Endoplasmic reticulum stress induces G2 cell-cycle arrest via mRNA translation of the p53 isoform p53/47.

p53 downstream pathways control G1 and G2 cell-cycle arrest, DNA repair, or apoptosis. However, it is still not clear how cells differentiate the cell-biological outcome of p53 activation in response to different types of stresses. The p53/47 isoform lacks the first 39 amino acids of full-length p53 including the Mdm2 binding site and the first trans-activation domain, and tetramers including p53/47 exhibit altered activity and biochemical properties. Here we show that endoplasmic reticulum stress promotes PERK-dependent induction of p53/47 mRNA translation and p53/47 homo-oligomerization. p53/47 induces 14-3-3sigma and G2 arrest but does not affect G1 progression. This is contrary to p53FL, which promotes G1 arrest but has no effect on the G2. These results show a unique role for p53/47 in the p53 pathway and illustrate how a cellular stress leads to a defined cell-biological outcome through expression of a p53 isoform.

P53 mRNA controls p53 activity by managing Mdm2 functions.

The E3 ubiquitin ligase Mdm2 is a focal regulator of p53 tumour suppressor activity. It binds p53, promoting its polyubiquitination and degradation, and also controls p53 synthesis. However, it is not known how this dual function of Mdm2 on p53 synthesis and degradation is achieved. Here we show that the p53 mRNA region encoding the Mdm2-binding site interacts directly with the RING domain of Mdm2. This impairs the E3 ligase activity of Mdm2 and promotes p53 mRNA translation. We also show that introduction of cancer-derived single silent point-mutations in the p53 mRNA weakens its binding to Mdm2 and results in reduced p53 activity. These data are consistent with a mechanism by which changes in silent nucleotides can affect the function of the encoded protein, and indicate that Mdm2-mediated control of p53 synthesis and degradation has evolved in the p53 mRNA sequence and its encoded amino acids.

Trends in International Cancer Research Investment 2006-2018.

The International Cancer Research Partnership (ICRP) is an active network of cancer research funding organizations, sharing information about funded research projects in a common database. Data are publicly available to enable the cancer research community to find potential collaborators and avoid duplication. This study presents an aggregated analysis of projects funded by 120 partner organizations and institutes in 2006-2018, to highlight trends in cancer research funding. Overall, the partners' funding for cancer research increased from $5.562 billion (bn) US dollars (USD) in 2006 to $8.511bn USD in 2018, an above-inflation increase in funding. Analysis by the main research focus of projects using Common Scientific Outline categories showed that Treatment was the largest investment category in 2018, followed by Early Detection, Diagnosis, and Prognosis; Cancer Biology; Etiology; Control, Survivorship, and Outcomes; and Prevention. Over the 13 years covered by this analysis, research funding into Treatment and Early Detection, Diagnosis, and Prognosis had increased in terms of absolute investment and as a proportion of the portfolio. Research funding in Cancer Biology and Etiology declined as a percentage of the portfolio, and funding for Prevention and Control, Survivorship and Outcomes remained static. In terms of cancer site-specific research, funding for breast cancer and colorectal cancer had increased in absolute terms but declined as a percentage of the portfolio. By contrast, investment for brain cancer, lung cancer, leukemia, melanoma, and pancreatic cancer increased both in absolute terms and as a percentage of the portfolio.

beta-arrestin 2 oligomerization controls the Mdm2-dependent inhibition of p53.

beta-arrestins (beta-arrs), two ubiquitous proteins involved in serpentine heptahelical receptor regulation and signaling, form constitutive homo- and heterooligomers stabilized by inositol 1,2,3,4,5,6-hexakisphosphate (IP6). Monomeric beta-arrs are believed to interact with receptors after agonist activation, and therefore, beta-arr oligomers have been proposed to represent a resting biologically inactive state. In contrast to this, we report here that the interaction with and subsequent titration out of the nucleus of the protooncogene Mdm2 specifically require beta-arr2 oligomers together with the previously characterized nucleocytoplasmic shuttling of beta-arr2. Mutation of the IP6-binding sites impair oligomerization, reduce interaction with Mdm2, and inhibit p53-dependent antiproliferative effects of beta-arr2, whereas the competence for receptor regulation and signaling is maintained. These observations suggest that the intracellular concentration of beta-arr2 oligomers might control cell survival and proliferation.

The p53 mRNA-Mdm2 interaction.

The E3 ligase Mdm2 is a key regulator of p53 activity via a complex regulatory feedback system that involves all levels of expression control including transcription, mRNA translation and protein degradation. Best known is the effect of p53 on Mdm2 transcription and the capacity of Mdm2 to target p53 for degradation, but more recently the role of Mdm2 as a positive regulator of p53 activity has also started to emerge. Mdm2 stimulates p53 mRNA translation by binding the p53 mRNA and, interestingly, this interaction also suppresses Mdm2's capacity to promote p53 polyubiquitination and degradation. Another interesting aspect of the p53 mRNA-Mdm2 interaction is that the p53 mRNA sequence encoding the amino acids which bind the N-terminus of Mdm2 is the same that interacts with the Mdm2 RING domain. Indeed, the regulatory elements for controlling Mdm2-dependent expression of p53 are derived from the same p53 genomic sequence. In addition, the RNA binding and the E3 ligase domain of Mdm2 overlap, indicati that the two functions of Mdm2 to control p53 synthesis and degradation have co-evolved in parallel in both p53 and Mdm2. Here we illustrate how the p53-Mdm2 protein-protein and p53 mRNA-Mdm2 interactions affect Mdm2-mediated control of p53 expression using the Phe19Ala p53 mutant. We discuss how the new insights into the regulation of p53 expression levels can help to shed light on the origin of this elegant feedback system and on the function of Mdm2 isoforms.

Stress-dependent changes in the properties of p53 complexes by the alternative translation product p53/47.

P53 plays a key role in the cellular response to damage exposure and in preventing the development of human cancers. Activation of p53 results in changes in the expression of a large number of gene products. However, relatively little is still known how p53 activation differentiates between different types of damages in different types of tissues or how this triggers either an apoptotic response or cell cycle arrest and DNA repair. The p53 message is translated into two products with distinct activities and stabilities through alternative mechanisms of initiation. P53/47 is initiated 40 codons down stream of the full length p53 and does not include the binding site for the E3 ubiquitin ligase Mdm2 or the transactivation domain I but retains the capacity to form p53 hetero- and homo-oligomers. Here we report that p53/47 controls the folding, the oligomerisation and the post-translational modification of p53 complexes and that it diversifies p53 properties in a cell stress-dependent fashion. P21 expression, for example, is under normal conditions not affected by p53/47 but is induced 18-fold after treatment of cells with the DNA damaging drug doxorubicin. This is accompanied by the recruitment of p53/47 to the p21 promoter.

The novel platinum(IV) complex LA-12 induces p53 and p53/47 responses that differ from the related drug, cisplatin.

The platinum(II)-based complex cisplatin is one of the most frequently used antitumour agents; however, a high incidence of harmful side effects and the frequent emergence of acquired resistance are the major clinical problems. The novel platinum(IV)-based complex LA-12 exhibits a high efficacy against cancer cell lines, including cisplatin-insensitive cells, but the mechanisms by which LA-12 perturbs cell growth are unclear. We tested the effects of LA-12 on the p53 response and demonstrate that LA-12 induces unique changes in the profile of gene expression compared with cisplatin and doxorubicin. Furthermore, the ability of LA-12 to disrupt cellular proliferation is greatly enhanced by the expression of p53 and p53/47 indicating both p53-dependent and p53-independent effects of LA-12. Exposure of the human cancer cell lines H1299, A2780, BT549 and BT474 to LA-12 alters the expression of p53 and p53/47 in both a time-dependent and dose-dependent manner. Treatment of cells with a low concentration of the drug results in accumulation of p53 and p53/47 concomitant with their posttranslational modification, whereas a high dose results in the disappearance of both the forms of p53. The distinct p53 activation profile of LA-12 compared with cisplatin and doxorubicin provides a molecular explanation for the ability of this drug to treat cisplatin-resistant cells and indicates its potential usefulness as an alternative antitumour agent in first-line therapy or as a second-line therapy in patients with acquired cisplatin resistance.