin is controlled and how competitive inhibitors of this binding play a role in integrin crosstalk. We conclude with a discussion of how integrin crosstalk impacts the interpretation of integrin inhibitor and knockdown studies in both the laboratory and clinical setting.

Emerging concepts in engineering extracellular matrix variants for directing cell phenotype

Directing specific, complex cell behaviors, such as differentiation, in response to biomaterials for regenerative medicine applications is, at present, a mostly unrealized goal. To date, current technological advances have been inspired by the reductionist point of view, focused on developing simple and merely adequate environments that facilitate simple cellular adhesion. However, even if extracellular matrix (ECM)-derived peptides, such as Arg-Gly-Asp (RGD), have largely demonstrated their utility in supporting cell adhesion, their lack of biological specificity is simply not optimal for controlling more integrated processes, such as cell differentiation. These more complex cellular processes require specific integrin-signaling scaffolds and presumably synergistic integrin and growth factor-receptor signaling. This article will introduce some current efforts to engineer ECM variants that incorporate additional levels of complexity for directing greater integrin specificity and synergistic ECM growth factor signaling toward directing cell phenotype.

BPAG1e maintains keratinocyte polarity through beta4 integrin-mediated modulation of Rac1 and cofilin activities

alpha6beta4 integrin, a component of hemidesmosomes, also plays a role in keratinocyte migration via signaling through Rac1 to the actin-severing protein cofilin. Here, we tested the hypothesis that the beta4 integrin-associated plakin protein, bullous pemphigoid antigen 1e (BPAG1e) functions as a scaffold for Rac1/cofilin signal transduction. We generated keratinocyte lines exhibiting a stable knockdown in BPAG1e expression. Knockdown of BPAG1e does not affect expression levels of other hemidesmosomal proteins, nor the amount of beta4 integrin expressed at the cell surface. However, the amount of Rac1 associating with beta4 integrin and the activity of both Rac1 and cofilin are significantly lower in BPAG1e-deficient cells compared with wild-type keratinocytes. In addition, keratinocytes deficient in BPAG1e exhibit loss of front-to-rear polarity and display aberrant motility. These defects are rescued by inducing expression of constitutively active Rac1 or active cofilin. These data indicate that the BPAG1e is required for efficient regulation of keratinocyte polarity and migration by determining the activation of Rac1.

MMP-14 mediated MMP-9 expression is involved in TGF-beta1-induced keratinocyte migration

The importance of expression of matrix metalloproteinase (MMP) in keratinocyte migration is well established, but its role remains unclear. Here we investigated the function of MMP-14 in TGF-beta1-induced keratinocyte migration. TGF-beta1 stimulated cell migration and the expression of MMP-2, -9 in HaCaT human keratinocyte cells. When we lowered MMP-14 mRNA with siRNA, cell migration, and MMP-9 expression decreased. Furthermore, the MMP-14 siRNA also reduced activation of JNK in response to TGF-beta1, and a JNK-specific inhibitor decreased both cell migration and MMP-9 expression. Taken together, these results suggest that TGF-beta1-induced HaCaT cell migration is mediated by MMP-14, which regulates MMP-9 expression via JNK signaling.

Paracrine factors of mesenchymal stem cells recruit macrophages and endothelial lineage cells and enhance wound healing

