A novel DNA-binding motif in prostate tumor overexpressed-1 (PTOV1) required for the expression of ALDH1A1 and CCNG2 in cancer cells

PTOV1 is a transcription and translation regulator and a promoter of cancer progression. Its overexpression in prostate cancer induces transcription of drug resistance and self-renewal genes, and docetaxel resistance. Here we studied PTOV1 ability to directly activate the transcription of ALDH1A1 and CCNG2 by binding to specific promoter sequences. Chromatin immunoprecipitation and electrophoretic mobility shift assays identified a DNA-binding motif inside the PTOV-A domain with similarities to known AT-hooks that specifically interacts with ALDH1A1 and CCNG2 promoters. Mutation of this AT-hook-like sequence significantly decreased the expression of ALDH1A1 and CCNG2 promoted by PTOV1. Immunohistochemistry revealed the association of PTOV1 with mitotic chromosomes in high grade prostate, colon, bladder, and breast carcinomas. Overexpression of PTOV1, ALDH1A1, and CCNG2 significantly correlated with poor prognosis in prostate carcinomas and with shorter relapse-free survival in colon carcinoma. The previously described interaction with translation complexes and its direct binding to ALDH1A1 and CCNG2 promoters found here reveal the PTOV1 capacity to modulate the expression of critical genes at multiple levels in aggressive cancers. Remarkably, the AT-hook motifs in PTOV1 open possibilities for selective targeting its nuclear and/or cytoplasmic activities

A Functional Proteomic Method for Biomarker Discovery

The sequencing of the human genome holds out the hope for personalized medicine, but it is clear that analysis of DNA or RNA content alone is not sufficient to understand most disease processes. Proteomic strategies that allow unbiased identification of proteins and their post-transcriptional and -translation modifications are an essential complement to genomic strategies. However, the enormity of the proteome and limitations in proteomic methods make it difficult to determine the targets that are particularly relevant to human disease. Methods are therefore needed that allow rational identification of targets based on function and relevance to disease. Screening methodologies such as phage display, SELEX, and small-molecule combinatorial chemistry have been widely used to discover specific ligands for cells or tissues of interest, such as tumors. Those ligands can be used in turn as affinity probes to identify their cognate molecular targets when they are not known in advance. Here we report an easy, robust and generally applicable approach in which phage particles bearing cell- or tissue-specific peptides serve directly as the affinity probes for their molecular targets. For proof of principle, the method successfully identified molecular binding partners, three of them novel, for 15 peptides specific for pancreatic cancer

Intracellular clusterin induces G2/M-phase arrest and cell death in PC-3 prostate cancer cells

Enhanced clusterin gene expression has been related frequently to organ remodeling, tissue involution, and cell death. Whether clusterin represents a leading cause or a consequence of apoptosis induction is still a matter of debate. Clusterin is known as an extracellular secreted glycoprotein in the mature form. However, truncated isoforms of the protein and nuclear localization of clusterin have been described recently in association to cell death. Here, we show the biological effects triggered in PC-3 androgen-independent prostate cancer cells by overexpression of an intracellular, not secreted form of clusterin (intracellular-clusterin). Transient transfection of PC-3 cells with intracellular-clusterin resulted in nuclear localization signal-independent massive nuclear localization of the protein leading to G(2)-M phase blockade followed by caspase-dependent apoptosis. Constitutive expression of intracellular-clusterin (pFLAG-intracellular-clusterin) in recombinant PC-3 cells caused clonogenic toxicity. The rare pFLAG-intracellular clusterin surviving clones showed inhibition of the proliferation rate and altered phenotype with impaired mitosis and endoreduplication. In these cells, caspase-independent cell death was induced. Impaired cell cycle progression in pFLAG-intracellular-clusterin clones was associated to arrest at the G(2)-M checkpoint by down-regulation of the mitotic complex cyclin B1/cyclin-dependent kinase 1. Intriguingly, intracellular-clusterin was localized exclusively in the cytoplasm in stably transfected cells, suggesting a negative correlation between nuclear clusterin accumulation and cell survival. These findings may possibly explain the conflicting results obtained in different laboratories, suggesting that clusterin might be a proapoptotic or a survival gene, also opening new perspectives for the characterization of androgen-independent and apoptosis-resistant prostate cancer cells