Assembly and function of fibroblast-derived extracellular matrices

For a tumor to develop and spread, the growth-repressive environment of the host tissue must undergo significant changes. These changes include dramatic modifications in the molecular composition and architecture of the extracellular matrix (ECM). Importantly, different tumors have distinct ECM components, depending on their anatomical site. Accordingly, differences can exist between the ECM of primary tumors and metastatic lesions. The ECM can impact treatment, including the efficacy of resection and accessibility of solid tumors to therapeutic antibodies and small molecules. Conversely, treatment can impact the ECM (e.g. radiotherapy, platinium-based drugs) by promoting the deposition of a dense fibrotic stroma. My laboratory seeks to unravel the cell-dependent mechanisms that drive matrix assembly, and to improve our understanding of the functional interplay between tumor cells and their matrix microenvironment. The tumor ECM is largely synthesized and remodeled by stromal fibroblasts. I will discuss our characterization of matrices produced by head and neck tumor-associated fibroblasts and discuss how these fibrillar networks enriched in so called “oncofetal” matrix proteins convey specific biological signals to the cells they encounter

Tensin links energy metabolism to extracellular matrix assembly.

The regulation of integrin function is key to fundamental cellular processes, including cell migration and extracellular matrix (ECM) assembly. In this issue, Georgiadou et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201609066) report that the metabolic sensor adenosine monophosphate-activated protein kinase influences tensin production to regulate α5β1-integrin and fibrillar adhesion assembly and thus reveal an important connection between energy metabolism and ECM assembly

Distinguished Brief

The Government of the Republic of Bretoria and the Kingdom of Pagonia have agreed to submit by Special Agreement the present controversy for final solution to the International Court of Justice pursuant to Article 36, paragraph 1 of the Statute of the International Court of Justice, in relation to Article 40, paragraph 1, of the Statute of the Court

Raf-1 Activation Prevents Caspase 9 Processing Downstream of Apoptosome Formation

In many cell types, growth factor removal induces the release of cytochrome-c from mitochondria that leads to activation of caspase-9 in the apoptosome complex. Here, we show that sustained stimulation of the Raf-1/MAPK1,3 pathway prevents caspase-9 activation induced by serum depletion in CCL39/ΔRaf-1:ER fibroblasts. The protective effect mediated by Raf-1 is sensitive to MEK inhibition that is sufficient to induce caspase-9 cleavage in exponentially growing cells. Raf-1 activation does not inhibit the release of cytochrome-c from mitochondria while preventing caspase-9 activation. Gel filtration chromatography analysis of apoptosome formation in cells shows that Raf-1/MAPK1,3 activation does not interfere with APAF-1 oligomerization and recruitment of caspase 9. Raf-1-mediated caspase-9 inhibition is sensitive to emetine, indicating that the protective mechanism requires protein synthesis. However, the Raf/MAPK1,3 pathway does not regulate XIAP. Taken together, these results indicate that the Raf-1/MAPK1,3 pathway controls an apoptosis regulator that prevents caspase-9 activation in the apoptosome complex

Human glycated albumin affects glucose metabolism in L6 skeletal muscle cells by impairing insulin-induced insulin receptor substrate (IRS) signaling through a protein kinase C alpha-mediated mechanism.

Nonenzymatic glycation is increased in diabetes and leads to increased levels of glycated proteins. Most studies have focused on the role of glycation products in vascular complications. Here, we have investigated the action of human glycated albumin (HGA) on insulin signaling in L6 skeletal muscle cells. Exposure of these cells to HGA inhibited insulin-stimulated glucose uptake and glycogen synthase activity by 95 and 80%, respectively. These effects were time- and dose-dependent, reaching a maximum after 12 h incubation with 0.1 mg/ml HGA. In contrast, exposure of the cells to HGA had no effect on thymidine incorporation. Further, HGA reduced insulin-stimulated serine phosphorylation of PKB and GSK3, but did not alter ERK1/2 activation. HGA did not affect either insulin receptor kinase activity or insulin-induced Shc phosphorylation on tyrosine. In contrast, insulin-dependent IRS-1 and IRS-2 tyrosine phosphorylation was severely reduced in cells preincubated with HGA for 24 h. Insulin-stimulated association of PI3K with IRS-1 and IRS-2, and PI3K activity were reduced by HGA in parallel with the changes in IRS tyrosine phosphorylation, while Grb2-IRS association was unchanged. In L6 myotubes, exposure to HGA increased PKC activity by 2-fold resulting in a similar increase in Ser/Thr phosphorylation of IRS-1 and IRS-2. These phosphorylations were blocked by the PKC inhibitor bisindolylmaleimide (BDM). BDM also blocked the action of HGA on insulin-stimulated PKB and GSK3 alpha. Simultaneously, BDM rescued insulin-stimulation of glucose uptake and glycogen synthase activity in cells exposed to HGA. The use of antibodies specific to PKC isoforms shows that this effect appears to be mediated by activated PKC alpha, independent of reactive oxygen species production. In summary, in L6 skeletal muscle cells, exposure to HGA leads to insulin resistance selectively in glucose metabolism with no effect on growth-related pathways regulated by the hormone

