Adenovirus-mediated p53AIP1 gene transfer as a new strategy for treatment of p53-resistant tumors

TP53AIP1 induce autophagy via the AKT/mTOR signaling pathway in the breast cancer cells

Breast cancer ranks the first in the incidence of female cancer and is the most common cancer threatening the life and health of women worldwide.Tumor protein p53-regulated apoptosis-inducing protein 1 (TP53AIP1) is a pro-apoptotic gene downstream of p53. However, the role of TP53AIP1 in BC needs to be investigated. In vitro and in vivo experiments were conducted to assess the biological functions and associated mechanisms. Several bioinformatics analyses were made, CCK8 assay, wound healing, transwell assays, colony formation assay, EDU, flow cytometry, Immunofluorescence, qRT-PCR and Western-blotting were performed. In our study, we discovered that BC samples had low levels of TP53AIP1 expression, which correlated with a lower survival rate in BC patients. When TP53AIP1 was up-regulated, it caused a decrease in cell proliferation, migration, and invasion. It also induced epithelial-to-mesenchymal transition (EMT) and protective autophagy. Furthermore, the over-expression of TP53AIP1 suppressed tumor growth when tested in vivo. We also noticed that TP53AIP1 up-regulation resulted in decreased levels of phosphorylation in AKT and mTOR, suggesting a mechanistic role. In addition, we performed functional rescue experiments where the activation of AKT was able to counteract the impact of TP53AIP1 on the survival and autophagy in breast cancer cell lines. This suggests that TP53AIP1 acts as an oncogene by controlling the AKT/mTOR pathway. These findings reveal TP53AIP1 as a gene that suppresses tumor growth and triggers autophagy through the AKT/mTOR pathway in breast cancer cells. As a result, TP53AIP1 presents itself as a potential target for novel therapeutic approaches in treating breast cancer.

Truncating mutations of TP53AIP1 gene predispose to cutaneous melanoma

Genetic predisposition to cutaneous malignant melanoma (CMM) involves highly penetrant predisposing genes and low and intermediate penetrant predisposing alleles. However, the missing heritability in (CMM) is still high. For such and in order to identify new genetic factors for CMM, we conducted an exome sequencing study in high-risk CMM patients. Two rounds of exome sequencing were successively performed in 33 and 27 high-risk patients. We focused on genes carrying rare nonsense, frameshift, and splice variants (allelic frequency <1%) that were present in both series of exomes. An extension study was then conducted in a large cohort (1 079 CMM patients and 1 230 Caucasian ethnically matched healthy controls), and the inactivating variants frequency was compared between groups using two-sided Fisher exact test. Two TP53AIP1 truncating mutations were identified in four patients: a frameshift c.63_64insG, p.Q22Afs*81 in two patients from the same family and in the proband of a second family; and a nonsense mutation c.95 C > A, p.Ser32Stop in a patient with multiple CMMs. In all patients, TP53AIP1 truncating variants were strongly associated with CMM risk (two-sided Fisher exact test = 0.004, OR = 3.3[1.3-8.5]). Additionally, we showed that TP53AIP1 mRNA was strongly down-regulated throughout different phases of melanoma progression. TP53AIP1 gene is a TP53 target which plays a key role by inducting apoptosis in response to UV-induced DNA damage. Constitutional mutations of TP53AIP1 had previously been involved in susceptibility to prostate cancer. Our results show that constitutional truncating TP53AIP1 mutations predispose to CMM in the French population. Replication studies in other populations should be performed.

Shifting p53-induced senescence to cell death by TIS21(/BTG2/Pc3) gene through posttranslational modification of p53 protein

Cellular senescence and apoptosis can be regulated by p53 activity, although the underlying mechanism of the switch between the two events remains largely unknown. Cells exposed to cancer chemotherapy can escape to senescence phenotype rather than undergoing apoptosis. By employing adenoviral transduction of p53 or TIS21 genes, we observed shifting of p53 induced-senescence to apoptosis in EJ bladder cancer cells, which express H-RasV12 and mutant p53; transduction of p53 increased H-RasV12 expression along with senescence phenotypes, whereas coexpression with TIS21 (p53+TIS21) induced cell death rather than senescence. The TIS21-mediated switch of senescence to apoptosis was accompanied by nuclear translocation of p53 protein and its modifications on Ser-15 and Ser-46 phosphorylation and acetylations on Lys-120, -320, -373 and -382 residues. Mechanistically, TIS21(/BTG2) regulated posttranslational modification of p53 via enhancing miR34a and Bax expressions as opposed to inhibiting SIRT1 and Bcl2 expression. At the same time, TIS21 increased APAF-1 and p53AIP1 expressions, but inhibited the interaction of p53 with iASPP. In vitro tumorigenicity was significantly reduced in the p53+TIS21 expresser through inhibiting micro-colony proliferation by TIS21. Effect of TIS21 on the regulation of p53 activity was confirmed by knockdown of TIS21 expression by RNA interference. Therefore, we suggest TIS21 expression as an endogenous cell death inducer at the downstream of p53 gene, which might be useful for intractable cancer chemotherapy.

