Using autophosphorylated Ca 2ϩ /calmodulindependent protein kinase II (CaM kinase II) as substrate, we now find that long-term potentian (LTP) induction and maintenance are also associated with a significant decrease in calyculin A-sensitive protein phosphatase (protein phosphatase 2A) activity, without changes in Mg 2ϩ -dependent protein phosphatase (protein phosphatase 2C) activity. This decrease in protein phosphatase 2A activity was prevented when LTP induction was inhibited by treatment with calmidazolium or D-2-amino-5-phosphonopentanoic acid. In addition, the application of highfrequency stimulation to 32 P-labeled hippocampal slices resulted in increases in the phosphorylation of a 55-kDa protein immunoprecipitated with anti-phosphatase 2A antibodies. Use of a specific antibody revealed that the 55-kDa protein is the BЈ␣ subunit of protein phosphatase 2A. Following purification of brain protein phosphatase 2A, the BЈ␣ subunit was phosphorylated by CaM kinase II, an event that led to the reduction of protein phosphatase 2A activity. These results suggest that the decreased activity in protein phosphatase 2A following LTP induction contributes to the maintenance of constitutively active CaM kinase II and to the long-lasting increase in phosphorylation of synaptic components implicated in LTP. Key Words: Hippocampus-Synaptic plasticityLong-term potentiation-Ca 2ϩ /calmodulin-dependent protein kinase II-Protein phosphatase 2A. J. Neurochem. 74, 807-817 (2000).Activation of Ca 2ϩ /calmodulin-dependent protein kinase II (CaM kinase II) (Fukunaga et al., 1993b), protein kinase C (PKC) (Klann et al., 1991), casein kinase II (Charriaut-Marlangue et al., 1991), cyclic AMP-dependent protein kinase (Roberson and Sweatt, 1996), and mitogen-activated protein kinase (English and Sweatt, 1996) has been reported to occur during the induction of long-term potentiation (LTP) in the hippocampus. For example, Ca 2ϩ -independent PKC activity remains elevated for 45-60 min after LTP induction (Klann et al., 1991(Klann et al., , 1992, and this persistent PKC activity may be due to a limited proteolytic cleavage of PKC, especially the isoform of the kinase by the Ca 2ϩ -dependent proteases, calpains (Sacktor et al., 1993). In contrast, CaM kinase II has a different mechanism for conversion to a Ca 2ϩ -independent form of the kinase: this mechanism involves autophosphorylation of the enzyme, an event reversed by protein phosphatases.In addition, high-frequency stimulation (HFS) applied to Schaffer collaterals resulted in a significant increase in the phosphorylation of PKC substrates such as GAP-43 (B-50/F1 protein/neuromodulin) (Lovinger et al., 1987;Gianotti et al., 1992;Ramakers et al., 1995) and neurogranin (Klann et al., 1992;Ramakers et al., 1995). Similarly, long-lasting increases in the phosphorylation of synapsin I, microtubule-associated protein 2 (MAP2), and ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptors were also evident in LTP slices (Fukunaga et al., 1995;Barria et al....

In a previous study, we found that human neural stem cells (HNSCs) exposed to high concentrations of secreted amyloid-precursor protein (sAPP) in vitro differentiated into mainly astrocytes, suggesting that pathological alterations in APP processing during neurodegenerative conditions such as Alzheimer's disease (AD) may prevent neuronal differentiation of HNSCs. Thus, successful neuroplacement therapy for AD may require regulating APP expression to favorable levels to enhance neuronal differentiation of HNSCs. Phenserine, a recently developed cholinesterase inhibitor (ChEI), has been reported to reduce APP levels in vitro and in vivo. amyloid precursor protein ͉ transplantation ͉ immunohistochemistry ͉ neurogenesis ͉ Alzheimer's disease T ransplantation of neural stem cells (NSCs) to the developing brain and in animal models of neurodegeneration has demonstrated that migration and differentiation of these cells is regulated primarily by environmental cues (1-4). Pathological changes that occur in neurodegenerative disorders such as Alzheimer's disease (AD) may profoundly affect the brain microenvironment, which may in turn affect the fate of NSCs.The amyloid hypothesis, which postulates that ␤-amyloid (A␤) neurotoxicity plays a causative role in AD, has dominated much of AD research (5) and the absence of a lethal phenotype in amyloid-precursor protein (APP) knockout mice (6) has detracted attention from the physiological functions of APP. Several studies have shown that APP is involved in regulating neurite outgrowth, cell proliferation, neuronal migration, and differentiation (7-10). APP expression is also increased after brain injury, and increased levels are observed in apoptotic cells (11,12). Other studies report that A␤ inhibits NSC migration by increasing amyloid-associated cell death and by dysregulation of cellular calcium homeostasis (13,14). These findings suggest that not only A␤ but that also altered APP processing during the course of AD may have effects on stem cell biology.Previously, we showed that human NSCs (HNSCs) transplanted into aged rats differentiated into neural cells and could reverse age-associated cognitive impairment in these animals (3). This study demonstrated that the aged rat brain was capable of providing necessary environmental conditions for HNSCs to retain their multipotency and provided some evidence for the potential of stem cell replacement therapies to improve memory and cognitive deficits in AD. However, we recently found increased in vitro glial differentiation of HNSCs treated with high doses of secreted APP or transfected with wild-type APP (15). This finding suggests that stem cell replacement approaches would have reduced effectiveness in the AD brain, in which impaired APP metabolism would prevent or reduce neuronal differentiation of implanted cells. Therefore, we suggest that regulation of APP levels in the brain is necessary for implementing neuroplacement strategies.(Ϫ)-Phenserine is a recently developed cholinesterase inhibitor (ChEI) currently in clinical ...

The Wnt/beta-catenin signaling pathway plays diverse roles in embryonic development and in maintenance of organs and tissues in adults. Activation of this signaling cascade inhibits degradation of the pivotal component beta-catenin, which in turn stimulates transcription of downstream target genes. Over the past two decades, intensive worldwide investigations have yielded considerable progress toward understanding the cellular and molecular mechanisms of Wnt signaling and its involvement in the pathogenesis of a range of human diseases. Remarkably, beta-catenin signaling is aberrantly activated in greater than 70% of colorectal cancers and to a lesser extent in other tumor types, promoting cancer cell proliferation, survival and migration. Accordingly, beta-catenin has gained recognition as an enticing molecular target for cancer therapeutics. Disruption of protein-protein interactions essential for beta-catenin activity holds immense promise for the development of novel anti-cancer drugs. In this review, we focus on the regulation of beta-catenin-dependent transcriptional activation and discuss potential therapeutic opportunities to block this signaling pathway in cancer.