A biosensor of S100A4 metastasis factor activation: inhibitor screening and cellular activation dynamics

Expression of S100A2 calcium-binding protein predicts response to pancreatectomy for pancreatic cancer

BACKGROUND & AIMS

Current methods of preoperative staging and predicting outcome following pancreatectomy for pancreatic cancer (PC) are inadequate. We evaluated the utility of multiple biomarkers from distinct biologic pathways as potential predictive markers of response to pancreatectomy and patient survival.

METHODS

We assessed the relationship of candidate biomarkers known, or suspected, to be aberrantly expressed in PC, with disease-specific survival and response to therapy in a cohort of 601 patients.

RESULTS

Of the 17 candidate biomarkers examined, only elevated expression of S100A2 was an independent predictor of survival in both the training (n = 162) and validation sets (n = 439; hazard ratio [HR], 2.19; 95% confidence interval [CI]: 1.48-3.25; P < .0001) when assessed in a multivariate model with clinical variables. Patients with high S100A2 expressing tumors had no survival benefit with pancreatectomy compared with those with locally advanced disease, whereas those without high S100A2 expression had a survival advantage of 10.6 months (19.4 vs 8.8 months, respectively) and a HR of 3.23 (95% CI: 2.39-4.33; P < .0001). Of significance, patients with S100A2-negative tumors had a significant survival benefit from pancreatectomy even in the presence of involved surgical margins (median, 15.7 months; P = .0007) or lymph node metastases (median, 17.4 months; P = .0002).

CONCLUSIONS

S100A2 expression is a good predictor of response to pancreatectomy for PC and suggests that high S100A2 expression may be a marker of a metastatic phenotype. Prospective measurement of S100A2 expression in diagnostic biopsy samples has potential clinical utility as a predictive marker of response to pancreatectomy and other therapies that target locoregional disease.

S100A1: Structure, Function, and Therapeutic Potential

S100A1 is a member of the S100 family of calcium-binding proteins. As with most S100 proteins, S100A1 undergoes a large conformational change upon binding calcium as necessary to interact with numerous protein targets. Targets of S100A1 include proteins involved in calcium signaling (ryanidine receptors 1 & 2, Serca2a, phopholamban), neurotransmitter release (synapsins I & II), cytoskeletal and filament associated proteins (CapZ, microtubules, intermediate filaments, tau, mocrofilaments, desmin, tubulin, F-actin, titin, and the glial fibrillary acidic protein GFAP), transcription factors and their regulators (e.g. myoD, p53), enzymes (e.g. aldolase, phosphoglucomutase, malate dehydrogenase, glycogen phosphorylase, photoreceptor guanyl cyclases, adenylate cyclases, glyceraldehydes-3-phosphate dehydrogenase, twitchin kinase, Ndr kinase, and F1 ATP synthase), and other Ca2+-activated proteins (annexins V & VI, S100B, S100A4, S100P, and other S100 proteins). There is also a growing interest in developing inhibitors of S100A1 since they may be beneficial for treating a variety of human diseases including neurological diseases, diabetes mellitus, heart failure, and several types of cancer. The absence of significant phenotypes in S100A1 knockout mice provides some early indication that an S100A1 antagonist could have minimal side effects in normal tissues. However, development of S100A1-mediated therapies is complicated by S100A1's unusual ability to function as both an intracellular signaling molecule and as a secreted protein. Additionally, many S100A1 protein targets have only recently been identified, and so fully characterizing both these S100A1-target complexes and their resulting functions is a necessary prerequisite.

Metastasis promoter S100A4 is a potentially valuable molecular target for cancer therapy

The growth, invasion and metastatic spread of cancer have been identified with the deregulation of cell proliferation, altered intercellular and cell-substratum adhesion and enhanced motility and the deposition of disseminated cancer cells at distant sites. The identification of therapeutic targets for cancer is crucial to human welfare. Drug development, molecular modelling and design of effective drugs greatly depend upon the identification of suitable therapeutic targets. Several genetic determinants relating to proliferation and growth, invasion and metastasis have been identified. S100A4 appears to be able to activate and integrate pathways to generate the phenotypic responses that are characteristic of cancer. S100A4 signalling can focus on factors associated with normal and aberrant proliferation, apoptosis and growth, and differentiation. It is able to activate signalling pathways leading to the remodelling of the cell membrane and the extracellular matrix; modulation of cytoskeletal dynamics, acquisition of invasiveness and induction of angiogenesis. Therefore S100A4 is arguably a molecular target of considerable potential possessing a wide ranging biological activity that can alter and regulate the major phenotypic features of cancer. The evolution of an appropriate strategy that permits the identification of therapeutic targets most likely to be effective in the disease process without unduly affecting normal biological processes and function is an incontrovertible imperative. By virtue of its ability to activate interacting and multi-functional signalling systems, S100A4 appears to offer suitable targets for developing new therapeutic procedures. Some effectors of the S100A4-activated pathways might also lend themselves as foci of therapeutic interest.

