Enhanced CD4+ T cell proliferation and Th2 cytokine production in DR6-deficient mice

We have found that DR6, a member of the TNF receptor family, is highly expressed in resting T cells and downregulated in activated T cells. DR6-targeted mutant mice were generated and showed normal development. However, DR6(-/-) CD4(+) T cells hyperproliferated in response to TCR-mediated stimulation and protein antigen challenge. Activated DR6(-/-) CD4(+) T cells exhibited upregulated CD25 expression and enhanced proliferation in response to exogenous IL-2 stimulation. In addition, increased CD28 and reduced CTLA-4 expression were observed in these cells. Enhanced Th2 cytokine production by activated DR6(-/-) CD4(+) T cells was associated with the increased transcription factor NF-ATc in nuclei. DR6, therefore, functions as a regulatory receptor for mediating CD4(+) T cell activation and maintaining proper immune responses.

In vivo demonstration that human parathyroid hormone 1-38 inhibits the expression of osteoprotegerin in bone with the kinetics of an immediate early gene

Osteoprotegerin (OPG) is a potent inhibitor of osteoclast formation and function. To elucidate how OPG is regulated in bone, we examined (1) the expression and localization of OPG protein in bone tissue, (2) the effect of human parathyroid hormone 1-38 (hPTH 1-38) on OPG messenger RNA (mRNA) levels in rat femur metaphyseal and diaphyseal bone, and (3) the effect of hPTH(1-38) on expression of OPG mRNA in cultured osteoblast-like cells derived from the metaphysis and diaphysis, and in ROS 17/2.8 osteosarcoma cells. Because PTH has been shown to stimulate osteoblast activity via the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signal transduction pathway we also investigated whether PTH action on OPG in vivo is dependent on activation of cAMP/PKA pathway. Immunohistochemistry was used to evaluate OPG protein expression and Northern blot hybridization was used to analyze OPG mRNA expression both in vivo and in vitro. Immunohistochemistry of OPG protein expression in the rat distal femur metaphysis revealed that it was localized predominantly in preosteoblasts, osteoblasts, lining cells, and the osteoid layer, with occasional immunoreactivity in osteocytes and cells of the bone marrow. Subcutaneous (sc) administration of a single injection of hPTH(1-38) at 80 microg/kg induced a rapid and transient decrease in OPG mRNA expression in both metaphyseal and diaphyseal bone. The decrease in OPG message was evident by 1 h and mRNA levels returned to baseline after 3 h. PTH analog PTH(1-31), which stimulates intracellular cAMP accumulation, inhibited OPG expression, whereas PTH analogs (3-34 and 7-34) that do not stimulate cAMP production had no effect on expression. In contrast to PTH, prostaglandin E2 (PGE2) had no effect on OPG mRNA expression in vivo in the metaphyseal bone cells, under conditions in which PGE2 does promote expression of the c-fos gene. The in vivo effects of hPTH(1-38) on OPG mRNA were confirmed in isolated primary osteoblast cultures derived from either metaphyseal or diaphyseal bone as well as in ROS 17/2.8 osteosarcoma cells. We propose that the rapid and transient decrease in OPG expression may initiate a cascade of events resulting in the differentiation of osteoclast progenitor. Such a spatially and temporally programmed effect of PTH might contribute to bone turnover.

Activation of the human estrogen receptor by estrogenic and antiestrogenic compounds in Saccharomyces cerevisiae: a positive selection system

The yeast URA3 gene was used as a reporter to investigate the activities of estrogenic and antiestrogenic compounds in yeast Saccharomyces cerevisiae. The control sequences of the wild type (wt) URA3 promoter were replaced with zero, two, or six copies of estrogen-response elements (ERE). Insertion of two and six copies of ERE rendered the expression of the URA3 gene to be dependent on the presence of the human estrogen receptor (ER) and the hormone 17beta-estradiol (E2). Two versions of the ER genes were constructed: a full-length wild-type ER (ERa-f) and a truncated ER with domains C, D, and E (ERcde). Both forms of the ER were able to activate the ERE-URA3 reporter in a hormone-dependent manner. The growth of yeast transformants were hormone-dependent when the reporter constructs were inserted into chromosomes using yeast integrating vectors (YIp) but not with the 2mu-based episomal (high-copy number, YEp) or centromeric (low-copy number, YCp) vectors. The integrated transformants were employed to investigate the effects of estrogenic and antiestrogenic compounds. The estrogenic compounds, E2, diethylstilbestrol (DES), and estrone (EST), activated expression of the reporter genes at 1 nM concentration, which is the same concentration exhibiting activity in mammalian cells. None of the antiestrogens, at concentrations up to 1 microM, including tamoxifen (TAM), raloxifene (RAL), and ICI 164,384 (ICI) antagonized 1 nM of E2 against either form of the ER. In fact, TAM, RAL, and ICI displayed slight agonistic activity at high concentrations of 300 nM or greater to the ERcde. This system can be used to investigate or clone the missing factor(s) that is responsible for the antagonistic activity of the ER in yeast, and is also suitable for screening for the effectors of the ER.

