Abstract
BackgroundThe histone H3 variant CENP-A is normally tightly regulated to ensure only one centromere exists per chromosome. Native CENP-A is often found overexpressed in human cancer cells and a range of human tumors. Consequently, CENP-A misregulation is thought to contribute to genome instability in human cancers. However, the consequences of such overexpression have not been directly elucidated in human cancer cells.ResultsTo investigate native CENP-A overexpression, we sought to uncover CENP-A-associated defects in human cells. We confirm that CENP-A is innately overexpressed in several colorectal cancer cell lines. In such cells, we report that a subset of structurally distinct CENP-A-containing nucleosomes associate with canonical histone H3, and with the transcription-coupled chaperones ATRX and DAXX. Furthermore, such hybrid CENP-A nucleosomes localize to DNase I hypersensitive and transcription factor binding sites, including at promoters of genes across the human genome. A distinct class of CENP-A hotspots also accumulates at subtelomeric chromosomal locations, including at the 8q24/Myc region long-associated with genomic instability. We show this 8q24 accumulation of CENP-A can also be seen in early stage primary colorectal tumors.ConclusionsOur data demonstrate that excess CENP-A accumulates at noncentromeric locations in the human cancer genome. These findings suggest that ectopic CENP-A nucleosomes could alter the state of the chromatin fiber, potentially impacting gene regulation and chromosome fragility.Electronic supplementary materialThe online version of this article (doi:10.1186/1756-8935-8-2) contains supplementary material, which is available to authorized users.
Highlights
The histone H3 variant CENP-A is normally tightly regulated to ensure only one centromere exists per chromosome
Semi-quantitative PCR analysis indicated that CENP-A mRNA is almost fourfold overexpressed in SW480 cells compared to normal colon cells (Figure 1B, lower panel depicts graphical representation of 4 replicates)
We examined levels of the CENP-A chaperone Holliday junction recognition protein (HJURP), which is required for accurate loading of CENP-A to centromeres [30,31,32]
Summary
The histone H3 variant CENP-A is normally tightly regulated to ensure only one centromere exists per chromosome. To elucidate consequences associated with CENP-A misregulation, we examined CENP-A mRNA and protein levels, partners, structure, and global nucleosome occupancy in human primary normal and colorectal cancers cells, as well as in primary tumors. We report that CENPA is overexpressed at the mRNA and protein level in some human colorectal cancers This excess CENP-A partners with histone H3, and associates with transcriptionally coupled chaperones ATRX and DAXX in colorectal cancer cell lines. This distinct class of noncentromeric CENP-A nucleosomes forms a stable octameric nucleosomal species as detected by atomic force microscopy (AFM) and confirmed by high-resolution DNA analysis, which demonstrates binding of 150 to 170 bp of DNA. Our data uncover a new role for a classical histone variant in human cancer cell lines
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