The effect of alpha-fetoprotein on the growth of placental cells in vitro

Biochemical Screening for Fetal Trisomy 21: Pathophysiology of Maternal Serum Markers and Involvement of the Placenta

It is now well established that maternal serum markers are often abnormal in fetal trisomy 21. Their determination is recommended for prenatal screening and pregnancy follow-up. However, mechanisms leading to abnormal maternal serum levels of such markers are still debated. Our objective was to help clinicians and scientists unravel the pathophysiology of these markers via a review of the main studies published in this field, both in vivo and in vitro, focusing on the six most widely used markers (hCG, its free subunit hCGβ, PAPP-A, AFP, uE3, and inhibin A) as well as cell-free feto-placental DNA. Analysis of the literature shows that mechanisms underlying each marker's regulation are multiple and not necessarily directly linked with the supernumerary chromosome 21. The crucial involvement of the placenta is also highlighted, which could be defective in one or several of its functions (turnover and apoptosis, endocrine production, and feto-maternal exchanges and transfer). These defects were neither constant nor specific for trisomy 21, and might be more or less pronounced, reflecting a high variability in placental immaturity and alteration. This explains why maternal serum markers can lack both specificity and sensitivity, and are thus restricted to screening.

The Emerging Influences of Alpha-Fetoprotein in the Tumorigenesis and Progression of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide, and its mortality rate is the third-highest, after lung cancer and colorectal cancer. Currently, systematic targeted therapies for HCC mainly include multiple kinase inhibitors and immunotherapy. However, these drugs carry a black-box warning about the potential for inducing severe toxicity, and they do not significantly prolong the survival period of patients due to the highly heterogeneous characteristics of HCC etiology. In order to improve the prediction, effective treatment and prognosis of HCC, the tools and different biomarkers in clinical practices are recommended. Alpha-fetoprotein (AFP) is the earliest and the most widely used serum marker in the detection of HCC. Interestingly, serum AFP and cytoplasmic AFP show different, even opposite, roles in the cancer progression of HCC. This review focuses on biological characteristics, regulatory mechanisms for gene expression, emerging influences of AFP in HCC and its possible implications in HCC-targeted therapy.

Integrated analysis of the rhesus monkey liver transcriptome during development and human primary HCC AFP-related gene expression

Embryonic development and tumorigenesis have a certain degree of similarity. Alpha-fetoprotein (AFP), a protein related to embryonic development, is a well-known biomarker for the diagnosis and prognosis of hepatocellular carcinoma (HCC). In this study, we analyzed the differences in gene expression profiles and molecular mechanisms in human HCC tissues from patients in AFP^high (serum AFP level ≥ 25 ng/mL) and AFP^low (serum AFP level < 25 ng/mL) groups. The results indicated that AFP^high HCC has more malignant biological characteristics. Single-sample gene set enrichment analysis (ssGSEA) showed significantly higher levels of genes expressed in dendritic cells, neutrophils, and natural killer cells in the AFP^low group than in the AFP^high group. Then, we defined a rhesus monkey fetal liver developmental landscape and compared it to the HCC gene expression profile. The gene signatures of AFP^high HCC tissues were similar to those of early embryonic liver tissues. In this study, we comprehensively analyzed the rhesus monkey liver transcriptome during development and human primary HCC AFP-related gene expression profiles and clarified the function of AFP in the occurrence and development of HCC from the perspective of developmental biology, which might provide a new perspective on the pathogenesis of HCC.

Changes in Tumor Markers and Their Implications in Selecting Liver Transplantation for Patients With Hepatocellular Carcinoma

BACKGROUND AND AIM

It has been suggested that tumor markers can provide additional information over tumor size and number-based liver transplantation (LT) criteria. We aimed to assess if changes in tumor markers are associated with the risk of tumor recurrence after LT for hepatocellular carcinoma (HCC) who received loco-regional therapies (LRTs).

METHODS

A total of 129 patients who received LT with pre-LT LRTs for HCC were analyzed. Milan criteria and tumor markers, alpha-fetoprotein, and protein induced by vitamin K antagonist II, at diagnosis and at transplant were assessed. The primary outcome was tumor recurrence.

RESULTS

When patients were stratified by radiologic criteria, cumulative recurrence rates at 3 years for patients who were not down-staged (outside Milan to outside Milan), progressed (within Milan to outside Milan), down-staged (outside Milan to within Milan), and bridged (within Milan to within Milan) were 66.7%, 58.3%, 18.7%, and 8.5%, respectively (P < .001). Among patients who were transplanted within Milan criteria at transplant (n = 113), cumulative recurrence rates at 3 years were highest for those with persistently high tumor markers (high to high, 21.7%), followed by those with increase in tumor markers (low to high, 11.1%), those with normalization of tumor markers (high to low, 5.6%), and those with persistently low tumor markers (low to low, 0%), respectively, after LRTs (P = .035).

