EXPRESSION OF A TRANSLATIONALLY REGULATED, DOMINANT-NEGATIVE CCAAT ENHANCER-BINDING-PROTEIN-BETA ISOFORM AND UP-REGULATION OF THE EUKARYOTIC TRANSLATION INITIATION-FACTOR 2-ALPHA ARE CORRELATED WITH NEOPLASTICTRANSFORMATION OF MAMMARY EPITHELIAL-CELLS/

A translationally regulated, dominant-negative isoform of CCAAT/enhanc er-binding protein beta is expressed in transplantable and primary mou se mammary tumors of different etiologies but is not expressed in pren eoplastic mammary hyperplasias or in primary prostate, lung, lens, ova ry, or lymphoid tumors. The eukaryotic initiation factor 2 alpha prote in is also expressed at significantly higher levels (69.8 +/- 7.2%) in these mammary tumors compared with normal and hyperplastic tissues. T hus, misregulation of eukaryotic initiation factor 2 alpha may promote the expression of a dominant-negative CCAAT/enhancer-binding protein beta isoform, which may inhibit terminal differentiation and facilitat e uncontrolled proliferation of mammary epithelial cells.