HP1 Proteins Are Essential for a Dynamic Nuclear Response That Rescues the Function of Perturbed Heterochromatin in Primary Human Cells

Abstract

Cellular information is encoded genetically in the DNA nucleotide sequence and epigenetically by the “histone code,” DNA methylation, and higher-order packaging of DNA into chromatin. Cells possess intricate mechanisms to sense and repair damage to DNA and the genetic code. However, nothing is known of the mechanisms, if any, that repair and/or compensate for damage to epigenetically encoded information, predicted to result from perturbation of DNA and histone modifications or other changes in chromatin structure. Here we show that primary human cells respond to a variety of small molecules that perturb DNA and histone modifications by recruiting HP1 proteins to sites of altered pericentromeric heterochromatin. This response is essential to maintain the HP1-binding kinetochore protein hMis12 at kinetochores and to suppress catastrophic mitotic defects. Recruitment of HP1 proteins to pericentromeres depends on histone H3.3 variant deposition, mediated by the HIRA histone chaperone. These data indicate that defects in pericentromeric epigenetic heterochromatin modifications initiate a dynamic HP1-dependent response that rescues pericentromeric heterochromatin function and is essential for viable progression through mitosis.

SUPPLEMENTAL MATERIAL

We thank Sandy Jablonski at the Fox Chase Cancer Center Cell Imaging Facility for technical help, William Earnshaw for the HP1α antibody, J. B. Rattner for the ACA antibody, Richard Katz for providing apicidin and valproic acid, Inma Ibanez and Paul Cairns for AzaC, Andy Godwin for human ovarian surface epithelial cells, and Kenneth Zaret for helpful comments.

This study was supported by NIH grant GM062281 and LLS grant 1520-04 to P.D.A.; an AFAR grant to R.Z.; NIH grant GM49351 to J.P.; and NIH grants GM44762, CA99423, and CA75138 and core grant CA06927 to T.J.Y. and S.-T.L.