Induction of alkaline phosphatase and the glycoprotein hormone alpha subunit in HeLa cells by inhibitors of DNA polymerase

Enhancement by theophylline of the butyrate-mediated induction of choriogonadotropin alpha-subunit in HeLa cells. I. Lack of correlation with cAMP

The glycoprotein hormone common alpha-subunit can be induced in HeLa and other nontrophoblastic tumor cell lines by sodium butyrate. This report demonstrates that production of alpha-subunit can be further modulated by theophylline, especially in conjunction with butyrate. This synergism was not observed with other phosphodiesterase inhibitors such as xanthine, caffeine, theobromine, or methylisobutylxanthine. Induction by a combination of the short chain fatty acid plus the methylxanthine results from a decrease in the lag time after effector addition as well as a change in the rate of subunit accumulation. The increase in alpha-subunit is correlated with an increase in the levels of alpha-subunit mRNA, suggesting that induction is manifest at a pretranslational stage. The production of alpha-subunit was only marginally affected in cultures treated with 8-Br-cAMP or forskolin. Intracellular levels of cAMP were increased approximately threefold by methylisobutylxanthine, twofold by theophylline, fourfold by forskolin, and about 50% by butyrate, yet significant induction was achieved only by butyrate and theophylline. Taken together, these data suggest that the synergism between butyrate and theophylline is not mediated by cAMP.

Modulation of glycoprotein hormone alpha-subunit levels, alkaline phosphatase activity, and DNA replication by antimetabolites in HeLa cultures

Synthesis of the glycoprotein hormone common alpha-subunit and alkaline phosphatase (placental isozyme) has been examined in HeLa S3 cells. A variety of compounds that inhibit DNA synthesis lead to the increased production of both proteins. Experiments presented in this communication were undertaken to determine whether protein induction and DNA synthesis inhibition are coordinated. In general, nucleoside analogs and compounds that alter deoxynucleotide metabolism were good inducers of these ectopic products, whereas agents that altered DNA by intercalation, crosslinking, and covalent modification were poor inducers. The former class of effectors includes 5-bromo-2'-deoxyuridine, 5-fluoro-2'-deoxyuridine, 2'-deoxythymidine, 1-beta-D-arabinofuranosylcytosine, methotrexate, hydroxyurea, N-phosphonoacetyl-L-aspartic acid, and sodium butyrate; and the latter class of compounds includes ethidium bromide, acridine, bleomycin, mitomycin C, cesalin, macromomycin, and cis-diamminedichloroplatinum(II). A direct correlation between protein induction and DNA synthesis inhibition is unlikely based on the following observations: (i) for some effectors, the concentrations required to induce alpha-subunit and PAP were significantly different from those necessary to inhibit DNA synthesis; (ii) several agents inhibit DNA replication but do not enhance hormone or enzyme production; (iii) the kinetics of ectopic protein induction were similar for a number of inducers whereas the kinetics of DNA synthesis inhibition elicited by the same compounds were quite different. It is difficult from the data obtained, however, to rule out the possibility that inhibition of DNA synthesis may be required but is not sufficient for protein induction.

Effect of pyrimidine deoxynucleosides and sodium butyrate on expression of the glycoprotein hormone alpha-subunit and placental alkaline phosphatase in HeLa cells

Production of the glycoprotein hormone common alpha-subunit and placental alkaline phosphatase activity can be modulated in HeLa cells by a variety of deoxynucleosides. Dose response curves for thymidine (Thd), fluorodeoxyuridine (FdUrd), bromodeoxyuridine (BrdUrd) and iododeoxyuridine (IdUrd) demonstrate that, in general, alkaline phosphatase was increased by lower concentrations of inducer than was alpha-subunit. The deoxynucleosides were not as effective as sodium butyrate as inducers of either protein. Whereas Thd and the halogenated dUrd derivatives enhanced protein expression, deoxycytidine (dCyd) had negative effects. Induction by deoxynucleosides of both alkaline phosphatase and alpha-subunit was inhibited by dCyd, but induction of alkaline phosphatase by butyrate was more sensitive to dCyd inhibition than was the butyrate-mediated induction of alpha-subunit. These results suggest that the two proteins are not regulated in a coordinate manner. Reversal of alkaline phosphatase induction by dCyd was not observed in cells preincubated with sodium butyrate for 6-24 h before the addition of dCyd, indicating that the deoxynucleoside interferes with an early event in the butyrate-mediated response. Combinations of butyrate with Thd, BrdUrd or IdUrd were synergistic with respect to the induction of HeLa-alpha. It is concluded that incorporation of the deoxynucleosides into DNA may not be required for the synergistic response since 2',5'-dideoxythymidine was an effective as Thd. Cytoplasmic dot hybridizations demonstrate that a primary effect of the various effectors is to increase the steady-state levels of alpha-subunit mRNA. There was a good correlation between alpha-subunit accumulation and corresponding levels of alpha-mRNA, suggesting that regulation occurs at a pretranslational site. Although the mechanism(s) is not understood, these data provide evidence that nucleosides or their derivatives can significantly affect gene expression.

