Antiproliferative activities of some selected Nigerian medicinal plants against breast, liver, and cervical cancer cells.

Background: Phytochemicals have become a growing source of alternative medicine in developing countries due to the poor prognosis, high cost of conventional pharmaceuticals, and undesirable effects associated with mainstream cancer treatment.

Objective: This study was aimed at investigating the anticancer effect of some selected Nigerian medicinal plants used in cancer treatment. These include ethanol extracts of Dialium guineense root (DGR), Dialium guineense leaves (DGL), Jateorhiza macrantha leaves (JML), Musanga cecropioides leaves (MCL), Musanga cecropioides stembark (MCSB), Piptadeniastrum africanum stembark (PASB), Piptadeniastrum africanum root (PAR), Pupalia lappacea flower tops (PLF), Raphiostylis beninensis root (RBR), Raphiostylis beninensis leaves (RBL), Ritchiea capparoides leaves (RCL), Ritchiea capparoides stembark (RCSB), and Triplochiton scleroxylon stembark (TSB).

Implications of differential transcription start site selection on chronic myeloid leukemia and prostate cancer cell protein expression.

The relevance of minor transcription start sites in broad promoters is not well understood. We have studied AGAP2 expression in prostate cancer and chronic myeloid leukemia (CML), showing transcription is initiated from alternative transcription start sites (TSSs) within a single TSS cluster, producing cancer-type-specific mRNAs with small differences in their 5' UTR length. Interestingly, in the CML cell lines where the 5' UTR is longer, AGAP2 protein levels are lower.

Water Solubility Enhancement of Pyrazolo[3,4-]pyrimidine Derivatives via Miniaturized Polymer-Drug Microarrays.

A miniaturized assay was optimized to evaluate the enhanced apparent water solubility of pyrazolo[3,4-]pyrimidine derivatives used extensively as anticancer drug scaffolds. The applied amount of drugs used in the reported strategy ranged from 5 to 10 μg per formulation which were dispensed by an inkjet 2D printer directly into a 96-well plate. The selected polymer/drug formulations with high water solubility demonstrated improved cytotoxicity against a human lung adenocarcinoma cancer cell line (A549) compared to the free drugs.

PRAME is a golgi-targeted protein that associates with the Elongin BC complex and is upregulated by interferon-gamma and bacterial PAMPs.

Preferentially expressed antigen in melanoma (PRAME) has been described as a cancer-testis antigen and is associated with leukaemias and solid tumours. Here we show that PRAME gene transcription in leukaemic cell lines is rapidly induced by exposure of cells to bacterial PAMPs (pathogen associated molecular patterns) in combination with type 2 interferon (IFNγ). Treatment of HL60 cells with lipopolysaccharide or peptidoglycan in combination with IFNγ resulted in a rapid and transient induction of PRAME transcription, and increased association of PRAME transcripts with polysomes.

Translational regulation of gene expression during conditions of cell stress.

A number of stresses, including nutrient stress, temperature shock, DNA damage, and hypoxia, can lead to changes in gene expression patterns caused by a general shutdown and reprogramming of protein synthesis. Each of these stress conditions results in selective recruitment of ribosomes to mRNAs whose protein products are required for responding to stress. This recruitment is regulated by elements within the 5' and 3' untranslated regions of mRNAs, including internal ribosome entry segments, upstream open reading frames, and microRNA target sites.

eIF4A inhibition allows translational regulation of mRNAs encoding proteins involved in Alzheimer's disease.

Alzheimer's disease (AD) is the main cause of dementia in our increasingly aging population. The debilitating cognitive and behavioral symptoms characteristic of AD make it an extremely distressing illness for patients and carers. Although drugs have been developed to treat AD symptoms and to slow disease progression, there is currently no cure.

Leucine-rich repeat protein PRAME: expression, potential functions and clinical implications for leukaemia.

