The principal pathological features of Alzheimer's disease (AD) are extracellular amyloid plaques and intracellular neurofibrillary tangles, the latter composed of the microtubule-binding protein tau assembled into paired helical and straight filaments. Recent studies suggest that these pathological entities may be functionally linked, although the mechanisms by which amyloid deposition promotes pathological tau filament assembly are poorly understood. Here, we report that tau is proteolyzed by multiple caspases at a highly conserved aspartate residue (Asp 421 ) in its C terminus in vitro and in neurons treated with amyloid-␤ (A␤) (1-42) peptide. Tau is rapidly cleaved at Asp 421 in A␤-treated neurons (within 2 h), and its proteolysis appears to precede the nuclear events of apoptosis. We also demonstrate that caspase cleavage of tau generates a truncated protein that lacks its C-terminal 20 amino acids and assembles more rapidly and more extensively into tau filaments in vitro than wild-type tau. Using a monoclonal antibody that specifically recognizes tau truncated at Asp 421 , we show that tau is proteolytically cleaved at this site in the fibrillar pathologies of AD brain. Taken together, our results suggest a novel mechanism linking amyloid deposition and neurofibrillary tangles in AD: A␤ peptides promote pathological tau filament assembly in neurons by triggering caspase cleavage of tau and generating a proteolytic product with enhanced polymerization kinetics. A lzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by accelerated neuronal cell death leading to dementia (1). Its hallmark pathologic features are extracellular amyloid plaques and intraneuronal fibrillar structures, the latter including neurofibrillary tangles (NFTs), neuropil threads, and dystrophic neurites invading amyloid plaques (2). Amyloid plaques are formed by the extracellular deposition of proteolytic fragments of the amyloid precursor protein (APP) termed amyloid-␤ (A␤) (1, 3), whereas the fibrillar pathologies are composed of the microtubule-associated protein tau assembled into polymeric filaments (paired helical and straight filaments) (2). The pathogenic role of amyloid deposition in AD is underscored by the evidence that each of the disease-causing mutations in familial AD results in enhanced production of amyloidogenic A␤ peptides; these peptides are sufficient to induce apoptosis in cultured neurons (1, 3). Furthermore, the recent observation that tau mutations cause hereditary frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17), a class of diseases characterized by NFT-like deposition of polymeric tau and dementia without amyloid plaques, emphasizes the critical role that tau plays in neurodegenerative events (4-6). Although amyloid plaques and NFTs have been largely regarded as independent neuropathologic entities, recent work suggests they may be functionally linked: mutation of APP that results in amyloid deposition or direct intracranial injection of A␤ peptide increase...

We investigated the role of the CXCR4 chemokine receptor in development of the mouse hippocampus. CXCR4 mRNA is expressed at sites of neuronal and progenitor cell migration in the hippocampus at late embryonic and early postnatal ages. mRNA for stromal cell-derived factor 1 (SDF-1), the only known ligand for the CXCR4 receptor, is expressed close to these migration sites, in the meninges investing the hippocampal primordium and the primordium itself. In mice engineered to lack the CXCR4 receptor, the morphology of the hippocampal dentate gyrus (DG) is dramatically altered. Gene expression markers for DG granule neurons and bromodeoxyuridine labeling of dividing cells revealed an underlying defect in the stream of postmitotic cells and secondary dentate progenitor cells that migrate toward and form the DG. In the absence of CXCR4, the number of dividing cells in the migratory stream and in the DG itself is reduced, and neurons appear to differentiate prematurely before reaching their target. Our findings indicate a role for the SDF-1͞CXCR4 chemokine signaling system in DG morphogenesis. Finally, the DG is unusual as a site of adult neurogenesis. We find that both CXCR4 and SDF-1 are expressed in the adult DG, suggesting an ongoing role in DG morphogenesis.C hemokines (chemotactic cytokines) are a family of small proteins that orchestrate the diverse functions of cells of the immune system (1). The effects of these proteins are transduced by a family of G protein-coupled receptors (1). In addition to their roles in the control of normal leukocyte trafficking, chemokines and their receptors also play important roles in the pathogenesis of inflammatory disease and of AIDS. In the latter case, some chemokine receptors, particularly CCR5 and CXCR4, have been shown to act as cellular binding sites for the HIV-1 virus (2).In addition to their widespread expression in the immune system, it now has been shown that chemokines and their receptors are expressed throughout the central nervous system. All of the major cell types in the brain, including neurons, glia, and microglia, have been shown to express many of the known receptors for chemokines (3, 4). Furthermore, many cells in the brain can synthesize and secrete chemokines under a variety of circumstances. It has been speculated widely that the chemokines and their receptors may be important in the genesis of the inflammatory component associated with diverse brain disorders and also with the pathogenesis of the widespread neurological symptoms associated with infection by the HIV-1 virus (3, 4). However, it is less clear which roles chemokines might play with respect to the normal functions of the brain. One possibility that has been raised, by analogy with their effects on leukocytes, is that chemokines and their receptors have an important chemotactic function in the migration of developing neurons during embryogenesis (5).The CXCR4 receptor is one of the most highly expressed chemokine receptors both during development and in the mature brain (6-8). Deletion of th...

