Non-histone chromosomal proteins in normal and abnormal growth

Monoclonal antibodies to nonhistone proteins associated with human colon cancer nuclear matrix

Hybridoma technology was applied in an effort to create highly specific probes for nonhistone proteins associated with human colon cancer nuclear matrix. Three stable monoclonal antibodies producing cloned cells No. 39, 54 and 58 are described here. All these antibodies showed high reactivity with human colon tumor nuclear matrix. Both antibodies No. 39 and 58 showed an extensive cross reactivity at high concentration of normal colon nuclear matrix. The antigens were determined to be a heterogeneous group of proteins with a major antigen of molecular weight of 140,000 for antibody No. 54 subclone 54-c-5-6 and two major antigens of molecular weight for 105,000 and 116,000 for antibody No. 39 subclone 39-d-11-12. Immunohistochemical localization of the antigens by the horseradish peroxidase bridge method demonstrated their presence in the nuclei.

DNA and nuclear protein measurement in isolated nuclei of human endometrium

Feulgen-DNA and nuclear light green-protein measurements have been performed in isolated nuclei of normal (nonmalignant) and malignant human endometrial homogenates. The DNA content of the G0/G1 fraction of malignant endometrium showed much overlap with that of normal endometrium, or was slightly increased. Two of the 18 carcinomas were clearly aneuploid. No correlation was found between the histological grade and the DNA content. The tumors of clinical stage II and higher all had a higher DNA content than that of normal endometrium. The percentage of cells present in the proliferative fraction was higher in proliferative endometrium than in secretory and post-menopausal atrophic endometrium. For malignant endometrium, percentages were found comparable to that of normal endometrium or higher. No correlation was found with the histological grade. Tumors of stage II and higher had intermediate values compared to those of carcinomas below stage II. The nuclear protein/DNA ratio of malignant endometrium completely overlapped that of normal endometrium. However, for post-menopausal women, most values of the carcinomas exceeded that of normal, atrophic, endometrium. Within the tumor population, no correlation was found with the histological grade. Higher values were found with tumors of clinical stage II and higher.

Could the loss of regulation of genetic expression in cancer cells be used to cause their necrosis?

In cancer cells the control over the genetic message involved in the induction of mitosis is irreversibly lost. This fact is indicated by certain phenomena displayed by cancer cells under restricted nutritional conditions. Cells transformed by DNA viruses (which stabilize "p53") keep on cycling and die. In starving cells at the inside of tumors the synthesis of pre-rRNA still proceeds while all other anabolic processes are already at a standstill. The reason is that glutamine, glycine and aspartate are channelled into the enzymatic pathways for the synthesis of nucleosides: thus, protein synthesis is denied those aminoacids. Such situations might be imitated through the administration of excess nucleosides and (within limits) the simultaneous restriction of some selected aminoacids. DNA replication depends on the stabilization of p53, but an accumulation of pre-rRNA might occur, which ultimately might be harmful for cancer cells. Several ways to improve this rationale might be tested on cultured cells and on research animals. They include the destruction of methionine with bacterial enzymes, or the addition of ornithine, a precursor of putrescine, which is an important factor of DNA and pre-rRNA synthesis.

Hepatoma-associated nonhistone chromosomal proteins

In order to compare nonhistone proteins in normal and neoplastic hepatocytes, we elicited antisera to Morris hepatoma 7777 dehistonized chromatin. By the enzyme-linked immunosorbent assay, the antisera demonstrated specificity for Morris hepatoma 7777 and little reactivity to normal rat liver chromatin. Morris hepatomas 7288c, 7800 and 5123tc shared some antigenic hepatoma nonhistone proteins. Neoplasia induced in rats fed 3'-methyl-4-dimethylaminoazobenzene changed the immunospecificity of the liver chromatin to a new type that was antigenically similar to Morris hepatoma 7777. Fetal rat liver chromatin and regenerating rat liver chromatin did not bind antibody. To further characterize the antigenic nonhistone proteins, we analyzed Morris hepatoma 7777 chromatin and normal rat liver chromatin by the immunoblot technique. Nonhistone proteins that demonstrated immunoreactivity were predominantly high molecular weight proteins.

