Mutant p53 regulates Dicer through p63-dependent and -independent mechanisms to promote an invasive phenotype

Reduction of protein kinase C α (PKC-α) promote apoptosis via down-regulation of Dicer in bladder cancer

In clinic, we examined the expression of protein kinase C (PKC)-α and Dicer in the samples of bladder cancer patients, and found that the two proteins have a line correlation. Our study confirmed this correlation existing by clearing the decreasing expression of Dicer after the PKC-α knockdown. Treatment of bladder cancer cell lines (T24, 5637) with the PKC-α or Dicer knockdown and the PKC inhibitors (Calphostin C and Gö 6976) can promote the apoptosis. Inhibition of PKC can increase the activities of caspase-3 and PARP, however, decrease the expression of Dicer. And knockdown of the PKC-α or Dicer can also activate the caspase-3 or the PARP. Considering the reduction of PKC-α can induce the Dicer down-regulation, we make the conclusion that the reduction of PKC-α can promote the apoptosis via the down-regulation of Dicer in bladder cancer.

Mutant p53 - Heat Shock Response Oncogenic Cooperation: A New Mechanism of Cancer Cell Survival

The main tumor suppressor function of p53 as a "guardian of the genome" is to respond to cellular stress by transcriptional activation of apoptosis, growth arrest, or senescence in damaged cells. Not surprisingly, mutations in the p53 gene are the most frequent genetic alteration in human cancers. Importantly, mutant p53 (mutp53) proteins not only lose their wild-type tumor suppressor activity but also can actively promote tumor development. Two main mechanisms accounting for mutp53 proto-oncogenic activity are inhibition of the wild-type p53 in a dominant-negative fashion and gain of additional oncogenic activities known as gain-of-function (GOF). Here, we discuss a novel mechanism of mutp53 GOF, which relies on its oncogenic cooperation with the heat shock machinery. This coordinated adaptive mechanism renders cancer cells more resistant to proteotoxic stress and provides both, a strong survival advantage to cancer cells and a promising means for therapeutic intervention.

Antitumor mechanisms when pRb and p53 are genetically inactivated

pRb and p53 are the two major tumor suppressors. Their inactivation is frequent when cancers develop and their reactivation is rationale of most cancer therapeutics. When pRb and p53 are genetically inactivated, cells irreparably lose the antitumor mechanisms afforded by them. Cancer genome studies document recurrent genetic inactivation of RB1 and TP53, and the inactivation becomes more frequent in more advanced cancers. These findings may explain why more advanced cancers are more likely to resist current therapies. Finding successful treatments for more advanced and multi-therapy resistant cancers will depend on finding antitumor mechanisms that remain effective when pRb and p53 are genetically inactivated. Here, we review studies that have begun to make progress in this direction.

p53 Family and Cellular Stress Responses in Cancer

p53 is an important tumor suppressor gene, which is stimulated by cellular stress like ionizing radiation, hypoxia, carcinogens, and oxidative stress. Upon activation, p53 leads to cell-cycle arrest and promotes DNA repair or induces apoptosis via several pathways. p63 and p73 are structural homologs of p53 that can act similarly to the protein and also hold functions distinct from p53. Today more than 40 different isoforms of the p53 family members are known. They result from transcription via different promoters and alternative splicing. Some isoforms have carcinogenic properties and mediate resistance to chemotherapy. Therefore, expression patterns of the p53 family genes can offer prognostic information in several malignant tumors. Furthermore, the p53 family constitutes a potential target for cancer therapy. Small molecules (e.g., Nutlins, RITA, PRIMA-1, and MIRA-1 among others) have been objects of intense research interest in recent years. They restore pro-apoptotic wild-type p53 function and were shown to break chemotherapeutic resistance. Due to p53 family interactions small molecules also influence p63 and p73 activity. Thus, the members of the p53 family are key players in the cellular stress response in cancer and are expected to grow in importance as therapeutic targets.

