Cell-specific posttranscriptional regulation of CFTR gene expression via influence of MAPK cascades on 3'UTR part of transcripts.

Expression of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene, which contains the mutations responsible for CF, is regulated by cytokines (TNF-alpha and IL-1beta) in a cell-specific manner. TNF-alpha decreases CFTR mRNA in human colon cell lines (HT-29), but not in pulmonary cell lines (Calu-3), and IL-1beta increases it only in Calu-3 cells. We looked for the cytokine-induced posttranscriptional regulation of CFTR gene expression and studied the modulation of CFTR mRNA stability linked to its 3' untranslated sequence (3'UTR) in HT-29 and Calu-3 cells. The stability of CFTR mRNA was analyzed by Northern blot after in vitro incubation of total RNAs from CFTR-expressing cells with cytosolic proteins extracted from control or cytokine-treated HT-29 and Calu-3 cells. CFTR mRNA was degraded only by extracts of TNF-alpha-treated HT-29 cells and not by cytosolic proteins from untreated or IL-1beta-treated HT-29 cells. In contrast, extracts of untreated Calu-3 cells enhanced CFTR mRNA degradation, and IL-1beta treatment inhibited this; TNF-alpha had no significant effect. The 3'UTR part of CFTR mRNA was found to be required for this posttranscriptional regulation. The 5' part of the 3'UTR (the 217 first bases), which contains two AUUUA sequences, was implicated in CFTR mRNA destabilization and the following 136 bases, containing several C-repeats in U-rich environment, in its protection. The proteins, which reacted with the U- and C-repeats of CFTR mRNA 3'UTR, were mainly controlled by stimulation of the p42/p44 and p38 MAP kinase cascades with interaction between these pathways. This posttranscriptional control of gene expression is a common feature of CFTR and many proteins of inflammation.