Regulation of human chorionic gonadotropin synthesis in cultured human placental cells by glucocorticoids

The synthesis of hCG and its subunits in temperature-sensitive, simian virus 40 tsA mutant-transformed human first trimester and term placental cells and in choriocarcinoma cells was studied in the presence and absence of glucocorticoid hormones. The tsA-transformed placental cells were studied at 33 C (the temperature at which the cells exhibit the transformed phenotype) and at 40 C (the temperature at which the cells regain their differentiated nontransformed phenotype). The glucocorticoids cortisol and dexamethasone did not affect the synthesis of hCG or hCG alpha in either transformed term placental cells or choriocarcinoma cells. In the tsA-transformed first trimester placental cells, however, glucocorticoids greatly inhibited hCG synthesis but induced hCG alpha synthesis. The inhibition on hCG synthesis was immediate, stronger at 40 C than at 33 C, and independent of the growth stage of the cells. The glucocorticoid effects were specific; neither estradiol nor progesterone affected the synthesis of hCG or hCG alpha. Furthermore, progesterone did not block the action of the glucocorticoid. These selective effects in cultured first trimester placental cells suggest that glucocorticoids may play an important role in the regulation of hCG production during early pregnancy.     

Detection of the free beta subunit of human chorionic gonadotropin (HCG) in cultures of normal and malignant trophoblast cells, pregnancy sera, and sera of patients with choriocarcinoma

Immunoaffinity adsorption techniques, utilizing specific antisera for hCG and its subunits bound to Sepharose 4B, have been employed to separate hCG alpha beta dimer and free subunits of hCG. As previously reported by this and a number of other laboratories, trophoblast cells (in vivo and in vitro) produce free alpha subunit in addition to hCG dimer. We have now shown that cultured JAr choriocarcinoma cells also secrete free beta subunit: 37% of the total beta subunit (combined and free) secreted by JAr cells is in the free form. Moreover, in pooled sera from choriocarcinoma patients 15% of total beta subunit is free, and in media from placental explant cultures and in pooled first trimester pregnancy sera 11% and 6.5%, respectively, of total beta subunit are in the free form. The free beta s are all of similar mol wt to the combined forms, and associate with urinary hCG alpha to form hCG. Free alpha s, which are larger than the combined forms, are unable to associate with urinary hCG beta to form hCG. We propose that the supply of combinable alpha subunit, rather than beta, limits dimer formation.     

Expression of a functional human insulin receptor from a cloned cDNA in Chinese hamster ovary cells.

We have placed human insulin receptor cDNA into a vector under the control of the simian virus 40 (SV40) early promoter and tested its function by transient expression in microinjected Xenopus oocytes and by expression in stably transformed CHO cells. The precursor and the alpha and beta subunits of the receptor were detected by immunoprecipitation from extracts of these cells. The human insulin receptor expressed in CHO cells specifically binds 125I-labeled insulin but not insulin-like growth factor I, displays insulin-stimulated autophosphorylation of the beta subunit, and mediates insulin-stimulated 2-deoxyglucose uptake. We conclude that the human insulin receptor is synthesized, processed normally, and functional in this heterologous cell system.     

Expression of human choriogonadotropin in monkey cells using a single simian virus 40 vector.

We have inserted the cDNAs coding for both polypeptide subunits, alpha and beta, of human choriogonadotropin (hCG) into a single simian virus 40 expression vector in such a way that they replace the viral VP2 and VP1 coding sequences, respectively. Monkey cells infected with this virus and the appropriate helper virus produce dimeric hCG. hCG produced in this system was shown to chromatograph identically to standard hCG preparations on gel filtration and to be biologically active in the mouse uterine weight assay.     

Synthesis and secretion of human chorionic gonadotropin and its subunits in choriocarcinoma cells: a comparative study with normal placental cells.

