Glutamine deprivation initiates reversible assembly of mammalian rods and rings.
Rods and rings (RR) are protein assemblies composed of cytidine triphosphate synthetase type 1 (CTPS1) and inosine monophosphate dehydrogenase type 2 (IMPDH2), key enzymes in CTP and GTP biosynthesis. Small-molecule inhibitors of CTPS1 or IMPDH2 induce RR assembly in various cancer cell lines within 15 min to hours. Since glutamine is an essential amide nitrogen donor in these nucleotide biosynthetic pathways, glutamine deprivation was examined to determine whether it leads to RR formation. HeLa cells cultured in normal conditions did not show RR, but after culturing in media lacking glutamine, short rods (<2 μm) assembled after 24 h, and longer rods (>5 μm) formed after 48 h. Upon supplementation with glutamine or guanosine, these RR underwent almost complete disassembly within 15 min. Inhibition of glutamine synthetase with methionine sulfoximine also increased RR assembly in cells deprived of glutamine. Taken together, our data support the hypothesis that CTP/GTP biosynthetic enzymes polymerize to form RR in response to a decreased intracellular level of glutamine. We speculate that rod and ring formation is an adaptive metabolic response linked to disruption of glutamine homeostasis.
Department of Oral Biology, University of Florida, 1395 Center Drive, Gainesville, FL, 32610-0424, USA.
S John
SJ
Calise
Wendy C
WC
Carcamo
Claire
C
Krueger
Joyce D
JD
Yin
Daniel L
DL
Purich
Edward K L
EK
Chan
D053898:Biosynthetic Pathways; D019731:Carbon-Nitrogen Ligases / Q000378:metabolism*; D003570:Cytidine Triphosphate / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007168:IMP Dehydrogenase / Q000378:metabolism*
D005973:Glutamine; D003570:Cytidine Triphosphate; D006160:Guanosine Triphosphate; D007168:IMP Dehydrogenase; C501687:IMPDH2 protein, human; D019731:Carbon-Nitrogen Ligases; D005974:Glutamate-Ammonia Ligase; C019951:CTP synthetase