Although p53–mediated cell–cycle arrest, senescence and apoptosis serve as critical barriers to cancer development, emerging evidence suggests that the metabolic activities of p53 are also important. Here we show that p53 inhibits cystine uptake and sensitizes cells to ferroptosis, a non–apoptotic form of cell death, by repressing expression of SLC7A11, a key component of the cystine/glutamate antiporter. Notably, p533KR, an acetylation–defective mutant that fails to induce cell–cycle arrest, senescence and apoptosis, fully retains the ability to regulate SLC7A11 expression and induce ferroptosis upon reactive oxygen species (ROS)–induced stress. Analysis of mutant mice shows that these non–canonical p53 activities contribute to embryonic development and the lethality associated with loss of Mdm2. Moreover, SLC7A11 is highly expressed in human tumours, and its overexpression inhibits ROS–induced ferroptosis and abrogates p533KR–mediated tumour growth suppression in xenograft models. Our findings uncover a new mode of tumour suppression based on p53 regulation of cystine metabolism, ROS responses and ferroptosis.

Summary Cell-cycle arrest, apoptosis, and senescence are widely accepted as major mechanisms by which p53 inhibits tumor formation. Nevertheless, it remains unclear whether they are rate-limiting steps in tumor suppression. Here, we have generated mice bearing lysine to arginine mutations at one (p53K117R) or three (p533KR; K117R+K161R+K162R) of the critical p53 acetylation sites. While p53K117R/K117R cells are competent for p53-mediated cell-cycle arrest and senescence, but not apoptosis, all three of these processes are ablated in p533KR/3KR cells. Surprisingly, unlike p53-null mice, which rapidly succumb to spontaneous thymic lymphomas, early-onset tumor formation does not occur in either p53K117R/K117R or p533KR/3KR animals. Notably, p533KR retains the ability to modulate energy metabolism and reactive oxygen species (ROS) production by regulating metabolic p53 target genes. These findings underscore the crucial role of acetylation in differentially modulating p53 responses and suggest that unconventional activities of p53, such as metabolic regulation and antioxidant function, are critical for suppression of early-onset spontaneous tumorigenesis.

Summary It is well established that ferroptosis is primarily controlled by glutathione peroxidase 4 (GPX4). Surprisingly, we observed that p53 activation modulates ferroptotic responses without apparent effects on GPX4 function. Instead, ALOX12 inactivation diminishes p53-mediated ferroptosis induced by ROS stress and abrogates p53-dependent inhibition of tumor growth in xenograft models, suggesting that ALOX12 is critical for p53-mediated ferroptosis. The ALOX12 gene resides on human chromosome 17p13.1, a hot spot of monoallelic deletion in human cancers. Loss of one ALOX12 allele is sufficient to accelerate tumorigenesis in Eμ-Myc lymphoma models. Moreover, ALOX12 missense mutations from human cancers abrogate its ability to oxygenate polyunsaturated fatty acids and to induce p53-mediated ferroptosis. Notably, ALOX12 is dispensable for ferroptosis induced by erastin or GPX4 inhibitors; conversely, ACSL4 is required for ferroptosis upon GPX4 inhibition but dispensable for p53-mediated ferroptosis. Thus, our study identifies an ALOX12-mediated, ACSL4-independent ferroptosis pathway that is critical for p53-dependent tumor suppression.