Bone marrow derived mesenchymal stem cells (BM-MSCs) have been shown to enhance wound healing; however, the mechanisms involved are barely understood. In this study, we examined paracrine factors released by BM-MSCs and their effects on the cells participating in wound healing compared to those released by dermal fibroblasts. Analyses of BM-MSCs with Real-Time PCR and of BM-MSC-conditioned medium by antibody-based protein array and ELISA indicated that BM-MSCs secreted distinctively different cytokines and chemokines, such as greater amounts of VEGF-alpha, IGF-1, EGF, keratinocyte growth factor, angiopoietin-1, stromal derived factor-1, macrophage inflammatory protein-1alpha and beta and erythropoietin, compared to dermal fibroblasts. These molecules are known to be important in normal wound healing. BM-MSC-conditioned medium significantly enhanced migration of macrophages, keratinocytes and endothelial cells and proliferation of keratinocytes and endothelial cells compared to fibroblast-conditioned medium. Moreover, in a mouse model of excisional wound healing, where concentrated BM-MSC-conditioned medium was applied, accelerated wound healing occurred compared to administration of pre-conditioned or fibroblast-conditioned medium. Analysis of cell suspensions derived from the wound by FACS showed that wounds treated with BM-MSC-conditioned medium had increased proportions of CD4/80-positive macrophages and Flk-1-, CD34- or c-kit-positive endothelial (progenitor) cells compared to wounds treated with pre-conditioned medium or fibroblast-conditioned medium. Consistent with the above findings, immunohistochemical analysis of wound sections showed that wounds treated with BM-MSC-conditioned medium had increased abundance of macrophages. Our results suggest that factors released by BM-MSCs recruit macrophages and endothelial lineage cells into the wound thus enhancing wound healing.

Topical application of laminin-332 to diabetic mouse wounds

BACKGROUND

Keratinocyte migration is essential for wound healing and diabetic wound keratinocytes migrate poorly. Keratinocyte migration and anchorage appears to be mediated by laminin-332 (LM-332). Impaired diabetic wound healing may be due to defective LM-332 mediated keratinocyte migration.

OBJECTIVE

To evaluate LM-332 expression in diabetic (db/db) and control (db/-) mice and to test LM-332 wound healing effects when applied to mouse wounds.

METHODS

LM-332 expression in mouse wounds was evaluated using immunohistochemistry. LM-332 wound healing effects were evaluated by directly applying soluble LM-332, a LM-332 biomaterial, or a control to mouse wounds. Percent wound closure and histology score, based on healing extent, were measured.

RESULTS

Precursor LM-332 expression was markedly reduced in db/db when compared to db/- mice. In vitro, soluble LM-332 and LM-332 biomaterial demonstrated significant keratinocyte adhesion. In vivo, soluble LM-332 treated wounds had the highest histology score, but significant differences were not found between wound treatments (p>0.05). No differences in percentage wound closure between treatment and control wounds were found (p>0.05).

CONCLUSION

The db/db wounds express less precursor LM-332 when compared to db/-. However, LM-332 application did not improve db/db wound healing. LM-332 purified from keratinocytes was primarily physiologically cleaved LM-332 and may not regulate keratinocyte migration. Application of precursor LM-332 rather than cleaved LM-332 may be necessary to improve wound healing, but this isoform is not currently available in quantities sufficient for testing.

Biological function of laminin-5 and pathogenic impact of its deficiency

The basement membrane glycoprotein laminin-5 is a key component of the anchoring complex connecting keratinocytes to the underlying dermis. It is secreted by keratinocytes as a cross-shaped heterotrimer of alpha3, beta3 and gamma2 chains and serves as a ligand of various transmembrane receptors, thereby regulating keratinocyte adhesion, motility and proliferation. In intact skin, laminin-5 provides essential links to both the hemidesmosomal alpha6beta4 integrin and the collagen type VII molecules which form the anchoring fibrils inserting into the dermis. If the basement membrane is injured, laminin-5 production increases rapidly. It then serves as a scaffold for cell migration, initiates the formation of hemidesmosomes and accelerates basement membrane restoration at the dermal-epidermal junction. Mutations of the laminin-5 genes or auto-antibodies against one of the subunits of laminin-5 may lead to a significant lack of this molecule in the epidermal basement membrane zone. The major contributions of laminin-5 to the resistance of the epidermis against frictional stress but also for basement membrane regeneration and repair of damaged skin are reflected by the phenotype of Herlitz junctional epidermolysis bullosa, which is caused by an inherited absence of functional laminin-5. This lethal disease becomes manifest in widespread blistering of skin and mucous membranes, impaired wound healing and chronic erosions containing exuberant granulation tissue. Here, we discuss current understanding of the biological functions of laminin-5, the pathogenic impact of its deficiency and implications on molecular approaches towards a therapy of junctional epidermolysis bullosa.

