Differential effects of dimethyl sulfoxide and sodium butyrate on α-fetoprotein,albumin, and transferrin production by rat hepatomas in culture

Summary Radioimmunoassay was used to determine α-fetoprotein (AFP), albumin, and transferrin production (ng/10⁵ cells/24 h) by two cell lines (7777 and 8994) derived from chemically induced rat hepatomas. α-Fetoprotein production was high (2000 to 4400) in 7777, but was very low (0.2 to 0.4) in 8994. Albumin production varied from 0.4–0.8 (7777) to 14–26 (8994). Both lines produced substantial amounts of transferrin (180 to 240 by 7777 and 29 to 42 by 8994). Addition of dimethyl sulfoxide (DMSO, 1 to 4%) or sodium butyrate (BA, 0.5 to 2.0 mM) to the medium inhibited growth in both lines, but 8994 was more sensitive to these agents than 7777. Dimethyl sulfoxide treatment (2 to 4%) resulted in a dose-related decrease (<10% of control at 4% DMSO) in AFP, albumin, and transferrin production by 7777, but in 8994, DMSO (1 to 2%) resulted in an increase, (up to sixfold) in albumin and transferrin production, without affecting AFP production. By contrast, BA (2 to 4 mM) stimulated the production of all three proteins in both lines, most notably that of albumin (up to sixfold) by 7777 and that of AFP (up to 20-fold) by 8994. It is concluded that both DMSO and BA can enhance the expression of differentiated functions of the hepatoma cell, and that DMSO at the same time can suppress the expression of an oncofetal function. However, neither DMSO nor BA is selective in its effects on specific genes (i.e., normal, adult vs. oncofetal genes), and it appears that their effects may be the result of a more general phenomenon, the expression of which may be related to the stage of differentiation of the cell.     

Effects of hexamethylene bisacetamide onα-fetoprotein,albumin, and transferrin production by two rat hepatoma cell lines

Summary α-Fetoprotein (AFP), albumin, and transferrin production by two rat hepatoma cell lines, McA-RH 7777 (7777) and McA-RH 8994 (8994), was determined after treatment with hexamethylene bisacetamide (HMBA, 2 to 6 mM). Radioimmunoassays were used to determine the levels of both secreted and intracellular AFP, albumin, and transferrin. Line 7777 normally produces large quantities of AFP and small quantities of albumin, thus resembling the less differentiated fetal liver with respect to the synthesis of these two proteins. Line 8994 normally produces small quantities of AFP and relatively larger amounts of albumin, thus resembling hepatic functions characteristic of a more differentiated state. After treatment with HMBA for a period of 28 to 96 h a threefold increase in AFP secretion by 7777 and a dose related increase in AFP, albumin, and transferrin secretion by 8994 were observed. In contrast, the secretion of albumin and transferrin in 7777 was inhibited by 60 and 40%, respectively, following treatment with HMBA. The intracellular concentrations of AFP in 7777 and AFP, albumin, and transferrin in 8994 were increased by treatment with HMBA indicating that HMBA is able to stimulate the synthesis of these proteins. The intracellular concentration of AFP, albumin, and transferrin in 7777, when expressed as a percentage of the extracellular concentration of these proteins, did not change significantly during HMBA treatment, indicating that the observed decrease in secreted albumin and transferrin by 7777 is due to decreased synthesis. Similarly, in Line 8994, when the intracellular concentration of the three proteins was expressed as percentage of the extracellular concentration, the only significant change observed was an increase in AFP after 72 h of HMBA (5 mM) treatment. The observed changes in the synthesis of AFP, albumin, and transferrin in both 7777 and 8994 after HMBA treatment were reversible, as judged by the return to control values upon removal of HMBA from the culture medium. Thus, HMBA stimulates synthesis of the oncofetal protein AFP, a result that appears to be independent of the stage of differentiation of the cell. However, its effect on the synthesis of albumin and transferrin are opposite in the two cell lines, suggesting that the regulation of the synthesis of these two proteins is controlled by factors or conditions that are dependent upon the stage of differentiation of the hepatoma cell lines.     

Bidirectional morphological changes induced by dexamethasone in Morris hepatoma cell lines McA-RH7777 and McA-RH8994: independence of fibronectin and its receptor.

