Low frequency of p53 gene mutation in tumors induced by aflatoxin B1 in nonhuman primates

Aflatoxin B1 has been suggested as a causative agent for a G to T mutation at codon 249 in the p53 gene in human hepatocellular carcinomas from southern Africa and Qidong in China. To test this hypothesis, nine tumors induced by aflatoxin B1 in nonhuman primates were analyzed for mutations in the p53 gene. These included four hepatocellular carcinomas, two cholangiocarcinomas, a spindle cell carcinoma of the bile duct, a hemangioendothelial sarcoma of the liver, and an osteogenic sarcoma of the tibia. None of the tumors showed changes at the third position of codon 249 by cleavage analysis of the HaeIII enzyme site at codon 249. A point mutation was identified in one hepatocellular carcinoma at the second position of codon 175 (G to T transversion) by sequencing analysis of the four conserved domains (II to V) in the p53 gene. These data suggest that mutations in the p53 gene are not necessary in aflatoxin B1 induced hepatocarcinogenesis in nonhuman primates. The occurrence of mutation in codon 249 of the p53 gene in selective samples of human hepatocellular cancers may indicate involvement of environmental carcinogens other than aflatoxin B1 or that hepatitis B virus-related hepatitis is a prerequisite for aflatoxin B1 induction of G to T transversion in codon 249.

Alterations in tumor angiogenesis associated with stable expression of the HIV tat gene

Recent evidence suggests that the human immunodeficiency virus type 1 (HIV) trans-activator gene (tat) has transforming properties and may be a causative factor in the development of certain types of cancers, in particular Kaposi's sarcoma (i.e., Vogel J. et al. Nature 335:606-611, 1988). To help elucidate the potential role or roles of the HIV tat gene in neoplastic transformation, cell lines were constructed that constitutively express a functional tat gene product. HeLa cells were coelectroporated with two plasmids, one containing the HIV tat gene in an expression cassette and another containing the dominant selectable marker gene xanthine guanine phosphoribosyltransferase (XGPRT). After XGPRT selection, single-cell clones that expressed a functional tat protein were identified by measuring chloramphenicol acetyltransferase (CAT) activity after electroporating a plasmid containing the CAT gene transcriptionally controlled by HIV trans-activation-responsive region (tar). Phenotypic alterations resulting from the expression of tat were then determined. Control cells and tat-expressing cells grew at similar rates in culture. However, when grown as tumors in nude mice, tat-expressing cells produced a lower percentage of tumors, and the tumors that were produced either regressed, stopped growing, or grew at a very reduced rate compared with cells not expressing tat. These differences may have resulted from a tat-associated reduction in neovascularization in the tumors. A comparison of total cellular proteins by two-dimensional polyacrylamide gel electrophoresis indicated only one reproducible alteration in a polypeptide of approximately 44 kDa and pl of approximately 6.2 associated with tat expression. These cells may be very useful in future in vitro and in vivo studies designed to examine the effects of HIV tat on endothelial and vascular smooth-muscle cells and the role of tat in the etiology of Kaposi's sarcoma.

The rat liver epithelial (RLE) cell protein database

Computer databases of rat liver epithelial (RLE) cellular polypeptides have been established using high resolution two-dimensional gel electrophoresis and computer-assisted analysis. Databases have been constructed utilizing both [35S]methionine- and [32P]orthophosphate-labeled as well as silver-stained polypeptides from normal RLE cells. The RLE database, which contains both qualitative and quantitative annotations, includes experiments with normal, chemically and oncogene transformed as well as spontaneously transformed cell lines. A total of 2537 [35S]methionine-labeled polypeptides from whole cell lysates (1920 acidic and 617 basic, separated in the first dimension using isoelectric focusing and nonequilibrium pH gradient electrophoresis, respectively) were analyzed and databases constructed using the Elsie 5 gel analysis system. To increase the "viewing window" and hence the usefulness of the RLE database, subcellular fractionation of whole cell preparations was performed and high resolution two-dimensional maps of the individual subcellular components were constructed. Databases representing 1229 cytosolic, 1539 acidic and 674 basic nuclear, 1746 membrane-associated, 415 mitochondrial, 773 in vitro translated and 350 phosphoproteins were established from these maps. The RLE databases contain the Elsie 5 identification number, protein name (if known), molecular weight and pI information, quantitative and spot shape data, and specific information regarding transformation-sensitive, growth-related (exponentially proliferating versus confluent) cell populations as well as those polypeptides modulated by specific growth factors. The RLE databases represent initial efforts toward the establishment of comprehensive databases of rat liver proteins and serve as a vital resource for on-going as well as future studies regarding the regulation of growth and differentiation as well as transformation of RLE cells.

