Cell-type-specific receptors for alpha-fetoprotein in a mouse T-lymphoma cell line

AFP-Inhibiting Fragments for Drug Delivery: The Promise and Challenges of Targeting Therapeutics to Cancers

Alpha fetoprotein (AFP) plays a key role in stimulating the growth, metastasis and drug resistance of hepatocellular carcinoma (HCC). AFP is an important target molecule in the treatment of HCC. The application of AFP-derived peptides, AFP fragments and recombinant AFP (AFP-inhibiting fragments, AIFs) to inhibit the binding of AFP to intracellular proteins or its receptors is the basis of a new strategy for the treatment of HCC and other cancers. In addition, AIFs can be combined with drugs and delivery agents to target treatments to cancer. AIFs conjugated to anticancer drugs not only destroy cancer cells with these drugs but also activate immune cells to kill cancer cells. Furthermore, AIF delivery of drugs relieves immunosuppression and enhances chemotherapy effects. The synergism of immunotherapy and targeted chemotherapy is expected to play an important role in enhancing the treatment effect of patients with cancer. AIF delivery of drugs will be an available strategy for the targeted treatment of cancer in the future.

URRENT CONCEPT OF THE STRUCTURAL AND FUNCTIONAL PROPERTIES OF ALFA-FETOPROTEIN AND THE POSSIBILITIES OF ITS CLINICAL APPLICATION

This paper was aimed to review the literature data from native and foreign sources accumulated for 40-years period of research of the features of the molecular structure, functions, production and application of human alpha-fetoprotein (AFP), which is known as one of the most studied and increasingly demanded proteins. Results of fundamental studies performed with the use of modern methods, including various types of electrophoresis, chromatography, electron microscopy and immunoassay, in order to characterize the principal physicochemical capacities and localization of free and bound forms of AFP, as well as polypeptide structure, heterogeneity and topography of AFP receptors are highlighted here. The data on the mechanisms of AFP synthesis, its conformational features, binding sites and intracellular metabolism are also presented. The concepts of physiological functions and mechanisms of AFP transport in an organism are presented. Data on AFP isolation from the natural primary products and its production by means of recombinant and synthetic methods are shown. This review also summarizes information on the current possibilities of clinical application of AFP and the prospects for its usage in anticancer therapy for targeted delivery of chemotherapy drugs, with emphasis on the description of the recent progress in this field.

First report of the unique expression of RECAF (receptor for alfa feto-protein) in adult B-NHL/CLL patients

Background

Lymphoproliferative disorders (LPDs) are a heterogeneous group of diseases characterized by an uncontrolled production of monoclonal lymphocytes. RECAF is the receptor for alpha-fetoprotein, which is re-expressed on malignant cells, thus serving as a broad-spectrum tumor marker.

Methods

The current study is a retrospective study carried out on 200 archival bone marrow trephine biopsy specimens [60 normal control (NC), 38 pathological control (PC) and 102 lymphoproliferative diseases (LPD) specimens]. RECAF expression was assessed using immunohistochemistry.

Results

The percentage of cells that are positive for RECAF was significantly higher in the LPD group than in the NC group (P=0.007), while there was no significant difference between non-Hodgkin lymphoma (NHL) patients and PC regarding the number of RECAF positive cells (P=0.1). RECAF showed a unique expression pattern among the different subtypes of LPD. None of the hairy cell leukemia (HCL) expressed RECAF, while the highest percentage was seen in follicular lymphoma (FL) and diffuse large B cell lymphoma (DLBCL) (P=0.001). Compared to routine histopathology, RECAF was more sensitive in detecting bone marrow (BM) infiltration in FL, mantle cell lymphoma (MCL), and DLBCL (P=0.01).

Conclusion

RECAF is significantly expressed in the BM of NHL/chronic lymphocytic leukemia (CLL) patients. RECAF shows a unique expression pattern among the different subtypes of LPD. Furthermore, RECAF may help to detect bone marrow infiltration in lymphoma cells. This may help in the diagnosis, follow-up, and targeting of LPD.

Efficacy and tolerability of AFPep, a cyclic peptide with anti-breast cancer properties

PURPOSE

The purpose of this study is to assess the efficacy and safety profile of AFPep, a 9-amino acid cyclic peptide prior to its entry into pre-clinical toxicology analyses en route to clinical trials.

METHODS

AFPep was assessed for anti-estrogenic activity in a mouse uterine growth assay and for breast cancer therapeutic efficacy in a human tumor xenograft model in mice. AFPep was assessed for tolerability in a variety of in vivo models, notably including assessment for effects on rat liver and human hepatocellular carcinoma cell lines and xenografts.

RESULTS

AFPep arrests the growth of human MCF-7 breast cancer xenografts, inhibits the estrogen-induced growth of mouse uteri, and does not affect liver growth nor stimulate growth of human hepatocellular carcinoma cell lines when growing in vitro or as xenografts in vivo. AFPep is well tolerated in mice, rats, dogs, and primates.

CONCLUSIONS

AFPep is effective for the treatment of ER-positive breast cancer and exhibits a therapeutic index that is substantially wider than that for drugs currently in clinical use. The data emphasize the importance of pursuing pre-clinical toxicology studies with the intent to enter clinical trials.

Binding characterization of the targeting drug AIMPILA to AFP receptors in human tumor xenografts

The main objective of this study was the characterization of preclinical tumor models based on their expression of alpha-fetoprotein receptor (RECAF) for targeting cancer cells with a new non-covalent complex (AIMPILA) containing alpha-fetoprotein as the carrier and Atractyloside as an apoptosis-inducing agent. For that purpose, we measured the amount of RECAF in the homogenates of the grafted tumors T47D and SW620 and in HepG2 cell extracts. We also determined the alpha-fetoprotein binding specificity of the targeting drug AIMPILA using a solid-phase chemiluminescent assay with AIMPILA-Acrdidinium. We found that RECAF is practically absent from healthy mice tissues (100 Units/mg) where in malignant cells, the amount of alpha-fetoprotein receptors follows this order: T47D (9152 Units/mg) > HepG2 (4865 Units/mg) > SW620 (2839 Units/mg). This agrees with our findings regarding AIMPILA-induced tumor growth inhibition (T47D (T/C = 22%) > HepG2 (T/C = 51%) > SW620 (T/C = 70%), where T/C is the ratio of tumor volume in treated vs control animals). Our results demonstrate that the therapeutic response to the targeting drug AIMPILA strongly depends on the RECAF expression by human tumors and confirms the choice of the tumor models used for an AIMPILA preclinical study.