CONCLUSIONS

Changes of tumor markers can provide additional information on the risk of recurrence after LT among HCC patients who received LRTs, indicating that they could be used to refine current LT selection criteria.

Alpha-fetoprotein: a renaissance

Alpha-fetoprotein (AFP) is a major mammalian embryo-specific and tumor-associated protein that is also present in small quantities in adults at normal conditions. Discovery of the phenomenon of AFP biosynthesis in carcinogenesis by G. Abelev and Yu. Tatarinov 50 years ago, in 1963, provoked intensive studies of this protein. AFPs of some mammalian species were isolated, purified and physico-chemically and immunochemically characterized. Despite the significant success in study of AFP, its three-dimensional structure, mechanisms of receptor binding along with a structure of the receptor itself and, what is the most important, its biological role in embryo- and carcinogenesis remain still obscure. Due to difficulties linked with methodological limitations, research of AFP was to some extent extinguished by the 1990 s. However, over the last decade a growing number of investigations of AFP and its usage as a tumor-specific biomarker have been observed. This was caused by the use of new technologies, primarily, computer-based and genetic engineering approaches in studying of this very important oncodevelopmental protein. Our review summarizes efforts of different scientific groups throughout the world in studying AFP for 50 years with emphasis on detailed description of recent achievements in this field.

Cytoplasmic alpha-fetoprotein functions as a co-repressor in RA-RAR signaling to promote the growth of human hepatoma Bel 7402 cells

The role of AFP in the retinoic acid-RAR signaling pathway was investigated in human hepatoma Bel 7402 cells. The results showed that AFP and RAR-beta were co-localized and interacted in cytoplasm. AFP may inhibit translocation of RAR-beta into the nucleus via competitive binding to RAR-beta with ATRA, which was reversed by AFP-siRNA transfection. Our data suggest that the ATRA resistance of Bel 7402 cells is at least in part attributable to their high level of cytoplasmic AFP. Thus, by counteracting the effect of AFP, it may be possible to increase the sensitivity of tumor cells to ATRA.

Silencing alpha-fetoprotein expression induces growth arrest and apoptosis in human hepatocellular cancer cell

The expression of alpha-fetoprotein (AFP), a tumor-associated antigen, is silenced in normal adult hepatocyte but reactivated in human hepatocellular carcinoma (HCC). To investigate the roles of AFP in the regulation of cell growth, we silenced AFP expression in the HCC cell line Huh7 by transfection of specific Stealth RNAi. After the transfection for 48 h, the expression of AFP gene was almost abolished, the cell proliferation was inhibited by 46.15%, and the number of cells undergoing early apoptosis was significantly increased to 63.93%. Inhibition of AFP expression also resulted in an increased in Bax/Bcl-2 ratio, the release of cytochrome c from mitochondria and activation of caspase-3. The results suggest that AFP may positively regulate cell proliferation by enhancing the apoptosis resistance via dysfunction of the p53/Bax/cytochrome c/caspase-3 signaling pathway in AFP-producing HCC cell line. As such, the knockdown of AFP gene should be further investigated in vivo as a novel approach to HCC treatment.

The alpha-fetoprotein-derived growth inhibitory peptide 8-mer fragment: review of a novel anticancer agent

This review describes the antigrowth and anticancer activities of the alpha-fetoprotein (AFP)-derived growth inhibitory peptide (GIP) 8-mer fragment. The 8-amino acid peptide (GIP-8) comprises the carboxy-terminal portion of a 34-amino acid peptide (GIP-34) previously identified as an occult epitopic segment of the full-length human AFP molecule. The GIP-8 segment has been chemically synthesized, purified, characterized, and bioassayed. The purified 8-mer segment was characterized as a random coil (disordered) structure extending from a C-terminal beta-hairpin that forms a horseshoe-shaped partially cyclic octapeptide; this structure can be formulated into a fully cyclic form by the addition of asparagine or glutamine residues. The pharmacophore of the octo- and nanopeptide forms is largely composed of a PXXP motif known to interact with Src-3 (SH3) domains of serine/theronine kinases. The GIP-8 has been shown to be growth-suppressive largely in estradiol (E2)-dependent neonatal and tumor-cell proliferation models and to inhibit tumor-cell adhesion to extracellular matrices. The 8-mer GIP displays antigrowth properties in immature mouse uterine cells and anticancer cell proliferation traits in estrogen receptor positive (ER(+)), but not (ER()) negative breast tumor cells. Even though its mechanism of action has not been fully elucidated, GIP-8 has been shown by computer modeling to dock with the extracellular loops of G-coupled seven transmembrane helical-like receptors, which could possibly interfere with signal transduction through MAP kinase pathways. It was apparent that the GIP-8 derived from the 34-mer GIP fragment of HAFP represented an E2-sensitive growth inhibitory motif, which allows the participation in cellular events, such as receptor binding, contact inhibition, extracellular matrix adhesion, angiogenesis, and T-cell activation. Thus, it was proposed that the 8-mer fragment derived from GIP could potentially serve as a lead compound for targeted cancer therapeutic agents of the biologic-response modifier type.