Bridging structure with function: structural, regulatory, and developmental role of laminins

The basement membrane is a highly intricate and organized portion of the extracellular matrix that interfaces with a variety of cell types including epithelial, endothelial, muscle, nerve, and fat cells. The laminin family of glycoproteins is a major constituent of the basement membrane. The 16 known laminin isoforms are formed from combinations of alpha, beta, and gamma chains, with each chain containing specific domains capable of interacting with cellular receptors such as integrins and other extracellular ligands. In addition to its role in the assembly and architectural integrity of the basement membrane, laminins interact with cells to influence proliferation, differentiation, adhesion, and migration, processes activated in normal and pathologic states. In vitro these functions are regulated by the post-translational modifications of the individual laminin chains. In vivo laminin knockout mouse studies have been particularly instructive in defining the function of specific laminins in mammalian development and have also highlighted its role as a key component of the basement membrane. In this review, we will define how laminin structure complements function and explore its role in both normal and pathologic processes.

Mechanical force modulates global gene expression and β-catenin signaling in colon cancer cells

At various stages during embryogenesis and cancer cells are exposed to tension, compression and shear stress; forces that can regulate cell proliferation and differentiation. In the present study, we show that shear stress blocks cell cycle progression in colon cancer cells and regulates the expression of genes linked to the Wnt/β-catenin, mitogen-activated protein kinase (MAPK) and NFκB pathways. The shear stress-induced increase of the secreted Wnt inhibitor DKK1 requires p38 and activation of NFκB requires IκB kinase-β. Activation of β-catenin, important in Wnt signaling and the cause of most colon cancers, is inhibited by shear stress through a pathway involving laminin-5, α6β4 integrin, phosphoinositide 3-kinase (PI 3-kinase) and Rac1 coupled with changes in the distribution of dephosphorylated β-catenin. These data show that colon cancer cells respond to fluid shear stress by activation of specific signal transduction pathways and genetic regulatory circuits to affect cell proliferation, and indicate that the response of colon cancers to mechanical forces such as fluid shear stress should be taken into account in the management of the disease.

Phosphorylation of ectopically expressed L-plastin enhances invasiveness of human melanoma cells

The leukocyte specific actin-binding protein L-plastin is aberrantly expressed in several nonhematopoetic malignant tumors. However, little is known about the functional consequences of L-plastin expression. Here, we investigated the function of L-plastin in human malignant melanoma cells. Knock-down of endogenous L-plastin by siRNA treatment reduced migration of the melanoma cell line IF6. However, in melanoma patients, no correlation existed between L-plastin expression and tumor stages. This implied that additional factors such as phosphorylation of L-plastin may influence its function in tumor cells. To investigate this further, EGFP-tagged wild-type L-plastin (wt-LPL-EGFP) and a mutated, nonphosphorylatable L-plastin protein (5A7A-LPL-EGFP), were expressed in the L-plastin negative melanoma cell line MV3. Biochemical analysis revealed that wt-LPL-EGFP is phosphorylated in MV3 cells while 5A7A-LPL-EGFP is not. Although both wt-LPL-EGFP and 5A7A-LPL-EGFP were targeted to, and promote the formation of, vinculin-containing adhesion sites, static adhesion to either Matrigel or isolated extracellular matrix molecules was neither influenced by expression of wt-LPL-EGFP nor by expression of 5A7A-LPL-EGFP when compared with EGFP expressing control cells. In contrast, haptotactic, but not chemotactic, migration of melanoma cells towards either Matrigel or isolated extracellular matrix molecules was similarly enhanced, if either 5A7A-LPL-EGFP or wt-LPL-EGFP were expressed in MV3 cells. Interestingly, only cells expressing the phosphorylatable wt-LPL-EGFP protein showed enhanced invasion into Matrigel. In line with these findings the in vivo metastatic capacity of mouse B16 melanoma cells correlates with expression and phosphorylation of L-plastin. These data show that an increase in melanoma cell invasiveness requires not only expression but also phosphorylation of L-plastin.

