Revisiting the Function of p21CDKN1A in DNA Repair: The Influence of Protein Interactions and Stability

Abstract

The p21CDKN1A protein is an important player in the maintenance of genome stability through its function as a cyclin-dependent kinase inhibitor, leading to cell-cycle arrest after genotoxic damage. In the DNA damage response, p21 interacts with specific proteins to integrate cell-cycle arrest with processes such as transcription, apoptosis, DNA repair, and cell motility. By associating with Proliferating Cell Nuclear Antigen (PCNA), the master of DNA replication, p21 is able to inhibit DNA synthesis. However, to avoid conflicts with this process, p21 protein levels are finely regulated by pathways of proteasomal degradation during the S phase, and in all the phases of the cell cycle, after DNA damage. Several lines of evidence have indicated that p21 is required for the efficient repair of different types of genotoxic lesions and, more recently, that p21 regulates DNA replication fork speed. Therefore, whether p21 is an inhibitor, or rather a regulator, of DNA replication and repair needs to be re-evaluated in light of these findings. In this review, we will discuss the lines of evidence describing how p21 is involved in DNA repair and will focus on the influence of protein interactions and p21 stability on the efficiency of DNA repair mechanisms.

From Double-Strand Break Recognition to Cell-Cycle Checkpoint Activation: High Content and Resolution Image Cytometry Unmasks 53BP1 Multiple Roles in DNA Damage Response and p53 Action

“…The average number of detected PLA spots grew 6 h after irradiation, whereas its value was significantly reduced at the 24-h time-point, even if the average content of the two proteins was still high, and p21, similarly to p53, presented a highly diffused localization in the nucleoplasm without evidence of local accumulation. The observed trend for the 53BP1–p21 PLA spots perfectly correlated with the DDR activity measured by γH2A.X: at 6 h, the interaction was maximum and localized at DD foci, in perfect agreement with the DNA repair activity exerted by p21 [ 34 ], whereas at 24 h, the reduced number of DDR foci led to the dramatic reduction in the number of PLA spots per cell.…”

The role of prelamin A post-translational maturation in stress response and 53BP1 recruitment

“…In this context, p21 plays a fundamental role as a negative regulator of DNA synthesis across a lesion ( Soria and Gottifredi, 2010 ). In fact, p21 binding to PCNA impedes PCNA ubiquitination and PCNA-polymerase η interaction ( Ticli et al, 2022 ). Here we show that the high amount of p21 elicited by unscheduled accumulation of prelamin A forms at the very early stage of DNA damage response ( Mattioli et al, 2018 and, 2019 ) affects PCNA dynamics.…”

“…However, lower levels of phosphorylated H2AX were detected in cells that accumulated non-farnesylated prelamin A (Figure 5A). Moreover, ubiquitination of PCNA, which is required at this stage to permit trans-lesion DNA synthesis (Cazzalini et al, 2003;Paiano et al, 2021;Ticli et al, 2022), occurred in untreated cells, while it was significantly less efficient in the presence of Frontiers in Cell and Developmental Biology frontiersin.org non-farnesylated prelamin A (Figure 5A). As p21-PCNA interaction is modulated at this stage through PCNA ubiquitination, which influences p21 degradation (Zlatanou et al, 2011), we also investigated p21 levels.…”

“…This condition triggers upregulation of p21 during stress response. In this respect, it is worth considering that p21 decrease is necessary at the early stages of DNA damage response to allow ubiquitination of PCNA and H2A histone phosphorylation at damaged DNA, while transient p21 increase is required to avoid replication of damaged DNA sequences and in all steps to modulate DNA damage repair mechanisms ( Ticli et al, 2022 ). However, fine tuning of p21 levels is important as unscheduled increase of p21 is a main determinant of geroconversion ( Blagosklonny, 2014 ; Cenni et al, 2020a ).…”

“…We also tested the effect of aberrant prelamin A accumulation at the very early stages of stress response, when only mature lamin A is detectable in nuclei. Soon after oxidative stress induction, PCNA mono-ubiquitination occurs in response to DNA damage, an event that requires reduction of p21 levels and in turn triggers gamma-H2AX histone activation ( Ticli et al, 2022 ). Our data show that aberrant accumulation of prelamin A forms at the very early stages of stress response alters timing of PCNA ubiquitination and reduces H2AX phosphorylation.…”