Ebola virus VP24 proteins inhibit the interaction of NPI-1 subfamily karyopherin a proteins with activated STAT1

The Zaire ebolavirus protein VP24 was previously demonstrated to inhibit alpha/beta interferon (IFN-(alpha/beta)and IFN-gamma-induced nuclear accumulation of tyrosine-phosphorylated STAT1 (PY-STAT1) and to inhibit IFN-alpha/beta- and IFN-gamma-induced gene expression. These properties correlated with the ability of VP24 to interact with the nuclear localization signal receptor for PY-STAT1, karyopherin alpha 1. Here, VP24 is demonstrated to interact not only with overexpressed but also with endogenous karyopherin alpha 1. Mutational analysis demonstrated that VP24 binds within the PY-STAT1 binding region located in the C terminus of karyopherin alpha 1. In addition, VP24 was found to inhibit PY-STAT1 binding to both overexpressed and endogenous karyopherin alpha 1. We assessed the binding of both PY-STAT1 and the VP24 proteins from Zaire, mouse-adapted Zaire, and Reston Ebola viruses for interaction with all six members of the human karyopherin a family. We found, in contrast to previous studies, that PY-STAT1 can interact not only with karyopherin alpha 1 but also with karyopherins 0 and alpha 6, which together comprise the NPI-1 subfamily of karyopherin as. Similarly, all three VP24s bound and inhibited PY-STAT1 interaction with karyopherins alpha 1, alpha 5, and alpha 6. Consistent with their ability to inhibit the karyopherin-PY-STAT1 interaction, Zaire, mouse-adapted Zaire, and Reston Ebola virus VP24s displayed similar capacities to inhibit IFN-beta-induced gene expression in human and mouse cells. These findings suggest that VP24 inhibits interaction of PY-STAT1 with karyopherins alpha 1, alpha 5, or alpha 6 by binding within the PY-STAT1 binding region of the karyopherins and that this function is conserved among the VP24 proteins of different Ebola virus species.