Insulin receptors in acute and chronic lymphoid leukaemias

Steroid effects on ZAP-70 and SYK in relation to apoptosis in poor prognosis chronic lymphocytic leukemia

There is resurgent interest in glucocorticoids (GCs) in the treatment of poor prognosis chronic lymphocytic leukemia (CLL). Little is known however on how GCs induce apoptosis in CLL. Methylprednisolone (MP) induces apoptosis in ZAP-70 positive CLL more readily than in ZAP-70 negative CLL, which is in contrast to the effects of radiation and chemotherapy. The increased GC sensitivity of ZAP-70+ CLL was studied in relation to the expression status of ZAP-70 and the related signal transducing tyrosine kinase SYK. Both ZAP-70 and SYK were downregulated by GC treatment. Moreover, SYK was dephosphorylated by the phosphatase PTP1B of which the expression and translation levels were induced by GCs. Inhibition of PTP1B successfully restored ZAP-70 expression and SYK phosphorylation but did not interfere with GC-induced apoptosis. Therefore, the downregulation of ZAP-70 and P-SYK per se during treatment with GCs is not sufficient to induce apoptosis, and different mechanisms must therefore be responsible for the increased steroid sensitivity of ZAP-70+ CLL.

Induction of insulin receptor expression of human leukemic cells by 1 alpha, 25 dihydroxyvitamin D3

The HL-60 and U-937 leukemic cell line and explants of fresh human leukemia cells were differentiated in vitro by incubation with 1 alpha, 25 dihydroxyvitamin D3 (Vit D). Morphologic change to monocytes was demonstrated in the promyelocytic (HL-60) line but not in the U-937 line and four of five leukemic cells. One patient with chronic granulocytic leukemia in the myeloid blast phase had incomplete morphologic change with Vit D treatment. In all cells studied, an increase in specific insulin receptor binding was independent of morphologic maturation. An increase in insulin receptor expression by Vit D was an early monocytic membrane marker dissociated from morphologic and functional alterations.

Differentiation of U-937 human monocyte-like cell line by 1 alpha,25-dihydroxyvitamin D3 or by retinoic acid. Opposite effects on insulin receptors

The monocyte-like human cell line U-937 has been differentiated in vitro by incubation with either 1 alpha,25-dihydroxyvitamin D3 or retinoic acid (RA) plus dibutyryl cyclic AMP (db-cAMP). Both methods were effective in inducing the appearance of maturation markers. Their actions on insulin receptors were the opposite, however; 1 alpha,25-dihydroxyvitamin D3 increased the binding of the hormone, while RA plus db-cAMP decreased the binding. These effects were specific for insulin, since the transferrin receptors were reduced by both methods of differentiation. Thus, the changes in insulin receptors during maturation in vitro depend on the inducing agent and are not causally related to the differentiation process.

Clinical and biologic correlates of insulin binding by leukemia lymphoblasts

The percentage of total 125I-labeled insulin specifically bound to lymphoblasts was measured in 46 children with leukemia. Among 35 children with newly diagnosed acute lymphoblastic leukemia (ALL), specific insulin binding ranged from 0.09 to 14.8% per 10(6) blasts. A lower level of insulin binding was correlated with T-cell surface markers (P less than 0.003), higher hemoglobin level (P less than 0.005), presence of a mediastinal mass (P less than 0.01), lower glucocorticoid receptor level (P less than 0.02), higher platelet count (P less than 0.04), age less than 2 or greater than 10 yr (P less than 0.05), white blood cell count greater than or equal to 100 X 10(3)/mm3 (P less than 0.06) and higher labeling index (P less than 0.07). It was not correlated with the presence of central-nervous-system disease, FAB classification, or sex. With a follow-up of 24 to 33 + months, insulin binding was not correlated with treatment outcome. Six patients with relapsed ALL and three with acute nonlymphoblastic leukemia showed insulin binding levels similar to those in newly diagnosed ALL patients. Blasts from one patient with B-cell ALL and one with chronic myelogenous leukemia were characterized by lower insulin binding, while lymphoblasts from a patient with T-cell lymphoma bound insulin at marginally detectable levels. In vitro studies with IM-9, NALM-1 and NALM-16 cell lines showed that changes in insulin binding caused by dexamethasone treatment were not correlated with hormone-induced cell death. Although study of insulin binding by malignant lymphoid cells may be important in understanding the biology of leukemic cells, it does not appear to have any obvious clinical utility.

beta-Adrenergic responsiveness of human peripheral lymphocytes after mitogenic transformation with phytohemagglutinin

In vitro transformation of human peripheral blood lymphocytes with the mitogen phytohemagglutinin did not alter the total number of beta-adrenergic binding sites for (+/-)-125iodocyanopindolol on the surface of intact cells, whereas binding to membrane fragments of transformed cells appeared to be diminished. In isolated membranes, there was also a marked decrease in basal, fluoride- and hormone-stimulated adenylate cyclase activity after phytohemagglutinin treatment. In whole cells, however, a lowering effect of phytohemagglutinin on levels of cyclic adenosine 3',5'-monophosphate was not apparent. The discrepancy between data on intact and broken cells indicates that the transformed cells do not acquire additional beta-adrenergic receptors or catalytic adenylate cyclase as their cell surface expands due to blastogenesis. It is therefore concluded that mitogenic transformation of human peripheral lymphocytes does not cause specific changes in the beta-adrenergic/adenylate cyclase system.

Isozyme distribution of hexokinase, phosphofructokinase and pyruvate kinase in lymphocytes from patients with chronic lymphocytic leukemia

The enzyme activities and isozyme distribution of the three glycolytic regulator enzymes hexokinase, phosphofructokinase and pyruvate kinase were studied in lymphocytes of patients with chronic lymphocytic leukemia. Isozyme distribution patterns were determined by kinetic measurements, electrophoresis and immunoprecipitation. The CLL lymphocytes were different from normal non-T lymphocytes with respect to hexokinase residual activity in the presence of glucose-1,6-P2, pyruvate kinase residual activity in the presence of alanine, and phosphofructokinase activity after stimulation by glucose-1,6-P2. No differences could be discerned in enzyme activities between the CLL and the normal T and non-T lymphocytes.