Plays a role in viral alternative pre-mRNA splicing. Activates dephosphorylation by protein phosphatase 2A of host SR proteins and converts their splicing properties. When expressed alone ex vivo, induces p53/TP53-independent apoptosis called cytoplasmic death. May mimic nutrient/growth signals to activate the host mTOR pathway. Interacts with host BAZ1A/ACF1, host PPP2R2A/PP2a-B55alpha subunit, and host PPP2R5E/PP2a-B'B56 subunit. May interact with host SRC. When expressed alone ex-vivo the majority is found in the nucleus. Tyrosinephosphorylation would promote cytoplasmic localization. May be phosphorylated by host SRC kinase. Belongs to the adenoviridae E4 ORF4 family.