Limits...
The transcription factor AP-1 is required for EGF-induced activation of rho-like GTPases, cytoskeletal rearrangements, motility, and in vitro invasion of A431 cells.

Malliri A, Symons M, Hennigan RF, Hurlstone AF, Lamb RF, Wheeler T, Ozanne BW - J. Cell Biol. (1998)

Bottom Line: Constitutively activated mutants of Rac or Rho introduced into A431 or A431 cells expressing TAM67 (TA cells) induce equivalent actin cytoskeletal rearrangements, suggesting that the effector pathways downstream of Rac and Rho required for these responses are unimpaired by sustained TAM67 expression.However, EGF-induced translocation of Rac to the cell membrane, which is associated with its activation, is defective in TA cells.Our data establish a novel link between AP-1 activity and EGFR activation of Rac and Rho, which in turn mediate the actin cytoskeletal rearrangements required for cell motility and invasion.

View Article: PubMed Central - PubMed

Affiliation: Beatson Institute for Cancer Research, Bearsden, Glasgow, G61 1BD, United Kingdom.

ABSTRACT
Human squamous cell carcinomas (SCC) frequently express elevated levels of epidermal growth factor receptor (EGFR). EGFR overexpression in SCC-derived cell lines correlates with their ability to invade in an in vitro invasion assay in response to EGF, whereas benign epidermal cells, which express low levels of EGFR, do not invade. EGF-induced invasion of SCC-derived A431 cells is inhibited by sustained expression of the dominant negative mutant of c-Jun, TAM67, suggesting a role for the transcription factor AP-1 (activator protein-1) in regulating invasion. Significantly, we establish that sustained TAM67 expression inhibits growth factor-induced cell motility and the reorganization of the cytoskeleton and cell-shape changes essential for this process: TAM67 expression inhibits EGF-induced membrane ruffling, lamellipodia formation, cortical actin polymerization and cell rounding. Introduction of a dominant negative mutant of Rac and of the Rho inhibitor C3 transferase into A431 cells indicates that EGF-induced membrane ruffling and lamellipodia formation are regulated by Rac, whereas EGF-induced cortical actin polymerization and cell rounding are controlled by Rho. Constitutively activated mutants of Rac or Rho introduced into A431 or A431 cells expressing TAM67 (TA cells) induce equivalent actin cytoskeletal rearrangements, suggesting that the effector pathways downstream of Rac and Rho required for these responses are unimpaired by sustained TAM67 expression. However, EGF-induced translocation of Rac to the cell membrane, which is associated with its activation, is defective in TA cells. Our data establish a novel link between AP-1 activity and EGFR activation of Rac and Rho, which in turn mediate the actin cytoskeletal rearrangements required for cell motility and invasion.

Show MeSH

Related in: MedlinePlus

A schematic representation of TAM67 inhibition of EGF-induced cytoskeletal rearrangements. (Top)  EGF treatment of A431 cells  activates Rac and subsequently Rho. In turn, activated Rac and Rho regulate  the cytoskeletal rearrangements required for cell migration and hence invasion.  EGF-induced activation of  Rac and Rho requires the  function of upstream activators(s) X and possibly decreased function of inhibitor(s) Y. (Bottom) Expression  of TAM67 inhibits EGF-induced activation of Rac and Rho and thus blocks migration  and invasion. EGF fails to activate Rac and Rho in TA cells because expression of TAM67 suppresses the expression or activity of  activators (X) and possibly increases the activity of inhibitors (Y).
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2132955&req=5

Figure 10: A schematic representation of TAM67 inhibition of EGF-induced cytoskeletal rearrangements. (Top) EGF treatment of A431 cells activates Rac and subsequently Rho. In turn, activated Rac and Rho regulate the cytoskeletal rearrangements required for cell migration and hence invasion. EGF-induced activation of Rac and Rho requires the function of upstream activators(s) X and possibly decreased function of inhibitor(s) Y. (Bottom) Expression of TAM67 inhibits EGF-induced activation of Rac and Rho and thus blocks migration and invasion. EGF fails to activate Rac and Rho in TA cells because expression of TAM67 suppresses the expression or activity of activators (X) and possibly increases the activity of inhibitors (Y).

Mentions: In conclusion, we propose that sustained expression of TAM67 functions as an inhibitor of a multigenic invasion program through suppressing the activity of AP-1. A subset of AP-1 target genes appear to provide molecular bridges between growth factor stimulation and activation of Rac and Rho, which in turn regulate morphological and motile responses (Fig. 10). In this respect, AP-1 target genes could include upstream activators of Rac and Rho (Fig. 10, X), but equally might include inhibitors of these molecules (Fig. 10, Y). The effect of TAM67 on downstream signaling from the EGFR appears specific to the Rho-like GTPase cascade, since the ability of EGFR to activate MAPK is unimpaired in TA cells (Fig. 10). Our findings strengthen the hypothesis that AP-1 activity is essential for the invasion of malignant human epithelial cells.