Purification and characterization of Alpha-Fetoprotein from the human hepatoblastoma HepG2 cell line in serum-free medium

Alpha-fetoprotein (AFP) is a tumor-associated embryonic molecule whose precise biological function remains unclear. A complete definition of the physiological activities of this oncofetal protein has been severely limited, until now, by the lack of a purification procedure appropriate to obtain pure AFP in appreciable amount. The present report describes a purification procedure extremely rapid and simple and takes advantage of the well-known fact that AFP contains copper. We have developed a single-step purification procedure by immobilized copper-chelate affinity chromatography using the culture medium from human hepatoblastoma cell line HepG2 grown in the absence of serum. This method yields AFP at high purity and high yield. Purified AFP amino acid sequence, molecular mass, carbohydrate structure, and copper content were found to be in line with previous studies. Moreover, we found that the purified AFP has superoxide dismutase activity with efficiency similar to that of the native Cu, Zn SODs at physiological pH. This result may provide further support to the idea that AFP is a bifunctional protein, acting in cellular defence against oxidative stress both as a copper buffer and as a superoxide radical scavenger.

Structural and functional mapping of alpha-fetoprotein

Alpha-fetoprotein (AFP) is a major mammalian oncofetal protein, which is also present in small quantities in adults. It is a member of the albuminoid gene superfamily, which consists of AFP, serum albumin, vitamin D binding protein, and alpha-albumin (afamin). Although physicochemical and immunological properties of AFP have been well-studied, its biological role in embryo- and carcinogenesis and in adult organisms as well as mechanisms underlying its functioning remain unclear. During the recent decades, the biological role of AFP has been evaluated by identification of its functionally important sites. Comparison of primary structure of AFP and some physiologically active proteins revealed similarity of some polypeptide regions. This has been used for prediction of AFP functions (i.e., its multifunctionality). Localization of functionally important sites followed by determination of their amino acid composition and type of biological activity has provided valuable information for structural-functional mapping of AFP. Some peptide fragments of AFP have been synthesized and tested for biological activity. This review summarizes data on structural-functional interrelationships. We also describe functionally important AFP sites found by various groups during the last decade of structural-functional mapping of AFP with experimentally confirmed and putative biologically active sites.

Expression and localization of alpha-fetoprotein mRNA and protein in human early villous trophoblasts

Alpha-fetoprotein (AFP) is a major plasma protein produced during human fetal life. It is a good marker for several possible disorders affecting gestation. We previously reported that afp gene expression, which takes place mainly in yolk sac and fetal liver, also occurs in normal human placenta, specifically in early pregnancy. The aim of the present study was to determine the precise location of AFP synthesis sites within the placental villi. In situ hybridization and immunohistochemical experiments were performed on sections obtained from placentas of first-trimester and full-term pregnancies. We found that the pattern of afp gene expression was restricted to specific villous trophoblastic areas in early placentas. Both afp transcripts and AFP protein were mainly located in discontinuous regions, at junctions between two villi and at budding sites. In contrast, no AFP expression was detected in the cytotrophoblastic extravillous proliferative zone or in other placental cell types. According to the earlier studies, no AFP synthesis was detected in placental villous tissue from full-term pregnancies, using in situ hybridization and immunohistochemistry.

Effects of alpha fetoprotein on escape of Bel 7402 cells from attack of lymphocytes

BACKGROUND

Involvement of AFP against apoptosis of tumor cell has been implicated in its evasion of immune surveillance. However, the molecular events of immune escape mechanisms are still unknown. The major observations reported here relate to a possible mechanism by which heptoloma Bel 7402 cells escape immune surveillance in vitro.

METHODS

Western blotting and a well-characterized cofocal scanning image were performed to analyze the expression of Fas/FasL and caspase-3 in co-cultured Bel 7402 and Jurkat cells.

