Eicosanoid biosynthesis during mucociliary and mucous metaplastic differentiation of bronchial epithelial cells.

The purpose of this study was to examine the profile of eicosanoids secreted by human bronchial epithelial cells (HBEC) during their in vitro differentiation toward mucociliary or mucous metaplastic phenotype. Eicosanoids were measured in supernatants by mass spectrometry, and corresponding gene expression by real-time PCR. Primary HBEC produced mainly prostaglandins (PGE2, PGD2) and epoxides (e.g. 14,15-EET), but during further mucociliary differentiation we observed a gradual increase in secretion of lipoxygenase derived HETEs. Treatment with IL-13 and IL-4 induced mucous metaplasia and resulted in downregulation of PG pathway, and potent induction of 15-lipoxygenase (marked release of 15-HETE). The deficiency in PG production sustained during long term culture of mucous metaplastic epithelia. In conclusions, Th2-type cytokines induce changes in eicosanoid metabolism of airway epithelial cells, resulting in an immense induction of 15-lipoxygenase pathway, and inhibition of PG pathways. Deficient production of immunomodulatory PGs may promote chronic inflammation and airway remodeling.

Transient ribosomal attenuation coordinates protein synthesis and co-translational folding.

Clustered codons that pair to low-abundance tRNA isoacceptors can form slow-translating regions in the mRNA and cause transient ribosomal arrest. We report that folding efficiency of the Escherichia coli multidomain protein SufI can be severely perturbed by alterations in ribosome-mediated translational attenuation. Such alterations were achieved by global acceleration of the translation rate with tRNA excess in vitro or by synonymous substitutions to codons with highly abundant tRNAs both in vitro and in vivo. Conversely, the global slow-down of the translation rate modulated by low temperature suppresses the deleterious effect of the altered translational attenuation pattern. We propose that local discontinuous translation temporally separates the translation of segments of the peptide chain and actively coordinates their co-translational folding.