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Synergistic and antagonistic activities of IRF8 and FOS enhancer pairs during an immune-cell fate switch

ABSTRACT: Cell-fate instructive genes tend to be regulated by large clusters of enhancers. Whether and how individual enhancers within such clusters cooperate in regulating gene expression is poorly understood. We have previously developed a computational method, SEGCOND, which identifies hubs that we termed Putative Transcriptional Condensates (PTCs), consisting of enhancer clusters and associated target genes. Here, we ue SEGCOND to identify PTCs in a CEBPA-induced B-cell to macrophage transdifferentiation system. We find that PTCs are enriched for highly expressed, lineage-restricted genes and associate with BRD4, a component of transcriptional condensates. Further, we performed single and combinatorial deletions of enhancers within two PTCs active during induced transdifferentiation, harboring IRF8 and FOS. Two enhancers within the IRF8 PTC were found to provide a backup mechanism when combined, safeguarding IRF8 expression and efficient transdifferentiation. Unexpectedly, two individual enhancers within the FOS PTC antagonize each other at day 1 of transdifferentiation, delaying the conversion of B-cells into macrophages and reducing FOS expression, while at day 7 they cooperate to increase FOS levels induced cells. Our results reveal complex, differentiation stage-specific interactions between individual enhancers within enhancer clusters.

SUBMITTER: Antonios Klonizakis

PROVIDER: S-SCDT-10_1038-S44318-025-00380-W | biostudies-other |

REPOSITORIES: biostudies-other

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Project description:UnlabelledHuman cytomegalovirus (HCMV) is a member of the betaherpesvirus family. During infection, an array of viral proteins manipulates the host cell cycle. We have previously shown that expression of HCMV pUL27 results in increased levels of the cyclin-dependent kinase (CDK) inhibitor p21(Cip1). In addition, pUL27 is necessary for the full antiviral activity of the pUL97 kinase inhibitor maribavir (MBV). The purpose of this study was to define the relationship between pUL27 and pUL97 and its role in MBV antiviral activity. We observed that expression of wild-type but not kinase-inactive pUL97 disrupted pUL27-dependent induction of p21(Cip1). Furthermore, pUL97 associated with and promoted the phosphorylation of pUL27. During infection, inhibition of the kinase resulted in elevated levels of p21(Cip1) in wild-type virus but not a pUL27-deficient virus. We manipulated the p21(Cip1) levels to evaluate the functional consequence to MBV. Overexpression of p21(Cip1) restored MBV activity against a pUL27-deficient virus, while disruption reduced activity against wild-type virus. We provide evidence that the functional target of p21(Cip1) in the context of MBV activity is CDK1. One CDK-like activity of pUL97 is to phosphorylate nuclear lamin A/C, resulting in altered nuclear morphology and increased viral egress. In the presence of MBV, we observed that infection using a pUL27-deficient virus still altered the nuclear morphology. This was prevented by the addition of a CDK inhibitor. Overall, our results demonstrate an antagonistic relationship between pUL27 and pUL97 activities centering on p21(Cip1) and support the idea that CDKs can complement some activities of pUL97.ImportanceHCMV infection results in severe disease upon immunosuppression and is a leading cause of congenital birth defects. Effective antiviral compounds exist, yet they exhibit high levels of toxicity, are not approved for use during pregnancy, and can result in antiviral resistance. Our studies have uncovered new information regarding the antiviral efficacy of the HCMV pUL97 kinase inhibitor MBV as it relates to the complex interplay between pUL97 and a second HCMV protein, pUL27. We demonstrate that pUL97 functions antagonistically against pUL27 by phosphorylation-dependent inactivation of pUL27-mediated induction of p21(Cip1). In contrast, we provide evidence that p21(Cip1) functions to antagonize overlapping activities between pUL97 and cellular CDKs. In addition, these studies further support the notion that CDK inhibitors or p21(Cip1) activators might be useful in combination with MBV to effectively inhibit HCMV infections.

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Synergistic and antagonistic activities of IRF8 and FOS enhancer pairs during an immune-cell fate switch

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