Anti-apoptotic roles for the mutant p53R248Q through suppression of p53-regulated apoptosis-inducing protein 1 in the RA-derived fibroblast-like synoviocyte cell line MH7A

We previously reported that somatic mutations in the p53 gene accumulated at a higher frequency in AID(activation induced cytidine deaminase)(+) RA-FLS, which may result in the malfunction of p53, causing the tumor-like properties of RA-FLS. Among the p53 mutations identified from 3 sources of AID(+) RA-FLS, we focused on the p53R248Q mutation because it was reported to enhance the invasiveness of lung cancer cells and to have dominant-negative activity for pro-apoptotic molecules. We obtained cDNA encoding the p53R248Q mutant and introduced it into the MH7A RA-FLS cell line. P53R248Q dramatically suppressed the expression of the pro-apoptotic molecule p53AIP1 even under oxidative stress, which normally upregulates p53AIP1, leading to apoptosis. Moreover, overexpression of p53AIP1 increased apoptosis, whereas p53AIP1 knockdown rescued the cells from apoptosis. Together, these studies indicate the critical role of p53AIP1 under DNA damaging stresses for cell fate determination in RA-FLS containing the p53R248Q mutation.

Reconstitution of human MCF-7 breast cancer cells with caspase-3 does not sensitize them to action of CDK inhibitors

Human MCF-7 breast cancer cells are resistant to pro-apoptotic stimuli due to caspase-3 inactivation. On the other hand, they should be sensitive to agents like selective pharmacological inhibitors of cyclin-dependent kinases (CDKs) that (re)activate p53 tumor suppressor protein because they harbor intact p53 pathways. In this study we examined whether reconstitution of caspase-3 in MCF-7 cells sensitizes them to inhibitors of CDKs, by analyzing the effects of roscovitine (ROSC) and olomoucine (OLO), two closely related selective pharmacological CDK inhibitors, on both mother MCF-7 cells and a secondary mutant line, MCF-7.3.28 that stably expresses human caspase-3. The results show that ROSC is, as expected, much more potent than OLO. Surprisingly; however, ROSC and OLO reduced proliferation of parental MCF-7 cells more strongly than caspase-3-proficient counterparts. Both inhibitors arrest human breast cancer cells at the G(2)-phase of the cell cycle. Analysis of cell-cycle regulators by immunoblotting revealed that ROSC strongly induces p53 protein activity by inducing its phosphorylation at Ser46 in the MCF-7 cells lacking caspase-3, but not in caspase-3-proficient cells. Furthermore, reconstitution of caspase-3 in MCF-7 cells neither elevates the mitochondrial apoptosis rate nor significantly increases caspases activity upon ROSC treatment. However, the stabilization of p53 in response to DNA damaging agents is the same in both caspase negative and positive MCF-7 cells. Cytotoxic agents induce caspase-3-dependent apoptosis in caspase-3-proficient cells. These results indicate that reconstitution of MCF-7 cancer cells with caspase-3 sensitize them to the action of DNA damaging agents but not to ATP-like pharmacological inhibitors of CDKs.

Adenovirus Ad-p53AIP1-mediated gene therapy and its regulation of p53-MDM2 interactions

We generated replication-defective adenovirus Ad-p53AIP1 and studied its anti-tumor efficacy both in vitro and in vivo. We demonstrated that Ad-p53AIP1 infection elicited high levels of p53AIP1 expression in cancer cells. We also found that Ad-p53AIP1 expression induced marked apoptosis and cell cycle arrest in HepG2 cells. Moreover, Ad-p53AIP1 infection significantly inhibited the tumorigenesis of 4T1 mouse mammary cancer cells in vivo. In particular, we discovered that p53AIP1 overexpression up-regulated the protein levels of p53 in HepG2 cells, which was accompanied by down-regulation of MDM2 mRNA and protein, suggesting an interaction between MDM2 and p53 in p53AIP1-induced apoptosis and cell cycle arrest. Our data demonstrated the feasibility of Ad-p53AIP1-mediated cancer gene therapy. p53AIP1-induced up-regulation of p53 protein through MDM2 suggests that p53AIP1 gene therapy may be more advantageous in tumors expressing high levels of oncoprotein MDM2 or having a mutation in MDM2 inhibitor p16INK4.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