Altered responsiveness of rat liver epithelial cells to transforming growth factor beta 1 following their transformation with v-raf

The effects of transforming growth factor beta (type 1) (TGF-beta 1) on DNA synthesis, cell proliferation, and protein synthesis were examined in a series of v-raf-transformed rat liver epithelial (RLE) cells, which exhibit a range of transformed phenotypes. All of the transformed cells were relatively resistant to the growth-inhibitory effects of TGF-beta 1, compared to normal RLE cells and control cells infected with a helper virus. The more tumorigenic cell lines had very few surface receptors for TGF-beta 1 and showed no increase in the secretion of a number of specific proteins, including fibronectin, following TGF-beta 1 treatment. In contrast, the more normal-looking, less tumorigenic v-raf-transformed cells bound similar amounts of TGF-beta 1 as normal RLE and control cells and showed a similar pattern of TGF-beta 1-stimulated protein secretion. These findings suggest that the effects of TGF-beta 1 on cell proliferation and on the expression of certain secreted proteins are mediated through different mechanisms. Following transformation of RLE cells with v-raf, the signalling pathways controlling TGF-beta 1 growth inhibition are perturbed, while those involved in regulating the synthesis of certain proteins may remain intact. Thus, the escape from the various distinct biological effects of TGF-beta 1 may be an important stage in the progression of neoplastic transformation of RLE cells in vitro.

Two-dimensional electrophoretic analysis of hepatitis-associated polypeptides in liver of LEC rats developing spontaneous hepatitis

High-resolution two-dimensional polyacrylamide gel electrophoresis in combination with silver staining was used to analyze between 800 and 1000 cytosolic and particulate polypeptides from age-matched livers of normal male Long-Evans rat with Agouti coat color (LEA) and Long-Evans rat with Cinnamon-like coat color (LEC) rats with hereditary trait of hepatitis at ages long before, immediately prior to, and just after the onset of hepatitis. Although the electrophoretic patterns of polypeptide expression were very similar with respect to the overall spot patterns, a number of polypeptides which differed either qualitatively or quantitatively were noted. Two constitutively expressed cytosolic polypeptides, P29.5 (Mr 29.5 kDa/pI 6.73) and P30 (30 kDa/6.70), were not detected in livers of LEC animals at any age. In the normal LEA rats both P29.5 and P30 were detected as early as one day after birth and both were expressed at similar concentrations at all ages. In the LEC rats P30-C (30 kDa/6.68) was constitutively expressed in close proximity to the expected position of P30, and P30-C was not detected in the LEA rats. By means of non-equilibrium pH gradient electrophoresis two relatively basic polypeptides were detected in the LEC rats. P18ne was detected immediately prior to and P27ne immediately after the clinical manifestation of hepatitis. Experiments in F1 backcross ([LEA x LEC] x LEC) animals, however, failed to demonstrate any genetic link between either the expression or lack of expression of P29.5, P30, P30-C, or P18ne and hepatitis development. P27ne was detected in all backcross animals exhibiting hepatitis, but was never observed in LEC rats prior to the onset of hepatitis. Although we were unable to identify any unique loss of expression of polypeptides which are genetically linked to hepatitis susceptibility in LEC rats, specific subsets of quantitatively modulated polypeptides were detected.

Regulation of alpha-smooth muscle actin and other polypeptides in proliferating and density-arrested vascular smooth muscle cells

We have examined alpha-smooth muscle actin (alpha-SM actin) protein and mRNA levels in proliferating and density-arrested rabbit vascular smooth muscle cells (SMC) and also studied overall polypeptide synthesis in these cells by two-dimensional (2-D) gel electrophoresis. Of the approximately 1,000 cellular polypeptides resolved by 2-D gel analysis, we consistently detected increased expression of 12 polypeptides in growth-arrested SMC. These polypeptides, with apparent molecular weights of 24,000 to 55,000 exhibited relative increases of between fourfold to greater than tenfold. Three of these polypeptides were expressed at undetectable levels in proliferating SMC. We also detected 12 secreted polypeptides that were expressed at higher levels in growth-arrested SMC. More changes were associated with the secreted polypeptides, since they represented approximately 4% of the total resolved secreted polypeptides, while only 1% of the cellular polypeptides were increased in high-density growth-arrested cells. Under these conditions we observed no change in relative alpha-SM actin protein content as determined by 2-D gel analysis and Western blots. This was corroborated by high levels of alpha-SM actin mRNA levels in both proliferating and high-density growth-arrested SMC. These results indicate rabbit vascular SMC maintain a high level of expression of a smooth muscle differentiation marker (alpha-SM actin) in a proliferation- and density-independent manner. We also examined polypeptide synthesis in SMC isolated by enzymatic digestion of the aorta vs. cells isolated by the explant method. We found that although overall protein patterns were remarkably similar, several differences were observed. These differences were not due to increased contamination by fibroblasts, since both enzymatically- and explant-derived SMC contained high levels of alpha-SM actin as determined by immunofluorescence and by Northern analysis.

