Membrane phosphoinositides control a variety of cellular processes through the recruitment and/or regulation of cytosolic proteins. One mechanism ensuring spatial specificity in phosphoinositide signalling is the targeting of enzymes that mediate their metabolism to specific subcellular sites. Phosphatidylinositol phosphate kinase type 1 gamma (PtdInsPKI gamma) is a phosphatidylinositol-4-phosphate 5-kinase that is expressed at high levels in brain, and is concentrated at synapses. Here we show that the predominant brain splice variant of PtdInsPKI gamma (PtdInsPKI gamma-90) binds, by means of a short carboxy-terminal peptide, to the FERM domain of talin, and is strongly activated by this interaction. Talin, a principal component of focal adhesion plaques, is also present at synapses. PtdInsPKI gamma-90 is expressed in non-neuronal cells, albeit at much lower levels than in neurons, and is concentrated at focal adhesion plaques, where phosphatidylinositol-4,5-bisphosphate has an important regulatory role. Overexpression of PtdInsPKI gamma-90, or expression of its C-terminal domain, disrupts focal adhesion plaques, probably by local disruption of normal phosphoinositide balance. These findings define an interaction that has a regulatory role in cell adhesion and suggest new similarities between molecular interactions underlying synaptic junctions and general mechanisms of cell adhesion.

Fission of clathrin-coated and other endocytic vesicles from the plasma membrane involves the cooperation of several membrane-associated proteins, among which the GTPase dynamin plays a key role (1, 2). The participation of dynamin in the fission of endocytic vesicles has been established by a variety of experimental approaches in Drosophila, cultured cells, and cell-free systems, although the precise mechanism of fission and the role of dynamin in this reaction remain unclear (3).Several dynamin partners thought to participate in dynamin recruitment or function have been identified (3,4). At the synapse, where endocytosis plays a key role in the recycling of synaptic vesicle membranes, two prominent dynamin partners are amphiphysin and endophilin (5-7). Amphiphysin has a three-domain structure with an evolutionarily conserved Nterminal module of ϳ250 amino acids called the Bin/amphiphysin/Rvs (BAR) 1 domain, a variable central region, and a Cterminal Src homology-3 (SH3) domain that binds dynamin. Endophilin has a similar domain structure (2). Although the N-terminal domain of endophilin is substantially divergent in amino acid composition from the BAR domain of amphiphysin, it shares some similarity at critical sites, leading to its classification as a BAR domain (8).2 Accordingly, the BAR domains of amphiphysin and endophilin share functional similarities because they both can bind and deform lipid bilayers and mediate homo-and heterodimerization (6, 8 -10). Dynamin also can bind and deform lipid bilayers, and it has been proposed that endophilin and amphiphysin might help to recruit and possibly assist dynamin in the generation of membrane curvature at endocytic pits (8, 10).The closest homologue of amphiphysin and endophilin in Saccharomyces cerevisiae is Rvs167, that forms a stable heterodimer with Rsv161; Rvs167 has a domain structure like amphiphysin, whereas Rvs161 (homologous to the mammalian protein Bin3) possesses only a BAR domain. Mutation of either one or both components of this heterodimer in yeast produces defects in endocytosis and actin function (11). Such a dual phenotype is typical of most mutations in actin regulatory and endocytosis genes in yeast (12). These observations, together with results from a variety of studies in mammalian cells, have suggested a link between endocytosis and actin, although such a link has remained mechanistically elusive (13,14). Foci of actin can often be seen at endocytic sites (15), and endocytic vesicles with actin tails have also been observed (16). Interest-* This work was supported in part by National Institutes of Health Grants NS36251 and CA46128 and United States Army Medical Research and Development Command Grant DAMD17-97-7068) (to P. D. C.); by National Institutes of Health Grant GM58801, a W. M. Keck Distinguished Young Scholar Award, and a McKnight Scholar Award (to F. B. G.); and by National Institutes of Health Grant GM62299 (to J. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article mu...

A common feature of non-coding repeat expansion disorders is the accumulation of RNA repeats as RNA foci in the nucleus and/or cytoplasm of affected cells. These RNA foci can be toxic because they sequester RNA-binding proteins, thus affecting various steps of post-transcriptional gene regulation. However, the precise step that is affected by C9orf72 GGGGCC (G4C2) repeat expansion, the major genetic cause of amyotrophic lateral sclerosis (ALS), is still poorly defined. In this work, we set out to characterise these mechanisms by identifying proteins that bind to C9orf72 RNA. Sequestration of some of these factors into RNA foci was observed when a (G4C2) 31 repeat was expressed in NSC34 and HeLa cells. Most notably, (G4C2) 31 repeats widely affected the distribution of Pur-alpha and its binding partner fragile X mental retardation protein 1 (FMRP, also known as FMR1), which accumulate in intra-cytosolic granules that are positive for stress granules markers. Accordingly, translational repression is induced. Interestingly, this effect is associated with a marked accumulation of poly(A) mRNAs in cell nuclei. Thus, defective trafficking of mRNA, as a consequence of impaired nuclear mRNA export, might affect translation efficiency and contribute to the pathogenesis of C9orf72 ALS.