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Articles by C Guo
Total Records ( 3 ) for C Guo
  C Guo , J Li , L Myatt , X Zhu and K. Sun

Cytosolic phospholipase A (cPLA2) catalyzes the formation of arachidonic acid in prostaglandin synthesis. In contrast to the well-described down-regulation of cPLA2, up-regulation of cPLA2 by glucocorticoids has been reported in human amnion fibroblasts, which may play a key role in parturition. The mechanisms underlying this paradoxical induction of cPLA2 by glucocorticoids remain largely unknown. Using cultured human amnion fibroblasts, we found that the induction of cPLA2 by cortisol required ongoing transcription and synthesis of at least one other protein. The induction of cPLA2 by cortisol was abolished by mutagenesis of a glucocorticoid response element (GRE) in the promoter. The same GRE was found mediating the classical inhibition of cPLA2 expression by cortisol in human fetal lung fibroblasts (HFL-1). Cortisol increased Gs expression in amnion fibroblasts but not in HFL-1 cells. Inhibition of Gs with NF449 attenuated the phosphorylation of cAMP response element-binding protein-1 (CREB-1) and the induction of cPLA2 by cortisol in amnion fibroblasts. Both glucocorticoid receptor (GR) and CREB-1 were found bound to the GRE upon cortisol stimulation of amnion fibroblasts. The induction of cPLA2 by cortisol was blocked by GR antagonist RU486 or protein kinase A inhibitor H89 or dominant-negative CREB-1. In conclusion, cortisol activates the cAMP/protein kinase A/CREB-1 pathway via Gs induction, and the phosphorylated CREB-1 interacts with GR at the GRE to promote cPLA2 expression in amnion fibroblasts.

  Y Chen , C Qian , C Guo , F Ge , X Zhang , X Gao , S Shen , B Lian , K Kitazato , Y Wang and S. Xiong

Nucleoside diphosphate phosphate transferase A (NDPK-A) has been shown to play critical roles in the regulation of proliferation, differentiation, growth and apoptosis of cells. Our previous study suggested that the disulphide cross-linkage between cysteine 4 (C4) and cysteine 145 (C145) of NDPK-A might be a possible regulator of its activity. To confirm this hypothesis, the C145 residue of NDPK-A was mutated to serine, and the isomerization and biological activities of the mutant were investigated and compared with those of its wild-type counterpart. It was found the C145S mutation eliminated the intramolecular disulphide bond (DB) and prevented the formation of intermolecular DB, which was known to dissociate the hexameric NDPK-A into dimeric one. We also demonstrated that the C145S mutation didn’t affect the autologous hexamerization of this protein, and the mutant had increased bioactivities including phosphate transferase and DNase. These findings support the hypothesis that the formation of DBs in NDPK-A is involved in the regulation of the oligomerization and bioactivity of this multiple function protein, and that C145 is a key residue in the regulation of NDPK-A. In addition, the C145S mutant that we have constructed might be an attractive candidate for use in applications that require NDPK-A.

  S Thangada , K. M Khanna , V. A Blaho , M. L Oo , D. S Im , C Guo , L Lefrancois and T. Hla

The sphingosine 1-phosphate receptor 1 (S1P1) promotes lymphocyte egress from lymphoid organs. Previous work showed that agonist-induced internalization of this G protein–coupled receptor correlates with inhibition of lymphocyte egress and results in lymphopenia. However, it is unclear if S1P1 internalization is necessary for this effect. We characterize a knockin mouse (S1p1rS5A/S5A) in which the C-terminal serine-rich S1P1 motif, which is important for S1P1 internalization but dispensable for S1P1 signaling, is mutated. T cells expressing the mutant S1P1 showed delayed S1P1 internalization and defective desensitization after agonist stimulation. Mutant mice exhibited significantly delayed lymphopenia after S1P1 agonist administration or disruption of the vascular S1P gradient. Adoptive transfer experiments demonstrated that mutant S1P1 expression in lymphocytes, rather than endothelial cells, facilitated this delay in lymphopenia. Thus, cell-surface residency of S1P1 on T cells is a primary determinant of lymphocyte egress kinetics in vivo.

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