The enhancement of specific gene transcription in isolated nuclei by added HeLa whole cell extract

Transcription was carried out in isolated rat liver nuclei by endogenous RNA polymerase with the addition of HeLa whole cell extract (HWCE) in the presence of nucleoside 5'-[gamma-S]triphosphate. The resulting 5'-gamma-thiophosphate on the synthesized RNA allows separation of in vitro initiated RNA from bulk RNA by mercury-agarose chromatography. HWCE not only increased initiation of new RNA chains greater than 3 times but also had no effect on the RNA synthesis by RNA polymerase II. The initiation of transcription of albumin and alpha-fetoprotein genes in an isolated nuclei system was selectively enhanced by HWCE. Using this system, we studied the effect of glucocorticoid on albumin and alpha-fetoprotein gene expression in vitro.

Comparison of kinetics of X-ray-induced cell killing in normal, ataxia telangiectasia and hereditary retinoblastoma fibroblasts

Survival, cumulative labeling indices and chromosomal aberrations were studied in normal, ataxia telangiectasia (AT) and hereditary retinoblastoma fibroblasts after X-irradiation during density-inhibition of growth and immediate release by subculture to low density. The D0 of the survival curves were: normal strains, 150-160 rad; Retinoblastoma strains AG 1880, 95 rad; AG 1978, 40-50 rad (sensitive fraction); AT5BI, 45 rad. Mainly chromosome-type Aberrations were induced in normal and retinoblastoma cells. The frequency of X-ray-induced chromosomal aberrations was much higher in AT5BI cells, and 33-45% were of the chromatid type. Normal and retinoblastoma cells showed a measureable X-ray induced G1 delay before entering S. In addition, a fraction of the cells showed an apparently irreversible G1 block; these cells did not initiate DNA synthesis up to 120 h post-irradiation and subculture. The G1 block was much more marked in retinoblastoma cells; after 400 rad about 70% of retinoblastoma cells did not enter S as compared with only 20% of normal cells. Neither a G1 delay nor a G1 block was observed in AT cells irradiated with up to 400 rad despite their hypersensitivity to cell killing by X-rays and evidence of severe chromosome damage. These results suggest different mechanisms for the X-ray hypersensitivity of AT and retinoblastoma cells.

Assembly of secondary intermediates during deoxyribonucleic acid replication in transformed human fibroblasts

The elongation of replicative DNA was studied in transformed WI-38 cells (designated 2RA). Shear effects were avoided by use of an alkaline sucrose gradient sedimentation method whereby cells were lysed directly on top of gradients, at 4 degrees C in the dark. The earliest detected intermediate is a short (2 S) piece of DNA which is converted first to a 25 S piece and then to a 100 S piece, within 10 min. The 100 S piece is next converted to a 212 S, and a 370 S, and finally to a chromosomal DNA of about 450 S. This pattern is quite different from that previously reported by us for normal WI-38 cells, where there was a 50 S intermediate which was not quickly converted into a much larger size, but which gradually elongated, by addition of smaller pieces, to a larger size, of 100 S.; another difference was the time required for formation of the 100 S piece, i.e., 75 min (Rawles, J.W., Jr. and Collins, J.M. (1977) J. Biol. Chem. 252, 4762-4766).

Regulation of specific genes during the cell cycle. Utilization of homologous cDNAs and cloned sequences for studying histone gene expression in human cells

Evidence for differential gene expression during the cell cycle and approaches for studying cell-cycle-stage specific gene expression are summarized. Attention is focused on regulation of histone gene expression during the cell cycle of continuously dividing cells and after stimulation of nondividing cells to proliferate. The level(s) at which control of histone gene expression occurs and the possible involvement of chromosomal proteins in the regulation of histone gene expression are discussed. The preparation of cloned human histone sequences and their use in studying the structural and functional properties of human histone genes are presented. Index Entries: Cell cycle, gene regulation during; gene regulation, during the cell cycle; regulation of specific genes, during the cell cycle; DNAs, homologous, and histone gene expression; cloned DNAs, and histone gene expression; histone gene expression; gene expression, histone; cloned human histone sequences.

