L-leucine sensitive, heat-stable alkaline-phosphatase isoenzyme detected in a patient with pleuritis carcinomatosa

Differential patterns of expression of glycosylphosphatidylinositol-anchored carcinoembryonic antigen and alkaline phosphatase in various cancer cell lines

The expression of glycosylphosphatidylinositol (GPI-anchored) carcinoembryonic antigen (CEA) and alkaline phosphatase (ALP) on the cell surface of various cancer cell lines and a lung diploid cell line (WI38) was investigated, with exposure of the cell lines to a cell differentiation agent (sodium butyrate) to induce cell differentiation and expression of the two tumor-associated antigens. In three colon (SW1222, SW1116, and HT-29) and stomach (MKN-45) cancer cell lines, all of which are double producers of CEA and ALP, the maximum expression of GPI-anchored CEA occurred with butyrate at a lower concentration than did that of GPI-anchored ALP. GPI-anchored ALP derived from colon (SW1222 and SW1116) and stomach (MKN-45 and MKN-1) cancer cell lines was heat-stable with and without exposure to butyrate, but GPI-anchored ALP derived from lung cancer cell lines (PC-6, PC13, PC-14, WI26VA4, and WI38VA13) showed a variety of heat stabilities, depending on cell line, butyrate exposure, and SV40 transformation.

Alkaline phosphatase retained in HepG2 hepatocarcinoma cells vs. alkaline phosphatase released to culture medium: difference of aberrant glycosylation

Liver tissue is the source of 90% of serum alkaline phosphatase (AP). The serum levels and structures of tumor marker proteins change under many disease conditions as well as cancer. The study was aimed at determining the type of alkaline phosphatase (AP) present in HepG2 hepatocellular carcinoma cell line. Alkaline phosphatase rich extracts of healthy human liver, HepG2 hepatocarcinoma cells, as well as the condition medium of HepG2 cells were prepared by extraction with 40% n-butanol and 30-50% acetone precipitation, and subjected to various chromatographic procedures. Lectin affinity chromatography of the samples with concanavalin A-Sepharose 4B showed considerable differences in the elution patterns. Non-denaturing polyacrylamide gel electrophoresis of the culture medium yielded a relatively slow migrating band of activity that coincided with none of the three bands of activity produced by the normal liver extract, nor with the bands of the cell pellet extract. Inhibition patterns were established by measuring the enzyme activities in the presence of varying concentrations of L-phenylalanine, L-leucine, L-homoarginine, and levamisole. The APs from the cell line were neuraminidase sensitive. According to the results the main AP produced and released to the medium by HepG2 cell line is an aberrantly glycosylated tissue non-specific AP. In addition, the differences between the cell-pellet AP and the culture medium AP seemed to stem from different sugar moieties in their structures.

Differential regulation of placental and germ cell alkaline phosphatases by glucocorticoid and sodium butyrate in human gastric carcinoma cell line TMK-1

The expression and regulation of alkaline phosphatase (AP) was studied in the human gastric cancer cell line TMK-1. Biochemical analysis, reverse transcription-polymerase chain reaction, and Northern blot analysis demonstrated that the cells express placental, germ cell, and intestinal AP isozymes constitutively. Dexamethasone (Dex), a synthetic glucocorticoid, was shown to specifically induce the placental AP activity to about 10-fold and sodium butyrate (NaBu) induced germ cell AP activity to about 4-fold, respectively. In contrast, these two agents showed little effect on the level of intestinal isozymes. Dex and NaBu also differentially induced the mRNA levels of the placental and germ cell APs. Northern blot analysis of the placental AP transcript in the presence of the transcription inhibitor, 5, 6-dichloro-1-beta-D-ribofuranosyl benzimidazole, revealed that the half-life of placental AP mRNA is about 27 h for both the Dex-treated and untreated cells. Nuclear run-on transcription analysis indicated an apparent increase in the rate of placental AP gene transcription in Dex-treated cells. These results indicated that the effect of Dex occurred primarily by activation of the placental AP gene transcription in the cells. In order to study the direct Dex and NaBu effect on AP gene expression, the proximal promoter regions of AP genes were fused to luciferase reporter vectors. Despite the high similarity in nucleotide sequences of these two genes, transient transfection analysis demonstrated that Dex and NaBu exerted a specific stimulation only through the respective placental and germ cell AP gene promoter. Taken together, this study indicates that the expression of PAP and GCAP isozymes have specific regulatory mechanisms that can be differentially controlled by signals including glucocorticoid and NaBu.

Allotype immunoglobulin enhances alkaline phosphatase activity: implications for the inflammatory response

To understand the interactions among components of the immune/inflammation response, we studied the effects of immunoglobulins on the phosphatase activity of alkaline phosphatase in vitro. Bovine intestinal alkaline phosphatase was incubated with substrate in the presence of allotypic and xenotypic immunoglobulin. We found that bovine but not rabbit immunoglobulin enhanced the phosphatase activity of bovine intestinal alkaline phosphatase. Similarly, human but not bovine immunoglobulin G enhanced human placental alkaline phosphatase activity. By enhancing alkaline phosphatase activity, immunoglobulins bound to alkaline phosphatase may assist physiologic transport functions and enhance resolution of the inflammatory response. Further, in clinical conditions with high immunoglobulin concentrations, the serum alkaline phosphatase recorded may have spuriously high values.

Alkaline phosphatase of cancerous larynx tissue in comparison with the placental enzyme. Biochemical and histochemical studies

Tissue specimens of squamous cell carcinoma of the larynx from twenty patients were processed for histological and histopathological characterization. A histochemical study of alkaline phosphatase (ALP) was carried out using the simultaneous azo coupling method, and biochemical studies were performed using disodium phenylphosphate as substrate. Full-term, normal placentae were used for comparison. The specific activity of ALP from cancerous laryngeal tissue was 8.9 mKAU/mg protein compared with 154.7 mKAU/mg protein in the placenta. The ALP was localized histochemically in tumor cells (tumor-specific), blood vessels (vascular) and fibrous tissue (interstitial). The tumor-specific phosphatase was sensitive to inhibition by L-phenylalanine, L-leucine and to a lesser degree by L-tryptophan and levamisole. Placental ALP, on the other hand, was completely inhibited by levamisole, more resistant to leucine and more sensitive to phenylalanine and tryptophan. Biochemical estimation of ALP in cancerous laryngeal tissue combined with inhibition studies revealed that the tumor-specific activity of ALP constitutes 15% of the total ALP activity while the major isoenzyme was the vascular ALP, and around one-third of ALP activity was attributed to the interstitial enzyme. The characterization and localization of these isoenzymes are described and compared with that of the placenta. The significance and implications of the above findings are presented.

