Direct interaction of hematopoietic transcription factors PU.1 and GATA-1:functional antagonism in erythroid cells

Malignant transformation usually inhibits terminal cell differentiation but the precise mechanisms involved are not understood. PU.1 is a hematopoieti c-specific Ets family transcription factor that is required for development of some lymphoid and myeloid lineages. PU.1 can also act as an oncoprotein as activation of its expression in erythroid precursors by proviral insert ion or transgenesis causes erythroleukemias in mice. Restoration of termina l differentiation in the mouse erythroleukemia (MEL) cells requires a decli ne in the level of PU.1, indicating that PU.1 can block erythroid different iation. Here we investigate the mechanism by which PU.1 interferes with ery throid differentiation. We find that PU.1 interacts directly with GATA-1, a zinc finger transcription factor required for erythroid differentiation. I nteraction between PU.1 and GATA-1 requires intact DNA-binding domains in b oth proteins. PU.1 represses GATA-1-mediated transcriptional activation. Bo th the DNA binding and transactivation domains of PU.1 are required for rep ression and both domains are also needed to block terminal differentiation in MEL cells. We also show that ectopic expression of PU.1 in Xenopus embry os is sufficient to block erythropoiesis during normal development. Further more, introduction of exogenous GATA-1 in both MEL cells and Xenopus embryo s and explants relieves the block to erythroid differentiation imposed by P U.1. Our results indicate that the stoichiometry of directly interacting bu t opposing transcription factors may be a crucial determinant governing pro cesses of normal differentiation and malignant transformation.