Human p300 protein is a cellular target of adenoviral E1A oncoprotein and a potential transcriptional coactivator. Both p300 and Rb family protein-binding regions of E1A are required for the repression of muscle gene expression, which is regulated by MyoD family transactivators. This implies that p300 is involved in MyoD-dependent transactivation. We show that the repression of MyoD-mediated E box (MyoD consensus) reporter activity by E1A is correlated with its interaction with p300, indicating that p300 participates in MyoD-dependent transactivation. In addition, p300 is able to interact both in vivo and in vitro with MyoD through a portion at the carboxyl-terminal cysteine/histidine-rich domain and associates with the components of the basal transcriptional complex through its two separate transactivation domains at the amino and carboxyl termini. Consistent with its role as a coactivator, p300 potentiates MyoD-activated transcription.

Differential gene expression of cell lines derived from a malignant melanoma or its autologous lymph node metastasis using cDNA arrays indicated down-regulation of PRSS11, a gene encoding the serine protease HtrA1, a homolog of the Escherichia coli protease HtrA, in the metastatic line. Stable PRSS11 overexpression in the metastatic cell line strongly inhibited proliferation, chemoinvasion and Nm23-H1 protein expression in vitro, as well as cell growth in vivo in nu/nu mice. A polyclonal anti-HtrA1 serum demonstrated a significantly higher expression in primary melanomas when compared to unrelated metastatic lesions in a human melanoma tissue array, and down-modulation of HtrA1 expression in autologous lymph node melanoma metastases in seven out of 11 cases examined. These results suggest that down-regulation of PRSS11 and HtrA1 expression may represent an indicator of melanoma progression.

During the terminal differentiation of skeletal myoblasts, the activities of myogenic factors regulate not only tissue-specific gene expressions but also the exit from the cell cycle. The induction of cell cycle inhibitors such as p21 and pRb has been shown to play a prominent role in the growth arrest of differentiating myoblasts. Here we report that, at the onset of differentiation, activation by MyoD of the Rb, p21, and cyclin D3 genes occurs in the absence of new protein synthesis and with the requirement of the p300 transcriptional coactivator. In differentiated myocytes, cyclin D3 also becomes stabilized and is found nearly totally complexed with unphosphorylated pRb. The detection of complexes containing cyclin D3, cdk4, p21, and PCNA suggests that cdk4, along with PCNA, may get sequestered into high-order structures held together by pRb and cyclin D3. Cyclin D3 up-regulation and stabilization is inhibited by adenovirus E1A, and this correlates with the ability of E1A to promote pRb phosphorylation; conversely, the overexpression of cyclin D3 in differentiated myotubes counteracts the E1A-mediated reactivation of DNA synthesis. These results indicate that cyclin D3 critically contributes to the irreversible exit of differentiating myoblasts from the cell cycle.Skeletal muscle differentiation is characterized by terminal withdrawal from the cell cycle, the coordinated activation of muscle-specific gene expression, and the fusion of myoblasts into multinucleated myotubes. As in most cell types, proliferation and differentiation of skeletal myoblasts are mutually exclusive events. Established mouse myogenic cell lines have allowed the identification of muscle-specific transcription factors, belonging to the MyoD family, which determine the initiation and the maintenance of the myogenic program (reviewed in references 8, 18, 60, and 94). Muscle regulatory factors (MRFs) are basic helix-loop-helix transcription factors, which promote skeletal muscle differentiation by binding to a consensus sequence, termed E-box, present in the regulatory region of many muscle-specific genes (12, 95).Besides regulating tissue-specific gene expression, the activity of MRFs is also involved in promoting cell cycle arrest (37,42). Although the molecular mechanisms responsible for the coupling of cell cycle arrest with terminal differentiation of muscle cells have not been completely elucidated, several functional interactions between myogenic factors and cell cycle regulatory proteins have now been clarified. We have previously reported that MyoD induces transcription of the retinoblastoma growth suppressor gene (pRb) by a mechanism independent of direct binding of MyoD to the Rb gene promoter (46). It has also been shown that MyoD can mediate the transcriptional induction of the cell cycle inhibitor p21 (28).A critical role for pRb activity in muscle cells was first suggested by the finding that the ability of DNA tumor virus oncoproteins, such as adenovirus E1A, simian virus 40 (SV40) large T antigen, and polyomavirus large T ...

