The L2 Minor Capsid Protein of Human Papillomavirus Type 16 Interacts with a Network of Nuclear Import Receptors

Abstract

ABSTRACT The L2 minor capsid proteins enter the nucleus twice during viral infection: in the initial phase after virion disassembly and in the productive phase when, together with the L1 major capsid proteins, they assemble the replicated viral DNA into virions. In this study we investigated the interactions between the L2 protein of high-risk human papillomavirus type 16 (HPV16) and nuclear import receptors. We discovered that HPV16 L2 interacts directly with both Kapβ 2 and Kapβ 3 . Moreover, binding of Ran-GTP to either Kapβ 2 or Kapβ 3 inhibits its interaction with L2, suggesting that the Kapβ/L2 complex is import competent. In addition, we found that L2 forms a complex with the Kapα 2 β 1 heterodimer via interaction with the Kapα 2 adapter. In agreement with the binding data, nuclear import of L2 in digitonin-permeabilized cells could be mediated by either Kapα 2 β 1 heterodimers, Kapβ 2 , or Kapβ 3 . Mapping studies revealed that HPV16 L2 contains two nuclear localization signals (NLSs), in the N terminus (nNLS) and C terminus (cNLS), that could mediate its nuclear import. Together the data suggest that HPV16 L2 interacts via its NLSs with a network of karyopherins and can enter the nucleus via several import pathways mediated by Kapα 2 β 1 heterodimers, Kapβ 2 , and Kapβ 3 .