Repeatable, convergent outcomes are prima facie evidence for determinism in evolutionary processes. Among fishes, well-known examples include microevolutionary habitat transitions into the water column, where freshwater populations (e.g., sticklebacks, cichlids, and whitefishes) recurrently diverge toward slender-bodied pelagic forms and deep-bodied benthic forms. However, the consequences of such processes at deeper macroevolutionary scales in the marine environment are less clear. We applied a phylogenomics-based integrative, comparative approach to test hypotheses about the scope and strength of convergence in a marine fish clade with a worldwide distribution (snappers and fusiliers, family Lutjanidae) featuring multiple water-column transitions over the past 45 million years. We collected genome-wide exon data for 110 (∼80%) species in the group and aggregated data layers for body shape, habitat occupancy, geographic distribution, and paleontological and geological information. We also implemented approaches using genomic subsets to account for phylogenetic uncertainty in comparative analyses. Our results show independent incursions into the water column by ancestral benthic lineages in all major oceanic basins. These evolutionary transitions are persistently associated with convergent phenotypes, where deep-bodied benthic forms with truncate caudal fins repeatedly evolve into slender midwater species with furcate caudal fins. Lineage diversification and transition dynamics vary asymmetrically between habitats, with benthic lineages diversifying faster and colonizing midwater habitats more often than the reverse. Convergent ecological and functional phenotypes along the benthic–pelagic axis are pervasive among different lineages and across vastly different evolutionary scales, achieving predictable high-fitness solutions for similar environmental challenges, ultimately demonstrating strong determinism in fish body-shape evolution.

Detection of viral double-stranded RNA (dsRNA) is an important component of innate immunity. However, many endogenous RNAs containing double-stranded regions can be misrecognized and activate innate immunity. The interferon inducible ADAR1-p150 suppresses dsRNA sensing, an essential function for ADAR1 in many cancers, including breast. Although ADAR1-p150 has been well established in this role, the functions of the constitutively expressed ADAR1-p110 isoform are less understood. We used proximity labeling to identify putative ADAR1-p110 interacting proteins in breast cancer cell lines. Of the proteins identified, the RNA helicase DHX9 was of particular interest. Knockdown of DHX9 in ADAR1-dependent cell lines caused cell death and activation of the dsRNA sensor PKR. In ADAR1-independent cell lines, combined knockdown of DHX9 and ADAR1, but neither alone, caused activation of multiple dsRNA sensing pathways leading to a viral mimicry phenotype. Together, these results reveal an important role for DHX9 in suppressing dsRNA sensing by multiple pathways.

The RNA editing enzyme ADAR has been identified as a therapeutic target for multiple cancers. Through its A-to-I editing activity the p150 isoform of ADAR suppresses activation of dsRNA sensors involved in the innate immune response and translational repression. Recently, our laboratory has shown that p150-ADAR is required for the viability of a subset of triple-negative breast cancer cell lines, thus making p150-ADAR a strong therapeutic target for a disease that lacks targeted therapies. Unlike the p150 isoform, which is interferon inducible, the p110 isoform of ADAR is ubiquitously expressed and has not been shown to suppress dsRNA sensing. To date there is much less known about the role of p110-ADAR in cancer, though it is known to be highly expressed in breast cancer. To begin to explore the role of p110-ADAR in breast cancer, we turned to proximity labeling by APEX2 to identify proteins that may interact with p110-ADAR. Mass-spectrometry of proximity labeled proteins revealed numerous nuclear and nucleolar proteins with roles in multiple aspects of RNA biology, including processing of rRNA and ribosome biogenesis. Among the list of enriched proteins were eight members of the DEAD-box RNA helicase family, including the nucleolar localized DDX54. Co-immunoprecipitation confirmed that p110-ADAR and DDX54 interact, furthermore both localize to nucleoli. Knockdown of DDX54 in non-TNBC cell lines (SK-BR-3 and MCF-7) caused apoptosis and reduced proliferation. Additionally, knockdown of DDX54 caused accumulation of dsRNA within the nucleolus and activation of the dsRNA sensor PKR. Knockdown of ADAR, which alone did not affect proliferation or phosphorylation of PKR in the above cell lines, synergized with DDX54 knockdown to cause increased cell death and further activation of PKR. ADAR knockdown did not synergize with knockdown of another ADAR-interacting DEAD-box helicase, DDX17, suggesting that the observed phenotype is not common to combined knockdown of ADAR and any RNA helicase. These findings suggest that combined inhibition/depletion of ADAR and DDX54 may serve as therapeutic strategy for breast tumors, including those that are refractory to ADAR inhibition/depletion alone. Citation Format: Kyle A. Cottrell, Sua Ryu, Luisangely Soto Torres, Angela Schab, Jason D. Weber. Proximity labeling reveals a role for ADAR and DDX54 in suppressing dsRNA sensing in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 876.

Adenosine deaminase acting on RNA (ADAR) is an RNA-editing enzyme that binds dsRNA and converts adenosine to inosine. ADAR promotes cell survival and proliferation in multiple types of tumors, including breast cancer. However, the mechanism of ADAR-driven oncogenicity is not fully established. We focused on ADAR p110, the constitutively expressed and nuclear-localized isoform, and its role in managing genotoxic stress in cancer. ADAR p110 is involved in resolving R-loops, the DNA-RNA hybrids produced during transcription, and DNA damage response (DDR). We sought to elucidate the mechanism of ADAR-associated R-loop resolution and DDR that can be targeted in breast cancer. To identify ADAR-interacting proteins, proximity labeling was performed using ADAR p110 fused to ascorbate peroxidase (APEX2), followed by mass spectrometry. Among the positively enriched hits, known ADAR-interacting proteins associated with R-loop and DDR were validated by immunoprecipitation and immunofluorescence. DEAD-box helicase DDX54 was among the nine RNA helicases interacting with ADAR. DDX54 and ADAR showed an additive effect on preventing γH2AX signal. Additionally, knockdown (KD) of DDX54 increased ADAR expression, whereas ADAR KD did not affect DDX54 expression. These results suggest that DDX54 coordinates with ADAR to prevent genotoxic stress in breast cancer cells. As DDX54 and ADAR are both associated with R-loop resolution and DDR, we hypothesize that DDX54 and ADAR suppress R-loop accumulation and/or other types of genotoxic stress. This may be through independent pathways despite the physical interaction between ADAR and DDX54. Citation Format: Sua Ryu, Kyle A. Cottrell, Luisángely Soto-Torres, Angela Schabb, Jason D. Weber. ADAR and DDX54 promote genomic stability in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 842.