The tumor suppressor p53 plays a central role in stress responses and tumor suppression. The increasingly complex p53 network is controlled by multiple layers of mechanisms, including the genetic level, transcriptional level, and protein level. Post-translational modifications (PTMs) of p53 represent a precise and efficient form of regulation. To date, the modification of p53 by ubiquitin and ubiquitin-like proteins (UBLs) has been studied extensively, including SUMOylation, NEDDylation, FATylation, ISGylation, and the recently identified UFMylation. They affect p53 stability, conformation, localization, transcriptional activity and binding partners. Here, we review these recent discoveries and summarize our understanding of ubiquitination and UBL modifications of p53 to better comprehend the complex landscape of p53 regulation. We will discuss how the ubiquitination and UBL modifications of p53 dynamically adjust its function to respond to various stress stimuli, thereby determining cell fate.
High-grade serous ovarian carcinoma (HGSOC) is responsible for the majority of ovarian cancer-associated deaths. PARP (poly-(ADP-ribose) polymerase) inhibitors (PARPi) (olaparib, rucaparib and niraparib) have been approved in recent years to be used in both the frontline setting as maintenance therapy and in the recurrent setting for patients with ovarian cancer (OC). Previous studies have reported an increased expression of PARP1, a sensor for DNA damage, in OC; however, its compartment (epithelial tumor vs stroma)-, anatomical site (fallopian tube, omentum, ovary and serous tubal in situ carcinoma)- and histotype-specific expression have not been studied. Here, we showed that PARP1 protein levels are higher in epithelial tumors compared to adjacent non-malignant stroma at four different anatomical locations in HGSOC, with the most significant difference in PARP1 levels in omental metastases. Furthermore, we found that PARP1 protein levels are elevated in tumors relative to normal tissue in the fallopian tube, omentum and ovary in patients with HGSOC, again with the most significant difference in the omentum. We also showed that PARP1 expression is increased in a malignant and invasive stage in mouse ovarian surface epithelium cells, and that PARP1 mRNA levels are lower in mucinous histotype compared to serous histotype of epithelial OC. These findings indicate that a better understanding of compartment-, anatomical location- and histotype-specific changes in PARP1 levels in OC is needed since PARP inhibitors are currently being used in the treatment of patients with OC.
Aberrant DNA methylation is a hallmark of acute myeloid leukemia (AML). Various studies showed that t(8;21) AML presented a distinct DNA methylation profile and could be categorized into a separate cluster according to DNA methylation sequencing. Yet, there is still a lack of understanding regarding the causes and mechanisms of this phenomenon. Knowing how the DNA methylation is regulated in t(8;21) AML would enhance our understanding of leukemogenesis and may assist clinical decision-making regarding DNA methylation-targeted therapy. Herein, we summarized our current knowledge concerning DNA methylation regulation in t(8;21) AML and discussed their potential clinical significance in this article.
The ufmylation ligase-UFL1 promotes ATM activation by monoufmylating H4 at K31 in a positive-feedback loop after double-strand breaks (DSB) occur, whereas UFM1 Specific Peptidase 2 (UfSP2) suppresses ATM activation, but the mechanism of recruitment of UfSP2 to the DSB finetuning DNA damage response is still not clear. Here, we report that UfSP2 foci formation is delayed compared to UFL1 foci formation following the radiation insult. Mechanistically, UfSP2 binds to the MRN complex in absence of DSB. Irradiation-induced phosphorylation of UfSP2 by ATM leads to the dissociation of UfSP2 from the MRN complex. This phosphorylation can be removed by the phosphatase WIP1, thereby UfSP2 is recruited to the DSBs, deufmylating H4 and suppressing ATM activation. In summary, we identify a mechanism of delicately negative modulation of ATM activation by UfSP2 and rewires ATM activation pathways.