The human choriocarcinoma cell line, BeWo, synthesizes the glycoprotein hormone, human chorionic gonadotropin (hCG). We have undertaken this study to compare the synthesized and secreted forms of hCG and their alpha- and beta-subunits in cell cultures of BeWo cells to those forms of normal placental cells by immunobinding techniques. BeWo cells appeared to synthesize and secrete one species of the respective hCG subunit. The immature alpha- and beta-subunits, synthesized in BeWo cells as well as those of placental cells, were digested by endoglycosidase H indicating N-linked sugar chain(s) to be the high-mannose type. The mature alpha- and beta-subunits, secreted by BeWo cells as well as subunits of urinary hCG which are usually used as a standard hCG secreted by normal placental cells, were sensitive to neuraminidase treatment indicating that these subunits have terminal sialic acid(s). Contrary to placental cells, mature subunits of BeWo hCG could not be found in any subcellular fraction indicating a rapid secretion rate or supporting the hypothesis that BeWo cells secrete hCG subunits without the formation of secretory granules. The alpha-subunit synthesized in BeWo cells had a slightly lower molecular weight than that of placental cells; however, the alpha-subunit secreted by BeWo cells had a slightly higher molecular weight than the alpha-subunit of urinary hCG. The beta-subunits synthesized and secreted by BeWo cells had slightly higher molecular weights than beta-subunits of both placental cells and urinary hCG. Even after digestion by N-glycanase as well as endoglycosidase H, molecular weights were still different between the respective subunits of BeWo and placental cells indicating that the apoprotein structures of BeWo hCG subunits may differ from those of placental cells. Moreover, urinary beta-subunit was sensitive to endo-alpha-N-acetylgalactosaminidase treatment but the beta-subunit secreted by BeWo cells was not, indicating that the structure of O-linked sugar chain(s), if present, may be unusual. Analysis of assembled and free forms of subunits of BeWo cell cultures by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions followed by immunobinding methods revealed that subunits are associated intracellularly and then secreted to the media as hCG. Moreover, only free beta-subunits, but not alpha-subunits, of BeWo hCG were found intra- and extracellularly.     

Preferential masking by the receptor of immunoreactive sites on the alpha subunit of human choriogonadotropin.

125I-Labeled human choriogonadotropin (125I-hCG) bound to rat ovarian receptor was solubilized in Triton X-100. By using increasing concentrations of nine different antisera specific for the individual subunits of human choriogonadotropin (hCG), free 125I-hCG or 125I-hCG-receptor complex was precipitated by double-antibody technique. The ability of any antiserum to bind to the hormone-specific beta subunit was not affected by hCG binding to receptor, suggesting that this subunit is not directly involved with the receptor in the final state of the hormone-receptor complex. In contrast, every antiserum specific for the alpha subunit was dramatically inhibited in binding to the solubilized 125I-hCG-receptor complex. These results suggest that the alpha subunit directly interacts with the receptor, thereby masking immunoreactive sites normally available on the free hormone. Because a number of reports describe binding activity of high concentrations of immunopurified beta subunits of hCG, we propose a two-step model for the binding of hCG to receptor and postulate separate and distinct roles for the subunits. We propose that the binding of hCG to the receptor involves a specific low-affinity initial interaction of the beta subunit with the receptor that activates a second site for the high-affinity binding of alpha subunit and stabilization of the hormone-receptor complex.     

Inhibin and activin modulate the release of gonadotropin-releasing hormone, human chorionic gonadotropin, and progesterone from cultured human placental cells.

Although it is clear that human chorionic gonadotropin (hCG) and progesterone play fundamental roles in pregnancy, the regulation of placental production of these hormones remains to be defined. Recent evidence suggests that the human placenta expresses proteins related to inhibin (alpha beta subunits) or activin (beta beta subunits). Inhibin and activin (follicle-stimulating hormone-releasing protein) possess opposing activities in several biological systems including pituitary follicle-stimulating hormone (follitropin) secretion, erythroid differentiation, and gonadal sex-steroid production. The actions of purified inhibin and activin on hormonogenesis by primary cultures of human placental cells were studied. The addition of activin increased gonadotropin-releasing hormone (GnRH) and progesterone production and potentiated the GnRH-induced release of hCG. Inhibin by itself did not modify placental immunoreactive GnRH, hCG, and progesterone secretion but reversed the activin-induced changes. Neither inhibin nor activin influenced the release of human placental lactogen. Furthermore, transforming growth factor beta, structurally related to inhibin/activin, did not significantly influence hormone release from cultured placental cells. These results support the hypothesis that inhibin and activin may play a role in regulating the release of GnRH, hCG, and progesterone from placenta and implicate inhibin-related proteins in the endocrine physiology of human pregnancy.     

