Mutant p53: from guardian to fallen angel?

Personalized and translational approach for malignant brain tumors in the era of precision medicine: the strategic contribution of an experienced neurosurgery laboratory in a modern neurosurgery and neuro-oncology department

Personalized medicine (PM) aims to optimize patient management, taking into account the individual traits of each patient. The main purpose of PM is to obtain the best response, improving health care and lowering costs. Extending traditional approaches, PM introduces novel patient-specific paradigms from diagnosis to treatment, with greater precision. In neuro-oncology, the concept of PM is well established. Indeed, every neurosurgical intervention for brain tumors has always been highly personalized. In recent years, PM has been introduced in neuro-oncology also to design and prescribe specific therapies for the patient and the patient's tumor. The huge advances in basic and translational research in the fields of genetics, molecular and cellular biology, transcriptomics, proteomics, and metabolomics have led to the introduction of PM into clinical practice. The identification of a patient's individual variation map may allow to design selected therapeutic protocols that ensure successful outcomes and minimize harmful side effects. Thus, clinicians can switch from the "one-size-fits-all" approach to PM, ensuring better patient care and high safety margin. Here, we review emerging trends and the current literature about the development of PM in neuro-oncology, considering the positive impact of innovative advanced researches conducted by a neurosurgical laboratory.

Anti-apoptotic NF-κB and "gain of function" mutp53 in concert act pro-apoptotic in response to UVB+IL-1 via enhanced TNF production

In response to genotoxic stress, including UVB radiation, transcription factors NF-κB and p53 inevitably influence the cellular fate. Loss of p53 function has been attributed to malignant transformation and interferes with therapeutic interventions, whereas “gain of function” mutants even enhance tumor promotion. Constitutive NF-κB activation is linked to tumor maintenance and resistance against chemotherapy. The cross talk between p53 and NF-κB, however, is still under debate. Using the non-transformed keratinocyte cell line HaCaT, we shed light on the interplay between p53 and NF-κB by providing clear evidence that chronically activated NF-κB together with designated “gain of function” mutp53 promotes apoptosis via cooperative tumor necrosis factor (TNF) production in response to UVB+IL-1. Performing chromatin immunoprecipitation analysis we demonstrate that both transcription factors bind to the TNF promoter, whereas UVB-induced inhibition of Ser-Thr-phosphatase protein phosphatase 2A facilitates prolonged phosphorylation of NF-κB and the transcriptional cofactor cAMP response element–binding protein, both being required for extended TNF transcription. Thus, two major anti-apoptotic factors, NF-κB and mutp53, in concert may generate pro-apoptotic responses. As human skin is constantly exposed to UVB, causing IL-1 production as well, we hypothesize that the remarkable amount of hotspot p53 mutations within the epidermis (4%) may serve a protective function to eliminate precancerous cells at an early stage.

Manganese superoxide dismutase in cancer prevention

SIGNIFICANCE

Cancer is the second leading cause of death in the United States. Considering the quality of life and treatment cost, the best way to fight against cancer is to prevent or suppress cancer development. Cancer is preventable as indicated by human papilloma virus (HPV) vaccination and tamoxifen/raloxifen treatment in breast cancer prevention. The activities of superoxide dismutases (SODs) are often lowered during early cancer development, making it a rational candidate for cancer prevention.

RECENT ADVANCES

SOD liposome and mimetics have been shown to be effective in cancer prevention animal models. They've also passed safety tests during early phase clinical trials. Dietary supplement-based SOD cancer prevention provides another opportunity for antioxidant-based cancer prevention. New mechanistic studies have revealed that SOD inhibits not only oncogenic activity, but also subsequent metabolic shifts during early tumorigenesis.

CRITICAL ISSUES

Lack of sufficient animal model studies targeting specific cancers; and lack of clinical trials and support from pharmaceutical industries also hamper efforts in further advancing SOD-based cancer prevention.

FUTURE DIRECTIONS

To educate and obtain support from our society that cancer is preventable. To combine SOD-based therapeutics with other cancer preventive agents to obtain synergistic effects. To formulate a dietary supplementation-based antioxidant approach for cancer prevention. Lastly, targeting specific populations who are prone to carcinogens, which can trigger oxidative stress as the mechanism of carcinogenesis.