Specific polypeptide differences in normal versus malignant breast tissue by two-dimensional electrophoresis

High resolution two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) in combination with computer-assisted densitometry was used to analyze 800-1000 silver stained postmitochrondrial and 600-800 cytosolic polypeptides extracted from malignant and nonmalignant human breast tissues. The 2D-PAGE patterns of polypeptides from malignant and normal tissues were similar, although both qualitative and quantitative polypeptide differences were noted. Six cytosolic polypeptides (pI/molecular mass x 10(-3), 5.20/80, 5.75/43, 6.20/40, 5.43/35, 5.46/34.5, and 5.50/34 were detected exclusively in malignant tissues. One constitutive polypeptide, p52 (7.25/52), was not detected in tumor samples. Marked quantitative differences in spot density were noted in polypeptides localized mainly in the molecular weight ranges of 22-40 kDa and pI of 5.65-7.00. An overall increase in polypeptide expression was noted in this region of 2D-PAGE gels of malignant tissues as compared to normal. Twenty-two acidic and 19 polypeptides separated under nonequilibrium isoelectric focusing conditions were significantly increased in tumor samples while one polypeptide was decreased. One polypeptide, p24 (6.15/24), was expressed in greatest concentrations in tumors which also expressed the greatest estrogen receptor content. Expression of p24 was markedly reduced in normal tissue and in malignant tissues expressing low levels of estrogen and progesterone receptors. No significant differences in the expression of the Yb and Ya subunits of glutathione-S-transferases (GST)-A, -B and ligandin were observed between normal and malignant breast tissue. None of the Yp subunits of the placental isoform of GST were detected in either normal or malignant breast tissues.

Secreted and cellular polypeptide patterns of MCF-7 human breast cancer cells following either estrogen stimulation or v-H-ras transfection

The polypeptide patterns of MCF-7 human breast cancer cells (MCF-7gpt) and a stably v-H-ras-transfected subclone (MCF-7ras) have been analyzed following estradiol treatment. Since both estradiol and v-H-ras transfection increase tumorigenicity of MCF-7 cells, this study was designed to ascertain if specific changes in polypeptides were common in both treatments. Separation of cellular and secreted polypeptides was accomplished by 2-dimensional polyacrylamide gel electrophoresis, and the consequent patterns were analyzed with computer assistance. Estradiol treatment of the MCF-7gpt cells reduced the number of differences found in the polypeptide patterns between MCF-7gpt and MCF-7ras. Twelve cellular polypeptides were consistently modulated by either estradiol or v-H-ras, with four polypeptides clearly affected in the same way by both treatments. Polypeptides Gchc-0845 (Mr 54,000, pI 6.9) and Gchc-0902 (Mr 52,000, pI 6.3) were suppressed by estradiol and v-H-ras, while Gchc-1240 (Mr 34,000, pI 4.4) and Gchc-1396 (Mr 23,000, pI 5.3) were induced by estradiol and v-H-ras. Sixteen secreted polypeptides were altered by at least 2-fold subsequent to estradiol treatment or v-H-ras transfection. Transfection with v-H-ras had a greater effect than estradiol, stimulating the secretion of eight polypeptides and suppressing the secretion of seven polypeptides compared to estradiol which increased secretion of five polypeptides and decreased secretion of an additional three polypeptides, respectively. Synergistic effects by estradiol and v-H-ras were noted for three polypeptides. The secretion of Gcls-175 (Mr 50,000, pI 5.7) and Gcls-320 (Mr less than 14,000, pI 3.6, p-S2) was increased, while the secretion of Gcls-112 (Mr 76,000, pI 6.9) was decreased. Opposing effects of estradiol and v-H-ras were seen for seven polypeptides including the Mr 48,000 derivative of the Mr 52,000 protein (cathepsin D). These studies support the possibility that an extremely few, but specific polypeptides are regulated in association with quite diverse tumorigenic stimuli in MCF-7 human breast cancer cells.

Comparison of gene expression in preneoplastic and neoplastic rat liver to adult, fetal, regenerating, and tumor-promoted liver

Computer-assisted analysis was performed on the in vitro translation products of polyadenylated RNA samples isolated from normal adult Fischer rat liver and from preneoplastic and neoplastic rat liver samples which were generated by the Solt Farber technique (Solt, D. and Farber, E., Nature 263:701-703, 1976). The vast majority of the differences in translation products observed throughout the progressive development of hepatocellular carcinoma was quantitative in nature. Importantly, this quantitative heterogeneity first became prevalent at the very early preneoplastic stage of hepatoma formation. Only 3 consistent qualitative alterations in translation products were observed to be associated with the hepatocarcinogenesis process. The appearance of two new polypeptides of molecular weight and isoelectric point of 32/5.2 and 43/5.1 appeared to be related to an early preneoplastic event in hepatoma development and the transition from a preneoplastic to a neoplastic state, respectively. Importantly, these new polypeptides were not observed in the in vitro translation products generated from fetal or regenerating liver samples or from liver samples which were chronically treated with phenobarbital or terachlorodibenzo-p-dioxin. One translation product (located at 35/6.6) of normal adult, fetal, and regenerating liver RNA samples was undetected in all preneoplastic, neoplastic, phenobarbital-, and terachlorodibenzo-p-dioxin-treated liver RNA translation products. The possibility exists that the specific loss of this gene product may promote the development of the transformed phenotype.