Two Morris hepatoma-derived cell lines, McA-RH7777 (7777) and McA-RH8994 (8994), exhibit different alterations in morphology upon exposure to glucocorticoid. After treatment with synthetic glucocorticoid dexamethasone (DEX), 7777 cells show increased adhesiveness and more flattened shape, while DEX-treated 8994 cells show decreased adhesiveness to substratum and exhibit a marked increase of round and detached cells. Since fibronectin has been thought to play an important role in cell adhesiveness to substratum in hepatoma cell culture, we have also compared the effects of DEX on the biosynthesis of fibronectin (FN) and the functional level of FN receptor in 7777 and 8994 cells. Northern blot analysis and immunofluorescent studies showed that 7777 cells have a high basal expression level of FN synthesis and that DEX treatment induces FN expression two- to threefold with establishment of an extensive fibrillar FN network around the cells. On the other hand, 8994 cells were shown to express little FN and no apparent FN was localized on nonstimulated 8994 cells. However, DEX-treatment drastically increased FN expression in 8994 cells to the level of more than that of DEX-treated 7777 cells and induced a detectable level of cell-associated FN around DEX-treated 8994 cells, which appears to be contradictory to the decreased adhesiveness to the substratum in DEX-treated 8994 cells. Cell attachment assays using FN-coated plates demonstrated that DEX does not exhibit significant effects on the attachment of either 7777 or 8994 cells to FN-coated dishes. Our results suggest that decrease of adhesiveness to the substratum and increase of round detached cells in DEX-treated 8994 cells are independent of changes in the FN expression and the function of FN receptor.     

Differential regulation of tissue transglutaminase in rat hepatoma cell lines McA-RH7777 and McA-RH8994: Relation to growth rate and cell death

Close correlation between tissue transglutaminase (tTG) induction and growth regulation and/or cell death processes has been suggested in many cell lineages. In this study, the regulation of the tTG levels by various growth and differentiation factors and its relation to growth rate and cell death processes were investigated in two rat hepatoma cell lines, McA-RH7777 and McA-RH8994, using a monoclonal antibody against liver tTG. Transforming growth factor-β1 (TGF-β1) and retinoic acid (RA) each increased tTG to the level of 8- to 32-fold above that of control cultures in both cell lines after 72-h treatment. Dexamethasone (DEX) induced a 16- to 32-fold of tTG in McA-RH8994 cells while it did not change the enzyme level in McA-RH7777 cells. Simultaneous addition of DEX and RA increased the tTG level to more than 50-fold in McA-RH7777 cells as well as McA-RH8994 cells. Other factors, such as TGF-α, hepatocyte growth factor, dimethyl sulfoxide, and protein kinase C activator, did not show significant increases of the tTG levels. Although tTG induction by TGF-β1 or DEX appeared to be correlated with their growth suppressive effects, RA increased the tTG level without suppressing the growth rate of hepatoma cells. TGF-β1 was also shown to induce cell death in both cell lines. Our results demonstrate that RA and DEX are capable of modulating the TGF-β1-induced cell death processes independent of the tTG levels. We present evidence here that tTG induction by itself is not the direct cause of growth suppression and cell death in these hepatoma cells.     

The expressions of oncogenes and liver-specific genes in Morris hepatomas

The expression of three liver-specific genes and four oncogenes was studied in the Morris hepatomas 8994, 7288c, 7777, 5123tc, and 7800. Total RNA isolated from these tumors was probed with cDNA's for alpha-fetoprotein (AFP), albumin, tyrosine aminotransferase (TAT), and the oncogenes Ha-ras, Ki-ras, myc and src. When compared to mRNA's levels expressed in normal adult liver, we found AFP levels elevated in AFP-producing tumors, albumin and TAT mRNA levels depressed in all tumors, except TAT is elevated in 5123tc and the oncogenes with the exception of src elevated in all tumors. These results argue against a coordinated expression of these genes as a result of transformation, but suggest that oncogene expression is related to tumorigenesis or proliferation.     

Inhibition of synthesis of alpha-fetoprotein by glucocorticoids in cultured hepatoma cells

alpha-Fetoprotein (AFP) synthesis was studied in the presence and absence of glucocorticoids in rat hepatoma Mc-A-RH-7777 cells. Radioimmunoassay of media from cell cultures grown in the presence of glucocorticoid (dexamethasone or cortisol) showed a reduction in AFP, an increase in albumin, and no significant change in transferrin accumulation, as compared to controls. Labeling experiments with L-[35S]methionine indicated that in both cells and media of dexamethasone-treated cultures there was a 50--80% reduction in polypeptide precipitated by anti-AFP serum, as compared with controls; no change was seen in polypeptide precipitated by anti-transferrin serum. Pulse and pulse-chase experiments demonstrated that dexamethasone inhibited the synthesis of AFP but not its secretion. The half-time for secretion of AFP in the presence and absence of dexamethasone was 43 min.     