PRAME/MAPE/OIP4 is a germinal tissue-specific gene that is also expressed at high levels in haematological malignancies and solid tumours. The physiological functions of PRAME in normal and tumour cells are unknown, although a role in the regulation of retinoic acid signalling has been proposed. Sequence homology and structural predictions suggest that PRAME is related to the leucine-rich repeat (LRR) family of proteins, which have diverse functions.

Dysregulation of protein synthesis and disease.

The regulation of protein synthesis plays as important a role as transcriptional control in the control of gene expression. Once thought solely to act globally, translational control has now been shown to be able to control the expression of most genes specifically. Dysregulation of this process is associated with a range of pathological conditions, notably cancer and several neurological disorders, and can occur in many ways.

The human insulin receptor mRNA contains a functional internal ribosome entry segment.

Regulation of mRNA translation is an important mechanism determining the level of expression of proteins in eukaryotic cells. Translation is most commonly initiated by cap-dependent scanning, but many eukaryotic mRNAs contain internal ribosome entry segments (IRESs), providing an alternative means of initiation capable of independent regulation. Here, we show by using dicistronic luciferase reporter vectors that the 5'-UTR of the mRNA encoding human insulin receptor (hIR) contains a functional IRES.

Translational reprogramming following UVB irradiation is mediated by DNA-PKcs and allows selective recruitment to the polysomes of mRNAs encoding DNA repair enzymes.

UVB-induced lesions in mammalian cellular DNA can, through the process of mutagenesis, lead to carcinogenesis. However, eukaryotic cells have evolved complex mechanisms of genomic surveillance and DNA damage repair to counteract the effects of UVB radiation. We show that following UVB DNA damage, there is an overall inhibition of protein synthesis and translational reprogramming.

Polypyrimidine-tract-binding protein: a multifunctional RNA-binding protein.

PTB (polypyrimidine-tract-binding protein) is a ubiquitous RNA-binding protein. It was originally identified as a protein with a role in splicing but it is now known to function in a large number of diverse cellular processes including polyadenylation, mRNA stability and translation initiation. Specificity of PTB function is achieved by a combination of changes in the cellular localization of this protein (its ability to shuttle from the nucleus to the cytoplasm is tightly controlled) and its interaction with additional proteins.

The mechanism of micro-RNA-mediated translation repression is determined by the promoter of the target gene.

MicroRNAs (miRNAs) are noncoding RNAs that base pair imperfectly to homologous regions in target mRNAs and negatively influence the synthesis of the corresponding proteins. Repression is mediated by a number of mechanisms, one of which is the direct inhibition of protein synthesis. Surprisingly, previous studies have suggested that two mutually exclusive mechanisms exist, one acting at the initiation phase of protein synthesis and the other at a postinitiation event.

SF2/ASF TORCs up translation.

In a recent issue of Molecular Cell, Michlewski et al. (2008) show that SF2/ASF, a splicing factor, stimulates translation initiation by directly recruiting the mammalian target of rapamycin (mTOR) to a subset of mRNAs.

Re-programming of translation following cell stress allows IRES-mediated translation to predominate.

There is now an overwhelming body of evidence to suggest that internal ribosome entry is required to maintain the expression of specific proteins during patho-physiological situations when cap-dependent translation is compromised, for example, following heat shock or during mitosis, hypoxia, differentiation and apoptosis. Translational profiling has been used by several groups to assess the extent to which alternative mechanisms of translation initiation selectively recruit mRNAs to polysomes during cell stress. The data from these studies have shown that under each condition 3-5% of coding mRNAs remain associated with the polysomes.

Identification of internal ribosome entry segment (IRES)-trans-acting factors for the Myc family of IRESs.

The proto-oncogenes c-, L-, and N-myc can all be translated by the alternative method of internal ribosome entry whereby the ribosome is recruited to a complex structural element (an internal ribosome entry segment [IRES]). Ribosome recruitment is dependent upon the presence of IRES-trans-acting factors (ITAFs) that act as RNA chaperones and allow the mRNA to attain the correct conformation for the interaction of the 40S subunit. One of the major challenges for researchers in this area is to determine whether there are groups of ITAFs that regulate the IRES-mediated translation of subsets of mRNAs.