Cell injury, retrodifferentiation and the cancer treatment paradox

This “opinion article” is an attempt to take an overview of some significant changes that have happened in our understanding of cancer status during the last half century and its evolution under the progressive influence of molecular biology. As an active worker in cancer research and developmental biology during most of this period, I would like to comment briefly on these changes and to give my critical appreciation of their outcome as it affects our knowledge of cancer development as well as the current treatment of the disease. A recall of my own contribution to the subject is also included. Two subjects are particularly developed: cell injury and cell-killing therapies. Cell injury, whatever its origin, has acquired the status of a pivotal event for the initiation of cancer emergence. It is postulated that cell injury, a potential case of cellular death, may also be the origin of a process of stepwise cell reversion (retrodifferentiation or retroprogrammation) leading, by division, mature or stem cells to progressive immaturity. The genetic instability and mutational changes that accompanies this process of cell injury and rejuvenation put normal cells in a status favourable to neoplastic transformation or may evolve cancer cells toward clones with higher malignant potentiality. Thus, cell injury suggests lifestyle as the major upstream initiator of cancer development although this not exclude randomness as an unavoidable contributor to the disease. Cell-killing agents (mainly cytotoxic drugs and radiotherapy) are currently used to treat cancer. At the same time, it is agreed that agents with high cell injury potential (ultraviolet light, ionising radiations, tobacco, environmental pollutants, etc.) contribute to the emergence of malignant tumours. This represents a real paradox. In spite of the progress accomplished in cancer survival, one is tempted to suggest that we have very few chances of really cure cancer as long as we continue to treat malignancies with cell-killing therapies. Indeed, the absence of alternatives to such treatments justifies the pursuit of current procedures of cancer care. But, this should be, precisely, an urgent stimulus to explore other therapeutic approaches. Tumour reversion, immunotherapy, stem cell management and genomic analysis of embryo-foetal development could be, among others, appropriated candidates for future active research.

The role of the gastrointestinal epithelium as a possible pathway for the transfer of nutrients to the embryo's circulation

The endodermal cells of the human yolk sac (YS) produce non-nucleated erythrocytes (NNEs) and numerous serum proteins that are transiently storage within the YS cavity. After their transfer via the vitelline duct to the embryo gastrointestinal lumen, the nutrients' final fate is unknown. With the aim of investigate how erythroid cells and nutrients are conveyed to embryo circulation, we studied, using a morphological and immunohistochemical approach, the embryo anatomy and the serum protein α-fetoprotein (AFP) presence, in 15 human embryos and their YS, collected from tubal pregnancies from 4 to 8 wpf. We observed at 5 wpf, a strong AFP staining in the endodermal cells of the YS, thereafter AFP was only present in the YS cavity and the gastrointestinal lumen. During 7 wpf, AFP expression declined and disappeared, concomitant with YS regression. Between 5 and 7 wpf, NNEs were observed in the gastrointestinal cavity, where they accumulate in the stomach. Here, the cells were attached to the endodermal epithelial cells or were free in the lumen. By scanning electron microscopy, we identified signs of NNEs phagocytized by endodermal cells. Those NNEs free in the lumen, after hemolysis, were probably removed by endocytosis (cell debris). Taking all together, we postulate that after reaching the endodermal epithelial cells of the stomach, nutrients are transferred to the embryo by a phagocytic/endocytic mechanism that is operative until the end of 6 wpf. After absorption, NNEs are probably degraded within phagosomes, nutrients delivered to the cell cytoplasm and then transported towards the embryonic circulation.

Increased alpha-fetoprotein receptor in the serum of patients with early-stage breast cancer

The alpha-fetoprotein (afp) receptor (recaf) is an oncofetal antigen found in most types of cancer. Using a competitive radioimmunoassay, we measured the concentration of serum recaf in three sets of samples.Set 1 was blind and consisted of 119 normal subjects, 43 breast cancer patients (stages i and ii), and 20 patients with benign breast conditions. In this set, the assay discriminated normal from cancer samples with a receiver operating characteristic for the area under the curve (ROC(AUC)) of 0.983; with 95% specificity and 93% sensitivity at a cut-off of 4.6 K (arbitrary) recaf units; and with 72% sensitivity and 100% specificity at a cut-off of 7.3 K units. At 7.3 K units, the specificity for benign breast conditions was 85%, and the sensitivity was 72% (ROC(AUC) was 0.773). Carcinoembryonic antigen and cancer antigen 15-3 respectively showed 39% and 41% sensitivity, with 95% specificity in comparisons of normal with cancer samples, and 34% and 44% sensitivity, with 85% specificity in comparisons of benign with cancer samples. Set 2 consisted of 353 normal, 30 benign, and 64 cancer samples (stages ii and iii). The recaf assay sensitivity in discriminating normal from cancer samples was 97%, with 97% specificity. Benign compared with cancer samples showed 87% sensitivity, with 97% specificity. Set 3 included only 40 normal and 40 cancer samples. The assay sensitivity was 89%, with 100% specificity. Sets 2 and 3 were not tested with carcinoembryonic antigen and cancer antigen 15-3.These results strongly suggest that the recaf assay could be used for detecting breast cancer in its early stages.

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.

