Neuronal Functions of the Novel Serine/Threonine Kinase Ndr2

Abstract

We have identified a novel member of the Ndr subfamily of serine/threonine protein kinases, Ndr2, as a gene product that is induced in the mouse amygdala during fear memory consolidation and examined a possible function of this kinase in neural differentiation. Expression of Ndr2 mRNA was detected in various cortical and subcortical brain regions, as well as non-neuronal tissues. Its expression in the amygdala was increased 6 h after Pavlovian fear conditioning training and returned to control levels within 24 h. To study intracellular localization and functions of Ndr2, EGFP::Ndr2 fusion proteins were expressed in rat pheochromocytoma (PC12) cells and acutely isolated cortical neurons, thereby revealing an association of Ndr2 with the actin cytoskeleton in somata, neurites and filopodia, in spines and at sites of cell contact. Co-precipitation and pulldown experiments support this finding. Evidence for an involvement of Ndr2 in actin-mediated cellular functions further comes from the observation of decreased cell spreading and changes in neurite outgrowth that were associated with protein serine phosphorylation in transfected PC12 cells. Together, our data suggest that Ndr2 is an interesting candidate gene for the regulation of structural processes in differentiating and mature neuronal cells.Stimulus-dependent modifications of cell structure and connectivity in the central nervous system are basic elements of long term memory formation. Protein kinases and protein phosphatases are key regulators of these processes, which they control and co-ordinate through the phosphorylation and/or dephosphorylation of neurotransmitter receptors and ion channels, cytoskeleton elements, cell surface molecules, and transcription factors (1).We have employed a classic fear conditioning paradigm to isolate candidate genes involved in memory-related functions in the brain (2). Fear conditioning is highly amenable to cellular and molecular approaches to learning and memory, because conditioned subjects (a) very quickly learn to associate a previously neutral sensory stimulus (conditional stimulus) and an aversive, unconditional stimulus during fear conditioning training and (b) develop a robust and easily measurable long term memory after a single training session. Moreover, the neuronal circuits and cellular mechanisms that underlie classic fear conditioning have been investigated in detail (reviewed in Ref.3). These conceptual and technical advantages have allowed researchers to show that, among other factors, protein kinase A, mitogen-activated protein kinase and calcium/calmodulin-dependent kinases are critical for fear conditioning (summarized in Ref. 4). Some of these protein kinase activities could even be tracked down to the amygdala (5-7). Recent evidence further suggests an involvement of Rho-mediated signaling pathways and the Rho-associated kinase (p160 ROCK ) in amygdala plasticity after fear conditioning (8). This pathway may be of particular importance, because it controls actinmediated changes in dendrite and spine...

The STE20/Germinal Center Kinase POD6 Interacts with the NDR Kinase COT1 and Is Involved in Polar Tip Extension inNeurospora crassa

“…Similar to the observation in the filamentous fungus, PKA in animal cells has been shown to promote a round cell shape during cytokinesis and to phosphorylate monomeric actin to prevent actin-fiber formation (Ohta et al, 1987;Prat et al, 1993). The fact the animal NDR kinase function has been implied in regulating actin organization (Geng et al, 2000;Zallen et al, 2000;Emoto et al, 2004;Stork et al, 2004) along with the stated effect of PKA on the cytoskeleton in a variety of organisms supports the possibility that the fungal components function in a similar manner. It is conceivable that COT1/POD6 may positively modulate actin dynamics in parallel to the negatively acting PKA pathway.…”

Human NDR Kinases Are Rapidly Activated by MOB Proteins through Recruitment to the Plasma Membrane and Phosphorylation

“…In particular, worm and fly NDR kinases have been shown previously to play central roles in neuronal processes (6,7). However, a recent report suggests that the murine NDR2 form also plays an Thus, it will be essential to test how much localized activation of NDR on the plasma membrane contributes to the neuronal functions described by Stork et al (21). Nevertheless, our work provides important information relevant to the role of NDR in cancer biology.…”

“…Although the basic mechanism of activation of human NDR protein kinase in vitro has been described in detail (3,16,20,23), the regulation of NDR in a cellular context still remains to be elucidated. Such information should bring insight into its cellular functions and, in particular, into its possible role in cancer.While NDR1 was reported to be localized predominantly in the nucleus (14), NDR2 was shown very recently to be mostly excluded from the nucleus, displaying a cytoplasmic distribution (4,5,20,21). This observation is intriguing given the high sequence similarity between these two kinases.…”

“…While NDR1 was reported to be localized predominantly in the nucleus (14), NDR2 was shown very recently to be mostly excluded from the nucleus, displaying a cytoplasmic distribution (4,5,20,21). This observation is intriguing given the high sequence similarity between these two kinases.…”

Critical role of the 65-kDa isoform of glutamic acid decarboxylase in consolidation and generalization of Pavlovian fear memory

“…In addition, the hippocampal formation processes multimodal information concerning contexts that define the time and place of aversive experiences during fear conditioning . Cellular and molecular correlates of synaptic plasticity as well as network activity patterns in these structures have been identified that relate to the formation of short-term and long-term fear memories (Adamec 2000;Buzsáki 2002;Paré et al 2002;Pelletier and Paré 2004;Santini et al 2004;Stork et al 2004). Specifically, increased theta synchronization between the amygdala and hippocampus has been postulated as a neural correlate of long-term cued fear memory (Seidenbecher et al 2003;Narayanan et al 2007).…”