Phosphorylation of the HP1β hinge region sequesters KAP1 in heterochromatin and promotes the exit from naïve pluripotency

Nucleic Acids Res. 2021 Jul 21;49(13):7406-7423. doi: 10.1093/nar/gkab548.

Abstract

Heterochromatin binding protein HP1β plays an important role in chromatin organization and cell differentiation, however the underlying mechanisms remain unclear. Here, we generated HP1β-/- embryonic stem cells and observed reduced heterochromatin clustering and impaired differentiation. We found that during stem cell differentiation, HP1β is phosphorylated at serine 89 by CK2, which creates a binding site for the pluripotency regulator KAP1. This phosphorylation dependent sequestration of KAP1 in heterochromatin compartments causes a downregulation of pluripotency factors and triggers pluripotency exit. Accordingly, HP1β-/- and phospho-mutant cells exhibited impaired differentiation, while ubiquitination-deficient KAP1-/- cells had the opposite phenotype with enhanced differentiation. These results suggest that KAP1 regulates pluripotency via its ubiquitination activity. We propose that the formation of subnuclear membraneless heterochromatin compartments may serve as a dynamic reservoir to trap or release cellular factors. The sequestration of essential regulators defines a novel and active role of heterochromatin in gene regulation and represents a dynamic mode of remote control to regulate cellular processes like cell fate decisions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Casein Kinase II / metabolism
  • Cell Differentiation
  • Cell Line
  • Cells, Cultured
  • Chromosomal Proteins, Non-Histone / chemistry
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism*
  • Chromosomal Proteins, Non-Histone / physiology
  • Cricetinae
  • Embryonic Stem Cells / cytology
  • Embryonic Stem Cells / metabolism*
  • Gene Knockout Techniques
  • Heterochromatin / metabolism*
  • Humans
  • Mice
  • Phosphorylation
  • Serine / metabolism
  • Tripartite Motif-Containing Protein 28 / genetics
  • Tripartite Motif-Containing Protein 28 / metabolism*
  • Tripartite Motif-Containing Protein 28 / physiology

Substances

  • Cbx1 protein, mouse
  • Chromosomal Proteins, Non-Histone
  • Heterochromatin
  • Serine
  • TRIM28 protein, human
  • Trim28 protein, mouse
  • Tripartite Motif-Containing Protein 28
  • Casein Kinase II