RESULTS

After co-culture with Jurkat cells, up-regulated Fas and reduced FasL expression could be observed. Treatment with AFP could remarkably inhibit the elevated Fas and, whereas, induce the FasL expression in co-cultured Bel 7402 cells. Cells co-culture could induce the expression of caspase-3 in both cells line. The elevated caspase-3 in Bel 7402 cells was abolished following the treatment of AFP. The expression of caspase-3 was elevated in co-cultured Jurkat cells treated with AFP. No detectable change on the expression of survivin was examined in both cells line. Monoclonal antibody against AFP treatment alone did not obviously influence the growth of cells, as well as the expression of Fas/FasL and caspase-3. However, the effect of AFP could be blocked by antibody.

CONCLUSIONS

our results provide evidence that AFP could promote the escape of liver cancer cells from immune surveillance through blocking the caspase signal pathway of tumor cells and triggering the Fas/FasL interaction between tumor cells and lymphocytes.

Effects of alpha fetoprotein on escape of Bel 7402 cells from attack of lymphocytes

BACKGROUND

Involvement of AFP against apoptosis of tumor cell has been implicated in its evasion of immune surveillance. However, the molecular events of immune escape mechanisms are still unknown. The major observations reported here relate to a possible mechanism by which heptoloma Bel 7402 cells escape immune surveillance in vitro.

METHODS

Western blotting and a well-characterized cofocal scanning image were performed to analyze the expression of Fas/FasL and caspase-3 in co-cultured Bel 7402 and Jurkat cells.

RESULTS

After co-culture with Jurkat cells, up-regulated Fas and reduced FasL expression could be observed. Treatment with AFP could remarkably inhibit the elevated Fas and, whereas, induce the FasL expression in co-cultured Bel 7402 cells. Cells co-culture could induce the expression of caspase-3 in both cells line. The elevated caspase-3 in Bel 7402 cells was abolished following the treatment of AFP. The expression of caspase-3 was elevated in co-cultured Jurkat cells treated with AFP. No detectable change on the expression of survivin was examined in both cells line. Monoclonal antibody against AFP treatment alone did not obviously influence the growth of cells, as well as the expression of Fas/FasL and caspase-3. However, the effect of AFP could be blocked by antibody.

CONCLUSIONS

our results provide evidence that AFP could promote the escape of liver cancer cells from immune surveillance through blocking the caspase signal pathway of tumor cells and triggering the Fas/FasL interaction between tumor cells and lymphocytes.

Alpha-fetoprotein gene expression in early and full-term human trophoblast

Alpha-fetoprotein (AFP) is a major serum glycoprotein synthesized during fetal life mainly by the yolk sac and the fetal liver. At term, it reaches high concentrations in the maternal intervillous blood, which is in direct contact with the placental trophoblastic microvillous membrane, and this suggests the placental origin of the AFP at the fetal-maternal interface. We used several experimental approaches to investigate the expression of AFP gene and fetal protein production in early gestation and term placentas. RT-PCR and immunological studies clearly identified AFP messenger RNA and AFP protein in the placental villi from first trimester of pregnancy. The AFP gene was also expressed in highly purified cytotrophoblasts from early placentas, and enzymo-immunoassay showed that AFP protein was synthesized and secreted by early cytotrophoblasts. AFP was also detected in the cytoplasm of these cells by immuno-cytochemistry. However, none of these methods detected any expression of the AFP gene in full-term placental villi or in cultured trophoblasts. These findings demonstrate that both AFP mRNA and protein are present in trophoblastic cells early in pregnancy. The absence of AFP gene expression in term placental villi also suggests, that the AFP at the fetal-maternal interface is attributable to a notable transplacental passage of AFP from fetal blood in late pregnancy.

The intracellular mechanism of alpha-fetoprotein promoting the proliferation of NIH 3T3 cells

AIM

The existence and properties of alpha-fetoprotein (AFP) receptor on the surface of NIH 3T3 cells and the effects of AFP on cellular signal transduction pathway were investigated.

METHODS

The effect of AFP on the proliferation of NIH 3T3 cells was measured by incorporation of 3H-TdR. Receptor-binding assay of 125I-AFP was performed to detect the properties of AFP receptor in NIH 3T3 cells. The influences of AFP on the [cAMP]i and the activities of protein kinase A (PKA) were determined. Western blot was used to detect the change of K-ras P21 protein expression.