Constitutive expression of non-bone/liver/kidney alkaline phosphatase in human osteosarcoma cell lines

Alkaline phosphatase (ALP) plays an important role in bone mineralization; high levels in differentiated osteoblasts allows their identification easily in vitro. It is generally assumed that the activity of ALP in osteosarcoma-derived cell lines commonly used in studies of bone cell biology is exclusively due to the bone/liver/kidney (BLK) isoenzyme. However, we noted that two human osteosarcoma cell lines, U-2 OS and U-393 OS, predominantly expressed a truncated 1.8 kb mRNA for BLK-ALP. This observation stimulated further investigation upon the ability of ALP to form functional protein. We found that, unlike the BLK-ALP of the Saos-2 osteosarcoma cell line, the activity of U-2 OS ALP was thermostable, unaffected by L-homoarginine and levamisole, but inhibited by L-phenylalanine; these properties are characteristic of the placental and/or placental-like (PL-/PL-like ALP) isoenzymes which are 98% homologous at the amino acid level. In the U-393 OS cell line, which expresses the normal-sized 2.5 kb mRNA in substantially higher levels than that produced by U-2 OS cells, the ALP activity had kinetic properties very similar to that produced by the Saos-2 line for all criteria tested. The HOS osteosarcoma cell line (also known as TE-85), which express the normal-sized 2.5 kb BLK-ALP mRNA only, exhibited ALP activity with kinetic properties of both the BLK and PL-/PL-like isoenzymes. The three test lines, U-2 OS, U-393 OS and HOS, produced PL-/PL-like ALP mRNA and protein constitutively, and levels of these increased in cells treated with 1 microM dexamethasone. However, dexamethasone treatment of cells did not alter the types of ALP isoenzyme expressed. Thus our results show that, like Saos-2 cells, U-393 OS cells produce active BLK-ALP exclusively, whereas U-2 OS cells produce PL-/PL-like ALP only, and the HOS cell line produces both. Our findings have important implications for phenotypic characterization of various human osteosarcoma cell lines, and suggest that the production of PL-/PL-like ALP may be a more common occurrence in osteosarcomas than was originally thought.

Amino acid phosphatase activity of alkaline phosphatase. A possible role of protein phosphatase

Alkaline phosphatase (ALP) hydrolyzed phosvitin and amino acid phosphates demonstrating nonisotropy at different pH. Orthovanadate, a protein phosphatase inhibitor, more specifically inhibited the serine and tyrosine phosphatase activities of ALP than that of threonine phosphatase at concentrations > 0.1 mM or 0.01 mM, respectively. Calyculin A and okadaic acid at increased concentrations increased ALP amino acid phosphatase activity. Bisphosphonates, such as disodium-1-hydroxy-1-aminopropylidine-1,1-diphosphonate (APD) and ethane-1-hydroxy-1,1-diphosphonate (HEBP), at increased concentrations, inhibited ALP amino acid phosphatase activity. These results suggest that ALP may function as a protein phosphatase. In terms of protein kinase inhibitors, N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide, N-(6-aminoheyxl)-5-chloro-1-naphthalenesulfomide hydrochloride and 4',5,7-trihydroxyisoflavone had little effect on ALP amino acid phosphatase activity. Staurosporine slightly enhanced ALP serine and threonine phosphatase activities at a concentration of 0.1 mM. These results suggest that protein phosphatase activity does not depend on the protein kinase activity of ALP, since duality between the former and the latter is not supported. ALP may function less as a protein kinase than as a protein phosphatase. The coupling mechanism of phosphate dynamics may be regulated indirectly.

Regulation of the expression of alkaline phosphatase in a human breast-cancer cell line

Treatment of the cultured human breast-cancer cells BC-M1 with dexamethasone induced a placental-type alkaline phosphatase (ALP). Both the ALP activity and the mRNA level in the cells were increased. The induction of ALP activity by dexamethasone was time- and dose-dependent. The accumulation of ALP mRNA was inhibited by both actinomycin D and cycloheximide, indicating that its induction is a complex event and may involve other regulatory proteins. Retinoic acid showed opposing effects with dexamethasone on the expression of alkaline phosphatase. Retinoic acid (RA) and phorbol 12-myristate 13-acetate also substantially reduced the dexamethasone-induced expression of ALP. Studies on thermostability and sensitivity to various amino acid inhibitors indicated that the BC-M1 ALP is most similar to the placental form. Northern hybridization analysis also revealed that ALP mRNA transcripts in BC-M1 and term placenta are similar in size and are distinct from that of the placental-like mRNA transcript in choriocarcinoma cells. Analysis of the degradation of BC-M1 ALP mRNA showed a similar half-life of 27 h in the untreated and in dexamethasone- or RA-treated cells. These findings demonstrated that the induction of ALP in BC-M1 cells by dexamethasone is mainly due to the increase in the transcription of the ALP gene.

