Inter-Organelle Interactions between the ER and Mitotic Apparatus Facilitates Zika Protease Cleavage of Human Kinesin-5 and Contributes to Distinct Mitotic Defects

Abstract

Zika virus infection can result in profound fetal deficits, such as microcephaly and blindness. Here we identify Kif11/Kinesin-5, as a cellular target of Zika protease with both in vitro and in vivo assays. We show that soluble Zika NS2-3 protease chimera targets several sites within the motor domain of HsEg5 either when free in solution or rigor-bound to microtubules. We tested two different forms of the protease in human cells. First, we find that soluble Zika protease chimera is cytotoxic and eventually leads to cell death. Second, the native integral ERmembrane-associated protease is not only better tolerated by human cells, but also imparts unusual mitotic spindle positioning defects in cultured cells and a prolonged metaphase delay. Our data suggests a model whereby interactions at the spatially restricted ER-mitotic spindle interface bring the protease into the proximity of the pool of mitotic spindle-associated HsEg5. The resulting phenotype is distinct from the monopolar phenotype that typically results from downregulation of HsEg5 due to genetic knock-down or small molecule inhibition. Our results support the idea that not all knockouts are the same; nonuniform down-regulation of protein function can result in unanticipated phenotypes. We postulate that the mitotic spindle mobility phenotype that we observe can prematurely terminate cell lineages that are dependent on asymmetric cell division, such as neuronal lineages. Additionally, our data raise questions about novel inter-organelle communication between the mitotic apparatus and the surrounding reticulate ER network. Finally, given that Kif11 is a monogenic haploinsufficient locus linked to microcephaly, we propose that a potential direct connection between this kinesin and the protease may be a cornerstone in the subsequent pathogenesis of microcephaly.