RESULTS

The proliferation of NIH 3T3 cells treated with 0-80 mg/L of AFP was significantly enhanced. The Scatchard analysis indicated that there were two classes of binding sites with KD of 2.722 x 10(-9)M (Bmax=12810 sites per cell) and 8.931 x 10(-8)M (Bmax=119700 sites per cell) respectively. In the presence of AFP (20 mg/L), the content of cAMP and activities of PKA were significantly elevated . The level of K-ras P21 protein was upregulated by AFP at the concentration of 20 mg/L. The monoclonal antibody against AFP could reverse the effects of AFP on the cAMP content, PKA activity and the expression of K-ras p21 gene.

CONCLUSION

The effect of AFP on the cell proliferation was achieved by binding its receptor to trigger the signal transduction pathway of cAMP-PKA and alter the expression of K- ras p21 gene.

Human alpha-fetoprotein contains potential heterodimerization motifs capable of interaction with nuclear receptors and transcription/growth factors

Alpha-fetoprotein (AFP) serum levels in man have long been utilized as a tumor marker and as a birth defect screening agent in the clinical laboratory. Although the physiological role of AFP has remained obscure, the stereotypic carrier/transport function of a fetal counterpart to albumin has been attributed to this oncofetal protein. However, reports from a multitude of investigators in the last decade have provided a rationale to reconsider and extend the biological role of AFP to include cell growth modulation during development. Previously, a leucine zipper-like (heptad) motif, which mimicked that found in the steroid/thyroid receptor superfamily, was postulated for portions of the third domain of AFP. The present report proposes the presence of additional potential heterodimerization sites for the nuclear receptor superfamily members and other growth factors in the second and third domains of human AFP.

Alpha-fetoprotein-producing male breast cancer accompanied with hepatocellular carcinoma: assessment by lectin-affinity profile

An autopsy case associated with both male breast cancer and hepatocellular carcinoma in which serum alpha-fetoprotein (AFP) was extremely elevated is described. The source of AFP production was investigated. In lectin-affinity chromatography of the patient's serum, concanavalin A (ConA) binding pattern was not consistent with that of hepatocellular carcinoma, and lens culinaris agglutinin A (LCA) affinity indicated a similar pattern to hepatocellular carcinoma. The immunohistochemistry staining for AFP revealed positive reactivity in breast cancer cells, but was negative in hepatocellular carcinoma cells. To the best of our knowledge, there have been no reports of breast cancer exhibiting immunohistochemically positive AFP in breast cancer cells. In the present case, ConA binding test was useful for identification of the source of AFP production. Furthermore, corresponding aggravation of breast cancer to the elevation of AFP suggested the possibility that AFP might enhance breast cancer growth.

Alpha-fetoprotein structure and function: relevance to isoforms, epitopes, and conformational variants

Mammalian alpha-fetoprotein (AFP) is classified as a member of the albuminoid gene superfamily consisting of albumin, AFP, vitamin D (Gc) protein, and alpha-albumin. Molecular variants of AFP have long been reported in the biomedical literature. Early studies identified isoelectric pH isoforms and lectin-binding variants of AFP, which differed in their physicochemical properties, but not in amino acid composition. Genetic variants of AFP, differing in mRNA kilobase length, were later extensively described in rodent models during fetal/perinatal stages, carcinogenesis, and organ regeneration. With the advent of monoclonal antibodies in the early 1980s, multiple antigenic epitopes on native AFP were detected and categorized, culminating in the identification of six to seven major epitopes. During this period, various AFP-binding proteins and receptors were reported to inhibit certain AFP immunoreactions. Concomittantly, human and rodent AFP were cloned and the amino acid sequences of the translated proteins were divulged. Once the amino acid composition of the AFP molecule was known, enzymatic fragments could be identified and synthetic peptide segments synthesized. Following discovery of the molten globule form in 1981, the existence of transitory, intermediate forms of AFP were acknowledged and their physiological significance was realized. In the present review, the various isoforms and variants of AFP are discussed in light of their potential biological relevance.

