Glycogen Synthase Kinase (GSK) 3 beta Phosphorylates and Protects Nuclear Myosin 1c from Proteasome-Mediated Degradation to Activate rDNA Transcription in Early G1 Cells
Number of Authors: 8
2014 (English)In: PLOS Genetics, ISSN 1553-7390, E-ISSN 1553-7404, Vol. 10, no 6, e1004390- p.Article in journal (Refereed) Published
Nuclear myosin 1c (NM1) mediates RNA polymerase I (pol I) transcription activation and cell cycle progression by facilitating PCAF-mediated H3K9 acetylation, but the molecular mechanism by which NM1 is regulated remains unclear. Here, we report that at early G1 the glycogen synthase kinase (GSK) 3 beta phosphorylates and stabilizes NM1, allowing for NM1 association with the chromatin. Genomic analysis by ChIP-Seq showed that this mechanism occurs on the rDNA as active GSK3 beta selectively occupies the gene. ChIP assays and transmission electron microscopy in GSK3 beta(-/-) mouse embryonic fibroblasts indicated that at G1 rRNA synthesis is suppressed due to decreased H3K9 acetylation leading to a chromatin state incompatible with transcription. We found that GSK3 beta directly phosphorylates the endogenous NM1 on a single serine residue (Ser-1020) located within the NM1 C-terminus. In G1 this phosphorylation event stabilizes NM1 and prevents NM1 polyubiquitination by the E3 ligase UBR5 and proteasome-mediated degradation. We conclude that GSK3 beta-mediated phosphorylation of NM1 is required for pol I transcription activation.
Place, publisher, year, edition, pages
2014. Vol. 10, no 6, e1004390- p.
IdentifiersURN: urn:nbn:se:su:diva-106760DOI: 10.1371/journal.pgen.1004390ISI: 000338847700011OAI: oai:DiVA.org:su-106760DiVA: diva2:738862