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THE ENDOCYTIC PROTEIN NUMB REGULATES APP METABOLISM AND NOTCH SIGNALING: IMPLICATIONS FOR ALZHEIMER'S DISEASE
Title
THE ENDOCYTIC PROTEIN NUMB REGULATES APP METABOLISM AND NOTCH SIGNALING: IMPLICATIONS FOR ALZHEIMER'S DISEASE.
Creator
Kyriazis, George, Chan, Sic, University of Central Florida
Abstract / Description
Increased production of amyloid beta (A-beta) peptide, via altered proteolytic cleavage of amyloid protein precursor (APP), and abnormalities in neuronal calcium homeostasis play central roles in the pathogenesis of Alzheimer's disease (AD). Notch1, a membrane receptor that controls cell fate decisions during development of the nervous system, has been linked to AD because it is a substrate for the gamma-secretase protein complex in which mutations cause early-onset inherited AD. Numb is...
Show moreIncreased production of amyloid beta (A-beta) peptide, via altered proteolytic cleavage of amyloid protein precursor (APP), and abnormalities in neuronal calcium homeostasis play central roles in the pathogenesis of Alzheimer's disease (AD). Notch1, a membrane receptor that controls cell fate decisions during development of the nervous system, has been linked to AD because it is a substrate for the gamma-secretase protein complex in which mutations cause early-onset inherited AD. Numb is an evolutionarily conserved endocytic adapter involved in the internalization of transmembrane receptors. Mammals produce four Numb isoforms that differ in two functional domains, a phosphotyrosine-binding domain (PTB) and a proline-rich region (PRR). Recent studies showed that the PTB domain of Numb interacts with the cytoplasmic tails of APP and Notch but the functional relevance of these interactions with respect to AD pathogenesis is not clear. In the current studies, we proposed to investigate the biological consequences of the interaction of the Numb proteins with APP and Notch in neural cells stably overexpressing each of the four human Numb proteins. In the first part of our studies, we found that expression of the Numb isoforms lacking the insert in the PTB (SPTB-Numb) caused the abnormal accumulation of cellular APP in the early endosomes, and increased the levels of C-terminal APP fragments and A-beta. By contrast, expression of the Numb isoforms with the insert in PTB (LPTB-Numb) leads to the depletion of cellular APP and coincides with significantly lower production of APP derivatives and A-beta. The contrasting effects of the Numb isoforms on APP metabolism were not attributed to differences in the expression of APP nor the activities of the various APP-processing secretases. In the second part of our studies, we found that expression of SPTB-Numb protein enhances neuronal vulnerability to serum deprivation-induced cell death by a mechanism involving the dysregulation of cellular calcium homeostasis. Neural cells expressing SPTB-Numb exhibited enhanced Notch activity, which markedly upregulated the expression of transient receptor potential canonical 6 (TRPC6) channels enhancing calcium entry in response to store depletion. We also found that serum deprivation increased TRPC6 expression, mediating the serum deprivation-induced death in neural cells. Interestingly, expression of LPTB-Numb protein suppressed serum deprivation-induced activation of Notch and the subsequent upregulation of TRPC6 and cell death. Finally, we showed that the Numb proteins differentially impact Notch activation by altering the endocytic trafficking and processing of Notch. Taken together, these studies demonstrate that aberrant expression of the Numb proteins may influence APP metabolism and Notch-mediated cellular responses to injury by altering their endocytic trafficking and processing.
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Date Issued
2008
Identifier
CFE0002233, ucf:47917
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002233
CHARACTERIZATION OF A NOVEL INTERACTOR/SUBSTRATE FOR THE PRO-APOPTOTIC SERINE PROTEASE OMI/HTRA2
Title
CHARACTERIZATION OF A NOVEL INTERACTOR/SUBSTRATE FOR THE PRO-APOPTOTIC SERINE PROTEASE OMI/HTRA2.
