Characterization of insulin binding to the erythroleukemia cell line K 562

IFN-gamma treatment increases insulin binding and MHC class I expression in erythroleukemia cells

We have investigated if interferon-gamma (IFN-gamma) treatment of human K562 tumor cells, which upregulates the expression of MHC class I antigens (MHC-I), simultaneously would influence insulin binding. Treatment of K562 cells with recombinant human IFN-gamma for 48 h caused a significant increase of insulin binding at 37 degrees C. Recombinant human tumor necrosis factor-alpha (TNF-alpha) alone had no effect but acted synergistically with IFN-gamma, leading to a two-fold increase of insulin binding. No change in affinity, number of binding sites or cell surface expression of insulin receptors (IR) after IFN-gamma treatment could be detected. The increased insulin binding observed at 37 degrees C was not seen at 4 degrees C, suggesting alteration of insulin internalization. The dose-response curve, as well as the time curve, for the increase in insulin binding after IFN-gamma treatment correlated with enhanced cell surface expression of MHC-I antigens. However, the correlation was not absolute. Our results show that IFN-gamma treatment alone or together with TNF-alpha, can alter the insulin binding to K562 cells without changing the expression or affinity of the IR. This correlates with the effect of IFN-gamma on MHC-I expression. These results support the findings that MHC-I molecules associate and interact with the IR at the cell surface.

The insulin-like growth factor system in regulation of normal and malignant hematopoiesis

The published data available on the insulin-like growth factor (IGF) family of peptides, its receptors and binding proteins in connection with normal and neoplastic hematopoietic processes are reviewed. It is found that nearly all the different hematopoietic cells, either normal or neoplastic, express IGF receptors. The IGFs are involved in normal erythropoiesis, granulopoiesis and lymphopoiesis. IGFs, especially IGF-1, are mitogenic for cell lines of myeloid and lymphoid leukemias and Burkitt's lymphoma. Differentiation of certain immature malignant cell lines is associated with a decrease in the number and affinity of IGF receptors. It might be concluded that the IGFs have an important role in the physiologic and neoplastic processes of the hematopoietic system, and the expanding knowledge of this issue will contribute to the understanding of proliferation and differentiation processes in specific hematologic disorders.

The effect of growth hormone and IGF-I on clonogenic growth of hematopoietic cells in leukemic patients during active disease and during remission--a preliminary report

The number of survivors of childhood leukemia treated with growth hormone for growth retardation is increasing. The debate about the direct or indirect relationship of GH and insulin-like growth factor I (IGF-I) to the occurrence or recurrence of malignancy, especially in the case of GH therapy in patients with leukemia, is still unresolved. We, therefore, studied the effect of GH and IGF-I on bone marrow of patients with acute leukemia (ALL and AML) in diagnosis and recurrence and in chronic leukemia patients (CML) in remission. GH increased blast colony numbers by a mean of 68% and 77% at GH concentrations of 250 and 300 ng/ml, respectively. IGF-I increased blast colony numbers in ALL patients by 50, 93 and 105%, and in AML patients by 33, 58 and 65%, at IGF-I concentrations of 0.05, 0.25 and 0.5 ng/ml, respectively. In 3 CML patients in remission a granulocyte-macrophage colony forming assay did not reveal stimulation of peripheral blood blast colony formation by GH or IGF-I. Our in vitro data (as previously reported) suggest that GH and IGF-I may promote blast cell proliferation, and the supplemental administration of these peptides in leukemia patients in remission must be carefully monitored for early relapse. Additional studies on bone marrow cells of leukemic patients in remission are needed in order to examine the effects of GH and IGF-I on these cells.

Enhancement of erythropoiesis in vitro by human growth hormone is mediated by insulin-like growth factor I

Insulin-like growth factor I (IGF-I) is the presumed paracrine or autocrine growth-promoting mediator of growth hormone in peripheral tissues. In order to evaluate the role of IGF-I as mediator of human growth hormone (hGH) in erythropoiesis, we compared the effects of both peptides upon in vitro colony formation by primitive (BFU-E) and relatively mature (CFU-E) human erythroid precursors. Biosynthetic IGF-I (2 ng/ml) and hGH (25 ng/ml) induced a significant increase in the growth of both BFU-E and CFU-E. BFU-E growth was maximally enhanced by 6 ng/ml IGF-I and by 50 ng/ml hGH, resulting in an increase in burst numbers of 62 +/- 12% and 52 +/- 12%, respectively. Maximal enhancement of CFU-E growth was detected at higher concentrations of IGF-I (20 ng/ml) and hGH (150 ng/ml), with respective increases of 121 +/- 35% and 137 +/- 18% in colony numbers. Enhancement of bone marrow and peripheral blood erythroid progenitor cell growth by hGH required the presence of monocytes and was abrogated by specific monoclonal antibodies directed against IGF-I membrane receptors. The in vitro growth-promoting effect of hGH upon human erythroid precursors thus appears to be mediated by paracrine IGF-I.

