Induction of H1⁰‐gene expression in B16 murine melanoma cells

Abstract

Histone H1 accumulation is associated with the terminal stage of differentiation. Unlike other HI histones, it is able to accumulate in the absence of DNA synthesis, however the transcription of its gene is cell-cycle dependent. The regulation of HIo-gene expression has been studied during the induced differentiation of B16 cells and during reversion of the process, which may be achieved when induced cells are released into an inducing-agent-free medium. During the earlier period of induced differentiation, HI0 mRNA showed over-expression when the cells were still proliferating. Then the amount of HI0 mRNA decreased as the cells became arrested in Go-G1. HI0 mRNA half-life measurements and run-on experiments demonstrated that such modulation of the amount of mRNA originated from a transcriptional control of HIo-gene expression. When induced cells reverted to a proliferative undifferentiated state, HI mRNA decreased very rapidly, indicating that an active process was involved in this decay. This behavior differed from that observed in rat liver hepatocytes allowed to proliferate and de-differentiate after partial hepatectomy, or in murine erythroleukemia cells when the inducing agent was removed from the culture.H 1 histones are involved in nucleosome stabilization and in the maintenance of a higher order of structure in chromatin. Their localization in the nucleus, and the existence of several variants in different organisms [I, 21, supports a hypothetical role as a repressor of transcription [3 -51. In-vitro experiments have confirmed that H1 histones are able to repress RNA polymerase I1 [6, 71 and RNA polymerase 111 [8, 91. HI0, one of the HI variants, was first detected in nonproliferative tissues [lo] and was later shown to appear at a terminal stage of differentiation [I 1 -151, or after growth inhibition [16]. It has been proposed that HI0 is associated with condensed chromatin, in agreement with its putative role in the repression of gene expression during the terminal stage of differentiation [17].HlO, unlike other histones, is accumulated in quiescent cells [18], and its synthesis may be uncoupled from that of DNA [18, 191. Nevertheless, like other histone mRNA, HI '-gene transcription is replication dependent in murine eryhtroleukemia (MEL) cells [20], and, moreover, the rate of transcription is enhanced when the cells are induced to differentiate [21-231. The replication-dependent accumulation of H 1 mRNA was also observed in hepatocytes during rat liver regeneration after partial hepatectomy [24], but in this case the protein accumulation appeared in the cells much later than the accumulation of mRNA, i.e. after the arrest of cell proliferation. It appears that H1° expression is under the control of a dual regulation process, the first one of which is related to DNA replication and concerns mostly the transcrip- tion step, the second occurs in the absence of cell proliferation and would affect primarily the translation step.In order to better understand the regulation of H1 during both proliferat...

Quantitative analysis of histone H1° protein synthesis in HTC cells

“…We observed that the transcript level greatly decreased following 4 h of culture into inducer-free medium, showing that the transcription induction could not be maintained in the absence of sodium butyrate. Such a rapid effect was also retrieved in B16 cells and the authors proposed that an active process was involved in this decay [3]. Interestingly, we found that H18 translation rate was Fig.…”

“…Cell growth arrest or differentiation induced by either serum deprivation or drugs, including sodium butyrate, hexamethylene bis-acetamide (HMBA) and dimethyl sulfoxide, were shown to increase H18 mRNA and protein levels in most mammalian cells in culture. Sodium butyrate induction led to the rapid accumulation of a 2.2-kb H18 mRNA in HeLa cells [2], B16 murine melanoma cells [3] and rat hepatoma tissue culture (HTC) cells used in this study [4]. Unlike HeLa and B16 cells which are stimulated to differentiate, HTC cells are progressively blocked at the early G1 phase of the cell cycle under sodium butyrate treatment [5,6].…”

“…Because this effect is reversible upon removal of the inducer, a 24-h sodium butyrate treatment can therefore be used for HTC cell synchronization [5]. Experiments performed on MEL, B16 and HTC cells showed that H18 mRNA accumulation resulted from an increase of H18 transcription rate [3,4,7], which did not require protein synthesis when stimulated by either HMBA [7] [4]. In the MEL cell line, H18 mRNA preferentially accumulates in mid or late S phase, even when cells have been pulse-induced by a 2-h treatment with HMBA [12,13].…”

“…Because this effect is reversible upon removal of the inducer, a 24-h sodium butyrate treatment can therefore be used for HTC cell synchronization [5]. Experiments performed on MEL, B16 and HTC cells showed that H18 mRNA accumulation resulted from an increase of H18 transcription rate [3,4,7], which did not require protein synthesis when stimulated by either HMBA [7] or sodium butyrate [4]. Although the H18 promoter has been isolated from mouse [8], Xenopus laevis [9], human [10] and rat [11], little is known about factors involved in the regulation of the gene.…”

An Upstream Control Region Required for Inducible Transcription of the Mouse H1° Histone Gene during Terminal Differentiation

“…However, after birth, H1Њ accumulates gradually in many tissues, and its levels in certain endocrine glands appear to depend on continuous hormonal stimulation (29). H1Њ also accumulates in a number of cell culture lines undergoing terminal differentiation in vitro, including neuroblastoma (35,58), embryonal carcinoma (2), and melanoma (8,63) cell lines, myeloid leukemia cells (51), and mouse erythroleukemia (MEL) cell lines (11,42,55,67,73).…”