Defects of the Heart, Eye, and Megakaryocytes in Peroxisome Proliferator Activator Receptor-binding Protein (PBP) Null Embryos Implicate GATA Family of Transcription Factors

Abstract

Peroxisome proliferator activator receptor (PPAR)-binding protein (PBP) is an important coactivator forPPAR␥ and other nuclear receptors. It has been identified as an integral component of a multiprotein thyroid hormone receptor-associated protein/vitamin D 3 receptor-interacting protein/activator-recruited cofactor complexes required for transcriptional activity. Here, we show that PBP is critical for the development of placenta and for the normal embryonic development of the heart, eye, vascular, and hematopoietic systems. The primary functional cause of embryonic lethality at embryonic day11.5 observed with PBP null mutation was cardiac failure because of noncompaction of the ventricular myocardium and resultant ventricular dilatation. There was a paucity of retinal pigment, defective lens formation, excessive systemic angiogenesis, a deficiency in the number of megakaryocytes, and an arrest in erythrocytic differentiation. Some of these defects involve PPAR␥ and retinoid-sensitive sites, whereas others have not been recognized in the PPARsignaling pathway. Phenotypic changes in four organ systems observed in PBP null mice overlapped with those in mice deficient in members of GATA, a family of transcription factors known to regulate differentiation of megakaryocytes, erythrocytes, and adipocytes. We demonstrate that PBP interacts with all five GATA factors analyzed, GATA-1, GATA-2, GATA-3, GATA-4, and GATA-6, and show that the binding of GATA-1, GATA-4, and GATA-6 to PBP is not dependent on the nuclear receptor recognition sequence motif LXXLL (where L is leucine and X is any amino acid) in PBP. Coexpression of PBP with GATA-3 markedly enhanced transcriptional activity of GATA-3 in nonhematopoietic cells. These observations identify the GATA family of transcription factors as a new interacting partner of PBP and demonstrate that PBP is essential for normal development of vital organ systems.

Specific erythroid-lineage defect in mice conditionally deficient for Mediator subunit Med1

“…In the present study, we showed that Mediator subunit Med1 is essential for erythroid development and correct induction of β-globin gene expression. As shown previously by others and us, Med1 is an important coactivator for the master regulator GATA-1 (9,10,28). Whereas other GATA factors have been shown to be essential for T-cell development (GATA-3) or hematopoietic stem cells (GATA-2) (as reviewed in ref.…”

The Med1 Subunit of Transcriptional Mediator Plays a Central Role in Regulating CCAAT/Enhancer-binding Protein-β-driven Transcription in Response to Interferon-γ

“…The Mediator protein complex regulates transcription from specific gene enhancers in response to hormones and other extracellular signals. Deletion of its constituent subunits leads to loss of a number of transcriptional events that participate in cell division, differentiation, and metabolism (21,(35)(36)(37). We have shown that Med1 dynamically and directly associates with C/EBP-␤.…”

“…Previous reports have shown that the N-terminal region of Med1 plays a critical role in mediating its interactions with other transcription factors, such as GATA1, GATA2, and Pit (21,39). Although the exact contact sites for these transcription factors in the Med1 protein have not been finely mapped, a broad region of Med1 consisting of residues 622-701 appears to form a critical binding domain (39).…”

“…hTERT-HME1, a nononcogenic human mammary epithelial cell line (Clontech), was grown in MCDB-170 medium as per the supplier's instructions. To obtain med1 Ϫ/Ϫ cells, MEFs established from mice containing floxed med1 allele (20,21) were infected with a recombinant adenovirus 5 coding for cre (22). Cell clones lacking Med1 (after Western blot analysis) were selected for these studies.…”

The mediator complex functions as a coactivator for GATA-1 in erythropoiesis via subunit Med1/TRAP220

“…Med1 deficiency leads to death at embryonic day 11.5. Although Med1 is not required for cell division, Med1 is critical for embryonic development of placental and cardiac development (10,14,16).…”