Induction of insulin-like growth factor binding protein expression by ICI 182,780 in a tamoxifen-resistant human breast cancer cell line

Earlier studies in our laboratory demonstrated that the steroidal antiestrogen ICI 182,780 is very effective in abolishing the tamoxifen-resistant proliferation of MCF 7/5-23 cells. In addition, preliminary binding studies showed that ICI 182,780 increased the binding of insulin-like growth factor (IGF)-I to the MCF 7/5-23 cells, although this finding was not the result of an increase in the expression of the insulin-like growth factor-I receptor (IGF-IR). Hence, we reasoned that the inhibition of tamoxifen-resistant cell growth by ICI 182,780 might have been due to increased expression of insulin-like growth factor binding proteins (IGFBPs). We observed the up-regulation of non-insulin-suppressible IGF-I binding in both the tamoxifen-sensitive MCF 7/5-21 cell line (1.5-fold) and the tamoxifen-resistant MCF 7/5-23 cell line (2.5-fold) after 5 days of treatment with ICI 182,780 (10(-7) M) in serum-free medium, suggesting a role for cell-associated IGFBPs. Affinity cross-linking experiments confirmed the presence of an IGF-I:IGFBP complex of approximately 38-kDa in tamoxifen or ICI 182,780-treated cells. Western ligand blots showed higher levels of a soluble 30-kDa IGFBP in media conditioned by either of the subclones that had been treated with ICI 182,780, an effect consistently opposed by estrogen (E2: 10(-9) M). RT-PCR showed higher levels of IGFBP-5 mRNA than any of the other known IGFBPs, suggesting that this was the major IGFBP subtype. The protein was subsequently identified by Western immunoblotting as IGFBP-5. In conclusion, we postulate that this may be a mechanism contributing to the greater potency of ICI 182,780 in the growth inhibition of the MCF 7/5-23, tamoxifen-resistant cell line.

Altered expression of the IGF-1 receptor in a tamoxifen-resistant human breast cancer cell line

The relationship between oestrogen (E2) and insulin-like growth factor-one (IGF-1) was examined in both tamoxifen-sensitive (MCF 7/5-21) and tamoxifen-resistant (MCF 7/5-23) subclones of the MCF 7 cell line. Both subclones were grown in defined, serum-free (SF) medium over a period of 7 days with the addition of E2 or IGF-1 or a combination of both agents. Growth of both MCF 7/5-21 and 7/5-23 cells was stimulated (245% and 350%, respectively) by E2. However, only the growth of MCF 7/5-23 cells was stimulated (266%) by IGF-1. A combination of E2 and IGF-1 significantly enhanced MCF 7/5-21 and 7/5-23 cell growth (581% and 695%, respectively). E2-induced IGF-1 receptor (IGF-1R) levels (as measured by 125I-IGF-1 binding and Northern analyses) in only MCF 7/5-23 cells. This effect was partially inhibited by tamoxifen. In medium containing serum, the growth of only the MCF 7/5-23 cells was significantly inhibited by the IGF-1R monoclonal antibody, alphaIR-3. The detection of E2-induced expression of IGF-2 using RT-PCR was demonstrated in the MCF 7/5-23 cells. These experiments indicate that E2 may sensitize tamoxifen-resistant MCF 7/5-23 cells to the growth stimulatory actions of IGF-2 via up-regulation of the IGF-1R and describes a cell-survival mechanism that may manifest itself as tamoxifen resistance.

