Aminohexanoic hydroxamate is a potent inducer of the differentiation of mouse neuroblastoma cells

The Importance of 6-Aminohexanoic Acid as a Hydrophobic, Flexible Structural Element

6-aminohexanoic acid is an ω-amino acid with a hydrophobic, flexible structure. Although the ω-amino acid in question is mainly used clinically as an antifibrinolytic drug, other applications are also interesting and important. This synthetic lysine derivative, without an α-amino group, plays a significant role in chemical synthesis of modified peptides and in the polyamide synthetic fibers (nylon) industry. It is also often used as a linker in various biologically active structures. This review concentrates on the role of 6-aminohexanoic acid in the structure of various molecules.

Deoxyhypusine synthase (DHPS) inhibitor GC7 induces p21/Rb-mediated inhibition of tumor cell growth and DHPS expression correlates with poor prognosis in neuroblastoma patients

PURPOSE

Neuroblastoma (NB) is an aggressive pediatric malignancy that typically occurs in infants and children under the age of 5 years. High-stage tumors relapse frequently even after aggressive multimodal treatment, resulting in therapy resistance and eventually in patient death. Clearly, new biologically-targeted drugs are needed that more efficiently suppress tumor growth and prevent relapse. We and others previously showed that polyamines such as spermidine play an essential role in NB tumorigenesis and that DFMO, an inhibitor of the central polyamine synthesis gene ODC, is effective in vitro and in vivo, prompting its evaluation in NB clinical trials. However, the specific molecular actions of polyamines remain poorly defined. Spermidine and deoxyhypusine synthase (DHPS) are essential components in the hypusination-driven post-translational activation of eukaryotic initiation factor 5A (eIF5A).

METHODS

We assessed the role of DHPS in NB and the impact of its inhibition by N(1)-guanyl-1,7-diaminoheptane (GC7) on tumor cell growth using cell proliferation assays, Western blot, immunofluorescence microscopy, and Affymetrix micro-array mRNA expression analyses in NB tumor samples.

RESULTS

We found that GC7 inhibits NB cell proliferation in a dose-dependent manner, through induction of the cell cycle inhibitor p21 and reduction of total and phosphorylated Rb proteins. Strikingly, high DHPS mRNA expression correlated significantly with unfavorable clinical parameters, including poor patient survival, in a cohort of 88 NB tumors (all P < 0.04).

CONCLUSIONS

These results suggest that spermidine and DHPS are key contributing factors in NB tumor proliferation through regulation of the p21/Rb signaling axis.

Molecular cloning and functional expression of bovine deoxyhypusine hydroxylase cDNA and homologs

Deoxyhypusine hydroxylase is the second of the two enzymes that catalyzes the maturation of eukaryotic initiation factor 5A (eIF5A). The mature eIF5A is the only known protein in eukaryotic cells that contains the unusual amino acid hypusine (N(epsilon)-(4-amino-2(R)-hydroxybutyl)lysine). Synthesis of hypusine is essential for the function of eIF5A in eukaryotic cell proliferation and survival. Here, we describe the cloning and characterization of bovine deoxyhypusine hydroxylase cDNA and its homologs. The deduced bovine deoxyhypusine hydroxylase protein is 87% identical to human enzyme and 45% identical to yeast enzyme. The overexpressed enzyme showed activity in catalyzing the hydroxylation of the deoxyhypusine residue in the eIF5A intermediate. An amino acid substitution from Glu 57 to Gly located at one of the four conserved His-Glu (HE) pairs, the potential metal coordination sites, resulted in severe reduction of deoxyhypusine hydroxylase activity. A deletion at the HEAT-repeats 1-3 resulted in complete losses of deoxyhypusine hydroxylase activity.

Profiling of nuclear extract proteins from human neuroblastoma cell lines: the search for fingerprints

PURPOSE

Neuroblastoma (NB) commonly presents with advanced disease at diagnosis and is associated with poor survival. If identified early, however, survival is improved suggesting a benefit of early detection. The authors have used proteomics technology in an attempt to identify novel markers that permit early detection of NB and characterize its molecular makeup.

