Aurora B expression and histone variant H1.4S27 phosphorylation are no longer coordinated during metaphase in aneuploid colorectal carcinomas.

Experimental model systems identified phosphorylation of linker histone variant H1.4 at Ser 27 (H1.4S27p) as a novel mitotic mark set by Aurora B kinase. Here, we examined expression of Aurora B and H1.4S27p in colorectal carcinoma (CRC) cell lines (HCT116, DLD1, Caco-2, HT29) and tissue specimens (n = 36), in relation to microsatellite instability (MSI) status and ploidy. In vitro, Aurora B (pro-/meta-/anaphase) and H1.4S27p (pro-/metaphase) were localized in mitotic figures. The proportion of labeled mitoses was significantly different between cell lines for Aurora B (p = 0.019) but not for H1.4S27p (p = 0.879). For Aurora B, these differences were not associated with an altered Aurora B gene copy number (FISH) or messenger RNA (mRNA) expression level (qRT-PCR). Moreover, Aurora B expression and H1.4S27 phosphorylation were no longer coordinated during metaphase in aneuploid HT29 cells (p = 0.039). In CRCs, immunoreactivity for Aurora B or H1.4S27p did not correlate with T- or N-stage, grade, or MSI status. However, metaphase labeling of H1.4S27p was significantly higher in diploid than in aneuploid CRCs (p = 0.011). Aurora B was significantly correlated with H1.4S27p-positive metaphases in MSI (p = 0.010) or diploid (p = 0.003) CRCs. Finally, combined classification of MSI status and ploidy revealed a significant positive correlation of Aurora B with H1.4S27p in metaphases of diploid/MSI (p = 0.010) and diploid/microsatellite-stable (MSS; p = 0.031) but not of aneuploid/MSS (p = 0.458) CRCs. The present study underlines the functional link of Aurora B expression and H1.4S27p during specific phases of mitosis in diploid and/or MSI-positive CRCs in vitro and in situ. Importantly, the study shows that the coordination between Aurora B expression and phosphorylation of H1.4 at Ser 27 is lost in cycling aneuploid CRC cells.