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Distinct roles of Akt1 and Akt2 in regulating cell migration and epithelial-mesenchymal transition.

Irie HY, Pearline RV, Grueneberg D, Hsia M, Ravichandran P, Kothari N, Natesan S, Brugge JS - J. Cell Biol. (2005)

Bottom Line: In contrast, Akt1 down-regulation in IGF-IR-stimulated cells promoted dramatic neomorphic effects characteristic of an epithelial-mesenchymal transition (EMT) and enhanced cell migration induced by IGF-I or EGF stimulation.The phenotypic effects of Akt1 down-regulation were accompanied by enhanced extracellular signal-related kinase (ERK) activation, which contributed to the induction of migration and EMT.These results highlight the distinct functions of Akt isoforms in regulating growth factor-stimulated EMT and cell migration, as well as the importance of Akt1 in cross-regulating the ERK signaling pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.

ABSTRACT
The Akt family of kinases are activated by growth factors and regulate pleiotropic cellular activities. In this study, we provide evidence for isoform-specific positive and negative roles for Akt1 and -2 in regulating growth factor-stimulated phenotypes in breast epithelial cells. Insulin-like growth factor-I receptor (IGF-IR) hyperstimulation induced hyperproliferation and antiapoptotic activities that were reversed by Akt2 down-regulation. In contrast, Akt1 down-regulation in IGF-IR-stimulated cells promoted dramatic neomorphic effects characteristic of an epithelial-mesenchymal transition (EMT) and enhanced cell migration induced by IGF-I or EGF stimulation. The phenotypic effects of Akt1 down-regulation were accompanied by enhanced extracellular signal-related kinase (ERK) activation, which contributed to the induction of migration and EMT. Interestingly, down-regulation of Akt2 suppressed the EMT-like morphological conversion induced by Akt1 down-regulation in IGF-IR-overexpressing cells and inhibited migration in EGF-stimulated cells. These results highlight the distinct functions of Akt isoforms in regulating growth factor-stimulated EMT and cell migration, as well as the importance of Akt1 in cross-regulating the ERK signaling pathway.

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Related in: MedlinePlus

Down-regulation of Akt1 enhances EGF-stimulated migration and ERK activation. (A) MCF-10A cells overexpressing empty vector or Akt1 or -2 shRNA vectors were generated. Isoform-specific down-regulation was confirmed by Western analysis and migration in response to EGF stimulation was assessed. Before plating in transwell assays, cells were starved overnight in the absence of EGF. Cells were stimulated with EGF at the indicated concentrations and migration was assessed. The histogram displays a representative experiment with mean values obtained by counting 10 independent fields. Error bars represent means ± SD. (B) MCF-10A cells overexpressing empty vector control or Akt1 or -2 shRNA vectors were starved in the absence of EGF. Cells were stimulated with the indicated concentrations of EGF, lysed, and immunoblotted with the indicated antibodies.
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fig8: Down-regulation of Akt1 enhances EGF-stimulated migration and ERK activation. (A) MCF-10A cells overexpressing empty vector or Akt1 or -2 shRNA vectors were generated. Isoform-specific down-regulation was confirmed by Western analysis and migration in response to EGF stimulation was assessed. Before plating in transwell assays, cells were starved overnight in the absence of EGF. Cells were stimulated with EGF at the indicated concentrations and migration was assessed. The histogram displays a representative experiment with mean values obtained by counting 10 independent fields. Error bars represent means ± SD. (B) MCF-10A cells overexpressing empty vector control or Akt1 or -2 shRNA vectors were starved in the absence of EGF. Cells were stimulated with the indicated concentrations of EGF, lysed, and immunoblotted with the indicated antibodies.

Mentions: The phenotypes observed with Akt1 down-regulation in IGF-IR cells suggested that Akt1 has an inhibitory effect on IGF-I–triggered migration and ERK activation. To determine whether similar effects are observed when cells are stimulated by other growth factor receptors, we examined migration and ERK activation in response to EGF stimulation (Fig. 8). Endogenous levels of EGF receptor are sufficient to robustly induce these activities upon EGF stimulation. The effects of Akt isoform down-regulation was examined in the context of subsaturating EGF concentrations. Akt1 down-regulation enhanced EGF-induced ERK activation and migration. In contrast, Akt2 down-regulation inhibited EGF-stimulated transwell migration at all concentrations evaluated. This inhibition is more readily apparent as EGF, in contrast to IGF-I, robustly induces migration. Thus, Akt1 down-regulation has similar effects on ERK activation and migration when cells are stimulated by another growth factor.


