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

Abstract

Binding and uptake of a-fetoprotein (AFP) by mouse T-lymphoma YAC-1 cells exhibited the characteristics of receptor-mediated endocytosis. The (2,3). On the other hand, AFP can be localized during ontogenic development in practically all tissue derived from the three embryonic germ layers (4). The intracellular presence of AFP in fetal tissues other than the liver and the yolk sac is due to active uptake of the protein (5, 6) and not local synthesis (3, 7). It has also been shown that the ability to internalize AFP may be shared by neoplastic cells of different origin, such as spontaneous mammary carcinomas growing in the mouse (8), as well as in two cultured cell lines derived from a rat rhabdomyosarcoma (9) and a human breast carcinoma (10). Preliminary morphological observations of AFP uptake by these cultured cells suggested the existence of a receptor-mediated mechanism. To confirm this and to assess whether AFP receptors in malignant cells are or are not shared by normal cell counterparts, we used as experimental models a lymphoid tumor cell line, YAC-1, and normal adult T lymphocytes. The YAC-1 cell line, derived from a Moloney murine leukemia virus-induced lymphoma, has several features that make it useful for receptor and uptake studies. It is a stable cell line with morphological characteristics of poorly differentiated cells that grow in suspension. The latter is advantageous for proteinuptake experiments using radiolabeled protein derivatives.In the present work, we show that YAC-1 cells take up AFP through receptor-mediated endocytosis. Normal adult T lymphocytes, on the contrary, do not incorporate AFP. Other serum proteins tested, such as transferrin and a2-macroglobulin (a2M), are indiscriminately taken up by YAC-1 cells and normal T lymphocytes. MATERIALS AND METHODSCells. YAC-1 cells were cultured in RPMI-1640 medium supplemented with antibiotics and 10% fetal bovine serum, and they were maintained at 37°C in a humidified atmosphere with 5% C02/95% air. Cells were seeded at densities of 5-10 x 104 cells per ml, and all experiments were done with cells harvested at a density of 5 x 105 cells per ml. Fetal calf serum contains 2-5 mg of AFP per ml. To avoid competitive effects between mouse and bovine AFP, prior to all experiments, cells were washed three or four times with RPMI-1640 medium. This was followed by a 60-min incubation at 37°C in the same medium, which removed most of internalized bovine AFP (see Fig. 5). After this treatment, immunocytochemical staining of cells with antibodies to bovine AFP was negative. The cells were then suspended (1.5-2 x 107 cells per ml) in RPMI-1640 medium at 4°C. In experiments carried out at 4°C, the pH of the medium was adjusted to 7.4 with a minimal amount of potassium phosphate. Suspensions of thymocytes were obtained from fetal (18-20 days of gestation), newborn, and 5-week-old Swiss mice. Thymuses were minced and passed through a 200-mm mesh stainless steel sieve, and the cells were subsequently washed with RPMI-1640 medium. The T lymphocy...

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

“…Many investigations have shown that AFP receptors exist on the membrane of various tumor cells [5,7,8,[11][12][13] , and play an important role in regulating growth of the cells [7,8,14] . The receptor may mediate intercellular signal transduction which influences the expression of genes related to proliferation, and the expression of these genes is the most direct factor that controls cell cycle.…”

Specific Uptake of Alpha-Fetoprotein and Albumin by Rat Morris 7777 Hepatoma Cells

“…Furthermore, Moroianu et al [26] have reported that albumin-binding proteins are present in all fetal organs and in adult tissues characterized by active renewal, in contrast with mature cells. AFP may compete with albumin for binding in different cell types [15,[27][28][29]. Cytochemical and kinetic studies, carried out in several tumoral cells as well as in normal human T lymphocytes [18,27,30,31] have shown that the AFP was taken up by a receptor-mediated endocytosis mechanism similar to that reported for transferrin [19,28,31].…”

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

“…Uriel been demonstrated the specific uptake ofAFP by certain malignant cells (3)(4)(5). They have shown kinetic analysis for putative receptors on blast transformed lymphocytes as well as on a murine T lymphoma cell line, but not on normal resting lymphocytes (6,7). In these reports, the authors suggested that AFP and AFP receptors may regulate the transfer of polyunsaturated fatty acids into cells undergoing growth and proliferation.…”