Discordant and variable production of human chorionic gonadotropin and its free alpha- and beta-subunits in early pregnancy

Monoclonal antibodies specific to dimer hCG (alpha beta), free beta-subunit (beta hCG), free alpha-subunit (alpha hCG), and total beta hCG (dimer + free beta hCG) were used to monitor discordant production of hCG and its subunits during the early stages of embryo implantation. Sera collected 3 to 22 days postovum retrieval were assayed from patients participating in an in vitro fertilization program. In the majority of patients with ongoing pregnancies (n = 16), rising levels using the dimer hCG assay were first detected at an average time of 9.2 days post retrieval compared to 8.3 days for the total beta hCG assay and 6.5 days for the free beta hCG assays. Between days 5 to 9 after retrieval, the rises in the total beta hCG assay were due to predominantly free beta hCG subunit production. The proportion of total beta hCG levels due to free beta hCG subunits declined progressively from day 9 to less than 5% by day 22. Free alpha hCG levels remained low with rising levels first detected from day 18. A second group of patients (n = 12) had delayed, slowly rising levels in the total beta hCG assay which were first detected at an average of 12.4 days and associated with mainly biochemical pregnancies (n = 10). In these patients, rising total beta hCG levels were due to predominantly free beta hCG production. The subsequent loss of their pregnancy may be due to poor luteal support associated with delayed rises in dimer hCG levels. In nonconceptual cycles (n = 47) no significant rises were detected in dimer or free hCG subunits. Although the major form of hCG in circulation is dimer hCG, the origin of free beta hCG production in the early stages of implantation may be due to poorly differentiated trophoblastic tissue. Thus falling levels of free beta hCG subunits associated with increasing dimer hCG production may reflect increasing alpha hCG production by the proliferating layer of cytotrophoblastic cells.     

O-glycosylation of the alpha-subunit does not limit the assembly of chorionic gonadotropin alpha beta dimer in human malignant and nonmalignant trophoblast cells

Biosynthetic experiments were carried out in cultures of human malignant trophoblast cells (the JAR cell line) and in explants of normal first trimester human placental tissue to test the hypothesis that the O-glycosylation of the glycoprotein hormone alpha-subunit at Thr-39 regulates the assembly of the CG alpha beta dimer. This modification of alpha has been shown to ablate its ability to combine in vitro with the beta-subunit of bovine LH and might explain why JAR cells and placental explants secrete uncombined alpha- and beta-subunits in addition to the hCG alpha beta dimer. We have previously detected an O-linked carbohydrate chain at Thr-39 in preparations of secreted free alpha-subunit, but not dimer CG alpha from JAR culture medium. We report here evidence that the O-glycosylation of alpha does not regulate the biosynthetic assembly of the hCG dimer in cultures of JAR choriocarcinoma cells or first trimester placental explants. The intracellular precursor forms of alpha and beta that accumulate in the endoplasmic reticulum and combine in that compartment are not yet modified with O-linked carbohydrate, as determined by measurements of their [3H]galactosamine content after biosynthetic labeling of amino sugars with [3H]glucosamine. Furthermore, only half of the free alpha-subunit secreted by JAR cells and less than 10% of free alpha secreted by 10-week-old placental explants received the O-linked chain. This was shown by determining the ratio of the unglycosylated and glycosylated forms of the tryptic peptide from free alpha that contains the O-glycosylation site (residues 36-42). Based on these findings, we make the following conclusions. 1) O-Glycosylation of alpha-subunit is a late event in the secretory pathway of trophoblasts compared to the rapid combination in the rough endoplasmic reticulum of hCG subunit precursors to form alpha beta dimer. 2) Association of alpha with beta precludes the subsequent addition of the glycan to alpha at Thr-39. 3) The alpha molecules that fail to combine with beta in the endoplasmic reticulum are substrates for the later addition of O-linked carbohydrate, presumably in the Golgi complex, but only a fraction of the free alpha molecules are modified with O-linked carbohydrate.     

Purification and properties of a monoclonal antibody specific to the free beta-subunit of human chorionic gonadotropin (hCG beta) and its use in the isolation of free hCG beta produced by choriocarcinoma cells

