Skp2 is required for survival of aberrantly proliferating Rb1-deficient cells and for tumorigenesis in Rb1+/− mice

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+/− mice. 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.

[1]  P. Pandolfi,et al.  p27 deficiency desensitizes Rb−/− cells to signals that trigger apoptosis during pituitary tumor development , 2003, Oncogene.

[2]  F. Bauzon,et al.  Disrupting Skp2-cyclin A interaction with a blocking peptide induces selective cancer cell killing , 2007, Molecular Cancer Therapeutics.

[3]  M. Vooijs,et al.  Flp-mediated tissue-specific inactivation of the retinoblastoma tumor suppressor gene in the mouse , 1998, Oncogene.

[4]  James M. Roberts,et al.  Cyclin E-CDK2 is a regulator of p27Kip1. , 1997, Genes & development.

[5]  Michele Pagano,et al.  An Rb-Skp2-p27 pathway mediates acute cell cycle inhibition by Rb and is retained in a partial-penetrance Rb mutant. , 2004, Molecular cell.

[6]  Chiaki Takahashi,et al.  Genetic Interaction between Rb and K-ras in the Control of Differentiation and Tumor Suppression , 2004, Molecular and Cellular Biology.

[7]  F. McCormick,et al.  Skp2 suppresses p53-dependent apoptosis by inhibiting p300. , 2008, Molecular cell.

[8]  M. Kitagawa,et al.  Targeted disruption of Skp2 results in accumulation of cyclin E and p27Kip1, polyploidy and centrosome overduplication , 2000, The EMBO journal.

[9]  Frederick A. Dick,et al.  Retinoblastoma protein and anaphase-promoting complex physically interact and functionally cooperate during cell-cycle exit , 2007, Nature Cell Biology.

[10]  James M. Roberts,et al.  Testing the importance of p27 degradation by the SCFskp2 pathway in murine models of lung and colon cancer , 2006, Proceedings of the National Academy of Sciences.

[11]  R. Bronson,et al.  E2F3 Loss Has Opposing Effects on Different pRB-Deficient Tumors, Resulting in Suppression of Pituitary Tumors but Metastasis of Medullary Thyroid Carcinomas , 2003, Molecular and Cellular Biology.

[12]  B. Lowell,et al.  Leptin Receptor Signaling in POMC Neurons Is Required for Normal Body Weight Homeostasis , 2004, Neuron.

[13]  R. Weinberg,et al.  Effects of an Rb mutation in the mouse , 1992, Nature.

[14]  T. Jacks,et al.  Loss of E2F-1 reduces tumorigenesis and extends the lifespan of Rb1(+/−) mice , 1998, Nature Genetics.

[15]  M. Pagano,et al.  Deregulated proteolysis by the F-box proteins SKP2 and β-TrCP: tipping the scales of cancer , 2008, Nature Reviews Cancer.

[16]  Chiaki Takahashi,et al.  Nras loss induces metastatic conversion of Rb1-deficient neuroendocrine thyroid tumor , 2006, Nature Genetics.

[17]  James M. Roberts,et al.  A mouse knock-in model exposes sequential proteolytic pathways that regulate p27Kip1 in G1 and S phase , 2001, Nature.

[18]  C. Wang,et al.  F-box protein Skp2: a novel transcriptional target of E2F , 2006, Oncogene.

[19]  A. Iavarone,et al.  Id2 Mediates Tumor Initiation, Proliferation, and Angiogenesis in Rb Mutant Mice , 2005, Molecular and Cellular Biology.

[20]  T. Jacks,et al.  Acute mutation of retinoblastoma gene function is sufficient for cell cycle re-entry , 2003, Nature.

[21]  D. Cobrinik,et al.  Rb induces a proliferative arrest and curtails Brn-2 expression in retinoblastoma cells , 2006, Molecular Cancer.

[22]  S. Jhanwar,et al.  Retinoblastoma Has Properties of a Cone Precursor Tumor and Depends Upon Cone-Specific MDM2 Signaling , 2009, Cell.

[23]  Joseph B. Rayman,et al.  E2F4 loss suppresses tumorigenesis in Rb mutant mice. , 2002, Cancer cell.

[24]  Shankar Srinivas,et al.  Cre reporter strains produced by targeted insertion of EYFP and ECFP into the ROSA26 locus , 2001, BMC Developmental Biology.

[25]  R. Bronson,et al.  A dynamic switch in Rb+/− mediated neuroendocrine tumorigenesis , 2004, Oncogene.

[26]  James M. Roberts,et al.  A Skp2 autoinduction loop and restriction point control , 2007, The Journal of cell biology.