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PKB/Akt phosphorylates p27, impairs nuclear import of p27 and opposes p27-mediated G1 arrest

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Abstract

Mechanisms linking mitogenic and growth inhibitory cytokine signaling and the cell cycle have not been fully elucidated in either cancer or in normal cells. Here we show that activation of protein kinase B (PKB)/Akt, contributes to resistance to antiproliferative signals and breast cancer progression in part by impairing the nuclear import and action of p27. Akt transfection caused cytoplasmic p27 accumulation and resistance to cytokine-mediated G1 arrest. The nuclear localization signal of p27 contains an Akt consensus site at threonine 157, and p27 phosphorylation by Akt impaired its nuclear import in vitro. Akt phosphorylated wild-type p27 but not p27T157A. In cells transfected with constitutively active AktT308DS473D (PKBDD), p27WT mislocalized to the cytoplasm, but p27T157A was nuclear. In cells with activated Akt, p27WT failed to cause G1 arrest, while the antiproliferative effect of p27T157A was not impaired. Cytoplasmic p27 was seen in 41% (52 of 128) of primary human breast cancers in conjunction with Akt activation and was correlated with a poor patient prognosis. Thus, we show a novel mechanism whereby Akt impairs p27 function that is associated with an aggressive phenotype in human breast cancer.

NOTE: In the version of the article initially published online, the abstract contained one extraneous sentence. This error has been corrected in the HTML and PDF versions. The abstract will appear correctly in the forthcoming print issue.

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Figure 1: Constitutive activation of Akt in TGF-β-resistant cell lines.
Figure 2: PI3K inhibition restores TGF-β response in resistant cells and Akt transfection mediates TGF-β resistance.
Figure 3: Cytoplasmic mislocalization of p27 in TGF-β-resistant, Akt activated cells.
Figure 4: p27 is a substrate of Akt and binds Akt in vivo.
Figure 5: T157 phosphorylation impairs nuclear import of p27.
Figure 6: Cytoplasmic mislocalization of p27 in primary breast cancers is associated with Akt activation and poor patient outcome.

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Change history

  • 23 September 2002

    This was incorrect in AOP version but corrected in print. See note for changes made.

Notes

  1. NOTE: In the version of the article initially published online, the following errors appeared. These errors have been corrected in the HTML and PDF versions, and will be corrected in the forthcoming print issue. Abstract: The third sentence should be deleted. Page 1, 2nd column: In the first sentence of the first paragraph, the words "effect on" should be "effector". Page 2, Fig. 2b: In the center panel, bottom blot, lanes 2 and 3 are transposed. Page 3, 1st column: At the end of the first, partial paragraph, "(Fig. 2d and e)" should be "(Fig. 2d)". Page 4, Fig. 4a: In the left panel, "Akt" should be moved up to align with the unlabelled positivity indicators. Page 6, left column: In the first, partial paragraph, the second, full sentence should be deleted. Page 7, left column: In the first sentence of the second paragraph, the first P-value stated, "P = 0.0018" should be "P = 0.003". References: Ref. 13 is incorrect. The correct reference is "Florenes, V.A. et al. Interleukin-6 dependent induction of the cyclin dependent kinase inhibitor p21WAF1/C1P1 is lost during progression of human malignant melanoma. Oncogene 18, 1023-1032 (1999)."

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Acknowledgements

We thank J. Woodgett for PKB/Akt vectors; M. Stampfer for 184 and 184A1L5R cells; K. Robertson for construction of the p27T157A mutant; L. Attisano, D. Dumont and J. Woodgett for helpful discussions; and C. Arteaga and G. Viglietto for sharing unpublished results. J.L. is supported by a US Army DOD Breast Cancer Research Program Pre-Doctoral Award. J.M.S. is supported by the US Army DOD Breast Cancer Research Program, the Burrough's Wellcome Fund and by Cancer Care Ontario. This work was funded by the Canadian Breast Cancer Research Initiative.

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Correspondence to Joyce M. Slingerland.

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Liang, J., Zubovitz, J., Petrocelli, T. et al. PKB/Akt phosphorylates p27, impairs nuclear import of p27 and opposes p27-mediated G1 arrest. Nat Med 8, 1153–1160 (2002). https://doi.org/10.1038/nm761

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