Laminin-5-deficient human keratinocytes: defective adhesion results in a saltatory and inefficient mode of migration

Laminin-5 is a major adhesion protein of the skin basement membrane and crucially involved in integrin-mediated cell substrate attachment of keratinocytes, which is important for hemidesmosomal anchorage as well as for keratinocyte migration during epidermal wound healing. To investigate its role in keratinocyte migration, we analyzed laminin-5-deficient cells of patients with a lethal variant of junctional epidermolysis bullosa. Normal migrating keratinocytes adopted monopolar morphology with a distinct front lamella and employed a continuous mode of translocation. In contrast, laminin-5-deficient cells assumed a stretched bipolar shape with two lamella regions and migrated in a discontinuous, saltatory manner characterized by significantly decreased directional persistence and reduced migration velocity. The distinct morphology as well as the migratory phenotype apparently resulted from a defect in the formation of cell substrate adhesions that were completely missing in the cell body and less stable in the lamella regions. Accordingly in normal keratinocytes, a bipolar shape and a saltatory migration mode were inducible by blocking laminin-5-mediated substrate adhesion. Our findings clearly point to an essential role of laminin-5 in forming dynamic cell substrate adhesion during migration of epidermal keratinocytes and provide an explanation for the cellular mechanisms that underlie the lethal form of junctional epidermolysis bullosa.

Integrin beta4 regulates migratory behavior of keratinocytes by determining laminin-332 organization

Whether alpha6beta4 integrin regulates migration remains controversial. beta4 integrin-deficient (JEB) keratinocytes display aberrant migration in that they move in circles, a behavior that mirrors the circular arrays of laminin (LM)-332 in their matrix. In contrast, wild-type keratinocytes and JEB keratinocytes, induced to express beta4 integrin, assemble laminin-332 in linear tracks over which they migrate. Moreover, laminin-332-dependent migration of JEB keratinocytes along linear tracks is restored when cells are plated on wild-type keratinocyte matrix, whereas wild-type keratinocytes show rotation over circular arrays of laminn-332 in JEB keratinocyte matrix. The activities of Rac1 and the actin cytoskeleton-severing protein cofilin are low in JEB keratinocytes compared with wild-type cells but are rescued following expression of wild-type beta4 integrin in JEB cells. Additionally, in wild-type keratinocytes Rac1 is complexed with alpha6beta4 integrin. Moreover, Rac1 or cofilin inactivation induces wild-type keratinocytes to move in circles over rings of laminin-332 in their matrix. Together these data indicate that laminin-332 matrix organization is determined by the alpha6beta4 integrin/actin cytoskeleton via Rac1/cofilin signaling. Furthermore, our results imply that the organizational state of laminin-332 is a key determinant of the motility behavior of keratinocytes, an essential element of skin wound healing and the successful invasion of epidermal-derived tumor cells.

Regulation of Xenopus gastrulation by ErbB signaling

During Xenopus gastrulation, mesendodermal cells are internalized and display different movements. Head mesoderm migrates along the blastocoel roof, while trunk mesoderm undergoes convergent extension (C&E). Different signals are implicated in these processes. Our previous studies reveal that signals through ErbB receptor tyrosine kinases modulate Xenopus gastrulation, but the mechanisms employed are not understood. Here we report that ErbB signals control both C&E and head mesoderm migration. Inhibition of ErbB pathway blocks elongation of dorsal marginal zone explants and activin-treated animal caps without removing mesodermal gene expression. Bipolar cell shape and cell mixing in the dorsal region are impaired. Inhibition of ErbB signaling also interferes with migration of prechordal mesoderm on fibronectin. Cell-cell and cell-matrix interaction and cell spreading are reduced when ErbB signaling is blocked. Using antisense morpholino oligonucleotides, we show that ErbB4 is involved in Xenopus gastrulation morphogenesis, and it partially regulates cell movements through modulation of cell adhesion and membrane protrusions. Our results reveal for the first time that vertebrate ErbB signaling modulates gastrulation movements, thus providing a novel pathway, in addition to non-canonical Wnt and FGF signals, that controls gastrulation. We further demonstrate that regulation of cell adhesive properties and cell morphology may underlie the functions of ErbBs in gastrulation.

