Inhibition of ␥-secretase, one of the enzymes responsible for the cleavage of the amyloid precursor protein (APP) to produce the pathogenic ␤-amyloid (A␤) peptides, is an attractive approach to the treatment of Alzheimer disease. In addition to APP, however, several other ␥-secretase substrates have been identified (e.g. Notch), and altered processing of these substrates by ␥-secretase inhibitors could lead to unintended biological consequences. To study the in vivo consequences of ␥-secretase inhibition, the ␥-secretase inhibitor LY-411,575 was administered to C57BL/6 and TgCRND8 APP transgenic mice for 15 days. Although most tissues were unaffected, doses of LY-411,575 that inhibited A␤ production had marked effects on lymphocyte development and on the intestine. LY-411,575 decreased overall thymic cellularity and impaired intrathymic differentiation at the CD4 ؊ CD8 ؊ CD44 ؉ CD25 ؉ precursor stage. No effects on peripheral T cell populations were noted following LY-411,575 treatment, but evidence for the altered maturation of peripheral B cells was observed. In the intestine, LY-411,575 treatment increased goblet cell number and drastically altered tissue morphology. These effects of LY-411,575 were not seen in mice that were administered LY-D, a diastereoisomer of LY-411,575, which is a very weak ␥-secretase inhibitor. These studies show that inhibition of ␥-secretase has the expected benefit of reducing A␤ in a murine model of Alzheimer disease but has potentially undesirable biological effects as well, most likely because of the inhibition of Notch processing. Alzheimer disease (AD)1 is the third most common cause of death and the leading cause of dementia in the United States (1). Although the exact cause of AD is still unknown, the etiology of the disease is almost certainly linked to several neuropathological hallmarks observed in the brains of AD victims, particularly extracellular neuritic amyloid plaques and intracellular neurofibrillary tangles (2-4). Although both of these neuropathological lesions probably contribute to progressive neuronal cell death in AD, the proximal lesion appears to be the amyloid plaques and their principal component, the A␤ peptides. A large body of evidence strongly suggests that overproduction, aggregation, and/or plaque deposition of the A␤ peptides, particularly A␤42, are central to the pathogenesis of AD (reviewed in Ref. 5). In fact, two recent studies of patients immunized against the A␤42 peptide have provided the first preliminary clinical evidence that A␤ does indeed contribute to the cognitive decline in AD patients (6, 7).The A␤ peptides are produced by the sequential proteolytic cleavage of the amyloid precursor protein (APP) by ␤-and ␥-secretase. ␥-Secretase is a complex composed of at least four proteins, namely presenilins (presenilin 1 or -2), nicastrin, PEN-2, and APH-1 (8). Presenilin 1 and -2 have been proposed to be the novel aspartyl proteases responsible for the catalytic activity of ␥-secretase (9, 10). Because of the essential role of ␥-secretase i...

Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates myeloid progenitor cell proliferation and enhances the function of terminally differentiated effector cells. Interleukin-3 (IL-3) stimulation results in the proliferation and maturation of early bone marrow progenitor cells. These activities are mediated by non-tyrosine kinase-containing receptors which consist of ligand-specific alpha subunits that complex with a common beta subunit required for signal transduction. Both GM-CSF and IL-3 rapidly and transiently induce expression of early growth response gene 1 (egr-1) in the human factor-dependent cell line TF-1. To define the mechanism of early response gene induction by GM-CSF and IL-3, growth factor-and serum-starved TF-1 cells transfected with recombinant constructs containing sequences of the human egr-1 promoter were stimulated with GM-CSF or IL-3. A 116-nucleotide (nt) region of the egr-1 promoter which contains sequences inducible by GM-CSF and IL-3 was defined. DNase I footprint analysis identified a 20-nt region, including nt -57 to -76, which contains a potential cyclic AMP (cAMP) response element (CRE). Electrophoretic mobility shift assays performed with CREB antibody confirmed the presence of CREB in the DNA-binding complex. Mutational analysis of the cytokine-responsive region of the egr-1 promoter revealed that both the cAMP response and serum response elements are required for induction by GM-CSF and IL-3. Nuclear extracts from GM-CSF-or IL-3-stimulated but not unstimulated TF-1 cells contain factors which specifically bind to the Egr-1-binding site in the nt -600 to -480 region of the promoter. Electrophoretic mobility shift assays were performed with antibodies against the Egr-1 protein to demonstrate the presence of the protein product in the shifted complex. Our studies suggest that the Egr-1 protein may further stimulate transcription of the egr-1 gene in response to GM-CSF as a secondary event.Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates the proliferation and maturation of hematopoietic progenitor cells and enhances the differentiated functions of mature granulocytes and monocytes/macrophages (12, 18). The pleiotropic biological activities of GM-CSF are mediated by a high-affinity receptor which consists of an alpha subunit that binds ligand with low affinity and a beta subunit that confers high-affinity binding to the receptor-ligand complex and is required for signal transduction. Both subunits are members of the hematopoietin receptor superfamily, which includes the receptors for interleukin-2 (IL-2), IL-3, IL-4, IL-5, IL-6, and IL-7, granulocyte colony-stimulating factor, erythropoietin, growth hormone, and prolactin (1, 7). The 120-kDa beta subunit of the human GM-CSF receptor (13-common) is also shared with the high-affinity human IL-3 and IL-5 receptors (23). Phosphorylation of similar sets of proteins has been demonstrated in factor-responsive cells stimulated by either GM-CSF or 20). In addition, pathways involving p2lras, c-Raf, and p42,4...