Nonhistone protein BA is a glutathione S-transferase localized to interchromatinic regions of the cell nucleus.

A DNA-binding nonhistone protein, protein BA, was previously demonstrated to co-localize with U-snRNPs within discrete nuclear domains (Bennett, F. C., and L. C. Yeoman, 1985, Exp. Cell Res., 157:379-386). To further define the association of protein BA and U-snRNPs within these discrete nuclear domains, cells were fractionated in situ and the localization of the antigens determined by double-labeled immunofluorescence. Protein BA was extracted from the nucleus with the 2.0 M NaCl soluble chromatin fraction, while U-snRNPs were only partially extracted from the 2.0 M NaCl-resistant nuclear structures. U-snRNPs were extracted from the residual nuclear material by combined DNase I/RNase A digestions. Using an indirect immunoperoxidase technique and electron microscopy, protein BA was localized to interchromatinic regions of the cell nucleus. Protein BA was noted to share a number of chemical and physical properties with a family of cytoplasmic enzymes, the glutathione S-transferases. Comparison of the published amino acid composition of protein BA and glutathione S-transferases showed marked similarities. Nonhistone protein BA isolated from saline-EDTA nuclear extracts exhibited glutathione S-transferase activity with a variety of substrates. Substrate specificity and subunit analysis by SDS polyacrylamide gel electrophoresis revealed that it was a mixture of several glutathione S-transferase isoenzymes. Protein BA isolated from rat liver chromatin was shown by immunoblotting and peptide mapping techniques to be two glutathione S-transferase isoenzymes composed of the Yb and Yb' subunits. Glutathione S-transferase Yb subunits were demonstrated to be both nuclear and cytoplasmic proteins by indirect immunolocalization on rat liver cryosections. The identification of protein BA as glutathione S-transferase suggests that this family of multifunctional enzymes may play an important role in those nuclear domains containing U-snRNPs.

Subcellular localization of DNA-binding protein BA by immunofluorescence and immunoelectron microscopy.

Nonhistone protein BA has been shown to decrease in amount in the chromatin of growth- stimulated normal rat liver (Yeoman et al. 1975. Cancer Res. 35:1249-1255) and in mitogen-stimulated normal human lymphocytes (Yeoman et al. 1976. Exp. Cell Res. 100:47- 55.). Subsequently, protein BA was purified and was shown to prefer to bind to double- stranded A-T-rich DNAs (Catino et al. 1978. Biochemistry. 17:983-987.). Immunization of rabbits with highly purified protein BA has resulted in the production of a specific antibody. A specific immunoreactivity for chromosomal protein BA has been demonstrated by immunoelectrophoresis and double antibody immunoprecipitation analysis with rabbit anti-BA immunoglobulin and IgG fractions. Light microscope examination of normal rat liver crysections by the indirect immunofluorescence procedure has demonstrated a cytoplasmic as well as a nuclear localization for protein BA with a pronounced perinucleolar fluorescence. Immunoelectron microscopy employing the peroxidase antiperoxidase method of antigen localization has confirmed the immunofluorescence data and has show a heterochromatin localization for protein BA. The relationship of the localization of protein BA to gene control in quiescent cells or to configurations of heterochromatin as well as the marked reduction in the amounts of protein BA which occur in stimulated growth states remains to be defined.

Antibodies to a nucleolar protein are localized in the nucleolus after red blood cell-mediated microinjection.

To determine whether red blood cell-mediated microinjection of antibodies can be used to study nuclear protein localization and function, we microinjected antibodies that have been shown to react specifically with nucleolar acidic phosphoprotein C23 into Walker 256 cells. The intracellular distribution of microinjected anti-C23 antibodies and preimmune immunoglobulins were determined by immunofluorescence. At 3 h after microinjection, affinity-purified anti-C23 antibodies were localized in the cytoplasm and nucleolus. At 17 h after microinjection, the affinity-purified antibody was localized to those nucleolar structures previously shown to contain protein C23. Furthermore, the antibody remained localized in the nucleolus for at least 36 h after microinjection. In contrast to the results obtained with specific antibodies, preimmune immunoglobulins remained in the cytoplasm 36 h after microinjection. These results indicate that red blood cell-mediated microinjection of antibodies can be used to study nucleolar and nuclear antigens.