Biochemical, molecular, and pharmacologic approaches to large bowel cancer: an overview

The role of the nucleolus in the control of cell proliferation in mammalian cells is becoming increasingly clear. Our expanding knowledge of the cellular and molecular mechanisms that regulate cell division in normal and cancerous cells opens new possibilities for improving the diagnosis, prognosis, and therapy of tumors.

Analysis of chromosomal proteins of fractionated chromatin from rat liver and transplantable hepatocellular carcinomas

The chromosomal proteins from a number of transplantable hepatocellular carcinomas (THC) induced by a single carcinogen or its derivatives and varying greatly in their growth rates were examined by sodium dodecyl sulfate (SDS) polyarcylamide gel electrophoresis. Before extraction and analysis of proteins, chromatin from hepatomas, as well as from normal and regenerating liver was fractionated into rapidly and slowly sedimenting gradient components. Ten non-histone chromosomal proteins (NHCP) present in the tumors and ranging in molecular weight from 220,000 to 55,000, were absent from normal liver. Further, each rapidly growing tumor possessed more non-histone protein bands in the most rapidly sedimenting chromatin fractions than did corresponding, slowly growing tumor fractions. A number of single protein occurrences common only to normal liver and/or rapidly or slowly growing tumors were also found. In contrast, NHCP banding patterns of rapidly growing 70% hepatectomized rat liver were identical to those of non-dividing liver. Of particular interest was the finding that the prototypic "minimal deviation tumor" 9618A varied more in its NHCP-banding pattern when compared to liver than did those tumors which were rapidly growing and poorly differentiated. These studies represent an initial attempt at seeking NHCP which might be uniquely related to the malignant process.

Studies of nuclear proteins in the skeletal muscle of the cardiomyopathic Syrian hamster

Nonhistone nuclear proteins (NHNP) were isolated from the skeletal muscle of dystrophic hamsters and their respective paired controls. These proteins were extracted with phenol and fractionated by polyacrylamide gel electrophoresis. One-dimensional gel electrophoresis using either sodium-dodecylsulfate or isoelectrofocusing revealed quantitative changes between the two groups. An improved resolution using a two-dimensional system showed both quantitative and very limited qualitative differences. There are differences in proteins focusing at pH 5.0, molecular weight 55,000, in the dystrophic tissue. In addition proteins from dystrophic muscle focusing between pH 5.0 and 7.0, molecular weight 45,000, and proteins focusing between pH 7.0 and 9.0, molecular weights 35,000--45,000 and 60,000--70,000 were reduced as compared to the controls. There were no detectable differences in the electrophoretic patterns between the two groups of proteins derived from skeletal muscle homogenates. The differences in NHNP appear to be reflections of alterations in the nuclear composition of the dystrophic muscle cell. Some of these differences may represent changes secondary to the muscle disease. However, if NHNP interacting with DNA play a major role in the control of genetic expression, some of the manifestations of hamster dystrophy could be due to a different constitution of NHNP in the skeletal muscle.

Effects of polyamines on prostatic chromatin- and non-histone-protein-associated protein kinase reactions

