Schistosoma mansoni: TGF-beta signaling pathways

Schistosome parasites have co-evolved an intricate relationship with their human and snail hosts as well as a novel interplay between the adult male and female parasites. We review the role of the TGF-beta signaling pathway in parasite development, host-parasite interactions and male-female interactions. The data to date support multiple roles for the TGF-beta signaling pathway throughout schistosome development, in particular, in the tegument which is at the interface with the host and between the male and female schistosome, development of vitelline cells in female worms whose genes and development are regulated by a stimulus from the male schistosome and embryogenesis of the egg. The human ligand TGF-beta1 has been demonstrated to regulate the expression of a schistosome target gene that encodes a gynecophoric canal protein in the schistosome worm itself. Studies on signaling in schistosomes opens a new era for investigation of host-parasite and male-female interactions.     

Platelet-neutrophil interactions. 12S,20- and 5S,12S-dihydroxyeicosapentaenoic acids: two novel neutrophil metabolites from platelet-derived 12S-hydroxyeicosapentaenoic acid

Dietary marine n-3 polyunsaturated fatty acids have demonstrated an antiinflammatory potential in epidemiologic and intervention studies in humans. Proposed mechanisms, involving only leukocytes, fall short of explaining this potential completely. Enriched by dietary means with eicosapentaenoic acid (EPA), stimulated human platelets release substantial amounts of eicosapentaenoic acid and 12S-hydroxyeicosapentaenoic acid (12S-HEPE) in addition to 12S-hydroxyeicosatetraenoic acid (12S-HETE) derived from arachidonic acid. Human neutrophils metabolize 12S-HETE to 5S,12S-DiHETE when stimulated, whereas unstimulated neutrophils produce 12S,20-DiHETE. This study was undertaken to characterize metabolism of 12S-HEPE in human neutrophils. We demonstrate herein for the first time that 12S-HEPE is metabolized by human neutrophils. In unstimulated neutrophils 20-hydroxylation to 12S,20-DiHEPE occurs, whereas in stimulated neurtrophils 5-lipoxygenation to 5S,12S-DiHEPE takes place. The structures of these metabolites were characterized by their relative retention times on reversed-phase high pressure liquid chromatography, by their UV absorbance spectra, and by gas-liquid chromatography-mass spectrometry. With increasing amounts of 12S-HEPE, stimulated neutrophils produced increasing amounts of 5S,12S-DiHEPE, which is virtually inactive biologically. Concomitantly, production of the potent chemokinetic and chemoattractant arachidonic acid derivative leukotriene B4 decreased. Thus, 12S-HEPE can compete with endogenous arachidonic acid for 5-lipoxygenation in stimulated human neutrophils. 12,20-DiHEPE, LTB5, and 5S,12S-DiHEPE were detectable after coincubating EPA-enriched platelets with unenriched neutrophils, and arachidonic acid-derived 5-lipoxygenase products were decreased. We conclude that 12S-HEPE can participate in platelet-neutrophil interactions in a manner similar to 12S-HETE. By providing competing substrates for neutrophil 5-lipoxygenase, platelets might contribute to the antiinflammatory potential of dietary n-3 fatty acids through platelet-neutrophil interaction.     

Quantitative phosphoproteomics of CXCL12 (SDF-1) signaling

CXCL12 (SDF-1) is a chemokine that binds to and signals through the seven transmembrane receptor CXCR4. The CXCL12/CXCR4 signaling axis has been implicated in both cancer metastases and human immunodeficiency virus type 1 (HIV-1) infection and a more complete understanding of CXCL12/CXCR4 signaling pathways may support efforts to develop therapeutics for these diseases. Mass spectrometry-based phosphoproteomics has emerged as an important tool in studying signaling networks in an unbiased fashion. We employed stable isotope labeling with amino acids in cell culture (SILAC) quantitative phosphoproteomics to examine the CXCL12/CXCR4 signaling axis in the human lymphoblastic CEM cell line. We quantified 4,074 unique SILAC pairs from 1,673 proteins and 89 phosphopeptides were deemed CXCL12-responsive in biological replicates. Several well established CXCL12-responsive phosphosites such as AKT (pS473) and ERK2 (pY204) were confirmed in our study. We also validated two novel CXCL12-responsive phosphosites, stathmin (pS16) and AKT1S1 (pT246) by Western blot. Pathway analysis and comparisons with other phosphoproteomic datasets revealed that genes from CXCL12-responsive phosphosites are enriched for cellular pathways such as T cell activation, epidermal growth factor and mammalian target of rapamycin (mTOR) signaling, pathways which have previously been linked to CXCL12/CXCR4 signaling. Several of the novel CXCL12-responsive phosphoproteins from our study have also been implicated with cellular migration and HIV-1 infection, thus providing an attractive list of potential targets for the development of cancer metastasis and HIV-1 therapeutics and for furthering our understanding of chemokine signaling regulation by reversible phosphorylation.     

Ski and SnoN: negative regulators of TGF-beta signaling

Ski and SnoN are unique proto-oncoproteins in that they can induce both oncogenic transformation and terminal muscle differentiation when expressed at high levels. Recent studies using in vitro and in vivo approaches have begun to unravel the complex roles of Ski and SnoN in tumorigenesis and embryonic development. The identification of Ski and SnoN as important negative regulators of signal transduction by the transforming growth factor-beta superfamily of cytokines provides a valuable molecular basis for the complex functions of Ski and SnoN.     

TGF-beta signaling: positive and negative effects on tumorigenesis.

TGF-beta binding to the cell surface triggers activation of multiple signal transduction pathways that are connected in intricate ways with each other, and with other response networks involved in sensing cellular information input. Recent data indicate that changes in signal intensity and connectivity of these pathways may underlie the complex transition of the TGF-beta pathway from tumor suppressor to oncogene during tumorigenesis.