Interference of AlF4- with nucleotide and DNA binding of rat histone H1 in vitro. Implications for the pathogenesis of Alzheimer's disease

Nucleotide and calcium-induced conformational changes in histone H1

The principal constituents of chromatin, histone H1 (H1) and the nucleosome have essential roles in regulation of eukaryotic gene expression. However, mechanisms for the H1-dependent inactivation and for the ATP-dependent chromatin remodeling upon activation are largely unelucidated. Using circular dichroism (CD) analysis we show that ATP and other nucleotides and Ca2+ induce structural changes in H1. ATP and Ca2+ also induce changes when H1 is interacting with DNA, and the changes in H1 are accompanied by alterations in its DNA interaction. These results suggest that nucleotide and Ca2+ binding may be important for H1-mediated chromatin changes.

Specific non-enzymatic glycation of the rat histone H1 nucleotide binding site in vitro in the presence of AlF4-. A putative mechanism for impaired chromatin function

We show here that an aluminium derivative, AlF4-, stimulates glycation of histone H1 selectively in the proximity of its nucleotide-binding site. This adduct formation interferes with nucleoside triphosphate hydrolysis by H1 and with nucleotide modulation of H1 DNA binding. The present mode of aluminium action may in part be responsible for its effects on the chromatin structure and expression of tissue-specific genes, and may constitute a mechanism in the pathogenesis of aluminium-induced encephalopathy and in that of Alzheimer's disease, for example.

DNA binding of histone H1 is modulated by nucleotides

Histone H1 acts as a general repressor of transcription in eukaryotes by organizing nucleosomes into inaccessible condensed forms of chromatin. The capability of H1 to bind to DNA with some sequence specificity is likely to be critical in the control of these processes. We show here that ATP and several other nucleotides, including non-hydrolyzable derivatives, can inhibit DNA binding of H1. The results also show that ATP differentially affects binding of H1 to DNA in a fashion enhancing nucleotide sequence specificity of the binding. The study suggests a novel mechanism of modulation of H1 activity that has important implications for the role of H1 as a transcriptional regulator.

Nucleoside triphosphate binding and hydrolysis by histone H1

We present here further evidence supporting that histone H1 contains a nucleotide binding site interacting e.g. with ADP, ATP, GDP and GTP. The finding is in accordance with the previous observation that nucleotides modulate recognition of DNA by H1. Most interestingly, H1 appears to be capable of hydrolyzing NTPs and incorporating phosphate to exogenous proteins. The mode of nucleotide action on H1 may be considered highly analogous to that of GTPases. Nuclear receptors may thus act through mechanisms similar to those for receptors on the plasma membrane.

Histone H1 and the regulation of transcription by nuclear receptors

Histone H1 is a eukaryotic repressor which recognizes specific DNA structures, and nucleotides regulate its interaction with DNA. Since their mode of action may be considered similar to that observed in the case of plasma membrane GTPases, H1 may be regarded as an ATP/GTPase involved in the action of nuclear receptors. A hypothesis is put forward here to suggest that transcriptional activators CTF/NF-I and AP-1 (fos/jun), for example, are effectors for H1. H1 and CTF/NF-I may be members of a stimulatory regulatory cascade for nuclear receptor action that ends with selective activation of chromatin through histone modification and the disruption or a more subtle structural change of a specific nucleosome, while an opposite effect may be obtained through modification of fos/jun by H1.