p53 suppresses BRCA2-stimulated ATPase and strand exchange functions of human RAD51

Elevated apoptosis and abnormal apoptosis signaling of regulatory T cells in patients with systemic lupus erythematosus

In systemic lupus erythematosus (SLE), immune tolerance is influenced by defects in naturally occurring T cells (Tregs). To investigate the apoptosis rate of Tregs and their suppressive activity in patients with SLE and then to recognize the genes and signaling pathways that cause Treg apoptosis. FACS was used to assess the frequency and apoptosis rates of Tregs in 48 SLE patients and 28 normal controls (NCs). Coculture of Tregs with CD4⁺CD25^-CD127^dim/- T cells was used to assess the suppressive activity of Tregs. Microarray analysis was used to generate unstimulated Tregs gene expression profiles from very high activity patients with SLE and NCs. Real-time PCR was used to confirm differential gene expression. In patients with SLE, the frequency of Tregs was substantially reduced compared to Tregs from NCs. Furthermore, Tregs from SLE patients had an elevated rate of apoptosis and a lower suppressing ability than Tregs from NCs. Tregs apoptosis was negatively associated with the total count of Tregs and positively related to disease activity. Unstimulated Tregs gene expression profiles from patients with recent-onset SLE revealed a biological response that can cause apoptosis, partially triggered by stress, DNA damage, and cytokine stimulation. The discovery of pathway-specific expression signatures is a significant step forward in understanding how Tregs defects contribute to the pathogenesis of SLE. Our findings may contribute to the development of new strategies for treating SLE based on abnormal Tregs apoptosis and restoring immune homeostasis in patients with SLE.

Investigation on the Genomic Characterization of Uterine Sarcoma for rAd-p53 Combined with Chemotherapy Treatment

The aim is to investigate the genomic characterization of uterine sarcoma for rAd-p53 (Gendicine^®) combined with chemotherapy treatment. We recently published an article on 12 cases of uterine sarcomas, which were treated with rAd-p53 combined with chemotherapy. We found that rAd-p53 combined with chemotherapy is effective for various uterine sarcomas. Pretreatment pathological specimens of four uterine sarcoma patients were collected from the above recent clinical research and numbered 1-4A/B. Tumor samples were subjected to targeted sequencing by using a 416 genes panel. We profiled the mutation spectrum and tumor mutation burden in the tumors, identified mutated genes, and explored their gene function. We also verified the p53 protein expression using immunohistochemistry. We identified a total of 30 mutated genes that were found from the next-generation sequencing test results. The average number of mutated genes was up to seven in the five samples. TP53 gene was mutated in two of the four patients, No. 1 and No. 4B. They are c.C833G (p.P278R) missense mutation and a point mutation (C141*) that result in a premature stop codon. We did not find a mutated TP53 gene in the other two cases, but we identified mutated genes, including CREBBP, LYN, CDKN2A, and JAK2, which were located upstream of the TP53 gene; they may have an impact on TP53. We also identified 11 additional genes which are involved in p53-related signaling pathways or have interaction with p53. Compared to solid tumor mutational burden (TMB) distribution, none of their TMB was ranking in the top 25%. Mutant p53 protein expression was positive in two specimens. Our results demonstrated that the TP53 signaling pathway plays an important role in uterine sarcoma tumorigenesis. TP53 and the upstream genes such as CREBBP, LYN, CDKN2A, and JAK2 may be involved in the genomic characterization for rAd-p53 (Gendicine) combined with chemotherapy in uterine sarcoma. Besides, the average amount of mutated genes from every patient is large.