The effect of a selective estrogen receptor modulator on the progression of spontaneous autoimmune disease in MRL lpr/lpr mice

The MRL lpr/lpr mouse strain is an animal model for the autoimmune disorder systemic lupus erythematosus (SLE). Pathologic changes in the mice include a severe proliferative glomerulonephritis, lymph node and spleen enlargement, increase in autoantibody titers, and shortened life spans. In the present investigation, female MRL lpr/lpr mice have been dosed po daily for 7 months with the selective estrogen receptor modulator (SERM) LY139478 (4 mg/kg) or 17alpha-ethinylestradiol (EE2, 1 mg/kg) and compared to vehicle control animals. The LY139478 group had an increase in survival (73% survival at 7 months, P = 0.02) but the EE2-treated animals did not (53% survival at 7 months, P = 0.4) when compared to the control group (32% survival at 7 months). Although there were no reductions in autoantibody levels as determined by anti-DNA antibody ELISA, histological analysis of kidney tissue indicated that both LY139478 and EE2 mitigated the progression of glomerular nephritis which was evident in the controls. In contrast, there were no significant differences in lymph node size although the LY139478 and EE2 groups retained a well-defined sinusoidal region. Finally, flow cytometric analysis documented that thymuses from animals treated for 7 months with LY139478 but not with EE2 contained predominantly CD4+/CD+ T cells consistent with a normal thymic phenotype observed in non-MRL lpr/lpr mouse strains. These studies demonstrate that SERMs may be potentially useful for the treatment of autoimmune disorders.

Identification of an estrogen response element activated by metabolites of 17beta-estradiol and raloxifene

17beta-Estradiol modulates gene transcription through the estrogen receptor and the estrogen response element in DNA. The human transforming growth factor-beta3 gene was shown to be activated by the estrogen receptor in the presence of estrogen metabolites or estrogen antagonists. Activation was mediated by a polypurine sequence, termed the raloxifene response element, and did not require the DNA binding domain of the estrogen receptor. Interaction of the estrogen receptor with the raloxifene response element appears to require a cellular adapter protein. The observation that individual estrogens modulate multiple DNA response elements may explain the tissue-selective estrogen agonist or antagonist activity of compounds such as raloxifene.

Cytokines in chronic inflammatory arthritis. I. Failure to detect T cell lymphokines (interleukin 2 and interleukin 3) and presence of macrophage colony-stimulating factor (CSF-1) and a novel mast cell growth factor in rheumatoid synovitis

Because previous studies showed low levels of IFN-gamma in rheumatoid arthritis (RA) synovial fluid (SF) and synovial tissue (ST) explant supernatants, we assayed RA SF and ST for IL-2 and IL-3-like activity. Using an IL-2 dependent murine CTLL line, 6 of 14 RA SF caused increased thymidine uptake (greater than three times control). The activity was distinct from IL-2 because it was not blocked by antibody to IL-2-R. In addition, IL-2 was not detected (less than 50 pg/ml) in 16 joint samples using an ELISA. Multi-colony-stimulating factor (CSF) activity was measured using two assays that can detect murine IL-3 (mast cell proliferation, and bone marrow CSF). In the mast cell assay, [3H]TdR uptake was 493 +/- 67 cpm for medium, 2,910 +/- 329 cpm in the presence of RA SF (p less than 0.001), 1,246 +/- 156 cpm in the presence of SF from patients with seronegative spondyloarthropathies (p less than 0.001), and 736 +/- 100 cpm in the presence of osteoarthritis SF (p greater than 0.1). In the CSF assay, four of five RA SF and five of five RA ST induced colony formation from bone marrow nonadherent cells. Macrophage colonies were most common, although mixed colonies and granulocytes were occasionally observed. The multi-CSF activity in RA is not due to IL-3 since human rIL-3 was not active in either murine assay, and IL-3 mRNA was not detected in RA synovium. Sephadex column chromatography of RA SF revealed that the mast cell growth factor (approximately 6 x 10(3) mol wt) and the CSF (approximately 40 and 100 x 10(3) mol wt) are distinct. The colony-stimulating aspect of the "IL-3-like" activity in RA SF is likely due to CSF-1 because it is the appropriate mol wt and because the activity was neutralized by specific anti-CSF-1 antibody. Finally, an RIA detected 1.6-25 ng/ml of CSF-1 in RA SF and ST and CSF-1 mRNA was detected in four of five RA synovial tissue samples tested.