Kimitoshi Kohno

The Y-box-binding protein (YB-1) represents the most evolutionary conserved nucleic-acid-binding protein currently known. YB-1 is a member of the cold-shock domain (CSD) protein superfamily. It performs a wide variety of cellular functions, including transcriptional regulation, translational regulation, DNA repair, drug resistance and stress responses to extracellular signals. As a result, YB-1 expression is closely associated with cell proliferation. In this review, we will begin by briefly describing the characteristics of YB-1 and will then summarize the pleiotropic functions brought about via DNA-RNA transaction and protein-protein interactions. In addition, we will discuss the diverse range of potential physiological and pathological functions of YB-1.

By targeting the ATP binding conserved domain in three ATP binding cassette superfamily proteins (P-glycoprotein, multidrug resistance protein, and cystic fibrosis transmembrane regulator), we isolated the cDNA of a new ATP binding cassette superfamily that was specifically enhanced in a cisplatin-resistant human head and neck cancer KB cell line. A human clone homologous to rat canalicular multispecific organic anion transporter (cMOAT) was found and designated human cMOAT. Fluorescence in situ hybridization demonstrated the chromosomal locus of the gene on chromosome 10q24. The human cMOAT cDNA hybridized a 6.5-kb mRNA that was expressed 4- to 6-fold higher by three cisplatin-resistant cell lines derived from various human tumors exhibiting decreased drug accumulation. Human cMOAT may function as a cellular cisplatin transporter.

The expression of vascular endothelial growth factor (VEGF) has been implicated in brain tumor angiogenesis, and the promoter region for the VEGF gene contains several SP-1 and AP-1 (c-Fos and c-Jun) binding motifs. Among eight human glioma cell lines, cellular mRNA levels of transcription factors SP-1 and AP-1 (c-Fos and c-Jun) were found to be closely correlated with those of VEGF. VEGF expression appears to be highly susceptible to hypoxia or exogenous cytokines and growth factors. Of various cytokines and growth factors, basic fibroblast growth factor (bFGF), tumor necrosis factor alpha (TNF-alpha), and interleukin 1 most potently enhanced VEGF mRNA levels of a glioma cell line, U251. Incubation of the glioma cells with bFGF or TNF-alpha increased both VEGF and SP-1 mRNA at 30 min and c-Fos mRNA at 1-3 h, over 5-fold. Nuclear run-on assays showed an apparent increase of the transcription of the VEGF gene as well as the SP-1 gene by bFGF or TNF-alpha. Gel mobility shift assays demonstrated that only SP-1 binding activity was increased 1 h after exposure to bFGF or TNF-alpha, and also that AP-1, but not SP-1, activity was significantly activated by hypoxia. Mithramycin, an inhibitor of SP-1, at 1-10 nM inhibited activation of the VEGF gene by bFGF or TNF-alpha but not that by hypoxia. Western blot analysis also demonstrated an increase in cellular amounts of VEGF by TNF-alpha and a decrease by co-administration with mithramycin. The promoter activity of the VEGF gene, which contains five SP-1 binding sites and one AP-1 binding site but not hypoxia regulatory elements, was enhanced by bFGF or TNF-alpha but not by hypoxia. The chloramphenicol acetyltransferase assay with VEGF promoter deletion constructs demonstrated that four clusterized SP-1 binding sites in the proximal promoter were essential for the basal transcription and the TNF-alpha-dependent activation. These data indicated that the expression of the VEGF gene enhanced by bFGF or TNF-alpha appeared to be mediated in part through the transcription factor SP-1, suggesting a different mechanism from that for hypoxia-induced activation of the VEGF gene.

Laminin is a basement membrane-specific glycoprotein (800 kDa) consisting of three chains: A, B1, and B2. Laminin has diverse biological functions, which include stimulating epithelial cell growth and differentiation. We have isolated two overlapping cDNA clones that span 5.9 kilobases and code for the entire B1 chain of mouse laminin. The nucleotide sequence of the clones reveals a 5358-base pair open reading frame that potentially codes for 1786 amino acids, including 20 amino acids of a presumptive signal peptide. Analysis of the deduced protein sequence predicts that the B1 chain has seven distinct domains that include cysteine-rich repeats, alpha-helical, and globular structures. Part of the cysteine-rich region is homologous to epidermal growth factor and other proteins that contain epidermal growth factor-like repeats.