Phosphorylation of lymphocyte nuclear acidic proteins: regulation by cyclic nucleotides

Interleukin II increases cyclic GMP levels in immature thymocytes and mitogen-primed T-lymphocytes

Interleukin II, also called T-cell growth factor, induces proliferation of immature peanut agglutinin positive murine thymocytes (PNA+) and renders them responsive to concanavalin A. It also, as shown by others, provides a second signal to induce phytohemagglutinin-primed mature human T-lymphocytes to enter DNA synthesis. Both actions are associated with early increases (2-60 min) in cellular levels of cyclic 3'5' guanosine monophosphate (cyclic GMP) without change of cyclic 3'5' adenosine monophosphate (cyclic AMP) levels. Cyclic GMP is postulated to represent part of the mechanism by which IL-2 acts.

Induction of DNA synthesis in isolated nuclei by cytoplasmic factors: inhibition by protease inhibitors

Cytoplasmic extracts from spontaneously proliferating and mitogen-activated lymphoid cells contain a protein factor called ADR (activator of DNA replication) that induces DNA synthesis in isolated quiescent nuclei. ADR-containing preparations have proteolytic activity, as indicated by their ability to degrade fibrin in a plasminogen-independent and plasminogen-dependent manner. In addition, aprotinin, a nonspecific protease inhibitor, abrogates ADR-induced DNA synthesis in a dose-dependent fashion. Preincubation studies demonstrated that the effect of aprotinin is not due to its suppressive effects on the nuclei themselves. Other protease inhibitors such as leupeptin, p-aminobenzamidine, and N-alpha-tosyllysine chloromethyl ketone are also inhibitory, but soybean trypsin inhibitor is without effect. ADR activity can be removed from active extracts by adsorption with aprotinin-conjugated agarose beads and can be recovered by elution with an acetate buffer (pH 5). These findings are consistent with the interpretation that the initiation of DNA synthesis in resting nuclei may be protease dependent and, further, that the cytoplasmic stimulatory factor we have called ADR may be a protease itself.

Are cyclic nucleotides involved in the initiation of mitogenic activation of human lymphocytes?

In order to obtain more insight into the possible role of cyclic AMP or cyclic GMP in modulating the initial cellular processes following activation of lymphocytes, we measured the effects of the T-cell mitogen concanavalin A and other substances including hormones on the cyclic nucleotide levels in human peripheral blood lymphocytes. The enzyme activities of the corresponding nucleotide cyclases, adenylate cyclase and guanylate cyclase were measured in both isolated plasma membranes or the cytosol of resting or concanavalin A stimulated rabbit thymocytes. Concanavalin A in a mitogenic concentration of about 5-10 micrograms/ml caused small, but consistent increases in cAMP but no changes in cGMP levels during the first hour of activation. Concomitantly, the specific activity of plasma membrane-bound adenylate cyclase was always increased at least 1.5-fold 30 min after stimulation of rabbit thymocytes with concanavalin A, but no effect could be detected on the specific activities of plasma membrane-bound or soluble guanylate cyclase. At high, supraoptimal concentrations of concanavalin A (more than 20 micrograms/ml) cAMP levels dramatically increased in human lymphocytes within minutes, but cGMP levels again were unaffected. Forskolin and beta-adrenergic hormones elevated cAMP in human lymphocytes, whereas cGMP levels were increased by the addition of sodium nitroprusside or alpha-adrenergic hormones. Sodium nitroprusside, in concentrations which elevated cGMP in human lymphocytes, had no influence on the incorporation of [3H]uridine into RNA of resting or concanavalin A stimulated human lymphocytes. Addition of forskolin resulted in an increase of cAMP levels and a dose-dependent decrease of [3H]uridine incorporation into RNA of concanavalin A-stimulated lymphocytes with no effect on resting lymphocytes. The data suggest that cGMP does not play a role in the initial phase of mitogenic activation of lymphocytes, whereas cAMP may be involved in the blast transformation process as an inhibitory signal.