Immunohistochemical demonstration of intestinal-type alkaline phosphatase in stomach tumors induced by N-methyl-N'-nitro-N-nitrosoguanidine in rats

A polyclonal antibody against rat intestinal-type alkaline phosphatase (I-ALP) was generated and proven to be applicable immunohistochemically to paraffin-embedded sections. Expression of I-ALP in normal tissues, intestinal metaplasia and stomach tumors induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was then investigated in five different strains of rats. Male SD (Crj:CD), Lewis (LEW/Crj), WKY (WKY/NCrj), Wistar (Crj:Wistar) and F344 (F344/DuCrj) animals were given drinking water containing 100 micrograms/ml of MNNG for 30 weeks and were killed at week 50. Among the 5 strains, stomach adenocarcinomas were found most frequently in the SD case. The susceptibility of rats to induction of stomach carcinoma did not correlate with the development of intestinal metaplasias in each strain. Histochemical staining for mucin demonstrated all stomach tumors (adenomatous hyperplasias and well-differentiated adenocarcinomas) to consist mainly of gastric type cells (pyloric gland cell and surface mucous cell types), with intestinal-type tumor cells (goblet cell and intestinal absorptive cell types) being only occasional findings. Immunohistochemically, I-ALP was strongly positive on the striated cell borders of small intestinal absorptive cells of the villus and on brush borders of epithelial cells of kidney proximal tubules. I-ALP was also detected in the normal stomach, limited to the striated cell borders of absorptive cells of the upper one-fourth of intestinal metaplastic glands. I-ALP may thus be a useful marker for stomach tumor cells of intestinal absorptive cell type, indicative of maturation and differentiation. No stomach tumors consisting mainly of intestinal-type cells were found, and therefore there was no suggestion of any derivation from intestinal metaplasias.

Expression of a heterodimeric (placental-intestinal) hybrid alkaline phosphatase in KB cells

A hybrid heterodimeric alkaline phosphatase expressed in KB cells, consisting of placental and intestinal (fetal) subunits, was purified by use of two different immunoaffinity columns using the monoclonal antibodies 2HIMS-1 and HPMS-1. The closely related subunits were found to yield a dimeric active enzyme glycosylated as the mature heterodimeric forms. This enzyme displays intermediate properties to the placental and intestinal (fetal) isozymes with regard to heat stability, inhibition patterns with amino acids and amino acid derivatives, as well as reactivity with monoclonal antibodies specific for human alkaline phosphatase isozymes. Peptide fragments obtained from the hybrid enzyme after cyanogen bromide cleavage belong to either the placental or intestinal (meconial) isozyme as evaluated by SDS polyacrylamid gel electrophoresis, and the N-terminal amino acid sequences, corresponding to the placental and intestinal subunits, can be identified in the peptide fragments. By N-glycanase digestion or tunicamycin treatment, the molecular mass of the subunits was reduced to 62 kDa compared to 69 kDa for the native ones. The results confirm that some cell lines can synthesize hybrid alkaline phosphatases.

Interpretation and clinical significance of alkaline phosphatase isoenzyme patterns

Alkaline phosphatase (ALP, EC 3.1.3.1) is a membrane-bound metalloenzyme that consists of a group of true isoenzymes, all glycoproteins, encoded for by at least four different gene loci: tissue-nonspecific, intestinal, placental, and germ-cell ALP. Through posttranslational modifications of the tissue-nonspecific gene, for example, through differences in carbohydrate composition, bone and liver ALP are formed. Nowadays, most commercially available methods for separating or measuring ALP isoenzymes are easy to perform and sensitive and allow for reproducible and quantitative results. As more isoenzymes and isoforms have been characterized, confusion has arisen due to the many different names they were given. For the sake of simplicity and because of structural analogies, we propose an alternative nomenclature for the ALP isoenzymes and isoforms based on their structural characteristics: soluble, dimeric (Sol), anchor-bearing (Anch), and membrane-bound (Mem) liver, bone, intestinal, and placental ALP. Together with lipoprotein-bound liver ALP and immunoglobulin-bound ALP, these names largely fit the many forms of ALP one can encounter in human serum and tissues. The clinically relevant isoenzymes are sol-liver, Mem-liver, lipoprotein-bound liver, and Sol-intestinal ALP in liver diseases, and Sol-bone and Anch-bone ALP in bone diseases. Many different isoenzyme patterns can be found in malignancies and renal diseases. This test provides the clinician with valuable information for diagnostic purposes as well as for follow-up of patients and monitoring of treatment. However, ALP isoenzyme determination will only provide clinically useful information if the patterns are correctly interpreted. In this respect, care should be taken to use the proper reference ranges, taking into account the age and sex of the patient. A normal total ALP activity does not rule out the presence of an abnormal isoenzyme pattern, particularly in children. Separating ALP into its isoenzymes adds considerable value to the mere assay of total ALP activity.

Hepatocellular carcinoma producing universal type of alkaline phosphatase

We report on a 54-year-old man with hepatocellular carcinoma (HCC) associated with a marked elevation of serum alkaline phosphatase (ALP) levels. Serum ALP was biochemically similar to that of universal (liver/bone/kidney) type. The noncarcinomatous area revealed typical micronodular cirrhosis due to excessive alcohol consumption. By histochemical staining, ALP activity was demonstrated diffusely within the cytoplasm of carcinoma cells. Immunohistochemical observation of the carcinoma cells excluded the intestinal or placental type of ALP. Tissue extracts from the carcinomatous area had much higher ALP activities than those from a noncarcinomatous area, which also showed characteristics of the universal type. The present HCC is the first reported to produce and excrete the universal type of ALP.

Control of alkaline phosphatase activity in C3H10T1/2 cells: role of retinoic acid and cell density

The enzyme alkaline phosphatase (AP) has been shown to be lost or inappropriately expressed during carcinogenesis in some tissues. Because retinoic acid (RA) appears to play a role in the normal regulation of the enzyme (RA up-regulates AP in a variety of cell types) we have suggested that altered AP expression in some cancers may be caused by a defect in the ability of the cells to respond normally to retinoid. We have begun to use the chemically transformable mouse embryo fibroblast cell, C3H10T1/2, to investigate this possibility. In this initial study we characterized AP regulation in normal C3H10T1/2 cells and show that: (1) 10(-7) M RA increases AP activity within 3-4 h in serum-free medium; (2) serum inhibits short-term induction (0-8 h) in a concentration-dependent manner (10% serum causes complete inhibition); (3) during long-term RA exposure (24 h and 48 h), induction can be detected in serum-containing medium; (4) AP induction is dose related at RA concentrations from 10(-10) M to 10(-6) M in serum-free medium; (5) 10(-5) M RA is ineffective at inducing AP in serum-free medium during 8 h but is the most effective concentration in serum-containing medium during 24 h and 48 h exposures; (6) AP inducibility by RA requires near-confluent cell densities; and (7) when cultures become confluent, cells become constitutive for AP and no longer require RA for enzyme expression. The effects of serum and cell density on AP inducibility by RA and implications of the RA up-regulation of AP for teratogenesis are discussed.

