title: CASK and protein 4.1 support F-actin nucleation on neurexins.
abstract: Rearrangements of the actin cytoskeleton are involved in a variety of cellular processes from locomotion of cells to morphological alterations of the cell surface. One important question is how local interactions of cells with the extracellular space are translated into alterations of their membrane organization. To address this problem, we studied CASK, a member of the membrane-associated guanylate kinase homologues family of adaptor proteins. CASK has been shown to bind the erythrocyte isoform of protein 4.1, a class of proteins that promote formation of actin/spectrin microfilaments. In neurons, CASK also interacts via its PDZ domain with the cytosolic C termini of neurexins, neuron-specific cell-surface proteins. We now show that CASK binds a brain-enriched isoform of protein 4.1, and nucleates local assembly of actin/spectrin filaments. These interactions can be reconstituted on the cytosolic tail of neurexins. Furthermore, CASK can be recovered with actin filaments prepared from rat brain extracts, and neurexins are recruited together with CASK and protein 4.1 into these actin filaments. Thus, analogous to the PDZ-domain protein p55 and glycophorin C at the erythrocyte membrane, a similar complex comprising CASK and neurexins exists in neurons. Our data suggest that intercellular junctions formed by neurexins, such as junctions initiated by beta-neurexins with neuroligins, are at least partially coupled to the actin cytoskeleton via an interaction with CASK and protein 4.1.
authors.affiliation: Center for Basic Neuroscience, Department of Molecular Genetics, and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA. thomas.biederer@utsouthwestern.edu
authors.forename: T
authors.initials: T
authors.lastname: Biederer
authors.forename: T C
authors.initials: TC
authors.lastname: Sudhof
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D003593:Cytoplasm / Q000378:metabolism; D003598:Cytoskeletal Proteins; D006021:Glycophorins / Q000378:metabolism; D051528:Guanylate Kinases; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009479:Neuropeptides; D009703:Nucleoside-Phosphate Kinase / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013049:Spectrin / Q000378:metabolism
chemical_list: D000199:Actins; D003598:Cytoskeletal Proteins; D006021:Glycophorins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; C028841:erythrocyte membrane band 4.1 protein; C120557:erythrocyte membrane protein band 4.1-like 1; D013049:Spectrin; C106868:CASK kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D009703:Nucleoside-Phosphate Kinase; D051528:Guanylate Kinases