Dysregulated activation of activator protein 1 in keratinocytes of atopic dermatitis patients with enhanced expression of granulocyte/macrophage-colony stimulating factor

Keratinocytes of patients with atopic dermatitis produce high amounts of gr anulecyte/macrophage colony-stimulating factor, a factor essential for dend ritic cell function and thus for the development of skin immune responses. In contrast to keratinocytes cultured from nonatopic, healthy individuals, granulocyte/macrophage colony-stimulating factor mRNA could be detected in unstimulated cultures of atopic dermatitis keratinocytes, and phorbol myris tate acetate induced much greater granulocyte/macrophage colony-stimulating factor mRNA levels in these cells, although the decay kinetics were not al tered. Using reporter gene (chloramphenicol acetyl transferase) analysis, a minimal granulocyte/macrophage colony-stimulating factor promoter was show n to confer constitutive and phorbol-myristate-acetate-induced regulation o f transcriptional activity in keratinocytes, and significantly higher level s of chloramphenicol acetyl transferase activity were measured in lysates o f unstimulated and phorbol-myristate-acetate-treated atopic dermatitis kera tinocytes than in control keratinocyte cultures. Electrophoretic mobility s hift assays showed that low levels of NF-kappaB binding activity could be i nduced by phorbol myristate acetate in both normal and atopic dermatitis ke ratinocytes. By contrast, activator protein 1 complexes were efficiently in duced, and they were invariably present at higher levels in nuclear lysates of atopic dermatitis keratinocytes. Atopic dermatitis keratinocyte nuclear lysates had higher constitutive levels of c-Jun, and phorbol myristate ace tate promoted an earlier and stronger expression of c-Jun, JunB, and of the phosphorylated forms of c-Fos. A dysregulated activation of activator prot ein 1 may be implicated in the molecular mechanisms leading to increased gr anulecyte/macrophage colony-stimulating factor expression in atopic dermati tis keratinocytes.