Interaction of the adenovirus type 5 E4 Orf3 protein with promyelocytic leukemia protein isoform II is required for ND10 disruption.

Nuclear domain 10 (ND10s), or promyelocytic leukemia protein (PML) nuclear bodies, are spherical nuclear structures that require PML proteins for their formation. Many viruses target these structures during infection. The E4 Orf3 protein of adenovirus 5 (Ad5) rearranges ND10s, causing PML to colocalize with Orf3 in nuclear tracks or fibers. There are six different PML isoforms (I to VI) present at ND10s, all sharing a common N terminus but with structural differences at their C termini. In this study, PML II was the only one of these six isoforms that was found to interact directly and specifically with Ad5 E4 Orf3 in vitro and in vivo; these results define a new Orf3 activity. Three of a series of 18 mutant Orf3 proteins were unable to interact with PML II; these were also unable to cause ND10 rearrangement. Moreover, in PML-null cells that contained neoformed ND10s comprising a single PML isoform, only ND10s formed of PML II were rearranged by Orf3. These data show that the interaction between Orf3 and PML II is necessary for ND10 rearrangement to occur. Finally, Orf3 was shown to self-associate in vitro. This activity was absent in mutant Orf3 proteins that were unable to form tracks and to bind PML II. Thus, Orf3 oligomerization may mediate the formation of nuclear tracks in vivo and may also be important for PML II binding.