Transcription-independent functions of p53 in DNA repair pathway selection

p53-deficient cancer cells hyperactivate DNA double-strand break repair pathways to overcome chemotherapeutic damage and augment survival

BACKGROUND

p53 deficiency in cancer is associated with chemoresistance and cancer progression. However, the precise role of p53 in regulating DDR in the context of chemoresistance is still unclear.

METHODS AND RESULTS

In the present study, we investigated the regulatory role of p53 on the cellular recovery potential upon transient DNA damage. p53 deficiency promotes cell survival following transient DNA damage induction. During recovery, p53 deficient cells display temporary S/G2/M arrest, returning to normal cell cycle profile, while p53 proficient cells remain permanently arrested in the S-phase. Additionally, colony formation assay revealed 50% clonogenicity in p53-proficient cells, while p53-deficient cells showed 90% clonogenicity. Chemoresistance also correlated with accelerated DNA repair in p53-deficient cells. Since doxorubicin induces DNA double-strand breaks, whose repair is driven by two major pathways: homology-directed repair and nonhomologous end joining, we measured their activity during the recovery period. During the early recovery period, both pathways were activated irrespective of p53 expression status. However, during the late recovery time point, NHEJ and HDR activities returned to basal in p53-deficient cells, while their activity was significantly reduced in p53-proficient cells. NHEJ inhibitor Ku57788 could overcome the chemoresistance in p53-deficient cells.

CONCLUSION

Thus, our findings suggest that sustained DDR promotes chemoresistance and enhanced survival in p53-deficient cancer cells.

Lipid Transfer Proteins and PI4KIIα Initiate Nuclear p53-Phosphoinositide Signaling

Phosphoinositide (PIP n ) messengers are present in non-membranous regions of nuclei where they are assembled into a phosphatidylinositol (PI) 3-kinase (PI3K)/Akt pathway that is distinct from the cytosolic membrane-localized pathway. In the nuclear pathway, PI kinases/phosphatases bind the p53 tumor suppressor protein (wild-type and mutant) to generate p53-PIP n complexes (p53-PIP n signalosome) that activate Akt by a PI3,4,5P 3 -dependent mechanism in non-membranous regions of the nucleus. This pathway is dependent on a source of nuclear PIP n s that is poorly characterized. Here we report that a subset of PI transfer proteins (PITPs), which transport PI between membranes to enable membrane-localized PIP n synthesis, also interact with p53 in the nucleus upon genotoxic stress. Class I PITPs (PITPα/β) specifically supply the PI required for the generation of p53-PIP n complexes and subsequent signaling in the nucleus. Additionally, the PI 4-kinase PI4KIIα binds to p53 and the PITPs to catalyze the formation of p53-PI4P. p53-PI4P is then sequentially phosphorylated to synthesize p53-PIP n complexes that regulate p53 stability, nuclear Akt activation and genotoxic stress resistance. In this way, PITPα/β and PI4KIIα bind p53 and collaborate to initiate p53-PIP n signaling by mechanisms that require PI transfer by PITPα/β and the catalytic activity of PI4KIIα. Moreover, the identification of these critical upstream regulators of p53-PIP n signaling point to PITPα/β and PI4KIIα as novel therapeutic targets in this pathway for diseases like cancer.

Significance statement

PI transfer proteins and a PI 4-kinase initiate nuclear p53-phosphoinositide signaling in membrane-free regions to promote stress resistance.

Activity of DNA Repair Systems in the Cells of Long-Lived Rodents and Bats

Damages of various origin accumulated in the genomic DNA can lead to the breach of genome stability, and are considered to be one of the main factors involved in cellular senescence. DNA repair systems in mammalian cells ensure effective damage removal and repair of the genome structure, therefore, activity of these systems is expected to be correlated with high maximum lifespan observed in the long-lived mammals. This review discusses current results of the studies focused on determination of the DNA repair system activity and investigation of the properties of its key regulatory proteins in the cells of long-lived rodents and bats. Based on the works discussed in the review, it could be concluded that the long-lived rodents and bats in general demonstrate high efficiency in functioning and regulation of DNA repair systems. Nevertheless, a number of questions around the study of DNA repair in the cells of long-lived rodents and bats remain poorly understood, answers to which could open up new avenues for further research.

