Unveiling the potential of prohibitin in cancer

Recently, research has shed new light on the role of Prohibitin (PHB) in cancer pathogenesis across an array of cancer types. Important mechanisms for PHB have been unveiled in several cancers, especially with regard to the androgen independent state of prostate cancer (PC) and oestrogen dependent breast cancer. However, PHB is often overlooked due to its complex but subtle roles within the cell. Having gathered both historical and current research exploring PHB's role in different cancer types including prostate and breast, here we aim to pair this information with its molecular properties in the hope of translating this information into a clinical perspective, thus discussing its possible use in future cancer therapy

The role of p53 in the chemotherapeutic responses to cisplatin, doxorubicin and 5-fluorouracil treatment

A panel of tumour models used extensively for in vivo evaluation of new drugs was characterised for their p53 status. Basal p53 protein levels were measured by immunodetection on both formalin-fixed tumour tissue and from protein extracts of fresh tumours. High levels of nuclear-specific staining, indicative of p53 mutation, was seen in 15/25 tumours, with the remainder showing intermittent or no staining. The functional status of p53 cDNA from these tumours was assayed within the functional analysis of separated alleles in yeast (F.A.S.A.Y.) reporter system. The cDNA from those tumours with high levels of p53 protein showed 14/15 failing to activate the reporter gene. The cDNA from tumours with low or non-detectable p53 levels showed 8/10 with wild-type p53. Tumours were grown subcutaneously in mice (n=10). Each mouse was given maximum tolerated doses for either doxorubicin, 5-fluorouracil or cisplatin. Tumour volumes were measured daily, alongside untreated controls. The specific growth delay values for each tumour were separated into two groups, those with functional p53 (wild-type) and those without (mutant and null status). The Mann-Whitney U test was performed on the groups of data, to evaluate differences in their response on the basis of p53 status. Cisplatin was moderately active against tumours with wild-type and mutant p53 genes with no significant difference seen between both groups. However, a significant difference in specific growth delay was seen between the two groups when treated with doxorubicin or 5-fluorouracil (P=0.05), indicating a role for p53 protein in modulating the in vivo efficacy of these agents

In vivo imaging of nuclear receptor transcriptional activity

Nuclear receptors drive key processes during development, reproduction, metabolism, and disease. In order to understand and analyze, as well as manipulate, their actions it is imperative that we are able to study them in whole animals and in a spatiotemporal manner. The increasing repertoire of transgenic animals, expressing reporter genes driven by a specific nuclear receptor, enables us to do this. Use of luciferase reporter genes is the method of choice of many researchers as it is well tolerated, relatively easy to use, and robust. Further, luciferase lends itself to the process as it can penetrate tissue and can be manipulated to degrade rapidly thus allowing a dynamic response. However, limited resolution, lack of quantitation, and the largely two-dimensional images acquired make it desirable to support results using ex vivo imaging and enzymatic and/or immunohistochemical analysis of dissected tissue. As well as enabling the visualization of nuclear receptor signaling in wild-type animals, crossing these mouse models with models of disease will provide invaluable information on how such signaling is dysregulated during disease progression, and how we may manipulate nuclear receptor signaling in therapy. The use of in vivo imaging therefore provides the power to determine where and when in development, aging, and disease nuclear receptors are active and how ligands or receptor modulators affect this

Current advances in the inhibition of the auto-regulatory interaction between the p53 tumour suppressor protein and MDM2 protein

The p53 tumour suppressor protein is involved in co-ordinating the cellular response to genotoxic stress through initiating a G1-growth arrest and/or induction of apoptosis and thereby influences the success of most anticancer treatments. p53 is a damage-inducible transcription factor whose activity is negatively regulated by the binding of MDM2 protein. The ability to disrupt the p53-MDM2 regulatory loop has identified a novel therapeutic opportunity. Potent peptide inhibitors of the interaction between p53 and MDM2 protein have been identified, with IC50 values in the nanomolar range, and activate the p53-dependent stress response. Potentially, such peptides might have a wider application as non-genotoxic therapeutic p53 activators, in tumours that retain expression of wild type p53 protein, to induce the p53-dependent apoptotic pathway

