Limits...
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.

Show MeSH

Related in: MedlinePlus

ERK activation is enhanced by Akt1 down-regulation. (A) Neo or IGF-IR cells with isoform-specific down-regulation of Akt were grown in monolayer cultures, starved, and stimulated with 2% horse serum ± 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted with the indicated antibodies. (B) IGF-IR cells overexpressing empty vector control, Akt1 shRNA, or both Akt1 and -2 shRNA vectors were starved and stimulated with 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted as indicated.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2171329&req=5

fig5: ERK activation is enhanced by Akt1 down-regulation. (A) Neo or IGF-IR cells with isoform-specific down-regulation of Akt were grown in monolayer cultures, starved, and stimulated with 2% horse serum ± 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted with the indicated antibodies. (B) IGF-IR cells overexpressing empty vector control, Akt1 shRNA, or both Akt1 and -2 shRNA vectors were starved and stimulated with 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted as indicated.

Mentions: Hyperactivation of the ERK/MAP kinase pathway, via either activation of Ras or a growth factor receptor, plays a cooperative role in many models of EMT (for review see Grunert et al., 2003). Akt1 overexpression has previously been reported to suppress ERK activation (Rommel et al., 1999; Zimmermann and Moelling, 1999). Therefore, we examined the effect of down-regulating Akt1 or -2 on activation of ERK signaling. Immunoblotting with antibody to activated ERK1/2 showed that Akt1 down-regulation caused an activation of ERK in nonstimulated cells and enhanced ERK activation under IGF-I–stimulated conditions (Fig. 5 A). Enhanced ERK activation was also observed with Akt1 down-regulation in cells overexpressing Akt2 (Fig. S2 B). In contrast, down-regulation of Akt2 in IGF-IR cells had no effect on ERK1/2 activation. Cells in which both Akt1 and -2 were down-regulated exhibited enhanced ERK activation, comparable with that observed with Akt1 down-regulation alone (Fig. 5 B).


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)

ERK activation is enhanced by Akt1 down-regulation. (A) Neo or IGF-IR cells with isoform-specific down-regulation of Akt were grown in monolayer cultures, starved, and stimulated with 2% horse serum ± 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted with the indicated antibodies. (B) IGF-IR cells overexpressing empty vector control, Akt1 shRNA, or both Akt1 and -2 shRNA vectors were starved and stimulated with 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted as indicated.
© Copyright Policy
Related In: Results  -  Collection

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

fig5: ERK activation is enhanced by Akt1 down-regulation. (A) Neo or IGF-IR cells with isoform-specific down-regulation of Akt were grown in monolayer cultures, starved, and stimulated with 2% horse serum ± 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted with the indicated antibodies. (B) IGF-IR cells overexpressing empty vector control, Akt1 shRNA, or both Akt1 and -2 shRNA vectors were starved and stimulated with 100 ng/ml IGF-I in the absence of EGF. Lysates were immunoblotted as indicated.
Mentions: Hyperactivation of the ERK/MAP kinase pathway, via either activation of Ras or a growth factor receptor, plays a cooperative role in many models of EMT (for review see Grunert et al., 2003). Akt1 overexpression has previously been reported to suppress ERK activation (Rommel et al., 1999; Zimmermann and Moelling, 1999). Therefore, we examined the effect of down-regulating Akt1 or -2 on activation of ERK signaling. Immunoblotting with antibody to activated ERK1/2 showed that Akt1 down-regulation caused an activation of ERK in nonstimulated cells and enhanced ERK activation under IGF-I–stimulated conditions (Fig. 5 A). Enhanced ERK activation was also observed with Akt1 down-regulation in cells overexpressing Akt2 (Fig. S2 B). In contrast, down-regulation of Akt2 in IGF-IR cells had no effect on ERK1/2 activation. Cells in which both Akt1 and -2 were down-regulated exhibited enhanced ERK activation, comparable with that observed with Akt1 down-regulation alone (Fig. 5 B).

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