RETRACTED: TIF1β functions as a coactivator for C/EBPβ and is required for induced differentiation in the myelomonocytic cell line U937 (Retracted Article. See vol 16, pg 2170, 2002)

Representational difference analysis (RDA) cloning has identified transcriptional intermediary factor 1 beta (TIF1 beta) as a gene inducibly expressed early during myeloid differentiation of the promyelocytic cell lines HL-60 and U937. To assess the role of TIF1 beta, U937 cell lines were made that expressed antisense-hammerhead ribozymes targeted specifically against TIF1 beta mRNA. These cells failed to differentiate into macrophages, as determined by several criteria: a nonadherent morphology, a failure to arrest cell cycle, lowered levels of macrophage-specific cell surface markers, resistance to Legionella pneumophila infection, a loss of the ability to phagocytose and chemotax, and decreased expression of chemokine mRNAs. One way TIF1 beta acts in macrophage differentiation is to augment C/EBP beta transcriptional activity. Furthermore, we show by EMSA supershifts and coimmunoprecipitation that C/EBP beta and TIF1 beta physically interact. Although TIF1 beta is necessary for macrophage differentiation of U937 cells, it is not sufficient, based on the inability of ectopically expressed TIF1 beta to induce or augment phorbol ester-induced macrophage differentiation. We conclude that TIF1 beta plays an important role in the terminal differentiation program of macrophages, which involves the coactivation of C/EBP beta and induction of C/EBP beta -responsive myeloid genes.