Cell-specific expression of CCAAT/enhancer-binding protein delta (C/EBP delta) in epithelial lung cells

CCAAT/enhancer-binding proteins (C/EBP) constitute a family of transcriptio n factors that are involved in regulation of proliferation and differentiat ion in several cell types. In epithelial lung cells the C/EBP alpha isoform seems to play a role in the regulation of surfactant proteins (SP) and Cla ra cell specific protein (CCSP), whereas the roles of C/EBP beta and C/EBP delta are unclear. We have examined the protein levels of C/EBP delta in br onchiolar Clara cells and alveolar type 2 cells, and its relation to the ex pression of lung specific proteins and cell proliferation. The protein expr ession of C/EBP delta was high in freshly isolated Clara cells compared to type 2 cells. In both cell types C/EBP delta levels increased during cultur e. Alterations of the levels of C/EBP delta did not correspond with the pro liferation levels of Clara cells, but seemed to correspond in type 2 cells. Clara cell secretory protein (CCSP) was highly expressed in freshly isolat ed Clara cells, in contrast to type 2 cells. SP-D and CYP2B1 were expressed at somewhat higher levels in Clara cells than in type 2 cells, whereas SP- A exhibited highest expression in type 2 cells. During culture the levels o f all these lung proteins were strongly reduced. However, compared to with serum we found an increase in CCSP in Clara cell cultures without serum, an d this correlated with an increase in C/EBP delta. Overall our in vitro dat a suggest that C/EBP delta alone is not related to the maintenance of prote ins involved in differentiation.