Control of cytoskeletal architecture by the src-suppressed C kinase substrate, SSeCKS.
Activation of protein kinase C (PKC) in many cell types results in cytoskeletal reorganization associated with cell proliferation. We previously described a new cell cycle-regulated myristylated PKC substrate, SSeCKS (pronounced essex), that interacts with the actin cytoskeleton [Lin et al., 1995, 1996]. SSeCKS shares significant homology with Gravin, which encodes kinase scaffolding functions for PKC and PKA [Nauert et al., 1997]. This article describes the cellular effects of ectopically expressing SSeCKS in untransformed NIH3T3 fibroblasts. Because the constitutive overexpression of SSeCKS is toxic [Lin et al., 1995], we developed cell lines with tetracycline (tet)-regulated SSeCKS expression. The induction of SSeCKS (removal of tet) caused significant cell flattening and the elaboration of an SSeCKS-associated cortical cytoskeletal matrix resistant to Triton X-100 extraction. Flattened cells were growth-arrested and marked by the formation of cellular projections and the temporary loss of actin stress fibers and vinculin-associated adhesion plaques. SSeCKS overexpression did not affect steady-state levels of actin, vinculin, or focal adhesion kinase (FAK) but did increase integrin-independent FAK tyrosine phosphorylation. Stress fiber loss was coincident with induced SSeCKS expression, strongly suggesting a direct effect. Cytochalasin, and to a lesser extent nocodazole, inhibited SSeCKS-induced cell flattening, however, only cytochalasin affected the shape of pre-flattened cells, suggesting a greater dependence on microfilaments, rather than microtubules. By contrast, only nocodazole caused retraction of the filopodia-like processes. These data indicate a role for SSeCKS in modulating both cytoskeletal and signaling pathways. Thus, we propose to expand SSeCKS scaffolding functions to include the ability to control actin-based cytoskeletal architecture, as well as mitogenic signal pathways.
Gelman
I H
IH
Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029-6574, USA. igelman@smtplink.mssm.edu
Lee
K
K
Tombler
E
E
Gordon
R
R
Lin
X
X
D016475:3T3 Cells; D054758:A Kinase Anchor Proteins; D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000032:analysis; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism; D018797:Cell Cycle Proteins; D002455:Cell Division; D048429:Cell Size; D015638:Cytochalasin D / Q000494:pharmacology; D004789:Enzyme Activation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005786:Gene Expression Regulation / Q000187:drug effects; D051379:Mice; D008840:Microfilament Proteins / Q000032:analysis; D008870:Microtubules / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1; D008934:Mitogens / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D017830:Octoxynol; D011493:Protein Kinase C; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011554:Pseudopodia; D000070876:Tensins; D013752:Tetracycline / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D054758:A Kinase Anchor Proteins; C491161:Akap12 protein, mouse; D015815:Cell Adhesion Molecules; D018797:Cell Cycle Proteins; D008840:Microfilament Proteins; D008934:Mitogens; D000070876:Tensins; D015638:Cytochalasin D; D017830:Octoxynol; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496051:Ptk2 protein, mouse; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D013752:Tetracycline; D013755:Tetradecanoylphorbol Acetate; D015739:Nocodazole