Promyelocytic leukemia (Pml) protein is required for Oct4 gene expression and the maintenance of its open chromatin conformation in stem cells. In proliferating stem cells, Pml-nuclear body, along with transcription factors TR2, SF1 and Sp1 and Brg1-dependent chromatin remodeling complex (BRGC), associates with conserved region 1 (CR1) of this promoter to maintain a nucleosome-free region for gene activity. Retinoic acid (RA) rapidly down-regulates Pml, resulting in the replacement of BRGC with Brm-containing remodeling complex (BRMC), disassociation of SF1 and SP1, retaining of TR2, recruitment of RIP140, G9a and HP1γ, and sequential insertion of two nucleosomes on CR1 that progressively displays repressive heterochromatin marks. This study demonstrates a functional role for Pml in maintaining a specific open chromatin conformation of the Oct4 promoter region for its constant expression in stem cells; and illustrates the mechanism underlying RA-induced chromatin remodeling of Oct4 gene in differentiating cells, in which Pml plays a critical role. The study also demonstrates a novel mode of chromatin remodeling which occurs by repositioning and sequentially inserting nucleosomes into a specific region of the gene promoter to compact the chromatin in differentiating cells.

Receptor-interacting protein 140 (RIP140) is abundantly expressed in mature adipocyte and modulates gene expression involved in lipid and glucose metabolism. Protein kinase C epsilon and protein arginine methyltransferase 1 can sequentially stimulate RIP140 phosphorylation and then methylation, thereby promoting its export to the cytoplasm. Here we report a lipid signal triggering cytoplasmic accumulation of RIP140, and a new functional role for cytoplasmic RIP140 in adipocyte to regulate lipolysis. Increased lipid content, particularly an elevation in diacylglycerol levels, promotes RIP140 cytoplasmic accumulation and increased association with lipid droplets (LDs) by its direct interaction with perilipin. By interacting with RIP140, perilipin more efficiently recruits hormone-sensitive lipase (HSL) to LDs and enhances adipose triglyceride lipase (ATGL) forming complex with CGI-58, an activator of ATGL. Consequentially, HSL can more readily access its substrates, and ATGL is activated, ultimately enhancing lipolysis. In adipocytes, blocking cytoplasmic RIP140 accumulation reduces basal and isoproterenol-stimulated lipolysis and the pro-inflammatory potential of their conditioned media (i.e. activating NF-κB and inflammatory genes in macrophages). These results show that in adipocytes with high lipid contents, RIP140 increasingly accumulates in the cytoplasm and enhances triglyceride catabolism by directly interacting with perilipin. The study suggests that reducing nuclear export of RIP140 might be a useful means of controlling adipocyte lipolysis.