ABSTRACT
The apolipoprotein B messenger RNA editing enzyme, catalytic polypeptide (APOBEC) family is composed of nucleic acid editors with roles ranging from antibody diversification to RNA editing. APOBEC2, a member of this family with an evolutionarily conserved nucleic acid-binding cytidine deaminase domain, has neither an established substrate nor function. Using a cellular model of muscle differentiation where APOBEC2 is inducibly expressed, we confirmed that APOBEC2 does not have the attributed molecular functions of the APOBEC family, such as RNA editing, DNA demethylation, and DNA mutation. Instead, we found that during muscle differentiation APOBEC2 occupied a specific motif within promoter regions; its removal from those regions resulted in transcriptional changes. Mechanistically, these changes reflect the direct interaction of APOBEC2 with histone deacetylase (HDAC) transcriptional corepressor complexes. We also found that APOBEC2 could bind DNA directly, in a sequence-specific fashion, suggesting that it functions as a recruiter of HDAC to specific genes whose promoters it occupies. These genes are normally suppressed during muscle cell differentiation, and their suppression may contribute to the safeguarding of muscle cell fate. Altogether, our results reveal a unique role for APOBEC2 within the APOBEC family.
Subject(s)
Chromatin , Muscle Proteins , APOBEC Deaminases/genetics , APOBEC-1 Deaminase/genetics , Cell Differentiation/genetics , Chromatin/genetics , Cytidine Deaminase/metabolism , DNA , Muscle Fibers, Skeletal/metabolism , Muscle Proteins/metabolism , Myoblasts/metabolism , RNA, Messenger/genetics , Animals , MiceABSTRACT
Increasing evidence links metabolism, protein synthesis, and growth signaling to impairments in the function of hematopoietic stem and progenitor cells (HSPCs) during aging. The Lin28b/Hmga2 pathway controls tissue development, and the postnatal downregulation of this pathway limits the self-renewal of adult vs fetal hematopoietic stem cells (HSCs). Igf2bp2 is an RNA binding protein downstream of Lin28b/Hmga2, which regulates messenger RNA stability and translation. The role of Igf2bp2 in HSC aging is unknown. In this study, an analysis of wild-type and Igf2bp2 knockout mice showed that Igf2bp2 regulates oxidative metabolism in HSPCs and the expression of metabolism, protein synthesis, and stemness-related genes in HSCs of young mice. Interestingly, Igf2bp2 expression and function strongly declined in aging HSCs. In young mice, Igf2bp2 deletion mimicked aging-related changes in HSCs, including changes in Igf2bp2 target gene expression and impairment of colony formation and repopulation capacity. In aged mice, Igf2bp2 gene status had no effect on these parameters in HSCs. Unexpectedly, Igf2bp2-deficient mice exhibited an amelioration of the aging-associated increase in HSCs and myeloid-skewed differentiation. The results suggest that Igf2bp2 controls mitochondrial metabolism, protein synthesis, growth, and stemness of young HSCs, which is necessary for full HSC function during young adult age. However, Igf2bp2 gene function is lost during aging, and it appears to contribute to HSC aging in 2 ways: the aging-related loss of Igf2bp2 gene function impairs the growth and repopulation capacity of aging HSCs, and the activity of Igf2bp2 at a young age contributes to aging-associated HSC expansion and myeloid skewing.
Subject(s)
Aging , Hematopoietic Stem Cells , RNA-Binding Proteins , Aging/genetics , Animals , Hematopoiesis/genetics , Hematopoietic Stem Cells/metabolism , Mice , Mice, Knockout , RNA-Binding Proteins/genetics , RNA-Binding Proteins/metabolismABSTRACT
Organism aging is characterized by increased inflammation and decreased stem cell function, yet the relationship between these factors remains incompletely understood. This study shows that aged hematopoietic stem and progenitor cells (HSPCs) exhibit increased ground-stage NF-κB activity, which enhances their responsiveness to undergo differentiation and loss of self-renewal in response to inflammation. The study identifies Rad21/cohesin as a critical mediator of NF-κB signaling, which increases chromatin accessibility in the vicinity of NF-κB target genes in response to inflammation. Rad21 is required for normal differentiation, but limits self-renewal of hematopoietic stem cells (HSCs) during aging and inflammation in an NF-κB-dependent manner. HSCs from aged mice fail to down-regulate Rad21/cohesin and inflammation/differentiation signals in the resolution phase of inflammation. Inhibition of cohesin/NF-κB reverts hypersensitivity of aged HSPCs to inflammation-induced differentiation and myeloid-biased HSCs with disrupted/reduced expression of Rad21/cohesin are increasingly selected during aging. Together, Rad21/cohesin-mediated NF-κB signaling limits HSPC function during aging and selects for cohesin-deficient HSCs with myeloid-skewed differentiation.
