Suramin action in African trypanosomes involves a RuvB-like DNA helicase

Abstract

Suramin is one of the oldest drugs in use today. It is still the treatment of choice for the hemolymphatic stage of African sleeping sickness caused byTrypanosoma brucei rhodesienseand it is also used for surra in camels, caused byTrypanosoma evansi. Yet despite one hundred years of use, suramin's mode of action is not fully understood. Suramin is a polypharmacologic molecule that inhibits diverse proteins. Here we demonstrate that a DNA helicase of the pontin/ruvB-like 1 family, termedT. bruceiRuvBL1, is involved in suramin resistance in African trypanosomes. Bloodstream-formT. b. rhodesienseunder long-term selection for suramin resistance acquired a homozygous point mutation, isoleucin-312 to valine, close to the ATP binding site ofT. bruceiRuvBL1. The introduction of this missense mutation, by reverse genetics, into drug-sensitive trypanosomes significantly decreased their sensitivity to suramin. Intriguingly, the corresponding residue ofT. evansiRuvBL1 was found mutated in a suramin-resistant field isolate, in that case to a leucin. RuvBL1 (Tb927.4.1270) is predicted to build a heterohexameric complex with RuvBL2 (Tb927.4.2000). RNAi-mediated silencing of gene expression of eitherT. bruceiRuvBL1 or RuvBL2 caused cell death within 72 h. At 36 h after induction of RNAi, bloodstream-form trypanosomes exhibited a cytokinesis defect resulting in the accumulation of cells with two nuclei and two or more kinetoplasts. Taken together, these data indicate that RuvBL1 DNA helicase is among the primary targets of suramin in African trypanosomes.