Mutagenicity and in vitro covalent DNA binding of 2-hydroxyamino-3-methylimidazolo[4,5-f]quinoline

The 2-hydroxyamino-3-methylimidazolo[4,5-f]quinoline (N-hydroxy-IQ), a metabolite of the food mutagen--carcinogen IQ, was mutagenic to Salmonella TA98 (nitroreductase deficient). When either rat hepatic cytosol, NADPH (1 mM) or ascorbate (0.5 mM) was added to the mutagenicity assay, mutagenicity increased up to 15-, 10- and 50-fold respectively. In light of the effects of ascorbate and NADPH, it appears likely that hepatic cytosol may contain factors that protect N-hydroxy-IQ from oxidative decomposition. In contrast, hepatic monooxygenase metabolism of N-hydroxy-IQ decreased mutagenicity. When pentachlorophenol, an inhibitor of O-acetyltransferase and sulfotransferase, was added to the mutagenicity assay, a dose-dependent inhibition of N-hydroxy-IQ mutagenicity was observed. 2,6-Dichloro-4-nitrophenol, a more specific inhibitor of sulfotransferase than O- acetyltransferase, did not inhibit the mutagenicity of N-hydroxy-IQ at concentrations which appear to selectively inhibit only bacterial sulfotransferase. The data suggest that bacterial O-acetyltransferase rather than sulfotransferase mutagenically activates N-hydroxy-IQ. N-hydroxy-IQ covalently bound to calf thymus DNA in vitro under non-enzymatic conditions at pH 7.4. Rat hepatic cytosolic O-acetyltransferase and sulfotransferase enhanced the covalent binding of N-hydroxy-IQ to DNA 30- and 5-fold respectively. The data suggest that the mutagenicity of N-hydroxy-IQ is due to the reactivity of N-hydroxy-IQ with DNA and the ability of N-hydroxy-IQ to be further activated by bacterial O-acetyltransferase.

Rat liver cytosolic protein changes after ethanol exposure studied by two-dimensional electrophoresis

Rats were fed liquid food containing ethanol in concentrations ranging from 1-5% for 13 weeks. Livers were removed for histopathology and the liver cytosolic protein fraction was prepared and used for two-dimensional gel electrophoresis (2D-PAGE). Polypeptides were visualized by silver staining. Scanning was made for estimation of the relative abundance of protein in each polypeptide spot in the gels and for comparison between rats. Visual inspection and scanning of gels with the stained polypeptide spots obtained after equilibrium isoelectric focusing and non-equilibrium pH gradient electrophoresis revealed that: 1) within the control rat and ethanol-treated rat livers the numbers of polypeptide spots detected using isoelectric focusing in the first dimension were approximately 500 and for non-equilibrium pH gradient electrophoresis 400; 2) in the control group the variation in the estimated amount of protein in each spot was remarkably small; 3) pronounced differences in the relative abundance of protein in several of the spots was observed in the ethanol-exposed rats as compared to controls. Dose-response relations and possible causes for the effects of ethanol are discussed.

Ligand-induced modulation of the hepatic receptor for asialoglycoproteins in the human hepatoblastoma cell line, Hep G2

Ligand-induced modulation of the hepatic receptor for asialoglycoproteins has been examined in the human hepatoblastoma cell line, Hep G2. When grown to confluence, approximately 80% of the functional receptors are expressed at the cell surface. In contrast, exposure of these cells to saturating levels of galactose- or N-acetylgalactosamine-terminated ligands, for extended periods of time, resulted in a drastic reduction in the number of cell surface receptors, as determined by the binding of 125I-asialo-orosomucoid at 4 degrees C. Recovery of binding capacity was slow and incomplete despite retention of cellular viability and normal growth characteristics. Under these conditions, the decreased number of surface receptors could not be accounted for by changes in binding affinity or by internalization since the intracellular receptor number remained essentially constant. No corresponding decrease was noted in the ability of insulin or transferrin to bind to their respective cell surface receptors in the modulated cells. Similarly, Northern blot analysis revealed no changes in the steady state levels of the asialoglycoprotein receptor transcripts. However, antibody prepared against the purified human receptor bound equally well to both control and modulated cells, thereby indicating the presence of a proportionate number of inactive surface receptors on the latter cells. Two-dimensional gel electrophoresis failed to detect any abnormality in the molecular weight or isoelectric point of the modulated receptor. These findings are interpreted as indicating that the Hep G2 cells are able to regulate the functional expression of this surface receptor without altering its immunologic integrity. A defect in cell surface sialylation appears to be involved in the regulatory response.