Studies are presented on the influence of polyamines on prostatic chromatin- and non-histone-protein-associated protein kinase reactions involving both exogenous and endogenous substrates. The activities toward the model acidic protein substrate, dephosphophosvitin, were maximal at 160--200mM-NaCl (or -KCl or -NH4Cl). Under these conditions, spermidine and spermine added in concentrations up to 2mM were essentially without effect. However, without addition of NaCl to the medium, marked stimulation of these reactions was elicited by these polyamines at 1--2mM concentrations. The stimulatory effects were not due to non-specific changes in the ionic strength or to substitution of spermine for Mg2+, as maximal stimulation by 1 mM-spermine was observed only at optimal (2--4mM) Mg2+ concentrations. Qualitatively similar effects of polyamines were observed with enzyme preparations from the prostates of castrated rats, and with chromatin and non-histone-protein preparations from other tissues besides ventral prostate. When phosphorylation of endogenous non-histone proteins of the chromatin was measured, spermine stimulated both the initial rates and the final extent of transphosphorylation, even in the presence of optimal concentration of NaCl. By contrast, spermine or spermidine had no effect on the chromatin- and non-histone-protein-associated protein kinase reactions determined with lysine-rich histones as substrates. Chemically NN-dimethylated dephosphophosvitin was a less active substrate for the chromatin-associated protein kinase, but its phosphorylation was more markedly stimulated by spermine in comparison with unmodified dephosphophosvitin. These observations hint that the polyamine stimulations of the various protein kinase reactions may be due to effects on the conformations of the non-histone protein substrates rather than on the kinases themselves.

Age related alterations in the chromosomal proteins from human diploid fibroblasts

Histone and non-histone chromosomal proteins from human diploid fibroblasts of different in vitro ages were extracted and subjected to SDS--polycrylamide gel electrophoresis. The proteins were taken from cells maintained in three distinct culture states: preconfluent (log phase of growth), confluent (stationary phase of growth), and arrested (presumptive G0 phase). Age associated alterations in the incorporation of radioactive amino acids were detected in the fractionated proteins in every culture state but were less pronounced during the arrested state. Age related difference detected under growth conditions may reflect variations in the proliferative nature of the populations. Differences seen during the arrested state may be indicative of basic changes in the chromosomal protein complement of different age populations.

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.

Chromosomal proteins in hepatocarcinogenesis

The chromosomal proteins of rat liver were studied by SDS-gel electrophoresis during the process of nitrosomorpholine-induced hepatocarcinogenesis, in the primary hepatomas thus obtained, and in their metastases. It was found that an increased proteolytic activity was present in liver homogenates from carcinogen-fed animals which caused differences between the nonhistone chromosomal proteins of control and carcinogen-treated livers. These differences disappeared in the presence of the protease inhibitor PMSF. In the primary hepatomas slight quantative changes were observed: an increased amount of two proteins of 43000 and 63000 daltons molecular weight, respectively, and a decrease in the histone subfraction H 1 degrees. In the metastases both quantative and qualitative differences were detected: a strong decrease in the protein bands corresponding to the contractile proteins alpha-tubulin, beta-tubulin, and actin; an increased content of the 63000 dalton protein; the appearance of new proteins of approximately 60000, 90000, and 120000 daltons molecular weight, and the complete disappearance of histone H 1 degrees.

Changes in liver nuclear protein metabolism after a single dose of urethane to suckling mice

Treatment of 8-9-day-old C57BL/A mice with a single carcinogenic dose of urethane, at 1.2 mg/g body wt., resulted in an immediate decrease in liver DNA synthesis reaching a maximum at about 16-18 h after injection, the rate of synthesis returning to normal after 48 h. When the nuclear proteins were radiolabelled, the non-histone protein (NHP) fraction showed a significant decrease in specific activity 8-18 h after injection of urethane and slight increase in specific activity after 24 h. Histone and residual proteins did not show any significant change. The liver NHP were analysed by isoelectric focusing (IEF) and sodium dodecyl sulphate (SDS) electrophoresis in polyacrylamide gels. The latter technique failed to show any distinctive differences but IEF results indicated some quantitative and qualitative changes in protein content and synthesis were induced by the urethane treatment. The most noticeable change in the stained gels was an increase in a protein component having a pI of 7.35 and the appearance of new bands at pI's of 7.85 and 5.55 in the 18 h treated livers. However, the [3H]tryptophan labelling pattern indicated that this was not due to an increased synthesis of these components. 24 h after urethane there appeared to be an increased rate of synthesis of some of the major components of the mixture, particularly at the pI 5.65 region. Histone and residual protein fractions were also analysed by electrophoresis and showed no difference between treated and control livers.

