Abstract
H1 histones are involved in the formation of higher order chromatin structures and in the modulation of gene expression. Changes in chromatin structure are a characteristic initial feature of apoptosis. We therefore have investigated the histone H1 pattern of the human leukemic cell line HL60 undergoing programmed cell death, as induced by topoisomerase I inhibition. Histone H1 proteins were isolated and analyzed by high performance liquid chromatography and capillary zone electrophoresis. DNA fragmentation after apoptosis induction was monitored by agarose gel electrophoresis. The patterns of the three H1 histone subtypes extractable from apoptotic HL60 cells significantly differed from those of control cells in showing a decrease of phosphorylated H1 subtypes and an increase of the respective dephosphorylated forms. This dephosphorylation of H1 histones could be observed already 45 min after apoptosis induction and preceded internucleosomal DNA cleavage by approximately 2 h. We conclude that during apoptotic DNA fragmentation, the H1 histones become rapidly dephosphorylated by a yet unknown protein phosphatase.
Highlights
During the last 5 years, our understanding of the process of apoptosis has dramatically increased. This highly regulated form of programmed death of a eukaryotic cell can either be induced by neighboring cells via receptor-mediated activation of an apoptotic cascade or by the cell itself, e.g. when irreversible DNA damage has been detected by cell cycle checkpoint control. Both forms of cell death share most of the signaling cascade mediated by caspases, and both forms result in a characteristic chromatin condensation and later in the degradation of the cell into apoptotic bodies, subcellular particles that can be removed by neighboring cells
The family of H1 histones consists of 7 subtypes, termed H1.1 to H1.5, H1°, and H1t [27], of which the proteins H1.2 and H1.4 are the predominant subtypes in most human cell lines [14, 28]
By using capillary electrophoresis alone, it was not possible to identify the nature of histone H1 subtype modifications [11]
Summary
During the last 5 years, our understanding of the process of apoptosis has dramatically increased. H1 histones from 4 ϫ 109 HL60 cells treated for 8 h with 150 ng/ml topotecan were extracted and purified by gel chromatography, and the H1 subtypes were separated by HPLC (Fig. 2A, right).
Sign-in/Register to view highlights & summary 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.
