KIBRA: A New Gateway to Learning and Memory?

The genetic locus encoding KIBRA, a member of the WWC family of proteins, has recently been shown to be associated with human memory performance through genome-wide single nucleotide polymorphism screening. Gene expression analysis and a variety of functional studies have further indicated that such a role is biologically plausible for KIBRA. Here, we review the existing literature, illustrate connections between the different lines of evidence, and derive models based on KIBRA's function(s) in the brain that can be further tested experimentally

Identification and characterization of Iporin as a novel interaction partner for rab1

BACKGROUND: The small GTPase rab1a and its isoform rab1b are essential regulating components in the vesicle transport between the ER and the Golgi apparatus. Rab1 is thought to act as a molecular switch and can change between an active GTP-bound and an inactive GDP-bound conformation. To elucidate the function of rab1, several approaches have been established to isolate effector proteins, which interact with the activated conformation of rab1. To date p115, GM130, golgin-84 and MICAL have been identified as direct interacting partners. Together with rab1, these molecules are components of a protein complex, which mediates and regulates intracellular vesicle transport. RESULTS: Here, we report the characterization of Iporin, which is similar to KIAA0375 as a novel rab1-interacting protein. It was initially identified by yeast two-hybrid screening experiments with the active mutant of rab1b (rab1b Q67R) as bait. Iporin contains a SH3 domain and two polyproline stretches, which are known to play a role in protein/protein interactions. In addition, Iporin encloses a RUN domain, which seems to be a major part of the rab1binding domain (R1BD). Iporin is ubiquitously expressed and immunofluorescence staining displays a cytosolic punctual distribution. Interestingly, we also show that Iporin interacts with another rab1 interacting partner, the GM130 protein. CONCLUSION: Our results demonstrate that Iporin is a potential new interacting partner of rab1. Iporin is different from already identified rab1 interacting proteins concerning protein structure and cellular localization. We conclude that Iporin might function as a link between the targeting of ER derived vesicles, triggered by the rab1 GTPase and a signaling pathway regulated by molecules containing SH3 and/or poly-proline regions. The characterization of this novel intermolecular relation could help to elucidate how vesicles find their way from ER to the Golgi apparatus

An aPKC-Exocyst Complex Controls Paxillin Phosphorylation and Migration through Localised JNK1 Activation

The exocyst/aPKC complex controls the spatiotemporal activation of the kinases JNK and ERK at the leading edge of migrating cells and thereby controls the dynamic behaviour of the adhesion protein paxillin during cell migration

Lasp-1 Regulates Podosome Function

Eukaryotic cells form a variety of adhesive structures to connect with their environment and to regulate cell motility. In contrast to classical focal adhesions, podosomes, highly dynamic structures of different cell types, are actively engaged in matrix remodelling and degradation. Podosomes are composed of an actin-rich core region surrounded by a ring-like structure containing signalling molecules, motor proteins as well as cytoskeleton-associated proteins

Lack of WWC2 Protein Leads to Aberrant Angiogenesis in Postnatal Mice

The WWC protein family is an upstream regulator of the Hippo signalling pathway that is involved in many cellular processes. We examined the effect of an endothelium-specific WWC1 and/or WWC2 knock-out on ocular angiogenesis. Knock-outs were induced in C57BL/6 mice at the age of one day (P1) and evaluated at P6 (postnatal mice) or induced at the age of five weeks and evaluated at three months of age (adult mice). We analysed morphology of retinal vasculature in retinal flat mounts. In addition, in vivo imaging and functional testing by electroretinography were performed in adult mice. Adult WWC1/2 double knock-out mice differed neither functionally nor morphologically from the control group. In contrast, the retinas of the postnatal WWC knock-out mice showed a hyperproliferative phenotype with significantly enlarged areas of sprouting angiogenesis and a higher number of tip cells. The branching and end points in the peripheral plexus were significantly increased compared to the control group. The deletion of the WWC2 gene was decisive for these effects; while knocking out WWC1 showed no significant differences. The results hint strongly that WWC2 is an essential regulator of ocular angiogenesis in mice. As an activator of the Hippo signalling pathway, it prevents excessive proliferation during physiological angiogenesis. In adult animals, WWC proteins do not seem to be important for the maintenance of the mature vascular plexus

