The interaction between androgens such as dihydrotestosterone (DHT) 1 and the androgen receptor (AR) plays a crucial role in the evolution of human prostate cancer, and modulation of this interaction represents a major therapeutic strategy (1, 2). The biological action of androgen is mediated via binding to the AR, a member of the nuclear hormone receptor family of transcription factors that regulate expression of androgen-responsive genes (3). Androgens promote the growth of prostate cancer cells, and androgen deprivation results in regression of most prostate cancers, although this effect is eventually abrogated by the emergence of androgen-insensitive disease. In contrast, AR expression correlates with better clinical outcome in human breast cancer (4, 5), and androgens have been shown to inhibit the growth of breast cancer cells expressing the AR (6, 7). To better understand the mechanisms underlying the expression of the AR gene, we recently utilized LNCaP prostate cancer cells and MDA453 breast cancer cells to determine the relative importance of transcriptional and post-transcriptional mechanisms in androgen-regulated AR gene expression (8). In LNCaP cells, androgens down-regulate transcription of the AR gene, but stabilize AR mRNA. In MDA453 cells, androgens produce rapid destabilization of AR mRNA in the absence of transcriptional change. These data suggest an important role for post-transcriptional events (in particular, AR mRNA turnover) in the regulation of AR gene expression in prostate and breast cancer cells. We therefore decided to investigate the mechanisms regulating AR mRNA stability. mRNA turnover is a central mechanism in the control of gene expression (9), where interactions between specific sequences within mRNA (cis-acting elements) and cellular RNA-binding proteins (trans-acting factors) regulate ribonuclease action and subsequent mRNA decay rates. Several cis-acting elements have been described, and the best characterized is the adenylate/uridylate (AU)-rich element (ARE). The ARE most often resides in the 3Ј-untranslated region (3Ј-UTR) and contains AUUUA pentamers and/or UUAUUUA(U/A)(U/A) nonamers

From little things big things grow: 14‐Helical N‐acetyl β3‐peptides spontaneously self‐assemble in a unique head‐to‐tail fashion to form fibers from solution. The fiber size can be controlled from the nano‐ to the macroscale. The inherent flexibility in design and ease of synthesis provide powerful new avenues for the development of novel bio‐ and nanomaterials by supramolecular self‐assembly.

The RNA-binding protein TIAR (related to TIA-1 [T-cell-restricted intracellular antigen 1]) was shown to associate with subsets of mRNAs bearing U-rich sequences in their 3 untranslated regions. TIAR can function as a translational repressor, particularly in response to cytotoxic agents. Using unstressed colon cancer cells, collections of mRNAs associated with TIAR were isolated by immunoprecipitation (IP) of (TIAR-RNA) ribonucleoprotein (RNP) complexes, identified by microarray analysis, and used to elucidate a common signature motif present among TIAR target transcripts. The predicted TIAR motif was an unexpectedly cytosine-rich, 28-to 32-nucleotide-long element forming a stem and a loop of variable size with an additional side loop. The ability of TIAR to bind an RNA oligonucleotide with a representative C-rich TIAR motif sequence was verified in vitro using surface plasmon resonance. By this analysis, TIAR containing two or three RNA recognition domains (TIAR12 and TIAR123) showed low but significant binding to the C-rich sequence. In vivo, insertion of the C-rich motif into a heterologous reporter strongly suppressed its translation in cultured cells. Using this signature motif, an additional ϳ2,209 UniGene targets were identified (2.0% of the total UniGene database). A subset of specific mRNAs were validated by RNP IP analysis. Interestingly, in response to treatment with short-wavelength UV light (UVC), a stress agent causing DNA damage, each of these target mRNAs bearing C-rich motifs dissociated from TIAR. In turn, expression of the encoded proteins was elevated in a TIAR-dependent manner. In sum, we report the identification of a C-rich signature motif present in TIAR target mRNAs whose association with TIAR decreases following exposure to a stress-causing agent.

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Background: Human growth factor receptor bound protein 7 (Grb7) is an adapter protein that mediates the coupling of tyrosine kinases with their downstream signaling pathways. Grb7 is frequently overexpressed in invasive and metastatic human cancers and is implicated in cancer progression via its interaction with the ErbB2 receptor and focal adhesion kinase (FAK) that play critical roles in cell proliferation and migration. It is thus a prime target for the development of novel anti-cancer therapies. Recently, an inhibitory peptide (G7-18NATE) has been developed which binds specifically to the Grb7 SH2 domain and is able to attenuate cancer cell proliferation and migration in various cancer cell lines.

TIAR and HuR are mRNA-binding proteins that play important roles in the regulation of translation. They both possess three RNA recognition motifs (RRMs) and bind to AU-rich elements (AREs), with seemingly overlapping specificity. Here we show using SPR that TIAR and HuR bind to both U-rich and AU-rich RNA in the nanomolar range, with higher overall affinity for U-rich RNA. However, the higher affinity for U–rich sequences is mainly due to faster association with U-rich RNA, which we propose is a reflection of the higher probability of association. Differences between TIAR and HuR are observed in their modes of binding to RNA. TIAR is able to bind deoxy-oligonucleotides with nanomolar affinity, whereas HuR affinity is reduced to a micromolar level. Studies with U-rich DNA reveal that TIAR binding depends less on the 2′-hydroxyl group of RNA than HuR binding. Finally we show that SAXS data, recorded for the first two domains of TIAR in complex with RNA, are more consistent with a flexible, elongated shape and not the compact shape that the first two domains of Hu proteins adopt upon binding to RNA. We thus propose that these triple-RRM proteins, which compete for the same binding sites in cells, interact with their targets in fundamentally different ways.

No abstract

Stress granule (SG) formation is a primary mechanism through which gene expression is rapidly modulated when the eukaryotic cell undergoes cellular stresses (including heat, oxidative, viral infection, starvation). In particular, the sequestration of specifically targeted translationally stalled mRNAs into SGs limits the expression of a subset of genes, but allows the expression of heatshock proteins that have a protective effect in the cell. The importance of SGs is seen in several disease states in which SG function is disrupted. Fundamental to SG formation are the T cell restricted intracellular antigen (TIA) proteins (TIA-1 and TIA-1 related protein (TIAR)), that both directly bind to target RNA and self-associate to seed the formation of SGs. Here a summary is provided of the current understanding of the way in which TIA proteins target specific mRNA, and how TIA self-association is triggered under conditions of cellular stress.