Characteristics of nuclear proteins from cells of rat brain and spleen which regulate interleukin-2 gene expression

Abstract

Molecular masses of the active fractions of nuclear proteins isolated from spleen cell nuclei (SNP) and from nuclei of various cells of brain (BNP) (astrocytes, neurons, and glial cells) of immunized rats which stimulated expression of the IL-2 gene were defined more precisely. Some of these protein fractions were described by us previously. Proteins with M r of 13.5, 17.5, 18, and 19 kDa were found both in the BNP and SNP. It was also shown that the electrophoresis spectra of the proteins isolated from nuclei of the various brain cells were qualitatively equal, similar to the spectrum of total BNP, and were more heterogeneous than that of SNP. Proteins with M r 36, 48, and 75 kDa dominated in these spectra along with those with M r 13.5–19 kDa. The BNP polypeptides of M r 13.5–19,36, and 75 kDa and the SNP polypeptides with M r 13.5–19 kDa formed stable complexes both with proximal (from +39 to −151 bp) and distal (from −152 to −548 bp) fragments of the regulatory DNA of the IL-2 gene. In contrast, the BNP polypeptide of M r 48 kDa specifically interacted only with the proximal fragment of the IL-2 gene promoter. Polypeptides of M r 13.5–19 kDa and the BNP polypeptide of M r 48 kDa interacted with IL-2 gene regulatory DNA through hydrophobic contacts, whereas the BNP polypeptides of M r 36 and 75 kDa exhibited electrostatic interactions. Western blotting of the BMP and SNP with the polyclonal antibodies to c-jun and c-fos components of the AP-1 transfactor demonstrated that BNP and SNP polypeptides of M r 17.5, 18, and 19 kDa and BNP polypeptides of M r 36 and 75 kDa contained antigenic determinants that are similar to those of c-jun. The BNP polypeptide with M r 75 kDa also had antigenic determinants similar to those of c-fos. Additional analysis of N-terminal amino acid sequences and a search for homology in the computer data bank were performed for the proteins of M r 13.5, 18, and 19 kDa. These results supported the suggestion that nuclei of spleen cells and various types of brain cells involved similar IL-2 gene transcriptional activators.