Mouse mammary tumor virus (MMTV) is a latently oncogenic retrovirus responsible for the neoplastic transformation of mammary epithelial cells. Its expression is regulated by steroids, polypeptide growth factors, and cell-type-specific factors. Using GR mouse mammary cells and NIH 3T3 fibroblasts stably transfected with chimeric constructs of the long terminal repeat region of MMTV, we have demonstrated a novel mechanism of cell-type-specific expression of this virus. In confluent monolayer cultures that permit cell-cell interaction, MMTV long terminal repeat expression is positively regulated by sequences within the hormone response element (HRE) that bind the transcription factors CTF/NFI and OTFI. Although these factors are present in NIH 3T3 cells, MMTV expression in these cells is not regulated by cell density. This is partially due to a negative regulatory factor that binds sequences between-164 and-151 in the HRE. Mutations that destroy
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.