ADAPTIVE REGULATION OF MDCK CELL TAURINE TRANSPORTER (PNCT) MESSENGER-RNA - TRANSCRIPTION OF PNCT GENE IS REGULATED BY EXTERNAL TAURINE CONCENTRATION

NaCl-dependent taurine transporter (pNCT) activity of MDCK cells (Madi n-Darby canine kidney) is up- or down-regulated by medium taurine mani pulation. In this study we found that the abundance of pNCT mRNA was u p- or down-regulated after cells were incubated in media containing 0 mu M taurine or 500 mu M taurine for 24 h. Down-regulation was observe d after 12 h exposure to high taurine (500 mu M) and mRNA abundance wa s appreciably reduced after 72 h exposure. Nuclear run-off assays show that the gene for pNCT is induced at the transcriptional level by tau rine. Addition of cycloheximide blocked the adaptive response and redu ced transcription of pNCT mRNA in MDCK cells. Cycloheximide had virtua lly no effect on pNCT mRNA stability, suggesting that ongoing protein synthesis is required for adaptive regulation of pNCT gene transcripti on.