Amplification and oscillations in the FAK/Src kinase system during integrin signaling

Scutellarin Prevents Angiogenesis in Diabetic Retinopathy by Downregulating VEGF/ERK/FAK/Src Pathway Signaling

BACKGROUND

Diabetic retinopathy (DR) is a serious microvascular complication of diabetes. This study demonstrates the antiangiogenic effects of scutellarin (SCU) on high glucose- and hypoxia-stimulated human retinal endothelial cells (HRECs) and on a diabetic rat model by oral administration. The antiangiogenic mechanisms of SCU in vitro and in vivo were investigated.

METHOD

HRECs were cultured in high glucose- (30 mM D-glucose) and hypoxia (cobalt chloride-treated)-stimulated diabetic condition to evaluate the antiangiogenic effects of SCU by CCK-8 test, cell migration experiment (wound healing and transwell), and tube formation experiment. A streptozotocin-induced type II diabetic rat model was established to measure the effects of oral administration of SCU on protecting retinal microvascular dysfunction by Doppler waveforms and HE staining. We further used western blot, luciferase reporter assay, and immunofluorescence staining to study the antiangiogenic mechanism of SCU. The protein levels of phospho-ERK, phospho-FAK, phospho-Src, VEGF, and PEDF were examined in HRECs and retina of diabetic rats.

RESULT

Our results indicated that SCU attenuated diabetes-induced HREC proliferation, migration, and tube formation and decreased neovascularization and resistive index in the retina of diabetic rats by oral administration. SCU suppressed the crosstalk of phospho-ERK, phospho-FAK, phospho-Src, and VEGF in vivo and in vitro.

CONCLUSIONS

These results suggested that SCU can be an oral drug to alleviate microvascular dysfunction of DR and exerts its antiangiogenic effects by inhibiting the expression of the crosstalk of VEGF, p-ERK, p-FAK, and p-Src.

A monoclonal antibody targeting neuropilin-1 inhibits adhesion of MCF7 breast cancer cells to fibronectin by suppressing the FAK/p130cas signaling pathway

Neuropilin-1 (NRP-1) is a nontyrosine kinase coreceptor for semaphorin 3A and the vascular endothelial growth factor involved in tumor angiogenesis, growth, and metastasis and is regarded as a promising target for cancer therapy. In the present study, we investigated the effects of an anti-NRP-1 monoclonal antibody (mAb) that we generated for MCF7 breast cancer cellular adhesion studies. MTT, colony formation, and adhesion assays showed that our anti-NRP-1 mAb dose-dependently inhibited MCF7 proliferation and fibronectin adhesion, leading to a rounded cellular morphology. Further, rhodamine phalloidin stain revealed that fibronectin-dependent formation of actin stress fibers was inhibited by anti-NRP-1 mAb. Immunoprecipitation and western blot showed that anti-NRP-1 mAb treatment inhibited the formation of NRP-1-α5β1 integrin complexes and suppressed the phosphorylation of focal adhesion kinase and p130cas in MCF7 cells. These findings contribute to further understanding the NRP-1 function in cell adhesion and tumor metastasis. Moreover, our anti-NRP-1 mAb is a prospective drug candidate for tumor treatment.

Network Modeling Approach to Predict Myofibroblast Differentiation

Fibrotic disease is a major cause of morbidity and mortality and is characterized by the transition of resident fibroblast cells into active myofibroblasts, identified by their expression of alpha smooth muscle actin. Myofibroblast differentiation is regulated by growth factor signaling and mechanical signals transduced through integrins, which converge at focal adhesion proteins (Src and FAK) and MAPK signaling, but lead to divergent outcomes. While details are known about individual pathways, little is known about their interactions. To this end, an ODE-based model of this cell signaling network was developed in parallel with in vitro experiments to analyze potential mechanisms of crosstalk and regulation of αSMA production. We found that cells lacking Src or FAK produce significantly less or more αSMA than wild type cells, respectively. Transforming growth factor beta 1 and fibroblast growth factor signal through ERK and MAPK p38 with different dynamic profiles to increase or decrease αSMA expression, respectively. Our model effectively recreated αSMA expression levels across a set of 22 experimental conditions and matched some features of transient phosphorylation of ERK and p38. These results support a potential mechanism for regulation of fibroblast differentiation: αSMA production is promoted by active p38 and Src and opposed by ERK.

Guiding cell migration by tugging

The ability of cells to move directionally toward areas of stiffer extracellular matrix (ECM) via a process known as 'durotaxis' is thought to be critical for development and wound healing, but durotaxis can also drive cancer metastasis. Migration is driven by integrin-mediated focal adhesions (FAs), protein assemblies that couple contractile actomyosin bundles to the plasma membrane, transmit force generated by the cytoskeleton to the ECM, and convert the mechanical properties of the microenvironment into biochemical signals. To probe the stiffness of the ECM, motile fibroblasts modulate FA mechanics on the nanoscale and exert forces that are reminiscent of repeated tugging on the ECM. Within a single cell, all FAs tug autonomously and thus act as local rigidity sensors, allowing discernment of differences in the extracellular matrix rigidity at high spatial resolution. In this article, we review current advances that may shed light on the mechanism of traction force fluctuations within FAs. We also examine plausible downstream effectors of tugging forces which may regulate cytoskeletal and FA dynamics to guide cell migration in response to ECM stiffness gradients.

