The atypical cyclin-like protein Spy1 overrides p53-mediated tumour suppression and promotes susceptibility to breast tumourigenesis

Abstract

BackgroundBreast cancer is the most common cancer to affect women and one of the leading causes of cancer-related deaths. Proper regulation of cell cycle checkpoints plays a critical role in preventing the accumulation of deleterious mutations. Perturbations in the expression or activity of mediators of cell cycle progression or checkpoint activation represent important events that may increase susceptibility to the onset of carcinogenesis. The atypical cyclin-like protein Spy1 was isolated in a screen for novel genes that could bypass the DNA damage response. Clinical data demonstrates that protein levels of Spy1 are significantly elevated in ductal and lobular carcinoma of the breast. We hypothesized that elevated Spy1 would override protective cell cycle checkpoints and support the onset of mammary tumourigenesis.MethodsWe generated a transgenic mouse model driving expression of Spy1 in the mammary epithelium. Mammary development, growth characteristics and susceptibility to tumourigenesis were studied. In vitro studies were conducted to investigate the relationship between Spy1 and p53.ResultsWe found that in the presence of wild-type p53, Spy1 protein is held ‘in check’ via protein degradation, representing a novel endogenous mechanism to ensure protected checkpoint control. Regulation of Spy1 by p53 is at the protein level and is mediated in part by Nedd4. Mutation or abrogation of p53 is sufficient to allow for accumulation of Spy1 levels resulting in mammary hyperplasia. Sustained elevation of Spy1 results in elevated proliferation of the mammary gland and susceptibility to tumourigenesis.ConclusionsThis mouse model demonstrates for the first time that degradation of the cyclin-like protein Spy1 is an essential component of p53-mediated tumour suppression. Targeting cyclin-like protein activity may therefore represent a mechanism of re-sensitizing cells to important cell cycle checkpoints in a therapeutic setting.

The Cyclin-Like Protein SPY1 Overrides Reprogramming Induced Senescence Through EZH2 Mediated H3K27me3

“…Quantification of immunofluorescence for p16, p21 and p53 protein levels (Figure 5A; left) indicate that the overexpression of SPY1 during reprogramming significantly decreases the number of cells positive for each one of the mentioned CKIs (Figure 5A; right). It is notable that a reduction in p53 has also been observed in established cell lines when overexpressing Spy1 using western blot analysis 42 . Although the knockdown of SPY1 resulted in an increase of p16, p21 and p53 protein, the trend was not statistically significant (Figure 5A; right).…”

Unraveling the Potential Role of NEDD4-like E3 Ligases in Cancer

“…NEDD4’s carcinogenic effect in NSCLC cells can be due to the inactivation of PTEN [ 97 ]. NEDD4 is the key pro-oncogenic ligase that mediates the ubiquitination of PTEN; however, NEDD4L is mainly involved in the degradation of the tumor suppressor gene p53 [ 98 , 99 , 100 ]. Moreover, in breast and prostate cancer cells, NEDD4 might enhance cell proliferation and migration by regulating the PTEN/Akt signaling pathway [ 101 ].…”

RINGO/Speedy proteins, a family of non-canonical activators of CDK1 and CDK2

“…The activation of ERa has been proposed to induce RingoA/Spy1 upregulation in MCF-7 cells, which might in turn control the ERK1/2 mediated phosphorylation of ERa on Ser118, and sensitivity to tamoxifen tested by injection of RingoA/Spy1 overexpressing MCF-7 cells in zebrafish [53]. RingoA/Spy1 levels have been also proposed to be controlled by p53 in HC11, MDA-MB-231 and HEK293 cells in which RingoA/Spy1 is overexpressed, but there is no evidence that the endogenous protein follows the same dynamics [54]. It should be noted that the quality of the loading controls in some of these experiments is not optimal, and further work would be needed to confirm the statements.…”