Non-histone chromatin proteins during various stages of activity of immunocompetent cells

Binding of low mobility group protein from rat liver chromatin with histones studied by chemical cross-linking

The protein of molecular weight about 160 kD (designated LMG160) was isolated from purified low mobility group chromatin proteins. Polyclonal antibody directed against the LMG160 protein in mouse was raised. The specificity of the antibody was determined with the use of ELISA. Using chemical cross-linking procedure followed by immunoprecipitation with the antiLMG160 antibody complex formation with chromatin proteins was demonstrated. Among the proteins that form complexes with LMG160, histones H3, H2A, and H4 were identified (Western blotting technique).

Identification of NGF receptor in chromatin of melanoma cells using monoclonal antibody to cell surface NGF receptor

A 230 KDa species of Nerve Growth Factor (NGF) receptor was immunoprecipitated from EcoRI-digested chromatin of melanoma cells using a monoclonal antibody to the 75 KDa cell surface NGF receptor. The chromatin NGF receptor was shown to exist tightly bound to DNase II-sensitive sequences which, upon growth factor binding, became resistant to DNase II digestion.

Chromatin binding of epidermal growth factor, nerve growth factor, and platelet-derived growth factor in cells bearing the appropriate surface receptors

We analyzed the uptake and intracellular distribution of 125I-labeled epidermal growth factor, nerve growth factor, and platelet-derived growth factor in different cell lines that express or do not express the respective surface receptors for these factors. After 1 hr of incubation, all three growth factors were detected in the cytoplasmic fraction and in the nucleus, tightly bound to chromatin. The amount of chromatin-bound growth factors continued to increase during the incubation, and analysis at 48 hr revealed each chromatin-bound labeled growth factor in a nondegraded form. After limited digestion of chromatin with DNase II (10-20% digested sequences), specific release of all three growth factors was detected only after 1 hr of incubation but not after 24 and 48 hr, suggesting that the DNA regions involved in growth factor binding became nuclease-resistant. Binding of labeled epidermal growth factor and nerve growth factor to isolated chromatin was inhibited by monoclonal antibodies specific for the respective growth factor receptor. The data suggest that chromatin binding may represent an important step in the pathway of growth factor action.

Incorporation of antigen 125I IgG into particular cell compartments: binding by chromatin

Incorporation of [125I]IgG into spleen cells was studied in vivo and in vitro. In vivo, the antigen after uptake into the cytoplasm migrated into cell nuclei, where it was bound to chromatin up to the saturation level. One day after immunization the constant level of [125I]IgG was 1.3 X 10(12) molecules per spleen (10(8) cells). The same number of [125I]IgG molecules were bound to chromatin in cell cultures. The uptake of [125I]IgG was competitively inhibited by non-labelled IgG. Binding of [125I]IgG molecules reextracted from cytoplasm and chromatin with specific anti-human IgG serum argues against the uptake of degraded [125I]IgG molecules. [125I]IgG was tightly bound to DNA. Approximately 50 per cent of [125I]IgG was present in the residual chromatin fraction (after removal of 0.35 M and 2 M NaCl-soluble fractions) and 40 per cent was complexed with DNA (after removal of histones and non-histones AP1, AP2, AP3 and AP4). Binding of [125I]IgG by isolated chromatin was inhibited by the cytoplasmic fraction but not by BSA. Binding of [125I]IgG by fractionated chromatin, (chromatins remaining after removal of 0.35M, and 2M NaCl-soluble fractions or histones + non-histones AP1 + AP2 + AP3 + AP4) occurred at a level similar to that observed with native chromatin. The results suggest that interaction of antigen with immunocompetent cells is not restricted to the cell surface but that antigen seems to be taken up into cytoplasm, migrates to the nuclei and is bound to chromatin, probably directly to DNA. The results are discussed in relation to the induction of the immune reaction.

Non-histone chromatin protein fractions associated with 'active' chromatin in embryonic chicken liver

Non-histone chromatin proteins synthesized during chicken embryonic liver development were labeled with [3H]tryptophan and [3H]methionine and characterized by electrophoresis. During embryonic development protein/DNA ratio in chromatin was low (1.30-1.62) but synthesis of non-histone protein was high. Especially one characteristic fraction K (MW 18 000), tightly bound with DNA was preferentially associated with DNAase II sensitive, active transcribed sequences. In 7-day old and adult chicken synthesis of all non-histone proteins was low, fraction K was absent or synthesized only in small amounts in association with non-active sequences, however protein/DNA ratio in chromatin was high (2.30-2.33).

Nuclear proteins associated with gene expression in mouse plasmacytoma cell lines

Nucleoplasmic and non-histone chromatin proteins from two unrelated and four related mouse plasmacytoma cell lines have been analysed by biosynthetic labelling with [35S]-methionine followed by one- and two-dimensional polyacrylamide gel electrophoresis. We have attempted to find a relationship between the patterns of nuclear proteins and gene expression in mutant plasmacytoma cell lines. The majority of nuclear proteins are common to all of the cell lines studied as would be expected if the majority of nuclear proteins are concerned with functions common to all plasma cells. There are, however, both qualitative and quantitative differences in the nuclear protein patterns of mutant and parent cell lines which appear to correlate with differences in gene expression. The turnover of nuclear proteins in two of the cell lines, MOPC 315.40 (IgA producer) and MOPC 315.32 (lambda 2 chain producer) was studied using pulse-chase techniques.

Specific non-histone protein fractions associated with 'active' chromatin in immunized rats

Non-histone proteins of normal, non-immunized rats and rats immunized with mouse spleen cells were labelled with three different amino acids: [3H]tryptophan, [3H]methionine and [3H]leucine. Chromatin was fractionated at increasing salt concentrations into three fractions: 0.35 M NaCl-soluble, 2 M NaCl-soluble and residual. Non-histone protein fractions F (Mr 12 000) and H (Mr 3 000) highly labelled with [3H]tryptophan, lower with [3H]methionine but not with [3H]leucine, were present mainly in the residual fraction. After DNAse II treatment non-histone protein fractions F and H disappeared in chromatin fractions and were present in Mg2+ soluble fractions which suggests that, similar to the fractions I (Mr below 3 000) and B (Mr 120 000) described previously (5), these fractions may be associated with active transcribed genes.

Differences in salt solubility, DNase II sensitivity and template activity of chromatin from antibody synthesizing spleen cells and myeloma cells RPC 5 and ABPC 22

Chromatin from myeloma cells RPC5 and ABPC22, and from spleen and liver cells of immunized rats and mice, and mice bearing tumours, was fractionated into three part: 0.35 M NaCl-soluble, 2 M NaCl-soluble and residual. The residual fraction from myeloma cells differed from that of immunized spleen cells, described previously as containing unique sequences (5), in that it has higher protein and DNA levels, lower DNase II sensitivity and lower template activity.