Browsing by Author "Xu, Haiming"

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    Influence of aminoacyl-tRNA synthetase complex-interacting multifunctional protein 1 on epithelial differentiation and organization during lung development
    (American Physiological Society, 2020-08) Lee, Daniel D.; Hochstetler, Alexandra; Sah, Eric; Xu, Haiming; Lowe, Chinn-Woan; Santiaguel, Sara; Thornton, Janet Lea; Pajakowski, Adam; Schwarz, Margaret A.; Anatomy and Cell Biology, School of Medicine
    Proper development of the respiratory bronchiole and alveolar epithelium proceeds through coordinated cross talk between the interface of epithelium and neighboring mesenchyme. Signals that facilitate and coordinate the cross talk as the bronchial forming canalicular stage transitions to construction of air-exchanging capillary-alveoli niche in the alveolar stage are poorly understood. Expressed within this decisive region, levels of aminoacyl-tRNA synthetase complex-interacting multifunctional protein 1 (AIMP1) inversely correlate with the maturation of the lung. The present study addresses the role of AIMP1 in lung development through the generation and characterization of Aimp1−/− mutant mice. Mating of Aimp1+/− produced offspring in expected Mendelian ratios throughout embryonic development. However, newborn Aimp1−/− pups exhibited neonatal lethality with mild cyanosis. Imaging both structure and ultrastructure of Aimp1−/− lungs showed disorganized bronchial epithelium, decreased type I but not type II cell differentiation, increased distal vessels, and disruption of E-cadherin deposition in cell-cell junctions. Supporting the in vivo findings of disrupted epithelial cell-cell junctions, in vitro biochemical experiments show that a portion of AIMP1 binds to phosphoinositides, the lipid anchor of proteins that have a fundamental role in both cellular membrane and actin cytoskeleton organization; a dramatic disruption in F-actin cytoskeleton was observed in Aimp1−/− mouse embryonic fibroblasts. Such observed structural defects may lead to disrupted cell-cell boundaries. Together, these results suggest a requirement of AIMP1 in epithelial cell differentiation in proper lung development.
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    N-terminus of pro-EMAP II regulates its binding with C-terminus, Arginyl-tRNA Synthetase, and Neurofilament light protein
    (2015-04) Xu, Haiming; Malinin, Nikolay L.; Awasthi, Niranjan; Schwarz, Roderich E.; Schwarz, Margaret A.; Department of Pediatrics, Indiana University School of Medicine
    Pro-EMAP II, one component of the Multi-Aminoacyl tRNA Synthetase (MSC) Complex, plays multiple roles in physiological and pathological processes of protein translation, signal transduction, immunity, lung development and tumor growth. Recent studies determined that pro-EMAP II has an essential role in maintaining axon integrity in central and peripheral neural systems where deletion of pro-EMAP IIs C-terminus was reported in a consanguineous Israeli Bedouin kindred suffering from Pelizaeus-Merzbacher-like disease. We hypothesized that pro-EMAP IIs N-terminus had an important role in the regulation of protein-protein interactions. Using a GFP reporter system, we defined a putative leucine-zipper in the N-terminus of human pro-EMAP II protein (amino acid residues 1-70), which can form specific strip-like punctate structures. Through GFP punctate analysis, we uncovered that pro-EMAP IIs C-terminus (147-312 amino acid residues) can repress the GFP punctate formation. Pull-down assays confirmed the binding between pro-EMAP II N-terminus and its C-terminus is mediated by a putative leucine-zipper. Furthermore, the pro-EMAP II 1-70 aa region was identified as the binding partner of the arginyl-tRNA synthetase (RARS), a polypeptide of MSC complex. We also determined that the punctate GFP pro-EMAP II 1-70aa aggregate co-localizes and binds to the neurofilament light (NFL) subunit protein that is associated with pathologic neurofilament network disorganization and degeneration of motor neurons. These findings indicate the structure and binding interaction of Pro-EMAP II protein and suggest a role of this protein in the pathological neurodegenerative diseases.
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    Rho GTPase CDC42 regulates directionality and random movement via distinct MAPK pathways in neutrophils
    (2006-12) Szczur, Kathleen; Xu, Haiming; Atkinson, Simon J; Zheng, Yi; Filippi, Marie-Dominique
    Neutrophil transmigration into tissue is a multiple-step process that results from a coordinated rearrangement of the cytoskeleton and adhesion complexes. Assembly and disassembly of actin and adhesion structures dictate motility behavior, while polarity and gradient sensing provide directionality to the cell movement. Here, using mice deficient in the CDC42 regulator CDC42 GTPase-activating protein (CDC42GAP), we demonstrate that CDC42 activity separately regulates neutrophil motility and directionality. CDC42GAP–/– neutrophils showed increased motility, while directed migration was defective. Podosome-like structures present at the leading edge in wild-type neutrophils were significantly reduced in CDC42GAP–/– cells. CDC42GAP–/– neutrophils also showed increased lateral and tail filopodia-like formation, and excess membrane protrusions. We further suggest that CDC42GAP-mediated extracellular signal–regulated kinase (ERK) activity regulates motility associated with podosome-like structures at the cell leading edge, while CDC42GAP-induced p38MAPK phosphorylation regulates directed migration by antagonizing filopodia assembly. Overall, this study reveals that CDC42 activity regulates both motility and directionality in neutrophils, but via distinct mitogen-activated protein kinase (MAPK) pathways.