Most arthropod-borne and invertebrate viruses are orally ingested and commence infection in cells of the invertebrate intestine. Infection of secondary sites and eventual transmission to other hosts is hindered by basal lamina, a tightly interwoven and virusimpenetrable noncellular layer, lining the intestine and other organ cell layers. The mechanisms for viral escape across basal laminae are unknown. We describe an elegant mechanism mediated by a baculovirus-encoded fibroblast growth factor (vFGF) that signals a previously undescribed stepwise cascade of protease activation wherein matrix metalloproteases activate effector caspases, leading to remodeling of basal lamina lining tracheal cells associated with the intestine and culminating in the establishment of efficient systemic infections. Because FGFs coordinate diverse functions during development, metabolic processes, and tissue repair, it is plausible that the vFGF-mediated pathway described here is widely used during developmental and pathogenic processes that involve basal lamina remodeling.basal lamina | FGF | midgut | virus

Although mitochondrial proteins play well-defined roles in caspase activation in mammalian cells, the role of mitochondrial factors in caspase activation in Drosophila is unclear. Using cell-free extracts, we demonstrate that mitochondrial factors play no apparent role in Drosophila caspase activation. Cytosolic extract from apoptotic S2 cells, in which caspases were inhibited, induced caspase activation in cytosolic extract from normal S2 cells. Mitochondrial extract did not activate caspases, nor did it influence caspase activation by cytosolic extract. Silencing of Hid, Reaper, or Grim reduced caspase activation by apoptotic cell extract. Furthermore, a peptide representing the amino terminus of Hid was sufficient to activate caspases in cytosolic extract, and this activity was not enhanced by addition of mitochondria or mitochondrial lysate. The Hid peptide also induced apoptosis when introduced into S2 cells. These results suggest that caspase activation in Drosophila is regulated solely by cytoplasmic factors and does not involve any mitochondrial factors.

While circadian dysfunction and neurodegeneration are correlated, the mechanism for this is not understood. It is not known if age-dependent circadian dysfunction leads to neurodegeneration or vice-versa, and the proteins that mediate the effect remain unidentified. Here, we show that the knock-down of a regulator (spag) of the circadian kinase Dbt in circadian cells lowers Dbt levels abnormally, lengthens circadian rhythms and causes expression of activated initiator caspase (Dronc) in the optic lobes during the middle of the day or after light pulses at night. Likewise, reduced Dbt activity lengthens circadian period and causes expression of activated Dronc, and a loss-of-function mutation in Clk also leads to expression of activated Dronc in a light-dependent manner. Genetic epistasis experiments place Dbt downstream of Spag in the pathway, and Spag-dependent reductions of Dbt are shown to require the proteasome. Importantly, activated Dronc expression due to reduced Spag or Dbt activity occurs in cells that do not express the spag RNAi or dominant negative Dbt and requires PDF neuropeptide signaling from the same neurons that support behavioral rhythms. Furthermore, reduction of Dbt or Spag activity leads to Dronc-dependent Drosophila Tau cleavage and enhanced neurodegeneration produced by human Tau in a fly eye model for tauopathy. Aging flies with lowered Dbt or Spag function show markers of cell death as well as behavioral deficits and shortened lifespans, and even old wild type flies exhibit Dbt modification and activated caspase at particular times of day. These results suggest that Dbt suppresses expression of activated Dronc to prevent Tau cleavage, and that the circadian clock defects confer sensitivity to expression of activated Dronc in response to prolonged light. They establish a link between the circadian clock factors, light, cell death pathways and Tau toxicity, potentially via dysregulation of circadian neuronal remodeling in the optic lobes.

In Drosophila S2 cells, the apical caspase DRONC undergoes a low level of spontaneous autoprocessing. Unintended apoptosis is prevented by the inhibitor of apoptosis DIAP1, which targets the processed form of DRONC for degradation through its E3 ubiquitin protein ligase activity. Recent reports have demonstrated that shortly after the initiation of apoptosis in S2 cells, DIAP1 is cleaved following aspartate residue Asp-20 by the effector caspase DrICE. Here we report a novel caspase-mediated cleavage of DIAP1 in S2 cells. In both living and dying S2 cells, DIAP1 is cleaved by DRONC after glutamate residue Glu-205, located between the first and second BIR domains. The mutation of Glu-205 prevented the interaction of DIAP1 and processed DRONC but had no effect on the interaction with full-length DRONC. The mutation of Glu-205 also had a negative effect on the ability of overexpressed DIAP1 to prevent apoptosis stimulated by the proapoptotic protein Reaper or by UV light. These results expand our knowledge of the events that occur in the Drosophila apoptosome prior to and after receiving an apoptotic signal. IAP1 proteins were first discovered in baculoviruses and have now been found in a wide range of organisms (1). IAPs are identified by the presence of at least one baculovirus IAP repeat (BIR), a roughly 70-amino acid domain shown to be important for protein-protein interactions. Many IAPs also contain a C-terminal RING finger domain, and several of these have been shown to possess E3 ubiquitin ligase activity (2-8).Although all IAP proteins contain a BIR domain, not all BIR-containing proteins can inhibit apoptosis, and some BIRcontaining proteins have been implicated in cell signaling and cell cycle regulation (9). Several IAPs have been shown to directly bind and inhibit the activity of a family of proapoptotic proteins known as caspases (10, 11). Caspases are cysteine proteases and are synthesized as zymogens, which must usually be proteolytically cleaved to become activated (12). They are divided into two types depending on the size of an Nterminal prodomain found on all caspases. Initiator caspases are identified by a long prodomain, whereas a short prodomain is indicative of an effector caspase. Upon reception of a death signal, upstream initiator caspases are first activated and in turn cleave and activate downstream effector caspases leading to apoptosis.In mammalian cells, caspase-9 functions as the initiator caspase for the intrinsic death pathway and upon induction of apoptosis associates with APAF-1, the mammalian CED-4 homolog. Caspase-9 and APAF-1 binding occur through their mutual CARD domains and along with the cofactors cytochrome c and dATP form the apoptosome. The apoptosome is a large complex that induces dimerization and activation of caspase-9 (13). Activated caspase-9 then activates effector caspases including caspase-3 and caspase-7, which bring about the morphological and biochemical events associated with apoptosis. In mammalian cells, apoptosome formation is thought to occur only afte...

Mouse models of neurodegenerative diseases such as Alzheimer’s disease (AD) are important for understanding how pathological signaling cascades change neural circuitry and in time interrupt cognitive function. Here, we introduce a non-genetic preclinical model for aging and show that it exhibits cleaved tau protein, active caspases and neurofibrillary tangles, hallmarks of AD, causing behavioral deficits measuring cognitive impairment. To our knowledge this is the first report of a non-transgenic, non-interventional mouse model displaying structural, functional and molecular aging deficits associated with AD and other tauopathies in humans with potentially high impact on both new basic research into pathogenic mechanisms and new translational research efforts. Tau aggregation is a hallmark of tauopathies, including AD. Recent studies have indicated that cleavage of tau plays an important role in both tau aggregation and disease. In this study we use wild type mice as a model for normal aging and resulting age-related cognitive impairment. We provide evidence that aged mice have increased levels of activated caspases, which significantly correlates to increased levels of truncated tau and formation of neurofibrillary tangles. In addition, cognitive decline was significantly negatively associated with increased levels of caspase activity and tau truncated by caspase-3. Experimentally induced inhibition of caspases prevented this proteolytic cleavage of tau truncation and the associated formation of neurofibrillary tangles. Our study shows the strength of using a non-transgenic model to study structure, function and molecular mechanisms in aging and age related diseases of the brain.