Serum-dependent depression of alkaline phosphatase in HeLa cells

Reduction in alkaline phosphatase activity was observed when HeLa S3 cells were grown in Puck's medium containing high concentrations of human serum. This effect was not seen with the enzyme of Chang liver 8A cells. The induction of increased alkaline phosphatase in HeLa S3 by prednisolone or by osmolality changes was not prevented by serum. The concentration of serum in the culture medium had no influence on acid phosphatase activity.     

Alkaline phosphatase in KB cells: influence of hyperosmolality and prednisolone on enzyme activity and thermostability

KB cells, derived from a human nasopharyngeal carcinoma, have high alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) activity. Specific activity is 150 times higher than in HeLa S3 cells. Alkaline phosphatase activity in KB cells exhibits heterogeneity consisting of a large heat-labile and a small heat-stable component. Enzyme activity is modulated by the osmolality of the culture medium. Increasing the osmolality by the addition of NaCl results in reduction of activity. A similar effect is noted when KB cells are grown with prednisolone (Δ′-hydrocortisone). The activities of acid phosphatase, β-galactosidase and N-acetyl-β-glucosaminidase are not affected by hyperosmolality and/or prednisolone. The reduction in alkaline phosphatase activity is accompanied by an increase in the proportion of the heat-stable and a decrease of the heat-labile enzyme components. The alterations in specific activity and thermostability are independent of the basal culture medium employed. Enzyme stability at 56 °C is inversely related to the buffer concentration, but the differences in stability between the alkaline phosphatases of control cultures and of KB cells grown in hyperosmolar medium or with prednisolone can be recognized with various buffering mixtures.     

Alkaline phosphatase activity in cultured urinary bladder cancer cells.

Established cell lines derived from human urinary bladder carcinomas produce heat-stable alkaline phosphatase [orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1] which resembles the oncofetal enzyme of HeLa S3. Rat bladder cancer cell lines derived from chemically induced tumors produce heat-labile alkaline phosphatase. Corticosteroids and/or hyperosmolality do not influence the enzyme of rodent cells, but induce increased levels of activity in human cells. The increase is most pronounced when human cells multiply in hyperosmolar medium containing prednisolone. Under these conditions a rise of over 100-fold in specific activity is noted. This synergistic effect, not seen with other cultured heteroploid cells, may represent a specific characteristic of cells derived from human bladder tumors.     

Alkaline Phosphatase Content and the Effects of Prednisolone on Mammalian Cells in Culture

The alkaline phosphatase content of different tissue culture cell lines has been shown to vary from no detectable activity to high enzyme concentration. Within the epithelial lines studied alkaline phosphatase is either constitutive or inducible. Two epithelial cell strains in which alkaline phosphatase was "absent" could be induced to develop significant amounts of the enzyme when grown in the presence of Δ¹-hydrocortisone. Phosphate did not repress enzyme induction by prednisolone. Under conditions of deadaptation the induced enzyme was diluted by cell multiplication. The mouse fibroblastic L line and several human fibroblastic lines did not contain alkaline phosphatase when grown under the conditions described nor could they be induced to produce the enzyme when cultivated in medium with prednisolone. Δ¹-Hydrocortisone has other characteristic effects on established mammalian cell cultures which vary among cell lines. Human epithelial lines show reduction in cell multiplication with increase in mitotic index. The cytoplasm is increased and cell volume is nearly doubled. Mouse fibroblasts show a similar reduction in cell multiplication with a decrease in mitotic index. There is no increase in cell cytoplasm. Human fibroblast strains show no inhibition of multiplication or alteration in total cell protein when grown in medium containing prednisolone. Antisera prepared against "negative" prednisolone-inducible human cell lines and against a positive human line inhibited alkaline phosphatase activity to an equal degree.     