Chromatin structure and nucleic acid synthesis in human lymphocyte activation by phytohemagglutinin

Alterations in chromatin structure were explored as a function of time following phytohemagglutinin (PHA) activation of human lymphocytes. Nuclear refringency (related to chromatin status), ultrastructural changes, and modifications of nucleic acid synthesis were compared. Chromatin dispersion was observed within 20 min of stimulation, with a concomitant increase in [3H]uridine incorporation; both were inhibited by actinomycin D. Recondensation of chromatin had occurred at 60 min when RNA synthesis was still increasing. The early chromatin dispersion thus was a reversible step and one of the most striking cellular events during the first phase of PHA activation. Late chromatin dispersion of blastic cells during the second phase of PHA response (after 24 h) was related to DNA synthesis in mitotic cells. This step was also inhibited by actinomycin D. These results suggest a relationship between the morphological changes in chromatin structure and the induction of RNA and DNA syntheses. The regulation of transcriptional and replicational states of the nucleus is discussed in terms of modifications of chromatin structure, considering PHA-induced calcium and cyclic nucleotide metabolism and interleukin II receptor expression.

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.

Induction of DNA synthesis in isolated nuclei by cytoplasmic factors from spontaneously proliferating and mitogen-activated lymphoid cells

Cytoplasmic extracts, prepared from continuously proliferating lymphoblastoid cells, as well as mitogen-activated normal lymphocytes, contain an extractable factor capable of inducing DNA synthesis in isolated quiescent nuclei. This factor is not detectable in resting cells. It is nondialyzable, precipitable by 30-50% saturated ammonium sulfate, and inactivated by trypsin. It is heat sensitive, but stable to cold and lyophilization. The molecular weight of the factor is greater than 100,000. This cytoplasmic activator of nuclear DNA replication is not released from the cell, and has no effect on intact cells. This suggests that it serves as an intracellular mitogenic signal in replicating cells.

Correlation of patterns of nuclear protein synthesis with differentiation of mitogen-stimulated B-lymphocytes

Nuclear proteins synthesised by mouse lymphocytes stimulated by the B-lymphocyte mitogen lipopolysaccharide have been analysed by 2-dimensional polyacrylamide gel electrophoresis. It has been shown that the rate of synthesis of both nucleoplasmic proteins and nonhistone chromatin proteins is stimulated dramatically by LPS and many nuclear proteins are synthesised that were undetectable in resting lymphocytes. The majority of these proteins are synthesised by lymphoblasts and plasma cells, the lymphocytes that remain small after LPS stimulation synthesizing relatively few proteins. Two chromatin proteins that have previously been shown to appear in the nucleus within 4h of mitogen stimulation exhibit a continuous increase in their rate of synthesis during lymphocyte differentiation. The possible roles of these proteins in differentiating lymphocytes are discussed.

Biochemical characterization of a specific phosphate acceptor of nuclear cyclic AMP-independent protein kinase

The regulatory mechanism of transcription involved in the phosphorylation of a 13 kDa non-histone chromatin protein from calf thymus, which is the most effective phosphate acceptor for cyclic AMP-independent protein kinase purified from the nuclei of mouse spleen cells, by the kinase has been studied in vitro. An analytical study of the circular dichroism (CD) spectra of the 13 kDa protein under different conditions showed that it underwent a major conformational change when incubated with DNA. The presented data suggest that the DNA-induced conformational change may result in a great increase of the 13 kDa protein phosphorylation by the kinase in vitro. Mg2+ (8-10 mM) enhanced the binding of the protein to DNA. Furthermore, the phosphorylated 13 kDa protein stimulated elongation of RNA synthesis by RNA polymerase II from calf thymus. However, neither the 13 kDa protein nor the phosphorylated 13 kDa protein had any affect on DNA synthesis. The available evidence suggests that the 13 kDa protein may play a role in the regulation of transcription through its phosphorylation by the kinase in vitro.

Activation of lymphocytes by brominated nucleoside and cyclic nucleotide analogues: implications for the "second messenger" function of cyclic GMP