Keratinocyte-secreted laminin 5 can function as a transient receptor for human papillomaviruses by binding virions and transferring them to adjacent cells

Human papillomaviruses (HPVs) replicate only in the terminally differentiating epithelium of the skin and mucosa. While infection of basal keratinocytes is considered a requirement for permissive infection, it remains unclear whether virions can specifically target basal cells for adsorption and uptake following epithelial wounding. We present evidence that HPV binds specifically to laminin 5 (LN5), a component of the extracellular matrix (ECM) secreted by migrating and basal keratinocytes. HPV type 11 capsids colocalized with LN5 in the ECM secreted by vaginal keratinocytes. Binding of both virions and virus-like particles to purified LN5 and to the LN5-rich ECM secreted by cultured keratinocytes was effectively blocked by pretreatment with anti-LN5 antibodies. HPV capsid binding to human cervical mucosa sections included the basement membrane which contains LN5. Cultured keratinocytes expressing alpha6 integrin, a transmembrane protein known to bind LN5, were readily infected by virions preadsorbed to LN5-containing substrates, whereas mutant keratinocytes lacking alpha6 integrin were relatively resistant to infection via this route. These findings suggest a model of natural HPV infection in which proliferating keratinocytes expressing alpha6 integrin at the site of epithelial wounding might be targeted by virions adsorbed transiently to LN5 secreted by migrating keratinocytes.

beta4 integrin and epidermal growth factor coordinately regulate electric field-mediated directional migration via Rac1

Endogenous DC electric fields (EF) are present during embryogenesis and are generated in vivo upon wounding, providing guidance cues for directional cell migration (galvanotaxis) required in these processes. To understand the role of beta (beta)4 integrin in directional migration, the migratory paths of either primary human keratinocytes (NHK), beta4 integrin-null human keratinocytes (beta4-), or those in which beta4 integrin was reexpressed (beta4+), were tracked during exposure to EFs of physiological magnitude (100 mV/mm). Although the expression of beta4 integrin had no effect on the rate of cell movement, it was essential for directional (cathodal) migration in the absence of epidermal growth factor (EGF). The addition of EGF potentiated the directional response, suggesting that at least two distinct but synergistic signaling pathways coordinate galvanotaxis. Expression of either a ligand binding-defective beta4 (beta4+AD) or beta4 with a truncated cytoplasmic tail (beta4+CT) resulted in loss of directionality in the absence of EGF, whereas inhibition of Rac1 blinded the cells to the EF even in the presence of EGF. In summary, both the beta4 integrin ligand-binding and cytoplasmic domains together with EGF were required for the synergistic activation of a Rac-dependent signaling pathway that was essential for keratinocyte directional migration in response to a galvanotactic stimulus.

A critical role for tetraspanin CD151 in alpha3beta1 and alpha6beta4 integrin-dependent tumor cell functions on laminin-5

The basement membrane protein laminin-5 supports tumor cell adhesion and motility and is implicated at multiple steps of the metastatic cascade. Tetraspanin CD151 engages in lateral, cell surface complexes with both of the major laminin-5 receptors, integrins alpha3beta1 and alpha6beta4. To determine the role of CD151 in tumor cell responses to laminin-5, we used retroviral RNA interference to efficiently silence CD151 expression in epidermal carcinoma cells. Near total loss of CD151 had no effect on steady state cell surface expression of alpha3beta1, alpha6beta4, or other integrins with which CD151 associates. However, CD151-silenced carcinoma cells displayed markedly impaired motility on laminin-5, accompanied by unusually persistent lateral and trailing edge adhesive contacts. CD151 silencing disrupted alpha3beta1 integrin association with tetraspanin-enriched microdomains, reduced the bulk detergent extractability of alpha3beta1, and impaired alpha3beta1 internalization in cells migrating on laminin-5. Both alpha3beta1- and alpha6beta4-dependent cell adhesion to laminin-5 were also impaired in CD151-silenced cells. Reexpressing CD151 in CD151-silenced cells reversed the adhesion and motility defects. Finally, loss of CD151 also impaired migration but not adhesion on substrates other than laminin-5. These data show that CD151 plays a critical role in tumor cell responses to laminin-5 and reveal promotion of integrin recycling as a novel potential mechanism whereby CD151 regulates tumor cell migration.