From experimental design to functional gene networks: DNA microarray contribution to skin ageing research

There is no doubt that the DNA microarray-based technology contributed to increase our knowledge of a wide range of processes. However, integrating genes into functional networks, rather than terms describing generic characteristics, remains an important challenge. The highly context-dependent function of a given gene and feedback mechanisms complexify greatly the interpretation of the data. Moreover, it is difficult to determine whether changes in gene expression are the result or the cause of pathologies or physiological events. In both cases, the difficulty relies on the involvement of processes that, at an early stage, can be protective and later on, deleterious because of their runaway. Each individual cell has its own transcription profile that determines its behaviour and its relationships with its neighbours. This is particularly true when a mechanism such as cell cycle is concerned. Another issue concerns the analyses from samples of different donors. Whereas the statistical tools lead to determine common features among groups, they tend to smooth the overall data and consequently, the selected values represent the 'tip of the iceberg'. There is a significant overlap in the set of genes identified in the different studies on skin ageing processes described in the present review. The reason of this overlap is because most of these genes belong to the basic machinery controlling cell growth and arrest. To get a more full picture of these processes, a hard work has still to be done to determine the precise mechanisms conferring the cell type specificity of ageing. Integrative biology applied to the huge amount of existing microarray data should fulfil gaps, through the characterization of additional actors accounting for the activation of specific signalling pathways at crossing points. Furthermore, computational tools have to be developed taking into account that expression values among similar groups may not vary 'by chance' but may reflect, along with other subtle changes, specific features of one given donor. Through a better stratification, these tools will allow to recover genes from the 'bottom of the iceberg'. Identifying these genes should contribute to understand how skin ages among individuals, thus paving the way for personalized skin care.

microRNAs: short non-coding bullets of gain of function mutant p53 proteins

TP53 gene mutations are present in more than half of all human cancers. The resulting proteins are mostly full-length with a single aminoacid change and are abundantly present in cancer cells. Some of mutant p53 proteins gain oncogenic activities through which actively contribute to the aberrant cell proliferation, increased resistance to apoptotic stimuli and ability to metastatize of cancer cells. Gain of function mutant p53 proteins can transcriptionally regulate the expression of a large plethora of target genes. This mainly occurs through the formation of oncogenic transcriptional competent complexes that include mutant p53 protein, known transcription factors, posttranslational modifiers and scaffold proteins. Mutant p53 protein can also transcriptionally regulate the expression of microRNAs, small non-coding RNAs that regulate gene expression at the posttranscriptional level. Each microRNA can putatively target the expression of hundred mRNAs and consequently impact on many cellular functions. Thus, gain of function mutant p53 proteins can exert their oncogenic activities through the modulation of both non-coding and coding regions of human genome.

Mutant p53 exerts oncogenic effects through microRNAs and their target gene networks

MicroRNAs are potent regulators of gene expression and modulate multiple cellular processes including proliferation, differentiation and apoptosis. A number of microRNAs have been shown to be regulated by p53, the most frequently mutated gene in human cancer. It is has been demonstrated that some mutant p53 proteins not only lose tumor suppressor activity, but also acquire novel oncogenic functions that are independent of wild-type p53. In this review, we highlight recent evidences suggesting that some mutant p53 proteins regulate the expression of specific microRNAs to gain oncogenic functions and identify a gene network regulated by the microRNAs downstream of mutant p53.

MicroRNAs and anticancer drugs

MicroRNAs (miRNAs) are a class of small, non-coding, and endogenous RNA molecules, which are evolutionarily conserved but play a significant role in regulation of protein-coding gene expression at posttranscriptional and translational levels. Strikingly, a single miRNA is able to trigger hundreds of putative target genes by incomplete or complete complementary binding to their 3' untranslated regions. Given their appearance in almost all types of tissues, miRNAs have been demonstrated to be intensively involved in normal and pathological processes of human cells. Aside from the role as invaluable biomarkers in indication of tumorigenesis and tumor progression, numerous studies have revealed the potential of miRNAs as novel targets of anticancer drugs in cancer therapy. In this review article, we focus on the summary of the latest publications on the topic of miRNA and anticancer drugs, and expect to shed light on understanding the molecular mechanisms of chemoresistance involving miRNA regulation. These pieces of evidence will eventually provide insight into the development of novel and more efficacious anticancer drugs in the future.