The free beta-subunit of hCG is secreted by several tumors and is reported to be different from native hCG beta. We have developed a monoclonal antibody, B158, specific for free hCG beta to facilitate the detection and isolation of tumor-derived free hCG beta in the presence of intact hCG and hCG alpha. B158 belongs to the immunoglobulin G1 subclass, has high affinity for hCG beta (Ka, 1.05 X 10(9) M-1), and can be obtained in large quantities. The sensitivity of this antibody to detect free hCG beta in a RIA is less than 1 ng. B158 has negligible cross-reactivity with hCG, human LH, and other intact glycoprotein hormones and reacts with the free beta-subunits of deglycosylated hCG, human LH, and ovine LH. The antibody completely inhibits the recombination of hCG beta with hCG alpha indicating the antigenic site to be in the subunit interaction region or its vicinity. Comparison of the amino acid sequences of the various cross-reacting and noncross-reacting hormones indicates that the antigenic site may be discontinuous and conformational. B158 was purified to homogeneity from ascites fluid by DEAE-Affi-Gel blue and hCG beta affinity chromatography. Immobilized pure B158 antibody was used to isolate free hCG beta in a homogeneous form and high yield from BeWo choriocarcinoma cell culture supernatants. This free hCG beta has a slightly higher mol wt than standard hCG beta and recombines normally with hCG alpha. BeWo cells appear to produce only one species of free hCG beta.     

Comparison of the biological and immunological properties of glycosylation deficient human chorionic gonadotropin variants produced by site directed mutagenesis and chemical deglycosylation.

Appropriate glycosylation of gonadotropins is essential for the full expression of their biological activity. In this investigation we have compared the properties of glycosylation deficient human chorionic gonadotropin (hCG) produced by chemical deglycosylation (HF treatment--DG-hCG) or recombinant techniques (site directed mutagenesis). Among the recombinant hCG molecules secreted into the culture medium, the following variants containing selective N-glycosylation deletions at delta alpha 1 or delta alpha 1,2 or in both subunits could not stimulate steroidogenesis in mouse Leydig tumor cells (MA-10 cell line) and in this respect were very similar to DG-hCG. The other variants were fully active like native hCG, but the alpha + delta beta 1,2 recombinant hCG was a partial agonist. In radioimmunoassay with antibodies against native hCG, the DG-hCG as well as all recombinant hCG variants, including the wild type (WT), were similar. However, with antisera against DG-hCG or affinity purified antibodies specific to DG-hCG the alpha/delta 1,2 beta mutant, the WT hormone and native hCG were less active. In this assay mutants containing N-glycosylation deletions in the alpha subunit as well as the delta alpha 1,2/delta beta 1,2, variant showed higher activity. A similar pattern was evident in reaction with a selected monoclonal antibody showing preferential binding of 125I-labeled DG-hCG (antagonist). Affinity purified antibody directed against native hCG conformation was successful in converting DG-hCG and some inactive glycosylation deficient variants into an active form by stimulating progesterone in MA-10 cells. These data suggest that there are similarities as well as subtle differences in conformation of DG-hCG and various recombinant hCG molecules.(ABSTRACT TRUNCATED AT 250 WORDS)     

Free alpha molecules from pregnancy stimulate secretion of prolactin from human decidual cells: a novel function for free alpha in pregnancy.

Free alpha molecules isolated from pregnancy, as well as highly purified reference preparations of hCG alpha subunit (CR119 or CR123), stimulated the release of prolactin from human decidual cells in culture. The amount of prolactin secreted during a 24 h incubation was concentration-dependent over a range of increasing doses of alpha from 0.2 to 20 ng/ml with an ED50 of about 1.6 ng/ml. These concentrations are well within the physiologic maternal serum free alpha levels which average 350 ng/ml during the third trimester of pregnancy. Incubation of decidual cells with a reference preparation of intact hCG (CR123) at a concentration of 260 ng/ml resulted in stimulated secretion of prolactin, however, the observed stimulation could be attributed to contamination of the preparation with free alpha or dissociated hCG alpha subunit. Purified hCG beta subunit had no stimulatory activity on the decidual cell culture. The effect of alpha subunit on the stimulated release of prolactin was not due to a generalized stimulation of protein synthesis and secretion since no increase was observed in the release of 35S-labeled proteins compared to controls. In addition, the observed increase in prolactin secretion was not due to a toxic effect of the alpha subunit since there was no visible effect on cell viability, and the cellular enzymes, LDH and alkaline phosphatase, were not detected in the culture medium. Addition of exogenous hCG alpha subunit to primary cultures of human trophoblast cultures did not result in stimulated release of human placental lactogen. We conclude that free alpha molecules of pregnancy stimulate release of prolactin from human decidual cells in culture. These results suggest a novel role for free alpha in the paracrine regulation of decidual prolactin secretion.     

Spatial relationships of the human chorionic gonadotropin (hCG) subunits in the assembly of the hCG-receptor complex in the luteinized rat ovary.

