Abstract
BackgroundThe distinct functional effects of the replication-dependent histone H2A isoforms have been demonstrated; however, the mechanistic basis of the non-redundancy remains unclear. Here, we have investigated the specific functional contribution of the histone H2A isoform H2A1H, which differs from another isoform H2A2A3 in the identity of only three amino acids.ResultsH2A1H exhibits varied expression levels in different normal tissues and human cancer cell lines (H2A1C in humans). It also promotes cell proliferation in a context-dependent manner when exogenously overexpressed. To uncover the molecular basis of the non-redundancy, equilibrium unfolding of recombinant H2A1H-H2B dimer was performed. We found that the M51L alteration at the H2A–H2B dimer interface decreases the temperature of melting of H2A1H-H2B by ~ 3 °C as compared to the H2A2A3-H2B dimer. This difference in the dimer stability is also reflected in the chromatin dynamics as H2A1H-containing nucleosomes are more stable owing to M51L and K99R substitutions. Molecular dynamic simulations suggest that these substitutions increase the number of hydrogen bonds and hydrophobic interactions of H2A1H, enabling it to form more stable nucleosomes.ConclusionWe show that the M51L and K99R substitutions, besides altering the stability of histone–histone and histone–DNA complexes, have the most prominent effect on cell proliferation, suggesting that the nucleosome stability is intimately linked with the physiological effects observed. Our work provides insights into the molecular basis of the non-redundancy of the histone H2A isoforms that are being increasingly reported to be functionally important in varied physiological contexts.
Highlights
The distinct functional effects of the replication-dependent histone H2A isoforms have been demonstrated; the mechanistic basis of the non-redundancy remains unclear
H2A1H/H2A1C expression level varies in cancer cell lines and amongst different normal tissues Previously, we have reported the upregulation of H2A.1 isoforms during the progress of hepatocellular carcinoma (HCC) [9]
Mass spectrometry followed by peptide fingerprinting of the eluted fractions 84 and 85 ml revealed high scores for the H2A.1 isoforms (H2A1H, H2A3, H2A1C, H2A1K) with the maximum score obtained for H2A1H (Fig. 1e)
Summary
The distinct functional effects of the replication-dependent histone H2A isoforms have been demonstrated; the mechanistic basis of the non-redundancy remains unclear. The core histones are comprised of H2A, H2B, H3 and H4 which form the octameric protein core of the fundamental repeating unit of chromatin, the nucleosome. The canonical histone proteins are synthesized during the S-phase, and to meet up with their high demand during DNA replication, genes that encode them are present in clusters. There are three clusters of canonical histone genes present in humans at chromosome numbers 1 and 6. Differences in the primary sequence are observed amongst the histone proteins encoded by these genes. Bhattacharya et al Epigenetics & Chromatin (2017) 10:48 there are 13 genes for H2A in rats that code for 9 isoforms (most are “predicted”)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 call