Rate of growth and extent of differentiation reflected by cytoplasmic proteins and antigens of human colon tumor cell lines.

The cytosolic proteins and antigens of 11 human colon tumor cell lines were examined with respect to their rate of growth and state of differentiation. Coomassie blue-stained protein analysis of sodium dodecyl sulfate-containing polyacrylamide gels revealed protein bands at Mr 30,000, 31,000, and 58,000, which were characteristic of slower growing and more differentiated cell lines. More rapidly dividing and disdifferentiated colon cell lines lacked the Mr 30,000 and Mr 58,000 bands; instead, they produced a single protein band that ran between the Mr 30,000 and Mr 31,000 positions on the gel. Western transfer analysis of cytoplasmic antigens further subdivided the 11 cell lines into 3 separate categories. Slowly growing and more differentiated lines produced a Mr 52,000 antigen. Intermediate lines, with respect to growth rate and state of differentiation, produced a Mr 38,000 antigen. The rapidly growing and highly disdifferentiated cell lines contained three cytosolic antigens with molecular weights of 37,000, 39,000, and 48,000. These criteria made it possible to classify these 11 human colon tumor tissue culture cell lines into 3 groups which reflect their state of growth activity and degree of differentiation.

Occurrence of cytosolic protein and phosphoprotein changes in human colon tumor cells with the development of resistance to mitomycin C.

The cytosolic proteins and phosphoproteins of a mitomycin C-sensitive cell line were examined as progressively greater doses of mitomycin C were administered over a period of 44 weeks. Resistance of the human colon carcinoma cell line increased from a 50% inhibitory concentration of 1 to 6 microM over this time period. Changes in cytosolic protein patterns included increases in the amounts of three proteins with molecular weight X 10(-3)/apparent isoelectric point (Mr/pl) values of 56/6.2, 37/7.3, and 27/6.1. Analysis of in vitro 32P-labeled phosphoprotein patterns revealed reductions in the amounts of four proteins with Mr/pl values of 42/6.3, 40/6.7, 31/6.3, and 25/6.1. One increase was detected in a phosphoprotein with a Mr/pl value of 33/6.1. These changes in cytosolic components paralleled the development of resistance to mitomycin C and may reflect changes in the clonal composition of the cell line as it becomes progressively more resistant to mitomycin C or changes in critical proteins or enzymes involved in the activation or biotransformation of the drug.

Chromatin-associated glycoproteins of normal rat liver and Novikoff hepatoma ascites cells.

Glycoproteins were demonstrated in the 0.6 M NaCl extract of chromatin of normal liver and Novikoff hepatoma cells by periodic acid-Schiff staining of sodium dodecyl sulfate-polyacrylamide gels. In chromatin extracts of Novikoff hepatoma cells, six major periodic acid-Schiff-positive bands coincident with Coomassie Blue-stained protein bands were found with molecular weights of 30,000, 54,000, 64,000, 75,000, 104,000, and 127,000. A corresponding extract from normal rat liver chromatin revealed the presence of four major periodic acid-Schiff-positive bands that migrated with protein bands at molecular weights of 16,000, 30,000, 54,000, and 75,000. The glycoproteins of these extracts contained either mannose or alpha-D-glucose, fucose, and N-acetylglucosamine as shown by the specificity of lectins in affinoelectrophoresis. One of the glycoproteins detected by affinoelectrophoresis was very basic.

Early and late changes in nonhistone chromatin proteins accompanying rat liver regeneration.

Chromatin was isolated from 0.025 M citric acid nuclei of regenerating rat liver at 1,5,18,24, and 48 hr posthepatectomy. The total protein to DNA ratios did not change significantly during this time period. However, 2-dimensional polyacrylamide gel electrophoresis of nonhistone proteins of "Chromatin Fraction II" revealed changes in the amounts of some protein spots. As early as 1 hr after hepatectomy, decreases in size and intensity were detected for protein spots Bp, B24, C18, and CQ, and increases were detected for protein spots CBL and C13. Late changes in size and intensity were found for protein spots BA and CN, which decreased in size and intensity 5 hr after hepatectomy. The spot densities and sizes for most of the nonhistone proteins underwent no significant changes in the course of liver regeneration. The increases and decreases observed in specific protein spots represent an ordered series of changes in a limited number of nonhistone proteins.