The transcription factor AP-1 is required for EGF-induced activation of rho-like GTPases, cytoskeletal rearrangements, motility, and in vitro invasion of A431 cells.

Malliri A, Symons M, Hennigan RF, Hurlstone AF, Lamb RF, Wheeler T, Ozanne BW - J. Cell Biol. (1998)

A schematic representation of TAM67 inhibition of EGF-induced cytoskeletal rearrangements. (Top)  EGF treatment of A431 cells  activates Rac and subsequently Rho. In turn, activated Rac and Rho regulate  the cytoskeletal rearrangements required for cell migration and hence invasion.  EGF-induced activation of  Rac and Rho requires the  function of upstream activators(s) X and possibly decreased function of inhibitor(s) Y. (Bottom) Expression  of TAM67 inhibits EGF-induced activation of Rac and Rho and thus blocks migration  and invasion. EGF fails to activate Rac and Rho in TA cells because expression of TAM67 suppresses the expression or activity of  activators (X) and possibly increases the activity of inhibitors (Y).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132955&req=5

Figure 10: A schematic representation of TAM67 inhibition of EGF-induced cytoskeletal rearrangements. (Top) EGF treatment of A431 cells activates Rac and subsequently Rho. In turn, activated Rac and Rho regulate the cytoskeletal rearrangements required for cell migration and hence invasion. EGF-induced activation of Rac and Rho requires the function of upstream activators(s) X and possibly decreased function of inhibitor(s) Y. (Bottom) Expression of TAM67 inhibits EGF-induced activation of Rac and Rho and thus blocks migration and invasion. EGF fails to activate Rac and Rho in TA cells because expression of TAM67 suppresses the expression or activity of activators (X) and possibly increases the activity of inhibitors (Y).
Mentions: In conclusion, we propose that sustained expression of TAM67 functions as an inhibitor of a multigenic invasion program through suppressing the activity of AP-1. A subset of AP-1 target genes appear to provide molecular bridges between growth factor stimulation and activation of Rac and Rho, which in turn regulate morphological and motile responses (Fig. 10). In this respect, AP-1 target genes could include upstream activators of Rac and Rho (Fig. 10, X), but equally might include inhibitors of these molecules (Fig. 10, Y). The effect of TAM67 on downstream signaling from the EGFR appears specific to the Rho-like GTPase cascade, since the ability of EGFR to activate MAPK is unimpaired in TA cells (Fig. 10). Our findings strengthen the hypothesis that AP-1 activity is essential for the invasion of malignant human epithelial cells.

Bottom Line: Constitutively activated mutants of Rac or Rho introduced into A431 or A431 cells expressing TAM67 (TA cells) induce equivalent actin cytoskeletal rearrangements, suggesting that the effector pathways downstream of Rac and Rho required for these responses are unimpaired by sustained TAM67 expression.However, EGF-induced translocation of Rac to the cell membrane, which is associated with its activation, is defective in TA cells.Our data establish a novel link between AP-1 activity and EGFR activation of Rac and Rho, which in turn mediate the actin cytoskeletal rearrangements required for cell motility and invasion.

View Article: PubMed Central - PubMed

Affiliation: Beatson Institute for Cancer Research, Bearsden, Glasgow, G61 1BD, United Kingdom.

ABSTRACT
Human squamous cell carcinomas (SCC) frequently express elevated levels of epidermal growth factor receptor (EGFR). EGFR overexpression in SCC-derived cell lines correlates with their ability to invade in an in vitro invasion assay in response to EGF, whereas benign epidermal cells, which express low levels of EGFR, do not invade. EGF-induced invasion of SCC-derived A431 cells is inhibited by sustained expression of the dominant negative mutant of c-Jun, TAM67, suggesting a role for the transcription factor AP-1 (activator protein-1) in regulating invasion. Significantly, we establish that sustained TAM67 expression inhibits growth factor-induced cell motility and the reorganization of the cytoskeleton and cell-shape changes essential for this process: TAM67 expression inhibits EGF-induced membrane ruffling, lamellipodia formation, cortical actin polymerization and cell rounding. Introduction of a dominant negative mutant of Rac and of the Rho inhibitor C3 transferase into A431 cells indicates that EGF-induced membrane ruffling and lamellipodia formation are regulated by Rac, whereas EGF-induced cortical actin polymerization and cell rounding are controlled by Rho. Constitutively activated mutants of Rac or Rho introduced into A431 or A431 cells expressing TAM67 (TA cells) induce equivalent actin cytoskeletal rearrangements, suggesting that the effector pathways downstream of Rac and Rho required for these responses are unimpaired by sustained TAM67 expression. However, EGF-induced translocation of Rac to the cell membrane, which is associated with its activation, is defective in TA cells. Our data establish a novel link between AP-1 activity and EGFR activation of Rac and Rho, which in turn mediate the actin cytoskeletal rearrangements required for cell motility and invasion.

Show MeSH
Related in: MedlinePlus