Human alpha-fetoprotein peptides bind estrogen receptor and estradiol, and suppress breast cancer

Alpha-fetoprotein (AFP) is a transporter of various serum ligands and regulator of cellular growth during pregnancy. Estrogens modify AFP to exhibit growth suppressive properties. We recently synthesized a peptide (P149) from human AFP that suppresses the growth of mouse uterus and MCF-7 breast cancer cells. Here it is shown that molar excess treatment of native AFP with estradiol-17 beta (E2) exposes the P149 site on AFP. The anti-estrogenic and anti-tumor activities of AFP-peptides were tested in vivo in the immature mouse uterine assay and mammary tumor (6WI-101)-induced ascites assay, and in vitro in a cytostatic assay using five different human breast tumor cell lines. AFP-peptide P149, and fragments of P149, P149A and P149C but not P149B, suppressed the growth in both in vivo assays. P149 also suppressed the in vitro growth of MCF-7, MDA-MB-231, MDA-MB435 breast cancer cells by more than 75%. P149 and P149A bound the estrogen receptor-alpha (ER) with low affinities compared to E2 and tamoxifen, while P149B bound 3H-E2 with 10(5) fold less affinity compared to ER. The recent epidemiologic observation that high AFP levels in young pregnant women reduce their subsequent risk of postmenopausal breast cancer may be related to the growth suppressive property of AFP with the exposed P149 epitope.

Does high polyunsaturated free fatty acid level at the feto-maternal interface alter steroid hormone message during pregnancy?

Polyunsaturated fatty acids (PUFA) are important in pregnancy, fetal development and parturition. We measured free fatty acids (FFA), albumin and alpha-fetoprotein (AFP) in the maternal and fetal circulations of women undergoing elective Caesarean section at term. We also studied the impact of PUFAs on estrogen (ER) and progesterone receptors (PR) binding properties in vitro in the myometria of pregnant women and ex vivo in human myometrial cells in culture. FFA in intervillous blood (I) (feto-maternal interface) and maternal peripheral blood (M) were similar, while those in the umbilical vein (V) and arteries (A) were 2-4 fold lower (P<0.001). PUFA levels were low in M and 3 fold higher in I, A and V (P< 0.001); consequently C20:4 and C22:6 were most abundant in intervillous space. Albumin was uniformly distributed throughout the maternal-fetal unit, but there was a transplacental gradient in AFP. The AFP in the intervillous space had a special conformation (less immuno-reactive, more anionic), suggesting loading with PUFA. Physiological concentrations of C20:4 stimulated estradiol binding, but inhibited progestin binding. C20:4 inhibited progesterone binding by decreasing the number of binding sites, with no change in apparent affinity, in vitro in myometrial tissue and ex vivo in myometrial cells. Thus PUFA may modulate the steroid hormone message, so that the high C20:4 concentration at the maternal-fetal interface at term may help amplify the estrogen signal and inhibit the progesterone signal.

Stimulation of tumor-cell growth by alpha-fetoprotein

It has been recognized that alpha-fetoprotein (AFP), as an oncofetal antigen, is re-expressed in large amounts in adult tumor cells and serves clinically useful purposes in tumor-marker assays. However, its biological activities are still undefined. In the present study, the ability of AFP to stimulate tumor-cell growth was observed by an in vitro experimental system. Mouse ascites cancer cells derived from hepatoma-22(H-22) or Ehrlich ascites carcinoma(EAC) were extracted intraperitoneally and cultured in RPMI 1640 medium containing 10% newborn calf serum for 48 hr. Cell growth was quantitated by a colorimetric assay using a MTT microculture tetrazolium dye. The results demonstrated that AFP significantly increased H-22-cell proliferation, with stimulation per cents of 122 to 156%. A similar growth-promoting effect of AFP was observed using EAC cells, with stimulation per cents of 86 to 210%. Moreover, the growth-stimulatory activity of AFP could be abrogated with anti-AFP antibodies. In addition, 5-fluorouracil could obviously inhibit AFP-induced proliferation of H-22 or EAC cells in vitro. These results suggest that AFP is associated with tumor-cell growth and may serve as an important target of tumor therapy.

Stimulation of tumor-cell growth by alpha-fetoprotein

It has been recognized that alpha-fetoprotein (AFP), as an oncofetal antigen, is re-expressed in large amounts in adult tumor cells and serves clinically useful purposes in tumor-marker assays. However, its biological activities are still undefined. In the present study, the ability of AFP to stimulate tumor-cell growth was observed by an in vitro experimental system. Mouse ascites cancer cells derived from hepatoma-22(H-22) or Ehrlich ascites carcinoma(EAC) were extracted intraperitoneally and cultured in RPMI 1640 medium containing 10% newborn calf serum for 48 hr. Cell growth was quantitated by a colorimetric assay using a MTT microculture tetrazolium dye. The results demonstrated that AFP significantly increased H-22-cell proliferation, with stimulation per cents of 122 to 156%. A similar growth-promoting effect of AFP was observed using EAC cells, with stimulation per cents of 86 to 210%. Moreover, the growth-stimulatory activity of AFP could be abrogated with anti-AFP antibodies. In addition, 5-fluorouracil could obviously inhibit AFP-induced proliferation of H-22 or EAC cells in vitro. These results suggest that AFP is associated with tumor-cell growth and may serve as an important target of tumor therapy.