The degree of methylation of alpha-fetoprotein in rat hepatoma cell lines and their clones producing and not producing this protein

The extent of methylation of MspI-HpaII sites of alpha-fetoprotein (AFP) gene in DNAs from normal rat livers, rat hepatoma cell lines and their clones was compared by Southern blot hybridization. The expression of this gene was controlled by measuring the level of AFP specific RNA and by immunoperoxidase staining with antibodies to AFP. It was found that the AFP gene contained several CCGG sites in the 5'-region methylated in the nonproductive cell lines and normal adult liver and undermethylated in productive cell lines. The same phenomena was observed for productive and nonproductive hepatoma McA-RH7777 clones. These findings suggest that specific changes in the methylation pattern are associated with changes in AFP gene expression.     

Reversible G1 arrest in the cell cycle of human lymphoid cell lines by dimethyl sulfoxide

Proliferation of human B- and T-lymphoid cell lines including Raji and Akata cells was found to be arrested at the G1 stage in the cell cycle by dimethyl sulfoxide (DMSO). The G1 arrest by DMSO occurred gradually and was completed within 96 h after addition of 1.5% DMSO concomitantly with a decrease in growth rate. Progression of G1-phase cells containing a larger amount of RNA into S-phase began 9-12 h after removal of DMSO. At 24 h, the DNA pattern of the cell cycle was similar to that of nontreated log-phase cells. The expression of six differentiation markers on the lymphoid cells was not appreciably changed by treatment with DMSO. On the other hand, the expression of transferrin receptor (one of the growth-related markers) on G1-phase cells 96 h after addition of DMSO was decreased to one-fourth that on log-phase cells and was completely restored 24 h after removal of DMSO. These results indicate that DMSO, known as an inducer of differentiation in several myeloid cell lines, acts as an agent inducing G1 arrest in the cell cycle of the lymphoid cells.     

Enhanced albumin production by malignantly transformed hepatocytes during in vitro exposure to dimethylsulfoxide

The murine BW 1 and rat 32III 6/d tumor cell lines, derived from a spontaneous mouse hepatoma and a carcinogen-induced rat hepatocellular carcinoma, were used to investigate the effect of dimethylsulfoxide (DMSO) on liver cells in vitro. After a 4-day exposure to DMSO in final concentrations of 0.5 and 1.0%, BW 1 cell-associated albumin increased by 41.6 and 94.2%; extracellular albumin levels in these same cultures rose by 131.4 and 214.2%. Exposure of 32III 6/d cells to 2% DMSO produced increases in cell-associated and extra-cellular albumin concentrations of 67.8 and 188.7%, respectively. The lack of inducible gamma-glutamyl transpeptidase in BW 1 cells and its decrease in 32III 6/d cultures following DMSO treatment suggests that the DMSO-mediated enhancement of albumin production is not reflective of a random increase in the expression of cellular genes.     

Changes in expression of albumin and alpha-fetoprotein genes during rat liver development and neoplasia.

Albumin mRNA was isolated and purified from rat liver polysomes by a combination of immunoprecipitation of specific polysomes, poly(U)-Sepharose 4B chromatography, and fractionation of the resulting poly(A)-containing RNA on a sucrose gradient. alpha-Fetoprotein (AFP) mRNA was isolated from Morris hepatoma 7777 by a similar procedure. The purity of the mRNA preparations was determined by analytical gel electrophoresis under denaturing conditions, analysis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the polypeptides synthesized in a wheat germ cell-free system, and the kinetics of hybridization to cDNA transcribed from albumin mRNA and AFP mRNA. The albumin mRNA possessed a chain length of approximately 2265 nucleotides and the AFP mRNA possesed a length of approximately 2235 nucleotides when examined under stringent denaturing conditions on agarose gels containing 10 mM methylmercury hydroxide. Analysis of poly(A) content by a hybridization assay with [3H]poly(U) revealed the presence in albumin mRNA of a poly(A) region containing approximately 100 adenosine residues. The AFP mRNA preparation was found to contain an average poly(A) tract of approximately 190 bases. Thus, albumin mRNA appears to contain approximately 330 untranslated nucleotides, and AFP mRNA appears to contain a similar number (approximately 285) of noncoding, nonpoly(A) bases. The purified albumin and AFP mRNA's were used as templates for synthesis of full-length cDNA hybridization probes. Both of the probes selectively hybridized to their templates with kinetics expected for single RNA species the sizes of albumin and AFP mRNA. ROt analysis was used to quantitate albumin and AFP mRNA sequences during normal liver postnatal development and liver oncogenesis. The number of polysomal AFP mRNA molecules per liver was found to drastically decrease during the first weeks of postnatal life, concomitant with a decline in the AFP synthetic capacity of the livers and in the serum concentrations of AFP. During this period, the concentration of albumin mRNA molecules per cell in the liver remained at high, approximately constant levels. In Morris hepatoma 7777, the concentration of AFP-specifying sequences was at least 10(3)-fold higher than that found in normal adult liver, whereas the content of albumin nRNA was four- to five-fold lower. These changes in concentration of albumin and AFP mRNA sequences closely correlated with a parallel variation in the specific protein synthetic capacity of the tissues.     

