Emerging role of the RNA-editing enzyme ADAR1 in stem cell fate and function

Abstract

Stem cells are critical for organism development and the maintenance of tissue homeostasis. Recent studies focusing on RNA editing have indicated how this mark controls stem cell fate and function in both normal and malignant states. RNA editing is mainly mediated by adenosine deaminase acting on RNA 1 (ADAR1). The RNA editing enzyme ADAR1 converts adenosine in a double-stranded RNA (dsRNA) substrate into inosine. ADAR1 is a multifunctional protein that regulate physiological processes including embryonic development, cell differentiation, and immune regulation, and even apply to the development of gene editing technologies. In this review, we summarize the structure and function of ADAR1 with a focus on how it can mediate distinct functions in stem cell self-renewal and differentiation. Targeting ADAR1 has emerged as a potential novel therapeutic strategy in both normal and dysregulated stem cell contexts.

Structurally Specific Z-DNA Proteolysis Targeting Chimera Enables Targeted Degradation of Adenosine Deaminase Acting on RNA 1

“…In addition to Western blotting, the mRNA levels of ADAR1 and ZBP1 were examined in various cell lines (Figure B). It has also been previously reported that ADAR1 inhibits the necroptosis pathway by inhibiting ZBP1 to downregulate RIPK3-mediated necroptosis in cancer. ,,− Consequently, other marker proteins in necroptosis, such as RIPK1 and RIPK3, were monitored. While RIPK1 exhibited similar expression levels in both normal and cancer cells, in keeping with a previous report, RIPK3 expression was found to be absent in most of the cell lines derived from solid tumors, such as HeLa cells.…”

“…The acquired Z-PROTACs 1c – 17c were introduced into HeLa cells at 5 μg/mL via lipofectamine-mediated transfection, and cell lysates were collected for Western blot analysis. As demonstrated in Figure C, ADAR proteins exist in various isoforms; therefore, ADAR1, ADAR2, and ADAR3 containing the A to I deaminase and another Z-DNA binding protein, ZBP1, with a Z α domain, need to be detected in this experimental condition as well. − Given the reported importance of Z α and Z β domains for Z-DNA binding, and the existence of distinct ADAR1 isoforms (Figure C), we conducted a specificity analysis of the Z-PROTACs to ascertain their capacity to degrade different isoforms. Encouragingly, Figure D reveals that Z-PROTACs 7c , 8c , and 9c exclusively induced the degradation of ADAR1 p110 and p150 isoforms, displaying pronounced specificity toward these ADAR1 protein variants over other isoforms and the ZBP1 protein, likely due to the differential presence of the Z-DNA-binding motif in different isoforms.…”

“…However, we detected RIPK3 expression in the A375 cancer cell line and in normal cell lines, such as MRC5. Given that ADAR1 is implicated in both apoptosis and necroptosis pathways, , experimental assays were conducted in cancer and normal cell lines to verify whether Z-PROTAC induces downstream pathway alterations. Following treatment of various cancer and normal cells with 5 μg/mL vehicle, ODN, 8c , and 9c for 24 h, Western blot analysis was employed to assess the apoptosis marker proteins.…”

“…Our investigation has unearthed intriguing facets of this interaction. Notably, the interaction between Z-DNA and ADAR1 has been found to impede the function of ZBP1, resulting in the suppression of apoptotic cascades via the caspase pathway and the inhibition of necroptotic processes through the MLKL pathway within the context of cancer biology. ,,− Concomitantly, ADAR1 binding exerts a regulatory influence on immune responses, acting as a negative modulator of intracellular innate immunity, chiefly by interfering with the MDA5/MAV5 axis, thereby fostering the progression of cancer cells. , Using the Z-PROTAC approach, we achieved the targeted degradation of ADAR1, while leaving ZBP1 unaffected, specifically within cancer cells. Moreover, Z-PROTAC manipulation has been shown to induce PANoptotic responses, encompassing both apoptosis and necroptosis, exclusively within cancerous cellular contexts as opposed to normal cells.…”

RNA editing enzymes: structure, biological functions and applications

“…The only other mammalian molecule containing a Zα domain is ZBP1 (Z-DNA binding protein 1) [ 46 , 109 ]. ADAR1 mutations can also affect ZBP1, which recognizes endogenous Alu element-derived dsRNA, leading to inflammatory transcription [ 110 , 111 ]. Immune tolerance occurs when cells mark immunogenic dsRNA as “self” through A-to-I RNA editing, thereby preventing an excessive immune response.…”