Guanethidine N-oxidation in human liver microsomes

The capacity of human liver microsomes to N-oxidize guanethidine from 25 subjects has been assessed. Guanethidine N-oxidation was optimal at pH 8.5 and proceeded at only 16% of the maximal rate at pH 7.4. The mean rates of guanethidine N-oxidation at pH 8.5 and 7.4 were 2.46 +/- 0.89 (mean +/- s.d., n = 25) and 0.38 +/- 0.22 (mean +/- s.d., n = 22), respectively. Interindividual differences in the rate of guanethidine N-oxidation at pH 8.5 and 7.4 were 17- and 11-fold, respectively. The cytochrome P450 inhibitors, proadifen and 2,4-dichloro-6-phenylphenoxyethylamine (DPEA), at both pH 8.5 and 7.4 caused less than 20% reduction in the rate of guanethidine N-oxidation by human liver microsomes. These data indicate that guanethidine N-oxidation can be used as a measure of flavin-containing monooxygenase activity in human liver.

Heterogeneity of intercellular adhesion in rat liver cells in culture

The intercellular homotypic adhesive properties of 14 clones derived from a nontumorigenic rat liver epithelial cell line (LEC), derived from neonatal Fischer rats, were examined and compared to those of the hepatoma H4-II-E cell line. Each clone was assayed also for the degree of chromosomal aneuploidy and the ability to grow in soft agar. Over 100-fold differences in adhesive properties were observed among the clones, but no correlation was observed between the degree of aneuploidy in the clones and intercellular adhesive properties. The parent LEC cell line and the clones derived from it were unable to grow in soft agar. The H4-II-E cells showed negligible capacity to reaggregate after dissociation into single cells and these cells readily formed colonies in soft agar. Many of the LEC clones were similar to the H4-II-E cells in their adhesive properties, which suggests that reduced cell-to-cell adhesiveness per se is not a necessary prerequisite of epithelial cells to be able to grow independent of anchorage. Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) of concanavalin A (Con A)-binding glycoproteins in the "most adhesive" clone 67 and the "least adhesive" clone 201 showed markedly elevated amounts of acidic 105 and 67-kDa glycoproteins in clone 67. Proteins with similar migration patterns in 2D-PAGE have previously been reported to participate in specific homotypic intercellular adhesion of liver cells. The Con A-binding glycoprotein pattern in H4-II-E cells was markedly different from that of LEC cells with a set of six proteins missing and nine proteins appearing new in the H4-II-E cells. It is suggested that, in addition to identifying known epithelial cell polypeptides, systematic screening of cell surface-associated glycoproteins in normal and transformed epithelial cells in vitro and in vivo may lead to identification of novel polypeptides intimately associated with the transformed phenotype.

Specific polypeptide differences in normal versus malignant human breast tissues by two-dimensional electrophoresis

Postmitochondrial and cytosolic polypeptides were extracted from human breast tumors and non-malignant breast tissue and analyzed using high resolution two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Approximately 800-1000 postmitochondrial and 600-800 silver stained cytosolic polypeptides were detected over the pH range of 4.8 to 7.5 and molecular weight range of 18-120 kDa. The 2D-PAGE patterns of polypeptides from normal and malignant tissue were very similar, although both qualitative and quantitative polypeptide differences were noted. Six cytosolic polypeptides (pI/molecular weight X 10(-3) 5.20/80 kDa, 5.75/43, 6.25/40, 5.43/35, 5.45/34.5, 5.50/34 and 6.15/24 were expressed only in malignant tissues. One constitutive polypeptide, 7.25/52, was not detected in any of the malignant tissue samples. Quantitatively, marked differences in spot density were noted in polypeptides localized mainly in the molecular weight ranges of 22-40 kDa and pI ranges of 5.65-7.00. A general increase in polypeptide expression was noted in malignant tissues as compared to normal. Twenty-two polypeptides were significantly and consistently increased in tumor samples while only one polypeptide was decreased. One polypeptide, p24 (6.15/24) was expressed in greatest concentrations in tumors which also expressed the greatest estrogen receptor content. Expression of p24 was markedly reduced in normal tissue and malignant tissues expressing low levels of estrogen and progesterone receptors.

Synthesis, purification and mutagenicity of 2-hydroxyamino-3-methylimidazolo[4,5-f]quinoline

Synthesis of 2-hydroxyamino-3-methylimidazolo[4,5-f]quinoline (N-hydroxy-IQ), a reactive metabolite of 2-amino-3-methylimidazolo[4,5-f]quinoline (IQ), was achieved by a modification of an earlier method. N-Hydroxy-IQ was purified by a two-step procedure involving C18 Sep-Pack and semi-preparative h.p.l.c. Additional h.p.l.c. methods were developed to monitor the synthesis of N-hydroxy-IQ, and to measure IQ and other IQ derivatives on the same h.p.l.c. profile. The structure of N-hydroxy-IQ was confirmed by mass spectral analysis following derivatization to azoxy-IQ, phenyl-azoxy-IQ and acetoxy-acetamido-IQ, and by chemical reactivity studies. Mutagenicity studies with the nitro-reductase-deficient strain of Salmonella TA98 showed that N-hydroxy-IQ is directly mutagenic, having a specific activity of 2 X 10(4) revertants/nmol. The data confirm that N-hydroxy-IQ is a mutagenic metabolite of IQ and further implicate the hydroxylamine in the carcinogenicity of IQ.

