Nup98, Nup153 and Nup62 are also involved in RNA export from the nucleus and therefore, cleavage by PV 2A pro might also impact on this process (Figure 4) . However, oligo d(T) hybridization studies showed that PV infection does not affect distribution of the polyadenylated mRNA bulk after 3 hpi [16] . A more detailed analysis revealed that expression of PV 2A pro in HeLa cells induces a number of disorders in RNA location. Nuclear export of cellular mRNAs is inhibited in 2A pro -expressing cells in a dose dependent manner concomitantly with Nup98, Nup62 and Nup153 cleavage [17] . Interestingly, mRNA export of constitutively expressed mRNAs such as β-actin is less affected than that of newly synthesized mRNAs. For example, tetracycline-induced luciferase mRNA was almost totally retained in the nucleus when these Nups are cleaved by PV 2A pro . This effect was also observed for endogenous mRNAs such as IL-6, c-myc or p53 mRNAs which are induced on PV 2A pro expression. Therefore, PV 2A pro could counteract the induction of proapoptotic (c-myc and p53) and proinflammatory (IL-6) responses by accumulating the c-myc, p53 and IL-6 mRNAs in the nucleus [17] . This export blockage may prevent the establishment of a hostcell response against PV infection. These findings could explain why PV 2A pro is essential for replication of PV in cells pre-treated with IFN-α [79] . Furthermore, impairment of mRNA export strongly alters the localization of mRNAs with high turnover as compared to constitutively expressed and highly stable mRNAs such as β-Actin [17] . As observed in PV-infected cells, oligo d(T) hybridization revealed that PV 2A pro expression hardly affects the distribution of the polyadenylated mRNA pool after short times of expression (8 h). However, nuclear accumulation of polyadenylated mRNA bulk is detected when cells are exposed to PV 2A pro for longer times (16 and 24 h) . In this regard, the progression of the alterations of polyadenylated mRNA localization in 2A pro -expressing cells takes place as follows: (i) disruption of nuclear mRNA-containing foci (ii) appearance of mRNAcontaining granules in the cytoplasm (most probably stress granules) and (iii) depletion of cytoplasmic mRNAs. These events were more clearly observed when high amounts of PV 2A pro are synthesized, reflecting that nuclear accumulation of mRNAs is a time-and dose-dependent process [17] .