Site-directed mutagenesis and epitope-mapped monoclonal antibodies define a catalytically important conformational difference between human placental and germ cell alkaline phosphatase

Placental (PLAP) and germ cell (GCAP) alkaline phosphatases were probed immunologically with a library of 18 murine monoclonal antibodies reacting with different conformational epitopes on PLAP. Three main antigenic domains (I, II and III) were mapped by antibody competition experiments and the relative binding of the antibodies to site-directed PLAP mutants. Relative affinities of each of the antibodies for the wild type (wt) GCAP were 2-3-fold lower than the values found for wt PLAP. Relative affinity was determined for a series of PLAP mutants, in which one, two or three amino acids were substituted for the corresponding wt GCAP residues by site-directed mutagenesis. Substitutions at residues 15, 38, 67, 241 or 254 induced a major decrease in affinity (6-10-fold) primarily for those antibodies reacting within domain I, whereas changes at positions 84 and 297 led to a 2-3-fold enhancement of affinities as measured with antibodies reacting within the three domains. Arg209 was found to constitute the only difference between the S and F allelic phenotypes of PLAP and to structure the epitope for the F/S allotype-discriminating antibodies. Arg241 was found to constitute the epitope for the antibody 17E3 that discriminates between PLAP and GCAP. Mutagenesis at position 68 or 133 had little effect on the overall reactivity with the antibody panel. Substitution in wt PLAP of Glu429 for Gly429 or even for His429 (found at this position in tissue-nonspecific alkaline phosphatase) and Ser429 (found in the intestinal alkaline phosphatase) induced a general decrease in affinities as detected by 16 of the 18 antibodies. The conformational change accompanying mutagenesis of Glu429 in PLAP, is important in view of the recent identification of Gly429 as the major determinant of the unique GCAP inhibition by the uncompetitive inhibitor L-Leu. Relative affinity values determined for the rare L-Leu sensitive heterodimeric FD and SD PLAP phenotypes, suggested that the reactivity pattern of the D homodimer with the antibody panel, would resemble more closely that of wt GCAP than wt PLAP. Our data suggest that the uncompetitive inhibition of GCAP by L-Leu is due to an enzymatically critical conformational change in a loop region proximal to the active site of the enzyme, induced by substitution of a single amino acid residue.

Further characterization of a heat-stable alkaline phosphatase with low sensitivity to L-phenylalanine

A heat-stable alkaline phosphatase, hitherto found in two families with inherited hyperphosphatasemia, was further characterized. The enzyme was similar to serum placental alkaline phosphatase from pregnant women concerning its apparent affinity constant (Km) for 4-nitrophenyl phosphate and its reactivity with H7 monoclonal anti-placental alkaline phosphatase (PLAP) antibodies, but different in the following respects: it exhibited greater heat stability, a higher pH optimum, lower sensitivity to inhibition by L-phenylalanine, and no reactivity with C2 monoclonal anti-PLAP antibodies. The low sensitivity to L-phenylalanine suggests that the enzyme might correspond to a rare phenotype of placental alkaline phosphatase found in human term placenta.

Expression of placental alkaline phosphatase in gastric and colorectal cancers. An immunohistochemical study using the prepared monoclonal antibody

The authors developed monoclonal antibodies (MoAb) against human placental alkaline phosphatase (PLAP). Four specific MoAb reacting only with PLAP and two nonspecific MoAb reacting equally with isozymes of alkaline phosphatase (hepatic, intestinal, and placental) were obtained. Immunohistochemical staining with the specific MoAb showed that the cell membrane and cytoplasm of cancer cells were stained in gastric and colorectal carcinoma. The incidence of PLAP positivity was 23% (25 of 107) of all gastric carcinomas. Among gastric carcinomas, the 42% (13 of 31) positivity of highly differentiated carcinoma (papillary adenocarcinoma and well-differentiated tubular adenocarcinoma) was a significantly higher rate than that found in poorly differentiated carcinoma (poorly differentiated adenocarcinoma and signet-ring cell carcinoma, five of 41, 12%). The incidence of PLAP positivity was 11% (four of 35) in colorectal carcinoma. In contrast, gastric adenoma, intestinal metaplasia, and noncancerous tissue adjacent to cancer did not show staining. These results indicated that expression of PLAP was apt to occur in more highly differentiated gastric carcinoma and was highly specific for carcinoma in the gastrointestinal tract, although its incidence was not high.

The expression of placental alkaline phosphatase (PLAP) and PLAP-like enzymes in normal and neoplastic human tissues. An immunohistological survey using monoclonal antibodies

The immunohistological expression of placental alkaline phosphatase (PLAP) and PLAP-like enzyme was studied in frozen sections from a wide variety (n = 254) of normal and malignant tissues using monoclonal antibodies reactive with PLAP (H317) and PLAP/PLAP-like enzyme (H17E2; H315). PLAP/PLAP-like reactivity was seen in normal thymus, and foetal and neonatal testis, and in 21 out of 22 malignant germ cell tumours (GCTs), but was also found in normal endocervix, normal Fallopian tube and in 28 out of 167 non-GCTs (particularly in ovarian and proximal gastrointestinal tract tumours). Positivity for true PLAP (as demonstrated with H317) was seen in term placenta, in endocervix, and in Fallopian tube (but not in other normal tissues) and was commonly found in ovarian and proximal gastrointestinal tract tumours. Reactivity with H317 was unusual in malignant GCTs (2 out of 22 cases). These findings confirm that PLAP/PLAP-like positivity is a highly sensitive immunohistological marker for malignant GCTs, but one which by itself is of only moderate specificity. Furthermore, expression of true PLAP is rare in GCTs and favours instead an origin from the ovary or proximal gastrointestinal tract. The results also indicate that the predominant heat-stable alkaline phosphatase species in normal foetal and neonatal testis, and in thymus has a similar immunohistological profile to that found in malignant GCTs, and is a PLAP-like enzyme ("germ cell alkaline phosphatase") distinct from true PLAP. The occurrence of this marker in GCTs would appear to reflect increased eutopic production of an enzyme present in trace amount in corresponding normal tissues rather than a genuine example of ectopic expression.

