Integrins: versatility, modulation, and signaling in cell adhesion.

https://www.auburn.edu/academic/classes/biol/6190/refs/L04/1-s2.0-S0092867402009716-main.pdf

Integrins: Bidirectional, Allosteric Signaling Machines

Cell signaling by receptor-tyrosine kinases

When epidermal growth factor and its relatives bind the ErbB family of receptors, they trigger a rich network of signalling pathways, culminating in responses ranging from cell division to death, motility to adhesion. The network is often dysregulated in cancer and lends credence to the mantra that molecular understanding yields clinical benefit: over 25,000 women with breast cancer have now been treated with trastuzumab (Herceptin), a recombinant antibody designed to block the receptor ErbB2. Likewise, small-molecule enzyme inhibitors and monoclonal antibodies to ErbB1 are in advanced phases of clinical testing. What can this pathway teach us about translating basic science into clinical use?

/pdf/untangling-the-erbb-signalling-network-1b92otnrud.pdf

Untangling the ErbB signalling network

The transdifferentiation of epithelial cells into motile mesenchymal cells, a process known as epithelial-mesenchymal transition (EMT), is integral in development, wound healing and stem cell behaviour, and contributes pathologically to fibrosis and cancer progression. This switch in cell differentiation and behaviour is mediated by key transcription factors, including SNAIL, zinc-finger E-box-binding (ZEB) and basic helix-loop-helix transcription factors, the functions of which are finely regulated at the transcriptional, translational and post-translational levels. The reprogramming of gene expression during EMT, as well as non-transcriptional changes, are initiated and controlled by signalling pathways that respond to extracellular cues. Among these, transforming growth factor-β (TGFβ) family signalling has a predominant role; however, the convergence of signalling pathways is essential for EMT.

Molecular mechanisms of epithelial–mesenchymal transition

Activity of combination trametinib/navitoclax in patients with RAS-mutated gynecologic (GYN) cancers in a Phase 1/2 study (LBA 12)

Tyrosine phosphorylation of multiple platelet proteins is regulated by the integrin alpha IIb beta 3. In order to further examine integrin-regulated tyrosine phosphorylation, we have used small Arg-Gly-Asp-containing snake venom proteins (termed disintegrins) that inhibit platelet aggregation to competitively block the agonist-induced binding of fibrinogen to alpha IIb beta 3. One structurally unique disintegrin, contortrostatin (which appears to be a disulfide-linked dimer of 13.5 kDa with two Arg-Gly-Asp sites), was found to trigger signaling events typically mediated by fibrinogen cross-linking of alpha IIb beta 3, as demonstrated by tyrosine phosphorylation of the tyrosine kinase pp72syk and a 140-kDa protein. Contortrostatin and another disintegrin, multisquamatin (a monomer of 5.7 kDa with a single Arg-Gly-Asp site), did not affect thrombin-induced platelet shape change, secretion, or integrin-independent tyrosine phosphorylation; however, they inhibited aggregation and aggregation-dependent tyrosine phosphorylation of numerous proteins, including the focal adhesion kinase pp125FAK. Our results suggest that structurally distinct disintegrins have varying effects on tyrosine phosphorylation; while monomeric multisquamatin and dimeric contortrostatin both inhibit aggregation-dependent tyrosine phosphorylation, contortrostatin also possesses a unique functional activity that allows it to activate an intracellular signaling pathway leading to tyrosine phosphorylation. This activity may be involved in the function of this snake venom protein on hemostasis.

Structurally Distinct Disintegrins Contortrostatin and Multisquamatin Differentially Regulate Platelet Tyrosine

The product of the avian sarcoma virus (ASV) transforming gene is a 60,000-dalton phosphoprotein, pp60src. Sera from mice and from an occasional rabbit bearing ASV-induced tumors are capable of immunoprecipitating a phosphoprotein of similar, but not identical, structure from normal avian and mammalian cells. This protein is presumed to be the product of the cellular sarc gene, and has been tentatively designated pp60sarc. Analysis of the tryptic phosphopeptides reveals that the viral and avian proteins have an apparently identical phosphoserine-containing peptide. They evidently also both have an analogous phosphothreonine residue surrounded by a different amino acid sequence. Immunoprecipitates containing either the viral or normal cellular pp60 protein catalyze the transfer of radiolabeled phosphate from [gamma-32P]-ATP to the heavy chain of immune rabbit IgG, therefore suggesting that both viral and cellular phosphoproteins may be protein kinases.

Transforming gene product of avian sarcoma viruses and its homolog in uninfected cells.

Investigations of retroviral oncogenes has led to the identification of many cellular genes (termed proto-oncogenes) that appear to play crucial roles in regulating cellular responses to extracellular signals. Many of these genes are directly involved in the regulation of cellular growth control, either serving as growth factors themselves (such as the c-sis gene product which is one of the two chains of platelet-derived-growth-factor) or as growth factor receptors, (such as the c-erb-b or c- fms gene products which are the receptors for epidermal growth factor and colony stimulating factor I). However, the protein products of proto-oncogenes have also been implicated in the induction of other aspects of signal transduction in a variety of cell types. including neural cells [i.e.the induction of neurite outgrowth in PC12 cells (Bar-Sagi and Feramisco, 1985; Hagag et al., 1986; Alema et al., 1985) and the response to the convulsant drug Metrazole (Morgan et al., 1987)]. Studies of one such proto-oncogene, c-src, have provided strong evidence that the c-src gene product, which functions as a tyrosine-specifle protein kinase, may serve a specialized function in neurons.

Expression of the C-SRC Proto-Oncogene Product in Neural Cells

Cells use multiple feedback controls to regulate metabolism in response to nutrient and signaling inputs. However, feedback creates the potential for unstable network responses. We examined how concentrations of key metabolites and signaling pathways interact to maintain homeostasis in proliferating human cells, using fluorescent reporters for AMPK activity, Akt activity, and cytosolic NADH/NAD + redox. Across various conditions including metabolic (glycolytic or mitochondrial) inhibition or cell proliferation, we observed distinct patterns of AMPK activity, including stable adaptation and highly dynamic behaviors such as periodic oscillations and irregular fluctuations, indicating a failure to reach a steady state. Fluctuations in AMPK activity, Akt activity, and cytosolic NADH/NAD + redox state were temporally linked in individual cells adapting to metabolic perturbations. By monitoring single-cell dynamics in each of these contexts, we identified PI3K/Akt regulation of glycolysis as a multifaceted modulator of single-cell metabolic dynamics that is required to maintain metabolic stability in proliferating cells.

https://www.biorxiv.org/content/biorxiv/early/2017/04/11/126771.full.pdf

Joan S. Brugge

Papers

Activity of combination trametinib/navitoclax in patients with RAS-mutated gynecologic (GYN) cancers in a Phase 1/2 study (LBA 12)

Structurally Distinct Disintegrins Contortrostatin and Multisquamatin Differentially Regulate Platelet Tyrosine

Transforming gene product of avian sarcoma viruses and its homolog in uninfected cells.

Expression of the C-SRC Proto-Oncogene Product in Neural Cells

Akt regulation of glycolysis mediates bioenergetic stability in epithelial cells