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In order to understand the role of microRNAs (miRNAs) in vascular physiopathology, we took advantage of deep-sequencing techniques to accurately and comprehensively profile the entire miRNA population expressed by endothelial cells exposed to hypoxia. SOLiD sequencing of small RNAs derived from human umbilical vein endothelial cells (HUVECs) exposed to 1% % O 2 or normoxia for 24 h yielded more than 22 million reads per library. A customized bioinformatic pipeline identified more than 400 annotated microRNA/microRNA* species with a broad abundance range: miR-21 and miR-126 totaled almost 40% % of all miRNAs. A complex repertoire of isomiRs was found, displaying also 59 variations, potentially affecting target recognition. Highstringency bioinformatic analysis identified microRNA candidates, whose predicted pre-miRNAs folded into a stable hairpin. Validation of a subset by qPCR identified 18 high-confidence novel miRNAs as detectable in independent HUVEC cultures and associated to the RISC complex. The expression of two novel miRNAs was significantly down-modulated by hypoxia, while miR-210 was significantly induced. Gene ontology analysis of their predicted targets revealed a significant association to hypoxiainducible factor signaling, cardiovascular diseases, and cancer. Overexpression of the novel miRNAs in hypoxic endothelial cells affected cell growth and confirmed the biological relevance of their down-modulation. In conclusion, deep-sequencing accurately profiled known, variant, and novel microRNAs expressed by endothelial cells in normoxia and hypoxia.

A class of small non-coding RNAs, the microRNAs (miRNAs), have recently attracted great attention in cancer research since they play a central role in regulation of gene-expression and miRNA aberrant expression is found in almost all types of human cancer. The discovery of circulating miRNAs in body fluids and the finding that they are often tumor specific and can be detected early in tumorigenesis has soon led to the evaluation of their possible use as cancer biomarkers and treatment-response predictors. The evidence that tumor cells communicate via the secretion and delivery of miRNAs packed into tumor-released microvesicles has prompted to investigate miRNA contribution as signaling molecules to the establishment and maintenance of the tumor microenvironment and the metastatic niche in cancer. In this review we highlight the recent advances on the role of exosomal miRNAs as mediators of cancer cell-to-cell communication.

The identification of early and stage-specific biomarkers for Alzheimer's disease (AD) is critical, as the development of disease-modification therapies may depend on the discovery and validation of such markers. The identification of early reliable biomarkers depends on the development of new diagnostic algorithms to computationally exploit the information in large biological datasets. To identify potential biomarkers from mRNA expression profile data, we used the Logic Mining method for the unbiased analysis of a large microarray expression dataset from the anti-NGF AD11 transgenic mouse model. The gene expression profile of AD11 brain regions was investigated at different neurodegeneration stages by whole genome microarrays. A new implementation of the Logic Mining method was applied both to early (1-3 months) and late stage (6-15 months) expression data, coupled to standard statistical methods. A small number of "fingerprinting" formulas was isolated, encompassing mRNAs whose expression levels were able to discriminate between diseased and control mice. We selected three differential "signature" genes specific for the early stage (Nudt19, Arl16, Aph1b), five common to both groups (Slc15a2, Agpat5, Sox2ot, 2210015, D19Rik, Wdfy1), and seven specific for late stage (D14Ertd449, Tia1, Txnl4, 1810014B01Rik, Snhg3, Actl6a, Rnf25). We suggest these genes as potential biomarkers for the early and late stage of AD-like neurodegeneration in this model and conclude that Logic Mining is a powerful and reliable approach for large scale expression data analysis. Its application to large expression datasets from brain or peripheral human samples may facilitate the discovery of early and stage-specific AD biomarkers.