Placental-like alkaline phosphatase in seminoma

Tumor marker identification in testicular cancer has contributed to early detection and monitoring of non-seminomatous disease. A placental alkaline phosphatase-like (PLAP-like) enzyme derived from seminomas has recently been focused upon as a possible marker for this disease. The biochemistry of the PLAP-like enzyme is reviewed, as well as its occurrence in tissue and sera from healthy persons and patients with testicular cancer.

Placental-type alkaline phosphatase in peritoneal fluid of women with endometriosis

Alkaline phosphatase (ALP) activities were studied in peritoneal fluid obtained from patients with untreated endometriosis and control women who had normal pelves. The patients (n = 18) had significantly higher total ALP (8.65 +/- 5.69 mU/mg, p less than 0.01) and thermostable ALP (0.28 +/- 0.23 mU/mg, p less than 0.05) than the controls (n = 7) (total ALP = 2.41 +/- 1.15; thermostable ALP = 0.09 +/- 0.04 mU/mg). The contents of the thermostable ALP in the total ALP were 4.5 +/- 2.4% for controls and 3.6 +/- 2.3% for patients. To define the biochemical characteristics of the thermostable ALP, the enzyme was partially purified from a mixture of peritoneal fluid from 16 patients. The partially purified, heated ALP (PFALP) responded to the various inhibitors, activators, and pH values tested in a significantly similar manner as a purified, heated human placental ALP did. Our data suggest that PFALP may be a placental-type (or Regan) ALP.

Purification and some properties of the fast migrating alkaline phosphatase in FL-amnion cells (the Kasahara isoenzyme) and its cDNA cloning

One of two main FL-amnion cell alkaline phosphatase (AP), the fast migrating one (FL-APF) has been reported to be identical to Kasahara isoenzyme (K.I.), which occurs preferentially in sera of patients with primary hepatoma. We purified FL-APF of which the apparent molecular weight was 135,000 by gel filtration, and that of the subunit was 62,000 on SDS/PAGE, indicating homodimeric structure of FL-AL-APF. FL-APF was found to react with monoclonal antibody against adult intestinal AP, but not with monoclonal antibody to placental AP. We isolated FL-APF cDNA clone from FL-amnion cells, of which cDNA was 2525 base pairs in length. Nucleotide sequence of the coding region and the 3' untranslated region was identical to the sequence of human adult intestinal AP cDNA. But the untranslated region of the 5' end of the isolated clone was slightly longer than that of intestinal AP. Hence, FL-APF (K.I.) may occur by altered glycosylation of intestinal AP.

The human alkaline phosphatases: what we know and what we don't know

A review of the human alkaline phosphatases dealing specifically with (1) the gene loci, (2) characterization and discrimination of the various enzymes, (3) polymorphism at the enzyme level, (4) cDNA and gene structures, (5) membrane binding, (6) the carbohydrate moieties, (7) hypophosphatasia, (8) alkaline phosphatases in malignancies, (9) function.

Placental alkaline phosphatase-like isoenzymes produced by human gastric cancer cells

The human gastric cancer cell lines, MKN1 and SCH, were biochemically and biologically characterized according to the monophenotypic expression of placental alkaline phosphatase (PLAP)-like enzymes. The MKN1 cell line, derived from adenosquamous carcinoma, showed the same enzyme properties as the Regan isoenzyme, whereas the SCH cell line, derived from primary gastric choriocarcinoma, had properties identical with the Nagao isoenzyme. Regan isoenzyme activity expressed by MKN1 cells was stimulated by glucocorticoid and suppressed by retinoic acid. Both agents had no significant effect on SCH cells. On the other hand, Nagao isoenzyme activity expressed by SCH cells was stimulated by sodium butyrate, which had no stimulatory effect on MKN1 cells. Moreover, the PLAP-like activity of MKN1 cells showed no observable relationship to human chorionic gonadotropin (hCG)-producibility. Whereas expression of the Nagao isoenzyme by the SCH cell line is presumably a result of functional differentiation in the trophoblastic direction, that of the Regan isoenzyme by the MKN1 cell line is probably not. Perhaps the Regan isoenzyme is related to carcinogenesis.

Lectin affinity electrophoresis of alkaline phosphatase for the differentiation of bone and hepatobiliary disease

An affinity electrophoresis procedure is described for the separation and quantification of the bone- and liver-derived fractions of alkaline phosphatase in plasma. Separation is carried out on cellulose acetate membrane pre-soaked with buffer containing wheat germ lectin. The electrophoretic mobility of the bone enzyme is preferentially retarded by the lectin and this fraction is well separated from the liver fraction. After separation, enzyme activity is demonstrated by staining using an indigogenic alkaline phosphatase substrate incorporated in agar gel, and the stained fractions quantified by densitometry. The procedure has low imprecision, good linearity, and the activities of the bone and liver fractions correlate well with values obtained using nonelectrophoretic quantification methods. The procedure is especially suitable for use in the diagnostic laboratory.

Monoclonal antibodies to enzymes

The production, identification, and utilisation of monoclonal antibodies to enzymes are reviewed. Such antibodies may be produced in vitro by the mouse-hybridoma technique, may occur naturally in vivo as enzyme-binding immunoglobulins and may be produced in the laboratory from the lymphocytes of patients whose sera contains such immunoglobulins. The diagnostic application of monoclonal antibodies to enzymes is considered, with special reference to their use in the measurement of the MB-isoenzyme of creatine kinase, pancreatic isoamylase, prostatic acid phosphatase, and the isoenzymes of alkaline phosphatase.

