GATA-1 Interferes with Monopoiesis by Blocking a Positive Regulatory Circuit Involving VDR and PU.1 - Results from a Retroviral Dominant Effector Screen.

In multipotent hematopoietic progenitors the co-expression of several lineage affiliated transcription factors occurs prior to commitment. The mechanism underlying the repression of alternative lineage pathways is poorly understood. We screened a complex retroviral fetal liver cDNA library for regulatory proteins that repress monopoiesis in a phenotype-based differentiation assay system. This functional genetic “dominant effector” strategy revealed a positive circuit regulating monopoiesis that is established by PU.1 and vitamin D receptor (VDR) as well as a novel repressor function of GATA-1. Increasing levels of PU.1 sensitize progenitors to VDR-dependent monopoiesis, and VDR/retinoic X receptor (RXR) signalling directly transactivates PU.1 gene expression. This positive regulatory loop is repressed by GATA-1 via the VDR. Specifically, we show that the GATA-1 N-terminal region, which is required for the inhibition of monocytic cell proliferation, represses and physically interacts with VDR. Additionally, PU.1 binding via the GATA-1 C-terminus is sufficient to inhibit monocyte differentiation without impairing myeloid cell proliferation. Thus, loss of GATA-1 N-terminal function allows for the expansion of immature myeloid progenitors. We propose that GATA-1 represses monopoiesis in multipotent myeloid progenitors or precursors by interacting with both VDR and PU.1, ultimately enabling alternative lineage programs.