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Variant surface glycoprotein RNA interference triggers a precytokinesis cell cycle arrest in African trypanosomes.

ABSTRACT: Trypanosoma brucei is a protozoan parasite that causes African sleeping sickness. T. brucei multiplies extracellularly in the bloodstream, relying on antigenic variation of a dense variant surface glycoprotein (VSG) coat to escape antibody-mediated lysis. We investigated the role of VSG in proliferation and pathogenicity by using inducible RNA interference to ablate VSG transcript down to 1-2% normal levels. Inhibiting VSG synthesis in vitro triggers a rapid and specific cell cycle checkpoint blocking cell division. Parasites arrest at a discrete precytokinesis stage with two full-length flagella and opposing flagellar pockets, without undergoing additional rounds of S phase and mitosis. A subset (<10%) of the stalled cells have internal flagella, indicating that the progenitors of these cells were already committed to cytokinesis when VSG restriction was sensed. Although there was no obvious VSG depletion in vitro after 24-h induction of VSG RNA interference, there was rapid clearance of these cells in vivo. We propose that a stringent block in VSG synthesis produces stalled trypanosomes with a minimally compromised VSG coat, which can be targeted by the immune system. Our data indicate that VSG protein or transcript is monitored during cell cycle progression in bloodstream-form T. brucei and describes precise precytokinesis cell cycle arrest. This checkpoint before cell division provides a link between the protective VSG coat and cell cycle progression and could function as a novel parasite safety mechanism, preventing extensive dilution of the protective VSG coat in the absence of VSG synthesis.

SUBMITTER: Sheader K

PROVIDER: S-EPMC1150830 | biostudies-literature | 2005 Jun

REPOSITORIES: biostudies-literature

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Variant surface glycoprotein RNA interference triggers a precytokinesis cell cycle arrest in African trypanosomes.

Sheader Karen K Vaughan Sue S Minchin James J Hughes Katie K Gull Keith K Rudenko Gloria G

Proceedings of the National Academy of Sciences of the United States of America 20050603 24

Trypanosoma brucei is a protozoan parasite that causes African sleeping sickness. T. brucei multiplies extracellularly in the bloodstream, relying on antigenic variation of a dense variant surface glycoprotein (VSG) coat to escape antibody-mediated lysis. We investigated the role of VSG in proliferation and pathogenicity by using inducible RNA interference to ablate VSG transcript down to 1-2% normal levels. Inhibiting VSG synthesis in vitro triggers a rapid and specific cell cycle checkpoint bl ...[more]

PMID: 15937117

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Project description:Variant Surface Glycoproteins (VSG) coat parasitic African trypanosomes and underpin antigenic variation and immune evasion. This VSG is a super-abundant virulence factor that is subject to post-transcriptional gene expression controls mediated via the VSG 3’-untranslated region (3’-UTR). To identify positive VSG regulators in bloodstream form cells, we used prior genome-scale screening data to prioritise mRNA binding protein (mRBPs) knockdowns that phenocopy VSG mRNA knockdown, displaying both loss-of-fitness and pre-cytokinesis accumulation. The top three candidate VSG regulators were CFB2 (cyclin F-box protein 2, Tb927.1.4650), MKT1 (Tb927.6.4770) and PBP1 (polyadenylate binding-protein binding-protein, Tb927.8.4540). Notably, CFB2 was recently found to regulate VSG transcript stability, and all three proteins were found to associate with each other. We used data-independent acquisition for accurate label-free quantification and deep proteome coverage to quantify expression profiles following depletion of each mRBP. Only CFB2 knockdown significantly reduced VSG expression and the expression of a reporter under the control of a VSG 3’-untranslated region (3’-UTR). CFB2 knockdown also triggered depletion of cytoplasmic ribosomal proteins, consistent with translation arrest observed when VSG synthesis is blocked. In contrast, PBP1 knockdown triggered depletion of CFB2, MKT1, and other components of the PBP1-complex. Finally, all three knockdowns triggered depletion of cytokinesis initiation factors, consistent with the cytokinesis defect that was confirmed here for all three knockdowns. Thus, genome-scale knockdown datasets facilitate the triage and prioritisation of candidate regulators. Quantitative proteomic analysis confirms 3’-UTR dependent positive control of VSG expression by CFB2 and interactions with additional mRBPs. Our results also reveal connections between VSG expression control by CFB2, ribosomal protein expression, and cytokinesis.

Dataset Information

Variant surface glycoprotein RNA interference triggers a precytokinesis cell cycle arrest in African trypanosomes.

Publications

Variant surface glycoprotein RNA interference triggers a precytokinesis cell cycle arrest in African trypanosomes.

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