The potential role of DFNA5, a hearing impairment gene, in p53-mediated cellular response to DNA damage

The tumor suppressor p53 plays a crucial role in the cellular response to DNA damage by transcriptional activation of numerous downstream genes. Although a considerable number of p53 target genes have been reported, the precise mechanism of p53-regulated tumor suppression still remains to be elucidated. Here, we report a novel role of the DFNA5 gene in p53-mediated etoposide-induced cell death. The DFNA5 gene has been previously reported to be responsible for autosomal-dominant, nonsyndromic hearing impairment. The expression of the DFNA5 gene was strongly induced by exogenous and endogenous p53. The chromatin immunoprecipitation assay indicated that a potential p53-binding sequence is located in intron 1 of the DFNA5 gene. Furthermore, the reporter gene assay revealed that the sequence displays p53-dependent transcriptional activity. The ectopic expression of DFNA5 enhanced etoposide-induced cell death in the presence of p53; however, it was inhibited in the absence of p53. Finally, the expression of DFNA5 mRNA was remarkably induced by gamma-ray irradiation in the colon of p53(+/+) mice but not in that of p53(-/-) mice. These results suggest that DFNA5 plays a role in the p53-regulated cellular response to genotoxic stress probably by cooperating with p53.

Identification of p53-46F as a super p53 with an enhanced ability to induce p53-dependent apoptosis

More than half of human cancers contain mutations in the tumor suppressor protein p53, most of which accumulate in the DNA binding domain of the protein. Here we report the identification of a mutant p53, designated p53-46F, in which Ser-46 is replaced with phenylalanine. In vitro, adenovirus-mediated transduction of the p53-46F gene induced apoptosis more efficiently than wild-type p53 in a number of cancer cell lines, whereas Ser-15 phosphorylation of p53-46F was enhanced in all cancer cell lines examined. Moreover, the expression level of the cell cycle inhibitor p21/WAF1 was decreased in cell lines infected with adenovirus p53-46F (Ad-p53-46F). p53-46F caused a more enhanced level of transcriptional activation of several p53-target genes, including Noxa, p53AIP1 and p53RFP, compared with wild-type p53. In vivo, adenovirus-mediated gene transfer of p53-46F enhanced apoptosis, thus suppressing tumor growth of a lung cancer cell line more effectively than wild-type p53 or p53-121F, another p53 mutant. Collectively, our data suggest that p53-46F is an active version of p53 that demonstrates enhanced induction of p53-dependent apoptosis. This is probably mediated by upregulated transactivation of genes downstream of p53, increased Ser-15 phosphorylation and a decrease in p21/WAF1 levels. We propose p53-46F as an alternative candidate to wild-type p53 for use in developing new therapeutic strategies for the treatment of cancer.

Roscovitine-induced up-regulation of p53AIP1 protein precedes the onset of apoptosis in human MCF-7 breast cancer cells

We reported recently that roscovitine arrested human MCF-7 cancer cells at G2-M phase of the cell cycle and concomitantly induced apoptosis. After roscovitine treatment, the level of wild-type p53 protein strongly increased and p53 was accumulated in the nucleus. Here, we raised the question of which pathway would be involved in roscovitine-induced apoptosis in MCF-7 cells, which are known to be caspase-3-deficient, and whether roscovitine-mediated activation of p53 protein might positively affect the execution of cell death. Roscovitine induced a depolarization of mitochondrial potential beginning at 6 hours posttreatment as evidenced by changes in J-aggregate formation and release of the mitochondrial proteins cytochrome c and apoptosis-inducing factor. Interestingly, roscovitine stimulated a site-specific phosphorylation of wild-type p53 protein in a time-dependent manner. p53 protein was specifically phosphorylated at Ser46. P-Ser46-activated wild-type p53 tumor suppressor up-regulated p53AIP1 protein, its downstream target known to mediate the depolarization of mitochondria. The onset of phosphorylation of p53 at Ser46 preceded the up-regulation of p53AIP1 protein and the depolarization of mitochondrial potential. We compared the kinetics of roscovitine-mediated p53 activation between caspase-3-deficient parental MCF-7 cells and cells reconstituted with caspase-3. The kinetics and the extent of p53 protein activation in caspase-3-proficient cells differed from those observed in caspase-3-deficient parental cells. Remarkably, roscovitine failed to induce phosphorylation at Ser46 in caspase-3-reconstituted MCF-7 cells. Our results indicate that, depending on the status of caspase-3 in MCF-7 cells, different apoptotic pathways were initialized.