The purine nucleoside guanosine, when derivatized at the C-8 position to give 8-bromoguanosine (8-BrGuo), acquires the capacity to stimulate high-level lymphocyte proliferation in the presence or absence of serum. Direct comparisons were undertaken to determine whether this activity is exerted only by virtue of the structural resemblance of 8-BrGuo to 8-bromo cyclic GMP (8-BrcGMP) (a known intracellular lymphocyte mitogen). They showed that, of the brominated guanosine derivatives studied, 8-BrGuo is the primary activator because (i) it is a far more potent lymphocyte activator than 8-BrcGMP, the order of mitogenic potency being 8-BrGuo greater than 8-bromo GMP (8-BrGMP) greater than 8-BrcGMP; (ii) it acts much more rapidly than 8-BrcGMP; (iii) it is not metabolized to 8-BrcGMP or cGMP; and (iv) it does not elevate intracellular cGMP content. cGMP is not likely to be the second messenger serving to activate B cells because (i) it does not induce significant proliferation unless brominated at the C-8 position; (ii) the brominated form is much less efficient than 8-BrGuo or 8-BrGMP; (iii) 8-BrGuo and many other mitogens do not increase intracellular cGMP; (iv) many agents that increase cGMP fail to initiate lymphocyte activation; (v) certain agents that increase cGMP (i.e., 15-hydroperoxyarachidonic acid, azide) inhibit lymphocyte activation; and (vi) addition of unbrominated cGMP to cultures stimulated with 8-BrGuo actually diminished stimulation. These data (i) indicate that, by interaction with cellular components, 8-BrGuo triggers high level lymphocyte activation and (ii) cast significant doubt on the role of cGMP as an intracellular second messenger in lymphocyte proliferation.

Non-histone chromatin proteins of B lymphocytes stimulated by lipopolysaccharide. III. De novo synthesis

Nuclear and cytoplasmic proteins synthesised by mouse lymphocytes stimulated in vitro by the B lymphocyte mitogen, lipopolysaccharide, have been analysed by one- and two-dimensional polyacrylamide gel electrophoresis at early and later times after the onset of stimulation. During the first 4 h no change was observed in the electrophoretic profiles but differences in turnover of various nuclear proteins within the same sample were noted. This is contrasted with the previous observations that phosphorylation of nuclear proteins is stimulated within 2 h. (Stott, D.I. and Williamson, A.R. (1978) Biochim. Biophys. Acta 521, 739-752). During prolonged culture, synthesis of nucleoplasmic proteins declined between day 2 and day 3, being reduced to undetectable levels at the end of the 3-day culture period. In contrast, synthesis of many non-histone chromatin proteins was stimulated between 24 and 48 h, the time course and degree of stimulation varying between different proteins. Certain proteins appeared to be synthesized de novo. These events occur at a time of rapidly increasing IgM synthesis and cell differentiation. It is suggested that an initial step in B lymphocyte triggering may involve phosphorylation of preexisting nuclear proteins leading to gene activation followed by synthesis and phosphorylation of new gene regulatory molecules.

Immunohistochemical studies of cyclic guanosine monophosphate and nuclear function

In previous immunohistochemical studies, it has been found that all nuclei contain cyclic (c)GMP, which occurs in discrete aggregates and in the nucleolus. We have studied the nature of the cGMP aggregates in isolated mouse fetal nuclei using a specific immunofluorescent technique. These aggregates correspond to the areas of condensation of DNA, demonstrable by either Felugen's or acridine orange stain. Treatment with DNAase eliminated DNA and cGMP staining. Staining for RNA, with a human anti-RNA antibody, demonstrated RNA to be distributed diffusely throughout the nucleus and not preferentially in the areas of discrete cGMP aggregates. The diffuse stain for nuclear RNA was eliminated by pretreatment with RNAase but not DNAase, but aggregates of cGMP were not affected by pretreatment with RNAase. Sites of active RNA synthesis were determined by autoradiography using [3H]uridine, and did not correspond to the aggregates of cGMP. The relationship of cGMP to nucleolar function was examined in the endothelial cells of the isthmus and ampulla of the rat fallopian tube. Previous studies have shown that in proestrous, a period of increased RNA synthesis, nucleoli detectable by staining for RNA appear in the endothelial cells lining the fallopian tube. After immunofluorescent staining, we found prominent accumulation of cGMP in the nucleoli. During other phases of the cycle, there is an absence of nucleoli detectable by staining for RNA, and an absence of nucleolar cGMP. After we treated hypophysectomized or oophorectomized rats with estrogen, which is known to increase nucleolar RMA synthesis in the fallopian tube and endometrium, nucleoli in the endothelial cells of the rat fallopian tube and uterus stained strongly for cGMP. In conclusion, our studies suggest that the discrete aggregates of nuclear cGMP are associated with a fraction of DNA uninvolved in RNA synthesis. In contrast, cGMP appears in the nucleolus during a period of increased RNA synthesis, suggesting a role for cGMP in regulating nucleolar synthesis and processing of RNA.