Nuclear non-histone protein content of G0/G1 cells as related to growth fraction in mouse mammary tumors

In eight mouse mammary tumors with varying growth fractions DNA and non-histone nuclear protein (NHNP) were determined by absorption cytophotometry of Feulgen-Naphthol Yellow S stained, isolated cells. It was found that: 1. The mean NHNP content of cells with postmitotic DNA content (G0 + G1) increased with increasing growth fraction. 2. The mean NHNP content of S and G2 cells in the eight tumors did not vary significantly with growth fraction. 3. The frequency distributions of NHNP in G0/G1 cells were unimodal and right-skewed. The results are interpreted as follows: A) G0 cells differ from G1 cells by their lower content of NHNP. B). If it is assumed that the G0 and G1 compartments are arranged in series, the cells in the transition from G0 to late G1 may account for the unimodality and skewedness of the NHNP frequency distributions of postmitotic cells.

Serum stimulation of human fibroblasts: effect on non-histones of nuclear ribonucleoprotein and chromatin

In quiescent human fibroblasts stimulated to proliferate by fresh medium plus 15% serum, no changes were seen in the incorporation of 3H tryptophan into the protein of nuclear ribonucleoprotein during the first three hours following re-feeding. This was in contrast to non-histone chromosomal proteins where the incorporation increased by 90% within ten minutes. The density of the formaldehyde fixed nuclear ribonucleoprotein in CsCl was 1.43-1.44 g/ml and this also did not change following stimulation. The electrophoretic profile of the proteins of nuclear ribonucleoprotein on SDS gels exhibited a predominant band corresponding to a molecular weight of 44,000 closely trailed by a band at 47,000 and other bands at higher molecular weight. This pattern was not altered by serum stimulation and the same was true for the more complex electrophoretic profile of the chromatin proteins. Following a 10-minute pulse of 3H-tryptophan at ten minutes after stimulation, there was a selective increase in the labeling of non-histone chromosomal protein of molecular weight 59,000; no change was seen in the labeling of any protein of nuclear ribonucleoprotein.

Changes in the morphology of ribosomes in uterine epithelial cells under various hormonal conditions

The ultrastructural morphology of "free" cytoplasmic ribosomes of rat uterine epithelial cells was studied during diestrus, estrus, after ovariectomy, and after estradiol-17 beta administration to rats that were ovariectomized 1 to 25 weeks before hormone treatment. A change in size and contrast of ribosomes was observed concomitant with a transition from pre-existing monosomes to polysomes depending on the dose of estradiol and its route of application. In 3 weeks ovariectomized rats these changes in ribosomal granules take place at approximately the same time (30-45 min) when synthesis of "induced protein" was described biochemically. The morphological events after estradiol administration are discussed with respect to a primary site of estrogen action.

Secondary activities of diverse inhibitors potentiate the response of hamster embryo cultures to a mitotic stimulus

The reversal of the density dependent inhibition of replication (DDIR) of Syrian hamster embryo cultures by fresh medium containg 30-50% fetal bovine serum was poorly synchronized. There were two waves of DNA synthesis eight to nine hours apart, which by examination of autoradiograms of cultures pulse-labeled with 3H-thymidine, were found to involve 55% and 45% of the cell population. The second wave was found to be due to a subpopulation of epithelioid cells set in the predominantly fibroblastic cell cultures. Pretreatment of the DDIR cultures with hydroxyurea (HU) or arabinosyl cytosine (ara-C), followed by serum stimulation in the absence of the drugs, led to an enhancement of the synchrony. The effect increased with lengthening of the contact with antimetabolites, to a maximum after 20 hours' pre-exposure, and was in part due to the shortening of the GI phase of the epithelioid elements, and in part to increasing the synchrony of the fibroblastic cells. The resulting synchrony involved some 95% of the cells in simultaneous DNA synthesis after a median Gl period of 12 hours. The effect had no relationship to the role of HU and ara-C as specific inhibitors of DNA synthesis since the cultures were mitotically quiescent, and a similar enhanced response could be induced in DDIR cultures by prestimulation exposure lasting only two hours to cycloheximide (cyx), an inhibitor of protein synthesis. Pre-exposure of DDIR cultures to actinomycin D did not potentiate the cell response. A survey of the known secondary inhibitions caused by these three antimetabolites suggests that they all may cause deficiencies in the glycolipid or glycoprotein moieties of the cell surface. These observation provide a use ful, simple means of improving synchrony in these systems and may prove to be a useful probe for investigating the role of the cell surface in regulating cell replication.