Dual effects of 2-deoxyglucose on synthesis of the glycoprotein hormone common alpha-subunit in butyrate-treated HeLa cells

Sodium butyrate (Btr) (3 mM) causes a 10-fold increase in production of the glycoprotein hormone alpha-subunit in HeLa cells. The following report demonstrates that this response could be inhibited about 95% by 5 mM 2-deoxy-D-glucose (dGlc), whereas alpha-subunit production in uninduced cells was affected little or not at all. Addition of D-mannose restored the Btr induction of Hela-alpha in cultures that had been treated with dGlc. When the alpha-subunits secreted by cells cultured in Btr plus dGlc or in Btr alone were compared by gel filtration (Sephadex G-75) and lectin affinity (concanavalin A and ricin) chromatography, differences were noted that probably reflect changes in their carbohydrate moieties. Immunoprecipitation of [35S]methionine-labeled HeLa-alpha and incubation with endoglycosidase H indicated that the subunit secreted from cells in the presence of dGlc contained oligosaccharide side chains that were not processed to the complex type. Cells that were simultaneously treated with Btr plus dGlc showed no increase in alpha-subunit production over cells receiving Btr only; in contrast, cells that were preincubated with Btr for either 16 or 36 h before dGlc was added exhibited high levels of subunit synthesis. Measurement of alpha-mRNA levels at various times after Btr and dGlc were added to cultures indicated that Btr brought about a dramatic increase in alpha-specific mRNA about 24 h after being added to cultures. This increase could be prevented by dGlc when added simultaneously with Btr but not when added after a 24-h preincubation. Although dGlc prevented the induction of alpha-subunit and alpha-mRNA in response to Btr, it had no effect on histone hyperacetylation, suggesting that if this chromatin modification is necessary for the induction process, it is not in itself sufficient. Together, the data demonstrate that dGlc inhibits the accumulation of alpha-subunit mRNA normally produced in response to Btr and that the subunit produced contains altered oligosaccharide constituents.

Dual effects of 2-deoxyglucose on synthesis of the glycoprotein hormone common alpha-subunit in butyrate-treated HeLa cells

Sodium butyrate (Btr) (3 mM) causes a 10-fold increase in production of the glycoprotein hormone alpha-subunit in HeLa cells. The following report demonstrates that this response could be inhibited about 95% by 5 mM 2-deoxy-D-glucose (dGlc), whereas alpha-subunit production in uninduced cells was affected little or not at all. Addition of D-mannose restored the Btr induction of Hela-alpha in cultures that had been treated with dGlc. When the alpha-subunits secreted by cells cultured in Btr plus dGlc or in Btr alone were compared by gel filtration (Sephadex G-75) and lectin affinity (concanavalin A and ricin) chromatography, differences were noted that probably reflect changes in their carbohydrate moieties. Immunoprecipitation of [35S]methionine-labeled HeLa-alpha and incubation with endoglycosidase H indicated that the subunit secreted from cells in the presence of dGlc contained oligosaccharide side chains that were not processed to the complex type. Cells that were simultaneously treated with Btr plus dGlc showed no increase in alpha-subunit production over cells receiving Btr only; in contrast, cells that were preincubated with Btr for either 16 or 36 h before dGlc was added exhibited high levels of subunit synthesis. Measurement of alpha-mRNA levels at various times after Btr and dGlc were added to cultures indicated that Btr brought about a dramatic increase in alpha-specific mRNA about 24 h after being added to cultures. This increase could be prevented by dGlc when added simultaneously with Btr but not when added after a 24-h preincubation. Although dGlc prevented the induction of alpha-subunit and alpha-mRNA in response to Btr, it had no effect on histone hyperacetylation, suggesting that if this chromatin modification is necessary for the induction process, it is not in itself sufficient. Together, the data demonstrate that dGlc inhibits the accumulation of alpha-subunit mRNA normally produced in response to Btr and that the subunit produced contains altered oligosaccharide constituents.

