MKT1 interacting RNA-binding protein and its role in the trypanosome Variant Surface Glycoprotein mRNA stabilization.

LARISSA NASCIMENTO ; ERBEN ESTEBAN DANIEL

Congreso; MPM XXXI; 2020

Control of gene expression in kinetoplastids such as trypanosomes depends heavily on RNA-binding proteins (RBPs) that influence mRNA decay and/or translation rates. Several RBPs do this by interacting with MKT1. MKT1 then, on one hand recruits a mRNA stabilisation complex (containing PBP1, XAC, LSM12 and an associated poly(A) binding protein, PABP2) while on the other, it interacts with EIF4G5 (a component of the EIF4E6-EIF4G5 translation initiation complex). One of the RBPs that interact with MKT1 is CFB2. CFB2 is an essential bloodstream-form specific protein that lacks known RNA-binding domains. CFB2 is highly enriched in the Variant Surface Glycoprotein mRNA bound proteome and is essential to maintain the VSG mRNA levels. Reporter experiments in procyclic forms show that the action of CFB2 depends on a conserved 16-mer element in the VSG 3?-untranslated region, while a conserved 8-mer in the 3'-UTR is implicated in VSG mRNA down-regulation. CFB2 interacts with MKT1 via a conserved HDPY motif, mutation of which abolishes CFB2?s expression-promoting activity. In addition, CFB2 has an N-terminal cyclin-F-box domain. F-box proteins are found in SCF complexes (SKP1-Cullin-F-Box), which are E3 ligase components of the ubiquitination machinery. We have demonstrated that the interaction between CFB2 and trypanosome SKP1 depends on the F-box domain and it is involved in auto-regulation of CFB2 abundance. Possible Cullin partners and further ubiquitination targets of this SCF-complex are currently under investigation. References: Benz and Clayton, 2007 (PMID: 17920137); Singh et al., 2014 (PMID: 24470144); Nascimento et al., 2020 (PMID: 32532821).