Effect of cyclic AMP on chromatin-bound protein kinases in WI-38 fibroblasts stimulated to proliferate

When resting confluent monolayers of WI-38 fibroblasts are stimulated to proliferate by serum, DNA synthesis begins to increase between 15-18 h after stimulation. Chromatin-bound protein kinase activity increases in stimulated cells within 1 h after the nutritional change, concomitant with an increase in the template activity of nuclear chromatin. Addition of dibutyryl 3' : 5'-cyclic adenosine monophosphate (dibutyryl cyclic) AMP to the stimulating medium inhibits the entrance of cells into S phase, but only if dibutyryl cyclic AMP (5-10(-4) M) is added before the onset of DNA synthesis. The increases in chromatin template activity and in the chromatin-bound kinase activity are not inhibited by dibutyryl cyclic AMP in the early hours after stimulation, but are completely inhibited after the 5th hour from the nutritional change. This seems to indicate that in stimulated WI-38 cells, dibutyryl cyclic AMP exerts its inhibitory action somewhere between 5 and 12 h after stimulation. A number of protein kinase activities were extracted from chromatin with 0.3 M NaCl and partially resolved on a phosphocellulose column. Two distinct peaks of protein kinase activity appeared to be markedly increased in WI-38 cells 6 h after serum stimulation. Both peaks of increased activity were inhibited by dibutyryl cyclic AMP in vivo. Adenosine, sodium butyrate and adenosine 5'-monophosphate (AMP) do not inhibit the increase in DNA synthesis nor the increase in protein kinase activity. The results suggest that stimulation of cell proliferation in confluent monolayers of WI-38 cells causes an increase (or the new appearance) of certain chromatin-bound protein kinases, and that this increase is inhibited by cyclic AMP in vivo.

Activation of in vitro histone gene transcription from Hela S3 chromatin by S-phase nonhistone chromosomal proteins

Using a 3H-labeled single-stranded complementary DNA probe for detection of histone mRNA sequences (Thrall, CL., Park, WD., Rashba, HW., Stein, JL.,Mans, RJ., and Stein, GS.(1974), biochem. Biophys. Res. Commun. 61,1443) we have found that histone genes are transcribed in vitro from chromatin isolated from S-phase HeLa cells but not from chromatin isolated from G1-phase cells (Stein, G., Park W., Thrall, C., Mans, R., and Stein, J. (1975a), Nature (London) 2578 764; Stein, G., Park, W., Thrall, C., Mans, R., Steins, J.(1975b), Biochem. Biophys. Res. Commun. 63, 945). Utilizing the technique of chromatin reconstitution, we have recently demonstrated that it is the nonhistone chromosomal protein portion of the genome that is responsible for this difference in in vitro histone gene expression (Stein et al., 1975a). In order to determine whether this is attributable to some component of the S-phase chromosomal proteins that promotes the transcriptin of histone genes, a component of the G1 phase chromosomal proteins that inhibits histone gene transcription, or both, in the present study chromatin from both G1 and S-phase cells was dissociated and then reconstituted in the presence of various chromosomal proteins. The results of this study confirm that it is the nonhistone chromosomal proteins that are responsible for the cell cycle stage specific differences in in vitro histone gene expression and further show that these differences can be accounted for by a component or components of the S-phase nonhistone chromosomal proteins that has the capacity, when reconstituted in the presences of G1 phase chromatin, to render the histone genes transcribable in a dose-dependent fashion.

