Expression of a translationally regulated, dominant-negative CCAAT/enhancer-binding protein beta isoform and up-regulation of the eukaryotic translation initiation factor 2alpha are correlated with neoplastic transformation of mammary epithelial cells.

A translationally regulated, dominant-negative isoform of CCAAT/enhancer-binding protein beta is expressed in transplantable and primary mouse mammary tumors of different etiologies but is not expressed in preneoplastic mammary hyperplasias or in primary prostate, lung, lens, ovary or lymphoid tumors. The eukaryotic initiation factor 2alpha protein is also expressed at significantly higher levels (69.8 +/- 7.2%) in these mammary tumors compared with normal and hyperplastic tissues. Thus, misregulation of eukaryotic initiation factor 2alpha may promote the expression of a dominant-negative CCAAT/enhancer-binding protein beta isoform, which may inhibit terminal differentiation and facilitate uncontrolled proliferation of mammary epithelial cells.