Regulation of AMPA receptor function by the human memory-associated gene KIBRA

KIBRA has recently been identified as a gene associated with human memory performance. Despite the elucidation of the role of KIBRA in several diverse processes in nonneuronal cells, the molecular function of KIBRA in neurons is unknown. We found that KIBRA directly binds to the protein interacting with C-kinase 1 (PICK1) and forms a complex with α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs), the major excitatory neurotransmitter receptors in the brain. KIBRA knockdown accelerates the rate of AMPAR recycling following N-methyl-D-aspartate receptor-induced internalization. Genetic deletion of KIBRA in mice impairs both long-term depression and long-term potentiation at hippocampal Schaffer collateral-CA1 synapses. Moreover, KIBRA knockout mice have severe deficits in contextual fear learning and memory. These results indicate that KIBRA regulates higher brain function by regulating AMPAR trafficking and synaptic plasticity

Lasp-1 mutants lacking either the LIM domain, the NEBU repeats and the Linker region, or the SH3 domain are still localized at podosomes.

<p>(<b>A</b>) Domain structure of Lasp-1 comprising an aminoterminal LIM domain, two nebulin (NEBU) repeats and an adjacent Linker region mediating actin binding, and a carboxyterminal SH3 (Src homology 3) domain that binds zyxin and palladin (N = aminoterminus, C = carboxyterminus). (<b>B</b>) Confocal micrographs of primary human macrophages transfected with EGFP-Lasp-1 deletion constructs (green) and stained with vinculin-specific antibody (with Alexa568-conjugated secondary antibody) for vinculin (red) and Cy5- phalloidin for F-actin. Constructs include EGFP-Lasp-1 wildtype (wt), EGFP-Lasp-1ΔLIM (lacking the LIM domain), EGFP-Lasp-1ΔSH3 (lacking the SH3 domain), and EGFP-Lasp-1ΔN-L (lacking the NEBU repeats and the Linker region). White boxes indicate detail images below. Bars represent 10 µm.</p

Lasp-1 is a component of the podosome ring structure.

<p>(<b>A, B</b>) Confocal micrographs of primary human macrophages transfected with constructs encoding (A) EGFP-Lasp-1 and (B) EYFP-Vinculin (green), respectively, and stained with vinculin- or Lasp-1-specific antibodies (with Alexa488- or Alexa 568-conjugated secondary antibody) for endogenous vinculin or Lasp-1, respectively, and Cy5-conjugated phalloidin for F-actin (blue). White box indicates detail images below. Bars represent 10 µm. (<b>C, D</b>) 3D reconstruction of single podosomes of primary human macrophages. Left panels: xyz mode, right panels: xzy mode for the same podosome. (C) Cells were transfected with EGFP-Lasp-1 and stained with Alexa568-phalloidin for F-actin (podosome core) or vinculin-specific antibody (with Alexa568-labeled secondary antibody) for vinculin (podosome ring structure; red). (D) Both untransfected cells (stained with Alexa488-phalloidin for F-actin; green) and cells transfected with EYFP-vinculin (green) were stained with Lasp-1-specific antibody (with Alexa568-labeled secondary antibody) for endogenous Lasp-1 (red). (<b>E</b>) Confocal micrographs of a rat smooth muscle cell (A7r5), stained with Alexa-594 phalloidin for F-actin (red, upper panel) or zyxin-specific antibody (with Alexa594-labeled secondary antibody) for endogenous zyxin (red, lower panel) and co-stained with Lasp-1-specific antibody (with Alexa488-labeled secondary antibody) for endogenous Lasp-1 (green). Lasp-1 and its binding partner zyxin colocalize at F-actin-rich podosomes (merge) in PDBu-treated A7r5 cells. Bars represent 25 µm.</p