Subcellular distribution of DNA-binding proteins from cultured hamster fibroblasts

The distribution between nuclei and cytoplasm of DNA-binding proteins from growing NIL cells was studied. To obtain the subcellular fractions, cell monolayers or cells previously detached from the culture dish were treated with non-ionic detergent N onidet P-40. Proteins with affinity for DNA were isolated from nuclear or cytoplasmic fractions by chromatography on DNA-cellulose columns and were further analyzed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The results show that P8, one of the major components in the 0.15 M NaC1-eluted proteins, is found predominantly in the cytoplasmic fractions, whereas P6, the other main protein peak in this eluate, is more prominent in the nuclear fraction. Among the other proteins eluted at 0.15 M NaC1 from the DNA-cellulose column, P5 and P5' are detected in both nuclear and cytoplasmic fractions. All the other proteins in the 0.15 M NaC1 eluate are present almost exclusively in the cytoplasmic fraction. On the other hand, most of the proteins with higher affinity for DNA, eluted from the column at 2 M NaC1, are present in the nuclear fraction, although they are also detected in the cytoplasm in amounts similar to those observed in the nuclei.

Effects of prolonged quiescence on neuclei and chromatin of WI-38 fibroblasts

DNA synthesis and cell division are markedly reduced in confluent mono-layers of WI-38 diploid fibroblasts, but resume again if the depleted medium is replaced by fresh medium containing 10% fetal calf serum. If the cells are kept quiescent for prolonged periods of time after confluence (1 or 2 weeks), the fraction of cells that can be stimulated to proliferate by fresh serum decreases and the length of the prereplicative phase increases. The template activity of isolated nuclei decreases with increasing time of quiescence, and parallel changes occur in chromatin as evidenced by circular dichroism spectra and capacity to bind the intercalating dye, ethidium bromide. When WI-38 cells are stimulated to proliferate after prolonged quiescence, the increase in template activity of nuclei is delayed by several hours in comparison to cells stimulated after short periods of quiescence. Two distinct steps, both requiring serum, can be identified in the prereplicative phase of cells stimulated to proliferative after prolonged quiescence. We interpret the results as indicating that, during prolonged quiescence, WI-38 fibroblasts go into a deeper GO state from which they can be rescued only after prolonged stimulation. In this respect, prolonged quiescence may bear some resemblance to the process of aging.

Human nucleolar organizer chromosomes: satellite associations

The D and G group chromosomes from cultured human lymphocytes exhibit single and multiple satellite associations when stained with silver. Unlike earlier methods this simple and highly repeatable procedure shows physical attachments between satellited regions of various acrocentric autosomes. After studying 1,000 satellite associations from 118 normal individuals, it was found that both single and multiple associations occur with frequencies that correlate with random expectancies.

A serum protein associated with chromatin of cultured fibroblasts

Antibodies to chromatin proteins from human and mouse fibroblasts which have been cultured for more than 25 generations with heterologous serum show specificity for a homologous alpha-serum protein. These results indicate that among the chromatin-associated proteins there is one (or more) which has extensive structural similarity to a serum protein. This is the first direct evidence that a serumlike protein or proteins could be chromatin associated in vivo, as has been suggested by experiments showing in vitro interaction between DNA and certain serum proteins.

Selective synthesis and accumulation of nuclear non-histone proteins during carcinogenesis of the colon induced by 1, 2-dimethylhydrazine

The complement of nuclear non-histone proteins in epithelial cells of the colon is progressively altered during the course of carcinogenesis induced by 1, 2-dimethylhydrazine, until finally the nuclear proteins of tumor cells are easily distinguishable from those of the surrounding normal tissue. These changes in nuclear protein compostion reflect earlier differences in the rates of synthesis of individual protein species. Radioisotopic double-labeling experiments show that the synthesis of nuclear proteins of molecular weights 44,000 and 62,000 is selectively accelerated within 4 weeks after administration of the carcinogen, long before any morphological indications of malignancy appear.

