1.Cytoskeleton Journal Club June 13, 2012Presented by Suk Namgoong

2. Adenomanous Polypolis Coli (APC) Main component of Wnt Signaling Pathway In the absence of bounded Wnt on Wnt receptor, it forms destructioncomplex for -catanin,- mediates proteolytic degradation of -catenin By the bound of wnt into wnt receptor Frizzled, APC release -catenin and -catenin was translocated into nucleus and ctivated various Wnt target genes(Development, Morphogenesis, Cancers..) Tumor Suppressor Gene- Mutations on APC gene cause a hereditary cancer syndrome called Familiar Adenomanous Polypolis (FAP)- Loss of APC functions by mutations has been found frequently in colorectal cancers 3. APC directly nucleates actin assembly via C-terminalBasic Domain 2010 Okada et al. Okada K et al. J Cell Biol 2010;189:1087-1096 4. ANS : Actin nucleation sequencesNo Sequence Homology with known actin binding domain/motifsIt is dimer in solutio 5. mDia1 and APC-B synergize to promote actin assembly inthe combined presence of profilin and capping protein.Okada K et al. J Cell Biol 2010;189:1087-1096 2010 Okada et al. 6. Two different binding mode of Actin nucleatorsArp2/3 complex stay on the pointed end (slow growing end) of actin filamentsFormins remains processively bound on barbed end (fast growing end) How about APC? From which side of actin filaments it initiate actin nucleation? 7. Synergistic actin nucleations by APC and mDia1(Cappuccino) Yeast Bnr1 bud6During the nucleation, Formins and other nucleationfactors interact each other and synergize nucleations.But what will happen after nucleation?Do formins and other nucleators dissociate afternucleation?or formins carry all other stuffs along with elongation?(not likely, but we dont know yet) 8. Fluorescence Probe Labeling with SNAP-tag (O6-alkylguanine-DNA alkyltransferase)54 9 SNAPFH1 FH2 SNAPAPC (Basic)64 7 Oregon-Green Labeled Actin 647 PEG ALaser excitation 9. Immobilized SNAP-APC Stepwise Photobleaching Addition of LatBCan generate actin filaments Inhibit new filament generation(APC is stay bound on pointed end) 10. Bulk Pyrene Actin Assay Stepwise photobleaching for the determination ofOligomeric state in single molecules 11. Complex Formations of mDia1, APC-C, OregonGreen-Actin (LatB treated) 12. Interaction via C-terminal region ofmDia1 13. Namgoong et al., Nature Struct Mol. Biol. 2011I feel De ja vu.. 14. APC VopLAPC stays bound on the pointedend of actin FilamentsVopL is dissociated from the filament endand spit out new filaments continuously vs Rocket Launcher Machine Gun