Alpha-fetoprotein stimulates leukotriene synthesis in P388D1 macrophages

Polyunsaturated Fatty Acid-Bound α-Fetoprotein Promotes Immune Suppression by Altering Human Dendritic Cell Metabolism

α-Fetoprotein (AFP) is expressed by stem-like and poor outcome hepatocellular cancer tumors and is a clinical tumor biomarker. AFP has been demonstrated to inhibit dendritic cell (DC) differentiation and maturation and to block oxidative phosphorylation. To identify the critical metabolic pathways leading to human DC functional suppression, here, we used two recently described single-cell profiling methods, scMEP (single-cell metabolic profiling) and SCENITH (single-cell energetic metabolism by profiling translation inhibition). Glycolytic capacity and glucose dependence of DCs were significantly increased by tumor-derived, but not normal cord blood-derived, AFP, leading to increased glucose uptake and lactate secretion. Key molecules in the electron transport chain in particular were regulated by tumor-derived AFP. These metabolic changes occurred at mRNA and protein levels, with negative impact on DC stimulatory capacity. Tumor-derived AFP bound significantly more polyunsaturated fatty acids (PUFA) than cord blood-derived AFP. PUFAs bound to AFP increased metabolic skewing and promoted DC functional suppression. PUFAs inhibited DC differentiation in vitro, and ω-6 PUFAs conferred potent immunoregulation when bound to tumor-derived AFP. Together, these findings provide mechanistic insights into how AFP antagonizes the innate immune response to limit antitumor immunity.

SIGNIFICANCE

α-Fetoprotein (AFP) is a secreted tumor protein and biomarker with impact on immunity. Fatty acid-bound AFP promotes immune suppression by skewing human dendritic cell metabolism toward glycolysis and reduced immune stimulation.

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.

The use of alpha-fetoprotein for the treatment of autoimmune diseases and cancer

Alpha-fetoprotein is a shuttle protein that delivers nutrients through receptor-mediated endocytosis to embryotic cells. In adults, alpha-fetoprotein can shuttle drugs into alpha-fetoprotein receptor-positive myeloid-derived suppressor, regenerating and also cancer cells. Drugs with high-binding affinity to alpha-fetoprotein can activate or deplete targeted cells. Myeloid-derived suppressor cells activation leads to immune suppression that can be used for treating autoimmune diseases. On the other hand, toxins delivered by alpha-fetoprotein can damage myeloid-derived suppressor cells and consequently unleash innate and adaptive immunity to destroy cancer cells. Innate immunity natural killers reduce cancer stem cells and metastases. The new alpha-fetoprotein drug noncovalent complexes for immunotherapy change the local immune balance and has potential in oncology, autoimmune and infectious diseases treatment, inflammation, transplantation, vaccination, etc.

Plasma protein levels in normal human fetuses: 13 to 41 weeks' gestation

OBJECTIVES

To establish reference ranges for the levels of alpha-fetoprotein, albumin, prealbumin (transthyretin) alpha-1-antitrypsin, transferrin, ceruloplasmin and total protein in the plasma of normal human fetuses and newborn babies.

DESIGN

Prospective study of individual normal cases to fulfil objectives.

SETTING

Pathology laboratories of the University of Edinburgh and the biochemistry laboratories of the University of Keele.

SUBJECTS

Twenty-two normal fetuses 13 to 22 weeks of gestation and 66 babies born between 24 and 41 weeks gestation.

RESULTS

Albumin is the predominant plasma protein throughout gestation. The levels of alpha-fetoprotein and prealbumin fell significantly with increasing gestation, whereas the concentrations of the other proteins studied increased. The ratios of individual proteins to total protein demonstrated similar trends.

CONCLUSIONS

This study provides developmental profiles of normal human fetal plasma proteins to serve as possible reference data for abnormal fetuses. Declining levels of prealbumin (transthyretin) were unexpected and suggest a functional role for this protein in early pregnancy.

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)

Regulation of constitutive and lymphokine-induced Ia expression by murine alpha-fetoprotein

alpha-Fetoprotein (AFP) has been shown to suppress a variety of immune responses in vitro. The immunosuppressive properties of AFP can be partly attributed to the ability of this protein to decrease the cell surface expression of Ia antigens on macrophages. The experiments described in this report define more precisely the regulatory effects of AFP on Ia expression. Using the "dendritic-like" cell line P388 AD2 and bone marrow-derived macrophages we have shown that AFP can suppress the constitutive expression of cell surface Ia antigens. This decrease is detectable on the cell surface 24 hr after the addition of AFP. In further experiments we also examined the effect of AFP on lymphokine-induced Ia expression. Our results show that AFP has no suppressive influence on the inductive phase of lymphokine-induced Ia antigen expression but can decrease elevated levels of Ia antigen subsequent to their induction.

A chymotryptic-type protease inhibitor decreases interleukin 2 synthesis and induces prostaglandin production in Jurkat T cells

TPCK (N-alpha-p-tosyl-L-phenylalanine chloromethylketone), a potent inhibitor of chymotryptic-type serine proteases, was found to decrease IL2 synthesis in Jurkat T cells. Conversely, the tryptic-type protease inhibitor, TLCK (N-alpha-p-tosyl-lysine chloromethylketone), which structurally is very similar to TPCK, had no effect on IL2 synthesis. Prostaglandin synthesis, a process that is known to reduce IL2 production in T cells, was increased by TPCK but not by TLCK, suggesting that this process could be, at least in part, responsible for the inhibition of IL2 production. Our results imply that a chymotryptic-type serine protease plays an active role in the regulation of IL2 synthesis and thus in the whole process of T-lymphocyte activation.

Alpha-fetoprotein and phagocytosis in athymic nude mice

Alpha-fetoprotein (AFP) was found to suppress the phagocytic activity of the blood monocytes and neutrophils in vitro. The amounts of AFP detectable by immunofluorescence in the livers of nu/nu, nu/+ and +/+ mice were quite comparable, and thus could not have been responsible for the alterations in phagocytosis found in leukocytes of athymic nude mice during their ontogenetic development.

Effect of alpha-fetoprotein and indomethacin on arachidonic acid metabolism in P388D1 macrophages: role of leukotrienes

Alpha-fetoprotein (AFP), is able to modify arachidonic acid metabolism in P388D1 macrophage-like cells. AFP has been shown to induce mobilization of arachidonic acid and consequently an enhanced production of leukotrienes. The action of AFP on the cyclooxygenase pathway appears, however, more complex, as this protein simultaneously decreases the total amount of cyclooxygenase products and raises the production of PGE2, 6-keto-PGF1 alpha and to a lesser extent of thromboxane B2. On the other hand, indomethacin abolishes the synthesis of PGE2 but has no effect on 6-keto-PGF1 alpha and thromboxane B2. Indomethacin used in combination with AFP partly loses its inhibiting effect on PGE2 synthesis and paradoxically leads to a "superactivation" of P388D1 cells demonstrated by a very high arachidonic acid mobilization, an enhancement of both leukotriene synthesis and cyclooxygenase activity. Evidence for a binding of indomethacin to AFP was obtained that partly explains these results. In addition, it is shown that the effects of AFP and AFP+Indomethacin on cyclooxygenase activity might be explained by the endogenous synthesis of leukotrienes.