Abstract
BackgroundHeterochromatin protein 1 (HP1) is important in the establishment, propagation, and maintenance of constitutive heterochromatin, especially at the pericentromeric region. HP1 might participate in recruiting and directing Mis12 to the centromere during interphase, and HP1 disruption or abrogation might lead to the loss of Mis12 incorporation into the kinetochore. Therefore, the centromere structure and kinetochore relaxation that are promoted in the absence of Mis12 could further induce chromosome instability (CIN) by reducing the capacity of the kinetochore to anchor microtubules. The aim of this study was to determine whether alterations in the localization of HP1 proteins induced by trichostatin A (TSA) modify Mis12 and Centromere Protein A (CENP-A) recruitment to the centromere and whether changes in the expression of HP1 proteins and H3K9 methylation at centromeric chromatin increase CIN in HCT116 and WI-38 cells.MethodsHCT116 and WI-38 cells were cultured and treated with TSA to evaluate CIN after 24 and 48 h of exposure. Immunofluorescence, Western blot, ChIP, and RT-PCR assays were performed in both cell lines to evaluate the localization and abundance of HP1α/β, Mis12, and CENP-A and to evaluate chromatin modifications during interphase and mitosis, as well as after 24 and 48 h of TSA treatment.ResultsOur results show that the TSA-induced reduction in heterochromatic histone marks on centromeric chromatin reduced HP1 at the centromere in the non-tumoral WI-38 cells and that this reduction was associated with cell cycle arrest and CIN. However, in HCT116 cells, HP1 proteins, together with MIS12 and CENP-A, relocated to centromeric chromatin in response to TSA treatment, even after H3K9me3 depletion in the centromeric nucleosomes. The enrichment of HP1 and the loss of H3K9me3 were associated with an increase in CIN, suggesting a response mechanism at centromeric and pericentromeric chromatin that augments the presence of HP1 proteins in those regions, possibly ensuring chromosome segregation despite serious CIN. Our results provide new insight into the epigenetic landscape of centromeric chromatin and the role of HP1 proteins in CIN.Electronic supplementary materialThe online version of this article (doi:10.1186/s13008-014-0006-2) contains supplementary material, which is available to authorized users.
Highlights
Heterochromatin protein 1 (HP1) is important in the establishment, propagation, and maintenance of constitutive heterochromatin, especially at the pericentromeric region
Our results show that the trichostatin A (TSA)-induced reduction in heterochromatic histone modification of centromeric chromatin reduced HP1 levels at the centromere in WI-38 cells and that this reduction was associated with cell cycle arrest and chromosome instability (CIN)
TSA induces differential changes in centromeric and pericentromeric chromatin and in CIN induction in HT116 and WI-38 cells TSA treatment promotes histone hyperacetylation, which becomes visible at the nuclear periphery, as well as the reduction of many heterochromatin regions in the nucleus [20,33,34]. Due to this reduction of heterochromatin, we evaluated whether short-term TSA treatment modifies the centromeric and pericentromeric regions due to HP1 protein enrichment. We found that both HP1α and HP1β were enriched in foci that co-localized with H3K9me3 and Centromere Protein A (CENP-A), suggesting that both HP1 proteins remained at pericentromeric heterochromatin but were enriched at constitutive heterochromatin and expanded to centromeric chromatin
Summary
Heterochromatin protein 1 (HP1) is important in the establishment, propagation, and maintenance of constitutive heterochromatin, especially at the pericentromeric region. HP1 function is highly important for the establishment, propagation, and maintenance of constitutive heterochromatin [2], especially at the pericentromeric region, which is enriched with H3K9me and H4K20me marks, hypoacetylated H3 and H4, and highly methylated regions along most of its satellite repeats [3,4]. HP1 plays a role in centromeric sister chromatid cohesion [6], telomere maintenance, and DNA repair [7] In humans, these functions are performed in a specific manner by each of the three identified HP1 subtypes: HP1α, HP1β, and HP1γ [8,9]. HP1 protein localization differs in the interphase nucleus, with HP1α typically found in pericentric and telomeric chromatin and HP1β normally found in heterochromatin regions [10]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
