Glucocorticoid resistance in thymocytes from mice expressing a T cell receptor transgene.

A majority of thymocytes undergo apoptosis during differentiation due to lack of survival signals provided by T cell receptor (TCR) activation. As glucocorticoids (GC) have been suggested to be involved in this process, we have investigated the GC sensitivity in thymocytes from mice expressing a transgenic selecting TCR. We now report that immature CD4(+)CD8(+) double-positive thymocytes from these mice are comparatively more resistant to corticosterone-induced apoptosis. This is associated with reduced glucocorticoid receptor (GR) expression, increased levels of membrane CD28, increased NF-kappaB DNA binding activity, and increased binding to the CD28 response element in the interleukin-2 gene promoter. Analysis of NF-kappaB/Rel proteins from nuclear extracts demonstrated altered levels of some of these proteins. Our results suggest that TCR recognition of self major histocompatibility antigens generates intracellular signals which alter the thymocyte GC sensitivity and thereby protect them against apoptosis induced by endogenous GC.

p57Kip2, a glucocorticoid-induced inhibitor of cell cycle progression in HeLa cells.

Glucocorticoids exert antiproliferative effects on a number of cell types, including the HeLa cervical carcinoma cell line. However, the mechanism responsible for the antiproliferative effect is poorly understood. In this report we have investigated the role of the recently identified cyclin-dependent kinase inhibitor (CDI) p57Kip2 in the antiproliferative effect conferred by glucocorticoids. When HeLa cells were treated with the synthetic glucocorticoid dexamethasone (DEX), the doubling time of exponentially growing cells increased 2-fold. Within 11 h of DEX treatment, this was accompanied by an accumulation of cells in the G1 phase of the cell cycle with a corresponding decreased proportion of cells in the S phase and decreased CDK2 activity. DEX treatment of the HeLa cells dramatically induced the protein and mRNA expression of the CDI p57Kip2. This induction was seen within 4 h of DEX treatment, preceding a major DEX-induced accumulation of cells in the G1 phase. DEX-induced mRNA expression of p57Kip2 did not require de novo protein synthesis, and the transcription of the p57Kip2 gene was increased as determined by a run-on transcription assay. Furthermore, DEX induction of p57Kip2 was not a consequence of the cell cycle arrest, since other growth inhibition signals did not result in strong p57Kip2 induction. Overexpression of p57Kip2 using HeLa cells stably transfected with a tetracycline-inducible vector showed that p57Kip2 is sufficient to reconstitute an antiproliferative effect similar to that seen in DEX-treated cells. Selective p57Kip2 expression by the tetracycline analog doxycycline to levels comparable to those observed on DEX induction resulted in a 1.7-fold increase in the doubling time and a shift of HeLa cells to the G1 phase as well as a decrease in CDK2 activity. Taken together, these results suggest that glucocorticoid treatment directly induces transcription of the p57Kip2 gene and that the p57Kip2 protein is involved in the glucocorticoid-induced antiproliferative effect.

Paracrine glucocorticoid activity produced by mouse thymic epithelial cells.

Previous data have suggested that glucocorticoids (GCs) are involved in the differentiation of thymocytes into mature T cells. In this report we demonstrate that the mouse thymic epithelial cells (TEC) express the cytochrome P450 hydroxylases Cyp11A1, Cyp21, and Cyp11B1. These enzymes, in combination with 3beta-hydroxysteroid dehydrogenase (3betaHSD), convert cholesterol into corticosterone, the major GC in rodents. In addition, when TEC were cocultured with 'reporter cells' containing the glucocorticoid receptor (GR) and a GR-dependent reporter gene, a specific induction of reporter gene activity was observed. Induction of reporter gene activity was blocked when the TEC and reporter cells were incubated in the presence of the Cyp11B1 inhibitor metyrapone or the 3betaHSD inhibitor trilostane, as well as by the GR antagonist RU486. Coculturing of TEC with thymocytes induced apoptosis in the latter, which was partially blocked by the enzyme inhibitors and RU486. We conclude that TEC secrete a GC hormone activity and suggest a paracrine role for this in thymocyte development.

Determination of selenium in blood serum of children with acute leukemia and effect of chemotherapy on serum selenium level.

The concentration of selenium in serum was measured by the neutron activation method in three groups of children: 30 healthy children, 20 children with Acute Myeloblastic Leukemia (AML) and 40 with Acute Lymphoblastic Leukemia (ALL) (L1; n = 20, L2; n = 20). The samples were taken before and after induction chemotherapy. Age, sex, FAB, initial WBC, BUN, creatinine and urinary analysis did not show a significant change in the amount of selenium in serum. Selenium concentration in serum samples of ALL children before chemotherapy showed no significant differences as compared with that of normal individuals, but there were significant differences between children with AML and normal individuals (76.46 +/- 24.59 micrograms/L vs 102.38 +/- 19.25 micrograms/L, with p < 0.02). In conclusion, the question of whether these deficiencies are responsible for the disease or are the result of a secondary effect of the cancer remain to be answered. Immediately after induction chemotherapy, the selenium concentration in the serum of ALL children decreased significantly (80.14 +/- 15.48 micrograms/L vs 110.72 +/- 28.3 micrograms/L, p < 0.001), but this was not the case for AML children. These findings may be due to the difference in the drugs administered in induction chemotherapy of ALL and AML children.

Determination of arsenic in hair using neutron activation.

Arsenic concentrations were measured in scalp hair of three groups of people of a village in west of Iran. One group consisted of healthy subjects, the second of subjects with suspected arsenic poisoning and the third with people infected with arsenic poisoning. The measurements were carried out using neutron activation analysis at Tehran Research Reactor. Along with these measurements, the arsenic content of water sources used by the inhabitants were also measured. The measurements revealed that the average arsenic concentration in the healthy group was 0.2 +/- 0.07 ppm, in the suspected group was 4.9 +/- 0.5 ppm, in the infected group was 5.6 +/- 0.5 ppm and in water samples varied between 0.03 +/- 0.01 and 1.04 +/- 0.10 ppm.