Bhattacharya Saikat, Reddy Divya, Jani Vinod, Gadewal Nikhil, Shah Sanket, Reddy Raja, Bose Kakoli, Sonavane Uddhavesh, Joshi Rajendra, Smoot Duane, Ashktorab Hassan, Gupta Sanjay
Epigenetics and Chromatin Biology Group, Gupta Lab, Cancer Research Institute, Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Tata Memorial Centre, Kharghar, Navi Mumbai, MH, 410210, India.
Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, MH, 400085, India.
Epigenetics Chromatin. 2017 Oct 18;10(1):48. doi: 10.1186/s13072-017-0155-z.
The 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.
H2A1H 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.
We 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.
复制依赖性组蛋白H2A亚型具有不同的功能效应，这一点已得到证实；然而，这种非冗余性的机制基础仍不清楚。在这里，我们研究了组蛋白H2A亚型H2A1H的特定功能贡献，它与另一种亚型H2A2A3仅在三个氨基酸的同一性上有所不同。
H2A1H在不同的正常组织和人类癌细胞系（人类中的H2A1C）中表现出不同的表达水平。当外源性过表达时，它还以依赖于背景的方式促进细胞增殖。为了揭示非冗余性的分子基础，我们对重组H2A1H-H2B二聚体进行了平衡去折叠实验。我们发现，与H2A2A3-H2B二聚体相比，H2A-H2B二聚体界面处的M51L改变使H2A1H-H2B的解链温度降低了约3°C。这种二聚体稳定性的差异也反映在染色质动力学中，因为含有H2A1H的核小体由于M51L和K99R取代而更稳定。分子动力学模拟表明，这些取代增加了H2A1H的氢键和疏水相互作用的数量，使其能够形成更稳定的核小体。
我们表明，M51L和K99R取代除了改变组蛋白-组蛋白和组蛋白-DNA复合物的稳定性外，对细胞增殖也有最显著的影响，这表明核小体稳定性与所观察到的生理效应密切相关。我们的工作为组蛋白H2A亚型的非冗余性的分子基础提供了见解，越来越多的报道表明这些亚型在不同的生理背景下具有重要的功能。
