Human prostate epithelial cells and prostate-derived stem cells malignantly transformed in vitro with sodium arsenite show impaired Toll like receptor -3 (TLR3)-associated anti-tumor pathway.

A therapeutic strategy for prostate cancer (PCa) involves the use of 9-cis-retinoic acid (9cRA) to induce cancer stem cells (CSCs) differentiation and apoptosis. Polyinosinic:polycytidylic acid (PIC) is a Toll-like receptor 3 (TLR3) agonist that induces tumor cells apoptosis after activation. PIC+9cRA combination activates retinoic acid receptor ß (RARß) re-expression, leading to CSC differentiation and growth arrest. Since inorganic arsenic (iAs) targets prostatic stem cells (SCs), we hypothesized that arsenic-transformed SCs (As-CSCs) show an impaired TLR3-associated anti-tumor pathway and, therefore, are unresponsive to PIC activation. We evaluated TLR3-mediated activation of anti-tumor pathway based in RARß expression, on As-CSC and iAs-transformed epithelial cells (CAsE-PE). As-CSCs and CAsE-PE showed lower TLR3 and RARß basal expression compared to their respective isogenic controls WPE-Stem and RWPE-1. Also, iAs transformants showed reduced expression of mediators in TLR3 pathway. Importantly, As-CSCs were irresponsive to PIC+9cRA in terms of increased RARß and decreased SC-markers expression, while CAsE-PE, a heterogeneous cell line having a small SC population, were partially responsive. These observations indicate that iAs can impair TLR3 expression and anti-tumor pathway activated by PIC+9cRA in SCs and prostatic epithelial cells. These findings suggest that TLR3-activation based therapy may be an ineffective therapeutic alternative for iAs-associated PCa.

p53 binds the mdmx mRNA and controls its translation.

MDMX and MDM2 are two nonredundant essential regulators of p53 tumor suppressor activity. MDM2 controls p53 expression levels, whereas MDMX is predominantly a negative regulator of p53 trans-activity. The feedback loops between MDM2 and p53 are well studied and involve both negative and positive regulation on transcriptional, translational and post-translational levels but little is known on the regulatory pathways between p53 and MDMX. Here we show that overexpression of p53 suppresses mdmx mRNA translation in vitro and in cell-based assays. The core domain of p53 binds the 5' untranslated region (UTR) of the mdmx mRNA in a zinc-dependent manner that together with a trans-suppression domain located in p53 N-terminus controls MDMX synthesis. This interaction can be visualized in the nuclear and cytoplasmic compartment. Fusion of the mdmx 5'UTR to the ovalbumin open reading frame leads to suppression of ovalbumin synthesis. Interestingly, the transcription inactive p53 mutant R273H has a different RNA-binding profile compared with the wild-type p53 and differentiates the synthesis of MDMX isoforms. This study describes p53 as a trans-suppressor of the mdmx mRNA and adds a further level to the intricate feedback system that exist between p53 and its key regulatory factors and emphasizes the important role of mRNA translation control in regulating protein expression in the p53 pathway.

Whisper mutations: cryptic messages within the genetic code.

Recent years have seen a great expansion in our understandings of how silent mutations can drive a disease and that mRNAs are not only mere messengers between the genome and the encoded proteins but also encompass regulatory activities. This review focuses on how silent mutations within open reading frames can affect the functional properties of the encoded protein. We describe how mRNAs exert control of cell biological processes governed by the encoded proteins via translation kinetics, protein folding, mRNA stability, spatio-temporal protein expression and by direct interactions with cellular factors. These examples illustrate how additional levels of information lie within the coding sequences and that the degenerative genetic code is not redundant and have co-evolved with the encoded proteins. Hence, so called synonymous mutations are not always silent but 'whisper'.

MDM2's social network.

MDM2 is considered a hub protein due to its capacity to interact with a large number of different partners of which p53 is most well described. MDM2 is an E3 ubiquitin ligase, and many, but not all, of its interactions relate directly to this activity, such as substrates, adaptors or bridges, promoters, inhibitors or complementary factors. Some interactions serve regulatory functions that in response to cellular stresses control the localisation and functions of MDM2 including protein kinases, ribosomal proteins and proteases. Moreover, interactions with nucleotides serve other functions such as mRNA to regulate protein synthesis and DNA to control transcription. To perform such a pleiotropic panorama of different functions, MDM2 is subjected to a multitude of post-translational modifications and is expressed in different isoforms. The large and diverse interactome is made possible due to the plasticity of MDM2 and in this review we have listed the MDM2 interactions until now and we will discuss how this multifaceted protein can interact with such a variety of substrates to provide a key intermediary role in different signalling pathways.

p53 isoforms gain functions.

Many different cell stress pathways converge on p53 to induce a number of distinct cell biological responses such as G1 or G2 arrest, senescence or apoptosis. One of the outstanding questions with regard to p53 is how the cells can differentiate between different stresses so that p53 activation leads to the correct response. It has been known for some time that the p53 gene expresses isoforms that carry unique domains and properties, and more recent works have started to reveal some of their functions. The alternative mRNA translation product p53/47, which lacks the first 40 codons, including the first of p53's two trans-activation domains, is being linked to endoplasmic reticulum stress and the unfolded protein response to which it causes a specific G2 arrest. On the other hand, p53 itself induces G1 arrest and has no effect on the G2. The two isoforms Δ133p53, which lacks the first 133 amino acids, and p53ß, which carries an alternative C-terminus, are derived from alternative promoter usage or splicing, respectively, and are together implied in controlling cellular senescence. Hence, through different mechanisms of gene expression control, alternative levels of p53 isoforms help the cell to differentiate between p53 activation and the response to diverse stresses. This holds promise to a better understanding of how upstream and downstream p53 pathways have evolved relative to specific p53 domains.

Characterization of a cell-associated inulosucrase from a novel source: a Leuconostoc citreum strain isolated from Pozol, a fermented corn beverage of Mayan origin.

A cell-associated fructosyltransferase was extracted from a novel source, a strain of Leuconostoc citreum isolated from Pozol, a Mexican traditional fermented corn beverage, where lactic microflora are partially responsible for the transformation process. The enzyme is associated with the cell wall. It was characterized both in its cell-associated insoluble form and after separation by urea treatment. The fructosyltransferase has a molecular mass of 170 kDa, the highest reported for this type of enzyme, and in its insoluble form is highly specific for polymer synthesis, with low fructose transferred to maltose and lactose added to the reaction medium (acceptor reactions). The synthesized polymer has an inulin-like structure with beta2-1 glycosidic linkages, as demonstrated by 13C nuclear magnetic resonance (NMR). Bacterial inulosucrases have only been reported in Streptococcus mutans.