Faithful chromosome segregation is essential for the maintenance of genomic integrity and requires functional centromeres. Centromeres are epigenetically defined by the histone H3 variant, centromere protein A (CENP-A). Here we highlight current knowledge regarding CENP-A-containing chromatin structure, specification of centromere identity, regulation of CENP-A deposition and possible contribution to cancer formation and/or progression. CENP-A overexpression is common among many cancers and predicts poor prognosis. Overexpression of CENP-A increases rates of CENP-A deposition ectopically at sites of high histone turnover, occluding CCCTC-binding factor (CTCF) binding. Ectopic CENP-A deposition leads to mitotic defects, centromere dysfunction and chromosomal instability (CIN), a hallmark of cancer. CENP-A overexpression is often accompanied by overexpression of its chaperone Holliday Junction Recognition Protein (HJURP), leading to epigenetic addiction in which increased levels of HJURP and CENP-A become necessary to support rapidly dividing p53 deficient cancer cells. Alterations in CENP-A posttranslational modifications are also linked to chromosome segregation errors and CIN. Collectively, CENP-A is pivotal to genomic stability through centromere maintenance, perturbation of which can lead to tumorigenesis.

The anti-tumor effects of calorie restriction (CR) and the possible underlying mechanisms were investigated using ethylnitrosourea (ENU)-induced glioma in rats. ENU was given transplacentally at gestational day 15, and male offspring were used in this experiment. The brain from 4-, 6-, and 8-month-old rats fed either ad libitum (AL) or calorie-restricted diets (40% restriction of total calories compared to AL rats) was studied. Tumor burden was assessed by comparing the number and size of gliomas present in sections of the brain. Immunohistochemical analysis was used to document lipid peroxidation [4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA)], protein oxidation (nitrotyrosine), glycation and AGE formation [methylglyoxal (MG) and carboxymethyllysine (CML)], cell proliferation activity [proliferating cell nuclear antigen (PCNA)], cell death [single-stranded DNA (ssDNA)], presence of thioredoxin 1 (Trx1), and presence of heme oxygenase-1 (HO-1) associated with the development of gliomas. The results showed that the number of gliomas did not change with age in the AL groups; however, the average size of the gliomas was significantly larger in the 8-month-old group compared to that of the younger groups. Immunopositivity was observed mainly in tumor cells and reactive astrocytes in all histological types of ENU-induced glioma. Immunopositive areas for HNE, MDA, nitrotyrosine, MG, CML, HO-1, and Trx1 increased with the growth of gliomas. The CR group showed both reduced number and size of gliomas, and tumors exhibited less accumulation of oxidative damage, decreased formation of glycated end products, and a decreased presence of HO-1 and Trx1 compared to the AL group. Furthermore, gliomas of the CR group showed less PCNA positive and more ssDNA positive cells, which are correlated to the retarded growth of tumors. Interestingly, we also discovered that the anti-tumor effects of CR were associated with decreased hypoxia-inducible factor-1α (HIF-1α) levels in normal brain tissue. Our results are very exciting because they not only demonstrate the anti-tumor effects of CR in gliomas, but also indicate the possible underlying mechanisms, i.e. anti-tumor effects of CR observed in this investigation are associated with reduced accumulation of oxidative damage, decreased formation of glycated end products, decreased presence of HO-1 and Trx1, reduced cell proliferation and increased apoptosis, and decreased levels of HIF-1α.

Centromere identity is defined and maintained epigenetically by the presence of the histone variant CENP-A. How centromeric CENP-A position is specified and precisely maintained through DNA replication is not fully understood. The recently released Telomere-to-Telomere (T2T) genome assembly containing the first complete human centromere sequences provides a new resource for examining CENP-A position. Mapping CENP-A position in clones of the same cell line to the T2T assembly identified highly similar CENP-A position after multiple cell divisions. In contrast, centromeric CENP-A epialleles were evident at several centromeres of different human cell lines, demonstrating the location of CENP-A enrichment and the site of kinetochore recruitment vary among human cells. Across the cell cycle, CENP-A molecules deposited in G1 phase are maintained in their precise position through DNA replication. Thus, despite CENP-A dilution during DNA replication, CENP-A is precisely reloaded onto the same sequences within the daughter centromeres, maintaining unique centromere identity among human cells.