Immunohistochemistry of germ cell and trophoblastic neoplasms

The immunoprofiles of 121 germ cell and trophoblastic neoplasms were defined, using a battery of antibodies against cytokeratin (CK), vimentin (VIM), epithelial membrane antigen (EMA), placental alkaline phosphatase (PLAP), S-100 protein, leukocyte common antigen (LCA), UCHL-1, LN-2, carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), chromogranin A, Leu-7, alpha-fetoprotein (AFP), alpha-1-antitrypsin (AAT), and the beta subunit of human chorionic gonadotropin (BHCG). In addition to 85 neoplasms of testicular origin, the cases included eight ovarian germ cell tumors and 28 extragonadal neoplasms. All tissues had been subjected to formalin fixation and paraffin embedding. Similar immunoreactivity patterns were seen in gonadal and extragonadal neoplasms, gestational and nongestational choriocarcinomas, components of mixed germ cell tumors and their pure counterparts, and metastatic and primary lesions. Placental alkaline phosphatase was a sensitive marker of germ cell differentiation, and expression of this marker in the absence of EMA appeared to be a staining pattern unique to germ cell tumors. Both LCA and S100 were absent in neoplastic germ cells, and thus were useful in differentiating these tumors from malignant lymphoma and malignant melanoma, respectively. Cytokeratin was helpful in distinguishing seminomas/dysgerminomas from nonseminomatous germ cell tumors, although 10% of seminomas showed focal or diffuse cytokeratin reactivity. Finally, 75% of all germ cell neoplasms displayed NSE, calling the specificity of this determinant into question.

The prevalence of variant alkaline phosphatase in hepatocellular carcinoma in southern African blacks

The prevalence of variant alkaline phosphatase in the serum of 335 southern African blacks with hepatocellular carcinoma was determined using polyacrylamide gel electrophoresis. The isoenzyme was detected in 2% (seven of 335) of the patients: it could not be found in the serum of 300 matched, healthy individuals or in 56 patients with various benign hepatic diseases. Variant alkaline phosphatase is thus of little use as a diagnostic marker of hepatocellular carcinoma in southern African blacks. The reported prevalence of this isoenzyme in hepatocellular carcinoma ranges between 3% and 31%. Higher frequencies usually are recorded in populations with a low incidence of the tumor, and the lowest frequencies have been found in Chinese patients. Our finding of variant alkaline phosphatase in only 2% of another high incidence population fits this trend. Patients with tumors that secreted the variant isoenzyme had a significantly higher serum total alkaline phosphatase activity than those with tumors lacking this property.

Seminoma-derived Nagao isozyme is encoded by a germ-cell alkaline phosphatase gene

A full-length placental alkaline phosphatase (PLAP) cDNA was used to identify and clone the PLAP-like Nagao isozyme gene from human genomic libraries. The entire nucleotide sequence of the gene reveals the existence of 11 exons interrupted by 10 small introns (76-427 base pairs). Putative regulatory sequences have been identified in the promoter regions as well as dispersed in the introns. The deduced amino acid sequence of the Nagao isozyme indicates that the mature molecule is composed of 513 amino acids, of which 12 residues are different from the sequence of PLAP (98% homology). A sequence derived from exon III of the Nagao isozyme gene was used to synthesize a peptide (NH2-Lys-Leu-Gly-Pro-Glu-Thr-Phe-Leu-Ala-COOH) that contains two mutations with respect to the corresponding PLAP sequence. This peptide elicited rabbit polyclonal antibodies that reacted specifically with the seminoma Nagao isozyme but not with PLAP in electrophoretic transfer blots. These results indicate that the tumor, and possibly the normal testis, Nagao isozyme is encoded by a gene referred to as germ-cell alkaline phosphatase gene that differs from the PLAP gene expressed by syncitiotrophoblastic cells.

Clinical and biological significance of an isozyme tumor marker--PLAP

In 1930 the determination of serum alkaline phosphatase in patients with bone or liver disease ushered in the era of clinical enzymology. The association of elevated (bone) alkaline phosphatase in serum of patients with osteogenic sarcoma was the first evidence that tumor cells themselves produced the enzyme. It became clear, however, in the 1960s that the serum alkaline phosphatase was not a single enzyme but consisted of a family of isozymes originating from liver, bone, intestine, and placenta. This was a consequence of the introduction of a combination of electrophoretic separations, heat inactivation, and organ-specific amino acid inhibitors. This combination of measurements made possible the demonstration of a serum alkaline phosphatase of lung cancer origin, as confirmed by the histochemical visualization in lung cancer of the Regan Isozyme (placental alkaline phosphatase-PLAP). At present, the measurement of PLAP has its greatest utility as a tumor marker in seminoma and ovarian cancer. A PLAP-like isozyme in normal testis and ovary is expressed in these and other neoplasias and appears to be related to rare alleles of placental alkaline phosphatase. Current studies have utilized a panel of monoclonal antibodies to detect useful epitopes that suggest that PLAP and PLAP-like isozymes are coded by different genes. The PLAP gene has now been cloned and sequenced by Millan and others. This fundamental new information is providing a base line that will make it possible to explain the overlapping specificities of intestinal and placental isozymes, the degree of uniqueness of the PLAP-like isozyme, the precise mechanism of uncompetitive inhibition by L-phenylalanine and the evolutionary history of the alkaline phosphatases.(ABSTRACT TRUNCATED AT 250 WORDS)

Placental-like alkaline phosphatase reactivity in human tumors: an immunohistochemical study of 520 cases

Placental-like alkaline phosphatase (PLAP) activity has been reported in various human neoplasms of both somatic and germ cell types. The expression of PLAP was examined with a polyclonal antibody and the immunoperoxidase technique in formalin-fixed, paraffin-embedded sections of 37 germ cell neoplasms and 483 somatic tumors. The expression of keratin and epithelial membrane antigen (EMA) was concurrently assessed to determine whether these stains were helpful in distinguishing germ cell neoplasms from somatic tumors that might mimic them microscopically. All germ cell lesions were reactive for PLAP, but so were 62 somatic carcinomas, usually in female müllerian, intestinal, and lung cancers and less often in carcinomas of the breast and kidney. PLAP-reactive somatic tumors exhibited EMA and keratin positivity in the absence of prior protease digestion, whereas germ cell neoplasms failed to do so. Malignant mesotheliomas were nonreactive for PLAP, as were carcinomas of the nasopharynx, adrenals, liver, pancreas, stomach, prostate, and urinary bladder. PLAP is a highly sensitive but nonspecific immunohistologic marker of germ cell differentiation. However, non-protease-enhanced stains for keratin and EMA allow separation of germ cell and somatic carcinomas, despite their shared capacity for PLAP expression. In somatic neoplasms, PLAP immunoreactivity might be of potential use in predicting possible primary sources for metastatic tumors of unknown origin.