Differences in nucleolar antigens of rat liver and Novikoff hepatoma ascites cells.

Antisera to nucleoli of Novikoff hepatoma ascites and normal rat liver cells were produced in rabbits by injection of whole, isolated nucleoli. These antisera have been used to compare the nucleolar antigens that were partially fractionated by differential solubilization from nucleoli. Fourteen antigens were detected by these antisera; ten of these antigens were detected by both antisera. Ouchterlony double diffusion analysis of soluble extracts from normal rat liver and Novikoff hepatoma ascites nucleoli and fetal rat liver nuclei provided evidence for antigens found only in liver extracts, only in tumor extracts, or only in tumor and fetal extracts. Antisera preabsorbed to remove antibodies to common antigens of liver and tumor provided confirmatory evidence for one nucleolar antigen in liver that was not found in tumor or fetal rat liver, one antigen in tumor that was not found in adult or fetal rat liver, and three antigens in both tumor and fetal rat liver that were not found in adult rat liver. In addition, the antitumor nucleolar antiserum preabsorbed with liver nuclear extracts still produced positive nucleolar fluorescence in Novikoff hepatoma ascites cells but not in liver cells. Conversely, anti-liver nucleolar antiserum preabsorbed with tumor nucleolar extracts did not produce detectable tumor nucleolar fluorescence but did produce positive fluorescence in liver nucleoli.

Identification of endogenous inhibitory growth factors from a human colon carcinoma cell line.

A line of human colon carcinoma cells, designated MOSER, was established which synthesized tumor-inhibitory factor (TIF) and transforming growth factor (TGF) activity. Both activities were found in serum-free conditioned medium and in cell extracts. The activities coelute on Bio-Gel P-10 in acetic acid, but can be completely separated by reverse-phase high-pressure liquid chromatography. The TIF and TGF activities were acid and heat stable and were sensitive to trypsin and dithiothreitol. MOSER cell TIF prevented the anchorage-independent growth of the more differentiated colon carcinoma cell lines tested but did not affect the less differentiated lines. Using anchorage-dependent growth conditions, the effect of TIF appeared to be noncytotoxic and partially reversible. Purified TGF stimulated the growth of normal rat kidney fibroblasts and the slow-growing CBS colon carcinoma cell line but did not stimulate MOSER cell growth. MOSER cells contain both positive (TGF) and negative (TIF) factors with relative concentrations that may be important parameters in the regulation of cell growth.

Antigenically active nonhistone chromatin proteins in cancer cells.

Two-dimensional polyacrylamide gel electrophoresis shows that in nuclei of Novikoff hepatoma ascites cells there are approximately 75 proteins in the chromatin fraction soluble in 3 M NaCl:7 M urea. Dialysis of this fraction to an ionic strength of 0.15 produces a soluble fraction and a precipitate. The proteins in the soluble fraction have been reported to be active in gene control. Antibodies to the soluble fraction distribute diffusely throughout the nucleus, and antibodies to the precipitate localized primarily in the nucleolus and the nuclear ribonucleoprotein network. The nucleolar proteins differ from the extranucleolar proteins in antigenicity and labeling patterns. The development of methods for isolation, purification, and identification of nuclear proteins provided the opportunity for analysis of chromatin antigens in tumor cells. Utilizing two-dimensional preparative polyacrylamide gel techniques as well as conventional procedures, several nuclear proteins have been isolated in electrophoretically homogeneous states including protein A-24, a histone-like nonhistone protein; C-14, a protein that stimulates nucleolar RNA polymerase; and a chromatin antigen soluble in 3 M NaCl:7 M urea that remains soluble after dialysis to 0.15 M NaCl to precipitate the histones and the DNA. This antigen has been found in the chromatin of both the Novikoff hepatoma and the Walker 256 carcinosarcoma but not in the chromatin of either normal or regenerating liver. It is a nonhistone nuclear protein as indicated by its amino acid analysis in which the ratio of the number of acidic to basic amino acids is approximately 1.4. Further studies are in progress on the function and structure of this chromatin protein. As an approach to analysis of relative rates of synthesis of this antigen and otherproteins, the products of translation of messenger RNA of Novikoff hepatoma and normal liver are being analyzed by autoradiography of two-dimensional electrophoretic gels.

