Assembly of IMPDH2-based, CTPS-based, and mixed rod/ring structures is dependent on cell type and conditions of induction

J Genet Genomics. 2015 Jun 20;42(6):287-99. doi: 10.1016/j.jgg.2015.04.002. Epub 2015 Apr 18.


Inhibition of guanosine triphosphate (GTP) and cytidine triphosphate (CTP) biosynthetic pathways induces cells to assemble rod/ring (RR) structures, also named cytoophidia, which consist of the enzymes cytidine triphosphate synthase (CTPS) and inosine-5'-monophosphate dehydrogenase 2 (IMPDH2). We aim to explore the interaction of CTPS and IMPDH2 in the generation of RR structures. HeLa and COS-7 cells were cultured in normal conditions or in the presence of 6-diazo-5-oxo-L-norleucine (DON), ribavirin, or mycophenolic acid (MPA). Over 90% of DON-treated cells presented RR structures. In HeLa cells, 35% of the RR structures were positive for IMPDH2 alone, 26% were CTPS alone, and 31% were IMPDH2/CTPS mixed, while in COS-7 cells, 42% of RR were IMPDH2 alone, 41% were CTPS alone, and 10% were IMPDH2/CTPS mixed. Ribavirin and MPA treatments induced only IMPDH2-based RR. Cells were also transfected with an N-terminal hemagglutinin (NHA)-tagged CTPS1 construct. Over 95% of NHA-CTPS1 transfected cells with DON treatment presented IMPDH2-based RR and almost 100% presented CTPS1-based RR; when treated with ribavirin, over 94% of transfected cells presented IMPDH2-based RR and 37% presented CTPS1-based RR, whereas 2% of untreated transfected cells presented IMPDH2-based RR and 28% presented CTPS1-based RR. These results may help in understanding the relationship between CTP and GTP biosynthetic pathways, especially concerning the formation of filamentous RR structures.

Keywords: CTPS; Enzyme aggregation; Enzyme inhibition; IMPDH2; Nucleotide synthesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biosynthetic Pathways
  • COS Cells
  • Carbon-Nitrogen Ligases / metabolism*
  • Chlorocebus aethiops
  • Cytidine Triphosphate / metabolism*
  • Guanosine Triphosphate / metabolism*
  • HeLa Cells
  • Humans
  • IMP Dehydrogenase / metabolism*
  • Protein Binding


  • Cytidine Triphosphate
  • Guanosine Triphosphate
  • IMP Dehydrogenase
  • IMPDH2 protein, human
  • Carbon-Nitrogen Ligases
  • CTP synthetase