In an attempt to examine the spatial relationships of the human chorionic gonadotropin (hCG) subunits in the assembly of the hCG-receptor complex, the recombined 125I-labeled hCG, with label in either the alpha subunit or the beta subunit, was cross-linked to the luteinizing hormone (LH)/hCG receptor. The efficacy of the cross-linking of the 125I-alpha subunit or the 125I-beta subunit of hCG to the LH/hCG receptor was then examined. The autoradiographic profile of 125I-hCG-receptor complex containing the label in the alpha subunit of hCG showed that the alpha subunit can cross-link with all four subunits of the LH/hCG receptor. However, only one faint labeled band, corresponding to Mr = 68,000, was detected when the 125I-hCG-receptor complex with label in the beta subunit was subjected to sodium dodecyl sulfate/polyacrylamide gel electrophoresis under reducing conditions. When the electrophoresis was performed under nonreducing conditions, the Mr 68,000 band disappeared concomitantly with the accumulation of radioactivity in the high molecular weight region. These results indicated that the beta subunit of hCG, unlike the alpha subunit, can cross-link only weakly with the smallest subunit of the LH/hCG receptor. A comparison of the differential effectiveness of the cross-linking of 125I-alpha subunit with 125I-beta subunit of hCG to the LH/hCG receptor suggests that both alpha and beta subunits of hCG are intimately associated with the receptor, but the bulk of the beta subunit of hCG is buried in between the receptor and the alpha subunit of hCG. On the basis of our data, a model for the spatial arrangement of hCG subunits in the hCG-receptor complex is proposed.     

Cellular localization of chorionic gonadotropin in human fetal kidney and liver

Earlier, we reported that second trimester human fetal kidney and, to a much lesser extent, human fetal liver were capable of synthesizing and secreting the beta-subunit of hCG. Recently, we also have shown that these tissues, likewise, synthesize and secrete the alpha-subunit of hCG. The hCG produced is biologically active. To determine the cellular localization of these peptides, immunocytochemical studies were performed on human fetal tissues using antibodies against beta hCG, alpha hCG, and the intact hormone. Placental syncytiotrophoblast served as an immunopositive control. In the human fetal kidney, the ascending (thick) limb of the loop of Henle, distal convoluted tubule, and occasional cells in the collecting ducts were distinctly immunopositive for both beta hCG and the alpha-subunit. Small amounts of light positive staining occurred in only a few hepatocytes. Placental syncytiotrophoblast was routinely positive for both subunits, but fetal lung and striated muscle were negative. These immunocytochemical results indicate that immunoreactive beta hCG as well as the alpha-subunit are present in placental syncytiotrophoblast, in the distal renal nephron, and in a limited population of hepatocytes. The qualitative number and intensity of immunopositive cells closely correlate with the quantitative amounts of their hCG subunit synthesis. Taken together with our previous biosynthetic data, the immunocytochemical localization reported here indicates the probable cellular sites of alpha- and beta hCG synthesis in these tissues. The presence of comparable alpha- and beta-subunit staining in identical cell populations suggests that both hCG subunits and, therefore, perhaps intact hCG are produced at these same cellular sites during fetal life.     

Biosynthesis of a biologically active single peptide chain containing the human common alpha and chorionic gonadotropin beta subunits in tandem.

One of the distinguishing features of the gonadotropin and thyrotropin hormone family is their heterodimeric structure, consisting of a common alpha subunit and a hormone-specific beta subunit. Subunit assembly is vital to the function of these hormones: The conformation of the heterodimer is essential for controlling secretion, hormone-specific posttranslational modifications, and signal transduction. To address whether alpha and beta subunits can be synthesized as one chain and also maintain biological activity, a chimera composed of the human chorionic gonadotropin (hCG) beta subunit genetically fused to the alpha subunit was constructed. The resulting polypeptide hCG molecule not only was efficiently secreted but also displayed an increased biological activity in vitro and in vivo. These data show that the alpha and hCG beta subunits encoded as a single chain retain a biologically active conformation similar to that seen in the heterodimer. This approach can be used to investigate structure-function relationships of the glycoprotein hormone family that were previously not tractable because of the absolute dependence on assembly for the biological response. Moreover, other bioactive multisubunit ligands can be engineered where the combination efficiency and specificity of heterodimers and homodimers are otherwise difficult to control.     

