Trypanosoma brucei TIF2 and TRF Suppress VSG Switching Using Overlapping and Independent Mechanisms.
Trypanosoma brucei causes debilitating human African trypanosomiasis and evades the host's immune response by regularly switching its major surface antigen, VSG, which is expressed exclusively from subtelomeric loci. We previously showed that two interacting telomere proteins, TbTRF and TbTIF2, are essential for cell proliferation and suppress VSG switching by inhibiting DNA recombination events involving the whole active VSG expression site. We now find that TbTIF2 stabilizes TbTRF protein levels by inhibiting their degradation by the 26S proteasome, indicating that decreased TbTRF protein levels in TbTIF2-depleted cells contribute to more frequent VSG switching and eventual cell growth arrest. Surprisingly, although TbTIF2 depletion leads to more subtelomeric DNA double strand breaks (DSBs) that are both potent VSG switching inducers and detrimental to cell viability, TbTRF depletion does not increase the amount of DSBs inside subtelomeric VSG expression sites. Furthermore, expressing an ectopic allele of F2H-TbTRF in TbTIF2 RNAi cells allowed cells to maintain normal TbTRF protein levels for a longer frame of time. This resulted in a mildly better cell growth and partially suppressed the phenotype of increased VSG switching frequency but did not suppress the phenotype of more subtelomeric DSBs in TbTIF2-depleted cells. Therefore, TbTIF2 depletion has two parallel effects: decreased TbTRF protein levels and increased subtelomeric DSBs, both resulting in an acute increased VSG switching frequency and eventual cell growth arrest.
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, Ohio, United States of America.
Sanaa E
SE
Jehi
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, Ohio, United States of America.
Vishal
V
Nanavaty
Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, Cleveland State University, Cleveland, Ohio, United States of America.|The Rockefeller University, New York, New York, United States of America.|Department of Immunology, Cleveland Clinic Lerner Research Institute, Cleveland, Ohio, United States of America.|Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, Ohio, United States of America.
Bibo
B
Li
D000483:Alleles; D000940:Antigenic Variation; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded; D016054:DNA, Protozoan / Q000235:genetics; D005785:Gene Conversion; D005838:Genotype; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry; D015800:Protozoan Proteins / Q000378:metabolism*; D034622:RNA Interference; D035341:Telomeric Repeat Binding Protein 2 / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics* / Q000378:metabolism; D014643:Variant Surface Glycoproteins, Trypanosoma / Q000235:genetics* / Q000378:metabolism
D002868:Chromosomal Proteins, Non-Histone; D016054:DNA, Protozoan; D015800:Protozoan Proteins; C000595357:TRF-interacting factor 2, Trypanosoma brucei; D035341:Telomeric Repeat Binding Protein 2; D014643:Variant Surface Glycoproteins, Trypanosoma; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease