Correspondence: gm89@leicester.ac.uk p73 and p63 are two homologs of the tumor suppressive transcription factor p53. Given the high degree of structural similarity shared by the p53 family members, p73 and p63 can bind and activate transcription from the majority of the p53-responsive promoters. Besides overlapping functions shared with p53 (i.e., induction of apoptosis in response to cellular stress), the existence of extensive structural variability within the family determines unique roles for p63 and p73. Their crucial and specific functions in controlling development and differentiation are well exemplified by the p63 and p73 knockout mouse phenotypes. Here, we describe the contribution of p63 and p73 to human pathology with emphasis on their roles in tumorigenesis and development.

SummaryTAp63α, a homolog of the p53 tumor suppressor, is a quality control factor in the female germline. Remarkably, already undamaged oocytes express high levels of the protein, suggesting that TAp63α's activity is under tight control of an inhibitory mechanism. Biochemical studies have proposed that inhibition requires the C-terminal transactivation inhibitory domain. However, the structural mechanism of TAp63α inhibition remains unknown. Here, we show that TAp63α is kept in an inactive dimeric state. We reveal that relief of inhibition leads to tetramer formation with ∼20-fold higher DNA affinity. In vivo, phosphorylation-triggered tetramerization of TAp63α is not reversible by dephosphorylation. Furthermore, we show that a helix in the oligomerization domain of p63 is crucial for tetramer stabilization and competes with the transactivation domain for the same binding site. Our results demonstrate how TAp63α is inhibited by complex domain-domain interactions that provide the basis for regulating quality control in oocytes.

The survival rate of cancer patients is steadily increasing, owing to more efficient therapies. Understanding the molecular mechanisms of chemotherapy-induced premature ovarian insufficiency (POI) could identify targets for prevention of POI. Loss of the primordial follicle reserve is the most important cause of POI, with the p53 family member p63 being responsible for DNA-damage-induced apoptosis of resting oocytes. Here, we provide the first detailed mechanistic insight into the activation of p63, a process that requires phosphorylation by both the priming kinase CHK2 and the executioner kinase CK1 in mouse primordial follicles. We further describe the structural changes induced by phosphorylation that enable p63 to adopt its active tetrameric conformation and demonstrate that previously discussed phosphorylation by c-Abl is not involved in this process. Inhibition of CK1 rescues primary oocytes from doxorubicin and cisplatin-induced apoptosis, thus uncovering a new target for the development of fertoprotective therapies.

p73 and p63, the two ancestral members of the p53 family, are involved in neurogenesis, epithelial stem cell maintenance and quality control of female germ cells. The highly conserved oligomerization domain (OD) of tumor suppressor p53 is essential for its biological functions, and its structure was believed to be the prototype for all three proteins. However, we report that the ODs of p73 and p63 differ from the OD of p53 by containing an additional a-helix that is not present in the structure of the p53 OD. Deletion of this helix causes a dissociation of the OD into dimers; it also causes conformational instability and reduces the transcriptional activity of p73. Moreover, we show that ODs of p73 and p63 strongly interact and that a large number of different heterotetramers are supported by the additional helix. Detailed analysis shows that the heterotetramer consisting of two homodimers is thermodynamically more stable than the two homotetramers. No heterooligomerization between p53 and the p73/p63 subfamily was observed, supporting the notion of functional orthogonality within the p53 family. p53, a well-known tumor suppressor that is mutated in more than 50% of all human tumors, induces genes leading either to cell-cycle arrest or to apoptosis. The discovery of two proteins with a high sequence identity to p53, called p63 and p73, has sparked speculations that tumor suppression is carried out by the combined action of several members of this protein family, for example, by direct interaction through heterooligomerization. Knockout mouse studies with p63 and p73, the two ancestral members, 1 have shown functional roles distinct from p53: p63 is essential for maintaining epithelial stem cells 2,3 and for protecting the genomic stability of oocytes, 4 whereas p73 is involved in neurogenesis, sensory pathways and homeostatic control. 5 p73 is further known as an important inducer of apoptosis in response to DNA damage. 6 Although only few mutations of p63 and p73 have been found in human tumors so far, overexpression of p63 is often observed in squamous cell carcinoma, 7-10 which has been shown to suppress p73-dependent apoptosis. 11 Among all p53 family members, including those from invertebrate species, the DNA binding domain is the most conserved domain, 12-15 followed by the oligomerization domain (OD), which is indispensable for the biological function of all p53 protein family members. [16][17][18] It is a structural domain that forms a tetramer, and mutations within the OD that inhibit tetramerization of p53 result in greatly reduced transcriptional activity. 19 In addition, several protein-protein interactions and posttranslational modifications require the tetrameric state as well, 16 and mutations in the OD of p53 that prevent oligomerization have been identified in human cancers. 20,21 Owing to its functional importance, the OD of p53 has been the target of several structure determination projects. 22,23 The p53 tetramer consists of a dimer of dimers, with each monomer contributing one b-strand and o...

Mammalian oocytes are arrested in the dictyate stage of meiotic prophase I for long periods of time, during which the high concentration of the p53 family member TAp63α sensitizes them to DNA damage-induced apoptosis. TAp63α is kept in an inactive and exclusively dimeric state but undergoes rapid phosphorylation-induced tetramerization and concomitant activation upon detection of DNA damage. Here we show that the TAp63α dimer is a kinetically trapped state. Activation follows a spring-loaded mechanism not requiring further translation of other cellular factors in oocytes and is associated with unfolding of the inhibitory structure that blocks the tetramerization interface. Using a combination of biophysical methods as well as cell and ovary culture experiments we explain how TAp63α is kept inactive in the absence of DNA damage but causes rapid oocyte elimination in response to a few DNA double strand breaks thereby acting as the key quality control factor in maternal reproduction.DOI: http://dx.doi.org/10.7554/eLife.13909.001