5 results on '"Mehta, H."'
Search Results
2. Structural studies on the eukaryotic chain initiation factor 2 from rabbit reticulocytes and brine shrimp Artemia embryos. Phosphorylation by the heme-controlled repressor and casein kinase II.
- Author
-
Mehta, H B, Dholakia, J N, Roth, W W, Parekh, B S, Montelaro, R C, Woodley, C L, and Wahba, A J
- Abstract
In contrast to reticulocyte polypeptide chain initiation factor 2 (eIF-2), the Artemia factor retains activity in the presence of Mg2+ or after phosphorylation of its alpha-subunit by rabbit reticulocyte heme-controlled repressor (Mehta, H. B., Woodley, C. L., and Wahba, A. J. (1983) J. Biol. Chem. 258, 3438-3441). Furthermore, we have so far been unable to demonstrate a requirement for a GDP/GTP nucleotide exchange factor with Artemia eIF-2. In order to explain these differences we compared the structure of eIF-2 from Artemia and rabbit reticulocytes by using one- and two-dimensional phosphopeptide and iodopeptide maps. Partial trypsin digestion of the alpha-subunit of Artemia eIF-2 after phosphorylation by the heme-controlled repressor generates a 4000 Mr phosphopeptide. Upon extensive trypsin digestion, the two-dimensional phosphopeptide maps of the alpha-subunits for the reticulocyte and Artemia factors are indistinguishable, whereas the iodopeptide maps are different. In addition, immunoblotting indicates that there is no consistent cross-reactivity of the reticulocyte subunits with antibodies prepared in rabbits against the Artemia eIF-2 subunits. A casein kinase II activity was isolated from Artemia embryos that phosphorylates the beta-subunit of reticulocyte eIF-2, but specifically phosphorylates the alpha-subunit of eIF-2 preparations from several non-mammalian sources, including Artemia, yeast, and wheat germ embryos. Since this kinase phosphorylates a site distinct from that recognized by the heme-controlled repressor, and this phosphorylation does not alter the ability of Artemia eIF-2 to undergo nucleotide exchange, caution must be exercised when interpreting the significance of eIF-2(alpha) phosphorylation in non-mammalian cells.
- Published
- 1986
- Full Text
- View/download PDF
3. Studies on the role of eukaryotic nucleotide exchange factor in polypeptide chain initiation.
- Author
-
Goss, D J, Parkhurst, L J, Mehta, H B, Woodley, C L, and Wahba, A J
- Abstract
Interactions of eukaryotic 5-dimethylaminonaphthalene-1-sulfonyl-initiation factor 2 (eIF-2) from rabbit reticulocytes and the guanine nucleotide exchange factor ( GEF ), Met-tRNAf, GTP, and GDP were monitored by changes in fluorescence anisotropy and radioactive filtration assays. At 1 mM Mg2+, radioactive filtration assays demonstrate that GEF is necessary for nucleotide exchange. We did not observe a GDP dependence in the association reaction of eIF-2 X GEF for GDP concentrations from 0.01 to 20 microM. This is in disagreement with the model: eIF-2 X GDP + GEF in equilibrium eIF-2 X GEF + GDP. The addition of GTP caused a decrease in fluorescence anisotropy which is interpreted as a dissociation of eIF-2 X GEF . We propose an asymmetrical model of ternary complex (eIF-2 X GTP X Met-tRNAf) formation where 1) GDP does not displace GEF and 2) GTP replaces GEF and presumably GDP. For reticulocyte eIF-2, phosphorylation of the alpha subunit greatly inhibits protein synthesis. This inhibition derives neither from failure of GEF to bind to eIF-2(alpha P) nor from greatly enhanced binding of GEF . The inhibition results from the requirement of very high levels of GTP (100 microM) to dissociate the eIF-2(alpha P) X GEF complex.
- Published
- 1984
- Full Text
- View/download PDF
4. Identification of critical residues within the conserved and specificity patches of nerve growth factor leading to survival or differentiation.