A keratinocyte hypermotility/growth-arrest response involving laminin 5 and p16INK4A activated in wound healing and senescence

Keratinocytes become migratory to heal wounds, during early neoplastic invasion, and when undergoing telomere-unrelated senescence in culture. All three settings are associated with expression of the cell cycle inhibitor p16INK4A (p16) and of the basement membrane protein laminin 5 (LN5). We have investigated cause-and-effect relationships among laminin 5, p16, hypermotility, and growth arrest. Plating primary human keratinocytes on the gamma2 precursor form of laminin 5 (LN5') immediately induced directional hypermotility at approximately 125 microm/hour, followed by p16 expression and growth arrest. Cells deficient in p16 and either p14ARF or p53 became hypermotile in response to LN5' but did not arrest growth. Plating on LN5' triggered smad nuclear translocation, and all LN5' effects were blocked by a transforming growth factor (TGF) beta receptor I (TGFbetaRI) kinase inhibitor. In contrast, plating cells on collagen I triggered a TGFbetaRI kinase-independent hypermotility unaccompanied by smad translocation or growth arrest. Plating on control surfaces with TGFbeta induced hypermotility after a 1-day lag time and growth arrest by a p16-independent mechanism. Keratinocytes serially cultured with TGFbetaRI kinase inhibitor exhibited an extended lifespan, and immortalization was facilitated following transduction to express the catalytic subunit of telomerase (TERT). These results reveal fundamental features of a keratinocyte hyper-motility/growth-arrest response that is activated in wound healing, tumor suppression, and during serial culture.

Overexpression of the epidermal growth factor receptor confers migratory properties to nonmigratory postnatal neural progenitors

Approaches to successful cell transplantation therapies for the injured brain involve selecting the appropriate neural progenitor type and optimizing the efficiency of the cell engraftment. Here we show that epidermal growth factor receptor (EGFR) expression enhances postnatal neural progenitor migration in vitro and in vivo. Migratory NG2-expressing (NG2+) progenitor cells of the postnatal subventricular zone (SVZ) express higher EGFR levels than nonmigratory, cortical NG2+ cells. The higher endogenous EGFR expression in SVZ NG2+ cells is causally related with their migratory potential in vitro as well as in vivo after cell engraftment. EGFR overexpression in cortical NG2+ cells by transient transfection converted these cells to a migratory phenotype in vitro and in vivo. Finally, cortical NG2+ cells purified from a transgenic mouse in which the EGFR is overexpressed under the CNP promoter exhibited enhanced migratory capability. These findings reveal a new role for EGFR in the postnatal brain and open new avenues to optimize cell engraftment for brain repair.

Laminin-5-integrin interaction signals through PI 3-kinase and Rac1b to promote assembly of adherens junctions in HT-29 cells

Human intestinal cell differentiation is mediated by signaling pathways that remain largely undefined. We and others have shown that cell migration and differentiation along the crypt-villus axis is associated with temporal and spatial modulations of the repertoire, as well as with the function of integrins and E-cadherins and their substrates. Cross-talk between integrin and cadherin signaling was previously described and seems to coordinate this differentiation process. Here, we report that engagement of alpha6 and, to a lesser extent, alpha3 integrin subunits after HT-29 cell adhesion on laminin 5 increases the expression of E-cadherin, which then organizes into nascent adherens junctions. We further identify that phosphoinositide 3-kinase (PI 3-kinase) activation plays a key role in this cross-talk. Indeed, integrin-dependent adhesion on laminin 5 stimulates PI 3-kinase activity. Immunofluorescence and immunoprecipitation experiments revealed that activated PI 3-kinase is recruited at cell-cell contacts. Using LY294002, an inhibitor of PI 3-kinase activity, we found that this activation is essential for E-cadherin connection with the cytoskeleton and for biogenesis of adherens junctions. Finally, we demonstrated that PI 3-kinase could signal through Rac1b activation to control adherens junction assembly. Our results provide a mechanistic insight into integrin-cadherin cross-talk and identify a novel role for PI 3-kinase in the establishment of adherens junctions.

