Deoxyhypusine synthase catalyzes the first step in the posttranslational synthesis of an unusual amino acid, hypusine, in the eukaryotic translation initiation factor 5A (eIF-5A) precursor protein. We earlier observed that yeast recombinant deoxyhypusine synthase was phosphorylated by protein kinase C (PKC) in vitro (Kang and Chung, 1999) and the phosphorylation rate was synergistically increased to a 3.5-fold following treatment with phosphatidylserine (P.Ser)/diacylglycerol (DAG)/ Ca2+, suggesting a possible involvement of PKC. We have extended study on the phosphorylation of deoxyhypusine synthase in vivo in different cell lines in order to define its role on the regulation of eIF5A in the cell. Deoxyhypusine synthase was found to be phosphorylated by endogenous kinases in CHO, NIH3T3, and chicken embryonic cells. The highest degree of phosphorylation was found in CHO cells. Moreover, phosphorylation of deoxyhypusine synthase in intact CHO cells was revealed and the expression of phosphorylated deoxyhypusine synthase was significantly diminished by diacyl ethylene glycol (DAEG), a PKC inhibitor, and enhanced by phorbol 12-myristate 13-acetate (PMA) or Ca2+/DAG. Endogenous PKC in CHO cell and cell lysate was able to phosphorylate deoxyhypusine synthase and this modification is enhanced by PMA or Ca2+ plus DAG. Close association of PKC with deoxyhypusine synthase in the CHO cells was evident in the immune coprecipitation and was PMA-, and Ca2+/phospholipiddependent. These results suggest that phosphorylation of deoxyhypusine synthase was PKC-dependent cellular event and open a path for possible regulation in the interaction with eIF5A precursor for hypusine synthesis.
Amine Oxidoreductases/*metabolism ; Animals ; Cell Line ; Chick Embryo ; Female ; Hamsters ; Mice ; Phosphorylation ; Protein Binding ; Protein Kinase C/antagonists & inhibitors/*metabolism

The biosynthesis of hypusine [Nepsilon-(4-amino-2-hydroxybutyl)-lysine] occurs in the eIF-5A precursor protein through two step posttranslational modification involving deoxyhypusine synthase which catalyzes transfer of the butylamine moiety of spermidine to the epsilon-amino group of a designated lysine residue and subsequent hydroxylation of this intermediate. This enzyme is exclusively required for cell viability and growth of yeast (Park, M.H. et al., J. Biol. Chem. 273: 1677-1683, 1998). In an effort to understand structure-function relationship of deoxyhypusine synthase, posttranslational modification(s) of the enzyme by protein kinases were carried out for a possible cellular modulation of this enzyme. And also twelve deletion mutants were constructed, expressed in E. coli system, and enzyme activities were examined. The results showed that deoxyhypusine synthase was phosphorylated by PKC in vitro but not by p56lck and p60c-src. Treatment with PMA specifically increased the relative phosphorylation of the enzyme supporting PKC was involved. Phosphoamino acid analysis of this enzyme revealed that deoxyhypusine synthase is mostly phosphorylated on serine residue and weakly on threonine. Removal of Met1-Glu10 (deltaMet1-Glu10) residues from amino terminal showed no effect on the catalytic activity but further deletion (deltaMet1-Ser20) caused loss of enzyme activity. The enzyme with internal deletion, deltaGln197-Asn212 (residues not present in the human enzyme) was found to be inactive. Removal of 5 residues from carboxyl terminal, deltaLys383-Asn387, retained only slight activity. These results suggested that deoxyhypusine synthase is substrate for PKC dependent phosphorylation and requires most of the polypeptide chains for enzyme activity except the first 15 residues of N-terminal despite of N- and C-terminal residues of the enzyme consist of variable regions. Copyright 2000 Academic Press.
Amine Oxidoreductases/metabolism* ; Amine Oxidoreductases/genetics ; Amino Acid Motifs ; Amino Acid Sequence ; Escherichia coli/genetics ; Fungal Proteins/metabolism* ; Fungal Proteins/genetics ; Human ; Molecular Sequence Data ; NAD/metabolism ; Phosphorylation ; Promoter Regions (Genetics) ; Protein Kinase C/metabolism* ; Recombinant Proteins/metabolism ; Recombinant Proteins/genetics ; Sequence Deletion ; Sequence Homology, Amino Acid ; Threonine/metabolism ; Yeasts/enzymology