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Immunosuppressants FK506 and rapamycin have different effects on the biosynthesis of cytoplasmic actin during the early period of T cell activation.

ABSTRACT: FK506 and rapamycin are immunosuppressants that interfere with T cell activation. FK506 inhibits early events of T cell activation such as the induction of cytokine transcription, whereas rapamycin inhibits later interleukin 2 signalling events. However, both reagents either directly or indirectly reduce protein synthesis. Therefore a kinetic study was conducted in human primary T lymphocytes examining increased synthesis of proteins stimulated by either ionomycin+phorbol myristate acetate (PMA) or PMA alone. Three patterns of protein expression were observed. Synthesis of one group of proteins had enhanced synthesis with FK506, but reduced synthesis with rapamycin. A second group had reduced synthesis with rapamycin and either no change or a slight reduction with FK506 and a third group had reduction with both FK506 and rapamycin. One major protein of the first group, p42, had a rapid increase in synthesis that decreased by 8 h. Its synthesis was strongly enhanced by FK506, but reduced by rapamycin after ionomycin+PMA stimulation. In contrast, this protein was strongly induced by PMA alone in these cells and not affected by FK506 treatment, but still reduced by rapamycin. p42 was identified as cytoplasmic actin. mRNA levels of both gamma- and beta-actin were found to be enhanced with FK506 treatment suggesting that regulation of actin was at a transcriptional or post-transcriptional level. Results with actinomycin D indicated that FK506 is regulating actin biosynthesis at the post-transcriptional level. Rapamycin, however, appeared to be operating at the level of translation.

SUBMITTER: Miyamoto S

PROVIDER: S-EPMC1220702 | biostudies-other | 1999 Dec

REPOSITORIES: biostudies-other

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Project description:BACKGROUND: FK506 (Tacrolimus) is an important immunosuppressant, produced by industrial biosynthetic processes using various Streptomyces species. Considering the complex structure of FK506, it is reasonable to expect complex regulatory networks controlling its biosynthesis. Regulatory elements, present in gene clusters can have a profound influence on the final yield of target product and can play an important role in development of industrial bioprocesses. RESULTS: Three putative regulatory elements, namely fkbR, belonging to the LysR-type family, fkbN, a large ATP-binding regulator of the LuxR family (LAL-type) and allN, a homologue of AsnC family regulatory proteins, were identified in the FK506 gene cluster from Streptomyces tsukubaensis NRRL 18488, a progenitor of industrial strains used for production of FK506. Inactivation of fkbN caused a complete disruption of FK506 biosynthesis, while inactivation of fkbR resulted in about 80% reduction of FK506 yield. No functional role in the regulation of the FK506 gene cluster has been observed for the allN gene. Using RT-PCR and a reporter system based on a chalcone synthase rppA, we demonstrated, that in the wild type as well as in fkbN- and fkbR-inactivated strains, fkbR is transcribed in all stages of cultivation, even before the onset of FK506 production, whereas fkbN expression is initiated approximately with the initiation of FK506 production. Surprisingly, inactivation of fkbN (or fkbR) does not abolish the transcription of the genes in the FK506 gene cluster in general, but may reduce expression of some of the tested biosynthetic genes. Finally, introduction of a second copy of the fkbR or fkbN genes under the control of the strong ermE* promoter into the wild type strain resulted in 30% and 55% of yield improvement, respectively. CONCLUSIONS: Our results clearly demonstrate the positive regulatory role of fkbR and fkbN genes in FK506 biosynthesis in S. tsukubaensis NRRL 18488. We have shown that regulatory mechanisms can differ substantially from other, even apparently closely similar FK506-producing strains, reported in literature. Finally, we have demonstrated the potential of these genetically modified strains of S. tsukubaensis for improving the yield of fermentative processes for production of FK506.

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Immunosuppressants FK506 and rapamycin have different effects on the biosynthesis of cytoplasmic actin during the early period of T cell activation.

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