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CELL BIOLOGY OF THE NEURON Polarity ... - Tavernarakis Lab

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Cell Biology of the Neuron: <strong>Polarity</strong>, Plasticity and Regeneration, Crete 2011<br />

Regulation of Neurofibromin RasGAP Activity and<br />

Localization during Neuronal Differentiation<br />

George Leondaritis 1 , Theodora Kalpachidou 2 , Dimitra Mangoura 2<br />

1<br />

Department of Pharamcology, Medical School, University of Thessaly, Larissa,<br />

Greece<br />

2<br />

Neurosciences, Biomedical Research Foundation Academy of Athens, Athens,<br />

Greece<br />

Ras and ERK1/2 signalling is pivotal to differentiation along the neuronal cell<br />

lineage. One crucial protein that may play a central role in this signalling pathway<br />

is the tumor suppressor RasGAP, neurofibromin (NF1). By studying the<br />

dynamics of PKC/Ras/ERK pathway signalling during differentiation of<br />

neuroblastoma cells upon treatment with a PKC agonist, we identified a<br />

phosphorylation event at the C-tail of NF1 on Ser2808 which correlated perfectly<br />

with acute and prolonged activation of Ras and ERK1/2. Importantly, Ser2808<br />

phosphorylation resulted in a shift of NF1 localization from the nucleus to the<br />

cytosol and mutation to Ala caused reduced PKC-dependent phosphorylation and<br />

increased nuclear localization of the NF1-C-terminal domain. Thus, sustained<br />

Ser2808 phosphorylation may result in prolonged recruitment of nuclear NF1 to<br />

cytosolic membranous Ras complexes. In search for NF1 domains that may<br />

confer cytosolic, cytoskeletal or vesicular localization we focused on a Sec14homology<br />

domain adjacent to GRD, the central RasGAP domain. Overexpressed<br />

Sec14 and GRD+Sec14 had a microtubule-associated and vesicular localization<br />

pattern reminiscent of the endogenous cytosolic pool of NF1 in differentiated<br />

neurons and COS-7 cells. Most importantly however, Sec14 induced an<br />

upregulation of RasGAP activity of GRD in vivo presumably by atypical direct<br />

interactions with Ras. A detailed kinetic analysis of NF1-GRD and NF1-<br />

GRD+Sec14 activities in EGF-stimulated cells suggested that Sec14 imposed a<br />

digital-like mode on the analog GAP activity of GRD. Thus, distinct NF1<br />

domains regulated by distinct mechanisms may dictate the localization and<br />

activity of the protein during differentiation.<br />

Presented by: Leondaritis, George<br />

Poster No 062<br />

Green Session<br />

144

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