expressed on the leading edge of membrane filopodia and colocalizes with a-actinin. Purified recombinant GPR56 extracellular domain protein inhibits glioma cell adhesion and causes abnormal cytoskeletal morphology and cell rounding. These results indicate that the extracellular domain may compete for unidentified ligand(s), and block the normal function of GPR56 in cell attachment. In reporter assays, overexpression of GPR56 activates the NF-jB, PAI-1 and TCF transcriptional response elements. These pathways have been implicated in cytoskeletal signaling, adhesion and tumor biology. The above results indicate that GPR56 serves as an adhesion GPCR and is involved in adhesion signaling.

Nerve growth factor binds to the TrkA and p75(NTR) (p75) and generates signals leading to neuronal cell survival, differentiation, and programmed cell death. Here we describe a series of experiments involving selective activation of either TrkA or p75 in which distinct cell-signaling intermediates promote different cellular consequences. We analyzed pheochromocytoma 12 (PC12) cells stably expressing chimeras consisting of the extracellular domain of PDGF receptor (PDGFR) fused to the transmembrane and cytoplasmic segments of p75 or TrkA. Because PC12 cells lack endogenous PDGFR, addition of PDGF to these cell lines permits selective activation of the p75 or TrkA responses without stimulating endogenous receptors. Although both p75 and TrkA activated nuclear factor-kappaB (NF-kappaB), we show that distinct proximal-signaling intermediates are used by each receptor. A dominant-negative mutant of TRAF6 blocked p75- but not TrkA-mediated induction of NF-kappaB. Conversely a dominant-negative mutant of Shc inhibited TrkA but not p75 activation of NF-kappaB. Both of these distinct signaling pathways subsequently converge, leading to activation of the IkappaB kinase complex. Moreover, the activation of NF-kappaB by these distinct pathways after stimulation of either TrkA or p75 leads to different physiological consequences. Blocking p75-mediated activation of NF-kappaB by ecdysone-inducible expression of a nondegradable mutant of IkappaBalpha significantly enhanced apoptosis. In contrast, blocking NF-kappaB induction via TrkA significantly inhibited neurite process formation in PC12 cells. Together these findings indicate that, although both of these receptors lead to the activation of NF-kappaB, they proceed via distinct proximal-signaling intermediates and contribute to different cellular outcomes.

Invasion of glioma cells involves the attachment of invading tumor cells to extracellular matrix (ECM), disruption of ECM components, and subsequent cell penetration into adjacent brain structures. Discoidin domain receptor 1 (DDR1) tyrosine kinases constitute a novel family of receptors characterized by a unique structure in the ectodomain (discoidin-I domain). These cell surface receptors bind to several collagens and facilitate cell adhesion. Little is known about DDR1 expression and function in glioblastoma multiforme. In this study we demonstrate that DDR1 is overexpressed in glioma tissues using cDNA arrays, immunohistochemistry and Western blot analysis. Functional comparison of two splice variants of DDR1 (DDR1a and DDR1b) reveal novel differences in cell based glioma models. Overexpression of either DDR1a or DDR1b caused increased cell attachment. However, glioma cells overexpressing DDR1a display enhanced invasion and migration. We also detect increased levels of matrix metalloproteinase-2 in DDR1a overexpressing cells as measured by zymography. Inhibition of MMP activity using MMP inhibitor suppressed DDR1a stimulated cell-invasion. Similarly, an antibody against DDR1 reduced DDR1a mediated invasion as well as the enhanced adhesion of DDR1a and DDR1b overexpressing cells. These results suggest that DDR1a plays a critical role in inducing tumor cell adhesion and invasion, and this invasive phenotype is caused by activation of matrix metalloproteinase-2.

Changes in synaptic plasticity required for memory formation are dynamically regulated through opposing excitatory and inhibitory neurotransmissions. To explore the potential contribution of NF-B/Rel to these processes, we generated transgenic mice conditionally expressing a potent NF-B/Rel inhibitor termed IB␣ superrepressor (IB␣-SR). Using the prion promoter-enhancer, IB␣-SR is robustly expressed in inhibitory GABAergic interneurons and, at lower levels, in excitatory neurons but not in glia. This neuronal pattern of IB␣-SR expression leads to decreased expression of glutamate decarboxylase 65 (GAD65), the enzyme required for synthesis of the major inhibitory neurotransmitter, ␥-aminobutyric acid (GABA) in GABAergic interneurons. IB␣-SR expression also results in diminished basal GluR1 levels and impaired synaptic strength (input/output function), both of which are fully restored following activity-based task learning. Consistent with diminished GAD65-derived inhibitory tone and enhanced excitatory firing, IB␣-SR ؉ mice exhibit increased late-phase long-term potentiation, hyperactivity, seizures, increased exploratory activity, and enhanced spatial learning and memory. IB␣-SR ؉ neurons also express higher levels of the activity-regulated, cytoskeleton-associated (Arc) protein, consistent with neuronal hyperexcitability. These findings suggest that NF-B/Rel transcription factors act as pivotal regulators of activity-dependent inhibitory and excitatory neuronal function regulating synaptic plasticity and memory.Stimulus-coupled changes in synaptic plasticity are required for the storage, retrieval, and removal of acquired information collectively referred to as memory formation (28,32,39). Such changes are facilitated by both modifications of existing synaptic effectors and the de novo synthesis of new gene products regulated by various transcriptional regulators. These processes are tightly controlled by the coordinated action of both excitatory and inhibitory neurotransmitters derived from glutamatergic neurons and GABAergic (where GABA is ␥-aminobutyric acid) interneurons, respectively (47, 54). While the vast majority of studies to date have focused on the cyclic AMPresponsive transcription factor (CREB) regulating excitatory neuron function (7, 32-34, 62, 72), more recently, other transcription factors, including members of the NF-B/Rel family of transcription factors, have been implicated in experiencebased synaptic adaptations (38,45,49,55). However, our understanding of their precise role in regulating synaptic plasticity remains rudimentary at best.Although NF-B/Rel factors were originally implicated as central regulators of the immune and inflammatory responses, both basal expression and stimulus-coupled induction of NF-B/Rel factors occur in neurons and glial cells (23,30,31,45,48,55). Activation of NF-B/Rel proceeds through the sitespecific phosphorylation, polyubiquitylation, and proteasomemediated degradation of the major NF-B/Rel inhibitor protein, IB␣ (41). The newly liberated NF-B/Rel complex ra...