Review of the adenocarcinoma cell surface receptor for human alpha-fetoprotein; proposed identification of a widespread mucin as the tumor cell receptor

The identification of a tumor cell receptor for alpha-fetoprotein (AFP) has long been sought in the field of medicine. The uptake and endocytosis of AFP by rat tumor cells in 1983 sparked a series of confirmatory reports which were extended to include multiple tumor types in rats, mice, and humans. The following year, French investigators characterized the binding properties of the AFP receptor but they did not purify and characterize the receptor. It was not until 1991-1992 that an AFP receptor was partially purified and characterized from both human monocytes and breast cancer cells. By 1993, monoclonal antibodies had been raised against the "AFP receptor" derived from breast cancer extracts with claims that the receptor was a widespread oncoprotein biomarker for cancer. To date, that receptor has yet to be identified due to its complex multimeric structure and carbohydrate composition. The present report will review the literature of the multiple AFP receptors previously including their cellular uptake, transmembrane passage, and partial biochemical characterization. . In addition, evidence derived from computer modeling, proteolytic/fragmentation cleavage patterns, domain structure analysis, and protein binding software analysis will be presented in a proposed identification of a widespread protein/gene family of transmembrane proteins which fits many, if not most, of the criteria attributed to the AFP receptor. The proposed receptor protein family is tentatively identified as an epithelial cell surface mucin constituting one (or more) of many classes of single-pass transmembrane proteins. Present data do not support the concept that the AFP receptor is a "universal" tumor receptor and/or biomarker, but rather a widespread mucin protein that functions primarily in protecting and lubricating epithelial mucosal layers, and engaging in signal transduction; the mucin only binds AFP as a molecule serving in a subordinate or ancillary function.

[Recombinant human alpha-fetoprotein as a regulator of adipose tissue stromal cell activity]

Recombinant human alpha-fetoprotein (rhAFP) expressed in yeast system as a glycoprotein, was isolated and purified to 98% by multistep method. The testing of the rhAFP in the culture of adipose tissue stromal cells (hASC) has revealed its ability to enhance hASC proliferation and migration as well as vascular endothelial growth factor production, with no significant influence on cell invasion and matrix metalloproteinase-2 and -9 secretion. It has been also estimated that rhAFP is internalized in hASC via clathrin-dependent mechanism. A study in the murine experimental model of hindlimb ischemia has shown the capability of rhAFP to enhance blood flow recovery. These data suggest that rhAFP is a promising agent for enhancement of the hASC regenerative ability.

HSP72 and gp96 in gastroenterological cancers

Heat shock protein 72 (HSP72) and glycoprotein 96 (gp96) are highly expressed in cancer tissues. Recent studies indicate the possible roles of HSP72 and gp96 in the development and progression of gastrointestinal carcinomas but detailed mechanisms are still ambiguous. Human esophageal cancer, gastric cancer, colon cancer and liver cancer are common gastrointestinal malignant carcinomas in the world. The studies indicated that there existed a significant correlation between the expression of HSP72, gp96 and the development and progression of digestive carcinomas. HSP72 and gp96 expression were significantly associated with the presence of tumor infiltration, lymph node and remote metastasis. Interestingly, studies have found that HSP72 chaperoned alpha-fetoprotein (AFP), HBx in hepatocellular carcinoma, and CD44 in colonic carcinomas. The further researches demonstrated that HSP72-AFP or gp96-AFP recombined vaccine could elicit specific anti-tumor immunity. The high-level expression of HSP72 and gp96 may be not only used as diagnostic or prognostic markers for gastrointestinal carcinomas but also as better immunotherapeutic vaccines in the cancers.

Regression of hepatocarcinoma cells using RNA aptamer specific to alpha-fetoprotein

Alpha-fetoprotein (AFP) is a cancer-associated fetal protein and has long been utilized as a serum fetal defect/tumor marker to monitor distress/disease progression. In addition, AFP is closely associated with the proliferation of hepatocellular carcinoma. Thus, direct targeting of AFP has been recommended for a therapeutic strategy against hepatocellular carcinoma. In this study, we developed and characterized an RNA aptamer that specifically bound to the alpha-fetoprotein using SELEX technology. The aptamer interacted with the AFP with a K(D) of ∼33 nM. Importantly, the identified aptamer specifically and efficiently inhibited the AFP-mediated proliferation of hepatocarcinoma cells in a dose dependent manner. Moreover, the aptamer efficiently down-regulated AFP-induced expression of oncogenes in the cells. These results indicate that an AFP-specific RNA aptamer could be a useful therapeutic and diagnostic agent against AFP-related hepatocellular carcinoma.

Design and synthesis of biologically active peptides: a 'tail' of amino acids can modulate activity of synthetic cyclic peptides

In earlier work, we synthesized a cyclic 9-amino acid peptide (AFPep, cyclo[EKTOVNOGN]) and showed it to be useful for prevention and therapy of breast cancer. In an effort to explore the structure-function relationships of AFPep, we have designed analogs that bear a short 'tail' (one or two amino acids) attached to the cyclic peptide distal to its pharmacophore. Analogs that bore a tail of either one or two amino acids, either of which had a hydrophilic moiety in the side chain (e.g., cyclo[EKTOVNOGN]FS) exhibited greatly diminished biological activity (inhibition of estrogen-stimulated uterine growth) relative to AFPep. Analogs that bore a tail of either one or two amino acids which had hydrophobic (aliphatic or aromatic) side chains (e.g., cyclo[EKTOVNOGN]FI) retained (or had enhanced) growth inhibition activity. Combining in the same biological assay a hydrophilic-tailed analog with either AFPep or a hydrophobic-tailed analog resulted in decreased activity relative to that for AFPep or for the hydrophobic-tailed analog alone, suggesting that hydrophilic-tailed analogs are binding to a biologically active receptor. An analog with a disrupted pharmacophore (cyclo[EKTOVGOGN]) exhibited little or no growth inhibition activity. An analog with a hydrophilic tail and a disrupted pharmacophore (cyclo[EKTOVGOGN]FS) exhibited no growth inhibition activity of its own and did not affect the activity of a hydrophobic-tailed analog, but enhanced the growth inhibition activity of AFPep. These results are discussed in the context of a two-receptor model for binding of AFPep and ring-and-tail analogs. We suggest that tails on cyclic peptides may comprise a useful method to enhance diversity of peptide design and specificity of ligand-receptor interactions.