- Author
-
Mahapatra S, Mehta H, Woo SB, and Neet KE
- Subjects
- Amino Acid Sequence, Amino Acids chemistry, Amino Acids genetics, Amino Acids metabolism, Animals, Binding Sites genetics, Cell Differentiation drug effects, Cell Line, Cell Survival drug effects, Cell Survival physiology, Dose-Response Relationship, Drug, Fibroblasts cytology, Fibroblasts drug effects, Fibroblasts metabolism, MAP Kinase Signaling System, Models, Molecular, Mutagenesis, Site-Directed, Mutant Proteins chemistry, Mutant Proteins metabolism, Mutant Proteins pharmacology, Nerve Growth Factor genetics, Nerve Growth Factor pharmacology, Neurites drug effects, Neurites physiology, PC12 Cells, Protein Binding, Protein Structure, Tertiary, Rats, Receptor, Nerve Growth Factor chemistry, Receptor, trkA chemistry, Recombinant Proteins chemistry, Recombinant Proteins metabolism, Recombinant Proteins pharmacology, Spodoptera, Surface Plasmon Resonance, Cell Differentiation physiology, Nerve Growth Factor metabolism, Receptor, Nerve Growth Factor metabolism, Receptor, trkA metabolism
- Abstract
Afflicted neurons in Alzheimer disease have been shown to display an imbalance in the expression of TrkA and p75(NTR) at the cell surface, and administration of nerve growth factor (NGF) has been considered and attempted for treatment. However, wild-type NGF causes extensive elaboration of neurites while providing survival support. This study was aimed at developing recombinant NGF muteins that did not support neuritogenesis while maintaining the survival response. Critical residues were identified at the ligand-receptor interface by point mutagenesis that played a greater importance in neuritogenesis versus survival. By combining point mutations, two survival-selective recombinant NGF muteins, i.e./7-84-103 and KKE/7-84-103, were generated. Both muteins reduced neuritogenesis in PC12 (TrkA(+)/p75(NTR+)) cells by >90%, while concurrently retaining near wild-type survival activity in MG139 (TrkA(+) only) and PCNA fibroblast (p75(NTR+)-only) cells. Additionally, survival in both naive and terminally differentiated PC12 cells was shown to be intermediate between NGF and negative controls. Dose-response curves with 7-84-103 showed that the differentiation curve was shifted by about 100-fold, whereas the EC(50) for survival was only increased by 3.3-fold. Surface plasmon resonance analysis revealed a 200-fold decrease in binding of 7-84-103 to TrkA. The retention of cell survival was attributed to maintenance of signaling through the Akt survival pathway with reduced MAPK signaling for differentiation. The effect of key mutations along the NGF receptor interface are transmitted inside the cell to enable the generation of survival-selective recombinant NGF muteins that may represent novel pharmacologic lead agents for the amelioration of Alzheimer disease.
- Published
- 2009
- Full Text
- View/download PDF
5. Adaptor protein SLAT modulates Fcgamma receptor-mediated phagocytosis in murine macrophages.
- Author
-
Mehta H, Glogauer M, Bécart S, Altman A, and Coggeshall KM
- Subjects
- Actins genetics, Actins metabolism, Animals, Cell Line, Cytoskeleton genetics, Cytoskeleton metabolism, DNA-Binding Proteins genetics, Guanine Nucleotide Exchange Factors genetics, Guanine Nucleotide Exchange Factors metabolism, Humans, Mice, Mice, Knockout, NFATC Transcription Factors genetics, NFATC Transcription Factors metabolism, Neuropeptides genetics, Neuropeptides metabolism, Nuclear Proteins genetics, Receptors, IgG genetics, T-Lymphocytes metabolism, cdc42 GTP-Binding Protein genetics, cdc42 GTP-Binding Protein metabolism, rac GTP-Binding Proteins genetics, rac GTP-Binding Proteins metabolism, rac1 GTP-Binding Protein genetics, rac1 GTP-Binding Protein metabolism, RAC2 GTP-Binding Protein, DNA-Binding Proteins metabolism, Macrophages metabolism, Nuclear Proteins metabolism, Phagocytosis physiology, Phagosomes physiology, Receptors, IgG metabolism
- Abstract
SLAT (SWAP-70-like adaptor protein of T cells) is an adaptor protein expressed in cells of the hematopoietic system. SLAT interacts with and alters the function of small GTPase Rac1 in fibroblasts. In these nonhematopoietic models, the SLAT-Rac interaction leads to changes in F-actin and causes cytoskeletal reorganization. In T cells, SLAT expression regulates the development of T helper cells through Cdc42- and Rac1-mediated activation of the NF-AT transcription factor. Here we show that SLAT is expressed in macrophages. Overexpression of SLAT in a macrophage cell line inhibits the IgG Fcgamma receptor-mediated phagocytic ability of THP1 cells. In bone marrow-derived macrophages, SLAT protein is recruited to the early phagosomes formed via Fcgamma receptor engagement. SLAT recruitment to the phagosome was most efficient when the macrophages express at least one isoform of Rac (Rac1 or Rac2), because SLAT recruitment was reduced in macrophages of Rac-deficient mice. Macrophages derived from animals lacking SLAT show an elevation in the rate of Fcgamma receptor-mediated phagocytosis. The absence of SLAT is associated with an increase in the amount of F-actin formed around these phagosomes as well as an increase in the amount of Rac1 protein recruited to the phagosome. Our results suggest that SLAT acts as a gatekeeper for the amount of Rac recruited to the phagosomes formed by Fcgamma receptor engagement and thus is able to regulate F-actin re-organization and consequently phagocytosis.
- Published
- 2009
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.