cDNA cloning and expression of a hamster α-thrombin receptor coupled to Ca2+ mobilization

AbstractThe serine protease α-thrombin (thrombin) potently stimulates G-protein-coupled signaling pathways and DNA synthesis in CCL39 hamster lung fibroblasts. To clone a thrombin receptor cDNA, selective amplification of mRNA sequences displaying homology to the transmembrane domains of G-protein-coupled receptor genes was performed by polymerase chain reaction. Using reverse transcribed poly(A)+ RNA from CCL39 cells and degenerate primers corresponding to conserved regions of several phospholipase C-coupled receptors, three novel putative receptor sequences were identified. One corresponds to an mRNA transcript of 3.4 kb in CCL39 cells and a relatively abundant cDNA. Microinjection of RNA transcribed in vitro from this cDNA in Xenopus oocytes leads to the expression of a functional thrombin receptor. The hamster thrombin receptor consists of 427 amino acid residues with 8 hydrophobic domains, including one at the extreme N-terminus that is likely to represent a signal peptide. A thrombin consensus cleavage site is present in the N-terminal extracellular region of the receptor sequence followed by a negatively charged cluster of residues present in a number of proteins that interact with the anion-binding exosite of thrombin

Improving 3D MA-TIRF Reconstruction with Deconvolution and Background Estimation

International audienceTotal internal reflection fluorescence microscopy (TIRF) produces 2D images of the fluorescent activity integrated over a very thin layer adjacent to the glass coverslip. By varying the illumination angle (multi-angle TIRF), a stack of 2D images is acquired from which it is possible to estimate the axial position of the observed biological structures. Due to its unique optical sectioning capability, this technique is ideal to observe and study biological processes at the vicinity of the cell membrane. In this paper, we propose an efficient reconstruction algorithm for multi-angle TIRF microscopy which accounts for both the PSF of the acquisition system (diffraction) and the background signal (e.g., autofluorescence). It jointly performs volume reconstruction, deconvolution, and background estimation. This algorithm, based on the simultaneous-direction method of mul-tipliers (SDMM), relies on a suitable splitting of the optimization problem which allows to obtain closed form solutions at each step of the algorithm. Finally, numerical experiments reveal the importance of considering the background signal into the reconstruction process, which reinforces the relevance of the proposed approach

Differential Role of Insulin Receptor Substrate (IRS)-1 and IRS-2 in L6 Skeletal Muscle Cells Expressing the Arg1152 → Gln Insulin Receptor *

In L6 muscle cells expressing the Arg1152 --> Gln insulin receptor (Mut), basal tyrosine phosphorylation of insulin receptor substrate (IRS)-1 was increased by 35% compared with wild-type cells (WT). Upon exposure to insulin, IRS-1 phosphorylation increased by 12-fold in both the Mut and WT cells. IRS-2 was constitutively phosphorylated in Mut cells and not further phosphorylated by insulin. The maximal phosphorylation of IRS-2 in basal Mut cells was paralleled by a 4-fold increased binding of the kinase regulatory loop binding domain of IRS-2 to the Arg1152 --> Gln receptor. Grb2 and phosphatidylinositol 3-kinase association to IRS-1 and IRS-2 reflected the phosphorylation levels of the two IRSs. Mitogen-activated protein kinase activation and [3H]thymidine incorporation closely correlated with IRS-1 phosphorylation in Mut and WT cells, while glycogen synthesis and synthase activity correlated with IRS-2 phosphorylation. The Arg1152 --> Gln mutant did not signal Shc phosphorylation or Shc-Grb2 association in intact L6 cells, while binding Shc in a yeast two-hybrid system and phosphorylating Shc in vitro. Thus, IRS-2 appears to mediate insulin regulation of glucose storage in Mut cells, while insulin-stimulated mitogenesis correlates with the activation of the IRS-1/mitogen-activated protein kinase pathway in these cells. IRS-1 and Shc-mediated mitogenesis may be redundant in muscle cells