Non-histone chromatin proteins of B lymphocytes stimulated by lipopolysaccharide. II. Phosphorylation

Stimulation of mouse lymphocytes with the B lymphocyte specific mitogen lipopolysaccharide results in an increased rate of phosphorylation of non-histone chromatin proteins. An initial small increase in phosphorylation occurs during the first 2 h and a much larger increase after 24 h of culture with mitogen. The phosphorylated nuclear and cytoplasmic proteins were analysed by polyacrylamide gel electrophoresis and the stimulation index of each prominent peak measured. It was inferred that selective stimulation of the phosphorylation of individual proteins had occurred from: (1) the range of stimulation indices for different proteins, and (2) the appearance, after 8 h stimulation of an apparently newly phosphorylated non-histone chromatin protein of molecular weight 115 000. The pool size of ATP was monitored and showed only small changes during the first 24 h of exposure to lipopolysaccharide. Phosphatase activity was found to be associated with lymphocyte chromatin and nucleoplasm and may help to regulate the level of phosphorylation of non-histone chromatin proteins in vivo. To preserve phosphorylated proteins during their isolation phosphatase activity was inhibited by Na2MoO4. The selective changes in phosphorylation of nuclear proteins precede, and continue during, the stimulation of immunoglobulin and DNA synthesis. Our results are thus consistent with the hypothesis that phosphorylation of non-histone chromatin proteins plays a role in the regulation of gene expression in B lymphocytes.

Non-histone chromatin proteins of B lymphocytes stimulated by lipopolysaccharide

The synthesis of non-histone chromatin proteins and nucleoplasmic proteins has been followed during lipopolysaccharide-induced division and differentiation of murine B lymphocytes. Synthesis was measured by pulse labelling with [3H]leucine, extraction of proteins was under conditions designed to prevent proteolysis and analysis of labelled proteins was by polyacrylamide gel electrophoresis. The average specific activity of non-histone chromatin proteins increased 3-fold, to a maximum, after culture for 24 h with lipopolysaccharide. Comparison of the relative synthesis of individual proteins (stimulation index) reveals three distinct responses: (1) those in the largest group show low stimulation indices, generally less than two; (2) a group of four proteins have indices between 4 and 5; (3) two proteins (molecular weights 21 000 and 22 000) both show an index of 5 at 24 h rising to between 7 and 8 by 48 h when the average specific activity is falling, coinciding with the period of rapid differentiation to high rate IgM secretion. Additionaly at this time, a newly labelled protein (Mr = 36 500) appears in the nucleoplasm followed by a second protein (Mr = 63 000) appearing between 48 and 72 h. The patterns of change are consistent with an overall increase in non-histone chromatin proteins synthesis, necessary for cell division, with superimposed specific changes in synthesis of non-histone chromatin proteins which could be related to regulation of cell differentiation.

Antineoplastic agents III: effects of dibromoethyl and vinyl esters of N-benzyloxycarbonyl-l-phenylalanine on Ehrlich ascites tumor cell metabolism

Evidence is presented that N-benzyloxycarbonyl-L-phenylalanine vinyl ester and 1,2-dibromoethyl ester are inhibitors of Walker 256 carcinosarcoma and Ehrlich ascites carcinoma tumor growth. The major effects of these two agents on Ehrlich ascites cell metabolism were the inhibition of deoxyribonucleic acid and protein synthesis and the alteration of cellular regulatory processes controlling cytokinetics. Deoxynucleotide (purine) kinase enzymes appeared to be the focal site for inhibition of deoxyribonucleic acid synthesis with marginal inhibition of thymidylate synthetase activity. Cyclic adenosine monophosphate levels were elevated by drug treatment whereas chromatin protein phosphorylation, cell respiration, and lysosomal activities were inhibited. N-Benzyloxycarbonyl-L-phenylalanine 1,2-dibromoethyl ester was a latent in vitro chymotrypsin inhibitor. Some preliminary evidence suggests that these activated esters may inhibit cellular enzymatic activity by alkylating imidazole and lysine residues of proteins.

