Retinoic acid-stimulated sequential phosphorylation, PML recruitment, and SUMOylation of nuclear receptor TR2 to suppress Oct4 expression

Abstract

We previously reported an intricate mechanism underlying the homeostasis of Oct4 expression in normally proliferating stem cell culture of P19, mediated by SUMOylation of orphan nuclear receptor TR2. In the present study, we identify a signaling pathway initiated from the nongenomic activity of all-trans retinoic acid (atRA) to stimulate complex formation of extracellular signal-regulated kinase 2 (ERK2) with its upstream kinase, mitogen-activated protein kinase kinase (MEK). The activated ERK2 phosphorylates threonine-210 (Thr-210) of TR2, stimulating its subsequent SUMOylation. Dephosphorylated TR2 recruits coactivator PCAF and functions as an activator for its target gene Oct4. Upon phosphorylation at Thr-210, TR2 increasingly associates with promyelocytic leukemia (PML) nuclear bodies, becomes SUMOylated, and recruits corepressor RIP140 to act as a repressor for its target, Oct4. To normally proliferating P19 stem cell culture, exposure to a physiological concentration of atRA triggers a rapid nongenomic signaling cascade to suppress Oct4 gene and regulate cell proliferation.

PML Nuclear Bodies

“…PML-enforced stem cell self-renewal may rely on its ability to modulate the AKT pathway through regulation of AKT phosphorylation or through the localization of its regulator PTEN (Trotman et al 2006;Song et al 2008;Ito et al 2009). TR2, a modulator of the critical Oct4 V. Lallemand-Breitenbach and H. de Thé stem cell transcriptional regulator, is dependent on PML for its sumoylation (Park et al 2007;Gupta et al 2008). The importance of PML in "stemness" highlights the distinctly uncommon morphologyof NBs in ES cells (Butleret al 2009) and questions the nature of the PML isoforms that they actually express.…”

Vitamin A and retinoid signaling: genomic and nongenomic effects

“…Subsequently, p38MAPK activates the downstream mitogen-and stress-activated kinase 1 (MSK1) ( 96 ). However, in neuronal cells, Sertoli cells, and embryonic stem cells, RA instead activates the p42/p44 extracellular signal-regulated kinases (Erk) or classical MAPKs (116)(117)(118)(119)(120)(121)(122). Then, whether Erks activate a downstream kinase, such as MSK1 or ribosomal protein S6 kinase 3 (RSK2) requires further investigation.…”

“…As an example, in RA-treated P19 cells, the activated Erks phosphorylate testicular nuclear receptor 2 (TR2) that then becomes a repressor of the octamer-binding transcription factor 4 ( Oct4 ) gene, thus facilitating the differentiation program that is expected to take place in response to RA ( 116 ). There is also the recent discovery that the retinol-activated JAKs phosphorylate the transcription factor STAT5, which then translocates in the nucleus ( Fig.…”

Nuclear and Extra-Nuclear Effects of Retinoid Acid Receptors: How They Are Interconnected

“…RA activates p38 mitogen activated kinase (MAPK) in fibroblasts, mouse embryo carcinoma cells, mammary breast tumor cells, and leukemia cells [5,25,52,100]. RA activates the p42/p44 MAPKs (also called Erks) in neurons, Sertoli cells, and embryonic stem cells [30,33,59,87,123].…”