Fertility and Polarized Cell Growth Depends on eIF5A for Translation of Polyproline-Rich Formins in Saccharomyces cerevisiae

Abstract

eIF5A is an essential and evolutionary conserved translation elongation factor, which has recently been proposed to be required for the translation of proteins with consecutive prolines. The binding of eIF5A to ribosomes occurs upon its activation by hypusination, a modification that requires spermidine, an essential factor for mammalian fertility that also promotes yeast mating. We show that in response to pheromone, hypusinated eIF5A is required for shmoo formation, localization of polarisome components, induction of cell fusion proteins, and actin assembly in yeast. We also show that eIF5A is required for the translation of Bni1, a prolinerich formin involved in polarized growth during shmoo formation. Our data indicate that translation of the polyproline motifs in Bni1 is eIF5A dependent and this translation dependency is lost upon deletion of the polyprolines. Moreover, an exogenous increase in Bni1 protein levels partially restores the defect in shmoo formation seen in eIF5A mutants. Overall, our results identify eIF5A as a novel and essential regulator of yeast mating through formin translation. Since eIF5A and polyproline formins are conserved across species, our results also suggest that eIF5A-dependent translation of formins could regulate polarized growth in such processes as fertility and cancer in higher eukaryotes.

Genome-Wide Analyses and Functional Classification of Proline Repeat-Rich Proteins: Potential Role of eIF5A in Eukaryotic Evolution

“…Considering the strong association of polyproline-encoding genes with some of these functions, it is tempting to speculate that the mutant phenotypes are due to decreased translation of these polyproline-rich proteins in the eIF5A mutant strains. Defects in fertility and polarized cell growth due to deficiency of polyproline-rich formins in a yeast eIF5A mutant strain supports this notion [51]. An independent study is underway to identify, by a proteomics approach, cellular proteins whose levels are altered upon eIF5A deficiency.…”

Deoxyhypusine Modification of Eukaryotic Translation Initiation Factor 5A (eIF5A) Is Essential for Trypanosoma brucei Growth and for Expression of Polyprolyl-containing Proteins

“…Depletion of eIF5A in S. cerevisiae also resulted in misshapen cells that were more sensitive to ethanol (49). Yeast formin also contains a long poly(Pro) tract, and its translation was also adversely effected by loss of eIF5A, leading to a loss of shmoo formation (24). Additionally, proline-rich regions are known to bind SRC homology 3 domains, which in turn have been shown to be involved in cytoskeleton organization in yeast (50).…”

“…Although eIF5A/elongation factor P function in the translation of only a subset of proteins, the percentage of proteins containing proline-stalling motifs is high, and it is greater in eukaryotes than in bacteria (33% (human) versus 5.8% (Escherichia coli)) (14,23). Although it is still yet to be determined whether poly(Pro) proteins are involved in the control of specific cellular processes, in yeast it was found that a high fraction of proteins involved in cytoskeleton organization and active polarization contains poly(Pro) tracts (24).…”

Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae

“…Partial inactivation of a temperature-sensitive eIF5A variant confers reduced expression of reporter genes or authentic yeast ORFs containing homopolyproline stretches (Gutierrez et al 2013), leading to defects in fertility and polarized cell growth (Li et al 2014). The requirement for eIF5A for synthesis of polyproline sequences was also observed in vitro and shown to be dependent on the hypusine modification in eIF5A.…”