Gene expression profile analysis of 4-phenylbutyrate treatment of IB3-1 bronchial epithelial cell line demonstrates a major influence on heat-shock proteins

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Abstract
Most individuals with cystic fibrosis (CF) carry one or two mutations that result in a maturation defect of the full-length CFTR protein. The ΔF508 mutation results in a mutant protein that is degraded by the proteosome instead of progressing to the apical membrane where it functions as a cAMP-regulated chloride channel. 4-Phenylbutyrate (PBA) modulates heat-shock protein expression and promotes trafficking of ΔF508, thus permitting maturation and membrane insertion. The goal of this study was to gain insight into the genetic mechanism of PBA action through a large-scale analysis of gene expression. The Affymetrix genome-spanning U133 microarray set was used to compare mRNA expression levels in untreated IB3-1 cell line cultures with cultures treated with 1 mM PBA for 12 and 24 h. The most notable changes in mRNA levels were transient elevations in heat-shock proteins. The majority of genes downregulated throughout the application period were functionally associated with control of gene expression. Another set of genes increased in expression starting at 24 h, suggesting these are downstream effects of altered gene expression initiated by PBA. More than one-third of the genes in this late expressing set were identified as having potential significance in understanding the pathology of CF. Our results demonstrate the usefulness of gene expression profile analysis in understanding the consequences of PBA treatment and provide insights in how this drug exerts its effect on the trafficking of CFTR.