Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As previously observed for FK506, we report here that cyclosporin A (CsA) treatment of mouse fibroblast cells stably transfected with the mouse mammary tumor virus-chloramphenicol acetyltransferase (MMTV-CAT) reporter plasmid (LMCAT cells) results in potentiation of dexamethasone (Dex)-induced CAT gene expression. Potentiation by CsA is observed in cells treated with 10-100 nM Dex but not in cells treated with 1 microM Dex, a concentration of hormone which results in maximum CAT activity. At 10 nM Dex, 1-5 microM CsA provokes an approximately 50-fold increase in CAT gene transcription, compared with transcription induced by Dex alone. No induction of CAT gene expression is observed in cells treated with CsA or FK506 in the absence of Dex. The antisteroid RU 486 abolishes effects obtained in the presence of Dex. Using a series of CsA, as well as FK506, analogs, including some devoid of calcineurin phosphatase inhibition activity, we conclude that the potentiation effects of these drugs on Dex-induced CAT gene expression in LMCAT cells do not occur through a calcineurin-mediated pathway. Western-blotting experiments following immunoprecipitation of glucocorticosteroid receptor (GR) complexes resulted in coprecipitation of GR, heat shock protein hsp90 and two immunophilins: the FK506-binding protein FKBP59 and the CsA-binding protein cyclophilin 40 (CYP40). Two separate immunophilin-hsp90 complexes are present in LMCAT cells: one containing CYP40-hsp90, the other FKBP59-hsp90. Thus, both FKBP59 and CYP40 can be classified as hsp-binding immunophilins, and their possible involvement as targets of immunosuppressants potentiating the GR-mediated transcriptional activity is discussed.
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PMID:Cyclosporin A potentiates the dexamethasone-induced mouse mammary tumor virus-chloramphenicol acetyltransferase activity in LMCAT cells: a possible role for different heat shock protein-binding immunophilins in glucocorticosteroid receptor-mediated gene expression. 753 38

It has recently been discovered that the steroid receptor-associated heat shock protein, hsp56, belongs to the FK506 family of immunophilin proteins. The ability of hsp56 to bind the immunosuppressive macrolide FK506 has led to the speculation that the steroid receptor and immunophilin signal transduction pathways are functionally interrelated. We have tested this idea by assessing the effects of FK506 on glucocorticoid receptor (GR)-mediated expression of the murine mammary tumor virus-chloramphenicol acetyltransferase (MMTV-CAT) reporter plasmid. We report that combined treatment with FK506 and low concentrations of dexamethasone (10(-8) or 10(-7) M) results in a large enhancement of MMTV-CAT gene expression over that seen in response to dexamethasone (Dex) alone. FK506 potentiation of MMTV-CAT expression did not occur at 10(-6) M Dex or in the complete absence of hormone. We also show that potentiation of Dex-mediated MMTV-CAT expression occurs in response to rapamycin, that glucocorticoid-regulated enhancer sequences are sufficient for the FK506-mediated potentiation effect, and that this effect can be blocked by RU486 antagonist. Finally, we provide evidence that FK506 potentiation of GR-mediated gene expression is the result of increased translocation to the nucleus of the GR.
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PMID:Potentiation of glucocorticoid receptor-mediated gene expression by the immunophilin ligands FK506 and rapamycin. 768 Oct 58