[Interaction of eukaryotic DNA with apolipoprotein A-I and its complexes with glucocorticoids]

A biochemically active complex of apolipoprotein A-I with tetrahydrocortisol was revealed, which increases gene expression in hepatocytes. It was shown by the method of fluorescent probe that titration of rat liver DNA by the apolipoprotein A-I-tetrahydrocortisol complex leads to the appearance of single-stranded fragments. The effect of the complex on the secondary structure of native DNA was confirmed by the method of small-angle X-ray scattering. It was shown that approximately 54 apolipoprotein A-I molecules carrying tetrahydrocortisol as a ligand bind to one molecule of isolated native DNA, inducing a break of hydrogen bonds between the pair of nitrous bases. It is concluded that the cooperative effect of high-density lipoproteins and cortisol in the regulation of gene expression in hepatocytes with the participation of resident liver macrophages is accomplished by a new biochemical mechanism. This mechanism makes itself evident as a result of the interaction of DNA with the apolipoprotein A-I-tetrahydrocortisol complex, the appearance of single-stranded DNA regions in binding sites, and subsequent initiation of gene transcription.