title: An adaptor role for cytoplasmic Sam68 in modulating Src activity during cell polarization.
abstract: The Src-associated substrate during mitosis with a molecular mass of 68 kDa (Sam68) is predominantly nuclear and is known to associate with proteins containing the Src homology 3 (SH3) and SH2 domains. Although Sam68 is a Src substrate, little is known about the signaling pathway that link them. Src is known to be activated transiently after cell spreading, where it modulates the activity of small Rho GTPases. Herein we report that Sam68-deficient cells exhibit loss of cell polarity and cell migration. Interestingly, Sam68-deficient cells exhibited sustained Src activity after cell attachment, resulting in the constitutive tyrosine phosphorylation and activation of p190RhoGAP and its association with p120rasGAP. Consistently, we observed that Sam68-deficient cells exhibited deregulated RhoA and Rac1 activity. By using total internal reflection fluorescence microscopy, we observed Sam68 near the plasma membrane after cell attachment coinciding with phosphorylation of its C-terminal tyrosines and association with Csk. These findings show that Sam68 localizes near the plasma membrane during cell attachment and serves as an adaptor protein to modulate Src activity for proper signaling to small Rho GTPases.
authors.affiliation: Terry Fox Molecular Oncology Group and Bloomfield Center for Research on Aging, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montréal, Québec, Canada H3T 1E2.
authors.forename: Marc-Etienne
authors.initials: ME
authors.lastname: Huot
authors.forename: Claire M
authors.initials: CM
authors.lastname: Brown
authors.forename: Nathalie
authors.initials: N
authors.lastname: Lamarche-Vane
authors.forename: Stéphane
authors.initials: S
authors.lastname: Richard
mesh_terms: D000199:Actins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency / Q000378:metabolism*; D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D002448:Cell Adhesion; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D016764:Cell Polarity; D003593:Cytoplasm / Q000201:enzymology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004622:Embryo, Mammalian / Q000166:cytology; D004789:Enzyme Activation; D005347:Fibroblasts / Q000166:cytology* / Q000201:enzymology*; D005353:Fibronectins / Q000378:metabolism; D022001:Focal Adhesions / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D019000:Phosphotyrosine / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012097:Repressor Proteins / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism; D019061:src-Family Kinases
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; C513041:Arhgap35 protein, mouse; D004268:DNA-Binding Proteins; D005353:Fibronectins; D020690:GTPase-Activating Proteins; C513253:Khdrbs1 protein, mouse; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D020742:rhoA GTP-Binding Protein