Requirement of serum pretreatment for induction of alkaline phosphatase activity with prednisolone, butyrate, dibutyryl cyclic adenosine monophosphate and NaCl in human liver cells continuously cultured in serum-free medium

A cell line (HuL-1) derived from normal fetal human liver was adapted to grow continuously in a modified Eagle's minimum essential medium without serum or hormones. The population doubling time of this adapted cell line (HuL-1-317) was about 72 h and the modal number of chromosomes was 54. The morphology of HuL-1-317 cells was round in the absence of serum, but at 37 degrees C with the addition of serum (1-10%), the cells flattened. HuL-1-317 cells had a low level of alkaline phosphatase activity. However the enzyme activity was slightly enhanced by the combination of prednisolone, butyrate, dibutyryl cyclic adenosine monophosphate and a hypertonic concentration of NaCl after 3 days of incubation at 37 degrees C. The increase in alkaline phosphatase activity with the four agents was further amplified dose-dependently by the pretreatment of the cells with serum. The stimulatory effect of the serum was evident at concentrations as low as 1%, and was maximal at 20%. The half life of the effect of serum on alkaline phosphatase induction was 48 h at 37 degrees C. Serum alone could not enhance the enzyme activity without the four agents. The present results indicate that serum contributes to the regulation of alkaline phosphatase induction by the combination of prednisolone, butyrate, dibutyryl cyclic adenosine monophosphate and NaCl in fetal human liver cells (HuL-1-317).     

Alkaline phosphatase protein increases in response to prednisolone in HeLa cells.

Quantification of term-placental alkaline phosphatase isoenzyme protein in HeLa TCRC-1 cells grown in the presence and absence of prednisolone indicates that there is a net increase in amount of enzyme-specific protein in prednisolone-stimulated cells. In a similar analysis of HeLa D98AH2 cells, prednisolone treatment causes the appearance of term-placental alkaline phosphatase protein and the loss of the intestinal isoenzyme protein. These results support the interpretation that the response of these cells to corticosteroids is the net accumulation of alkaline phosphatase protein rather than the modification of pre-existing enzyme to a more active state.     

Alkaline phosphatase in HeLa cells. Stimulation by phospholipase A2 and lysophosphatidylcholine.

Treatment of homogenates and plasma membrane preparations from HeLa cells with phospholipase A2 (EC 3.1.1.4) caused a 50% increase in activity of membrane-associated alkaline phosphatase. Lysophosphatidylcholine, dispersed in 0.15 M KCl, affected alkaline phosphatase in a similar fashion by releasing the enzyme from particulate fractions into the incubation medium and by elevating its specific activity. Higher concentrations of lysophosphatidylcholine solubilized additional protein from particulate fractions but did not further increase the specific activity of the released alkaline phosphatase. Particulate fractions from HeLa cells were exposed to the effects of liposomes prepared from lysophosphatidylcholine and cholesterol. The ratio of particulate protein/lysophosphatidylcholine (by weight) required for optimal activation of alkaline phosphatase was one. Kinetic studies indicated that phospholipase A2 and lysophosphatidylcholine enhanced the apparent V of the enzyme but did not significantly alter its apparent Km. The increased release of alkaline phosphatase from the particulate matrix by lysophosphatidylcholine was confirmed by disc electrophoresis. The release of the enzyme by either phospholipase A2 or by lysophosphatidylcholine appeared to be followed by the formation of micelles that contained lysophosphatidylcholine. The new complexes had relatively less cholesterol and more lysophosphatidylcholine than the native membranes. The possibility that lysophosphatidylcholine formed a lipoprotein complex with the solubilized alkaline phosphatase was indicated by a break point in the Arrhenius plot which was evident only in the lysophosphatidylcholine-solubilized enzyme but could not be demonstrated in alkaline phosphatase that had been released with 0.15 M KCl alone.     

Acid phosphatase of HeLa cells: properties and regulation of lysosomal activity by serum.