Visualizing and quantifying adhesive signals

Understanding the structural adaptation and signaling of adhesion sites in response to mechanical stimuli requires in situ characterization of the dynamic activation of a large number of adhesion components. Here, we review high-resolution live cell imaging approaches to measure forces, assembly, and interaction of adhesion components, and the activation of adhesion-mediated signals. We conclude by outlining computational multiplexing as a framework for the integration of these data into comprehensive models of adhesion signaling pathways.

Rap1 activation in collagen phagocytosis is dependent on nonmuscle myosin II-A

Rap1 enhances integrin-mediated adhesion but the link between Rap1 activation and integrin function in collagen phagocytosis is not defined. Mass spectrometry of Rap1 immunoprecipitates showed that the association of Rap1 with nonmuscle myosin heavy-chain II-A (NMHC II-A) was enhanced by cell attachment to collagen beads. Rap1 colocalized with NM II-A at collagen bead-binding sites. There was a transient increase in myosin light-chain phosphorylation after collagen-bead binding that was dependent on myosin light-chain kinase but not Rho kinase. Inhibition of myosin light-chain phosphorylation, but not myosin II-A motor activity inhibited collagen-bead binding and Rap activation. In vitro binding assays demonstrated binding of Rap1A to filamentous myosin rods, and in situ staining of permeabilized cells showed that NM II-A filaments colocalized with F-actin at collagen bead sites. Knockdown of NM II-A did not affect talin, actin, or beta1-integrin targeting to collagen beads but targeting of Rap1 and vinculin to collagen was inhibited. Conversely, knockdown of Rap1 did not affect localization of NM II-A to beads. We conclude that MLC phosphorylation in response to initial collagen-bead binding promotes NM II-A filament assembly; binding of Rap1 to myosin filaments enables Rap1-dependent integrin activation and enhanced collagen phagocytosis.

The renal cortical interstitium: morphological and functional aspects

The renal interstitial compartment, situated between basement membranes of epithelia and vessels, contains two contiguous cellular networks. One network is formed by interstitial fibroblasts, the second one by dendritic cells. Both are in intimate contact with each other. Fibroblasts are interconnected by junctions and connected to basement membranes of vessels and tubules by focal adhesions. Fibroblasts constitute the “skeleton” of the kidney. In the renal cortex, fibroblasts produce erythropoietin and are distinguished from other interstitial cells by their prominent F-actin cytoskeleton, abundance of rough endoplasmic reticulum, and by ecto-5′-nucleotidase expression in their plasma membrane. The resident dendritic cells belong to the mononuclear phagocyte system and fulfil a sentinel function. They are characterized by their expression of MHC class II and CD11c. The central situation of fibroblasts suggests that signals from tubules, vessels, and inflammatory cells converge in fibroblasts and elicit an integrated response. Following tubular damage and inflammatory signals fibroblasts proliferate, change to the myofibroblast phenotype and increase their collagen production, potentially resulting in renal fibrosis. The acquisition of a profibrotic phenotype by fibroblasts in renal diseases is generally considered a main causal event in the progression of chronic renal failure. However, it might also be seen as a repair process.

Structure of Ca2+-bound S100A4 and its interaction with peptides derived from nonmuscle myosin-IIA

S100A4, also known as mts1, is a member of the S100 family of Ca2+-binding proteins that is directly involved in tumor invasion and metastasis via interactions with specific protein targets, including nonmuscle myosin-IIA (MIIA). Human S100A4 binds two Ca2+ ions with the typical EF-hand exhibiting an affinity that is nearly 1 order of magnitude tighter than that of the pseudo-EF-hand. To examine how Ca2+ modifies the overall organization and structure of the protein, we determined the 1.7 A crystal structure of the human Ca2+-S100A4. Ca2+ binding induces a large reorientation of helix 3 in the typical EF-hand. This reorganization exposes a hydrophobic cleft that is comprised of residues from the hinge region,helix 3, and helix 4, which afford specific target recognition and binding. The Ca2+-dependent conformational change is required for S100A4 to bind peptide sequences derived from the C-terminal portion of the MIIA rod with submicromolar affinity. In addition, the level of binding of Ca2+ to both EF-hands increases by 1 order of magnitude in the presence of MIIA. NMR spectroscopy studies demonstrate that following titration with a MIIA peptide, the largest chemical shift perturbations and exchange broadening effects occur for residues in the hydrophobic pocket of Ca2+-S100A4. Most of these residues are not exposed in apo-S100A4 and explain the Ca2+ dependence of formation of theS100A4-MIIA complex. These studies provide the foundation for understanding S100A4 target recognition and may support the development of reagents that interfere with S100A4 function.