Moloney murine leukemia virus (Mo-MuLV) is a thymotropic and leukemogenic retrovirus which causes T lymphomas. The long terminal repeat (LTR) of Mo- MuLV affects the regulation of a number of cellular genes, including collagenase IV, monocyte chemoattractant protein-1, and c-jun genes, all of which contain 12-O-tetradecanoylphorbol-13-acetate-responsive element consensus sites within their promoters. We report here that Mo-MuLV stimulates the collagenase IV gene through transcription factor AP-1, and that the expression of a subgenomic portion of Mo-MuLV LTR alone is sufficient for this effect. Transient or stable expression of the viral LTR increases cellular AP-1 DNA binding activity. The collagenase IV 12-O- tetradecanoylphorbol-13-acetate-responsive element consensus sequence was shown to be required for this trans-activation. Deletions or mutations of this consensus site which abolished AP-1 binding also abolished trans- activation by the LTR. Transient or stable transfection of the viral LTR into cells stimulated c-jun gene expression, suggesting one mechanism whereby the vital LTR may induce cellular AP-1 activity. Thus, the Mo-MuLV LTR, through activation of the transcription factor AP-1, is capable of regulating cellular gene expression, including the induction of proto-oncogenes. This activity may be relevant to the mechanisms whereby retroviruses which do not contain oncogenes induce neoplasia.
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