Recent gene profiling studies have identified a new breast cancer subtype, the basal-like group, which expresses genes characteristic of basal epithelial cells and is associated with poor clinical outcomes. However, the genes responsible for the aggressive behavior observed in this group are largely unknown. Here we report that the small heat shock protein α-basic-crystallin (αB-crystallin) was commonly expressed in basal-like tumors and predicted poor survival in breast cancer patients independently of other prognostic markers. We also demonstrate that overexpression of αB-crystallin transformed immortalized human mammary epithelial cells (MECs). In 3D basement membrane culture, αB-crystallin overexpression induced luminal filling and other neoplastic-like changes in mammary acini, while silencing αB-crystallin by RNA interference inhibited these abnormalities. αB-Crystallin overexpression also induced EGF-and anchorage-independent growth, increased cell migration and invasion, and constitutively activated the MAPK kinase/ERK (MEK/ERK) pathway. Moreover, the transformed phenotype conferred by αB-crystallin was suppressed by MEK inhibitors. In addition, immortalized human MECs overexpressing αB-crystallin formed invasive mammary carcinomas in nude mice that recapitulated aspects of human basal-like breast tumors. Collectively, our results indicate that αB-crystallin is a novel oncoprotein expressed in basal-like breast carcinomas that independently predicts shorter survival. Our data also implicate the MEK/ERK pathway as a potential therapeutic target for these tumors.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor ␣ family of cytokines that preferentially induces apoptosis in transformed cells, making it a promising cancer therapy. However, many neoplasms are resistant to TRAIL-induced apoptosis by mechanisms that are poorly understood. We demonstrate that the expression of the small heat shock protein ␣B-crystallin (but not other heat shock proteins or apoptosis-regulating proteins) correlates with TRAIL resistance in a panel of human cancer cell lines. Stable expression of wild-type ␣B-crystallin, but not a pseudophosphorylation mutant impaired in its assembly and chaperone function, protects cancer cells from TRAIL-induced caspase-3 activation and apoptosis in vitro. Furthermore, selective inhibition of ␣B-crystallin expression by RNA interference sensitizes cancer cells to TRAIL. In addition, wild-type ␣B-crystallin promotes xenograft tumor growth and inhibits TRAIL-induced apoptosis in vivo in nude mice, whereas a pseudophosphorylation ␣B-crystallin mutant impaired in its anti-apoptotic function inhibits xenograft tumor growth. Collectively, these findings indicate that ␣B-crystallin is a novel regulator of TRAILinduced apoptosis and tumor growth. Moreover, these results demonstrate that targeted inhibition of ␣B-crystallin promotes TRAIL-induced apoptosis, thereby suggesting a novel strategy to overcome TRAIL resistance in cancer.Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), 1 also known as Apo2L, is a promising antitumor agent currently in preclinical studies that preferentially induces apoptosis in cancer cells, but not normal cells (1, 2). Like other members of the tumor necrosis factor family of cytokines, TRAIL is a type II transmembrane protein with an extracellular carboxyl terminus that mediates trimerization and receptor binding (3, 4). TRAIL plays a critical role in immune surveillance against tumors: TRAIL-deficient mice are more sensitive to chemical carcinogens and more susceptible to metastasis from mammary carcinoma xenografts (5). Recombinant soluble TRAIL induces apoptosis in many cancer cells in vitro and in vivo, and the native recombinant protein (amino acids 114 -281) appears to be quite tumor-selective (1, 6, 7). In addition, an antibody against one of the receptors of TRAIL (DR5) potently induces apoptosis in human hepatocellular carcinomas in vitro and in vivo, but not in normal human hepatocytes, thereby suggesting an additional therapeutic strategy to activate TRAIL apoptotic signaling (8). Although the mechanisms underlying the differential sensitivity of cancer and normal cells to TRAIL-induced apoptosis are poorly understood, the potential tumor selectivity of TRAIL distinguishes it from many other cancer therapies.TRAIL-induced apoptosis is mediated by the death-inducing signaling complex (DISC), which is composed of the TRAIL death receptors (DR4 and DR5), Fas-associated death domain (FADD), and the apical procaspases-8 and -10 (2). Trimeric TRAIL binds to its dea...