The role of subunit sialic acid in the thyrotropic and gonadotropic activities of human chorionic gonadotropin

The present studies were undertaken to delineate the role of sialic acid residues in the two subunits of hCG in relation to its hormonal activity. Sialic acid was removed by treatment of the individual subunits or intact hCG with insolubilized neuraminidase. Desialylated variants of hCG were obtained by combining an asialo subunit (as alpha or as beta) with its complementary intact or desialylated subunit. When tested in the hCG receptor assay using a rat testis fraction, none of the hCG variants exhibited any loss of activity compared with that of intact purified hCG. In in vitro bioassays that employed cAMP and testosterone generation in rat Leydig cells as indices of response, intact hCG and as alpha in combination with intact beta (as alpha-beta) were equipotent. In contrast, intact alpha-subunit combined with as beta (alpha-as beta) and desialylated intact hCG (asialo-hCG) showed activity that at the highest concentration of each tested (20 ng/ml) was no more than half of that evoked by intact hCG. In a TSH receptor assay in human thyroid membranes, loss of sialic acid from either one or both hCG subunits resulted in enhancement of binding affinity; the rank order of decreasing potency was asialo-hCG, alpha-as beta, as alpha-beta. However, despite their enhanced binding affinity, and like intact hCG itself, none of the variants elicited a cAMP response in either human thyroid membranes or cultured human thyroid cells. Rather, asialo-hCG and alpha-as beta, but not intact hCG and as alpha-beta, were effective antagonists of the stimulatory response induced by bovine TSH in thyroid cells. These findings indicate that desialylation of hCG enhances its binding affinity for hCG receptors in testis and, much more so, for TSH receptors in human thyroid. Desialylation also changes hCG from a full agonist to a partial agonist in testis and from a nonagonist to an antagonist in human thyroid. In all cases, sialic acid in the beta-subunit of hCG appears to have a predominant role in these effects.     

Differential processing of subunits of human chorionic gonadotropin by granulosa cells in vivo.

The question of whether the two subunits of the glycoprotein hormone human chorionic gonadotropin (hCG) are handled separately or as a unit by target cells was addressed by using a dual-labeling procedure. The individual alpha and beta subunits of hCG were labeled with 131I or 125I, recombined, chromatographed, and injected intravenously into hormonally primed immature rats. The ovaries of these rats contained large numbers of antral follicles, the granulosa cells of which possess high concentrations of receptor for hCG. Comparisons of the distribution of the different radioisotopic labels in various tissues over time indicated the activity associated with the beta subunit was preferentially retained by the ovarian granulosa cells in a hormone-specific manner, while the activity associated with the alpha subunit was preferentially lost. This contrasted with other tissues, including other ovarian cells with receptor for hCG, in which both radiolabels were either handled nondifferentially or handled differentially in a hormonally nonspecific manner.     

Synthesis and processing of human chorionic gonadotropin subunits in cultured choriocarcinoma cells.

Pulse and pulse-chase experiments have identified the presence of partially glycosylated precursors of the alpha and beta subunits of human chorionic gonadotropin (hCG) in cultured JAR choriocarcinoma cells. The alpha subunit precursor has an apparent molecular weight (by sodium dodecyl sulfate/polyacrylamide gel electrophoresis) of 18,000 (compared to 22,000 for fully processed alpha subunit); the beta subunit precursor has an apparent molecular weight of 24,000 (fully processed, 34,000). Both of these precursors appear to have an intracellular half-life of at least 1 hr and to contain the mannose core but not the terminal carbohydrate sequences. Fully processed alpha and beta subunits do not accumulate intracellularly, indicating that further processing of the precursors is followed by rapid secretion.     

HUMAN CHORIONIC GONADOTROPHIN AND SUBUNITS—HETEROGENEITY IN SERUM OF MALE PATIENTS WITH TUMOURS OF THE GENITAL TRACT

The pattern of secretion of human chorionic gonadotrophin (hCG) and its subunits in male subjects with tumours of the genital tract was examined by gel filtration, radioimmunoassay, immunoradiometric assay, bioassay and binding to Concanavalin A. The predominant form of hCG was the intact molecule but all patients had increased levels of free beta subunit. The intact hCG was active in a mouse Leydig cell bioassay and was normally glycosylated. High concentrations of free alpha subunit were not found and the ratio of alpha subunit: beta subunit was less than that in normal pregnancy. It is concluded that hCG-secreting tumours of the male genital tract are similar to choriocarcinoma in the female in that large quantities of intact hormone are produced with a disproportionate increase in free beta sub-unit.