Immunocytochemical localization of polyamines during attachment and spreading of retinal pigment epithelial and intestinal epithelial cells

Aminopropyltransferases involved in polyamine biosynthesis localize preferentially in the nucleus of plant cells

Plant aminopropyltransferases consist of a group of enzymes that transfer aminopropyl groups derived from decarboxylated S-adenosyl-methionine (dcAdoMet or dcSAM) to propylamine acceptors to produce polyamines, ubiquitous metabolites with positive charge at physiological pH. Spermidine synthase (SPDS) uses putrescine as amino acceptor to form spermidine, whereas spermine synthase (SPMS) and thermospermine synthase (TSPMS) use spermidine as acceptor to synthesize the isomers spermine and thermospermine respectively. In previous work it was shown that both SPDS1 and SPDS2 can physically interact with SPMS although no data concerning the subcellular localization was reported. Here we study the subcellular localization of these enzymes and their protein dimer complexes with gateway-based Bimolecular Fluorescence Complementation (BiFC) binary vectors. In addition, we have characterized the molecular weight of the enzyme complexes by gel filtration chromatography with in vitro assembled recombinant enzymes and with endogenous plant protein extracts. Our data suggest that aminopropyltransferases display a dual subcellular localization both in the cytosol and nuclear enriched fractions, and they assemble preferably as dimers. The BiFC transient expression data suggest that aminopropyltransferase heterodimer complexes take place preferentially inside the nucleus.

Immunocytochemical demonstration of polyamines in nucleoli and nuclei

Although biochemical studies have shown that polyamines (PAs) occur in the nucleus, only few studies have examined the intranuclear distribution of these organic cations. By immunocytochemistry, we have previously demonstrated that PAs are located in ribosomes. We now show that PAs also are present in both nucleoli and nuclei of a variety of cell types. Detection of nucleolar and nuclear PAs required novel pretreatment procedures involving protease and/or DNase digestion of specimens prior to immunoreaction. Double fluorescence staining confirmed the localizations. This suggests that PAs may be important to the formation of ribosomes in nucleoli, as well as adds support to biochemical studies suggesting that PAs are involved in many biological events in the nucleus. Further biochemical studies will be needed to substantiate this hypothesis.