Rotundic acid induces Cas3-MCF-7 cell apoptosis through the p53 pathway

In the present study, the functions and mechanisms of rotundic acid (RA) underlying its induction of apoptosis in caspase-3-transfected MCF-7 human breast cancer cells (Cas3-MCF-7 cells) were investigated. RA induced apoptosis in Cas3-MCF-7 cells more efficiently compared with that in MCF-7 cells transfected with control plasmid. The results from an MTT assay demonstrated that RA effectively inhibited Cas3-MCF-7 cell viability in a dose-dependent manner and induced cell apoptosis via caspase-3 activity within 12 to 48 h. Western blotting and fluorescence-activated cell sorting demonstrated that RA initiated Cas3-MCF-7 cell apoptosis via p53 activation. The silencing of the p53 gene in the Cas3-MCF-7 cell line led to decreased RA-induced Cas3-MCF-7 cell caspase-3 activity and cell apoptosis. Collectively, the results of the present study indicate that caspase-3 serves a critical function in rotundic acid-induced apoptosis, and suggest that caspase-3 deficiency may contribute to the chemotherapy-resistance of breast cancer. Reconstitution of caspase-3 sensitizes MCF-7 breast cancer cells to chemotherapy. RA has the potential for development as a novel drug combined with reconstitution of caspase-3 gene therapy for the treatment of human breast cancer with caspase-3 deficiency.

Human RAD52 protein regulates homologous recombination and checkpoint function in BRCA2 deficient cells

Cancer cells exhibit HR defects, increased proliferation and checkpoint aberrations. Tumour suppressor proteins, BRCA2 and p53 counteract such aberrant proliferation by checkpoint regulation. Intriguingly, chemo-resistant cancer cells, exhibiting mutated BRCA2 and p53 protein survive even with increased DNA damage accumulation. Such cancer cells show upregulation of RAD52 tumour suppressor protein implying that RAD52 might be providing survival advantage to cancer cells. To understand this paradoxical condition of a tumour suppressor protein facilitating cancer cell survival, in the current study, we investigate the role of RAD52 overexpression in BRCA2 deficient cells. We provide evidence that RAD52 protein alleviates HR inhibition imposed by p53 in BRCA2 deficient cells. In addition, we study the role of RAD52 protein during short replication stress in BRCA2 deficient cells. BRCA2 deficient cells exhibit excessive origin firing and checkpoint evasion in the presence of prevailing DNA damage. Interestingly, overexpression of RAD52 rescues the excessive origin firing and checkpoint defects observed in BRCA2 deficient cells, indicating RAD52 protein compensates for the loss of BRCA2 function. We show that RAD52 protein, just as BRCA2, interacts with pCHK1 checkpoint protein and helps maintain the checkpoint control in BRCA2 deficient cells during DNA damage response.

A comprehensive analysis of BRCA2 gene: focus on mechanistic aspects of its functions, spectrum of deleterious mutations, and therapeutic strategies targeting BRCA2-deficient tumors

BRCA2is the main susceptibility gene known to be involved in the pathogenesis of breast cancer. It plays an important role in maintaining the genome stability by homologous recombination through DNA double-strand breaks repairing, by interacting with various other proteins including RAD51, DSS1, RPA, MRE11, PALB2, and p53. BRCA2-deficient cells show the abnormalities of chromosome number. BRCA2 is also found to be involved in centrosome duplication specifically in the metaphase to anaphase transition. Inactivation or depletion of BRCA2 leads to centrosome amplification that results in unequal separation of chromosomes. BRCA2 localizes with central spindle and midbody during telophase and cytokinesis. Inactivation or depletion of BRCA2 leads to multinucleation of cell. Around 2000 mutations have been reported in BRCA2 gene. BRCA2-deficient tumors are being taking into consideration for targeted cancer therapy by using different inhibitors like poly ADP-ribose polymerase and thymidylate synthase. The present review focusses on the role of BRCA2 in various critical cellular processes based on the mechanistic approaches. Mutations reported in the BRCA2 gene in various ethnic groups till date have also been compiled with an insight into the functional aspects of these alterations. The therapeutic strategies for targeting BRCA2-deficient tumors have also been targeted.

Anticancer effects of liriodenine on the cell growth and apoptosis of human breast cancer MCF-7 cells through the upregulation of p53 expression