Distinct roles of Akt1 and Akt2 in regulating cell migration and epithelial-mesenchymal transition.

Irie HY, Pearline RV, Grueneberg D, Hsia M, Ravichandran P, Kothari N, Natesan S, Brugge JS - J. Cell Biol. (2005)

Down-regulation of Akt1 enhances EGF-stimulated migration and ERK activation. (A) MCF-10A cells overexpressing empty vector or Akt1 or -2 shRNA vectors were generated. Isoform-specific down-regulation was confirmed by Western analysis and migration in response to EGF stimulation was assessed. Before plating in transwell assays, cells were starved overnight in the absence of EGF. Cells were stimulated with EGF at the indicated concentrations and migration was assessed. The histogram displays a representative experiment with mean values obtained by counting 10 independent fields. Error bars represent means ± SD. (B) MCF-10A cells overexpressing empty vector control or Akt1 or -2 shRNA vectors were starved in the absence of EGF. Cells were stimulated with the indicated concentrations of EGF, lysed, and immunoblotted with the indicated antibodies.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171329&req=5

fig8: Down-regulation of Akt1 enhances EGF-stimulated migration and ERK activation. (A) MCF-10A cells overexpressing empty vector or Akt1 or -2 shRNA vectors were generated. Isoform-specific down-regulation was confirmed by Western analysis and migration in response to EGF stimulation was assessed. Before plating in transwell assays, cells were starved overnight in the absence of EGF. Cells were stimulated with EGF at the indicated concentrations and migration was assessed. The histogram displays a representative experiment with mean values obtained by counting 10 independent fields. Error bars represent means ± SD. (B) MCF-10A cells overexpressing empty vector control or Akt1 or -2 shRNA vectors were starved in the absence of EGF. Cells were stimulated with the indicated concentrations of EGF, lysed, and immunoblotted with the indicated antibodies.
Mentions: The phenotypes observed with Akt1 down-regulation in IGF-IR cells suggested that Akt1 has an inhibitory effect on IGF-I–triggered migration and ERK activation. To determine whether similar effects are observed when cells are stimulated by other growth factor receptors, we examined migration and ERK activation in response to EGF stimulation (Fig. 8). Endogenous levels of EGF receptor are sufficient to robustly induce these activities upon EGF stimulation. The effects of Akt isoform down-regulation was examined in the context of subsaturating EGF concentrations. Akt1 down-regulation enhanced EGF-induced ERK activation and migration. In contrast, Akt2 down-regulation inhibited EGF-stimulated transwell migration at all concentrations evaluated. This inhibition is more readily apparent as EGF, in contrast to IGF-I, robustly induces migration. Thus, Akt1 down-regulation has similar effects on ERK activation and migration when cells are stimulated by another growth factor.

Bottom Line: In contrast, Akt1 down-regulation in IGF-IR-stimulated cells promoted dramatic neomorphic effects characteristic of an epithelial-mesenchymal transition (EMT) and enhanced cell migration induced by IGF-I or EGF stimulation.The phenotypic effects of Akt1 down-regulation were accompanied by enhanced extracellular signal-related kinase (ERK) activation, which contributed to the induction of migration and EMT.These results highlight the distinct functions of Akt isoforms in regulating growth factor-stimulated EMT and cell migration, as well as the importance of Akt1 in cross-regulating the ERK signaling pathway.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.

ABSTRACT
The Akt family of kinases are activated by growth factors and regulate pleiotropic cellular activities. In this study, we provide evidence for isoform-specific positive and negative roles for Akt1 and -2 in regulating growth factor-stimulated phenotypes in breast epithelial cells. Insulin-like growth factor-I receptor (IGF-IR) hyperstimulation induced hyperproliferation and antiapoptotic activities that were reversed by Akt2 down-regulation. In contrast, Akt1 down-regulation in IGF-IR-stimulated cells promoted dramatic neomorphic effects characteristic of an epithelial-mesenchymal transition (EMT) and enhanced cell migration induced by IGF-I or EGF stimulation. The phenotypic effects of Akt1 down-regulation were accompanied by enhanced extracellular signal-related kinase (ERK) activation, which contributed to the induction of migration and EMT. Interestingly, down-regulation of Akt2 suppressed the EMT-like morphological conversion induced by Akt1 down-regulation in IGF-IR-overexpressing cells and inhibited migration in EGF-stimulated cells. These results highlight the distinct functions of Akt isoforms in regulating growth factor-stimulated EMT and cell migration, as well as the importance of Akt1 in cross-regulating the ERK signaling pathway.

Show MeSH
Related in: MedlinePlus