Mutational analyses of human eIF5A-1--identification of amino acid residues critical for eIF5A activity and hypusine modification.

The eukaryotic translation initiation factor 5A (eIF5A) is the only protein that contains hypusine [Nepsilon-(4-amino-2-hydroxybutyl)lysine], which is required for its activity. Hypusine is formed by post-translational modification of one specific lysine (Lys50 for human eIF5A) by deoxyhypusine synthase and deoxyhypusine hydroxylase. To investigate the features of eIF5A required for its activity, we generated 49 mutations in human eIF5A-1, with a single amino acid substitution at the highly conserved residues or with N-terminal or C-terminal truncations, and tested mutant proteins in complementing the growth of a Saccharomyces cerevisiae eIF5A null strain. Growth-supporting activity was abolished in only a few mutant eIF5As (K47D, G49A, K50A, K50D, K50I, K50R, G52A and K55A), with substitutions at or near the hypusine modification site or with truncation of 21 amino acids from either the N-terminus or C-terminus. The inactivity of the Lys50 substitution proteins is obviously due to lack of deoxyhypusine modification. In contrast, K47D and G49A were effective substrates for deoxyhypusine synthase, yet failed to support growth, suggesting critical roles of Lys47 and Gly49 in eIF5A activity, possibly in its interaction with effector(s). By use of a UBHY-R strain harboring genetically engineered unstable eIF5A, we present evidence for the primary function of eIF5A in protein synthesis. When selected eIF5A mutant proteins were tested for their activity in protein synthesis, a close correlation was observed between their ability to enhance protein synthesis and growth, lending further support for a central role of eIF5A in translation.

Global gene expression profiles of human head and neck squamous carcinoma cell lines.

For genomewide monitoring and identification of biomarkers of head and neck squamous cell carcinoma (HNSCC), we have conducted a systematic characterization of gene expression profiles, using human cDNA microarrays containing 9K clones, in 25 HNSCC cell lines and 1 immortalized human oral keratinocyte cell line. We used normal human oral keratinocytes (NHOKs) as a reference. Our study showed that genes primarily involved in cell cycle regulation, oncogenesis, cell proliferation, differentiation, apoptosis and cell adhesion were widely altered in the 26 cell lines. Upregulated genes included known oncogenes, protein kinases, DNA-binding proteins and cell cycle regulators, while those commonly downregulated included differentiation markers, cell adhesion proteins, extracellular matrix proteins, structural proteins (keratins) and protease inhibitor proteins. Compared to NHOK, we observed a striking reduction in the expression of genes involved in terminal differentiation, suggesting that a loss in this process is an important signature of HNSCC. In addition, hierarchical clustering analysis as well as principal component analysis revealed 2 distinctive subtypes of gene expression patterns among the 26 cell lines, reflecting a degree of heterogeneity in HNSCC. By applying significance analysis of microarrays, 128 genes were selected for being distinctively expressed between the 2 groups. Genes differentially expressed in the 2 subgroups include cell proliferation-related genes, IGFBP6, EGFR and VEGFC; tumor suppression and apoptosis-related genes such as Tp53, Tp63; as well as cell cycle regulators such as CCND1 and CCND2 (cyclins D1 and D2), suggesting that the 2 subgroups might have undergone different pathways of carcinogenesis.

Membrane-bound alkaline phosphatase gene induces antitumor effect by G2/M arrest in etoposide phosphate-treated cancer cells.

Gene therapy is used to induce immune responses, regulate tumor growth, or sensitize tumor cells to specific treatment. For sensitizing tumor cells to specific drug, we considered a prodrug-converting system using membrane-bound intestinal alkaline phosphatase (IAP) as the prodrug-activating genes. The IAP is capable of converting a relatively non-cytotoxic prodrug, etoposide phosphate (EP), into etoposide with a significant antitumor activity. We used the retroviral vector for transducing IAP gene into SNU638 gastric cancer cells and EP was prepared by phosphorylation of etoposide. To determine the chromosomal incorporation of membrane-bound IAP gene and AP activity in IAP gene-transduced cells (SNU638/IAP), we performed genomic PCR and AP activity analysis. In genomic DNA of SNU638/IAP cells, full cDNA fragment of a 2.5 kb IAP was detected, and AP activity was shown at most 15 approximately 18-fold increase compared with control cells. According to the in vitro cytotoxicity study, SNU638/IAP cells greatly enhanced the cytotoxic effect in proportion to the concentration of EP, while control cells didn't cause any cytotoxic effects after EPtreatment. Especially, the cell population of G2/M phase was increased in EP-treated SNU638/ IAP cells because P4 DNA unknotting activity of topoisomerase II was decreased by EP treatment such as the action mechanism of etoposide. Finally, a strong antitumor response was observed in SNU638/IAP cancer cells-bearing nude mice that were treated with EP. These results suggest that the prodrug-converting system by membrane-bound IAP gene and EP prodrug is useful as the strong strategy of gene therapy for cancer treatment.