Liriodenine has wide pharmacological functions in phytochemistry, pharmacology and antitumor activities. The anticancer effects of liriodenine on the cell growth and apoptosis of human breast cancer MCF-7 cells, and the underlying mechanisms, are yet to be elucidated. Therefore, the present study investigated the anticancer effects of liriodenine on the cell growth and apoptosis of human breast cancer MCF-7 cells. We used MTT assay to measure cell growth, and flow cytometer and DAPI staining was used to analyze cell apoptosis. Then, Western blot analysis was executed to measure B-cell lymphoma-2 protein (Bcl-2), cyclin D1, vascular endothelial growth factor (VEGF), and p53 protein expression. The effect of liriodenine induced significant apoptosis and suppression of cell growth of the MCF-7 cells. Furthermore, the potential mechanism underlying its antitumor effect on MCF-7 cells may result from activation of caspase-3 activity, Bcl-2, cyclin D1 and VEGF, and promotion of p53 protein expression in MCF-7 cells. Therefore, the present results indicated that the anticancer effects of liriodenine suppress cell growth and induce the apoptosis of human breast cancer MCF-7 cells through inhibition of Bcl-2, cyclin D1 and VEGF expression, and upregulation of p53 expression. Therefore, liriodenine may be a potential therapy for the treatment of human breast cancer.

Influence of Human p53 on Plant Development

Mammalian p53 is a super tumor suppressor and plays a key role in guarding genome from DNA damage. However, p53 has not been found in plants which do not bear cancer although they constantly expose to ionizing radiation of ultraviolet light. Here we introduced p53 into the model plant Arabidopsis and examined p53-conferred phenotype in plant. Most strikingly, p53 caused early senescence and fasciation. In plants, fasciation has been shown as a result of the elevated homologous DNA recombination. Consistently, a reporter with overlapping segments of the GUS gene (1445) showed that the frequency of homologous recombination was highly induced in p53-transgenic plants. In contrast to p53, SUPPRESSOR OF NPR1-1 INDUCIBLE 1 (SNI1), as a negative regulator of homologous recombination in plants, is not present in mammals. Comet assay and clonogenic survival assay demonstrated that SNI1 inhibited DNA damage repair caused by either ionizing radiation or hydroxyurea in human osteosarcoma U2OS cancer cells. RAD51D is a recombinase in homologous recombination and functions downstream of SNI1 in plants. Interestingly, p53 rendered the sni1 mutants madly branching of inflorescence, a phenotype of fasciation, whereas rad51d mutant fully suppressed the p53-induced phenotype, indicating that human p53 action in plant is mediated by the SNI1-RAD51D signaling pathway. The reciprocal species-swap tests of p53 and SNI1 in human and Arabidopsis manifest that these species-specific proteins play a common role in homologous recombination across kingdoms of animals and plants.

Uncovering the basis of ATP hydrolysis activity in purified human p53 protein: a reinvestigation

p53 is one of the most well studied tumor suppressor proteins and regarded as the guardian of the genome. The protein mediates cell-cycle arrest, apoptosis in response to myriads of cellular stresses including DNA damage via its transcriptional as well as non-transcriptional roles. ATP binding/hydrolysis by p53 had been implicated in its DNA binding functions. However, till date, no ATP binding/hydrolysis domains have been mapped in p53. In the current study, we have reinvestigated the ATP hydrolysis activity associated with recombinant human p53 protein expressed and purified from E.coli. We confirmed the source of ATPase activity using various deletion constructs of p53 and an In-gel ATPase assay followed by LC-ESI-MS/MS analysis of the activity band. The activity was associated with Hsp70 homologue in E.coli, DnaK, a known interactor of p53. We clarify that wildtype human p53, expressed in E. coli BL21 (DE3) strain, carries no ATPase activity.

Acetylation of lysine 382 and phosphorylation of serine 392 in p53 modulate the interaction between p53 and MDC1 in vitro

Occurrence of DNA damage in a cell activates the DNA damage response, a survival mechanism that ensures genomics stability. Two key members of the DNA damage response are the tumor suppressor p53, which is the most frequently mutated gene in cancers, and MDC1, which is a central adaptor that recruits many proteins to sites of DNA damage. Here we characterize the in vitro interaction between p53 and MDC1 and demonstrate that p53 and MDC1 directly interact. The p53-MDC1 interaction is mediated by the tandem BRCT domain of MDC1 and the C-terminal domain of p53. We further show that both acetylation of lysine 382 and phosphorylation of serine 392 in p53 enhance the interaction between p53 and MDC1. Additionally, we demonstrate that the p53-MDC1 interaction is augmented upon the induction of DNA damage in human cells. Our data suggests a new role for acetylation of lysine 382 and phosphorylation of serine 392 in p53 in the cellular stress response and offers the first evidence for an interaction involving MDC1 that is modulated by acetylation.