Although the subcellular distribution profile of acid phosphatase in HeLa cells is typical of a lysosomal enzyme, different lysosomal (70–80%) and supernatant forms (20–30%) have been demonstrated by their differences in pH activity curves, substrate specificities, thermal stability, sensitivity to inhibitors, and kinetics. Enzymes of the lysosomal fraction displayed anomalous kinetics in the hydrolysis of p-nitrophenyl phosphate. The major lysosomal acid phosphatase activity appears to be associated with the membrane.The total acid phosphatase activity in the cell is controlled by the concentration of serum in the medium. The specific activity in the homogenates of cells grown in high serum concentration (30%) is about twice that of cells grown in low serum concentration (1%). This doubling of specific activity holds for the lysosomal enzyme (or enzymes), but little change occurs in the supernatant form (or forms). Two other lysosomal enzymes, β-glucuronidase and N-acetyl-β-d-hexosaminidase, do not increase in specific activity. The serum-dependent formation of acid phosphatase is sensitive to cycloheximide, actinomycin D, and cordycepin. Cycloheximide blocks the increase in enzymatic activity immediately, whereas cordycepin and actinomycin D have no effect for at least 8 h. These findings suggest that de novo protein synthesis is involved in the induction of lysosomal acid phosphatase by serum and that the mRNA for this enzyme is relatively stable.     

Alkaline phosphatase activation and collagen synthesis in human skin fibroblasts in culture

It has been noted in regenerating wounds that alkaline phosphatase activity in fibroblasts reaches a maximum when the collagen production is greatest. Tissue culture studies were carried out to show that prednisolone phosphate, while increasing the specific activity of alkaline phosphatase in human diploid skin fibroblasts, did not affect accumulation of collagen-hydroxyproline in monolayers or media. Addition of sodium ascorbate, resulted in rapid accumulation of hydroxyproline in the culture over a 13-day interval, while alkaline phosphatase activity increased only slightly over the last 6 days. When prednisolone and ascorbate were added in combination, alkaline phosphatase activity was significantly increased: but accumulation of hydroxyproline was no greater than in cultures to which ascorbate alone was added. Activation of alkaline phosphatase induced by prednisolone phosphate does not appear to be directly related to the biosynthesis of collagen in human skin fibroblasts in tissue culture.     

CELL CYCLE EVENTS IN THE HYDROCORTISONE REGULATION OF ALKALINE PHOSPHATASE IN HELA S3 CELLS

The increase in alkaline phosphatase in asynchronous cultures of HeLa S₃ cells grown in medium supplemented with hydrocortisone is characterized by a lag period of 10–12 hr. Present studies utilizing synchronous cell populations indicate: (a) a minimum of 8–10 hr of incubation with hydrocortisone is necessary for maximum induction of alkaline phosphatase; (b) the increase in enzyme activity produced by hydrocortisone is initiated exclusively in the synthetic phase of the cell cycle; (c) alkaline phosphatase activity does not vary appreciably over a normal control cell cycle. Radioactive hydrocortisone is rapidly distributed into HeLa cells irrespective of their position in the cell cycle, indicating that inductive effects are not governed by selective permeability during the cell cycle. Hydrocortisone-1,2-[³H] diffuses back from the cell into the medium when the cells are incubated in fresh medium containing no hydrocortisone, and the alkaline phosphatase induction, under these conditions, is completely reversible.     

A study of protein profiles in two strains of HeLa cells including membrane preparations

Summary Steroid-mediated induction of alkaline phosphatase in HeLa cells could not be ascribed to detectable qualitative or quantitative changes in cell proteins separable by disc gel electrophoresis. Similarly, neither qualitative nor quantitative differences in membrane proteins were observed after HeLa cell strains with either inducible or suppressible alkaline phosphatases were exposed to prednisolone. However, differences in protein profiles of the two cell strains were present. This work was supported, in part, by a Public Health Service research grant (CA-08315) from the National Cancer Institute.     

