Helen Lu Yin

Phosphatidylinositol 4 phosphate (PI4P) is highly enriched in the trans-Golgi network (TGN). Here we establish that PI4P is a key regulator of the recruitment of the GGA clathrin adaptor proteins to the TGN and that PI4P has a novel role in promoting their recognition of the ubiquitin (Ub) sorting signal. Knockdown of PI4KIIalpha by RNA interference (RNAi), which depletes the TGN's PI4P, impaired the recruitment of the GGAs to the TGN. GGAs bind PI4P primarily through their GAT domain, ...

Gelsolin is a calcium binding protein that shortens actin filaments. This effect occurs in the presence but not in the absence of micromolar calcium ion concentrations and is partially reversed following removal of calcium ions. Once two actin molecules have bound to gelsolin in solutions containing Ca2+, one of the actins remains bound following chelation of calcium, so that the reversal of gelsolin's effect cannot be accounted for simply by its dissociation from the ends of the ...

BACKGROUND: Phosphatidylinositol 4,5-bisphosphate (PIP(2)) has been implicated in the regulation of the actin cytoskeleton and vesicle trafficking. It stimulates de novo actin polymerization by activating the pathway involving the Wiskott-Aldrich syndrome protein (WASP) and the actin-related protein complex Arp2/3. Other studies show that actin polymerizes from cholesterol-sphingolipid-rich membrane microdomains called 'rafts', in a manner dependent on tyrosine phosphorylation. Although ...

BACKGROUND: Previously, proteomic methods were applied to characterise differentially expressed proteins in microdissected pancreatic ductal adenocarcinoma cells.

AIMS: To report that CapG and a related protein, gelsolin, which have established roles in cell motility, are overexpressed in metastatic pancreatic cancer; and to describe their pattern of expression in pancreatic cancer tissue and their effect on cell motility in pancreatic cancer cell lines.

METHODS: CapG was identified by ...

Gelsolin participates in the reorganization of the actin cytoskeleton that is required during such phenomena as cell movement, cytokinesis, and apoptosis. It consists of six structurally similar domains, G1-G6, which are arranged at resting intracellular levels of calcium ion so as to obscure the three actin-binding surfaces. Elevation of Ca(2+) concentrations releases latches within the constrained structure and produces large shifts in the relative positioning of the domains, ...

Gelsolin complexes with calcium (gelsolin-Ca2+) binds to the ends of actin filaments to which monomers add preferentially during elongation. It forms a stable complex with actin in a low ionic strength solution which does not normally favor the polymerization of actin. Gelsolin-Ca2+ increases the rate of nucleation of actin which precedes polymerization, but decreases the rate of elongation of the filaments. The final average length of filaments formed in the presence of gelsolin-Ca2+ is ...

To gain insight into the physiological function of phosphoinositide 3-kinase (PI 3-kinase) lipid products, this study examines the interactions of the D-3 phosphoinositides with profilin and the consequent effects on actin dynamics and phosphoinositide turnover. Profilin, a ubiquitous actin-regulating protein, plays a putative role in regulating actin assembly and PLC-gamma 1 signaling in light of its unique interactions with actin and phosphatidylinositol 4,5-bisphosphate ...

gCap39 is an actin filament end-capping protein which has a threefold repeated domain structure similar to the N-terminal half of gelsolin. However, unlike gelsolin, gCap39 does not sever actin filaments and dissociates completely from filament ends after calcium removal. We have capitalized on these differences to explore the structural basis for actin filament capping, severing, and their regulation. Using truncated gCap39, generated by limited proteolysis or deletion mutagenesis, we ...

Flightless-I (fliI) is a novel member of the gelsolin family that is important for actin organization during Drosophila embryogenesis and myogenesis. Drosophila fliI and the human homolog FLI both contain the classic gelsolin 6-fold segmental repeats and an amino-terminal extension of 16 tandem leucine-rich repeats (LRR). LRR repeats form amphipathic beta-alpha structural units that mediate protein-protein interactions. Although there are close to 100 known LRR domain-containing ...

The beta-thymosins are a family of related peptides. Recently, thymosin beta 4 was identified as a significant actin monomer sequestering protein in cells. To determine if other beta-thymosins also bind actin, and how they may participate in the regulation of actin polymerization, we expressed thymosin beta 4 and its major homolog, thymosin beta 10, in bacteria and characterized their interactions with actin. Equilibrium sedimentation studies showed that thymosin beta 4 behaved as a ...

Gelsolin is a Ca2+- and polyphosphoinositide-modulated actin-binding protein which severs actin filaments, nucleates actin assembly, and caps the "barbed" end of actin filaments. Proteolytic cleavage analysis of human plasma gelsolin has shown that the NH2-terminal half of the molecule severs actin filaments almost as effectively as native gelsolin in a Ca2+-insensitive but polyphosphoinositide-inhibited manner. Further proteolysis of the NH2-terminal half generates two unique fragments ...

Phosphoinositides such as phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,4-bisphosphate promote cell survival and protect against apoptosis by activating Akt/PKB, which phosphorylates components of the apoptotic machinery. We now report that another phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PIP2) is a direct inhibitor of initiator caspases 8 and 9, and their common effector caspase 3. PIP2 inhibited procaspase 9 processing in cell extracts and in a ...

The Ca2+-activated actin-binding protein gelsolin regulates actin filament length by severing preformed filaments and by binding actin monomers, stabilizing nuclei for their assembly into filaments. Gelsolin binds to phosphatidylinositol 4,5-bisphosphate (PIP2), with consequent inhibition of its filament severing activity and dissociation of EGTA-resistant complexes made with rabbit macrophage or human plasma gelsolin and rabbit muscle actin. This study provides evidence for an ...

Phosphatidylinositol 4 phosphate [PI(4)P] is essential for secretion in yeast, but its role in mammalian cells is unclear. Current paradigms propose that PI(4)P acts primarily as a precursor to phosphatidylinositol 4,5 bisphosphate (PIP2), an important plasma membrane regulator. We found that PI(4)P is enriched in the mammalian Golgi, and used RNA interference (RNAi) of PI4KIIalpha, a Golgi resident phosphatidylinositol 4 kinase, to determine whether PI(4)P directly regulates the Golgi. ...

The Atg8 autophagy proteins are essential for autophagosome biogenesis and maturation. The γ-aminobutyric acid receptor-associated protein (GABARAP) Atg8 family is much less understood than the LC3 Atg8 family, and the relationship between the GABARAPs' previously identified roles as modulators of transmembrane protein trafficking and autophagy is not known. Here we report that GABARAPs recruit palmitoylated PI4KIIα, a lipid kinase that generates phosphatidylinositol 4-phosphate (PI4P) ...