Negative Regulation of Erythroid Differentiation via the CBX8-TRIM28 Axis

Abstract

Although the mechanism of chronic myeloid leukemia (CML) initiation through BCR/ABL oncogene has been well characterized, CML cell differentiation into erythroid lineage cells remains poorly understood. Using CRISPR-Cas9 screening, we identify Chromobox 8 (CBX8) as a negative regulator of K562 cell differentiation into erythrocytes. CBX8 is degraded via proteasomal pathway during K562 cell differentiation, which activates the expression of erythroid differentiation-related genes that are repressed by CBX8 in the complex of PRC1. During the differentiation process, the serine/threonine-protein kinase PIM1 phosphorylates serine 196 on CBX8, which contributes to CBX8 reduction. When CD235A expression levels are analyzed, the result reveals that the knockdown of PIM1 inhibits K562 cell differentiation. We also identify TRIM28 as another interaction partner of CBX8 by proteomic analysis. Intriguingly, TRIM28 maintains protein stability of CBX8 and TRIM28 loss significantly induces proteasomal degradation of CBX8, resulting in an acceleration of erythroid differentiation. Here, we demonstrate the involvement of the CBX8-TRIM28 axis during CML cell differentiation, suggesting that CBX8 and TRIM28 are promising novel targets for CML research.

Generation of TRIM28 Knockout K562 Cells by CRISPR/Cas9 Genome Editing and Characterization of TRIM28-Regulated Gene Expression in Cell Proliferation and Hemoglobin Beta Subunits

“…The multi-domain of TRIM28 contributes to the regulation of a variety of cellular processes such as cell proliferation, apoptosis, protein degradation, autophagy and EMT, and several reports have shown the positive clinical relevance between TRIM28 expression levels and specific cancer types [ 43 ]. Compared to normal samples, TRIM28 mRNA level is higher in blood-related cancer patients and cell lines [ 21 , 44 ].…”

“…It is required for the maintenance and pluripotency of embryonic stem cells [ 14 , 15 ] and for controlling the gene regulatory network in hematopoietic stem cell development, including T-cells, B-cells, and erythropoiesis [ 16 , 17 , 18 , 19 , 20 ]. Recently, a report showed that the knockdown of TRIM28 increases K562 cell differentiation [ 21 ].…”

Intrinsic and Extrinsic Regulation of Hematopoiesis in Drosophila

“…In a nutshell, LG progenitor maintenance is regulated by various intrinsic signaling factors, such as Dpp, Notch, Hh, col, Wnt, ROS, and JAK/STAT, largely mirroring the mechanisms underlying myeloid differentiation in vertebrates ( Chavakis et al, 2019 ; Dzierzak and Bigas, 2018 ; Kim et al, 2021 ; Yamashita et al, 2020 ; Zhu and Emerson, 2002 ). Notably, the heterogeneity of the LG progenitor population and existence of intermediate progenitor cells have been frequently proposed ( Cho et al, 2020 ; Ferguson and Martinez-Agosto, 2014 ; Krzemien et al, 2010b ; Spratford et al, 2021 ).…”