ADAR1 editing dependency in triple-negative breast cancer

Abstract

14Triple-negative breast cancer (TNBC) is the deadliest form of breast cancer. Unlike other 15 types of breast cancer that can be effectively treated by targeted therapies, no such targeted 16 therapy exists for all TNBC patients. The ADAR1 enzyme carries out A-to-I editing of RNA to 17 prevent sensing of cellular double-stranded RNAs (dsRNA). ADAR1 is highly expressed in 18 breast cancer including TNBC. Here, we demonstrate that ADAR1 expression and editing 19 activity is required in TNBC cell lines but not in ER+ and/or Her2+ cells. In TNBC cells, 20 knockdown of ADAR1 attenuates proliferation and tumorigenesis. PKR expression is elevated in 21 TNBC and its activity is induced upon ADAR1-knockdown, which correlates with a decrease in 22 translation. ADAR1-dependent TNBC cell lines also exhibit elevated IFN stimulated gene 23 expression. IFNAR1 reduction significantly rescues the proliferative defects of ADAR1 loss. 24These findings establish ADAR1 as a novel therapeutic target for TNBC tumors. 25 26 Keywords: ADAR1, triple-negative breast cancer, RNA editing, Type I IFN, PKR 27 28 65highlighting the therapeutic potential of ADAR1 inhibitors for the treatment of TNBC. 66 Results 67ADAR1 is highly expressed in all breast cancer subtypes 68 Using publicly available data from TCGA (The Cancer Genome Atlas) (Han et al., 2015, 69 Fumagalli et al., 2015, we found that high expression of ADAR1 correlated with poor prognosis 70 of breast cancers ( Figure 1A). Recent studies indicated that ADAR1 promotes tumorigenesis of 71 metaplastic breast cancers, and that high expression of ADAR1 correlates with poor prognosis in 72 basal-like breast cancers (Sagredo et al., 2018, Dave et al., 2017. Since both basal-like and 73 5 metaplastic breast cancers share similar characteristics with TNBC, we sought to determine the 74 importance of ADAR1 in the tumorigenesis of TNBC. By evaluating the TCGA database, we 75 found that while mRNA expression of ADAR1 was higher in TNBC compared to normal, it was 76 not significantly different between TNBC and non-TNBC tumors ( Figure 1B). Additionally, 77 ADAR1 expression was not significantly higher in any one subtype of breast cancer based on 78 PAM50 classification(Lehmann et al., 2016) (Supplemental Figure 1A). This observation is 79 consistent with data from the Cancer Cell Line Encyclopedia (CCLE), which uses both RNA-seq 80 and Reverse Phase Protein Array (RPPA) to determine RNA and protein expression levels in 81 numerous cancer cell lines (Supplemental Figure 1B-C). Data from both the TCGA and CCLE 82 datasets also revealed that both p150 and p110 isoforms of ADAR1 were expressed at similar 83 levels between TNBC and non-TNBC specimen (Supplemental Figure 1D-H), with p110 84 expression being consistently higher than p150 in all samples. Additionally, we assessed p150 85 isoform expression by immunohistochemistry in TNBC and non-TNBC patient tumors, Figure 86 1D. We sought to determine the protein expression level of the ADAR1-p150 isoform in a panel 87 of established breast ca...

LncRNAs and microRNAs as Essential Regulators of Stemness in Breast Cancer Stem Cells

“…Thus, it has been shown in several studies that the transcriptomic as well as proteomic diversity introduced by A-to-I editing is exploited by tumor cells to promote cancer progression; for example, more editing events regulated by ADAR1 have been associated with cancer development, primarily due to the more abundant expression of ADAR1 in BC. The knockdown of ADAR1 attenuates proliferation and tumorigenesis, leading to robust translational repression [ 92 , 93 , 94 ]. Recently, ADAR1 and lncRNA interplay has been shown to play a role in cancer, suggesting that ADAR1 could alter the expression levels of lncRNAs, and these changes could be related to BC biology.…”

8-Azaadenosine and 8-Chloroadenosine are not Selective Inhibitors of ADAR

“…The sequences for the shRNA-scramble (shSCR) and shADAR were described and validated previously (13). For ADAR overexpression cell lines, SK-BR-3 cells were transduced with lentivirus produced from pLVX-IRES-Hygro-EV, pLVX-IRES-Hygro-p110 or pLVX-IRES-Hygro-p150 described previously (18).…”