Regulation of MUC5 and MUC1 gene expression: correlation with airway mucous differentiation

The purpose of this paper was to obtain probes to study the structure and function of mucins in rat models of airway cell differentiation and disease. We report the isolation and characterization of the rat cDNA homologue of the human airway secretory mucin, MUC5. Furthermore, we demonstrate the coordinate regulation of the expression of MUC5 and MUC1 (a membrane-bound mucin) and mucous differentiation. The rat MUC5 was cloned by the RT-PCR using motifs conserved in the secretory mucins, MUC2 and MUC5. The rat cDNA revealed a high degree of sequence similarity to human MUC5 (73% at the amino acid level). Alignments with three other secretory mucins (human MUC5, human MUC2, rat MUC2), indicated a conservation of the cysteines and of the octapeptide motifs, but a lack of conservation of a short tandem repeat sequence that is found only in the human MUC5. Northern analysis of MUC1 and MUC5 indicated a specific tissue-restricted pattern of expression. Surprisingly, rat MUC5 exhibited a monodisperse signal, a characteristic that is unusual for most secretory mucins, including the human MUC5. Expression of MUC1 and MUC5 correlated with mucous differentiation. Both genes were expressed at undetectable or very low levels in undifferentiated cultures, but both mucins became strongly expressed during mucous differentiation. Furthermore, neither mucin gene was expressed in retinoid-deficient cultures that undergo squamous instead of mucous differentiation. These studies demonstrate that expression of MUC1 and MUC5 is coordinately regulated with airway mucous cell differentiation. These cDNAs should provide useful tools to study mucin synthesis during differentiation and disease.