METHODS

Three different human NB cell lines SK-N-AS, SK-N-DZ, and SK-N-FI were subjected to series of biochemical fractionation steps to extract nuclear proteins. These proteins were analyzed for differential expression by 2-dimensional polyacrylamide gel electrophoresis. Polypeptides of interest were subsequently identified by liquid chromatography-linked tandem mass spectrometry.

RESULTS

Multiple proteins were identified in these human NB cell lines including SET (a ubiquitous nuclear protein), stathmin (a cytosolic signal transduction protein), and grp94 (a heat shock protein). SET is a putative oncogene associated with the chromosomal translocation (6;9) leading to acute undifferentiated leukemia. Stathmin is an oncogene found in greater abundance in leukemic cells compared to nonleukemic cells. A total of 94-kDa glucose-regulated protein has been shown to be protective in human breast cancer cells in vitro and related with the occurrence, differentiation, and progression of human lung cancer. The first protein has not been previously associated with NB.

CONCLUSIONS

The identification of these 3 previously unrecognized cancer-related potential biomarkers in human NB cell lines may prove useful in developing diagnostic tests. The proteomic methodology of 2-dimensional polyacrylamide gel electrophoresis/mass spectrometry also provides an improved opportunity to understand the natural history of NB and develop novel chemotherapeutic agents for this prevalent childhood malignancy with a dismal outcome.

Molecular cloning of bovine eIF5A and deoxyhypusine synthase cDNA

Deoxyhypusine synthase is the first of the two enzymes that catalyzes the maturation of eukaryotic initiation factor 5A (eIF5A). The mature eIF5A is the only known protein in eukaryotic cells that contains the unusual amino acid hypusine (N(epsilon)-(4-amino-2(R)-hydroxybutyl)-lysine). Synthesis of hypusine is essential for the function of eIF5A in eukaryotic cell proliferation and survival. Here we describe the cloning and characterization of bovine eIF5A and bovine deoxyhypusine synthase. The deduced bovine eIF5A protein is 100% identical to human eIF5A-1, and the deduced bovine deoxyhypusine synthase protein showed a 93% identity to the human protein.

Identification and characterization of eukaryotic initiation factor 5A-2

The phylogenetically conserved eukaryotic translation initiation factor 5A (eIF5A) is the only known cellular protein to contain the post-translationally derived amino acid hypusine [Nepsilon-(4-amino-2-hydroxybutyl)lysine]. Both eIF5A and its hypusine modification are essential for sustained cell proliferation. Normally only one eIF5A protein is expressed in human cells. Recently, we identified a second human EIF5A gene that would encode an isoform (eIF5A-2) of 84% sequence identity. Overexpression of eIF5A-2 mRNA in certain human cancer cells, in contrast to weak normal expression limited to human testis and brain, suggests EIF5A2 as a potential oncogene. However, eIF5A-2 protein has not been described in human or mammalian cells heretofore. Here, we describe the identification of eIF5A-2 protein in human colorectal and ovarian cancer lines, SW-480 and UACC-1598, that overexpress eIF5A-2 mRNAs. Functional characterization of the human isoforms revealed that either human EIF5A gene can complement growth of a yeast strain in which the yeast EIF5A genes were disrupted. This indicates functional similarity of the human isoforms in yeast and suggests that eIF5A-2 has an important role in eukaryotic cell survival similar to that of the ubiquitous eIF5A-1. Detectable structural differences were also noted, including lack of immunological cross-reactivity, formation of different complexes with deoxyhypusine synthase, and Km values (1.5 +/- 0.2 vs. 8.3 +/- 1.4 microm for eIF5A-1 and -2, respectively) as substrates for deoxyhypusine synthase in vitro. These physical characteristics and distinct amino acid sequences in the C-terminal domain together with differences in gene expression patterns imply differentiated, tissue-specific functions of the eIF5A-2 isoform in the mammalian organism and in cancer.