Spatial Physiological Heterogeneity in Pseudomonas aeruginosa Biofilm Is Determined by Oxygen Availability

The role of oxygen availability in determining the local physiological activity of Pseudomonas aeruginosa growing in biofilms was investigated. Biofilms grown in an ambient-air environment expressed approximately 1/15th the alkaline phosphatase specific activity of planktonic bacteria subjected to the same phosphate limitation treatment. Biofilms grown in a gaseous environment of pure oxygen exhibited 1.9 times the amount of alkaline phosphatase specific activity of air-grown biofilms, whereas biofilms grown in an environment in which the air was replaced with pure nitrogen prior to the inducing treatment did not develop alkaline phosphatase activity. Frozen cross sections of biofilms stained for alkaline phosphatase activity with a fluorogenic stain demonstrated that alkaline phosphatase activity was concentrated in distinct bands adjacent to the gaseous interfaces. These bands were approximately 30 μm thick with biofilms grown in air, 2 μm thick with biofilms grown in pure nitrogen, and 46 μm thick with biofilms grown in pure oxygen. Overall biofilm thickness ranged from approximately 117 to approximately 151 μm. Measurements with an oxygen microelectrode indicated that oxygen was depleted locally within the biofilm and that the oxygen-replete zone was of a dimension similar to that of the biologically active zone, as indicated by alkaline phosphatase induction. These experiments revealed marked spatial physiological heterogeneity within P. aeruginosa biofilms in which active protein synthesis was restricted by oxygen availability to the upper 30 μm of the biofilm. Such physiological heterogeneity has implications for microbial ecology and for understanding the reduced susceptibilities of biofilms to antimicrobial agents.     

Serum factors that stimulate fatty acid oxidation: properties of factors

Cultured heart muscle cells, but not HeLa cells, oxidize long-chain fatty acids in medium containing dialyzed serum. Addition of chicken serum dialysate (or non-dialized serum) stimulated palmitic acid oxidation by HeLa cells 10 to 20 fold. This serum activity was not eliminated by lipid extraction, ethanol or acid precipitation, alkaline phosphatase treatment, or autoclaving. About 80% was lost after any one of the following treatments: 6N HCl at 110 degrees C for 16 hr, pepsin, Dowex cation exchange at pH 3, or 1N KOH at 100 degrees C for 1 hr. Serum activity was separated into five or more peaks by gel filtration with Sephadex G-10. Each of these peak fractions was further purified by HPLC using a cyanopropyl-bonded resin. Carnitine, which is important for the transport of long-chain fatty acids into mitochondria for oxidation, also stimulated the oxidation of palmitate. However, these serum factors are not known precursors to carnitine since its immediate precursor 4-n-trimethylaminobutyrate, did not stimulate palmitate oxidation. Total carnitine, including that in acylcarnitine compounds, was approximately 15 microM in the chicken sera to give approximately 0.7 microM in the medium. Based on the fraction of total activity accountable by carnitine and fractional stability to acid, alkali, and pepsin, about 75% of the activity is from non-carnitine compounds. Only one of the factors appears to be carnitine or an acylcarnitine derivative. Several lines of evidence suggest that the other factors are peptide compounds.     

Analysis of growth dynamics and the relationship to the fluctuations in alkaline phosphatase in two strains of cells of HeLa S3 derivation

Summary Studies have been carried out to determine an association between glucocorticoid-induced changes in the pattern of growth and the fluctuations of alkaline phosphatase in two HeLa strains. The results showed that growth arrest in steroid-treated cells did not have the characteristics of density-induced growth inhibition. Alkaline phosphatase increased with increased cell density, the increase being greater than control in steroid-treated cells of the “inducible” strain (HeLa S3G, HeLa₆₅) and less than control in the “suppressible” strain (HeLa S3K, HeLa₇₁). Increased serum concentration in the growth medium (0 to 20%) caused an increase in alkaline phosphatase in S3G strain and a decrease in the S3K strain. This investigation was supported by the Veterans Administration and by USPHS Research Grant CA-08315 from the National Cancer Institute.     

