dGTP Starvation in Escherichia coli Provides New Insights into the Thymineless-Death Phenomenon

Abstract

Starvation of cells for the DNA building block dTTP is strikingly lethal (thymineless death, TLD), and this effect is observed in all organisms. The phenomenon, discovered some 60 years ago, is widely used to kill cells in anticancer therapies, but many questions regarding the precise underlying mechanisms have remained. Here, we show for the first time that starvation for the DNA precursor dGTP can kill E. coli cells in a manner sharing many features with TLD. dGTP starvation is accomplished by combining up-regulation of a cellular dGTPase with a deficiency of the guanine salvage enzyme guanine-(hypoxanthine)-phosphoribosyltransferase. These cells, when grown in medium without an exogenous purine source like hypoxanthine or adenine, display a specific collapse of the dGTP pool, slow-down of chromosomal replication, the generation of multi-branched nucleoids, induction of the SOS system, and cell death. We conclude that starvation for a single DNA building block is sufficient to bring about cell death.

Author Summary

Starvation of cells for DNA precursor dTTP is strikingly lethal in many organisms, like bacteria, yeast, and human cells. This type of death is unusual in that starvation for other nutritional requirements generally results in growth arrest, but not in death. The phenomenon is called thymineless death (TLD), because it was first observed some 60 years ago when a thymine-requiring ( thyA) E. coli strain was exposed to growth medium lacking thymine. The TLD phenomenon is of significant interest as it is the basis for several chemotherapeutic (anticancer) treatments in which rapidly growing cells are selectively killed by depletion of the cellular dTTP pool. The precise mechanisms by which cells succumb to dTTP depletion are of significant interest, but have remained elusive for a long time. In the present work, we demonstrate for the first time that the effect is not specific for dTTP starvation. We show that an E. coli strain starved for the DNA precursor dGTP dies in a manner similar to dTTP-starved cells. The effect, which we have termed dGTP starvation, might be exploited - like TLD - therapeutically.