Cellular growth response to epidermal growth factor in colon carcinoma cells with an amplified epidermal growth factor receptor derived from a familial adenomatous polyposis patient.

The receptor binding and cellular growth responses to exogenous epidermal growth factor (EGF) were studied using the DiFi cell line established from a familial adenomatous polyposis patient. The number of cell membrane EGF receptors on DiFi cells, as measured by competitive radioligand binding assays and Scatchard analysis of 125I-EGF binding isotherms, was calculated to be 4.8 x 10(6) receptors/cell. An acid prewash step performed prior to ligand binding assays did not reveal additional receptor numbers. A single, low-affinity receptor population was identified by Scatchard analysis, with an apparent Kd of 4.6 nM. This result was confirmed by radioligand binding studies performed in the presence and absence of the receptor-antagonist monoclonal antibody 528 IgG that binds predominantly to the low-affinity form of the EGF receptor. DiFi cells at 50-60% confluence, when exposed to 50 nM exogenous EGF, exhibited a rapid but partial (30%) reduction in their cell membrane-associated receptor, characteristic of sequestration. Exposure of DiFi cells to 50 nM EGF for longer periods of time (4 h) did not result in any further reduction in EGF-receptor number. The cellular growth response of DiFi cells to exogenous EGF was studied in monolayer cultures as well as in a soft agarose assay. Inhibition of soft agar colony formation was observed at exogenous EGF concentrations greater than 1.7 nM, and inhibition of monolayer growth occurred at EGF concentrations greater than 1 nM. In immune complex kinase assays, the DiFi receptor showed similar specific activity to that from the well-characterized A431 cell line. Additionally, phosphorylation of the receptor on tyrosine was qualitatively similar to that of A431 cells, further suggesting that the DiFi receptors identified by EGF-binding studies were biologically functional.

Transforming growth factor-alpha production and autoinduction in a colorectal carcinoma cell line (DiFi) with an amplified epidermal growth factor receptor gene.

The DiFi colorectal carcinoma cell line, derived from a patient with familial adenomatous polyposis, was examined for gene expression and production of the autocrine growth factor transforming growth factor alpha (TGF-alpha) and for epidermal growth factor receptor (EGFR) gene expression and gene copy number. DiFi cells expressed TGF-alpha transcripts as identified on Northern (RNA) blots. Addition of TGF-alpha (10 ng/ml) or EGF (10 ng/ml) to DiFi cell cultures (lacking EGF or serum) up-regulated DiFi cell basal TGF-alpha mRNA levels, suggesting that autoinduction of TGF-alpha occurs in these cells. DiFi cell cultures in log phase growth secreted measurable amounts of TGF-alpha (347 pg/10(6) cells/24 h) into their culture medium, as determined by radioimmunoassay. DiFi cells showed strong overexpression of the EGFR gene on Northern blots relative to three other colon cancer cell lines examined. Immunoperoxidase staining showed enhanced EGFR expression in a cell subpopulation among the original (uncultured) ascitic fluid cells from which the DiFi cell line was established. This cell subpopulation was observed to expand dramatically between passages 1 and 25. Immune complex kinase assay of DiFi cells showed that EGFR were functional as determined by their ability to autophosphorylate. The EGFR gene in these cells was not found to be rearranged or genetically altered using Southern blot analysis. Dot blot analysis of DiFi cell DNA revealed EGFR gene amplification in the range of 60-80 copies/cell, which is approximately twice the copy number seen in A-431 epidermoid carcinoma cells. To our knowledge DiFi cells represent the first example of EGFR gene amplification in a colorectal adenocarcinoma. Because DiFi colorectal cancer cells uniquely show production and auto-induction of TGF-alpha in addition to amplification and overexpression of the EGFR gene, these cells represent a valuable tool for studying the role(s) of the EGFR in the regulation of tumor cell growth.

