In higher plants, the numbers of cytoplasmic-distributed Golgi stacks differ based on function, age and cell type. It has not been clarified how the numbers are controlled, whether all the Golgi apparatus in a cell function equally and whether the increase in Golgi number is a result of the de novo formation from the endoplasmic reticulum (ER) or fission of pre-existing stacks. A tobacco prolyl 4-hydroxylase (NtP4H1.1), which is a cis-Golgi-localizing type II membrane protein, was tagged with a photoconvertible fluorescent protein, mKikGR (monomeric Kikume green red), and expressed in tobacco bright yellow 2 (BY-2) cells. Transformed cells were exposed to purple light to convert the fluorescence from green to red. A time-course analysis after the conversion revealed a progressive increase in green puncta and a decrease in the red puncta. From 3 to 6 h, we observed red, yellow and green fluorescent puncta corresponding to pre-existing Golgi; Golgi containing both pre-existing and newly synthesized protein; and newly synthesized Golgi. Analysis of the number and fluorescence of Golgi at different phases of the cell cycle suggested that an increase in Golgi number with both division and de novo synthesis occurred concomitantly with DNA replication. Investigation with different inhibitors suggested that the formation of new Golgi and the generation of Golgi containing both pre-existing and newly synthesized protein are mediated by different machineries. These results and modeling based on quantified results indicate that the Golgi apparatuses in tobacco BY-2 cells are not uniform and suggest that both de novo synthesis from the ER and Golgi division contribute almost equally to the increase in proliferating cells.

We have recently developed a new method aimed at mass photo-conversion of photo-convertible fluorescence protein (PFP) fluorescence in transformed tobacco BY-2 cells. Using this method we reported recently that the Golgi apparatus is generated by the de novo formation from ER and the division of pre-existing Golgi stacks with similar extents In this work we report that the proliferation of the Golgi apparatus in tobacco cells that enter the growing cycle from the non-dividing cycle is quite similar to that in rapidly growing cells and that de novo formation from the ER and division of pre-existing stacks seems to contribute almost equally to the proliferation.

Histone deacetylases (HDACs) are representative targets for the natural and synthetic chemicals used to transform cells to confer antitumor properties. In the current study, curcumin and hydroxamate-derivative PCI-34058-bound HDAC1 were subjected to atomistic simulation. The results support the view that fitting of curcumin and PCI-34058 within the HDAC1 pocket depends on extensive interactions between the aromatic moieties of the inhibitors and the extensive network of aromatic amino acid side chains lining the pocket of HDAC1. The interaction forces a local perturbation of the coiled structures connecting the pocket residues resulting in ligand-induced tightening of the pocket. In addition to the competitive occupancy of the histone-acetyl-lysine binding pocket by the inhibitors, interference with the in-pocket aspartate-histidine (ASP-HIS) charge relay system was also observed in inhibitor-bound HDAC1 systems. In conclusion, curcumin and PCI-34058-mediated ligand-dependent HDAC1 tunnel closure interferes negatively with the ASP-HIS charge relay system in HDAC1. Future design of HDAC inhibitors may benefit from optimizing competitive interaction with the ligand site and interference with the charge relay system.

No abstract