Effects of insulin on body composition in patients with insulin-dependent and non-insulin-dependent diabetes

Insulin is used to control blood glucose but may have an adverse effect on the amount and distribution of fat mass and other cardiovascular risk factors. To test this hypothesis the effect of insulin therapy on blood glucose, body composition, and lipid levels was measured during 6 months in 9 patients with newly diagnosed insulin-dependent (Type 1) diabetes mellitus (IDDM) and 15 patients with non-insulin dependent (Type 2) diabetes (NIDDM) and secondary failure of therapy with oral hypoglycaemic agents. Both groups received similar daily doses of insulin (approximately 0.6 units kg-1 day-1). Glycaemic control improved during 6 months treatment in both groups, although the reduction in HbA1c was greater in IDDM (5.2 +/- 0.7%) than in NIDDM (2.0 +/- 0.4%, p < 0.001). All parameters of the lipid profile improved in IDDM but not in NIDDM. Body weight, lean mass, and fat mass, measured by dual energy x-ray absorptiometry, increased at 1 month in IDDM but not in NIDDM. By 6 months, body weight had increased more in IDDM than NIDDM (9.1 +/- 1.2 vs 3.77 +/- 0.5 kg, p < 0.01). The increase in weight was predominantly lean mass in IDDM (60.4 +/- 9.3%) and fat mass in NIDDM (59.9 +/- 8.4%). The increase in lean mass was greater in IDDM than NIDDM (5.6 +/- 1.1 vs 1.4 +/- 0.3 kg, p < 0.001). Fat mass increased by similar increments in IDDM and NIDDM (3.4 +/- 0.8 vs 2.4 +/- 0.5 kg, p = ns) and was predominantly an increase in trunk fat (IDDM: 2.3 +/- 0.6 kg, NIDDM: 2.0 +/- 0.4 kg, p = ns). The central/peripheral fat mass ratio prior to treatment was lower in IDDM than NIDDM (0.64 +/- 0.05 vs 1.09 +/- 0.09, p < 0.01) and then increased in IDDM by 0.32 +/- 0.15 (p = 0.07) and in NIDDM by 0.22 +/- 0.06 (p < 0.001). In conclusion, insulin therapy is associated with weight gain in both IDDM and NIDDM. In the former, weight gain reflects increases in lean mass whereas in NIDDM it reflects an increase in trunk fat mass. It remains to be determined whether this trend to central obesity partly offsets other benefits of insulin therapy in NIDDM.

The pure antiestrogen ICI 182,780 binds to a high-affinity site distinct from the estrogen receptor

Both estrogen receptor-positive (ER+), tamoxifen-sensitive (5-21) and tamoxifen-resistant (5-23) subclones of the parental MCF-7 breast cancer cell line were used in competitive ligand binding studies involving either [3H]ICI 182,780 or 4-OH-[3H]tamoxifen (4OHT) displacement by unlabelled estradiol (E2) or the antiestrogens (AE) 4OHT and ICI 182,780. Neither radioligand was displaced significantly by E2 over a range of concentrations; binding was predominantly inhibited by the corresponding radio-inert ligand. Scatchard analysis of the data revealed that the binding capacities of both cell lines for ICI 182,780 were approximately 7-fold greater than the previously determined number of ER sites per cell, with the affinity being an order of magnitude less than that of E2 for ER. No difference was found between the TAM-sensitive and -resistant cells in their binding of either AE. When cells were preincubated with either E2, TAM or 4OHT at a high, fixed concentration to block the ER or AE binding sites (AEBS), respectively, displaceable binding of [3H]ICI 182,780 was still observed, indicating binding at a site other than the classical ER or previously described AEBS. Our results suggest that there is a specific, saturable and relatively high-affinity binding site for ICI 182,780 in MCF 5-21 and MCF 5-23 breast cancer cells. However, the physiological relevance of this binding site requires further clarification because in cell growth assays, E2 (at 1/10 the dose of ICI 182,780) overcame the inhibitory effect of the antiestrogen in both of the cell lines.