Relationship between alkaline phosphatase and neomycin formation in Streptomyces fradiae

Studies on phosphatase activity of Streptomyces fradiae 3535 grown in three different media indicate that neomycin formation varies directly with enzyme activity, sodium nitrate-maltose-mineral salts medium giving the highest yields of alkaline phosphatase and neomycin. S. fradiae contains more than one alkaline phosphatase and the phosphatase responsible for hydrolysis of neomycin phosphate appears to be substrate specific. The same enzyme apparently hydrolyses both the N-P and P-O-P bonds of neomycin pyrophosphate. The enzyme is stimulated by Ca(2+), is inactive at a pH below 7 and is inhibited by EDTA. Enzymic activity increases when mycelia are incubated in mineral salts medium, but decreases when phosphate or glucose is included in the medium, although the latter is more effective. The inhibitory effect of EDTA on neomycin formation by resting mycelia is completely reversed by Ca(2+).     

Role of serum in the developmental expression of alkaline phosphatase in MC3T3-E1 osteoblasts

MC3T3-E1 cells in culture exhibit a temporal sequence of development similar to in vivo bone formation. To examine whether the developmental expression of the osteoblast phenotype depends on serum derived factors, we compared the timedependent expression of alkaline phosphatase (ALP)-a marker of osteoblastic maturation- in MC3T3-E1 cells grown in the presence of fetal bovine serum (FBS) or resin/charcoal-stripped (AXC) serum. ALP was assessed by measuring enzyme activity, immunoblotting, and Northern analysis. Growth of MC3T3-E1 cells in FBS resulted in the programmed upregulation of alkaline phosphatase (ALP) post-proliferatively during osteoblast differentiation. In the presence of complete serum, actively proliferating cells during the initial culture period expressed low ALP levels consistent with their designation as pre-osteoblasts, whereas postmitotic cultures upregulated ALP protein, message, and enzyme activity. In addition, undifferentiated early cultures of MC3T3-E1 cells were refractory to forskolin (FSK) stimulation of ALP, but became forskolin responsive following prolonged culture in FBS containing media. In contrast, MC3T3-E1 cells grown in AXC serum displayed limited growth and failed to show a time-dependent increase in alkaline phosphatase. Neither the addition of IGF-I to AXC serum to augment cell number or plating at high density restored the time-dependent upregulation of alkaline phosphatase. Cells incubated in AXC serum for 14 days, however, though expressing low alkaline phosphatase levels, maintained the capacity to upregulate ALP after FBS re-addition or forskolin activation of cAMP-dependent pathways. Such time-dependent acquisition of FSK responsiveness and serum stimulation of ALP expression only in mature osteoblasts indicate the possible presence of differentiation switches that impart competency for a subset of osteoblast developmental events that require complete serum for maximal expression. © 1994 Wiley-Liss, Inc.     

Acid ribonuclease from HeLa cell lysosomes.

An acid ribonuclease has been purified from HeLa cell lysosomes. The specific activity of the RNase in lysosomes is 8-fold higher than that in nuclei and 15-fold higher than that in the postlysosomal fraction. The purified enzyme showed no detectable DNase, phosphodiesterase, phosphatase, or alkaline RNase activity. The acid RNase binds to Con A-agarose and is inferred to be a glycoprotein. It has a low isoelectric point at pH 3.0 to 3.5, and the optimal pH for activity is between 5.0 and 5.5. The enzyme requires no divalent cation for optimal activity and is totally inhibited by 1 mM Cu2+ or Hg2+. Monovalent cations including Na+, K+, and NH4+ stimulate the activity in low ionic strength buffer. The enzyme degrades rRNA faster than tRNA, and tRNA faster than poly(U); poly(A) and poly(C) are highly resistant. The products from rRNA are mostly oligonucleotides with 3'-phosphate ends. An acid RNase is also present in the lysosomes of L-cells grown in a medium free of serum; it is probably identical to the one described here.