Creator
Stratico, Valerie Anne, Zervos, Antonis, University of Central Florida
Abstract / Description
Omi/HtrA2 is a highly conserved mammalian serine protease that belongs to the HtrA family of proteins. Omi shares homology with the bacterially expressed heat shock protease HtrA, which functions as a protease at higher temperatures and a chaperone at lower temperatures. Additionally, Omi shares sequence similarity with the mammalian homologs L56/HtrA1 and PRSP/HtrA3. Omi was first isolated as an interacting protein of Mxi2, an alternatively spliced form of the p38 stress-activated kinase,...
Show moreOmi/HtrA2 is a highly conserved mammalian serine protease that belongs to the HtrA family of proteins. Omi shares homology with the bacterially expressed heat shock protease HtrA, which functions as a protease at higher temperatures and a chaperone at lower temperatures. Additionally, Omi shares sequence similarity with the mammalian homologs L56/HtrA1 and PRSP/HtrA3. Omi was first isolated as an interacting protein of Mxi2, an alternatively spliced form of the p38 stress-activated kinase, using a modified yeast two-hybrid system. Omi localizes in the mitochondria and in response to apoptotic stimuli the mature form of this protein translocates to the cytoplasm. In the cytoplasm Omi participates in both the caspase-dependent as well as caspase-independent apoptosis. Additionally, recent studies suggest that Omi may have another unique function, maintaining homeostasis within the mitochondria. In an effort to further elucidate the function of Omi, a yeast two-hybrid screening was performed to isolate novel interacting proteins. This screening identified a novel protein (HOPS), as a specific interactor of Omi. The predicted amino acid sequence of this protein does not provide any information about its potential function in mammalian cells. However, experiments show that HOPS is cleaved in vitro by Omi. Furthermore, in response to apoptotic stimuli, HOPS is also degraded in vivo. This study suggests that HOPS could be a physiological substrate of Omi that is cleaved and removed during apoptosis.
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Date Issued
2004
Identifier
CFE0000144, ucf:46161
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000144
USE OF CERIUM OXIDE NANOPARTICLES FOR PROTECTION AGAINSTRADIATION-INDUCED CELL DEATH
Title
USE OF CERIUM OXIDE NANOPARTICLES FOR PROTECTION AGAINSTRADIATION-INDUCED CELL DEATH.
Creator
Colon, Jimmie, Kolattukudy, Pappachan, University of Central Florida
Abstract / Description
The ability of engineered cerium oxide nanoparticles to confer radioprotection was examined. Rat astrocytes were treated with cerium oxide nanoparticles to a final concentration of 10 nanomolar, irradiated with a single 10 Gy dose of ionizing radiation and cell death was evaluated by propidium iodine uptake at 24 and 48 hours after radiation insult. Treatment of rat astrocytes with nanoceria resulted in an approximate 3-fold decrease in radiation induced death. These results suggest that the...
Show moreThe ability of engineered cerium oxide nanoparticles to confer radioprotection was examined. Rat astrocytes were treated with cerium oxide nanoparticles to a final concentration of 10 nanomolar, irradiated with a single 10 Gy dose of ionizing radiation and cell death was evaluated by propidium iodine uptake at 24 and 48 hours after radiation insult. Treatment of rat astrocytes with nanoceria resulted in an approximate 3-fold decrease in radiation induced death. These results suggest that the nanoceria are conferring protection from radiation induced cell death. Further experiments with human cells were conducted. Human normal and tumor cells (MCF-7 and CRL8798) were treated with the same dosage of cerium oxide nanoparticles, irradiated and evaluated for cell survival. Treatment of normal cells (MCF-7) conferred nearly 99% protection from radiation-induced cell death while the same concentration of nanoceria showed almost no protection in tumor cells (CRL8798). TUNEL analysis results of similarly treated cells demonstrated that nanoceria reduced radiation-induced cell death by 3-fold in normal breast cells but not in MCF-7 tumor cell lines when cultured under the same conditions. We concluded that cerium oxide nanoparticles confer radioprotection in a normal human breast line (CRL 8798) but not in a human breast tumor line (MCF-7). It is hoped that the outcome of this study will guide future endeavors toward a better elucidation of the molecular pathways involved in the protection of cells with nanoceria against radiation-induced cell death, as well as the minimization of the bystander effect in radiation therapy.
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Date Issued
2006
Identifier
CFE0001048, ucf:46823
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001048