Search

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 reactive oxygen species stress and abrogates p53-dependent inhibition of tumour growth in xenograft models, suggesting that ALOX12 is critical for p53-mediated ferroptosis. The ALOX12 gene resides on human chromosome 17p13.1, a hotspot 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 tumour suppression.

It is well established that the p53 tumor suppressor plays a crucial role in controlling cell proliferation and apoptosis upon various types of stress. There is increasing evidence showing that p53 is also critically involved in various metabolic pathways, both in tumor and normal cells. Here, we have identified a novel p53 metabolic target pantothenate kinase-1 (PANK1) via ChIP-on-chip. PanK1 catalyzes the rate-limiting step for CoA synthesis and, therefore, controls intracellular CoA content; Pank1-knockout mice exhibit defect in β-oxidation and gluconeogenesis in the liver after starvation due to insufficient CoA levels. We demonstrated that PANK1 gene is a direct transcriptional target of p53. Although DNA damage-induced p53 upregulates PanK1 expression, depletion of PanK1 expression does not affect p53-dependent growth arrest or apoptosis. Interestingly, upon glucose starvation, PanK1 expression is significantly reduced in HCT116 p53 (-/-) but not in HCT116 p53 (+/+) cells, suggesting that p53 is required to maintain PanK1 expression under metabolic stress conditions. Moreover, by using p53-mutant mice, we observed that, similar to the case in Pank1-knockout mice, gluconeogenesis is partially impaired in p53-null mice. Together, our findings show that p53 plays an important role in regulating energy homeostasis through transcriptional control of PANK1, independent of its canonical functions in apoptosis and cell cycle arrest.

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.

Human DDX11 and DDX12 are closely related genes encoding the helicases ChlR1 and ChlR2, which belong to the CHL1 DNA helicase family. Recently, it was shown that human ChlR1 interacts with components of the cohesin complex and is required for proper centromeric cohesion. To establish the function of ChlR1 in development we made a mutant mouse lacking Ddx11, the single mouse ChlR gene. The absence of Ddx11 resulted in embryonic lethality at E10.5. The mutant embryos were smaller in size, malformed and exhibited sparse cellularity in comparison to normal or heterozygous litter mates. Importantly, loss of Ddx11 resulted in the inability to form a proper placenta, indicating that ChlR1 is essential for placental formation. Detailed analysis of cells isolated from Ddx11-/- embryos revealed a G2/M cell cycle delay, an increased frequency of chromosome missegregation, decreased chromosome cohesion, and increased aneuploidy. To examine whether ChlR proteins are required for arm cohesion and for loading of the cohesin complex, further studies were preformed in ChlR1 siRNA treated cells. These studies revealed that ChlR1 is required for proper sister chromatid arm cohesion and that cohesin complexes bind more loosely to chromatin in the absence of ChlR1. Taken together, these studies provide the first data indicating that the ChlR1 helicase is essential for proper binding of the cohesin complex to both the centromere and the chromosome arms, and indicate that ChlR1 is essential for embryonic development and the prevention of aneuploidy in mammals.

The CDK11(p110) protein kinases are part of large-molecular-weight complexes that also contain RNA polymerase II, transcriptional elongation factors, and general pre-mRNA splicing factors. CDK11(p110) isoforms may therefore couple transcription and pre-mRNA splicing by their effect(s) on certain proteins required for these processes. The CDK11(p58) kinase isoform is generated from the CDK11(p110) mRNA through the use of an internal ribosome entry site in a mitosis-specific manner, suggesting that this kinase may regulate the cell cycle during mitosis. The in vivo role and necessity of CDK11(p110/p58) kinase function during mammalian development were examined by generating CDK11(p110/p58)-null mice through targeted disruption of the corresponding gene using homologous recombination. While heterozygous mice develop normally, disruption of both CDK11(p110/p58) alleles results in early embryonic lethality due to apoptosis of the blastocyst cells between 3.5 and 4 days postcoitus. Cells within these embryos exhibit both proliferative defect(s) and a mitotic arrest. These results are consistent with the proposed cellular functions of the CDK11(p110/p58) kinases and confirm that the CDK11(p110/p58) kinases are essential for cellular viability as well as normal early embryonic development.