Oxygen stress increases prolyl cis/trans isomerase activity and expressionof cyclophilin 18 in rabbit blastocysts

The peptidyl-prolyl cis/trans isomerase (PPlase) activity and the expressio n of cyclophilins were studied in 6-day-old rabbit preimplantation embryos cultured under physiological and increased oxygen concentrations of 5% and 20% O-2 respectively. The PPlase activity was completely inhibited by cyclo sporin A (CsA). The inhibitor of FK506-binding proteins, rapamycin, had no effect on the PPlase activity, indicating that the PPlase activity in rabbi t blastocysts originates from cyclophilins. Using CsA affinity chromatograp hy, only one cyclophilin with a molecular mass of about 17.8 kDa was separa ted. The cDNA of rabbit cyclophilin was cloned and sequenced. Analysis of t he 682-base pair cDNA revealed an open reading frame coding for a polypepti de of 164 amino acid residues with a molecular weight of 17.83 kDa. Homolog ies of 90% and 96% for the cDNA and amino acid sequence, respectively to th e human CyP18 were found, suggesting that the novel rabbit cyclophilin is a member of the CyP18 family (rabCyP18). The transcription level of rabCyP18 mRNA was 8.3 +/- 0.6 pg in 100 ng total RNA in noncultured blastocysts. In vitro culture with moderate oxygen stress (20% O-2) resulted in a 1.5-fold increase in rabCyP18 transcription and an increased PPlase activity compar ed to that of blastocysts cultured with 5% O-2. Increase in transcription r ate and PPlase activity by oxygen stress suggests an involvement of CyP18 i n oxygen defense in rabbit preimplantation embryos.