A mouse hepatoma cell line which secretes several serum proteins including albumin and alpha-foetoprotein.

A permanent cell line (BW) was established from a transplantable mouse hepatoma, BW7756, which produces alpha-foetoprotein (AFP). Three clones were isolated from the uncloned culture: BW1, BW2 and BWTG3. The cells of the latter clone, which was isolated after selection in the presence of thioguanine, are deficient in the enzyme hypoxanthine-guanine-phosphoribosyl transferase. Both BW1 and BWTG3 cells have mean chromosome number of 64 (60 telocentric and 4 metacentric chromosomes). All three clones secrete at least five serum proteins into the culture medium: albumin, AFP, and alpha 2 globulin, transferrin and C3, the third component of complement. The approximate rate of albumin secretion by BW1 and BWTG3 cells is 10 mug/24 h/10(6) cells. Both albumin and AFP can easily be detected in cell extracts. The simultaneous production of AFP and a hepatocyte specific marker (albumin) by cloned hepatoma cells show that the production of AFP by the tumour is due to the tumoural hepatocytes themselves.     

The control of serum protein synthesis in hepatoma-fibroblast hybrids.

Hybrids between mouse hepatoma cells (which secrete several serum proteins) and mouse or rat fibroblasts (which do not secrete these proteins) produce transferrin and the third component of complement (C3) like the parental hepatoma cells, while they do not secrete either albumin or alpha-fetoprotein (AFP). This lack of albumin and AFP secretion is probably due to a lack of synthesis, rather than to a simple defect in secretion. The cessation of albumin and AFP production is not dependent upon the parental fibroblast nor upon the selection conditions; it is best explained by a shut-off synthesis and could thus reflect the existence of a regulatory mechanism. This would imply a difference between the control of albumin and AFP synthesis and that of transferrin and C3 synthesis. On the other hand, in agreement with Peterson and Weiss (1972), hybrids between rat hepatoma cells and mouse fibroblasts continue to product rat albumin. This suggests that the mouse hepatoma cells differ from the rat hepatoma cells in the way they control albumin production.     

A Mouse Hepatoma Cell Line which Secretes Several Serum Proteins Including Albumin and α-foetoprotein

A permanent cell line (BW) was established from a transplantable mouse hepatoma, BW7756, which produces α-foetoprotein (AFP).Three clones were isolated from the uncloned culture: BW1, BW2 and B WTG3. The cells of the latter clone, which was isolated after selection in the presence of thioguanine, are deficient in the enzyme hypoxanthine-guanine-phosphoribosyl transferase. Both B W1 and BWTG3 cells have mean chromosome number of 64 (60 telocentric and 4 metacentric chromosomes). All three clones secrete at least'five serum proteins into the culture medium: albumin, AFP, an a2 globulin, transferrin and C3, the third component of complement. The approximate rate of albumin secretion by BW1 and BWTG3 cells is 10 μg/24 h/10⁶ cells. Both albumin and AFP can easily be detected in cell extracts. The simultaneous production of AFP and a hepatocyte specific marker (albumin) by cloned hepatoma cells show that the production of AFP by the tumour is due to the tumoural hepatocytes themselves.     

Unfolded transferrin polypeptide chain is immunologically crossreactive with similar derivatives of serum albumin and alpha-fetoprotein

Radioimmunoassays utilizing reduced and carboxymethylated (RC) proteins as antigens reveal a cross-reactivity between alpha-fetoprotein (AFP) and albumin. Similar assays were used to study the relationships of AFP and albumin to other serum proteins. Of the several serum proteins tested, transferrin showed the most similarity with AFP and albumin. There was no cross-reactivity of the native proteins, but antisera prepared against RC-albumin and RC-AFP bound 125I-labeled RC-transferrin at high titers, and antiserum to RC-transferrin bound labeled RC-AFP but not RC-albumin. Inhibition assays utilizing binding of 125I-RC-AFP or 125I-RC-transferrin to anti-RC-albumin showed that the RC derivatives of AFP, albumin, and transferrin were equally efficient inhibitors, whereas other serum proteins inhibited much less. The serum vitamin D carrier protein (Gc protein) showed intermediate reactivity. The reactivities of the antisera to RC-albumins with RC-transferrin and RC-Gc protein were corroborated by immunostaining of proteins separated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and transferred to nitrocellulose filters. These antisera stained the bands formed by RC derivatives of albumin, AFP, transferrin, and Gc protein, but not other proteins tested. AFP and albumin are known to have amino acid sequence homology. Our results suggest that transferrin and possibly also Gc protein may be structurally related to AFP and albumin.