Angiotensin II induces phosphorylation of glucose-regulated protein-75 in WB rat liver cells |
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Authors: | Krishna Sharath B Alfonso Lloyd F Thekkumkara Thomas J Abbruscato Thomas J Bhat G Jayarama |
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Institution: | Department of Pharmaceutical Sciences and Cancer Biology Center, Texas Tech University Health Sciences Center, 1300 Coulter Drive, Amarillo, TX 79106, USA. |
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Abstract: | Studies in vascular smooth muscle cells suggest that, angiotensin II (Ang II)-mediated cellular response requires transactivation of epidermal growth factor receptor (EGF-R), and involves tyrosine phosphorylation of caveolin-1. Here we demonstrate that, exposure of WB rat liver cells to Ang II does not cause transactivation of EGF-R, but did rapidly activate p42/p44 mitogen-activated protein (MAP) kinases suggesting that it activates MAP kinases independent of EGF-R transactivation. We observed that the phospho-specific anti-caveolin-1 antibody detected a tyrosine phosphorylated, 75kDa protein in Ang II-treated cells which we identified as glucose regulated protein-75 (GRP-75). Phosphoamino acid analysis showed that Ang II induced its phosphorylation at tyrosine, serine and threonine residues and was localized to the cytoplasm. The ability of Ang-II to induce GRP-75 phosphorylation suggests that it may play a role in the protection of cytoplasmic proteins from the damaging effect of oxidative stress known to be produced during Ang-II induced signaling. |
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Keywords: | Angiotensin II GRP-75 Phosphorylation Signal transduction Oxidative stress Mitochondria Chaperone EGF-R transactivation |
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