Induction of common patterns of polypeptide synthesis and phosphorylation by calcium and 12-O-tetradecanoylphorbol-13-acetate in mouse epidermal cell culture

Terminal differentiation can be induced in cultured basal cells by either increasing the Ca2+ level in the medium from 0.05 to 1.4 mM or by exposure to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). If Ca2+ and TPA act by a common mechanism, then a common pattern of protein synthesis and/or phosphorylation would be expected. Computer-assisted analysis of radioactively labeled polypeptides separated by two-dimensional-polyacrylamide gel electrophoresis was utilized to study protein synthesis and phosphorylation. Within 1 h of increasing the Ca2+ level in the medium, the synthesis of 57 polypeptides was altered by 2-fold or more. Similarly, exposure to TPA for 1 h affected the synthesis of 106 polypeptides. Sixteen polypeptides were affected by both Ca2+ and TPA; the synthesis of nine was increased and seven was decreased, with changes in the same direction for both effectors. By 4 h, the synthesis of 32 polypeptides was similarly modulated by both Ca2+ and TPA. Only one polypeptide which was increased at 1 h was still elevated at 4 h. These results suggest that a common dynamic program of protein synthesis, likely to be related to terminal keratinocyte differentiation, is induced by both Ca2+ and TPA. Overall phosphorylation of epidermal proteins was increased after 30 min of TPA treatment, but was not increased by Ca2+ at this time. Keratin polypeptides were heavily phosphorylated in low Ca2+ medium, but the level or pattern of phosphorylation of these proteins was not altered by either Ca2+ or TPA. Although phosphorylation of a minor polypeptide (pI 5.1/Mr 45,000) was increased 2-3-fold by both Ca2+ and TPA, most of the specific protein phosphorylation changes induced in keratinocytes by Ca2+ and TPA appear to be unique. Thus, if protein phosphorylation is an early signal for epidermal differentiation by each effector, only a single apparent common substrate is involved and multiple kinases are activated. Alternatively, substrate specificity of a single kinase may be differentially altered by each effector.

Coordinate polypeptide expression during hepatocarcinogenesis in male F-344 rats: comparison of the Solt-Farber and Reddy models

The Solt-Farber resistant hepatocyte (RH) and Reddy (dietary peroxisome proliferator) hepatocarcinogenesis protocols were utilized to induce both preneoplastic and neoplastic nodules in male F-344 rats. Total cellular polypeptides from normal liver, ciprofibrate (CP)-induced and RH nodules were analyzed for both qualitative and quantitative changes using computer-assisted, high resolution two-dimensional polyacrylamide gel electrophoresis. Approximately 800-1000 cytosolic and 1000-1200 particulate polypeptides were readily separated and detected using an ultrasensitive silver stain. The two-dimensional polyacrylamide gel electrophoresis patterns were very similar for each tissue with respect to both the number of polypeptides detected and the overall patterns. Three cytosolic polypeptides, E, 6.90/47; F, 6.90/46; and G, 6.50/28 (designated pI/Mr X 10(-3], and two particulate polypeptides, B, 5.90/43; and D, 5.70/21; were detected in CP nodules but not in normal liver. Polypeptides B and D were also detected in RH nodules. No qualitative polypeptide differences were detected among the individual preneoplastic or individual neoplastic CP nodules or between preneoplastic and neoplastic CP nodules. Numerous quantitative changes in both known markers for hepatocarcinogenesis and in as yet unidentified polypeptides were noted. In RH nodules the Ya subunit of glutathione-S-transferase B (GST-B) and the Yb subunit of GST-A were increased 2-4-fold as compared to normal liver or in replicating liver following a 70% partial hepatectomy, while in CP nodules the Yb subunit was unaltered and the Ya subunit increased 4-fold as compared to normal. The Yp subunits of GST-P were increased from almost nondetectable levels in normal liver to one of the most abundant cytosolic polypeptides in RH nodules. In contrast, the Yp subunits were not detected in any of the CP nodules either on the two-dimensional polyacrylamide gel electrophoresis gels themselves or following Western transfer and immunoblot analysis with antibody against GST-P. Two additional polypeptide spots, which may represent Yc charge shift variants, appeared at the same molecular weight as the constitutively expressed Yc subunit of GST-B but shifted one charge unit each toward the acidic region in CP nodules. DT-diaphorase which was increased 2-3-fold in RH nodules was unaltered in CP nodules. In addition to these changes in known markers, 34 (22 cytosolic and 12 particulate) polypeptides were significantly increased while 27 (12 cytosolic and 15 particulate) polypeptides were decreased during CP-induced hepatocarcinogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Induction by phenobarbital in McA-RH7777 rat hepatoma cells of a polycyclic hydrocarbon inducible cytochrome P450

The metabolism of 2-acetylaminofluorene (AAF) to its six oxidative metabolites has been used to study cytochrome P450 monooxygenase activity in two rat hepatoma cell lines, McA-RH7777 and Reuber H4-II-E. McA-RH7777 cells exhibited considerably higher basal activities than H4-II-E cells for all metabolic pathways studied. Phenobarbital induced AAF metabolite formation in McA-RH7777 cells to a similar extent as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but was only a weak inducer of these activities in H4-II-E cells. Northern blot analysis utilizing specific phenobarbital or 3-methylcholanthrene inducible cytochrome P450 cDNA probes indicated that there was at least a 10-fold increase in a 3-methylcholanthrene inducible cytochrome P450 transcript in phenobarbital treated McA-RH7777 cells. These data suggest that in this transformed cell line phenobarbital behaves as a polycyclic hydrocarbon-like inducer.