Evidence for coordinate genetic control of Na,K pump density in erythrocytes and lymphocytes

The erythrocyte is widely used as a model cell for studies of the Na,K pump in health and disease. However, little is known about the factors that control the number of Na,K pumps expressed on the erythrocytes of a given individual, nor about the extent to which erythrocytes can be used to validly assess the pump density on other cell types. In this report, we have compared the interindividual variance of Na,K pump density in erythrocytes of unrelated individuals to that seen with identical twins. Unlike unrelated individuals, in whom pump parameters, ie, ouabain binding sites. 86Rb uptake, cell Na concentration vary widely, identical twin pairs showed no significant intrapair variation for these values. Thus, a role for genetic factors is suggested. In addition, we established and validated a method for determining Na,K pump density and pump-mediated 86Rb uptake in human peripheral lymphocytes. Using this method, we show that whereas Na,K pump density differs markedly between erythrocytes (mean of 285 sites per cell) and lymphocytes (mean 40,600 sites per cell), there is a strong and highly significant correlation (r = 0.79, P less than 0.001) between the pump density in these cell types in any given individual. Taken together, these studies suggest that genetic factors are important determinants of Na,K pump expression, and that pump density appears to be coordinately regulated in two cell types in healthy individuals.

Erythrocyte Na,K pump in uremia. Acute correction of a transport defect by hemodialysis

We studied the erythrocyte Na,K-pump in chronically hemodialyzed uremic patients, immediately before and after a 4-h period of hemodialysis. Using [3H]ouabain as a probe, the number of Na,K-pump units per erythrocyte did not differ in uremic and control subjects, and hemodialysis had no acute effect on this parameter. In contrast, in these same cells the mean level of Na,K-pump-mediated 86Rb transport was 30% lower in predialysis uremic patients than in controls, and this diminution in the rate of 86Rb transport per pump unit was improved after 4 h of hemodialysis in 17 of 18 subjects. The results of in vitro incubation of normal cells with pre- and post-dialysis sera from uremic patients suggested that a serum factor is responsible for the observed inhibition of Na,K-pump activity. Changes in cell Na concentration during dialysis did not appear to be responsible for the increased rate of Na,K-pump turnover after hemodialysis. However, there was a significant correlation between the extent of rise in pump-mediated 86Rb uptake and the weight loss that occurred during dialysis. We conclude that the ion transport turnover rate of the erythrocyte Na,K-pump is impaired in uremia by a nonouabain like circulating factor. This factor, whose activity is diminished acutely by hemodialysis, may play an important role in the systemic manifestations of the uremic syndrome, and could be an important endogenous regulator of the Na,K-ATPase.

Effect of diet upon the erythrocyte Na,K pump

The number of erythrocyte Na,K-ATPase pump units has been found to be reduced in some populations of obese humans, but the effect of dietary factors upon the status of the erythrocyte pump has not been delineated. We have measured the number of Na,K-ATPase pump units by [3H]ouabain binding and the activity of the pump by ouabain-inhibitable 86rubidium uptake in response to nutritional maneuvers in several patient groups. There was no consistent change in the number or activity of Na,K-ATPase units in response to 1) an acute 600-cal meal, 2) a 3-day fast or refeeding after a fast in normal weight or obese subjects, 3) 2 weeks of hypocaloric (600 cal) feeding in obese subjects. Individuals with anorexia nervosa were also not significantly different from age- and sex-matched control subjects with respect to the erythrocyte Na,K pump. It is concluded that the circulating erythrocyte does not regulate the number or activity of Na,K pump units in response to short or medium term nutritional maneuvers. Differences between obese and thin populations with respect to the Na,K pump are not likely to be secondary to nutritional differences between the two groups.

Status of the red cell Na,K-pump in hyper- and hypothyroidism

To investigate the status of the sodium-potassium pump in cells of human subjects with abnormal thyroid function, we measured the number of pump units as well as the cation transport activity of the pump in erythrocytes from 23 hyperthyroid and 7 hypothyroid patients. It was found that the number of Na+-K+-ATPase units in erythrocytes (as measured by ouabain binding) was significantly reduced in hyperthyroidism (mean 36% below controls, p less than 0.001). The rate of rubidium uptake by the same cells was also reduced, but to a smaller extent (mean 9%, p less than 0.02). These changes were reversible with control of the hyperthyroidism. Hypothyroid individuals showed changes in erythrocyte Na+-K+ pump which were in the opposite direction to those seen in hyperthyroidism. It is concluded that thyroid hormone exerts a marked negative influence on the number of Na+-K+ pump units in one easily available human cell type. The direction of the effect suggests a complex relationship between thyroid hormone and the level of the Na,K-ATPase in any one tissue. Whatever the cellular mechanism responsible for the effects observed in the red cell, these changes should provide a measure of thyroid hormone action at a cellular level and this may prove useful in the study of thyroid hormone physiology in man.