Characterization of the insulin-like growth factor (IGF) receptor in K562 erythroleukemia cells; evidence for a biological function for the type II IGF receptor

Erythroleukemia cells (K562) were found to bind insulin-like growth factor-II (IGF-II) about 10 times as much as IGF-I, insulin and human growth hormone. The specific binding of IGF-II increased as a function of cell number in a range of 0.5-6 X 10(6) cell/ml. Kinetic studies revealed that binding was time and temperature dependent and showed a broad pH optimum. Specificity studies showed no inhibition of 125I-IGF-II binding by insulin or unrelated peptide hormones. The half-maximal inhibition of 125I-IGF-II binding to K562 cells was achieved at 87 and 28 ng/ml of IGF-I and IGF-II respectively. However, the addition of 7.5 and 1.7 ng/ml of unlabeled IGF-I and IGF-II respectively increased the binding of 125I-IGF-II by 55%. This 'hook' effect was greatly reduced when K562 cell membranes were used. Scatchard analysis of IGF-II binding showed a comparable equilibrium constant with either intact cells (Ka = 8.9 X 10(8) M-1) or microsomal membranes (Ka = 5.4 X 10(8) M-1). Cross-linking studies indicated that both 125I-IGF-II and 125I-IGF-I bound to an entity of 215 kDa which increased to 260 kDa under reducing conditions. Both IGF-I and II stimulated 3H-thymidine incorporation into K562 cells whereas insulin was without effect. These data show that both IGF-I and II bind predominantly to a type II-IGF receptor in K562 cells. Since both peptides stimulate 3H-thymidine incorporation in these cells it is possible that the type II-IGF receptor is mediating an anabolic biological response in these cells.

IGF-2 stimulated growth mediated by the somatomedin type 2 receptor

Human Insulinlike Growth Factor 2 (IGF-2) can promote cell proliferation via the type 2 receptor in K562 cells, a human erythroleukemia cell line with IGF-2/type 2 receptors and insulin receptors but lacking IGF-1/type 1 receptors. Cells are grown in semi-solid agar in the absence and presence of increasing amounts of insulin, IGF-1 and IGF-2. Two strains of K562 cells have been studied, with different concentrations of insulin and IGF-2 receptors. The effect of IGF-2 is proportional to the IGF-2 receptor concentration.

The specificity of the human IGF-2 receptor

The specificity of the type 2 insulinlike growth factor (IGF) receptor is evaluated in human placenta membranes and the human cell line K562. K562 cells have type 2 but not type 1 IGF receptors. Native IGF-2 isolated from human plasma and synthetic IGF-2 were equipotent in competing with labeled IGF-2 in both systems. Pure IGF-1 isolated from plasma, synthetic IGF-1 and recombinant IGF-1 could not crossreact with the type 2 IGF receptor in concentrations up to 1 microgram/ml in both systems. Studies on placenta membrane were done in the presence of 300 ug/ml insulin to block the type 1 IGF receptors. It is concluded that IGF-1, as well as insulin, cannot crossreact with the human type 2 IGF receptor.

The binding of insulin-like growth factor II to the erythroleukemia cell line K562

The erythroleukemia cell line K562 was previously shown to have specific binding sites for insulin but not for insulin-like growth factor I (IGF-I). In this study the presence of specific receptors for insulin-like growth factor II (IGF-II) is established. Scatchard analysis of the competition curve for IGF-II disclosed a non-cooperative binding kinetic with a calculated affinity constant 2.4 X 10(8) M-1 and a receptor number of 4.8 X 10(4) sites/cell. IGF-I displayed 10% crossreactivity over the IGF-II receptor but insulin did not crossreact at all. Instead insulin, present in high concentrations, enhanced the binding of IGF-II. The presence of IGF II but not IGF-I receptors makes the K562 cell line suitable for studying properties of the type-2 receptor.