We observed prominent effects of doxorubicin (Dox), an anthracycline widely used in
anti-cancer therapy, on the aggregation and intracellular distribution of both partners
of the H2A-H2B dimer, with marked differences between the two histones. Histone aggregation,
assessed by Laser Scanning Cytometry via the retention of the aggregates in isolated
nuclei, was observed in the case of H2A. The dominant effect of the anthracycline
on H2B was its massive accumulation in the cytoplasm of the Jurkat leukemia cells
concomitant with its disappearance from the nuclei, detected by confocal microscopy
and mass spectrometry. A similar effect of the anthracycline was observed in primary
human lymphoid cells, and also in monocyte-derived dendritic cells that harbor an
unusually high amount of H2B in their cytoplasm even in the absence of Dox treatment.
The nucleo-cytoplasmic translocation of H2B was not affected by inhibitors of major
biochemical pathways or the nuclear export inhibitor leptomycin B, but it was completely
diminished by PYR-41, an inhibitor with pleiotropic effects on protein degradation
pathways. Dox and PYR-41 acted synergistically according to isobologram analyses of
cytotoxicity. These large-scale effects were detected already at Dox concentrations
that may be reached in the typical clinical settings, therefore they can contribute
both to the anti-cancer mechanism and to the side-effects of this anthracycline.
