Netrins, a family of secreted molecules, play critical roles in axon guidance and cell migration during neuronal development 1,2. In addition to its role as a chemotropic molecule, netrin-1 also acts as a survival factor 3-7 . Both UNC5 (i.e. UNC5A, B, C or D) and DCC are transmembrane receptors for netrin-1 8 ,9. In the absence of netrin-1, DCC and UNC5 act as dependence receptors and trigger apoptosis 3,6, 10 . However, how netrin-1 suppresses the apoptotic activity of the receptors remains elusive. Here, we show that netrin-1 induces interaction of UNC5B with the brain specific GTPase PIKE-L. This interaction triggers activation of PI 3-kinase signaling, prevents UNC5B's proapoptotic activity and enhances neuronal survival. Moreover, this process tightly relies on Fyn as PIKE-L is tyrosine phosphorylated in response to netrin-1 and the netrin-1-mediated interaction of UNC5B with PIKE-L is inhibited in Fyn null mice. Thus, PIKE-L acts as a downstream survival effector for netrin-1 through UNC5B in the nervous system. PIKE-L is a brain specific GTPase, which binds and stimulates PI 3-kinase in a GTP-dependent manner 11, 12 . PIKE-L binds Homer, an adaptor protein for metabotropic glutamate receptor (mGluR). Activation of mGluRIs enhances formation of an mGluRI-Homer-PIKE-L complex, leading to activation of PI 3-kinase and prevention of neuronal apoptosis 13 . PIKE is also a substrate for caspases. PIKE can be phosphorylated on tyrosine residues by Fyn, leading to its resistance to caspase cleavage 14. To search for PIKE-L-binding proteins, we conducted yeast two-hybrid screening using GTPase domain as bait. Four out of twelve clones are both His and β-gal positive, one of which encodes the C-terminus of UNC5B ( Figure 1A). In HEK293 cells, transfected GFP-PIKE-L selectively binds to 569-946 fragment of UNC5B but not other fragments. Compared to the binding by the C-terminal motif (a.a. 569-946), truncation of death domain (a.a. 854-946) decreases UNC5B affinity to PIKE-L. Reciprocal immunoprecipitation reveals that the interaction occurs no matter PIKE-L or UNC5B is precipitated by its antibody ( Figure 1B, middle panels). Full-length UNC5B and its C-terminal fragment released after caspase cleavage 5 , 7 specifically interact with GTPase domain but not with other regions of PIKE-L, consistent with our yeast two-hybrid findings ( Figure 1B, right panels). We also 5To whom all correspondence should be addressed, Phone: 404-712-2814; Fax: 404-712-2979, kye@emory observed the robust interaction between endogenous PIKE-L and UNC5B in both the cortex and hippocampus of rat brain ( Figure 1C). Immunostaining of hippocampal and cortical primary neurons reveals that PIKE-L and UNC5B colocalize in the cell body and throughout all neuronal processes ( Figure 1D, left panel). The staining is specific as GST-PIKE-L (a.a. 268-384) antigen but not control GST abolishes PIKE-L staining in neurons ( Figure 1D, right panels).To examine whether netrin-1 modulates PIKE-L interaction with UNC5B, we cotransfected UNC5B into...

Neurofibromatosis 2 (NF2) is a tumor suppressor, although the molecular mechanism accounting for this effect remains unknown. Here, we show that merlin exerts its activity by inhibiting phosphatidylinositol 3-kinase (PI3-kinase), through binding to PIKE-L. Wild-type merlin, but not patient-derived mutant (L64P), binds PIKE-L and inhibits PI3-kinase activity. This suppression of PI3-kinase activity results from merlin disrupting the binding of PIKE-L to PI3-kinase. In addition, merlin suppression of PI3-kinase activity as well as schwannoma cell growth is abrogated by a single PIKE-L point mutation (P187L) that cannot bind merlin but can still activate PI3-kinase. Knocking down PIKE-L with RNA interference abolishes merlin's tumor-suppressive activity. Our data support the hypothesis that PIKE-L is an important mediator of merlin growth suppression.

The neurofibromatosis-2 (NF2) tumour-suppressor gene encodes an intracellular membrane-associated protein, called merlin, whose growth-suppressive function is dependent on its ability to form interactions through its intramolecular amino-terminal domain (NTD) and carboxy-terminal domain (CTD). Merlin phosphorylation plays a critical part in dictating merlin NTD/CTD interactions as well as in controlling binding to its effector proteins. Merlin is partially regulated by phosphorylation of Ser 518, such that hyperphosphorylated merlin is inactive and fails to form productive intramolecular and intermolecular interactions. Here, we show that the protein kinase Akt directly binds to and phosphorylates merlin on residues Thr 230 and Ser 315, which abolishes merlin NTD/CTD interactions and binding to merlin's effector protein PIKE-L and other binding partners. Furthermore, Akt-mediated phosphorylation leads to merlin degradation by ubiquitination. These studies demonstrate that Akt-mediated merlin phosphorylation regulates the function of merlin in the absence of an inactivating mutation.

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Alcohol dehydrogenases (ADHs), which belong to the oxidoreductase superfamily, catalyze the interconversion between alcohols and aldehydes or ketones with high stereoselectivity under mild conditions. ADHs are widely employed as biocatalysts for the dynamic kinetic resolution of racemic substrates and for the preparation of enantiomerically pure chemicals. This review provides an overview of biotechnological applications for ADHs in the production of chiral pharmaceuticals and fine chemicals.