Structural studies and two-dimensional gel electrophoresis of gamma-glutamyl transpeptidase

The heterodimeric enzyme gamma-glutamyl transpeptidase (EC 2.3.2.2) was isolated from adult rat kidney and purified to homogeneity for structural studies using papain solubilization and multiple chromatographies. Two-dimensional gel electrophoresis was found to resolve the active papain-purified enzyme into at least 18 components. Seven components with apparent molecular masses of 23,000-26,000 and isoelectric point range of 5.4-7.0 constitute the light subunit, and 11 components with apparent molecular mass of 51,000-53,000 and isoelectric point range of 5.8-7.1 constitute the heavy subunit. Immunoblot analysis of two-dimensional gels showed that all of these components are immunoreactive with a mixture of the two antibodies generated separately against the light and heavy subunits. Preparative subunit separation was achieved using reverse-phase HPLC under acidic but nonreducing conditions. N-Terminal amino acid sequencing of the separated subunits of the papain-purified enzyme yielded sequence information for the first 32 residues of the heavy chain with the N-terminal starting sequence Gly-Lys-Pro-Asp-His-Val-Tyr-Ser-Arg-Ala, and for the first 36 residues of the light subunit with the N-terminal starting sequence Thr-Ala-His-Leu-Ser-Val-Val-Ser-Glu-Asp.

Studies of gene transcription and translation in regenerating rat liver

Specific transcriptional and translational products associated with regenerating liver were analyzed by differential hybridization to a cDNA library and by two-dimensional electrophoresis of hepatic proteins, respectively. Comparisons of approximately 800 soluble and 800 particulate liver proteins from normal and 70% partially hepatectomized Fischer rats resulted in the identification of only three apparently unique polypeptides in 70% partially hepatectomized livers, although many quantitative changes were observed. A subset of these quantitative changes were also observed after sham operation. A cDNA library was generated from polyadenylated RNA isolated 18 hr post-70% partial hepatectomy. Comparative analysis of 6,000 transformants with single-stranded cDNA probes prepared from 18 hr post-70% partial hepatectomy and sham-operated animals identified three clones whose sequences were preferentially expressed 4- to 6-fold 18 hr post-70% partial hepatectomy. Southern blot analysis of one clone, REG-A, showed no homology to albumin, alpha-fetoprotein, three different forms of cytochrome P-450, ornithine decarboxylase, globin, or to a putative tumor promotion associated gene called PRO-2. A single, REG-A specific 2.5 kb band was identified by Northern blot analysis of liver samples. REG-A expression was increased 2-fold 18 hr postsham operation; 4-fold 18 hr post-70% partial hepatectomy and following chronic 2,3,7,8-tetrachlorodibenzo-p-dioxin or phenobarbital treatment. REG-A expression returned to control levels 1 week after 70% partial hepatectomy. Furthermore, expression of REG-A was reduced in chemically induced preneoplastic nodules and in primary and transplantable hepatomas. Hybrid selection studies indicated that the REG-A sequence selected a mRNA(s) species, that in an in vitro translation assay, produced two major polypeptides of 21,000 and 25,000 molecular weight with a pI of 6.9. Thus, these data support the hypothesis that liver regeneration is characterized by quantitative changes in genes normally expressed at low levels in the Go hepatocyte and is not the result of major qualitative changes in gene expression.

Formation of DNA adducts from N-acetoxy-2-acetylaminofluorene and N-hydroxy-2-acetylaminofluorene in rat hemopoietic tissues in vivo

Administration of [ring-3H]-N-acetoxy-2-acetylaminofluorene (10 mg/kg i.v.) to male F344 rats resulted in substantial binding of [ring-3H]-N-acetoxy-2-acetylaminofluorene to DNA isolated from bone marrow [20.3 +/- 1.7 (SD) pmol/mg DNA] and spleen (23.6 +/- 5.8 pmol/mg DNA) compared to liver (39.4 +/- 2.1 pmol/mg DNA) and kidney (27.1 +/- 1.0 pmol/mg DNA) 2 h after dosing. High-performance liquid chromatography analyses of trifluoroacetic acid hydrolyzed DNA from bone marrow and spleen revealed the presence of N-(guanin-8-yl)-2-aminofluorene as the major adduct comprising more than 80% of total adducts, while N-(guanin-8-yl)-2-acetylaminofluorene and ring opened derivatives of N-(guanin-8-yl)-2-aminofluorene were only minor adducts. Dose dependent binding of [ring-3H]-N-hydroxy-2-acetylaminofluorene (N-OH-AAF) to DNA and formation of individual adducts in spleen and bone marrow was observed at a dose range of 1.0-10.0 mg/kg. There was a 3- and 6-fold more DNA adduct formation in bone marrow and spleen, respectively, following treatment with [ring-3H]-N-acetoxy-2-acetylaminofluorene compared to N-OH-AAF. However, the pattern of DNA adducts formed was similar. Pretreatment of rats with the cytotoxic agent 5-fluorouracil (150 mg/kg i.p.), which causes transient depletion of hemopoietic cells, on days -10, -7, -4, -2, and -1 prior to the administration of [ring-3H]-N-OH-AAF (10 mg/kg) on day 0 resulted in different levels of N-OH-AAF binding to spleen and bone marrow DNA without altering the pattern of DNA adducts compared to that in control animals. These data suggest a possible existence of a target cell population for N-OH-AAF and perhaps other aromatic amines and amides in both bone marrow and spleen of F344 rat.

