Overexpression of histone variant H2A.1 and cellular transformation are related in N-nitrosodiethylamine-induced sequential hepatocarcinogenesis

Abstract

Histones through a complex repertoire of non-allelic variants and their post-translational modifications regulate gene expression. Though alterations in histone-modifying enzymes and post-translational modifications of histones have been studied in cancer, expression of histone variants has not been clearly associated with dedifferentiation and malignant transformation of hepatocyte in vivo. In the present work, the pattern of variants of histones was investigated during N-nitrosodiethylamine (NDEA)-induced hepatocarcinogenesis. Our studies show for the first time in vivo overexpression of a major histone H2A variant H2A.1 and a decrease in H2A.2 at protein and mRNA levels by sodium dodecyl sulfate-Acetic acid-Urea-Triton (SDS-AUT) two-dimensional gel electrophoresis followed by matrix-assisted-laser desorption/ionization time-of-flight (TOF)/TOF mass spectrometry and reverse transcriptase-polymerase chain reaction analysis during sequential development of hepatocellular carcinoma (HCC). H2A.1 and H2A.2 are highly homologous, replication-dependent, non-allelic variants of histone H2A differing at only three amino acid positions. Our results of increase in proliferating cell nuclear antigen expression indicate that with increase in replicating population of transformed cells in HCC, H2A.1 expression increases, suggesting association of H2A.1 overexpression with hyper-proliferation of hepatocytes during cellular dedifferentiation and progressive transformation of normal liver to preneoplastic and neoplastic stages of HCC.

Histone onco-modifications

“…On HIRA depletion, the induction of VEGFR1 and other angiogenic genes is impaired. A direct link between histone variant expression and cancer development has recently been drawn by Khare et al (2011). They showed that during sequential development of hepatocellular carcinoma, H2A and H2A.1 are overexpressed, whereas H2A.2 is decreased.…”

“…They showed that during sequential development of hepatocellular carcinoma, H2A and H2A.1 are overexpressed, whereas H2A.2 is decreased. The increased expression of H2A.1 has been linked to hyperproliferation (Khare et al, 2011). In addition, the histone variant macroH2A appears to suppress tumor progression of malignant melanoma through regulation of CDK8 (Kapoor et al, 2010).…”

Expression of histone variant, H2A.1 is associated with the undifferentiated state of hepatocyte

“…11,13 The animals (22-24 weeks) for liver regeneration studies were subjected to two-third PH. The surgeries were performed under sterile conditions as per protocol.…”

“…10 Previous report from laboratory has also shown over-expression of H2A.1 with decrease in expression of H2A.2 during de-differentiation of mature hepatocytes to HCC. 11 Recently, replication-dependent histone coded by human HIST1H2AC gene locus, sequence similar to rat H2A.1, has been associated with cell proliferation and tumorigenicty of bladder cancer cells. 12 In order to define alteration in H2A.1 and H2A.2 variants in the same organ system during development, de-differentiation, and normal cellular proliferation, their comparative profiling at RNA and protein level was studied during liver regeneration post PH and differentiating embryonic liver.…”

Global histone post-translational modifications and cancer: Biomarkers for diagnosis, prognosis and treatment?

“…Z and macroH2A have also been reported to express aberrantly [18][19][20] . Also, histones proteins can undergo a variety of PTMs some of which are methylation (me), acetylation (ac), ubiquitylation (ub), sumoylation (su) and phosphorylation (ph) on specific amino acid ( Figure 1) [10] .…”