REGULATION OF CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR (CFTR) GENE-TRANSCRIPTION AND ALTERNATIVE RNA SPLICING IN A MODEL OF DEVELOPING INTESTINAL EPITHELIUM

Transcriptional and post-transcriptional regulation of CFTR (cystic fibrosis transmembrane conductance regulator) gene expression was studied in HT29 cells. It is known that the abundance of CFTR mRNA increases during differentiation of pluripotent HT29-18 cells and is maintained at high levels in the stably differentiated HT29-18-C1 subclone. Nuclear run-on assays suggest that increased transcription of the CFTR gene explains the increased abundance of total CFTR mRNA in differentiated HT29 cells. The increased transcription cannot be ascribed to cell cycle-dependent expression of the CFTR gene or to changes in CFTR gene copy number between subcloned cells. Similar to native tissue cells, differentiated HT29 cells contain low copy numbers of CFTR transcripts (1-5/cell), and a portion of the CFTR transcripts are alternatively spliced to remove exon 9 (and make 9- mRNA). During differentiation of HT29-18 cells, the absolute amount of full-length CFTR mRNA increases 8-fold, whereas the amount of 9- mRNA increases 18-fold. The fraction of 9- mRNA in the CFTR mRNA pool is increased in differentiated HT29 cells. The results show that gene transcription regulates the abundance of CFTR transcripts and that regulatory control of alternative RNA splicing may also be a cellular mechanism to modulate CFTR function.