Polypyrimidine tract binding protein regulates IRES-mediated gene expression during apoptosis.

During apoptosis there is a substantial reduction in the rate of protein synthesis, and yet some mRNAs avoid this translational inhibition. To determine the impact that receptor-mediated cell death has on the translational efficiency of a large number of mRNAs, translational profiling was performed on MCF7 cells treated with the apoptosis-inducing ligand TRAIL. Our data indicate that approximately 3% of mRNAs remain associated with the polysomes in apoptotic cells, and genes that are involved in transcription, chromatin modification/remodeling, and the Notch signaling pathway are particularly prevalent among the mRNAs that evade translational inhibition.

Identification of a motif that mediates polypyrimidine tract-binding protein-dependent internal ribosome entry.

We have identified a novel motif which consists of the sequence (CCU)(n) as part of a polypyrimidine-rich tract and permits internal ribosome entry. A number of constructs containing variations of this motif were generated and these were found to function as artificial internal ribosome entry segments (AIRESs) in vivo and in vitro in the presence of polypyrimidine tract-binding protein (PTB). The data show that for these sequences to function as IRESs the RNA must be present as a double-stranded stem and, in agreement with this, rather surprisingly, we show that PTB binds strongly to double-stranded RNA.

Bag-1 internal ribosome entry segment activity is promoted by structural changes mediated by poly(rC) binding protein 1 and recruitment of polypyrimidine tract binding protein 1.

We have shown previously that an internal ribosome entry segment (IRES) directs the synthesis of the p36 isoform of Bag-1 and that polypyrimidine tract binding protein 1 (PTB-1) and poly(rC) binding protein 1 (PCBP1) stimulate IRES-mediated translation initiation in vitro and in vivo. Here, a secondary structural model of the Bag-1 IRES has been derived by using chemical and enzymatic probing data as constraints on the RNA folding algorithm Mfold. The ribosome entry window has been identified within this structural model and is located in a region in which many residues are involved in base-pairing interactions.

L-Myc protein synthesis is initiated by internal ribosome entry.

An internal ribosome entry segment (IRES) has been identified in the 5' untranslated region (5' UTR) of two members of the myc family of proto-oncogenes, c-myc and N-myc. Hence, the synthesis of c-Myc and N-Myc polypeptides can involve the alternative mechanism of internal initiation. Here, we show that the 5' UTR of L-myc, another myc family member, also contains an IRES.

Members of the poly (rC) binding protein family stimulate the activity of the c-myc internal ribosome entry segment in vitro and in vivo.

The 5' untranslated region of the proto-oncogene c-myc contains an internal ribosome entry segment and c-Myc translation can be initiated by cap-independent as well as cap-dependent mechanisms. In contrast to the process of cap-dependent initiation, the trans-acting factor requirements for cellular internal ribosome entry are poorly understood. Here, we show that members of the poly (rC) binding protein family, poly (rC) binding protein 1 (PCBP1), poly (rC) binding protein 2 (PCBP2) and hnRNPK were able to activate the IRES in vitro up to threefold when added in combination with upstream of N-ras and unr-interacting protein.

The Apaf-1 internal ribosome entry segment attains the correct structural conformation for function via interactions with PTB and unr.

We have shown previously that polypyrimidine tract binding protein 1 (PTB) binds and activates the Apaf-1 internal ribosome entry segment (IRES) when the protein upstream of N-ras (unr) is prebound. Here we show that the Apaf-1 IRES is highly active in neuronal-derived cell lines due to the presence of the neuronal-enhanced version of PTB, nPTB. The unr and PTB/nPTB binding sites have been located on the Apaf-1 IRES RNA, and a structural model for the IRES bound to these proteins has been derived.