Targeted delivery of anti-cancer growth inhibitory peptides derived from human alpha-fetoprotein: review of an International Multi-Center Collaborative Study

The alpha-fetoprotein derived growth inhibitory peptide (GIP) is a 34-amino acid peptide composed of three biologically active subfragments. GIP-34 and its three constituent segments have been synthesized, purified, and studied for biological activity. The GIP-34 and GIP-8 have been characterized as anticancer therapeutic peptides. An multicenter study was initiated to elucidate the means by which these peptide drugs could be targeted to tumor cells. The study first established which cancer types were specifically targeted by the GIP peptides in both in vitro and in vivo investigations. It was next demonstrated that radiolabeled peptide ((125)I GIP-34) is specifically localized to rodent breast tumors at 24 h post-injection. The radionuclide studies also provided evidence for a proposed cell surface receptor; this was confirmed in a further study using fluorescent-labeled GIP-nanobeads which localized at the plasma membrane of MCF-7 breast cancer cells. Finally, it was readily demonstrated that GIP conjugated to either fluorescein or doxorubicin (DOX) underwent tumor cell uptake; subsequently, DOX-GIP conjugates induced cytotoxic cell destruction indicating the utility of GIP segments as cancer therapeutic agents. Following a discussion of the preceding results, a candidate cell surface receptor family was proposed which correlated with previous published reports for a putative AFP/GIP receptor.

Review of the putative cell-surface receptors for alpha-fetoprotein: identification of a candidate receptor protein family

The identification of a receptor for alpha-fetoprotein (AFP) has long been sought in the field of medicine. The uptake and endocytosis of AFP by rat tumor cells in 1984 sparked a series of confirmatory reports and the original studies were then extended to include multiple tumor types in rats, mice, and humans. The following year, French investigators partially characterized the binding properties of the AFP receptor, but they were not able to purify the receptor. It was not until 1991-1992 that an AFP receptor was partially purified and characterized from both human monocytes and breast cancer cells. By 1993, a monoclonal antibody had been raised against the AFP receptor produced from a breast cancer extract with claims that the receptor was a widespread (universal) oncofetal biomarker for cancer. However, that receptor has yet to be cloned and/or purified due to its complex multimeric binding interactions and associations. The present report will review the literature of the multiple putative AFP receptors described to date, the cellular uptake and endocytosis of AFP, and the biochemical characterization of these putative cell-surface proteins. In addition, evidence derived from computer modeling, proteolytic degradation patterns, and amino acid sequence analysis will be presented in a proposed identification of a family of multi-ligand binding receptors; this family fits many, if not most, of the criteria required for an AFP receptor. The purposed receptor protein family is tentatively identified as the Scavenger receptors which comprise several classes of single- and double-pass integral transmembrane proteins. Present data do not support the concept that the AFP receptor is a "universal" tumor receptor and/or biomarker.

Computational approaches for the design of peptides with anti-breast cancer properties

Background: Breast cancer is the most common cancer among women. Tamoxifen is the preferred drug for estrogen receptor-positive breast cancer treatment, yet many of these cancers are intrinsically resistant to tamoxifen or acquire resistance during treatment. Therefore, scientists are searching for breast cancer drugs that have different molecular targets. Methodology: Recently, a computational approach was used to successfully design peptides that are new lead compounds against breast cancer. We used replica exchange molecular dynamics to predict the structure and dynamics of active peptides, leading to the discovery of smaller bioactive peptides. Conclusions: These analogs inhibit estrogen-dependent cell growth in a mouse uterine growth assay, a test showing reliable correlation with human breast cancer inhibition. We outline the computational methods that were tried and used along with the experimental information that led to the successful completion of this research.

Protein multifunctionality: principles and mechanisms

In the review, the nature of protein multifunctionality is analyzed. In the first part of the review the principles of structural/functional organization of protein are discussed. In the second part, the main mechanisms involved in development of multiple functions on a single gene product(s) are analyzed. The last part represents a number of examples showing that multifunctionality is a basic feature of biologically active proteins.

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.

Interaction between heat shock protein 72 and alpha-fetoprotein in human hepatocellular carcinomas

BACKGROUND

AFP in adult serum often signals pathological conditions, particularly the presence of hepatocellular carcinoma (HCC) and germ cell tumors containing yolk sac cell elements. Heat shock protein 72 (HSP72) as a molecular chaperone has been confirmed to overexpress in epithelial carcinoma cells. There may be a possible correlation between the expression of HSP72 and AFP during the growth and differentiation of hepatocellular carcinoma cells. We investigated the interaction between heat shock protein 72 (HSP72) and alpha-fetoprotein (AFP) in human hepatocellular carcinomas.

METHODS

The expression and localization of HSP72 and AFP in human hepatocellular carcinomas were determined by immunohistochemistry and confocal laser microscopy. The interaction between HSP72 and AFP in hepatocellular carcinoma cells was analyzed by immunoprecipitation and Western immunoblots.

RESULTS

Hepatocellular carcinoma synchronously co-expressed higher level of HSP72 and AFP than in adjacent normal liver tissues. HSP72 were stained in cell nuclei and cytoplasm respectively, while AFP stained in cell plasma. Based on Western blotting methods, AFP was detected in the immunoprecipitate of anti-HSP72 monoclonal antibody (mAb), while HSP72 existed in the immunoprecipitate of anti-AFP mAb.

CONCLUSIONS

HSP72 and AFP expression are higher in hepatocellular carcinoma tissues. HSP72 was associated with alpha-fetoprotein in human hepatocellular carcinoma cells. The interaction between HSP72 and AFP in human hepatocellular carcinoma cells can be a new route for studying the pathogenesis and immunotherapy of hepatocellular carcinoma.

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.

Heat shock protein 70 chaperoned alpha-fetoprotein in human hepatocellular carcinoma cell line BEL-7402

AIM: To investigate the interaction between heat shock protein 70 (HSP70) and α-fetoprotein (AFP) in human hepatocellular carcinoma (HCC) cell line BEL-7402.

METHODS: The expression and localization of HSP70 and AFP in human HCC cell line BEL-7402 were determined by immunocytochemistry and indirect immunofluorescence cytochemical staining. The interaction between HSP70 and AFP in HCC cells was analyzed by immunoprecipitation and Western blot.

RESULTS: Immunocytochemical staining detection showed that HCC cell BEL-7402 expressed a high level of HSP70 and AFP synchronously. Both were stained in cell plasma. AFP existed in the immunoprecipitate of anti-HSP70 mAb, while there was HSP70 in the immunoprecipitate of anti-AFP mAb.

CONCLUSION: HSP70 chaperones AFP in human HCC cell BEL-7402. The interaction between HSP70 and AFP in human HCC cell can be a new route to study the pathogenesis and immunotherapy of HCC.

