title: Proteolysis of the docking protein HEF1 and implications for focal adhesion dynamics.
abstract: The dynamic regulation of focal adhesions is implicated in cellular processes of proliferation, differentiation, migration, and apoptosis. The focal adhesion-associated docking protein HEF1 is cleaved by caspases during both mitosis and apoptosis. Common to both of these cellular processes is the loss of focal adhesions, transiently during mitosis and permanently during apoptosis. The proteolytic processing of HEF1 during both mitosis and apoptosis therefore posits a general role for HEF1 as a sensor of altered adhesion states. In this study, we find that HEF1 undergoes proteolytic processing specifically in response to cellular detachment, while HEF1 proteolysis is prevented by specific integrin receptor ligation and focal adhesion formation. We show that overexpression of a C-terminal caspase-derived 28-kDa HEF1 peptide causes cellular rounding that is demonstrably separable from apoptosis. Mutation of the divergent helix-loop-helix motif found in 28-kDa HEF1 significantly reduces the induction of apoptosis by this peptide, while deletion of the amino-terminal 28 amino acids of 28-kDa HEF1 completely abrogates the induction of apoptosis. Conversely, these mutations have no effect on the rounding induced by 28-kDa HEF1. Finally, we detect a novel focal adhesion targeting domain located in the C terminus of HEF1 and show that this activity is necessary for HEF1-induced cell spreading. Together, these data suggest that proteolytic and other posttranslational modifications of HEF1 in response to loss of adhesion serve to modulate the disassembly of focal adhesions.
authors: Division of Basic Science, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
authors: G M
authors: GM
authors: O'Neill
authors: E A
authors: EA
authors: Golemis
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000590:Amino Acid Chloromethyl Ketones / Q000378:metabolism; D000595:Amino Acid Sequence; D017209:Apoptosis; D015153:Blotting, Western; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002448:Cell Adhesion; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D002455:Cell Division; D002470:Cell Survival; D022001:Focal Adhesions / Q000378:metabolism; D017353:Gene Deletion; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008938:Mitosis; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D020033:Protein Isoforms; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D008164:Luminescent Proteins; C099942:NEDD9 protein, human; D010455:Peptides; D010750:Phosphoproteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D049452:Green Fluorescent Proteins; D020169:Caspases