FIG 9.
Timeline of 2A/3Cpro activity and cellular localization during HRV16 infection. Following infection, 2Apro activity is observed from 2 h p.i., as indicated by eIF4G cleavage. By 3 h p.i., 3D and 3CD are present in both the cytoplasm and nucleus, whereas 3Cpro is observed only in the cytoplasm and cleavage of Nup98 by 2Apro is evident, although which specific 3C/3CD protease activity is responsible at this stage is not clear (denoted by a question mark). Since 3CD cannot target efficiently to the nucleus without disruption to nuclear entry points (cleavage of NPC proteins or disruption to other nucleocytoplasmic trafficking proteins), this can be speculated to have occurred by this time. By 4 h p.i., 3CD is seen in the cytoplasm and nucleus, and 2Apro activity against eIF4G is maximal. By 6 to 7 h p.i, breakdown (indicated by broken lines) of the nuclear pore complex (NPC) is clearly evident, as indicated by the relocalization of hnRNP-A1 to the cytoplasm; both 3CD and 3Cpro are present in the nucleus and cytoplasm. By 8 to 9 h p.i., 3CD/3Cpro activity is maximal (as indicated by the loss of full-length PABP and Nup153), as is the effect of 2Apro activity on the NPC, with extensive cleavage of Nup62. 2Apro and 3Cpro are observed in the cytoplasm and the nucleus, 3Dpol is present mostly in the cytoplasm, and 3CD is mostly processed to 3Cpro and 3Dpol. The figure summarizes data for cellular proteins that have been studied to date, but it can be assumed that various other host cell factors will also be impacted as a result of the effect of HRV proteases on the host cell NPC/nucleocytoplasmic trafficking. NE, nuclear envelope.