Neuregulin-1 Regulates Cell Adhesion via an ErbB2/Phosphoinositide-3 Kinase/Akt-Dependent Pathway: Potential Implications for Schizophrenia and Cancer

Neuregulin-1 (NRG1) is a putative schizophrenia susceptibility gene involved extensively in central nervous system development as well as cancer invasion and metastasis. Using a B lymphoblast cell model, we previously demonstrated impairment in NRG1alpha-mediated migration in cells derived from patients with schizophrenia as well as effects of risk alleles in NRG1 and catechol-O-methyltransferase (COMT), a second gene implicated both in schizophrenia susceptibility and in cancer.Here, we examine cell adhesion, an essential component process of cell motility, using an integrin-mediated cell adhesion assay based on an interaction between ICAM-1 and the CD11a/CD18 integrin heterodimer expressed on lymphoblasts. In our assay, NRG1alpha induces lymphoblasts to assume varying levels of adhesion characterized by time-dependent fluctuations in the firmness of attachment. The maximum range of variation in adhesion over sixty minutes correlates strongly with NRG1alpha-induced migration (r(2) = 0.61). NRG1alpha-induced adhesion variation is blocked by erbB2, PI3K, and Akt inhibitors, but not by PLC, ROCK, MLCK, or MEK inhibitors, implicating the erbB2/PI3K/Akt1 signaling pathway in NRG1-stimulated, integrin-mediated cell adhesion. In cell lines from 20 patients with schizophrenia and 20 normal controls, cells from patients show a significant deficiency in the range of NRG1alpha-induced adhesion (p = 0.0002). In contrast, the response of patient-derived cells to phorbol myristate acetate is unimpaired. The COMT Val108/158Met genotype demonstrates a strong trend towards predicting the range of the NRG1alpha-induced adhesion response with risk homozygotes having decreased variation in cell adhesion even in normal subjects (p = 0.063).Our findings suggest that a mechanism of the NRG1 genetic association with schizophrenia may involve the molecular biology of cell adhesion

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Cre, TPH1-Cre-ERT2; CNS-NB, CNS neuroblastoma; E-NB, enteric neuroblastoma; SI-ADC, small intestinal adenocarcinoma, ICH, islet cell hyperplasia; n, no tumor found; LM, liver metastasis; PNECH, pulmonary neuroendocrine cell hyperplasia; P-NET, pancreatic neuroendocrine tumor; SCLC, small cell lung carcinoma; SM, spleen metastasis; sp, spontaneous without tamoxifen (TAM); Tom, tdTomato; *, sacrificed due to illness; **, days after TAM treatment; @, age (days) when examined.</p

A stem cell marker-expressing subset of enteroendocrine cells resides at the crypt base in the small intestine

The spatial orientation of the enteroendocrine cells along the crypt-villus axis is closely associated with their differentiation in the intestine. Here we studied this relationship using primary duodenal crypts and an ex vivo organoid system established from cholecystokinin-green fluorescent protein (CCK-GFP) transgenic mice. In the primary duodenal crypts, GFP+ cells were found not only in the upper crypt but also at the crypt base, where the stem cells reside. Many GFP+ cells below +4 position were positive for the putative intestinal stem cell markers, leucine-rich repeat-containing G protein-coupled receptor 5, CD133, and doublecortin and CaM kinase-like-1, and also for the neuroendocrine transcription factor neurogenin 3. However, these cells were neither stem nor transient amplifying precursor cells because they were negative for both Ki-67 and phospho-Histone H3 and positive for the mature endocrine marker chromogranin A. Furthermore, these cells expressed multiple endocrine hormones. Tracking of GFP+ cells in the organoids from CCK-GFP mice indicated that GFP+ cells were first observed around the +4 position, some of which localized to the crypt base later in the culture period. These results suggest that a subset of enteroendocrine cells migrates down to the crypt base or stays localized at the crypt base, where they express stem and postmitotic endocrine markers. Further investigation of the function of this subset may provide novel insights into the genesis and development of enteroendocrine cells as well as enteroendocrine tumorigenesis

Phosphorylation-dependent protein interaction with Trypanosoma brucei 14-3-3 proteins that display atypical target recognition.

BACKGROUND: The 14-3-3 proteins are structurally conserved throughout eukaryotes and participate in protein kinase signaling. All 14-3-3 proteins are known to bind to evolutionally conserved phosphoserine-containing motifs (modes 1 and/or 2) with high affinity. In Trypanosoma brucei, 14-3-3I and II play pivotal roles in motility, cytokinesis and the cell cycle. However, none of the T. brucei 14-3-3 binding proteins have previously been documented. METHODOLOGY/PRINCIPAL FINDINGS: Initially we showed that T. brucei 14-3-3 proteins exhibit far lower affinity to those peptides containing RSxpSxP (mode 1) and RxY/FxpSxP (mode 2) (where x is any amino acid residue and pS is phosphoserine) than human 14-3-3 proteins, demonstrating the atypical target recognition by T. brucei 14-3-3 proteins. We found that the putative T. brucei protein phosphatase 2C (PP2c) binds to T. brucei 14-3-3 proteins utilizing its mode 3 motif (-pS/pTx(1-2)-COOH, where x is not Pro). We constructed eight chimeric PP2c proteins replacing its authentic mode 3 motif with potential mode 3 sequences found in Trypanosoma brucei genome database, and tested their binding. As a result, T. brucei 14-3-3 proteins interacted with three out of eight chimeric proteins including two with high affinity. Importantly, T. brucei 14-3-3 proteins co-immunoprecipitated with an uncharacterized full-length protein containing identified high-affinity mode 3 motif, suggesting that both proteins form a complex in vivo. In addition, a synthetic peptide derived from this mode 3 motif binds to T. brucei 14-3-3 proteins with high affinity. CONCLUSION/SIGNIFICANCE: Because of the atypical target recognition of T. brucei 14-3-3 proteins, no 14-3-3-binding proteins have been successfully identified in T. brucei until now whereas over 200 human 14-3-3-binding proteins have been identified. This report describes the first discovery of the T. brucei 14-3-3-binding proteins and their binding motifs. The high-affinity phosphopeptide will be a powerful tool to identify novel T. brucei 14-3-3-binding proteins