Polycomb protein RING1A limits hematopoietic differentiation in myelodysplastic syndromes

Abstract

Genetic lesions affecting epigenetic regulators are frequent in myelodysplastic syndromes (MDS). Polycomb proteins are key epigenetic regulators of differentiation and stemness that act as two multimeric complexes termed polycomb repressive complexes 1 and 2, PRC1 and PRC2, respectively. While components and regulators of PRC2 such as ASXL1 and EZH2 are frequently mutated in MDS and AML, little is known about the role of PRC1.To analyze the role of PRC1, we have taken a functional approach testing PRC1 components in loss- and gain-of-function experiments that we found overexpressed in advanced MDS patients or dynamically expressed during normal hematopoiesis.This approach allowed us to identify the enzymatically active component RING1A as the key PRC1 component in hematopoietic stem cells and MDS. Specifically, we found that RING1A is expressed in CD34+ bone marrow progenitor cells and further overexpressed in high-risk MDS patients. Knockdown of RING1A in an MDS-derived AML cell line facilitated spontaneous and retinoic acid-induced differentiation. Similarly, inactivation of RING1A in primary CD34+ cells augmented erythroid differentiation. Treatment with a small compound RING1 inhibitor reduced the colony forming capacity of CD34+ cells from MDS patients and healthy controls. In MDS patients higher RING1A expression associated with an increased number of dysplastic lineages and blasts. Our data suggests that RING1A is deregulated in MDS and plays a role in the erythroid development defect.

Ezh1 Targets Bivalent Genes to Maintain Self-Renewing Stem Cells in Ezh2-Insufficient Myelodysplastic Syndrome

“…In fact, we found that this mark strongly co-localized with H3K27me3 at Ezh1 core TG in Ezh1 +/- Ezh2 Δ/Δ HSPCs ( Figure 7 B). Intriguingly, inhibition of Ring1A, an enzymatic component of PRC1, has been shown to have an antitumor effect on an MDS cell line and primary CD34 + cells from patients with MDS ( Palau et al., 2017 ). Therefore, the functional inhibition of PRC1, especially variant PRC1, would represent an interesting approach to eradicate MDS stem cells by inducing the de-repression of Ezh1 core TG in Ezh2 -insufficient MDS.…”

Inhibition of RING1B alters lineage specificity in human embryonic stem cells

“…Using PRT4165 an pharmacological inhibitor of RIN1G1B, we have shown that in differentiating human pluripotent stem cells, RING1B and BMI1 are repressors of ectoderm specification. We hereby report the effect of PRT4165 induced inhibition hESC growth and differentiation, while all the previous reports been performed on cancer cell lines (Palau et al, 2017) as well as mice/rat models (Eliades et al, 2016). Although Ring1b knockout studies have unraveled the indispensable functions of Ring1b protein during murine development and these studies are crucial, in reality subtle changes in certain proteins generate interesting outcomes, and hence we used an inhibition approach to study function of RING1B in lineage specification, also no studies on effect of its inhibition in human ES cells have been reported.…”

“…We observed that PRT4165 though is catalytic activity inhibitor of RING1B, yet is caused reduction at the transcript and protein level. Palau et al (2017) showed that when SKK‐1 (cell line derived from adult acute leukemia cells) was treated with PRT4165 there was reduction of RING1B and BMI1 at protein level. Although we do not have a mechanism to explain, such observation has been previously reported where a histone modifier activity inhibitor has also led to reduced expression of histone deacetylases at RNA and protein level (Krämer et al, 2003, Yang et al, 2015, Cai et al, 2018).…”

“…Statistical significance is represented as *P < 0.05, **P < 0.01. Ismail et al, 2013;Palau et al, 2017), we are first to report the use of sublethal concentration of PRT4165 on human embryonic stem cells to study lineage specification. Once the concentration was standardized, we wanted to check the effect of PRT4165 on the undifferentiated cells so we used 0.1 µM concentration for a period 24 and 36 h without any media change.…”

Anticancer innovative therapy: Highlights from the ninth annual meeting

“…This highlights the key role of this epigenetic regulator in the pathogenesis of MDS. However, RING1A pharmacological inhibition affects the stem cell compartment in both MDS patients and healthy donors, hampering its clinical applicability (Palau, Garz et al 2017). The Buschbeck group applies genetic screening methods (Fellmann, Hoffmann et al 2013) and cell culture models to identify chromatin regulators able to increase the response to the nucleoside-analogue azacitidine.…”