Acid phosphatase and phosphoamino acid phosphatases in murine erythroleukaemic cells

The activities of acid and alkaline phosphatases and phosphotyrosine, phosphoserine and phosphothreonine phosphatases were measured in Friend murine erythroleukaemic (MEL) cells. The effects of treating the cells with dimethyl sulphoxide (DMSO), an inducer of differentiation, were examined. In untreated cells alkaline phosphatase activity was undetectable, though there were significant amounts of acid phosphatase (76 +/- 15 mU/mg protein) and phosphotyrosine phosphatase (16 +/- 0.9mU/mg protein); phosphoserine and phosphothreonine phosphatase activities (9 +/- 0.4 and 7 +/- 0.6mU/mg protein, respectively) were lower than for phosphotyrosine phosphatase. Addition of 1 or 2% DMSO to the culture medium resulted in the expected cell death within 2 weeks. With 0.5% DMSO, cells remained viable for at least 8 weeks, but while some appeared to have smaller nuclei and retained their rounded appearance, others became fibroblastic within several days and adhered to the culture vessel. The treated cells which had kept their morphology showed no difference in acid phosphatase activities as compared with untreated controls; phosphotyrosine phosphatase was lower (9 +/- 0.8mU/mg protein) and phosphoserine and phosphothreonine phophatases higher (11 +/- 0.5 and 10 +/- 0.4mU/mg protein, respectively) than in the controls. The Km values for p-nitrophenyl phosphate were similar in untreated and treated cells (0.069 and 0.068mM, respectively); for phosphotyrosine the Km value was lower in the treated cells (0.97mM) than in the controls (1.9mM).

Independent regulation by sodium butyrate of gonadotropin alpha gene expression and cell cycle progression in HeLa cells

Sodium butyrate alters the growth and gene expression of a variety of differentiating and neoplastic cell types. For example, addition of 5 mM butyrate to HeLa cells is reported to both induce gonadotropin alpha subunit biosynthesis and block cell cycling in G1. We have studied these two actions of butyrate on HeLa cells and found that they are regulated in distinct ways. The induction of alpha subunit synthesis was due to an increase in the rate of transcription of the alpha gene. Using synchronized populations of HeLa cells, we determined that butyrate stimulates alpha transcription throughout the cell cycle. In contrast, treated cells arrest in G1 only if exposed to butyrate for a discrete period during the previous S phase. We conclude that butyrate inhibits DNA synthesis through a cell cycle-specific action that is independent from its direct action to stimulate transcription of the gonadotropin alpha gene.

Independent regulation by sodium butyrate of gonadotropin alpha gene expression and cell cycle progression in HeLa cells

Sodium butyrate alters the growth and gene expression of a variety of differentiating and neoplastic cell types. For example, addition of 5 mM butyrate to HeLa cells is reported to both induce gonadotropin alpha subunit biosynthesis and block cell cycling in G1. We have studied these two actions of butyrate on HeLa cells and found that they are regulated in distinct ways. The induction of alpha subunit synthesis was due to an increase in the rate of transcription of the alpha gene. Using synchronized populations of HeLa cells, we determined that butyrate stimulates alpha transcription throughout the cell cycle. In contrast, treated cells arrest in G1 only if exposed to butyrate for a discrete period during the previous S phase. We conclude that butyrate inhibits DNA synthesis through a cell cycle-specific action that is independent from its direct action to stimulate transcription of the gonadotropin alpha gene.

Measurement of biosynthetic rates and intracellular transit times for a cell-surface membrane glycoprotein, alkaline phosphatase in HeLa cells

The techniques for measurement of biosynthetic rates and intracellular transit times of an integral membrane protein isoenzyme have now been validated. Thus, induction of placental alkaline phosphatase in cultured HeLa cells by prednisolone and by butyrate is shown to result in its increased biosynthesis as measured by uptake of [35S]methionine into immunoprecipitated cell-surface placental alkaline phosphatase. The cell-surface placental alkaline phosphatase is liberated from the cells by proteolytic cleavage by bromelain, which results in a decrease of the placental alkaline phosphatase subunit mass from 64,000 to 62,000 daltons. The time of transit of new placental alkaline phosphatase molecules from their ribosomal site of synthesis to their terminal cell-surface, bromelain-sensitive site is approximately 55 min. This system may be useful in studies of regulation of intracellular protein processing and transport to the cell surface of proteins destined to become integral membrane proteins.