To understand the system of secreted proteins and receptors involved in cell-cell signaling, we produced a comprehensive set of recombinant secreted proteins and the extracellular domains of transmembrane proteins, which constitute most of the protein components of the extracellular space. Each protein was tested in a suite of assays that measured metabolic, growth, or transcriptional responses in diverse cell types. The pattern of responses across assays was analyzed for the degree of functional selectivity of each protein. One of the highly selective proteins was a previously undescribed ligand, designated interleukin-34 (IL-34), which stimulates monocyte viability but does not affect responses in a wide spectrum of other assays. In a separate functional screen, we used a collection of extracellular domains of transmembrane proteins to discover the receptor for IL-34, which was a known cytokine receptor, colony-stimulating factor 1 (also called macrophage colony-stimulating factor) receptor. This systematic approach is thus useful for discovering new ligands and receptors and assessing the functional selectivity of extracellular regulatory proteins.

SummaryThe human pathogen Helicobacter pylori colonizes the mucous layer of the stomach. During parasitic infection, freely swimming bacteria adhere to the gastric epithelial cells and trigger intracellular signalling pathways. This process requires the translocation of the effector protein CagA into the host cell through a specialized type IV secretion system encoded in the cag pathogenicity island. Following transfer, CagA is phosphorylated on tyrosine residues by a host cell kinase. Here, we describe how the tyrosine phosphorylation of CagA is restricted to a previously identified repeated sequence called D1. This sequence is located in the C-terminal half of the protein and contains the five-amino-acid motif EPIYA, which is amplified by duplications in a large fraction of clinical isolates. Tyrosine phosphorylation of CagA is essential for the activation process that leads to dramatic changes in the morphology of cells growing in culture. In addition, we observed that two members of the src kinases family, c-Src and Lyn, account for most of the CagA-specific kinase activity in host cell lysates. Thus, CagA translocation followed by tyrosine phosphorylation at the EPIYA motifs promotes a growth factor-like response with intense cytoskeletal rearrangements, cell elongation effects and increased cellular motility. IntroductionHelicobacter pylori colonizes the antrum and the corpus of the gastric mucosa and its presence is associated with severe pathologies such as peptic ulcer disease (PUD), mucosa-associated lymphoid tissues (MALT) lymphoma CagA-phosphorylating kinases that are present in host cell lysates. Results In vitro tyrosine phosphorylation of CagA occurs within the EPIYA motifTo determine which tyrosine residues on CagA are phosphorylated, we generated fusion proteins of different CagA domains from strains CCUG17874 and G27 with glutathione-S-transferase (GST) and histidine (His) tags (Fig. 1). After expression in Escherichia coli BL21 and purification by affinity chromatography, the CagA fragments were assayed for their ability to be substrates for tyrosine kinases. An in vitro kinase assay (tyrosine kinase phosphorylation assay, TKPA) was carried out in which purified CagA molecules were incubated with purified c-Src kinase for 10 min at 30°C in a phosphorylation buffer.In most of the clinical isolates, CagA contains from two to six copies of a short amino acid sequence, EPIYA, located in the carboxy-terminal half of the protein. The EPIYA motif is present in two copies in a strain without repeats (CCUG17874), in three copies in a strain with one repeat (Ba185 and 342) and in four copies in a strain with two repeats (G27) (Figs 1 and 2). As shown in Fig. 1 the tyrosine-phosphorylated region of G27CagA was located between amino acids 846 and 1049, which contained all four EPIYA motifs (Fig. 1, CagA-4). The homologous region in strain CCUG17874 containing only two EPIYA motifs was also tyrosine phosphorylated ( Fig. 1, CagA-5). In both CagA fusions no further tyrosine residues were present. A fusion p...

The ras p21 GTPase-activating protein (GAP) was purified from human placental tissue. Internal amino acid sequence was obtained from this 120,000-dalton protein and, by means of this sequence, two types of complementary DNA clones were isolated and characterized. One type encoded GAP with a predicted molecular mass of 116,000 daltons and 96% identity with bovine GAP. The messenger RNA of this GAP was detected in human lung, brain, liver, leukocytes, and placenta. The second type appeared to be generated by a differential splicing mechanism and encoded a novel form of GAP with a predicted molecular mass of 100,400 daltons. This protein lacks the hydrophobic amino terminus characteristic of the larger species, but retains GAP activity. The messenger RNA of this type was abundantly expressed in placenta and in several human cell lines, but not in adult tissues.

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Apoptosis is a highly regulated form of cell death, characterized by distinctive features such as cellular shrinkage and nuclear condensation. We demonstrate here that proteolytic activation of hPAK65, a p21-activated kinase, induces morphological changes and elicits apoptosis. hPAK65 is cleaved both in vitro and in vivo by caspases at a single site between the N-terminal regulatory p21-binding domain and the C-terminal kinase domain. The C-terminal cleavage product becomes activated, with a kinetic profile that parallels caspase activation during apoptosis. This C-terminal hPAK65 fragment also activates the c-Jun N-terminal kinase pathway in vivo. Microinjection or transfection of this truncated hPAK65 causes striking alterations in cellular and nuclear morphology, which subsequently promotes apoptosis in both CHO and Hela cells. Conversely, apoptosis is delayed in cells expressing a dominant-negative form of hPAK65. These findings provide a direct evidence that the activated form of hPAK65 generated by caspase cleavage is a proapoptotic effector that mediates morphological and biochemical changes seen in apoptosis.

Aberrant activation of anaplastic lymphoma kinase (ALK) has been described in a range of human cancers, including non-small cell lung cancer and neuroblastoma (Hallberg and Palmer, 2013). Vertebrate ALK has been considered to be an orphan receptor and the identity of the ALK ligand(s) is a critical issue. Here we show that FAM150A and FAM150B are potent ligands for human ALK that bind to the extracellular domain of ALK and in addition to activation of wild-type ALK are able to drive 'superactivation' of activated ALK mutants from neuroblastoma. In conclusion, our data show that ALK is robustly activated by the FAM150A/B ligands and provide an opportunity to develop ALK-targeted therapies in situations where ALK is overexpressed/activated or mutated in the context of the full length receptor.DOI: http://dx.doi.org/10.7554/eLife.09811.001

Induction of apoptosis by death receptors such as Fas or tumour necrosis factor (TNF) R1 leads to distinct changes in cell morphology, activation of the caspase protease cascade, and the degradation of nuclear chromatin by activated nucleases. Here, we describe the purification and cDNA cloning of a novel 40 kDa endonuclease from Jurkat cells that is activated by caspases. This protein, designated caspase-activated nuclease (CPAN), is sufficient to degrade naked DNA and to induce apoptotic morphology and DNA fragmentation in naive nuclei. CPAN is highly homologous to a recently described mouse nuclease, CAD [1], and may represent the human homologue. Our data on the human cDNA as well as additional data on the mouse homologue suggest that a 30 amino-acid portion of the recently published mouse sequence [1] is incorrect. We show that the activity of human CPAN is regulated by DFF45 [2], an inhibitor necessary for CPAN expression and stabilization in an inactive state in living cells. Proteolytic cleavage of DFF45 by caspases in vitro leads to dissociation of DFF45 fragments from CPAN and activation of CPAN as an endonuclease. CPAN is a tightly regulated endonuclease with unique characteristics that might represent a distinctive family of endonucleases.

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