Erratum: Senescence and tumour clearance is triggered by p53 restoration in murine liver carcinomas

Abstract

Although cancer arises from a combination of mutations in oncogenes and tumour suppressor genes, the extent to which tumour suppressor gene loss is required for maintaining established tumours is poorly understood. p53 is an important tumour suppressor that acts to restrict proliferation in response to DNA damage or deregulation of mitogenic oncogenes, by leading to the induction of various cell cycle checkpoints, apoptosis or cellular senescence 1,2 . Consequently, p53 mutations increase cell proliferation and survival, and in some settings promote genomic instability and resistance to certain chemotherapies 3 . To determine the consequences of reactivating the p53 pathway in tumours, we used RNA interference (RNAi) to conditionally regulate endogenous p53 expression in a mosaic mouse model of liver carcinoma 4,5 . We show that even brief reactivation of endogenous p53 in p53-deficient tumours can produce complete tumour regressions. The primary response to p53 was not apoptosis, but instead involved the induction of a cellular senescence program that was associated with differentiation and the upregulation of inflammatory cytokines. This program, although producing only cell cycle arrest in vitro, also triggered an innate immune response that targeted the tumour cells in vivo, thereby contributing to tumour clearance. Our study indicates that p53 loss can be required for the maintenance of aggressive carcinomas, and illustrates how the cellular senescence program can act together with the innate immune system to potently limit tumour growth.p53 mutations are common in human liver cancer 6 , which is typically highly aggressive and resistant to non-surgical therapies. To determine the requirement for p53 loss in the maintenance of such carcinomas, we used reversible RNAi 7 to control p53 in a chimaeric liver cancer mouse model (Fig. 1a) 4,5 . Purified embryonic liver progenitor cells (hepatoblasts) were transduced with retroviruses expressing oncogenic ras (HrasV12), the tetracycline transactivator protein tTA ('tet-off') and a tet-responsive p53 miR30 design short hairpin RNA (shRNA; Supplementary Fig. 1a) 7,8 , and seeded into the livers of athymic nude mice following intrasplenic injection 4,5 . To facilitate in vivo imaging, the oncogenic ras retrovirus co-expressed green fluorescent protein (GFP) and, in some experiments, hepatoblasts were also co-transduced with a luciferase reporter.p53 expression was efficiently suppressed in the absence of doxycycline (Dox) and rapidly restored following Dox addition ( Supplementary Fig. 1b, c). On transplantation into the livers of recipient mice, hepatoblast populations co-expressing Ras and the conditional p53 shRNA rapidly produced invasive hepatocarcinomas in the absence of Dox (Fig. 1b), whereas cells expressing each vector alone did not (data not shown). These tumours were GFP-positive and, if expressing luciferase, could be visualized externally by bioluminescence imaging (Fig. 1b).

Fluctuations in p53 Signaling Allow Escape from Cell-Cycle Arrest

“…In response to DNA damage, proliferating cells can either repair the damage and resume growth, or activate anti-proliferative programs such as cell death (apoptosis) or senescence, a state characterized by the long-term enforcement of cell cycle arrest and the loss of recovery potential (Fig 1A). While pro- apoptosis therapy has been used for several decades as a tool for destroying the growth of cancerous cells, recent studies also highlighted the therapeutic potential of pro-senescence cancer therapy (Collado and Serrano, 2010; Nardella et al, 2011; Xue et al, 2011). However, as opposed to apoptosis, which is a terminal cell fate, senescing cells require continuous activation of the pathways responsible for maintaining the arrested state (Beauséjour et al, 2003; Dirac and Bernards, 2003) (Figure 1A).…”

Cellular Senescence: Aging, Cancer, and Injury

“…Interestingly, in recent years, several regulators of PICS have been identified. For instance, the inhibition of S-phase kinase-associated protein 2 (Skp2) restores senescence in PTEN-and p53-deficent tumors through the upregulation of p27 (351). SMAD4 inactivation or overexpression of COUP-TFII, a SMAD4 inhibitor, also promotes the bypass of PICS by allowing the transcription of cyclin D1 in Ptennull tumors (263).…”

Senolytics: A Translational Bridge Between Cellular Senescence and Organismal Aging

“…Since it is likely that even a small percentage of senescent cells can promote substantial deleterious effects, there may be natural mechanisms that clear these senescent cells in vivo to maintain overall fitness. One primary response to p53 activation in murine liver carcinoma was found to be the accumulation of senescent cells, which were subsequently shown to be cleared by the innate immune response (Xue et al, 2011). NK cells were also found to eliminate senescent cells in vivo by perforin (Prf) mediated granule exocytosis (Sagiv et al, 2013) and Prf1 −/− mice showed a 4X accumulation of senescent cells and a 21% decrease in median lifespan, which was alleviated by senescent cell clearance (Ovadya et al, 2018).…”