Alpha-fetoprotein triggers hepatoma cells escaping from immune surveillance through altering the expression of Fas/FasL and tumor necrosis factor related apoptosis-inducing ligand and its receptor of lymphocytes and liver cancer cells

AIM: To investigate the mechanism of α-fetoprotein (AFP) in escaping from the host immune surveillance of hepatoc-ellular carcinoma.

METHODS: AFP purified from human umbilical blood was administrated into the cultured human lymphoma Jurkat T cell line or hepatoma cell line, Bel7402 in vitro. The expression of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) and its receptor (TRAILR) mRNA were analyzed by Northern blot and Western blot was used to detect the expression of Fas and Fas ligand (FasL) protein.

RESULTS: AFP (20 mg/L) could promote the expression of FasL and TRAIL, and inhibit the expression of Fas and TRAILR of Bel7402 cells. For Jurkat cell line, AFP could suppress the expression of FasL and TRAIL, and stimulate the expression of Fas and TRAILR. AFP also could synergize with Bel7402 cells to inhibit the expression of FasL protein and TRAIL mRNA in Jurkat cells. The monoclonal antibody against AFP (anti-AFP) could abolish these functions of AFP.

CONCLUSION: AFP is able to promote the expression of FasL and TRAIL in hepatoma cells and enhance the expression of Fas and TRAILR in lymphocytes. These could elicit the escape of hepatocellular carcinoma cells from the host’s lymphocytes immune surveillance.

Processing and transport of matrix gamma-carboxyglutamic acid protein and bone morphogenetic protein-2 in cultured human vascular smooth muscle cells: evidence for an uptake mechanism for serum fetuin

Matrix gamma-carboxyglutamic acid protein (MGP) is a member of the vitamin K-dependent protein family with unique structural and physical properties. MGP has been shown to be an inhibitor of arterial wall and cartilage calcification. One inhibitory mechanism is thought to be binding of bone morphogenetic protein-2. Binding has been shown to be dependent upon the vitamin K-dependent gamma-carboxylation modification of MGP. Since MGP is an insoluble matrix protein, this work has focused on intracellular processing and transport of MGP to become an extracellular binding protein for bone morphogenetic protein-2. Human vascular smooth muscle cells (VSMCs) were infected with an adenovirus carrying the MGP construct, which produced non-gamma-carboxylated MGP and fully gamma-carboxylated MGP. Both forms of MGP were found in the cytosolic and microsomal fractions obtained from the cells by differential centrifugation. The crude microsomal fraction was shown to contain an additional, more acidic Ser-phosphorylated form of MGP believed to be the product of Golgi casein kinase. The data suggest that phosphorylation of MGP dictates different transport routes for MGP in VSMCs. A proteomic approach failed to identify a larger soluble precursor of MGP or an intracellular carrier protein for MGP. Evidence is presented for a receptor-mediated uptake mechanism for fetuin by cultured human VSMCs. Fetuin, shown by mass spectrometry not to contain MGP, was found to be recognized by anti-MGP antibodies. Fetuin uptake and secretion by proliferating and differentiating cells at sites of calcification in the arterial wall may represent an additional protective mechanism against arterial calcification.

Biological roles of alpha-fetoprotein during pregnancy and perinatal development

The use of alpha-fetoprotein (AFP) as a serum marker in cancer actually predates its employment in the detection of congenital defects; however, the latter use of AFP as a fetal defect marker has propelled its clinical utilization. Although the serum-marker capacity of AFP has long been exploited, less is known of the biological activities of this oncofetal protein during fetal and perinatal development. In the present review, the biological activities of AFP are discussed in light of this glycoprotein's presence in various biological fluid compartments: embryonic and fetal tissues, serum, urine, and reproductive fluids. After a review of the histochemical detection of AFP in various cells and tissues during development, AFP concentrations within various biological fluids were discussed in the context of gestational age and anatomic location. Discussion follows concerning the relationships and roles of AFP in developmental events such as erthyropoiesis, histogenesis/organogenesis, and ligand binding and in developmental disorders such as hypothyroidism, folate deficiencies, and acquired immunodeficiency disorder (AIDS). Based on its association with so many types of birth defects, malformations, and congenital anomalies, AFP can be viewed as a molecular "troubleshooter" until signal transduction pathways are established during pregnancy and prenatal development. The review concludes with a discussion of the place of AFP in the rapidly expanding field of proteomics.

Alpha-fetoprotein stimulated the expression of some oncogenes in human hepatocellular carcinoma Bel 7402 cells

AIM: To investigate the molecular mechanism of alpha-fetoprotein (AFP) on regulating the proliferation of human hepatocellular carcinoma cells.

METHODS: Alpha-fetoprotein purified from human umbilical blood was added to cultured human hepatocellular carcinoma Bel 7402 cells in vitro for various treatment periods. The expression of c-fos, c-jun, and N-ras mRNA involved in proliferation and differentiation of cells was analyzed by Northern blot, and the expression of mutative p53 and p21^ras proteins was determined by Western blot.

RESULTS: The results showed that AFP (20 mg/L) stimulated mRNA expression of these oncogenes in Bel 7402 cells. The expression of c-fos mRNA increased by 51.1%, 60.9%, 96.0%, and 25.5% at 2, 6, 12, and 24 h, respectively. The expression of c-jun and N-ras mRNA reached to the maximum which increased by 81.3% and 59.9% as compared with the control after 6 h and 24 h incubation with AFP, respectively. Western blot assay also demonstrated that AFP promoted the expression of mutative p53 and p21^ras proteins, and the increased rate of those proteins was 13.0%, 39.9%, and 70.9%, as well as 35.2%, 102.6%, and 46.8% at 6, 12, and 24 h, respectively, as compared with the control. Both human serum albumin (the same dosage as AFP) and monoclonal anti-AFP antibody failed to stimulate the expression of these oncogenes, but anti-AFP antibody could block the functions of AFP.

CONCLUSION: The data indicate that AFP can stimulate the expression of some oncogenes to enhance the proliferation of human hepatocellular carcinoma Bel 7402 cells.

