Dominant mutations in the amyloid precursor protein (APP) gene are associated with rare cases of familial Alzheimer's disease; however, the normal functions of APP and related proteins remain unclear. The nematode Caenorhabditis elegans has a single APP-related gene, apl-1, that is expressed in multiple tissues. Loss of apl-1 disrupts several developmental processes, including molting and morphogenesis, and results in larval lethality. The apl-1 lethality can be rescued by neuronal expression of the extracellular domain of APL-1. These data highlight the importance of the extracellular domain of an APP family member and suggest that APL-1 acts noncell-autonomously during development. Overexpression of APL-1 also causes several defects, including a high level of larval lethality. Decreased activity of sel-12, a C. elegans homologue of the human ␥-secretase component presenilin 1, partially rescues the lethality associated with APL-1 overexpression, suggesting that SEL-12 activity regulates APL-1 activity either directly or indirectly. Determining the in vivo functions of APP in mammals is complicated by the presence of two APP-related genes, APLP1 and APLP2 (for review see ref. 5). APP and APP-related proteins share two conserved domains in the extracellular region (E1 and E2) and one in the cytoplasmic domain, but the APP-related proteins do not contain the ␤-amyloid peptide (5). Mice in which APP, APLP1, or APLP2 is inactivated are viable and have minor behavioral and growth deficits (6-8). However, inactivation of APLP2 and either APP or APLP1 results in early postnatal lethality (6,8), indicating that the APP family is essential for viability. The brains of double knockout animals exhibit no obvious morphological defects (6, 8). By contrast, animals in which the entire APP gene family is inactivated show cortical dysplasia and type 2 lissencephaly, indicating that the APP gene family is necessary for neurodevelopment and adhesion (9).Although no APP gene has been identified in Drosophila melanogaster or Caenorhabditis elegans, each organism contains a single APP-related gene (10, 11). Inactivation of the Drosophila APP-related gene, Appl, causes abnormal synaptic differentiation (12), axonal transport (13,14), and phototactic behavior (15), the latter of which can be partially rescued with a human APP transgene (15). Expression of human APP in Drosophila wing imaginal discs results in a blistered wing phenotype, showing that overexpression of APP can disrupt cell adhesion in the transgenic animals (16).In this article, we examine the role of apl-1 in C. elegans. Zambrano et al. (17) have reported mild pharyngeal defects when apl-1 activity is decreased by dsRNA-mediated interference by feeding. We genetically inactivated apl-1 and found that, like the mammalian APP gene family, apl-1 has an essential role in C. elegans. In particular, APL-1 is necessary for proper molting and morphogenesis. Furthermore, expression of the extracellular domain of APL-1 in neurons is sufficient to rescue the apl-1 lethality. Th...

Death domain-containing receptors of the tumor necrosis factor (TNF)/nerve growth factor (NGF) family can induce apoptosis upon activation in many cellular systems. We show here that a conserved phosphotyrosine-containing motif within the death domain of these receptors can mediate inhibitory functions. The Src homology domain 2 (SH2)-containing tyrosine phosphatase-1 (SHP-1), SHP-2 and SH2-containing inositol phosphatase (SHIP) bound to this motif in a caspase-independent but cell-dependent manner. We also found that stimulation of death receptors disrupted anti-apoptosis pathways initiated (at least under certain conditions) by survival factors in neutrophils. In these cells, activation of the tyrosine kinase Lyn, an important anti-apoptotic event, was prevented as a consequence of death-receptor stimulation, most likely through association of the receptor with activated SHP-1. Thus, we provide molecular and functional evidence for negative signaling by death receptors.

The major component of senile plaques found in the brains of Alzheimer disease patients is the 3-amyloid peptide, which is derived from a larger amyloid precursor protein (APP). Recently, a number of APP and APP-related proteins have been identified in different organisms and constitute the family of APP proteins. We have isolated several cDNAs encoding an APP-related protein in the nematode Caenorhabdiis elegans and have designated the corresponding gene as apl-i. The apl-i transcripts undergo two forms of posttranscriptional modification: trans-splicing and alternative polyadenylylation. In vitro translation of an apl-i cDNA results in a protein of approximately the expected size. Similar to the Drosophila, human, and mouse APP-related proteins, APL-1 does not appear to contain the 13-amyloid peptide. Because APP-related proteins seem to be conserved through evolution, the apl-i gene from C. elegans should be important for determining the normal function of human APP. ', where Y is T or C, N is G, A, T, or C, and R is A or G) corresponding to a highly conserved cytoplasmic region between APP and APP-related proteins. Prehybridization and hybridization were carried out at 37°C. Filters were washed at 40°C and exposed to film using intensifying screens at -700C.Positive clones were isolated and excised from the AZAP vector according to the manufacturer's protocol (Stratagene) to yield pBluescript plasmids. DNA sequencing using the double-stranded dideoxynucleotide method (38) identified three APP-related clones (APL3.2, -6.2, and -1.2.2). To isolate additional clones, the cDNA library was rescreened with APL3.2, which was 32P-labeled by random priming. For this second screen, prehybridization and hybridization were done at 650C in 6x standard saline citrate (SSC)/5x Denhardt's solution/1% SDS/0.05% sodium pyrophosphate/ salmon sperm DNA (100 ,ug/ml). Filters were then washed in 2x SSC/0.1% SDS/0.05% sodium pyrophosphate for 30 min at room temperature, followed by two 15-min washes at 680C in 0.lx SSC/0.1% SDS/0.05% sodium pyrophosphate. Hybridizing plaques were visualized by autoradiography. Isolated clones were excised and sequenced as described above.

T cells constitute a large population of cellular infiltrate in atopic/allergic inflammation and a dysregulated, Th2-biased peripheral immune response appears to be an important pathogenetic factor. In atopic dermatitis, circulating cutaneous lymphocyte-associated antigen-bearing (CLA+) CD45RO+ T cells with skin-specific homing property represent an activated memory/effector T cell subset. They express high levels of Fas and Fas ligand and undergo activation-induced apoptosis. The freshly purified CLA+ CD45RO+ T cells of atopic individuals display distinct features of in vivo-triggered apoptosis such as pro-caspase degradation and active caspase-8 formation. In particular, the Th1 compartment of activated memory/effector T cells selectively undergoes activation-induced cell death, skewing the immune response toward surviving Th2 cells in atopic dermatitis patients. The apoptosis of circulating memory/effector T cells was confined to atopic individuals whereas non-atopic patients such as psoriasis, intrinsic-type asthma, contact dermatitis, intrinsic type of atopic dermatitis, bee venom allergic patients, and healthy controls showed no evidence for enhanced T cell apoptosis in vivo. These results define a novel mechanism for peripheral Th2 response in atopic diseases.

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