Altered polypeptide expression associated with neoplastic transformation of Syrian hamster cells by bisulfite

Neoplastic transformation of Syrian hamster fetal cells by bisulfite is associated with qualitative and quantitative polypeptide changes. Amino acid-labeled [14C]polypeptides from neoplastic and nontransformed parental fetal cells were separated by two-dimensional gel electrophoresis and analyzed by computerized microdensitometry of autoradiographic patterns. Approximately 1000 polypeptides from parental fibroblasts at population doublings ranging from 4 to 20, and those from colony-derived malignant cell lines were compared. Most were identical. Seven malignant lines exhibited 4 qualitative polypeptide changes: 2 polypeptides had shifted slightly to the acidic side, 1 new polypeptide was observed, and 1 polypeptide was absent. The transformed bisulfite lines differed quantitatively from control cells in that 10-25% and 2-4% of the polypeptides exhibited differences in expression greater than 2- and 4-fold, respectively. Furthermore, there were 21 specific polypeptides with coordinate quantitative changes in all transformed lines. Because bisulfite at neutral pH fails to induce any significant DNA changes at concentrations that cause transformation, polypeptides expressed immediately or 48 h after bisulfite treatment were compared to those of non-treated controls, and no differences were found. Even though bisulfite does not induce detectable DNA damage or early post-treatment changes in polypeptide expression, a consistent set of qualitative and quantitative changes were observed after transformation. The qualitative polypeptide changes found in the bisulfite-induced malignant lines were similar to those seen in a benzo(a)pyrene-induced malignant line. This suggests that there is a convergence of pathways responsible for carcinogenesis independent of the nature of initiation.

Sequential analysis of chemically induced hepatoma development in rats by two dimensional electrophoresis

Using the Solt-Farber hepatocarcinogenesis model, a large population of preneoplastic and neoplastic nodules were induced in male Fischer 344 rats. Total cellular polypeptides from normal liver and individual preneoplastic and neoplastic nodules were analyzed for both qualitative and quantitative changes using computer assisted high resolution two-dimensional electrophoresis. Approximately 800-1000 cytosolic and 1200-1400 membrane associated polypeptides were readily separated and detected using an ultrasensitive silver stain. The polypeptide patterns were remarkably similar for each tissue and only four qualitative polypeptide differences were noted. One cytosolic polypeptide, 6.8/57 (designated pl/Mr X 10(-3), and three membrane associated polypeptides, 6.25/41, 6.75/24, and 6.05/21, were expressed in both preneoplastic and neoplastic nodules but not in normal liver. No qualitative polypeptide differences were detected among the individual preneoplastic or individual neoplastic nodules or between preneoplastic and neoplastic nodules. Numerous quantitative changes in both known markers for hepatocarcinogenesis and in as yet unidentified polypeptides were noted. In particular, the Ya subunit of glutathione S-transferase B, the Yb subunit of glutathione S-transferase A, as well as the three isoelectric point variants of the Yp subunit of glutathione S-transferase P were increased 2-, 4-, and 7-fold, respectively, in preneoplastic and neoplastic nodules. Whereas DT-diaphorase was increased 2-3-fold in hyperplastic nodules as compared to normal liver, no differences in the expression of albumin were noted. Although no differences were observed in the expression of aldehyde dehydrogenase in preneoplastic and neoplastic nodules, polypeptide b (6.9/54) was shifted slightly toward the basic region in normal liver. alpha-Fetoprotein was not detected in either preneoplastic or neoplastic nodules. In addition to these changes in known markers, comparison of 500-800 cytosolic and 750-1000 membrane associated polypeptides showed that roughly 4-10% of the polypeptides were undergoing quantitative changes of at least 4-fold during these stages of hepatocarcinogenesis. Thirty (10 cytosolic and 20 membrane) polypeptides were significantly down-regulated while 22 (7 cytosolic and 15 membrane) polypeptides were up-regulated in both preneoplastic and neoplastic nodules. In all cases the direction and magnitude of change were the same in both preneoplastic and neoplastic nodules with the exception of three polypeptides.(ABSTRACT TRUNCATED AT 400 WORDS)