Gain of function of mutant TP53 in glioblastoma: prognosis and response to temozolomide

PURPOSE

Our aim was to investigate the relationship between mutant p53 and the prognosis of malignant glioma treated with temozolomide, and the regulation of mutant TP53 induced drug resistance, by molecular experimentation and a clinical trial.

METHODS

Adult patients with newly surgical diagnosed glioblastoma were randomly assigned to receive either temozolomide or semustine after radiation treatment. The statuses of TP53 and expression of TP53 and O(6)-methylguanine DNA-methyltransferase (MGMT) were determined retrospectively in tumor tissue from enrolled patients. The primary end point was overall survival. Synthetic small interfering RNA was used to knock down mutant TP53 in T98G and U138 cells, which are human glioblastoma cells with a P53 mutation, by screening of exons 4-8. Viable cell survival was measured when these cells were exposed to temozolomide or semustine. Expression of MGMT at the messenger RNA level was also determined.

RESULTS

The overall survival was 34.3 % at 2 years, 22.9 % at 3 years, 11.4 % at 4 years, and 8.6 % at 5 years with temozolomide, versus 18.2, 12.1, 3.0, and 0 %, respectively, with semustine. TP53 mutation and expression of mutant TP53 and MGMT showed significant inverse correlations with overall survival. Knockdown of mutant TP53 led to a fivefold increase in chemosensitivity to temozolomide but not semustine. Mutant TP53 knockdown induced down-regulation of MGMT expression.

CONCLUSIONS

Mutant TP53 is strongly associated with a poor prognosis for overall survival in patients with glioblastoma. Also, TP53 mutation may decrease the chemosensitivity of glioblastoma to temozolomide by increasing MGMT expression.

Mutant TP53 enhances the resistance of glioblastoma cells to temozolomide by up-regulating O(6)-methylguanine DNA-methyltransferase

The "gain of function" of mutant TP53 is an important determinant in human tumor development and progression. This study aimed to investigate the possible mechanism of mutant TP53 inducing temozolomide resistance in glioblastoma cells. Three established human glioma cell lines, T98G, U87, and U138, were chemoresistant cells. The mRNA of cells was sequenced to confirm the status of TP53. Synthetic small interfering RNA (siRNA) was used to knock down TP53 in cells. TP53 mRNA was detected "silenced" by reverse transcriptase-polymerase chain reaction (RT-PCR) in five consecutive days. Viable cell survival was measured when these cells were exposed to temozolomide or semustine in step-up concentrations. The expression of O(6)-methylguanine DNA-methyltransferase (MGMT) at mRNA level was also determined. T98G, U87, and U138 cells were resistant to temozolomide. T98G and U138 cells expressed mutant-type TP53 with positive MGMT, while U87 cell expressed wild-type TP53 with negative MGMT. TP53-siRNA knocked down TP53 effectively (P = 0.021) in five consecutive days. Knockdown of mutant TP53 in T98G and U138 cells led to a fivefold increase in chemosensitivity to temozolomide, but not semustine. Knockdown of wild TP53 in U87 cell did not affect the chemoresistance. In addition, mutant TP53 knockdown induced a dramatic decrease of MGMT expression (P = 0.0000034). TP53 mutation decreases the chemosensitivity of malignant gliomas to temozolomide. This "gain of function" in drug resistance may be obtained by increasing MGMT expression.

Cross talk between stimulated NF-kappaB and the tumor suppressor p53

Nuclear factor-kappaB (NF-kappaB) and p53 critically determine cancer development and progression. Defining the cross talk between these transcription factors can expand our knowledge on molecular mechanisms of tumorigenesis. Here, we show that induction of replicational stress activates NF-kappaB p65 and triggers its interaction with p53 in the nucleus. Experiments with knockout cells show that p65 and p53 are both required for enhanced NF-kappaB activity during S-phase checkpoint activation involving ataxia-telangiectasia mutated and checkpoint kinase-1. Accordingly, the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) also triggers formation of a transcriptionally active complex containing nuclear p65 and p53 on kappaB response elements. Gene expression analyses revealed that, independent of NF-kappaB activation in the cytosol, TNF-induced NF-kappaB-directed gene expression relies on p53. Hence, p53 is unexpectedly necessary for NF-kappaB-mediated gene expression induced by atypical and classical stimuli. Remarkably, data from gain- and loss-of function approaches argue that anti-apoptotic NF-kappaB p65 activity is constitutively evoked by a p53 hot-spot mutant frequently found in tumors. Our observations suggest explanations for the outstanding question why p53 mutations rather than p53 deletions arise in tumors of various origins.