Laminin-332-beta1 integrin interactions negatively regulate invadopodia

Adhesion of epithelial cells to basement membranes (BM) occurs through two major structures: actin-associated focal contacts and keratin-associated hemidesmosomes, both of which form on laminin-332 (Ln-332). In epithelial-derived cancer cells, additional actin-linked structures with putative adhesive properties, invadopodia, are frequently present and mediate BM degradation. A recent study proposed that BM invasion requires a proper combination of focal contacts and invadopodia for invading cells to gain traction through degraded BM, and suggested that these structures may compete for common molecular components such as Src kinase. In this study, we tested the role of the Ln-332 in regulating invadopodia in 804G rat bladder carcinoma cells, a cell line that secretes Ln-332 and forms all three types of adhesions. Expression of shRNA to Ln-332 gamma2 chain (gamma2-kd) led to increased numbers of invadopodia and enhanced extracellular matrix degradation. Replating gamma2-kd cells on Ln-332 or collagen-I fully recovered cell spreading and inhibition of invadopodia. Inhibition of alpha3 or beta1, but not alpha6 or beta4, phenocopied the effect of gamma2-kd, suggesting that alpha3beta1-mediated focal contacts, rather than alpha6beta4-mediated hemidesmosome pathways, intersect with invadopodia regulation. gamma2-kd cells exhibited alterations in focal contact-type structures and in activation of focal adhesion kinase (FAK) and Src kinase. Inhibition of FAK also increased invadopodia number, which was reversible with Src inhibition. These data are consistent with a model whereby actin-based adhesions can limit the availability of active Src that is capable of invadopodia initiation and identifies Ln-332-beta1 interactions as a potent upstream regulator that limits cell invasion.

Toggle switches, pulses and oscillations are intrinsic properties of the Src activation/deactivation cycle

Src-family kinases (SFKs) play a pivotal role in growth factor signaling, mitosis, cell motility and invasiveness. In their basal state, SFKs maintain a closed autoinhibited conformation, where the Src homology 2 domain interacts with an inhibitory phosphotyrosine in the C-terminus. Activation involves dephosphorylation of this inhibitory phosphotyrosine, followed by intermolecular autophosphorylation of a specific tyrosine residue in the activation loop. The spatiotemporal dynamics of SFK activation controls cell behavior, yet these dynamics remain largely uninvestigated. In the present study, we show that the basic properties of the Src activation/deactivation cycle can bring about complex signaling dynamics, including oscillations, toggle switches and excitable behavior. These intricate dynamics do not require imposed external feedback loops and occur at constant activities of Src inhibitors and activators, such as C-terminal Src kinase and receptor-type protein tyrosine phosphatases. We demonstrate that C-terminal Src kinase and receptor-type protein tyrosine phosphatase underexpression or their simultaneous overexpression can transform Src response patterns into oscillatory or bistable responses, respectively. Similarly, Src overexpression leads to dysregulation of Src activity, promoting sustained self-perpetuating oscillations. Distinct types of responses can allow SFKs to trigger different cell-fate decisions, where cellular outcomes are determined by the stimulation threshold and history. Our mathematical model helps to understand the puzzling experimental observations and suggests conditions where these different kinetic behaviors of SFKs can be tested experimentally.

Targeting focal adhesions:Helicobacter pylori-host communication in cell migration

Highly dynamic integrin-based focal adhesions provide an important structural basis for anchoring the cellular actin cytoskeleton to the surrounding extracellular matrix. The human pathogen Helicobacter pylori (H. pylori) directly targets integrins with drastic consequences on the epithelial cell morphology and migration, which might contribute to the disruption of the gastric epithelium in vivo. In this review, we summarize the recent findings concerning the complex mechanism through which H. pylori interferes with host integrin signaling thereby deregulating focal adhesions and the actin cytoskeleton of motile epithelial cells.

Mathematics of cell motility: have we got its number?

Mathematical and computational modeling is rapidly becoming an essential research technique complementing traditional experimental biological methods. However, lack of standard modeling methods, difficulties of translating biological phenomena into mathematical language, and differences in biological and mathematical mentalities continue to hinder the scientific progress. Here we focus on one area-cell motility-characterized by an unusually high modeling activity, largely due to a vast amount of quantitative, biophysical data, 'modular' character of motility, and pioneering vision of the area's experimental leaders. In this review, after brief introduction to biology of cell movements, we discuss quantitative models of actin dynamics, protrusion, adhesion, contraction, and cell shape and movement that made an impact on the process of biological discovery. We also comment on modeling approaches and open questions.