Sugar-chain heterogeneity of human alkaline phosphatases: differences between normal and tumour-associated isozymes

The sugar-chain heterogeneity of alkaline phosphatases (ALPs) from various human organs was investigated by using the serial lectin affinity technique. This technique revealed a possible structure of the sugar chain(s) of ALP isozymes and clarified a difference in affinity on the lectin column not only among three genetically different isozymes (liver/bone/kidney, intestinal and placental types) but also among liver, bone, and kidney ALPs. Lectin-binding profiles of ALPs in these human organs closely resembled those in the corresponding organs of the rat, as reported previously, suggesting that heterogeneities in sugar chains of ALPs have a specificity for the respective organs rather than being species-specific. Lectin-binding profiles of tumour-produced placental and liver ALPs were significantly different from those of ALPs in the respective normal organs. However, the two altered ALPs exhibited similar lectin-binding affinities. Isoelectric focusing analysis showed essentially no difference in protein charge between the normal and tumor-produced ALPs. Moreover, tumour-produced ALPs had the same N-terminal amino acid sequence and peptide mapping as normal ALPs. From these results, it is possible to suggest that organ-specific sugar chains in ALP isozymes are changed into those peculiar to tumours in association with malignant transformation.

Isolation of placental-type alkaline phosphatase associated with human syncytiotrophoblast membranes using monoclonal antibodies

Placental-type alkaline phosphatase (PLAP) has been purified from human term syncytiotrophoblast microvillous plasma membranes by immunoaffinity chromatography using the immobilized monoclonal antibodies H317 and H315. The eluted enzymatically active PLAP had a molecular weight in the regions of 115K and 130K, with an occasional higher molecular weight form at 180K. On reduction to a 66K monomeric form, both enzymatic activity and immunoactivity against the PLAP-reactive monoclonal antibodies were lost. The monomeric form of syncytiotrophoblast microvillous plasma membrane- (StMPM-)associated PLAP displayed electrophoretic polymorphism on 2D-PAGE.

Expression of different-sized placental alkaline phosphatase mRNAs in placenta and choriocarcinoma cells

The expression of human placental-type alkaline phosphatase (ALPase) in the placenta and in three choriocarcinoma cell lines was examined by translation in vitro and RNA blot analysis using a cDNA for placental ALPase. Placental RNA directed the synthesis of two polypeptides that could be immunoprecipitated with antiserum to placental ALPase. Translation of RNA from the choriocarcinoma cell lines, with or without sodium butyrate treatment, yielded a single immunoprecipitable product of molecular weight intermediate between those of the products from the placenta mRNA. Two cDNA clones for placental ALPase were isolated by antibody screening of a placental cDNA library constructed in lambda gt11. The overlapping cDNAs include 462 nucleotides of coding sequence. RNA blot analysis has confirmed that induction of placental-type ALPase levels during placental development is accompanied by an increase in steady-state placental ALPase mRNA concentrations. Examination of the mRNAs revealed a placental ALPase mRNA of 3.0 kilobases (kb) and a distinct choriocarcinoma placental-type ALPase mRNA of 2.6 kb, implying that transformation of normal to malignant trophoblast is associated with the expression of a distinct placental-type ALPase gene transcript and its protein product.

Tissue origin of serum placental-like alkaline phosphatase in cigarette smokers

A variety of solubilised tissue extracts from cigarette smokers and non-smokers have been screened quantitatively for both placental alkaline phosphatase (PLAP) and placental-like alkaline phosphatase (PLAP-like AP) in order to identify the possible tissue origins of the circulating PLAP-like AP found in most smokers. Lung alveolar tissue, and to a lesser extent colonic tissues, contained both PLAP-like AP and PLAP. Tissues from smokers and non-smokers contained comparable proportions and amounts of PLAP and PLAP-like AP. No other tissue source of PLAP-like AP was found other than those previously reported for testicular, endometrial and thymic tissue. Selective release of PLAP-like AP from the lung in cigarette smokers seems likely to be a major source for this isoenzyme in peripheral circulation.

Serum marker potential of placental alkaline phosphatase-like activity in testicular germ cell tumours evaluated by H17E2 monoclonal antibody assay

A monoclonal antibody (H17E2) was used in a solid-phase localisation of enzyme activity (ILEA) assay to evaluate placental-like alkaline phosphatase (PLAP) as a serum marker of testicular germ cell tumours. Single or repeated assays were performed on 213 normal blood donor and a smaller number of term pregnancy and testicular cancer sera. The detection limit of PLAP by this system was 0.14 O.D. units equivalent to 0.04iul-1. Of 50 patients with established metastatic disease tested before treatment, 88% of 16 with seminoma, 54% of 13 with mixed seminoma and malignant teratoma and 33% of 21 with malignant teratoma had serum PLAP greater than 0.2 O.D. units. This compared to an incidence of 2% in non-smokers and of 29% in smokers who had been free of disease for more than 12 months. In 15 of 22 successfully treated patients, pre-treatment serum PLAP exceeded 0.2 O.D. units (mean 0.69 O.D.) and varying (53-97%) reductions in the initial levels occurred with treatment. These results with monoclonal antibody ILEA assay suggest that measurement of PLAP levels will be useful in the management of patients with germ cell tumours, particularly seminoma.

