Distinct features of the Leishmania cap-binding protein LeishIF4E2 revealed by CRISPR-Cas9 mediated heterozygous deletion

Abstract

Leishmania parasites cycle between sand-fly vectors and mammalian hosts, adapting to alternating environments by stage-differentiation, accompanied by changes in the proteome profiles. Translation regulation plays a central role in driving the differential program of gene expression, since control of gene regulation in Leishmania is mostly post-transcriptional. The Leishmania genome encodes six eIF4E candidates, each assumed to have specific functions, although overlaps are expected. It is noted that some of them can bind to a dedicated eIF4G candidate partners, and LeishIF4E2 does not bind any known eIF4G ortholog. LeishIF4E2 was previously shown to comigrate in the polysomal fractions of sucrose gradients, whereas initiation factors usually comigrate with pre-initiation and initiation complexes. Using the CRISPR-Cas9 methodology, we deleted one of the two LeishIF4E2 gene copies. The deletion caused severe alterations in the morphology of mutant cells that turned round and equipped with a very short flagellum, but their growth rate and general translation remained unaffected. Proteomic analysis of the LeishIF4E2(+/-) mutant cells compared to wild type controls showed that the number of proteins that were upregulated exceeded the number of downregulated proteins, possibly indicating that a repressor function was eliminated. The upregulated proteins were related mainly to general metabolic processes, DNA repair and replication, signaling, and cellular motor activity. The downregulated proteins included several groups, including cytoskeletal and ribosomal proteins. Despite the fact that only one of the two LeishIF4E2 alleles was deleted, the mutant cells were impaired in their ability to infect cultured macrophages. LeishIF4E2 does not behave like a general translation factor and its function remains elusive. Although it could have a repressive function, we cannot exclude the possibility that it is responsible for translation of a specific set of transcripts. Overall, our results are in line with the possibility that the different LeishIF4Es are assigned unique functions. Author summaryLeishmania parasites cause a broad spectrum of diseases that lead to different pathological symptoms. During their life cycle, the parasites shuffle between sand-fly vectors and mammalian hosts, while adapting to changing environments via a stage specific program of gene expression that assists the survival of Leishmania under the changing conditions. Translation initiation plays a key role in control of gene expression, in Leishmania this is exemplified by the presence of multiple cap-binding complexes that interact with mRNAs. The parasites encode multiple paralogs of the cap-binding translation initiation factor eIF4E, and of its corresponding binding partner eIF4G, forming complexes with different potential functions. Using the CRISPR-Cas9 methodology, we generated a heterozygous mutant of the least studied cap-binding paralog, LeishIF4E2, eliminating one of its two alleles. The mutation caused morphological defects, resulting in short and rounded up cells with a significant reduction in their flagellar length. Although general translation rates and growth of the mutant parasite were not affected, total proteome analysis and translation assay suggested that LeishIF4E2 could possibly function as a translation repressor. Alternatively, LeishIF4E-2 could be responsible for promoting translation of a specific set of transcripts.