Altered erythrocyte Na+ + K+ pump in adolescent obesity

The number of Na/K pump units and the cation transport activity of the pump were measured in erythrocytes from two etiologically different groups of obese adolescents and a group of normal controls. There was a significant reduction in the number of pump units, as measured by saturation ouabain binding, in erythrocytes from adolescents with idiopathic, early onset obesity. Individuals whose obesity developed subsequent to the appearance of a variety of hypothalamic lesions showed no reduction in the red cell complement of Na/K pump when compared to controls and the cation transport activity of their cells was higher than both the controls and the subjects with idiopathic obesity. These results support data obtained in adults that reduced red cell Na/K pump levels are seen in a group of individuals with idiopathic obesity. They further suggest that such reductions are not likely to be secondary to the obese state per se.

Functionally abnormal Na+-K+ pump in erythrocytes of a morbidly obese patient

The Na(+)-K(+) pump in the erythrocytes of a mordibly obese patient shows a unique constellation of functional abnormalities. The number of pump units, measured by [(3)H]ouabain binding to intact cells, as well as the enzymatic activity of the (Na(+)-K(+))-dependent ATPase in erythrocyte membranes were found to be markedly increased compared with control cells (18-fold and 14-fold, respectively). There was a concomitant fivefold increase in the rate of pump-mediated uptake of (86)Rubidium (a K analogue); this was balanced by an increased rate of (86)Rb efflux. In striking contrast to normal cells, however, a major portion of this efflux (80%) was inhibited by ouabain, and thus appeared to be mediated by the Na(+)-K(+) pump. Erythrocytes from this patient had elevated levels of intracellular K(+) and reduced levels of intracellular Na(+). This finding, taken together with the ouabain inhibition of K(+) efflux and the absence of associated abnormalities, argues against the possibility that the increased number of Na(+)-K(+) pump units was a compensation for a primary increase in the permeability of the erythrocyte membrane to monovalent cations, as is seen in a variety of erythrocyte disorders. Further evidence for a primary abnormality of the enzyme was our observation that the cardiac glycoside ouabain bound to these cells with reduced affinity and had a right shifted dose response for pump inhibition. The markedly increased number of Na(+)-K(+) pump units in these cells did not appear to extend to mononuclear leukocytes.In conclusion, the erythrocytes from this patient have a very large number of functionally abnormal Na(+)-K(+) ATPase units. A unique abnormality of the erythrocyte Na(+)-K(+) ATPase of these cells is the most likely explanation for these findings.

The effects of digestive enzymes on characteristics of placental insulin receptor. Comparison of particulate and soluble receptor preparations

The role of the surrounding membrane structure on the binding characteristics of the insulin receptor was studied by using several digestive enzymes. The effects observed with particulate membrane preparations are compared with those from soluble receptor preparations. beta-Galactosidase and neuraminidase had no effect on insulin binding to either particulate or soluble receptors from human placentae. Exposure to 2 units of phospholipase C/ml increased insulin binding to particulate membranes, but was without effect on the soluble receptor preparation. The increase in binding to particulate membranes was shown to be due to an increase in apparent receptor number. After 5 min exposure to 500 microgram of trypsin/ml there was an increase in insulin binding to the particulate membrane fraction, owing to an increase in receptor affinity. After 15 min exposure to this amount of trypsin, binding decreased, owing to a progressive decrease in receptor availability. In contrast, this concentration of trypsin had no effect on the solubilized receptor preparation. Because of the differential effects of phospholipase C and trypsin on the particulate compared with the solubilized receptor preparations, it is concluded that the effects of these enzymes were due to an effect on the surrounding membrane structure. Changes in receptor configuration due to alterations within the adjoining membrane provide a potential mechanism for mediating short-term alterations in receptor function.