Zinc finger transcription factors designed for bispecific coregulation of ErbB2 and ErbB3 receptors: insights into ErbB receptor biology

Signaling through the ErbB family of tyrosine kinase receptors in normal and cancer-derived cell lines contributes to cell growth and differentiation. In this work, we altered the levels of ErbB2 and ErbB3 receptors, individually and in combination, by using 6-finger and 12-finger synthetic zinc finger protein artificial transcription factors (ATFs) in an epidermoid squamous cell carcinoma line, A431. We successfully designed 12-finger ATFs capable of coregulating ErbB3 and ICAM-1 or ErbB2 and ErbB3. With ATFs, the effects of changes in ErbB2 and ErbB3 receptor levels were evaluated by using cell proliferation, cell migration, and cell signaling assays. Cell proliferation was increased when ErbB2 and ErbB3 were both overexpressed. Cell migration on collagen was decreased when ErbB2 was down-regulated, yet migration on laminin was significantly increased with ErbB3 overexpression. ErbB2 and ErbB3 overexpression also stimulated the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways. Our ATF approach has elucidated differences in ErbB receptor-mediated proliferation, migration, and intracellular signaling that cannot be explained merely by the presence or absence of particular ErbB receptors and emphasizes the dynamic nature of the ErbB signaling system. The transcription factor approach developed here provides a gene-economical route to the regulation of multiple genes and may be important for complex gene therapies.

Non-angiogenic functions of VEGF in breast cancer

This review advances the hypothesis that the function of vascular endothelial growth factor (VEGF) in breast cancer is not limited to angiogenesis, and that VEGF signaling in breast carcinoma cells is important for the ability of these cells to evade apoptosis and progress towards invasive and metastatic disease. In other terms, VEGF signaling provides a selective advantage for the survival and dissemination of breast carcinoma cells that may be independent of angiogenesis. The key component of this hypothesis is that breast carcinoma cells express specific VEGF receptors and that these receptors respond to autocrine VEGF, resulting in the activation of signaling pathways that impede apoptosis and promote cell migration. A related hypothesis, which is developed in this review, is that the alpha6beta4 integrin, which has been implicated in the survival and motility of breast cancer cells, can stimulate the translation of VEGF mRNA and, consequently, autocrine VEGF signaling. These findings imply that VEGF and VEGF receptor-based therapeutics, in addition to targeting angiogenesis, may also target tumor cells directly.

Mobilization and activation of a signaling competent α6β4integrin underlies its contribution to carcinoma progression

This review examines the hypothesis that the function of the alpha 6beta 4 integrin is altered substantially as normal epithelia undergo malignant transformation and progress to invasive carcinoma and that the functions of this integrin contribute to the behavior of aggressive carcinoma cells. Specifically, alpha 6beta 4 functions primarily as an adhesion receptor in normal epithelia, often as a component of hemidesmosomes and associated with intermediate filaments. Factors in the host-tumor microenvironment have the potential to mobilize alpha 6beta 4 from hemidesmosomes and promote its association with F-actin in lamellae and filopodia, a process that is mediated by PKC-dependent phosphorylation of the beta 4 cytoplasmic domain. Importantly, this altered localization of alpha 6beta 4 appears to be coupled to an activation of its signaling potential, which may occur through its association with growth factor receptors or lipid rafts, possibilities that are not mutually exclusive. The primal signaling event triggered by alpha 6beta 4 appears to be activation of PI3-K and this activation has profound consequences on the migration, invasion and survival of carcinoma cells. Arguably, the ability of alpha 6beta 4 to stimulate the PI3-K-dependent translation of VEGF and possibly other growth factors may be the most significant contribution of this integrin to carcinoma because of the potential autocrine and paracrine effects of these factors.