Cargo-specific recruitment in clathrin- and dynamin-independent endocytosis.

Spatially controlled, cargo-specific endocytosis is essential for development, tissue homeostasis and cancer invasion. Unlike cargo-specific clathrin-mediated endocytosis, the clathrin- and dynamin-independent endocytic pathway (CLIC-GEEC, CG pathway) is considered a bulk internalization route for the fluid phase, glycosylated membrane proteins and lipids. While the core molecular players of CG-endocytosis have been recently defined, evidence of cargo-specific adaptors or selective uptake of proteins for the pathway are lacking.

GTP-specific fab fragment-based GTPase activity assay.

GTPases are central cellular signaling proteins, which cycle between a GDP-bound inactive and a GTP-bound active conformation in a controlled manner. Ras GTPases are frequently mutated in cancer and so far only few experimental inhibitors exist. The most common methods for monitoring GTP hydrolysis rely on luminescent GDP- or GTP-analogs.

A homogeneous quenching resonance energy transfer assay for the kinetic analysis of the GTPase nucleotide exchange reaction.

A quenching resonance energy transfer (QRET) assay for small GTPase nucleotide exchange kinetic monitoring is demonstrated using nanomolar protein concentrations. Small GTPases are central signaling proteins in all eukaryotic cells acting as a "molecular switches" that are active in the GTP-state and inactive in the GDP-state. GTP-loading is highly regulated by guanine nucleotide exchange factors (GEFs).

The R-Ras/RIN2/Rab5 complex controls endothelial cell adhesion and morphogenesis via active integrin endocytosis and Rac signaling.

During developmental and tumor angiogenesis, semaphorins regulate blood vessel navigation by signaling through plexin receptors that inhibit the R-Ras subfamily of small GTPases. R-Ras is mainly expressed in vascular cells, where it induces adhesion to the extracellular matrix (ECM) through unknown mechanisms. We identify the Ras and Rab5 interacting protein RIN2 as a key effector that in endothelial cells interacts with and mediates the pro-adhesive and -angiogenic activity of R-Ras.

Distinct recycling of active and inactive β1 integrins.

Integrin trafficking plays an important role in cellular motility and cytokinesis. Integrins undergo constant endo/exocytic shuttling to facilitate the dynamic regulation of cell adhesion. Integrin activity toward the components of the extracellular matrix is regulated by the ability of these receptors to switch between active and inactive conformations.

Homogeneous single-label biochemical Ras activation assay using time-resolved luminescence.

Mutations of the small GTP-binding protein Ras have been commonly found in tumors, and Ras oncogenes have been established to be involved in the early steps of cancerogenesis. The detection of Ras activity is critical in the determination of the cell signaling events controlling cell growth and differentiation. Therefore, development of improved methods for primary screening of novel potential drugs that target small GTPase or their regulators and their signaling pathways is important.

SHARPIN is an endogenous inhibitor of β1-integrin activation.

Regulated activation of integrins is critical for cell adhesion, motility and tissue homeostasis. Talin and kindlins activate β1-integrins, but the counteracting inhibiting mechanisms are poorly defined. We identified SHARPIN as an important inactivator of β1-integrins in an RNAi screen.

Competitive binding of Rab21 and p120RasGAP to integrins regulates receptor traffic and migration.

Integrin trafficking from and to the plasma membrane controls many aspects of cell behavior including cell motility, invasion, and cytokinesis. Recruitment of integrin cargo to the endocytic machinery is regulated by the small GTPase Rab21, but the detailed molecular mechanisms underlying integrin cargo recruitment are yet unknown. Here we identify an important role for p120RasGAP (RASA1) in the recycling of endocytosed α/β1-integrin heterodimers to the plasma membrane.

RPGR and RP2: targets for the treatment of X-linked retinitis pigmentosa?

Retinitis pigmentosa is the most important hereditary eye disease and there is currently no cure available. Although mutations were found in more than 40 genes in patients with retinitis pigmentosa, only two genes have thus far been found to be responsible for one of the most severe forms of the disease, X-linked retinitis pigmentosa. In this review, we highlight the current knowledge about the two gene products RPGR and RP2 and try to link genetic data from patients with functional data on the corresponding proteins.

Specificity of Arl2/Arl3 signaling is mediated by a ternary Arl3-effector-GAP complex.

Arl2 and Arl3, members of the Arf subfamily of small G proteins, are believed to be involved in ciliary and microtubule-dependent processes. Recently, we could identify RP2, responsible for a variant of X-linked retinitis pigmentosa, as the Arl3-specific GAP. Here, we have characterized Arl2/3 interactions.

The retinitis pigmentosa 2 gene product is a GTPase-activating protein for Arf-like 3.

The retinitis pigmentosa 2 (RP2) gene is responsible for a particular variant of X chromosome-linked eye disease. Previously, RP2 was shown to bind the GTP form of the small G protein Arf-like 3 (Arl3), thus qualifying as an effector. Here we present the Arl3-GppNHp-RP2 complex structure, which shows features resembling complexes with GTPase-activating proteins (GAPs).

Crystal structure of the human retinitis pigmentosa 2 protein and its interaction with Arl3.

The crystal structure of human retinitis pigmentosa 2 protein (RP2) was solved to 2.1 angstroms resolution. It consists of an N-terminal beta helix and a C-terminal ferredoxin-like alpha/beta domain.

Postsynaptic recruitment of Dendrin depends on both dendritic mRNA transport and synaptic anchoring.

Synaptic plasticity and memory formation involve remodeling of the postsynaptic cytoskeleton, a process that is in part based on both local translation of dendritic mRNAs and synaptic recruitment of newly synthesized proteins. The postsynaptic component Dendrin that is encoded by a dendritically localized mRNA is thought to modulate the structure of the synaptic cytoskeleton. However, molecular mechanisms that control extrasomatic Dendrin mRNA transport and postsynaptic protein recruitment are unknown.

Characterization of KIBRA, a novel WW domain-containing protein.

In a yeast two hybrid screen with the human isoform of Dendrin (KIAA0749), a putative modulator of the postsynaptic cytoskeleton, we isolated a cDNA coding for a novel protein, KIBRA, possessing two amino-terminal WW domains, an internal C2-like domain and a carboxy-terminal glutamic acid-rich stretch. Northern blot analysis revealed that the expression of KIBRA mRNA was predominately found in kidney and brain. In vitro interaction studies revealed that the first KIBRA WW domain binds specifically to PPxY motifs.