Human alpha-fetoprotein binds to primary macrophages

We have previously reported that alpha-fetoprotein (AFP) inhibits infection of human monocyte-derived macrophages (MDM) by R5-HIV-1 strains and that a peptide mimicking the clade B HIV-1 gp120 consensus V3 domain (V3Cs) binds to CCR5. We demonstrate here that AFP binds high- and low-affinity binding sites of MDM, characterized, respectively, by 5.15 and 100nM K(d) values. Heat denaturation or neuraminidase treatment of AFP inhibits this binding, suggesting the involvement of protein-protein and lectin-carbohydrate interactions. Moreover, AFP displaces V3Cs binding to MDM. In addition, MIP-1beta, the most specific CCR5 ligand, displaces AFP binding to MDM (IC(50)=4.3nM). Finally, we demonstrate that AFP binds to a ligand of HIV-gp120 V3Cs domain, CCR5, expressed by MDM and by HeLa cells expressing CCR5. Such binding is not observed in the presence of HeLa cells lacking CCR5. The present results provide strong evidence that AFP directly binds to CCR5 expressed by human primary macrophages and by transfected CCR5+ HeLa cells.

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.

Diagnostic and prognostic tumor markers in the gastrointestinal tract

The gastrointestinal tract is the most common site of malignancies of any anatomic system in the body. An early detection of primary tumors of the bowel, pancreas, liver, stomach, and esophagus is often difficult in asymptomatic patients and for this reason these tumors are often detected at a relatively advanced stage, when symptoms lead to a diagnostic evaluation. Furthermore, gastrointestinal tract tumors have an extremely variable prognosis; thus, the identification of new prognostic parameters may be useful for selecting patients to more tailored therapies. In this work, the main molecular, genetic, tissular, and circulating tumor markers proposed for diagnosis and prognosis of gastrointestinal malignancies are reviewed and discussed.

Structure and function of alpha-fetoprotein: a biophysical overview

alpha-Fetoprotein (AFP) is a large serum glycoprotein belonging to the intriguing class of onco-developmental proteins. AFP has attracted considerable attention since it was shown that the change in its serum level during pregnancy is a hallmark of the development of numerous embryonic disorders, while the increase in its content in the plasma of adults correlates with the appearance of several pathological conditions. Over the past 30 years, some 11000 papers have been published concerning AFP, an average rate of over a publication a day since 1969. The majority of publications are about the application of the protein in diagnostics, or about other uses of AFP in biomedicine; though some of them describe the biochemical and functional properties of AFP, two aspects have been extensively reviewed. However, surprisingly little is currently known about structural properties of this protein as well as about the molecular mechanism of its function. The present review pursues the aim to describe the current state of the art in studies of structural properties and conformational stability of AFP. An attempt to establish the relationship between conformational transformations in AFP and its function is also made.

Expression of serum albumin and of alphafetoprotein in murine normal and neoplastic primitive embryonic structures

Alphafetoprotein (AFP), a major serum protein synthesized during the embryo-fetal and postnatal period (in the yolk sac, then in the liver), is also an oncoprotein. The intracellular presence of AFP and of serum albumin (SA) in normal and neoplastic neural crest and neural tube derivatives was previously demonstrated. In this work we have studied the comparative expression of AFP and SA in primitive neuroectoblastic structures of mouse embryos (6 and 7 days "post coitum") and mouse teratocarcinomas (derived from the PCC4 cell line). Using immunofluorescence technique, antibodies to SA gave a positive reaction in embryos of 7 days, while AFP was not detected during this period. By mRNA in situ hybridization, SA mRNA gave a strong signal in both 6 and 7 day embryos, whereas AFP mRNA gave a weak signal only in 7-day embryos. The distribution of SA and AFP and their mRNAs was investigated in primitive neuroectoblastic structures of the teratocarcinomas by in situ hybridization and immunostaining. Only SA protein was detectable by immunostaining. SA mRNA gave a strong signal in differentiating structures as well as in undifferentiated cell clusters. AFP mRNA was observed only in differentiating structure. Dot-blot hybridization indicated that the level of SA transcripts was at least 6-fold higher than that of AFP transcripts in the teratocarcinomas investigated. In teratocarcinoma-bearing mice injected intraperitoneally with 125I-radiolabeled SA and AFP, significant accumulations of both SA and AFP were demonstrated in the tumors, SA being about 3-fold higher than that of AFP after normalization to quantity of uptake in liver. External in vivo photoscanning confirmed this relationship of accumulated radiolabeled proteins. The last observation could be useful in vivo for diagnosis of teratocarcinoma. We conclude that the expression of SA relative to AFP and the external cellular uptake of SA relative to AFP are similar in normal embryonic developing tissues and in the corresponding morphologically neoplastic tissues of the teratocarcinomas. The same SA:AFP relationship constitutes an oncofetal marker of primitive neuroectoblastic structures.

Endocytosis of three serum proteins of a multigene family and of arachidonic acid in human lectin-stimulated T lymphocytes

Alpha-fetoprotein (AFP), serum albumin (SA), and vitamin D binding protein (DBP) are members of a multigene family of proteins showing high structural homology. AFP and SA exhibit a reciprocal relation during development and carry mostly fatty acids, while DBP carries vitamin D and its metabolites in the plasma. Covalent conjugates of these proteins with horseradish peroxidase (HRP) were used to follow by cytochemistry, at the electron microscope level, the protein uptake and intracellular pathways in peripheral blood human lymphocytes stimulated to blast formation by phytohemagglutinin (PHA). Transferrin (Tf), an iron-binding plasma protein, was used as a control. Combined with the results of competition and saturability experiments reported elsewhere, the ultrastructural observations are in favour of a specific endocytosis of the four proteins through cell surface receptors. Tf and AFP enter the cells via small vesicles and endosomes and move to multivesicular bodies (MVBs) and tubular vesicular elements located in the Golgi-centrosphere region to be finally recycled back into the medium. A noncovalent conjugate of AFP-HRP with 3H arachidonic acid [3H-(20:4)] is strongly internalized at 37 degrees C in PHA-stimulated lymphocytes; the autoradiographic labelling, localized in cellular membranes and mostly in lipid droplets, was only occasionally associated with organelles where the presence of AFP-HRP was cytochemically detected. SA, which competes with AFP for a common binding site on the surface of activated T cells, is endocytosed through small vesicles, endosomes, and MVBs before being released in a degraded form from the cells, in agreement with the localization of SA-HRP in lysosome-like organelles. DBP-HRP is poorly internalized through noncoated vesicles, endosomes, and MVBs and is finally routed to lysosomes. The physiological role of AFP and SA would be to mediate the transfer of fatty acids into cells, while that of DBP would be to facilitate the intracellular delivery of vitamin D.

