Abstract
Heterozygosity of the retinoblastoma gene Rb1 elicits tumorigenesis in susceptible tissues following spontaneous loss of the remaining functional allele. Inactivation of previously studied retinoblastoma protein (pRb) targets partially inhibited tumorigenesis in Rb1+/− mice1,2,3,4,5,6. Here we report that inactivation of pRb target Skp2 (refs. 7,8) completely prevents spontaneous tumorigenesis in Rb1+/− mice. Targeted Rb1 deletion in melanotrophs ablates the entire pituitary intermediate lobe when Skp2 is inactivated. Skp2 inactivation does not inhibit aberrant proliferation of Rb1-deleted melanotrophs but induces their apoptotic death. Eliminating p27 phosphorylation on T187 in p27T187A knock-in mice reproduces the effects of Skp2 knockout, identifying p27 ubiquitination by SCFSkp2 ubiquitin ligase as the underlying mechanism for Skp2's essential tumorigenic role in this setting. RB1-deficient human retinoblastoma cells also undergo apoptosis after Skp2 knockdown; and ectopic expression of p27, especially the p27T187A mutant, induces apoptosis. These results reveal that Skp2 becomes an essential survival gene when susceptible cells incur Rb1 deficiency.
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Acknowledgements
We thank J. Cui for expert technical assistance, R. Mahmood for help with tissue preparation and histological analysis, D. Abramson and S. Jhanwar for support of retinoblastoma cell analysis, A. Koff for comments on the manuscript and A. Burns and W. Zhang for encouragement. We are grateful to T. Jacks for providing Rb1+/− mice (from L. Yamasaki and A. Iavarone) and Rb1lox/lox mice, B. Lowell and S. Chua for POMC-Cre mice, J. Roberts for p27T187A knock-in mice and F. Costantini for Rosa26YFP mice (from J. Pollard). This work was supported by grants from the National Institute of Diabetes and Digestive and Kidney Diseases and National Cancer Institute of the US National Institutes of Health to L.Z. Albert Einstein Comprehensive Cancer Research Center and Liver Research Center provided core facility support. F.B. was supported by the Training Program in Cellular and Molecular Biology and Genetics (T32 GM007491) at the Albert Einstein College of Medicine. L.Z. is a recipient of the Irma T. Hirschl Career Scientist Award.
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H.W., P.J., F.B., D.S. and L.Z. designed and performed experiments with mice mutant for Rb1, Skp2, p27 or targeted deletion of Rb1. J.L. and R.S.S. performed pathology studies. D.C. and X.X. designed and performed analyses of retinoblastoma cells; H.W. performed protein blot experiments. K.N. and K.I.N. provided Skp2+/− mice. H.W., J.L., D.C. and L.Z. wrote the paper.
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Wang, H., Bauzon, F., Ji, P. et al. Skp2 is required for survival of aberrantly proliferating Rb1-deficient cells and for tumorigenesis in Rb1+/− mice. Nat Genet 42, 83–88 (2010). https://doi.org/10.1038/ng.498
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DOI: https://doi.org/10.1038/ng.498
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