Regulation of chromatin epigenetic modification by the nucleosomal kinase VRK1, implications for new cancer therapies

Resumen del trabajo presentado en el EACR 2022 Congress - Innovative Cancer Science: Translating Biology to Medicine, celebrado en Sevilla (España) del 20 al 23 de junio de 2022.[Introduction]: Epigenetic alterations are one of the main mechanisms driving different human diseases, including many cancer types and neurological diseases. Histone posttranslational modifications (PTMs) are changes in the amino acid residues of the histone tail which regulate gene expression. The coordination of PTMs requires the strictly regulation of multiple epigenetic enzymes, termed writer and eraser proteins. Chromatin active states are characterized by PTMs such as H3K4me3 and H3K27ac, whereas repressive states are enrichment in H3K9me3 and H3K27me3 among others. Thus, it could be crucial to understand the mechanisms that mediate the coordination of such enzymes. VRK1 (Vaccinia-related kinase 1) is a nuclear kinase implicated in different cellular process like transcription or DNA damage response. In this context, we studied the potential role of VRK1 in the regulation of those epigenetic modifiers. [Material and Methods]: We compared the transient VRK1 silencing with the effect of modulators of various epigenetic enzymes. In our study, we evaluated the expression levels of different PTMs (H3K4me3, H3K9ac/me3, H3K27ac/me3, and H4K16ac), by immunodetection in two different human cancer cell lines, lung adenocarcinoma A549 and osteosarcoma U2OS. We studied the interaction of VRK1 with the histonemodifying enzymes of this PTMs by co-immunoprecipitation. [Results and Discussions]: Our results showed that VRK1 depletion caused an alteration of post-translational histone marks in cells. We observed that VRK1 depletion promotes a decrease of chromatin active marks (H3K4me3, H3K9ac, H3K27ac, and H4K16ac), and an increase of H3K9me3 and H3K27me3. Treatments with drugs targeting histone-modifying enzymes also remodel the acetylation and methylation pattern. HAT (C646 and MG149) and KDM (JMJD2i and ORY-1001) inhibitors mimic the effect of VRK1 depletion. HDAC (Vorinostat, Entinostat, Panobinostat, Selisistat, Thiomyristoil, AGK2, and AK7) and KMT (Chaetocin and Tazemetostat) inhibitors mimic the effect of VRK1 on histone marks. VRK1 forms a stable protein complex with KDM1a, KDM3a, KDM4a, HDAC1, Sirt1/2, and SETDB1. [Conclusion]: Our findings revealed that permissive chromatin marks decreased (H3K4me3, H3K9ac, H3K27ac, H4K16ac) while repressive marks (H3K9me3, H3K27me3) increased in VRK1-depleted cells. Therefore, the loss of VRK1 expression in the cells had the same effect than the inhibition of these enzymes, suggesting that VRK1 might be a regulator of those epigenetic enzymes and used as new target in synthetic lethality strategie