Evaluation of histological and ultrastructural changes provoked by prenatal tramadol on postnatal cortical cerebellar neuronal development in rats: possible implication of Ki67, GFAP and MicroRNA-7/P53 signalling trajectories

Tramadol is a novel centrally acting analgesic. Despite, its implementation during pregnancy may impair neuronal survival and synaptic development in neonatal cerebella. The current investigation assessed the histological and ultrastructural alterations in postnatal cortical cerebellar neuronal development induced by prenatal tramadol. 30 offsprings were divided to control group I: fifteen pups born to mothers given saline from D10 till D21 of gestation. Tramadol-treated group II: fifteen pups born to mothers received tramadol HCL (50 mg/kg/day) from D10 till D21 of gestation. Pups were categorized into three subgroups (a, b, and c) and offered for sacrifice on the seventh, fourteenth and twenty-first post-natal days. Light microscopic examination revealed the overcrowding and signs of red degeneration affecting purkinje cell layer. Neurodegenerative signs of both purkinje and granule cell neurons were also confirmed by TEM in form of chromatin condensation, dilated Golgi channels, disrupted endoplasmic reticulum, marked infolding of the nuclear envelope and decrease in granule cell precursors. In addition, the astrocytic processes and terminal nerve axons appeared with different degrees of demyelination and decreased number of oligodendrocytes and degenerated mitochondria. Furthermore, group II exhibited an increase in P53 immune expression. The area percentage of apoptotic cells detected by TUNEL assay was significantly increased. Besides to the significant decrease of Ki67 immunoreactivity in the stem neuronal cell progenitors. Quantitative PCR results showed a significant decline in micro RNA7 gene expression in tramadol treated groups resulting in affection of multiple target genes in P53 signaling pathways, improper cortical size and defect in neuronal development.

The inverse association between DNA gaps and HbA1c levels in type 2 diabetes mellitus

Naturally occurring DNA gaps have been observed in eukaryotic DNA, including DNA in nondividing cells. These DNA gaps are found less frequently in chronologically aging yeast, chemically induced senescence cells, naturally aged rats, D-galactose-induced aging model rats, and older people. These gaps function to protect DNA from damage, so we named them youth-associated genomic stabilization DNA gaps (youth-DNA-gaps). Type 2 diabetes mellitus (type 2 DM) is characterized by an early aging phenotype. Here, we explored the correlation between youth-DNA-gaps and the severity of type 2 DM. Here, we investigated youth-DNA-gaps in white blood cells from normal controls, pre-DM, and type 2 DM patients. We found significantly decreased youth-DNA-gap numbers in the type 2 DM patients compared to normal controls (P = 0.0377, P = 0.0018 adjusted age). In the type 2 DM group, youth-DNA-gaps correlate directly with HbA1c levels. (r = - 0.3027, P = 0.0023). Decreased youth-DNA-gap numbers were observed in patients with type 2 DM and associated with increased HbA1c levels. Therefore, the decrease in youth-DNA-gaps is associated with the molecular pathogenesis of high blood glucose levels. Furthermore, youth-DNA-gap number is another marker that could be used to determine the severity of type 2 DM.

Decreased Alu methylation in type 2 diabetes mellitus patients increases HbA1c levels

INTRODUCTION

Alu hypomethylation is a common epigenetic process that promotes genomic instability with aging phenotypes, which leads to type 2 diabetes mellitus (type 2 DM). Previously, our results showed significantly decreased Alu methylation levels in type 2 DM patients. In this study, we aimed to investigate the longitudinal changes in Alu methylation levels in these patients.

RESULTS

We observed significantly decreased Alu methylation levels in type 2 DM patients compared with normal (p = 0.0462). Moreover, our findings demonstrated changes in Alu hypomethylation over a follow-up period within the same individuals (p < 0.0001). A reduction in Alu methylation was found in patients with increasing HbA1c levels (p = 0.0013) and directly correlated with increased HbA1c levels in type 2 DM patients (r = -0.2273, p = 0.0387).

CONCLUSIONS

Alu methylation in type 2 DM patients progressively decreases with increasing HbA1c levels. This observation suggests a potential association between Alu hypomethylation and the underlying molecular mechanisms of elevated blood glucose. Furthermore, monitoring Alu methylation levels may serve as a valuable biomarker for assessing the clinical outcomes of type 2 DM.