Peptide aptamers targeting mutant p53 induce apoptosis in tumor cells

Mutations in the p53 tumor suppressor gene frequently result in expression of p53 point mutants that accumulate in cancer cells and actively collaborate with tumor progression through the acquisition of novel properties. Interfering with mutant p53 functions may represent a valid alternative for blocking tumor growth and development of aggressive phenotypes. The interactions and activities of selected proteins can be specifically modulated by the binding of peptide aptamers (PA). In the present work, we isolated PAs able to interact more efficiently with p53 conformational mutants compared with wild-type p53. The interaction between mutant p53 and PAs was further characterized using molecular modeling. Transient expression of PAs was able to reduce the transactivation activity of mutant p53 and to induce apoptosis specifically in cells expressing mutant p53. These PAs could provide a potential strategy to inhibit the oncogenic functions of mutant p53 and improve mutant p53-targeted cancer therapies.

Versatile functions of p53 protein in multicellular organisms

The p53 tumor suppressor plays a pivotal role in multicellular organism by enforcing benefits of the organism over those of an individual cell. The task of p53 is to control the integrity and correctness of all processes in each individual cell and in the organism as a whole. Information about the state of ongoing events in the cell is gathered through multiple signaling pathways that convey signals modifying activities of p53. Changes in the activities depend on the character of damages or deviations from optimum in processes, and the activity of p53 changes depending on the degree of the aberration, which results in either stimulation of repair processes and protective mechanisms, or the cessation of further cell divisions and the induction of programmed cell death. The strategy of p53 ensures genetic identity of cells and prevents the selection of abnormal cells. By accomplishing these strategic tasks, p53 may use a wide spectrum of activities, such as its ability to function as a transcription factor, by inducing or repressing different genes, or as an enzyme, by acting as an exonuclease during DNA reparation, or as an adaptor or a regulatory protein, intervening into functions of numerous signaling pathways. Loss of function of the p53 gene occurs in virtually every case of cancer, and deficiency in p53 is an unavoidable prerequisite to the development of malignancies. The functions of p53 play substantial roles in many other pathologies as well as in the aging process. This review is focused on strategies of the p53 gene, demonstrating individual mechanisms underlying its functions.

cAMP and protein kinase A in endocrine (and other) tumors

Studies of the biological role of cAMP have indicated dual and often opposing effects on proliferation and differentiation. Elevation of the intracellular cAMP in normal and transformed cells may lead to cell proliferation; in other cells, it induces changes in morphology, apoptosis and/or differentiation. The best known mediator of cAMP action in the cell is cAMP-dependent protein kinase or protein kinase A (PKA). PKA exists as two different isozymes, designated type I (PKA-I) and type II (PKA-II); the two isoforms are essentially distinct in their physicochemical properties. The relative ratio of PKA-I and PKA-II varies throughout the cell cycle in cells of the same type, it changes significantly during development and follows different patterns in the various tissues. Disruption of the apparently fine balance between the main two PKA isozymes is strongly associated with tumorigenesis and tumor growth, and vice versa. The enormous variety of cAMP/PKA functions and the net effect of this signaling system on cellular growth, proliferation and differentiation have been the subject of debate for more than 30 years among investigators in the field. The relatively recent identification of PRKAR1A mutations and PKA-I deficiency as a cause of endocrine and other tumors in human and mice was instrumental in advancing our understanding of how cAMP and PKA work in regulating the cell cycle. This article reviews the current state of knowledge in the field; the use of pharmacologic modulation of the cAMP/PKA system with the goal of treating certain tumors appears to be near, although very little has been accomplished so far, at least in terms of studies on humans.