An improved procedure for the 'dot immunobinding' analysis of hybridoma supernatants.

The recently introduced dot immunobinding assay is well suited as a rapid and sensitive procedure for the analysis of those hybridoma clones that are producers of a specific antibody. We present a modification of the dot immunobinding assay which utilizes a single nitrocellulose sheet for up to 96 assays. By using a single nitrocellulose sheet, sample manipulation is greatly reduced, reaction conditions can be better standardized and a comparison of background reactivities is provided. Results are presented which demonstrate the effectiveness of this modified dot immunobinding assay.

Transfer of proteins from acrylamide gels to nitrocellulose paper after silver stain detection.

A method is described for the silver staining of polyacrylamide gels and transfer to nitrocellulose sheets which couples the advantages of silver stain detection sensitivity with efficient transfer to nitrocellulose sheets. Using this procedure, a detection sensitivity of 10 ng was achieved while retaining a transfer efficiency for most proteins that is equivalent or better than methodology that does not permit prior visualization of protein. When coupled with the use of an acrylamide template, this procedure permits protein detection, simultaneous transfer of a large number of cored protein products from many one- or two-dimensional polyacrylamide gels to a single sheet of nitrocellulose, and retention of immunoreactivity. Prior detection, simultaneous transfer, and retention of immunoreactivity provide a substantial number of biochemical and technical advantages.

Comparison of immunoelectrophoretic techniques for the analysis of cytosol antigens.

Crossed immunoelectrophoresis was employed in the analysis of cytosol antigens of a human colon adenocarcinoma cell line. Other immunoelectrophoretic techniques - crossed immunoelectrophoresis in the presence of Ampholine (incorporation of Ampholine in the first dimension electrophoresis gel), crossed immunotachophoresis and crossed immunoelectrofocusing - were also investigated ad compared with crossed immunoelectrphoresis in an attempt to select the optimal immunoelectrophoretic system for the analysis of cytosol antigens. The results of these comparisons showed that each technique offered its own advantages. The maximum number of immunoprecipitin peaks were detected by crossed immunoelectrophoresis. Both crossed immunoelectrophoresis in the presence of Ampholine and crossed immunotachophoresis provided the greatest resolution of electrophoretically similar antigens. Crossed immunoelectrofocusing provided IP values for these antigens. It was concluded that these techniques, when employed in combination, provided a more complete analysis of the complex cytosol antigenic mixture and may be useful when employed in combination to other antigen-antibody systems.

Characterization of two monoclonal antibodies that recognize high molecular weight colon antigens.

Two monoclonal antibodies, M32-1 (Ig-G1,k) and M39-2 (IgM,k), were prepared against high molecular weight (greater than 650 kDa) cytosol antigens (HMW-CA) of a human adenocarcinoma of the colon (GW-39). These monoclonal antibodies appeared to bind to determinants on two distinct high molecular weight colon antigens. One was shown by gel filtration to be a 650 kDa glycoprotein (gp650) containing at least one 300 kDa antigenic subunit (gp300). The other antigen eluted from a S-300 Sephacryl column at a molecular size of 600 kDa (gp600) and was resistant to dissociation by detergents, salts and chaotropic agents. The differential sensitivity of these two high molecular weight glycoproteins to treatment with trypsin, chondroitinase ABC, HNO2, endoglycosidase H and 2-mercaptoethanol suggest that monoclonal antibodies M39-1 and M39-2 react with distinct antigenic determinants located on two separate, high molecular weight, colon antigens. Since these antigens are only detected in extracts prepared from normal mucosa, well-differentiated tumors or margins of well-differentiated tumors, their expression appears to be related to a well-differentiated cell phenotype.

Different epidermal growth factor growth responses and receptor levels in human colon carcinoma cell lines.