Prohibitin Links Cell Cycle, Motility and Invasion in Prostate Cancer Cells

Prohibitin (PHB) is a tumour suppressor gene with several different molecular activities. PHB overexpression leads to G1/S-phase cell cycle arrest, and PHB represses the androgen receptor (AR) in prostate cancer cells. PHB interacts with and represses members of the E2F family in a manner that may also be AR-linked, therefore making the AR:PHB:E2F interaction axis highly complex. PHB siRNA increased the growth and metastatic potential of LNCaP mouse xenografts in vivo. Conversely, PHB ectopic cDNA overexpression affected several hundred genes in LNCaP cells. Furthermore, gene ontology analysis showed that in addition to cell cycle regulation, several members of the WNT family were significantly downregulated (WNT7B, WNT9A and WNT10B), as well as pathways for cell adhesion. Online GEO data studies showed PHB expression to be decreased in clinical cases of metastatic prostate cancer, and to be correlated with higher WNT expression in metastasis. PHB overexpression reduced prostate cancer cell migration and motility in wound-healing assays, reduced cell invasion through a Matrigel layer and reduced cellular attachment. In LNCaP cells, WNT7B, WNT9A and WNT10B expression were also upregulated by androgen treatment and downregulated by androgen antagonism, indicating a role for AR in the control of these WNT genes. However, these WNTs were strongly cell cycle regulated. E2F1 cDNA ectopic expression and PHB siRNA (both cell cycle promoting effects) increased WNT7B, WNT9A and WNT10B expression, and these genes were also upregulated as cells were released from G1 to S phase synchronisation, indicating further cell cycle regulation. Therefore, the repressive effects of PHB may inhibit AR, E2F and WNT expression and its loss may increase metastatic potential in human prostate cancer

Insights into roles of the miR-1, -133 and -206 family in gastric cancer (Review)

Gastric cancer (GC) remains the third most common cause of cancer deaths worldwide and carries a high rate of metastatic risk contributing to the main cause of treatment failure. An accumulation of data has resulted in a better understanding of the molecular network of GC, however, gaps still exist between the unique bio-resources and clinical application. MicroRNAs are an important part of non-coding RNAs and behave as major regulators of tumour biology, alongside their well-known roles as intrinsic factors of gene expression in cellular processes, via their post-transcriptional regulation of components of signalling pathways in a coordinated manner. Deregulation of the miR-1, -133 and -206 family plays a key role in tumorigenesis, progression, invasion and metastasis. This review aims to provide a summary of recent findings on the miR-1, -133 and -206 family in GC and how this knowledge might be exploited for the development of future miRNA-based therapies for the treatment of GC

Androgen-regulated processing of the oncomir MiR-27a, which targets Prohibitin in prostate cancer

MicroRNAs (miRs) play an important role in the development of many complex human diseases and may have tumour suppressor or oncogenic (oncomir) properties. Prostate cancer is initially an androgen-driven disease, and androgen receptor (AR) remains a key driver of growth even in castration-resistant tumours. However, AR-mediated oncomiR pathways remain to be elucidated. We demonstrate that miR-27a is an androgen-regulated oncomir in prostate cancer, acting via targeting the tumour suppressor and AR corepressor, Prohibitin (PHB). Increasing miR-27a expression results in reduced PHB mRNA and protein levels, and increased expression of AR target genes and prostate cancer cell growth. This involves a novel mechanism for androgen-mediated miR regulation, whereby AR induces a transient increase in miR-23a27a24-2 transcription, but more significantly accelerates processing of the primiR-23a27a24-2 cluster. Androgens therefore regulate miR-27a expression both transcriptionally (via AR binding to the cluster promoter) and post-transcriptionally (accelerating primiR processing to the mature form). We further show that a miR-27a anti-sense oligonucleotide, by opposing the effects of mir-27a, has therapeutic potential in prostate cancer