Characterizing the functions of Trypanosoma brucei TIF2 and TRF in regulation of antigenic variation
Year: 2014
Type: article
Abstract: Subtelomeres consist of sequences adjacent to telomeres and contain genes involved in important cellular functions, as subtelomere instability is associated with several human diseases.Balancing between subtelomere stability and plasticity is particularly important for Trypanosoma brucei, a protozoan parasite that causes human African trypanosomiasis.T. brucei regularly switches its major surface antigen, variant surface glycoprotein (VSG), to evade the host immune response.VSGs are expressed exclusively from subtelomeres in a strictly monoallelic fashion.Telomere proteins are important for protecting chromosome ends from illegitimate DNA processes.However, whether they contribute to subtelomere integrity and stability has not been well studied.We have identified a novel T. brucei telomere protein, T. brucei TRF-Interacting Factor 2 (TbTIF2), as a functional homolog of mammalian TIN2.A transient depletion of TbTIF2 led to an elevated VSG switching frequency and an increased amount of DNA doublestrand breaks (DSBs) in both active and silent subtelomeric VSG expression sites (BESs).Therefore, TbTIF2 plays an important role in VSG switching regulation and is important for subtelomere integrity and stability.TbTIF2 depletion increased the association of TbRAD51 with the telomeric and subtelomeric chromatin, and TbRAD51 deletion further increased subtelomeric DSBs in TbTIF2-depleted cells, suggesting that TbRAD51mediated DSB repair is the underlying mechanism of subsequent VSG switching.Surprisingly, significantly more TbRAD51 associated with the active BES than with the viii silent BESs upon TbTIF2 depletion, and TbRAD51 deletion results in much more DSBs in the active BES than in the silent BESs in TbTIF2-depleted cells, suggesting that TbRAD51 preferentially repairs DSBs in the active BES.Interestingly, depletion of TbTIF2 affects the protein's level of its interacting TTAGGG Repeat binding Factor, TbTRF.In addition, a transient depletion of TbTRF led to a significant increase in the VSG switching frequency and many switchers arose through gene conversion events.As collaboration with Dr. Zhao at Hong Kong Polytechnic University, we solved the NMR structure of TbTRF myb domain.Based on the structure, we identified several residues of the TbTRF myb domain, when mutated, lead to weakened DNA binding activities and elevated VSG switching frequencies.Similarly to TbTIF2 and TbTRF depleted cells, the predominant switching events in weakened DNA binding TbTRF mutants were mediated by gene conversion.Our data indicate that the DNA binding activity of TbTRF is critical for VSG switching regulation in T. brucei.TbTIF2 and TbTRF interact strongly and both play important roles in VSG switching regulation.Our results suggest that TbTIF2 and TbTRF function in the same pathway in antigenic variation, which is an important T. brucei pathogenesis mechanism.Our study will help develop new anti-parasite drugs and better understand conserved telomere functions in other organisms.
Author: Sanaa E. Jehi
Institution: Cleveland State University
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2623272283