Similarity between natural and recombinant human alpha-fetoprotein as inhibitors of estrogen-dependent breast cancer growth

Alpha-fetoprotein (AFP) isolated from rodent amniotic fluid or human cord sera, upon incubation with a molar excess of estradiol, is converted to a form which inhibits estrogen-stimulated tissue growth. The purpose of this study was to determine whether recombinant human AFP produced in an E. coli expression system retained this function. The recombinant protein was similar to the natural protein isolated from pooled human cord sera in all functional aspects evaluated. It was detected by monoclonal and polyclonal antibodies to the natural protein. Following exposure to estradiol, it was converted to an inhibitor of estrogen-stimulated growth of immature mouse uterus yielding a dose/response curve similar to that of the natural protein. It inhibited the growth of estrogen-dependent (MCF-7) but not estrogen-independent (MDA-MB-231) breast cancer xenografts with the same schedule dependency and resultant histological changes as the natural protein. Availability of large quantities of homogeneous, biologically active recombinant human AFP will facilitate further studies of structure/function, mechanism, and therapeutic potential of this agent as a regular of breast cancer growth.

PL48: a novel gene associated with cytotrophoblast and lineage-specific HL-60 cell differentiation

The cDNA for a novel gene, PL48, isolated by subtractive hybridization between undifferentiated human term cytotrophoblast and differentiating cytotrophoblast, has been cloned and sequenced. PL48 contains an open reading frame coding for a 537-amino acid protein, has multiple potential PKC, casein kinase II, and cAMP/cGMP-dependent kinase phosphorylation sites, and N-linked glycosylation sites. It is not present in a wide variety of proliferating cancer cells, but PL48 mRNA shows marked expression during cytotrophoblast and granulocyte lineage-specific HL-60 promyelocytic cell differentiation induced by DMSO.

Alpha-fetoprotein derived synthetic peptides: assay of an estrogen-modifying regulatory segment

This study describes the estrogen bioassay of a synthetic peptide fashioned after an amino acid sequence from human alpha-fetoprotein (HAFP). The synthetic peptide (P149), modeled after a portion of the estrogen binding pocket of rat/human AFP chimeras, was produced via F-MOC solid phase chemistry. Bioassay of P149 in the estrogen-sensitive immature rodent uterus demonstrated an anti-estrogenic (40-50% inhibitory) activity in the 23 h but not the 3-4 h uterine response. In contrast to purified HAFP, incubation of the peptide with estrogen was not a prerequisite for inhibitory activity. The estrogen-dependent increase in uterine thrombin and tissue factor, as determined by an enzymatic esterase assay, was inhibited by 30% in rat uterine cytosols. In an in vitro bioassay of estrogen-induced focus formation in MCF-7 human breast cancer cultures, focus development was inhibited by 70% following peptide exposure. The mechanism of the AFP-derived peptide inhibition of estrogen-dependent growth remains to be determined.

Alpha-fetoprotein binding proteins: implications for transmembrane passage and subcellular localization

Alpha-fetoprotein (AFP) is an oncofetal protein classified in a super-family together with albumin and Vitamin-D binding (Gc) protein which present as globular proteins comprised of three domains. Several subdomain regions on AFP have been previously proposed to serve as dimerization interfaces for nuclear receptors or perhaps other co-factors/inhibitors. The cellular uptake and internalization of AFP together with its subcellular compartmentalization is now well documented in a variety of cell types. A myriad of reports have emerged which have detected, identified, and characterized various binding proteins associated with AFP in different cellular compartments. However, the literature is devoid of any attempts to summarize, categorize, and relate these proteins to the various physiological activities attributed to this fetal protein. It is conceivable that AFP could interact and/or bind cytoplasmic chaperone proteins that normally escort nuclear factors or transcription co-factors through the cytoplasm toward organelle interfaces. A dual concept proposing binding or escort proteins for AFP together with subdomain dimerization interfaces on the AFP molecule can be reconciled into a composite hypothesis to formulate a rationale for the growth regulating properties ascribed to AFP during the last decade. Thus, AFP might serve as a modulator/modifier of various cell growth regulatory pathways during embryonic and fetal development in vertebrates.

