Cytoplasmic localization of p21Cip1/WAF1 by Akt-induced phosphorylation in HER-2/neu-overexpressing cells

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Abstract

Amplification or overexpression of HER-2/neu in cancer cells confers resistance to apoptosis and promotes cell growth. The cellular localization of p21Cip1/WAF1 has been proposed to be critical either in promoting cell survival or in inhibiting cell growth. Here we show that HER-2/neu-mediated cell growth requires the activation of Akt, which associates with p21Cip1/WAF1 and phosphorylates it at threonine 145, resulting in cytoplasmic localization of p21Cip1/WAF1. Furthermore, blocking the Akt pathway with a dominant-negative Akt mutant restores the nuclear localization and cell-growth-inhibiting activity of p21Cip1/WAF1. Our results indicate that HER-2/neu induces cytoplasmic localization of p21Cip1/WAF1 through activation of Akt to promote cell growth, which may have implications for the oncogenic activity of HER-2/neu and Akt.

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Figure 1: The Akt pathway is required for HER-2/neu-mediated cell proliferation.
Figure 2: Threonine 145 of p21Cip1/WAF1 is phosphorylated in vivo.
Figure 3: Akt interacts with p21Cip1/WAF1 and phosphorylates it at threonine 145.
Figure 4: Akt alters the cellular localization of p21Cip1/WAF1.
Figure 5: Cellular localization of endogenous p21Cip1/WAF1.
Figure 6: HER-2/neu activates Akt and induces cytoplasmic localization of p21Cip1/WAF1 in breast tumours.
Figure 7: Growth-inhibiting activities of p21Cip1/WAF1 mutants.
Figure 8: Model for HER-2/neu-induced cytoplasmic localization of p21Cip1/WAF1 through activation of Akt.

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Acknowledgements

We thank D. Yu, R. B. Arlinghaus and W. H. Klein for critical comments on the manuscript. This work was supported by grants from the National Institutes of Health (to M-C.H.), by a SPORE grant in ovarian cancer (to M-C.H.), and by the Nellie Connally Breast Cancer Research Fund at the M. D. Anderson Cancer Center (M-C.H.). B.P.Z. is a recipient of a postdoctoral fellowship from the US Department of Defense Breast Cancer Research.

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Correspondence to Mien-Chie Hung.

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