An actin-binding protein of the Sla2/Huntingtin interacting protein 1 family is a novel component of clathrin-coated pits and vesicles.
The actin cytoskeleton has been implicated in endocytosis, yet few molecules that link these systems have been identified. Here, we have cloned and characterized mHip1R, a protein that is closely related to huntingtin interacting protein 1 (Hip1). These two proteins are mammalian homologues of Sla2p, an actin binding protein important for actin organization and endocytosis in yeast. Sequence alignments and secondary structure predictions verified that mHip1R belongs to the Sla2 protein family. Thus, mHip1R contains an NH(2)-terminal domain homologous to that implicated in Sla2p's endocytic function, three predicted coiled-coils, a leucine zipper, and a talin-like actin-binding domain at the COOH terminus. The talin-like domain of mHip1R binds to F-actin in vitro and colocalizes with F-actin in vivo, indicating that this activity has been conserved from yeast to mammals. mHip1R shows a punctate immunolocalization and is enriched at the cell cortex and in the perinuclear region. We concluded that the cortical localization represents endocytic compartments, because mHip1R colocalizes with clathrin, AP-2, and endocytosed transferrin, and because mHip1R fractionates biochemically with clathrin-coated vesicles. Time-lapse video microscopy of mHip1R-green fluorescence protein (GFP) revealed a blinking behavior similar to that reported for GFP-clathrin, and an actin-dependent inward movement of punctate structures from the cell periphery. These data show that mHip1R is a component of clathrin-coated pits and vesicles and suggest that it might link the endocytic machinery to the actin cytoskeleton.
Engqvist-Goldstein
A E
AE
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California 94720-3202, USA.
Kessels
M M
MM
Chopra
V S
VS
Hayden
M R
MR
Drubin
D G
DG
D016475:3T3 Cells; D000199:Actins / Q000378:metabolism*; D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism*; D018699:Coated Vesicles / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000378:metabolism; D004268:DNA-Binding Proteins; D003902:Detergents; D004285:Dogs; D004705:Endocytosis / Q000502:physiology; D005656:Fungal Proteins / Q000096:biosynthesis / Q000378:metabolism; D006801:Humans; D006816:Huntington Disease / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins; D008969:Molecular Sequence Data; D011485:Protein Binding; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D016608:Talin / Q000378:metabolism
D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D003902:Detergents; D005656:Fungal Proteins; C073368:HIP1 protein, human; C489536:Hip1 protein, mouse; C489534:Hip1r protein, mouse; D008565:Membrane Proteins; D008840:Microfilament Proteins; C082266:SLA2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D016608:Talin