An apparent dimerization motif in the third domain of alpha-fetoprotein: molecular mimicry of the steroid/thyroid nuclear receptor superfamily

Alpha-fetoprotein (AFP) is a tumor-associated fetal marker, associated both with tumor growth and with birth defects. AFP, whose precise function is unknown, has been classified as belonging to a protein superfamily together with albumin and vitamin D-binding (Gc) protein. AFP has been shown to bind various ligands in vitro including fatty acids, estrogens, thyroid hormones and retinoic acids. The steroid/thyroid nuclear receptor superfamily of proteins has recently become a major focus of biomedical investigation regarding regulation of gene expression. These receptors are thought to bind to DNA-hormone response elements (HRE) that affect growth, development, differentiation, reproduction and homeostasis. The HREs are known to share DNA sequences with the various members of the nuclear receptor superfamily. In the present report, the possibility of a leucine-zipper dimerization (heptad) motif in the carboxy-terminal third domain of both rodent and human AFP is postulated. The presence of nine such hydrophobic repeats in the third domain of the AFP molecule mimics the heptad dimerization repeats found in the retinoic acid, thyroid, c-erbA and other members of the nuclear receptor superfamily. Computer analysis revealed that the most conservative matching occurred between AFP and the retinoic acid class of receptors. However, other superfamily members displayed 40-60% homology with 5 of 9 AFP heptads. These findings could provide a possible mechanism for explaining the growth-regulatory properties (both inhibition and enhancement) that have been ascribed to AFP in the last decade.

Human alpha-fetoprotein purified from amniotic fluid enhances growth factor-mediated cell proliferation in vitro

Using a primary monolayer culture of porcine granulosa cells (pGC) as an in vitro cell proliferation assay, we have examined the growth-promoting activity of alpha-fetoprotein (AFP) purified from term cord blood and midtrimester amniotic fluid. Increasing concentrations (2.5-20%) of crude human cord blood (CB) increased pGC proliferation, while identical concentrations of crude amniotic fluid (AF) were ineffective. When the cell system was maximally stimulated, AF dose dependently decreased cell proliferation. AFP purified from AF and CB (1.25-5.0 micrograms/ml) was not mitogenic alone, but, in the presence of epidermal growth factor (EGF) + insulin-like growth factor (IGF-I) (10 ng/ml each), AFP dose dependently increased cell proliferation to nearly double that of EGF + IGF-I alone. The response of pGC to the proliferative effects of AF-AFP and CB-AFP were identical at each dose of AFP tested. These results indicate that although crude, pooled midtrimester AF does not display the mitogenic activity seen in cord blood, AFP purified from pooled AF significantly synergizes with growth factors to increase cell proliferation markedly.

Mouse model for the treatment of immune pregnancy loss

Spontaneous abortions can be associated with preimplantation embryo loss, implantation problems and a variety of postimplantation pregnancy failures. The long list of possible causes for the postimplantation pregnancy loss includes, among others, genetic abnormalities in fetus, anatomical abnormalities of the uterus, endocrinological insufficiency, and microbiological problems. However, more than 50% of recurrent miscarriages still have no recognized causes. The concept that many such abortions may be immunologically mediated has gained increasing support over the years. Moreover, immunization of such women with husband's or third party leukocytes has resulted in more than 70% of subsequent pregnancies resulting in live births. Since neither the mechanisms leading to pregnancy loss nor the success of immunotherapy are clear, the set-up of animal models for recurrent abortions would be of supreme significance. Our recent data show that immunopotentiation of maternal immune system by Complete Freund Adjuvant significantly improves pregnancy rate in CBA x DBA/2 mouse combination with high percentage of fetal resorptions. This effect is followed by decrease of IL 2 production in spleen; increase of MAC 1-positive cells at placenta; amplification of suppressive activity of local and systemic lymphocytes and by reverse of embryotoxic effect of maternal serum. Data obtained in this model seems to be valuable in substantiation of rationale for nonspecific immunotherapy of human abortions.

Effect of alpha-fetoprotein on arachidonic acid metabolism in the preadipocyte cell line OB 17

Previous work has shown that alpha-fetoprotein (AFP) is able to bind specifically polyunsaturated fatty acids, one of the major ligands being arachidonic acid (C20:4). In the present study, we demonstrate that AFP is able to reduce the metabolism of exogenous C20:4 by ob17 cells. Both prostaglandins and lipoxygenase products formation were reduced when cells were maintained in the presence of AFP. This decrease was counterbalanced by a higher release of C20:4 into the culture medium by the cells. The amount of C20:4 incorporated into cellular lipids was decreased but the distribution of C20:4 in the different lipid classes remained unchanged. The modification of C20:4 metabolism by AFP might be of primordial importance in developmental biology and may shed a new light on the physiological actions of AFP which have been described in the past years such as ovarian inhibition, cell growth control and immuno-suppressive activity.