S Jayadev

National Institutes of Health, Bethesda, MD, United States

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Publications (4)17.12 Total impact

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    ABSTRACT: The angiotensin AT(2) receptor is an atypical seven transmembrane domain receptor that is coupled to activation of tyrosine phosphatase and inhibition of MAP kinase, and does not undergo agonist-induced internalization. An investigation of the occurrence and nature of AT(2) receptor phosphorylation revealed that phorbol ester-induced activation of protein kinase C (PKC) in HA-AT(2) receptor-expressing COS-7 cells caused rapid and specific phosphorylation of a single residue (Ser(354)) located in the cytoplasmic tail of the receptor. Agonist activation of AT(2) receptors by angiotensin II (Ang II) also caused rapid PKC-dependent phosphorylation of Ser(354) that was prevented by the AT(2) antagonist, PD123177, and by inhibitors of PKC. In cells coexpressing AT(1) and AT(2) receptors, Ang II-induced phosphorylation of the AT(2) receptor was reduced by either PD123177 or the AT(1) receptor antagonist, DuP753, and was abolished by treatment with both antagonists or with PKC inhibitors. These findings indicate that the AT(2) receptor is rapidly phosphorylated via PKC during homologous activation by Ang II, and also undergoes heterologous PKC-dependent phosphorylation during activation of the AT(1) receptor. The latter process may regulate the counteracting effects of AT(2) receptors on growth responses to AT(1) receptor activation.
    Molecular Pharmacology 12/2000; 58(5):1156-61. · 4.41 Impact Factor
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    ABSTRACT: The nature and role of glycosylation in AT1 angiotensin receptor (AT1-R) function were investigated by expressing glycosylation-deficient influenza hemagglutinin (HA) epitope-tagged rat AT1a-Rs (HA-AT1a-Rs) in COS-7 cells. All three asparagine residues (Asn4, Asn176, Asn188) contained within consensus sites for N-linked glycosylation could be glycosylated in Cos-7 cells and appeared to be glycosylated on the endogenous AT1-R in bovine adrenal glomerulosa cells. Heterogeneity of glycosylation at each site accounted for the broad migration pattern of the AT1-R in SDS-PAGE. Mutation at each glycosylation site, either alone or in combination, had little effect on ligand binding parameters (although the N4K mutant had higher affinity) or signaling activity. However, an increasing number of mutated glycosylation sites was associated with decreasing cell surface receptor expression, which was minimal for the unglycosylated N4K/N176Q/N188Q receptor. Decreased surface expression of mutant HA-AT1a-Rs was correlated with decreased total cell receptor content as revealed by immunoblotting with an anti-HA antibody. These findings suggest that glycosylation enhances receptor stability, possibly by protecting nascent receptors from proteolytic degradation.
    Endocrinology 06/1999; 140(5):2010-7. · 4.72 Impact Factor
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    ABSTRACT: The agonist-induced phosphorylation sites of the rat AT1a angiotensin receptor were analyzed using epitope-tagged mutant receptors expressed in Cos-7 cells. Angiotensin II-stimulated receptor phosphorylation was unaffected by truncation of the cytoplasmic tail of the receptor at Ser342 (Delta342) but was abolished by truncation at Ser325 (Delta325). Truncation at Ser335 (Delta335), or double-point mutations of Ser335 and Thr336 to alanine (ST-AA), reduced receptor phosphorylation by approximately 50%, indicating that in addition to Ser335 and/or Thr336, amino acids within the Ser326-Thr332 segment are also phosphorylated. Agonist-induced phosphorylation of the ST-AA and Delta335 receptors was partially inhibited by staurosporine, suggesting that the single protein kinase C consensus site in the Ser326-Thr332 segment (Ser331) is phosphorylated. The impairment of receptor phosphorylation was broadly correlated with the attenuation of agonist-induced internalization rates (Delta325 < Delta335 < ST-AA < Delta342 < wild-type) and with the increasing rank order of magnitude of inositol phosphate production normalized to an equal number of receptors (Delta325 > Delta335 > ST-AA = Delta342 > wild-type). These results demonstrate that agonist-induced phosphorylation of the AT1a receptor is confined to an 11-amino-acid serine/threonine-rich segment of its carboxyl-terminal cytoplasmic tail and implicate this region in the mechanisms of receptor internalization and desensitization.
    Molecular Pharmacology 01/1999; 54(6):935-41. · 4.41 Impact Factor
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    ABSTRACT: A series of deletion mutants was created to analyze the function of the membrane-proximal region of the cytoplasmic tail of the rat type 1a (AT1a) angiotensin receptor. In transiently transfected COS-7 cells, the truncated mutant receptors showed a progressive decrease in surface expression, with no major change in binding affinity for the peptide antagonist, [Sar1,Ile8]angiotensin II. In parallel with the decrease in receptor expression, a progressive decrease in angiotensin II-induced inositol phosphate responses was observed. Alanine substitutions in the region 307-311 identified the highly conserved phenylalanine309 and adjacent lysine residues as significant determinants of AT1a receptor expression.
    FEBS Letters 06/1998; 428(3):147-51. · 3.58 Impact Factor

Publication Stats

73 Citations
17.12 Total Impact Points

Institutions

  • 1999
    • National Institutes of Health
      • Section on Reproductive Endocrinology
      Bethesda, MD, United States
  • 1998
    • National Institute of Child Health and Human Development
      Maryland, United States