Placental alkaline phosphatase as a tumour marker in seminoma using the H17 E2 monoclonal antibody assay

Serum samples from 62 patients with seminoma were assayed for placental alkaline phosphatase-like activity using the monoclonal antibody H17 E2, in order to evaluate its utility as a serum tumour marker. Fifteen of 16 patients (94%) with active seminoma had elevated serum PLAP levels. Sixteen of 46 (35%) of patients considered to be in remission had elevated PLAP levels (false positive rate 35%). Fifteen false positive results were considered attributable to concomitant smoking, and if these patients are excluded, only one false positive case was detected. In 7 out of 7 patients sequential PLAP assays reflected clinical response to treatment.

5-Bromo-2'-deoxyuridine induces placental alkaline phosphatase biosynthesis in cultured choriocarcinoma cells

5-Bromo-2'-deoxyuridine (BrdUrd) stimulated the biosynthesis and hence increased the activity of placental alkaline phosphatase in choriocarcinoma cells. While BrdUrd had no effect on the rate of degradation or processing of placental alkaline phosphatase, it increased the rate of phosphatase synthesis. The stimulation of enzyme activity could be completely accounted for by the increase in alkaline phosphatase protein. Both control and BrdUrd-induced cells contained polypeptides of 61,500 and 64,500 Da, identified as the precursor and fully processed forms of placental alkaline phosphatase monomer. The half-life of this enzyme monomer in both control and BrdUrd-treated cells was estimated to be 36 h. BrdUrd induced a specific increase in the placental alkaline phosphatase mRNA leading to the observed enhancement of biosynthesis. The continued rise in alkaline phosphatase biosynthesis in BrdUrd-induced cells following BrdUrd removal indicated that this analog acted by incorporation into DNA.

A new alkaline phosphatase isoenzyme abnormality

We report on a new alkaline phosphatase isoenzyme abnormality occurring as an incidental finding in a male infant aged 4 months. Isoenzyme electrophoresis on cellulose acetate showed a prominent, diffuse alkaline phosphatase staining band in the alpha 1-globulin position together with a second band in the alpha 2/beta region and minor 'trailing' in the intermediate alpha 2 region. Normal liver and bone alkaline phosphatase were absent and intestinal phosphatase was not detected. On acrylamide gel electrophoresis a marked origin band was detectable suggesting the presence of high molecular weight enzyme. In addition, a series of compact bands in the alpha 2/beta position was present cathodal to the usual liver and bone isoenzymes. Total alkaline phosphatase activity was marginally elevated and was heat labile, L-phenylalanine resistant and partially L-homoarginine and L-leucine sensitive.

Serum placental type alkaline phosphatase in cigarette smokers

By means of enzyme immunoassays based on two monoclonal antibodies with specificities for distinct forms of placental type alkaline phosphatase (Pl-ALP), together with L-leucine inhibition studies, it has been possible to distinguish the Nagao type carcinoplacental enzyme from other placental type alkaline phosphatases. This approach has shown that it is the Nagao type (placental like) enzyme which is detectable in small amounts in the plasma of healthy individuals, particularly cigarette smokers.

Preparation and characterization of monoclonal antibodies against placental alkaline phosphatase and other human trophoblast-associated determinants

We have prepared monoclonal antibodies by immunizing BALB/c mice with purified human term placental plasma membranes. The antibodies were selected to show predominant specificity for trophoblast and trophoblast derivatives. Four of these antibodies have been found to recognize the placenta-specific isozyme of alkaline phosphatase (EC 3.1.3.1), and to cross-react with the closely related testis form of this enzyme. One antibody recognized transferrin, a serum protein with an abundant placental receptor. The specificities of the other antibodies, whose target antigens are unknown, are described. Their reactivity with some human tumour-derived epithelial cell lines suggests that they may provide useful markers of human trophectoderm differentiation, as well as for properties selected for during tumour progression.

Demonstration of placental and placental-like alkaline phosphatase in non-malignant human tissue extracts using monoclonal antibodies in an enzyme immunoassay

The occurrence and nature of heat-stable placental-type alkaline phosphatase (Pl-ALP) in extracts from a variety of non-malignant human tissues has been investigated using monoclonal antibodies in a sensitive solid-phase enzyme immunoassay. The presence of Pl-ALP was confirmed in testicular, cervical and lung tissue extracts, and trace amounts were also detected in extracts from mammary and ovarian tissue. Evidence is presented that normal testis contains at least two forms of Pl-ALP, the major component being an L-leucine-inhibitable placental-like enzyme which is not the D-variant of Pl-ALP. These results have a bearing on the occurrence of Pl-ALP and placental-like ALP activity in malignancy.

Immunochemical data suggesting a pattern for the evolution of human placental alkaline phosphatase

Hyperimmune absorbed rabbit antisera which were reactive with epitopes specific for individual variants of human placental alkaline phosphatase were tested for their reactivity with primate placental alkaline phosphatases. Using the three epitope-specific reactivities defined previously, we found that: epitope I is present in the S-, D- and I-variants of human placental phosphatase, and in the chimpanzee and pygmy chimpanzee placentae; epitope II is present in the F- and 17-variants, and in the Nagao isoenzyme of human placental alkaline phosphatase, and in some orangutan placentae and all spider monkey placentae tested; epitope III is present in the F- and 17-variants, and the Nagao isoenzyme of human placental alkaline phosphatase, and in all the spider monkey placentae and the single squirrel monkey placenta examined. The binding assay was complemented by a competitive radioimmunoassay, which confirmed that the spider monkey placental samples were binding to the same antibody population which bound the human enzymes. The presence of epitopes characteristic of rare human placental phosphatase variants in these remote primate relatives suggests that the rare variants in the current human population have been present during the entire course of evolution. The presence of both epitopes characteristic of the Nagao isoenzyme in spider monkeys suggests that this variant isoenzyme is closely related to the enzyme present in the primate placenta at the time of species divergence (humans and New World monkeys). A hypothetical scheme for this divergence is proposed.