Integrin signaling and mechanotransduction in regulation of somatic stem cells

Somatic stem cells are characterized by their capacity for self-renewal and differentiation, making them integral for normal tissue homeostasis. Different stem cell functions are strongly affected by the specialized micro-environment surrounding the cells. Consisting of soluble signaling factors, extracellular matrix (ECM) ligands and other cells, but also biomechanical cues such as the viscoelasticity and topography of the ECM, these factors are collectively known as the niche. Cell-ECM interactions are mediated largely by integrins, a class of heterodimeric cell adhesion molecules. Integrins bind their ligands in the extracellular space and associate with the cytoskeleton inside the cell, forming a direct mechanical link between the cells and their surroundings. Indeed, recent findings have highlighted the importance of integrins in translating biophysical cues into changes in cell signaling and function, a multistep process known as mechanotransduction. The mechanical properties of the stem cell niche are important, yet the underlying molecular details of integrin-mediated mechanotransduction in stem cells, especially the roles of the different integrin heterodimers, remain elusive. Here, we introduce the reader to the concept of integrin-mediated mechanotransduction, summarize current knowledge on the role of integrin signaling and mechanotransduction in regulation of somatic stem cell functions, and discuss open questions in the field

Integrin beta 1 inhibition alleviates the chronic hyperproliferative dermatitis phenotype of SHARPIN-deficient mice

SHARPIN (Shank-Associated RH Domain-Interacting Protein) is a component of the linear ubiquitin chain assembly complex (LUBAC), which enhances TNF-induced NF-kappa B activity. SHARPIN-deficient (Sharpin(cpdm/cpdm)) mice display multi-organ inflammation and chronic proliferative dermatitis (cpdm) due to TNF-induced keratinocyte apoptosis. In cells, SHARPIN also inhibits integrins independently of LUBAC, but it has remained enigmatic whether elevated integrin activity levels in the dermis of Sharpin(cpdm/cpdm) mice is due to increased integrin activity or is secondary to inflammation. In addition, the functional contribution of increased integrin activation to the Sharpin(cpdm/cpdm) phenotype has not been investigated. Here, we find increased integrin activity in keratinocytes from Tnfr1(-/-) Sharpin(cpdm/cpdm) double knockout mice, which do not display chronic inflammation or proliferative dermatitis, thus suggesting that SHARPIN indeed acts as an integrin inhibitor in vivo. In addition, we present evidence for a functional contribution of integrin activity to the Sharpin(cpdm/cpdm) skin phenotype. Treatment with an integrin beta 1 function blocking antibody reduced epidermal hyperproliferation and epidermal thickness in Sharpin(cpdm/cpdm) mice. Our data indicate that, while TNF-induced cell death triggers the chronic inflammation and proliferative dermatitis, absence of SHARPIN-dependent integrin inhibition exacerbates the epidermal hyperproliferation in Sharpin(cpdm/cpdm) mice

Integrin Binding Dynamics Modulate Ligand-Specific Mechanosensing in Mammary Gland Fibroblasts

The link between integrin activity regulation and cellular mechanosensing of tissue rigidity, especially on different extracellular matrix ligands, remains poorly understood. Here, we find that primary mouse mammary gland stromal fibroblasts (MSFs) are able to spread efficiently, generate high forces, and display nuclear YAP on soft collagen-coated substrates, resembling the soft mammary gland tissue. We describe that loss of the integrin inhibitor, SHARPIN, impedes MSF spreading specifically on soft type I collagen but not on fibronectin. Through quantitative experiments and computational modeling, we find that SHARPIN-deficient MSFs display faster force-induced unbinding of adhesions from collagen-coated beads. Faster unbinding, in turn, impairs force transmission in these cells, particularly, at the stiffness optimum observed for wild-type cells. Mechanistically, we link the impaired mechanotransduction of SHARPIN-deficient cells on collagen to reduced levels of collagen-binding integrin α11β1. Thus integrin activity regulation and α11β1 play a role in collagen-specific mechanosensing in MSFs.</p

Molecular targets for the protodynamic action of cis-urocanic acid in human bladder carcinoma cells

