Inter-organelle interactions between the ER and mitotic spindle facilitates Zika protease cleavage of human Kinesin-5 and results in mitotic defects.

Here we identify human Kinesin-5, Kif11/HsEg5, as a cellular target of Zika protease. We show that Zika NS2B-NS3 protease targets several sites within the motor domain of HsEg5 irrespective of motor binding to microtubules. The native integral ER-membrane protease triggers mitotic spindle positioning defects and a prolonged metaphase delay in cultured cells. Our data support a model whereby loss of function of HsEg5 is mediated by Zika protease and is spatially restricted to the ER-mitotic spindle interface during mitosis. The resulting phenotype is distinct from the monopolar phenotype that typically results from uniform inhibition of HsEg5 by RNAi or drugs. In addition, our data reveal novel inter-organelle interactions between the mitotic apparatus and the surrounding reticulate ER network. Given that Kif11 is haplo-insufficient in humans, and reduced dosage results in microcephaly, we propose that Zika protease targeting of HsEg5 may be a key event in the etiology of Zika syndrome microcephaly.