The growth response to epidermal growth factor (EGF) and the numbers and types of EGF receptors were studied in three human colon tumor cell lines from each of two groups of cell lines that differ markedly in their growth properties and extent of differentiation. Aggressively growing and poorly differentiated colon cells (group I) did not respond to EGF alone, while less aggressively growing and more differentiated cells (group III) responded with increased growth when EGF was added to their chemically defined, serum-free medium. The average number of EGF receptors (EGF-R) measured at the surface of group III cell lines by radioligand binding assays, was eight-fold higher than that measured for group I cell lines. These observations provide evidence for possible autocrine mechanisms that maintain available EGF-R levels in more differentiated group III colon tumor cells and down-regulate EGF-R levels in group I colon tumor cells.

Sensitivity of nuclear c-myc levels and induction to differentiation-inducing agents in human colon tumor cell lines.

Six human colon tumor cell lines were analyzed for their constitutive levels of the c-myc protein. The nuclear proto-oncogene, c-myc, was detected as an expressed product in all of the human colon tumor cell lines analyzed. The poorly differentiated cell lines HCT116, RKO and C showed c-myc levels that averaged 2-fold greater than their well-differentiated counterparts, i.e., GEO, CBS and FET. When c-myc levels and responses to serum induction were analyzed in the presence of inducers of differentiation, i.e., dimethylformamide, retinoic acid, sodium butyrate and TGF-beta, distinct patterns of sensitivity and resistance emerged. Nuclear c-myc levels were reduced in all the colon cell phenotypes treated with dimethylformamide or sodium butyrate. Only the well-differentiated human colon tumor cell lines were responsive to transforming growth factor-beta. Only one of the human colon tumor cell lines (GEO) responded to retinoic acid. Increased levels of c-myc protein were found to correlate well with greater growth rates and with poor differentiation class. Similarly, a parallel sensitivity to down-regulation of c-myc levels and attenuation of c-myc induction curves for inducers of differentiation were observed in growth sensitive human colon tumor cell lines.

Characterization and reactivity of a monoclonal antibody that recognizes a 76 kilodalton human colon tumor antigen.

A monoclonal antibody (MAb 76) was produced by immunizing mice with a soluble cytoplasmic protein fraction from a human adenocarcinoma of the colon. MAb 76 showed specific immunoreactivity against a 76 kDa protein in immunoblot studies using total colon tumor cytosol proteins. Immunoprecipitation of phosphorylated cytosolic protein products with MAb 76 and subsequent analysis on SDS containing polyacrylamide gels revealed a single 38 kDa band, indicating that the 76 kDa antigen is associated with a 38 kDa phosphoprotein species. Indirect immunofluorescence analysis of primary tumor specimens and human colon tumor cell lines showed positive immunoreactivity with 6/7 human colon adenocarcinoma tissues and 15/18 human colon tumor cell lines. MAb 76 was unreactive with normal colon, liver and lung specimens from human, mouse and hamster. The epitope-bearing monomer detected by MAb 76 is immunologically conserved in a high percentage of colon tumor cells and tissues and may represent a cellular product that is characteristic of the transformed colon cell phenotype.

An autocrine model for cell- and matrix-associated fibroblast growth factor.

While the prototypic fibroblast growth factors (FGFs) are known to have important roles in the stimulation of cell proliferation and angiogenesis, their lack of a conventional secretory signal peptide sequence has presented a challenge to our understanding of the mechanisms by which they are released from cells and subsequently engaged at cell-membrane-localized receptors. The autocrine and paracrine function of polypeptide growth factors has frequently involved the delivery of a large, transmembrane precursor molecule to the cell surface and its subsequent proteolytic release. Through the use of chimeric growth factors, and enhanced proteolytic release of cell-associated populations of growth factor precursors, it has been established that cell-associated growth factor populations can exhibit autocrine and paracrine activity. This commentary will draw upon the potential role of cell- and matrix-associated FGF populations to develop a model for the release of prototypic FGFs from low-affinity sites on the cell surface, or from extracellular matrix, to high-affinity, cellular receptors. It is proposed that cell- and matrix-associated FGF may exhibit autocrine function and provide the capacity to be regulated in a variety of normal and transformed cell systems. It is also proposed that growth factor delivery mechanisms involving cell- and matrix-associated ligand populations represent a specialized form of regulated delivery. This specialized delivery mechanism may confer autocrine advantages upon a variety of growth factor family gene products.