Phorbol ester-induced regulation of transferrin receptors in human leukemia K562 cells.

Abstract

ABSTRACT. The treatment of human leukemia K562 cells with 12-0-tetradecanoyl phorbol-13-acetate (TPA) caused a decrease of transferrin receptors. The mechanism of the decrease of the receptors with TPA has been investigated. In cells incubated with TPA, the rate of biosynthesis of transferrin receptors was reduced to 10-20 % of that in untreated cells. Pulsechase experiments showed that turnover of the receptors in TPA-treated cells was accelerated over that in untreated cells. These results indicated that the decrease of transferrin receptors in TPA-treated cells was caused by reduced biosynthesis and accelerated degradation of the receptors.Human transferrin receptor is an integral membrane protein which consists of two identical subunits of molecular weight 95,000, linked by a disulfide bridge (29, 36). Transferrin receptor mediates iron uptake for growth in tumor cells and hemoglobin synthesis in erythropoietic cells. Transferrin receptor-diferric transferrin complexes enter cells exclusively by endocytosis via coated pits and endosomes (12). Iron is released from transferrin in the acidic environment of the endosomes (43). The subsequent route of iron to the cytoplasm is presumed to be ferritin or other iron binding proteins (16). Apotransferrin remains tightly bound to the receptor at low pH and is recirculated along with the receptor back to the cell surface (5,12, 44). Then the complex dissociates and the components are reutilized. Barnes and Sato (1) have reported that depriving cultured cells of transferrin halts the growth of the cells. Trowbridge and Lopez have reported that blocking the transferrin receptor with a monoclonal antibody leads to an arrest in cell proliferation (42). Furthermore, it has been found that the expression of transferrin receptor correlates with requirement for iron and that the receptor is also readily detectable on dividing cells, including most tumor cells, but it is undetectable in fully differentiated non-dividing cells (41). Based on these observations, this correlation between the receptor expression and cell proliferation of cultured cells could be a useful system for studying the regulation of the cellular metabolism of cell growth involving iron.Several reports (13,32,33) have recently appeared to the effect that the tumorpromoting reagent 12-0-tetradecanoyl phorbol-13-acetate (TPA) causes inhibition of the growth of human leukemic cells and then accelerates the differentiation of the cells. It has also been observed that the phosphorylation of the transferrin receptor Abbreviations used : TPA, 12-0-tetradecanoyl phorbol-13-acetate; SDS, sodium dodecyl sulfate; PAGE, polyacrylamide gel electrophoresis.

Diacylglycerol-Stimulated Endocytosis of Transferrin in Trypanosomatids Is Dependent on Tyrosine Kinase Activity

“…Finally, enhanced uptake of Tf in response to DAG (or phorbol ester) treatment is unique to trypanosomatids. In human cells, PMA treatment does not increase endocytosis of Tf [53], [54]. During a trypanosome infection of vertebrates, the parasite competes with host cells for Tf in host blood.…”

The effect of lead on iron uptake from transferrin in human erythroleukemia (K562) cells

“…Furthermore, we reported diminished biosynthesis of transferrin receptor in K562 cells treated with phorbol ester (Kohno et al 1986). In all of these cases, down-regulation of transferrin receptors was observed.…”

“…In addition, we have previously shown that the decrease in transferrin receptor expression in phorbol ester-treated K562 cells is attributable in part to a reduction in biosynthesis of the receptors (Kohno et al 1986). We therefore attempted to establish whether or not the reduction of transferrin receptor expression by lead treatment was due to a decrease in the receptor biosynthesis.…”

“…Ascites containing monoclonal antibody (5E9) to human transferrin receptor (Haynes et al 1981) were prepared as described (Kohno et al 1986). …”

In vitro Effects of Phorbol and Phorbol Ester on the Proliferation and Enzyme Activities of Bone Marrow Stromal Cells in Rats

“…Phorbol esters are mitogenic for human blood lymphcoytes and induce differentiation of T and B cells, they can also modu late cell-mediated cytotoxicity and antibody produc tion. In macrophages, phorbol esters induce DNA synthesis and phagocytosis, and human promyelocytic leukemia cells mature to macrophages when treated with these compounds [5][6][7][8], Phorbol esters enhance transferrin endocytosis and iron uptake by immature erythroid cells [9], they also influence trans ferrin receptors in human leukemic cells [10]. Results of numerous studies suggested that phorbol esters arc able to stimulate human and animal granulocytemacrophage [GM] progenitor cells in long-term cul ture of bone marrow [11][12][13][14][15], It is now widely believed that the microenviron ment created in bone marrow by stromal cells plays a very important role in such processes as self-regenera tion, differentiation and maturation of progenitor cells during hematopoiesis.…”