Nuclear proteins in the heart of the cardiomyopathic Syrian hamster. Phosphorylation of phenol-soluble nonhistone proteins

We examined incorporation of 32P into phenol-soluble nonhistone nuclear acidic proteins (NHNP) obtained from myolytic, hypertrophic, and failing phases of hamster cardiomyopathy. NHNP from these dystrophic hamster hearts were phosphorylated much less than their controls, despite a 9-fold increase in uptake of 32P into their nuclei. After fractionation of NHNP by isoelectrofocusing polyacrylamide gel electrophoresis, two major fractions focusing from pH 6.0 to 6.2 and 6.6 to 6.8 were highly phosphorylated in both the control and dystrophic hearts. The latter fraction was much more phosphorylated in the control. Two fractions of NHNP focusing at pH 4.9 and 5.1 were more highly phosphorylated in the dystrophic hearts than in the controls. Autoradiographs obtained from the two-dimensional polyacrylamide slab gel electrophoresis showed that two proteins (pH 4.9 and 5.1; mol wt 25,000 and 60,000, respectively) were highly phosphorylated in the dystrophic heart. There was no detectable phosphorylation of these proteins in the controls. These changes in the phosphorylation of cardiac NHNP may be important in determining the alteration of gene expression in hamster cardiomyopathy.

Effects of zinc chloride on the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart

In the presence of 10 micrometer Ca2+ and 5 mM Mg2+ (or 0.25 mM Mg2+), the addition of 100 micrometer Zn2+, Ni2+, Co2+, Fe2+, Cu2+ or 1 mM Mn2+ resulted in varying degrees of stimulation or inhibition of 10(-6) M cyclic GMP and cyclic AMP hydrolysis by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart in the absence or presence of phosphodiesterase activator. The substrate specificity of the enzyme was altered under several conditions. The addition of Zn2+ in the presence of 5 mM Mg2+ and the absence of activator resulted in the stimulation of cyclic GMP hydrolysis over a narrow substrate range while reducing the V 65% due to a shift in the kinetics from non-linear with Mg2+ alone to linear in the presence of Zn2+ and Mg2+. Zn2+ inhibited the hydrolysis of cyclic GMP and cyclic AMP in the presence of activator with Ki values of 70 and 100 micrometer, respectively. Zn2+ inhibition was non-competitive with substrate, activator and Ca2+ but was competitive with Mg2+. In the presence of 10 micrometer Ca2+ and activator, a Ki of 15 micrometer for Zn2+ vs. Mg2+ was noted in the hydrolysis of 10(-6) M cyclic GMP. Several effects of Zn2+ are discussed which have been noted in other studies and might be due in part to changes in cyclic nucleotide levels following phosphodiesterase inhibition.

The effect of adenosine-3':5'-cyclic monophosphate on the mitotic rate in regenerating Dugesia dorotocephala

Regenerating posterior sections of the flatworm, Dugesia dorotocephala, were treated with varying concentrations of 5'-adenosine monophosphate (AMP), cyclic AMP (cAMP) and dibutyryl cyclic AMP (Bt2cAMP) for 24 h. M/2000 colchicine was added to the medium during the final 4 h of treatment to collect mitotic figures. The mitotic rate was significantly increased at 0.5, 0.1 and 0.01 mM concentrations of Bt2-cAMP. While Bt2cAMP and cAMP produced comparable results at 0.01 mM, only the Bt2-cAMP-treated organisms exhibited a significantly higher mitotic rate at the 0.1 mM concentration. Theophylline and sodium butyrate did not evoke any stimulatory effect on mitotic rate.

Stimulation of uterine nonhistone protein phosphorylation and nuclear protein kinase activity by estradiol-17beta

Changes in the phosphorylation of nonhistone chromosomal proteins have been followed in rat uterus stimulated by 17beta-estradiol. Isolated uteri were found to incorporate 32Pi into nonhistone proteins via an endogenous neclear protein kinase reactin. The rate of 32P labeling of nonhistone proteins and the activity of nuclear protein kinase(s) were found to be elevated over three- and two-fold respectively in uteri obtained from ovariectomized animals treated with estrogen. A dramatic change was observed in the radioactivity profile of 32P-labeled proteins fractionated via sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These observations are compatable with the hypothesis that phosphorylation of nonhistone proteins plays a role in the regulation of gene activity in the uterus.