Isolation and partial characterization of a specific alpha-fetoprotein receptor on human monocytes

Since a large body of data has suggested a significant role for alpha-fetoprotein (AFP) in the regulation of the immune response at a number of levels, we examined the possibility of a specific receptor for AFP on the immune recognition cell, the monocyte/macrophage. Microscopic autoradiography exhibited an obvious binding of AFP almost exclusively on human peripheral monocytes but not on lymphocytes. In a human monocyte cell line (U937) Scatchard plot analysis indicated the presence of two distinct AFP-specific binding sites with a Kd of 5 x 10(-11) M, 49 binding sites per cell, and 2.5 x 10(-7) M, 7,800 binding sites per cell. 125I-ASD-AFP, AFP-radiolabeled bifunctional photoactivatable thio-cleavable cross-linker, was used to isolate the AFP binding protein from U937 cells. After ultraviolet photoactivation, 125I-sulfosuccinimidyl 2-(p-azido-salicylamido)ethyl-1,3'-dithiopropionate was covalently linked to the putative receptor. Autoradiography of SDS gradient PAGE under reducing conditions showed a major radiolabeled band at between 62 and 65 kD. To confirm the specificity of the finding, recombination of AFP with the isolated receptor was examined in artificially reconstituted membrane vesicles, which also resulted in a single band at approximately 62-65 kD by SDS-PAGE autoradiography. From the data above, we concluded that human monocytes possess a specific AFP binding protein on the membrane, a putative receptor, which may be involved with the physiological regulation of the immune response.

Alpha-fetoprotein-mediated uptake of fatty acids by human T lymphocytes

The binding to resting and activated T lymphocytes of two radiolabelled fatty acids (oleic and arachidonic) was studied in the presence or in the absence of alpha-fetoprotein (AFP) as carrier protein. Fatty acid binding by resting and activated T lymphocytes was determined at 4 degrees C as a function of the concentration of fatty acid and AFP. Under the conditions employed, the following observations were made: (1) in the presence of AFP, fatty acids (oleic and arachidonic acid) are bound to cells by a two-component pathway; one is a saturable process, evidenced when the fatty acid to AFP (FA/AFP) molar ratio was fixed at 1 and the concentration of the fatty acid and the protein varied from 0.1 to 3.2 microM, and the second is a nonsaturable function of FA/AFP molar ratio and was linearly related to the unbound fatty acid concentration in the medium over the entire range studied; (2) in the absence of AFP, the nonsaturable process appears to be the only component of fatty acid binding; 3) at all tested concentrations of free (unbound) fatty acid in the medium, net fatty acid binding by either resting or activated T cells was considerably greater in the presence than in the absence of AFP; (4) in the presence of AFP, fatty acid binding was much higher in activated T cells than in resting T cells, whereas in the absence of AFP, nonsignificant differences were observed between activated and resting T cells; and (5) the time course of fatty acid and AFP binding at 4 degrees C revealed that, at equilibrium, the number of fatty acid molecules bound to the cell was much greater than that of AFP suggesting an accelerated dissociation of the fatty acid upon interaction of the AFP-fatty acid complex with putative cell receptors. It is concluded to the existence of an AFP/AFP-receptor pathway that facilitates the binding of fatty acids to T lymphocytes, particularly upon their blast transformation. This pathway may fulfill the increased requirement for fatty acids characteristic of proliferating cells and may serve to regulate the endocytosis of fatty acids with modulatory effects on lymphocyte function and to protect cells from their cytotoxic potential when internalized in excess.

Activation of an alpha-fetoprotein (AFP)/receptor autocrine loop in HT-29 human colon carcinoma cells

Immunological and morphological approaches have been used to demonstrate, respectively, alpha-fetoprotein (AFP) synthesis and receptor expression in the HT-29 human colon carcinoma parental cell line. HT-29 cells cultivated in the presence of glucose synthesized and secreted AFP in the medium from 48 to 96 hr after seeding, as revealed by monoclonal antibodies (MAbs) to human AFP. Light microscopic observations of cells incubated with fluoresceinated AFP showed that the protein was specifically bound to the cell surface at 4 degrees C, and was internalized in the cytoplasm at 37 degrees C. At the ultrastructural level, horseradish peroxidase (HRP)-conjugated AFP, as well as HRP-transferrin (Tf) (used as a control), appeared to be internalized via coated pits and vesicles before being delivered to endosomes, from which they were apparently recycled back to the cell surface via small vesicles. Our results suggest that a AFP/receptor autocrine pathway might operate in these cells, be preferentially active at the beginning of the exponential phase of cell culture growth, and contribute to cell proliferation.

Receptor-mediated endocytosis and recycling of alpha-fetoprotein in human B-lymphoma and T-leukemia cells

The kinetics of iodinated human alpha-fetoprotein (AFP) binding and uptake by 2 human neoplastic lymphoid cell lines (CEM and RAJI) have been studied. Three saturation plateaus were obtained by incubating CEM and RAJI cells at 4 degrees C with 125I-AFP at different concentrations. Scatchard analysis suggested the presence of 3 types of receptor site with different affinities and capacities on cells of both lines. AFP binding was inhibited by unlabelled human and bovine AFP, and to a lesser extent by human serum albumin (SAH); no significant competition was observed with human transferrin (Tf) or ovalbumin (Ova). Pulse-chase experiments showed that 125I-AFP was released practically undegraded from the cells. Covalent conjugates of AFP and Tf with horseradish peroxidase (HRP) were used to follow the endocytosis and intracellular pathway of these serum proteins by electron microscopy. Both proteins were observed in coated vesicles, endosomes and a tubular vesicular network localized in the Golgi-centrosphere region. SAH-HRP was internalized to a much lesser extent. Ova-HRP was poorly internalized and was observed in lysosome-like organelles.