Stimulated phosphorylation of non-histone phosphoproteins in SV-40 transformed WI-38 human diploid fibroblasts

Because the phosphorylation of non-histone proteins has been suggested to play a role in the regulation of eukaryotic gene transcription, we have compared the phosphorylation of these proteins in normal and SV-40 transformed WI-38 human diploid fibroblasts. The rate of phosphorylation was found to be roughly ten-fold higher in the transformed cells, and this striking difference could not be accounted for by either an increased rate of phosphate transport or by the synthesis of new species of non-histone proteins which subsequently become phosphorylated. To our knowledge this is the most dramatic alteration in non-histone protein phosphorylation ever described, and therefore may have important implications for our understanding of malignant transformation.

Effect of cell trypsinization on nuclear proteins of WI-38 fibroblasts in culture

When resting confluent monolayers of WI-38 fibrolasts are trypsinized and replated at a lower density they are stimulated to proliferate again with an interval of 18 hours between replating and the onset of DNA synthesis. Trypsinization of resting cells causes a 40% loss of nuclear proteins as well as of cytoplasmic proteins. The amount of nuclear proteins remains low for the first six hours after the cells have been replated and then it increases rapidly, reaching the same level of non-trypsinized resting cells by ten hours after plating. The proteins that are lost from the nucleus immediately after trypsinization are chromatin-associated proteins and most of them are non-histone chromosomal proteins, although a modest loss of histones cannot be ruled out. The loss of non-histone chromosomal proteins from cells that have been trypsinized causes changes in the structure of chromatin that can be detected by circular dichroism and by viscosity measurements. These results show that cell trypsinization causes an extensive loss of proteins from chromatin and that the loss is restored only several hours after the cells have been replated at a lower density.

Changes in template activity and structure of nuclei from WI-38 cells in the prereplicative phase

Quiescent confluent monolayers of WI-38 fibroblasts were stimulated to proliferate by either adding 10% fetal calf serum or by trypsinization and replating at lower density. The length of the prereplicative phase was 12 hr after serum stimulation and 18 hr after trypsinization and replating at lower density. Nuclei were isolated from WI-38 cells at different time intervals after either type of stimulation and their template activity, circular dichroism spectra, and ability to bind ethidium bromide were investigated. All these parameters were similarly increased after either type of stimulation. However, these changes, like the onset of DNA synthesis, were delayed 6 hr in cells trypsinized and replated at lower density. While there were no detectable changes in nuclear protein content after serum stimulation, at least 40% of nuclear protein, mostly nonhistone chromosomal proteins, were lost after trypsinization. The amount of nuclear proteins returned to prestimulation levels only 6-8 hr after replating. These data seem to suggest that nonhistone chromosomal proteins lost by trypsinization are essential for the entrance of WI-38 cells into the "prereplicative phase".

Effect of chromosomal proteins extractable with low concentrations of NaCl on chromatin structure of resting and proliferating cells

When quiescent WI-38 cells are stimulated to proliferate by nutritional changes, the chromatin of stimulated cells shows an increased ellipticity in circular dichroism spectra and an increased ability to bind ethidium bromide. The differences between the chromatins of quiescent and stimulated cells are abolished if both chromatins are treated with 0.25 M NaCl. However, when salt-treated chromatins are reconstituted by dialysis agains 10 mM Tris-HCl, the difference in circular dichroism spectra and ethidium bromide binding re-appear. Furthermore, addition of the 0.25 M NaCl extract from chromatin of stimulated cells to chromatin of quiescent cells causes an increased ellipticity in circular dichroism spectra similar to that of stimulated chromatin. Since only proteins (mostly nonhistones) are detectable in the 0.25 M NaCl extract, these results strongly suggest that the chromosomal proteins extractable with low concentrations of salt are responsible for the functional and structural changes occurring in chromatin of WI-38 cells stimulated to proliferate.