In a previous study [Nachaliel et al., 1993], we identified an RNA-binding protein (RBP) in FTO-2B rat hepatoma cells whose activity was stimulated upon the dissociation of a protein factor. We report in this article that the RBP is a complex protein of about 400 kDa, composed of RNA-binding subunit(s) (RBS), and regulatory subunit(s) (RS). We purified the RS to near-homogeneity (Mr approximately 25,000) and determined the amino acid sequence of a peptide derived from RS. On the basis of this sequence information, the cDNA for RS was obtained. Recombinant RS protein expressed in Escherichia coli had the capacity to bind RBS and inhibit its RNA-binding activity. The cDNA contains the complete coding sequence because the recombinant protein has the same electrophoretic mobility as that of the native RS in SDS-polyacrylamide gels. Sequence comparison showed that RS is almost identical to DJ-1, a recently discovered protein with an oncogenic potential, and CAP1, a rat sperm protein. However, the protein does not contain any known motifs that can provide a clue as to its exact function. Indirect immunofluorescence analyses showed that in addition to the cytoplasm, where RS is associated with microtubular filaments, the polypeptide is localized to the cell nucleus. The possible role of RS is discussed.

Ingestion of aristolochic acids (AAs) contained in herbal remedies results in a renal disease and, frequently, urothelial malignancy. The genotoxicity of AA in renal cells, including mutagenic DNA adducts formation, is well documented. However, the mechanisms of AA-induced tubular atrophy and renal fibrosis are largely unknown. To better elucidate some aspects of this process, we studied cell cycle distribution and cell survival of renal epithelial cells treated with AAI at low and high doses. A low dose of AA induces cell cycle arrest in G2/M phase via activation of DNA damage checkpoint pathway ATM-Chk2-p53-p21. DNA damage signaling pathway is activated more likely via increased production of reactive oxygen species (ROS) caused by AA treatment then via DNA damage induced directly by AA. Higher AA concentration induced cell death partly via apoptosis. Since mitogen-activated protein kinases play an important role in cell survival, death and cell cycle progression, we assayed their function in AA-treated renal tubular epithelial cells. ERK1/2 and p38 but not JNK were activated in cells treated with AA. In addition, pharmacological inhibition of ERK1/2 and p38 as well as suppression of ROS generation with N-acetyl-L-cysteine resulted in the partial relief of cells from G2/M checkpoint and a decline of apoptosis level. Cell cycle arrest may be a mechanism for DNA repair, cell survival and reprogramming of epithelial cells to the fibroblast type. An apoptosis of renal epithelial cells at higher AA dose might be necessary to provide space for newly reprogrammed fibrotic cells.

In a previous study [Nachaliel et al., 1993], we identified an RNA-binding protein (RBP) in FTO-2B rat hepatoma cells whose activity was stimulated upon the dissociation of a protein factor. We report in this article that the RBP is a complex protein of about 400 kDa, composed of RNA-binding subunit(s) (RBS), and regulatory subunit(s) (RS). We purified the RS to near-homogeneity (Mr approximately 25,000) and determined the amino acid sequence of a peptide derived from RS. On the basis of this sequence information, the cDNA for RS was obtained. Recombinant RS protein expressed in Escherichia coli had the capacity to bind RBS and inhibit its RNA-binding activity. The cDNA contains the complete coding sequence because the recombinant protein has the same electrophoretic mobility as that of the native RS in SDS-polyacrylamide gels. Sequence comparison showed that RS is almost identical to DJ-1, a recently discovered protein with an oncogenic potential, and CAP1, a rat sperm protein. However, the protein does not contain any known motifs that can provide a clue as to its exact function. Indirect immunofluorescence analyses showed that in addition to the cytoplasm, where RS is associated with microtubular filaments, the polypeptide is localized to the cell nucleus. The possible role of RS is discussed.

Abstract. As the most common noncutaneous malignancy in American men, prostate cancer currently accounts for 29% of all diagnosed cancers, and ranks second as the cause of cancer fatality in American men. Prostatic cancer is rarely symptomatic early in its course and therefore disease presentation often implies local extension or even metastatic disease. Thus, it is extremely critical to detect and diagnose prostate cancer in its earliest stages, often prior to the presentation of symptoms. Three of the most common techniques used to detect prostate cancer are the digital rectal exam, the transrectal ultrasound, and the use of biomarkers. This review presents an update regarding the field of prostate cancer biomarkers and comments on future biomarkers. Although there is not a lack of research in the field of prostate cancer biomarkers, the discovery of a novel biomarker that may have the advantage of being more specific and effective warrants future scientific inquiry.

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Bone metastasis is the most frequent complication of prostate cancer (PC). Elucidation of the biological basis of this specificity is required for the development of approaches for metastatic inhibition. We investigated the possibility that the preferential attachment of PC cells to bone marrow endothelium (as opposed to endothelium from other organs) affects this specificity. We selected, from peptide phage-displayed libraries, peptide ligands to surfaces of PC cells (C4-2B) attenuated (30 -40%) binding of C4-2B cells to bone marrow endothelial cells (BMECs). We then determined the molecules on the surface of C4-2B cells interacted with the selected peptides using column affinity chromatography and a cDNA expression phage-displayed library generated from C4-2B cells in T7 phage. We identified a phage from the cDNA library that specifically bound to one of the selected peptides-L11. This phage displayed the amino acid sequence homologous for the COOH-terminal portion of prostatespecific antigen (PSA). To examine the possible direct involvement of PSA in the interactions between PC and BMECs, we performed a cell-cell adhesion assay. Antibodies to PSA attenuated PC cells adhesion to BMECs. In addition, exogenous proteolytically active PSA modulated this adhesion. Finally, inactivation of mRNA coding PSA by a small interfering RNA (siRNA) diminished C4-2B cell adhesion to BMECs. These results indicate that PSA expressed as secreted and surface-associated molecules in C4-2B cells is involved in cell-cell interactions and/or digests components of bone marrow endothelium for preferential adhesion and penetration of PC cells. The suggested experimental approach is a promising strategy for identification of cell surface molecules involved in intercellular interactions.