Chemistry and biology of alpha-fetoprotein

Alpha-Fetoprotein (AFP) is a product of specific fetal tissues and of neoplastic cells of hepatocyte or germ cell origin in adults. This protein belongs to a gene family that is phylogenetically most closely related to serum albumin. Its primary, secondary, and tertiary structural aspects appear similar to the three-domain concept proposed for the latter protein. The primary sequence of AFP departs most widely from serum albumin in the first 135 amino acid residues, with about 42% of the remaining 590 residues of the human proteins being identical. Some evidence exists that there are limited sequence differences in the AFP of a given animal species. AFP shows considerable charge heterogeneity that appears to relate mostly to its glycoid moiety. The proteins of some species such as the rat show more pronounced heterogeneities than that of humans. The variations in extent and type of glycosylations are evidenced by differences in the binding to various lectins. These interactions are being extensively explored in attempts to differentiate the sources of the protein produced by various normal and neoplastic cells and may provide valuable diagnostic methods. AFP, like serum albumin, shows relatively strong binding affinities for a variety of ligands. The most notable difference is the strong preferential binding of polyunsaturated fatty acids by AFP. This protein may play a role in transporting these substances to developing and to malignant cells. Various agents affect the synthesis of this protein both by specific fetal tissues and by neoplastic cells. Marked differences in the responses of cells, particularly those of neoplastic types, are indicative of variations in the genetic factors responsible for control of its synthesis. The subject of the genomic repression of the synthesis of AFP seen in fetal life upon maturation of the liver and the reoccurrence of synthesis upon malignant conversion of hepatocytes and of certain germ cells are of particular interest. The regulation of the closely related AFP and albumin genes is providing a powerful and attractive model to examine molecular events in the activation and inactivation of specific genes during development and in oncogenic processes. Extensive measurements of AFP during pregnancy and in the course of neoplasias, notably hepatoma, are being made to aid in following changes in such developments. Various specific physiological roles for this protein are also being proposed. One of these is its possible action in the regulation of immune processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Defective uptake of alpha-fetoprotein (AFP) and transferrin (Tf) by PHA-activated peripheral blood lymphocytes from patients with AIDS and related syndromes

Serum alpha-fetoprotein (AFP) and transferrin (Tf) are actively endocytosed by many growing cells during ontogenic and neoplastic growth, but also by peripheral T lymphocytes upon mitogen activation. AFP and Tf uptake occurs through receptor-mediated endocytosis. The purpose of the present work was to assess whether the expression and functional activity of AFP and Tf receptors are impaired in mitogen-activated T cells from several groups of HIV-1 seropositive (HIV+) individuals. Forty HIV+ cases were studied, including 12 patients with AIDS, 12 with lymphoadenopathy syndrome (LAS), as well as 16 asymptomatic homosexuals (As). Quantification of AFP and Tf uptake was carried out by fluorescence-activated cell sorting (FACS) using fluoresceinated derivatives of these proteins. Compared with healthy blood donors, the three HIV-1 seropositive groups exhibited clear impairment in the ability of their peripheral blood mononuclear cells (PBMC) to internalize AFP and Tf. The decrease in mean values of AFP uptake correlates roughly with the severity of the clinical status. Although these observations need to be confirmed after a much wider study groups, the AFP-Tf-endocytosis assay presented here clearly reveals early defective functions of mitogen-responsive T cells in disease-free subjects and may provide the basis for a prognostic test. The pathophysiological implications of these facts are discussed in relation to the structural and/or metabolic activities of fatty acids and iron, the ligands carried by AFP and Tf, respectively.

Transplacental estrogen responses in the fetal rat: increased uterine weight and ornithine decarboxylase activity

The synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE2), are more potent than 17 beta-estradiol (E2) in inducing uterine weight gain in the neonatal rat, due to the binding of E2 to serum alpha-fetoprotein (AFP). However, all three hormones are equipotent in inducing neonatal uterine ornithine decarboxylase (ODC) activity. The present study assessed estrogen potency in fetal rats. Pregnant CD rats were injected sc daily on gestation days (GD) 16-20 with DES, EE2, or E2 in sesame oil. Both DES and EE2, but not E2, significantly increased uterine weight at birth, to more than twice that of controls. In addition, implants which continuously release E2 only slightly increased uterine weight at birth. Alternatively, dams were given a single estrogen injection on GD 20 and were sacrificed at various times after injection. Peak fetal uterine ODC activity occurred at 6-8 hours after maternal injection for all three estrogens. E2 had a relative potency about tenfold less than either DES or EE2 in stimulating fetal ODC activity, in contrast to equal potencies of the three estrogens in the postnatal rat uterus. Similar patterns were found following direct fetal injection with E2 or DES. In summary, these data demonstrate a transplacental induction of fetal uterine ODC activity and uterine weight gain by both DES and EE2. In addition, the lack of correlation between these endpoints in response to E2 suggests that they may be useful as selective indicators of potential toxicity of both natural and synthetic estrogens.

Specific uptake of alpha-fetoprotein by malignant human lymphoid cells

We have studied the ability of human B- and T-lymphoblastoid cell lines, as well as of peripheral lymphoid cells from leukemia patients, to take up alpha-fetoprotein (AFP) and other serum proteins. Two technical approaches have been employed, both using fluorescent protein derivatives (FITC-proteins): microscopic examination of labelled cells using epifluorescent illumination and quantitation of endocytosed proteins by fluorescence-activated cell sorting (FACS). Compared to human resting T-lymphocytes, all T- and B-cell lines tested exhibited positive staining for fluoresceinated AFP and transferrin (Tf) and a significant increase, up to 100-fold, of the number of AFP and Tf molecules endocytosed per cell. Labelling was prevented or strongly diminished by a 100-fold excess of unlabelled protein. Preliminary results with peripheral lymphoid cells harvested from leukemia patients showed the presence of AFP- and Tf-positive cells in the blood of all patients examined. Intensity of labelling was related to the type of leukemia cells and/or the degree of cell maturation. Most cell lines exhibited positive staining for alpha 2-macroglobulin (alpha 2M) and also, to a lesser extent, for serum Vitamin D3 binding protein (DBP). In contrast, no labelling was observed with FITC-serum albumin (FITC-Alb) or FITC-ovalbumin (FITC-OVA). Comparative uptake of several FITC-proteins by a single cell population revealed significant quantitative and qualitative differences.