<p>Abstract</p> <p>Background</p> <p>cis-urocanic acid (cis-UCA) is an endogenous amino acid metabolite capable of transporting protons from the mildly acidic extracellular medium into the cell cytosol. The resulting intracellular acidification suppresses many cellular activities. The current study was aimed at characterizing the molecular mechanisms underlying cis-UCA-mediated cytotoxicity in cultured cancer cells.</p> <p>Methods</p> <p>5367 bladder carcinoma cells were left untreated or treated with cis-UCA. Cell death was assessed by measuring caspase-3 activity, mitochondrial membrane polarization, formation and release of cytoplasmic histone-associated DNA fragments, and cellular permeabilization. Cell viability and metabolic activity were monitored by colorimetric assays. Nuclear labelling was used to quantify the effects of cis-UCA on cell cycle. The activity of the ERK and JNK signalling pathways was studied by immunoblotting with specific antibodies. Phosphatase activity in cis-UCA-treated cells was determined by assay kits measuring absorbance resulting from the dephosphorylation of an artificial substrate. All statistical analyses were performed using the two-way Student's t-test (p < 0.05).</p> <p>Results</p> <p>Here we report that treatment of the 5637 human bladder carcinoma cells with 2% cis-UCA induces both apoptotic and necrotic cell death. In addition, metabolic activity of the 5637 cells is rapidly impaired, and the cells arrest in cell cycle in response to cis-UCA. Importantly, we show that cis-UCA promotes the ERK and JNK signalling pathways by efficiently inhibiting the activity of serine/threonine and tyrosine phosphatases.</p> <p>Conclusions</p> <p>Our studies elucidate how cis-UCA modulates several cellular processes, thereby inhibiting the proliferation and survival of bladder carcinoma cells. These anti-cancer effects make cis-UCA a potential candidate for the treatment of non-muscle invasive bladder carcinoma.</p

PP2A inhibitor PME-1 drives kinase inhibitor resistance in glioma cells

Glioblastoma multiforme (GBM) lacks effective therapy options. Although deregulated kinase pathways are drivers of malignant progression in GBM, glioma cells exhibit intrinsic resistance towards many kinase inhibitors, and the molecular basis of this resistance remains poorly understood. Here we show that overexpression of the protein phosphatase 2A (PP2A) inhibitor protein PME-1 drives resistance of glioma cells to various multikinase inhibitors. The PME-1-elicited resistance was dependent on specific PP2A complexes and was mediated by a decrease in cytoplasmic HDAC4 activity. Importantly, both PME-1 and HDAC4 associated with human glioma progression, supporting clinical relevance of the identified mechanism. Synthetic lethality induced by both PME-1 and HDAC4 inhibition was dependent on the co-expression of pro-apoptotic protein BAD. Thus, PME-1-mediated PP2A inhibition is a novel mechanistic explanation for multikinase inhibitor resistance in glioma cells. Clinically, these results may inform patient stratification strategies for future clinical trials with selected kinase inhibitors in GBM

Targeted intracellular delivery of hydrophobic agents using mesoporous hybrid silica nanoparticles as carrier systems

Targeted nanoparticle-mediated intracellular delivery is demonstrated using two hydrophobic fluorophores as model drug cargo. The presented hybrid carrier system exhibits both cancer cell-targeting ability and capacity to retain a hydrophobic agent with subsequent specific release into the endosomal compartment. Furthermore, the incorporated agent is shown to be able to escape from the endosomes into the cytoplasm, making the particles promising candidates as carriers for targeted drug delivery for cancer treatment. © 2009 American Chemical Society

Cancer-cell-specific induction of apoptosis using mesoporous silica nanoparticles as drug-delivery vectors

Targeted delivery of the chemotherapeutic agent methotrexate (MTX) to cancer cells using poly(ethyleneimine)-functionalized mesoporous silica particles as drug-delivery vectors is reported. Due to its high affinity for folate receptors, the expression of which is elevated in cancer cells, MTX serves as both a targeting ligand and a cytotoxic agent. Enhanced cancer-cell apoptosis (programmed cell death) relative to free MTX is thus observed at particle concentrations where nonspecific MTX-induced apoptosis is not observed in the nontargeted healthy cell line, while corresponding amounts of free drug affect both cell lines equally. The particles remain compartmentalized in endo-/lysosomes during the time of observation (up to 72 h), while the drug is released from the particle only upon cell entry, thereby inducing selective apoptosis in the target cells. As MTX is mainly attached to the particle surface, an additional advantage is that the presented carrier design allows for adsorption (loading) of additional drugs into the pore network for therapies based on a combination of drugs. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA