The Lck binding domain of herpesvirus saimiri Tip-484 constitutively activates Lck and STAT3 in T cells

Constitutive activation of signal transducers and activators of transcripti on (STATs) has been associated with oncogenesis. Previously, a protein requ ired for T-cell transformation by the DNA tumor virus herpesvirus saimiri ( HVS) strain 484, designated tyrosine kinase-interacting protein (Tip-484), was shown to interact with and dramatically upregulate the activity of the STATs in an Lck-dependent manner. The minimal region of Tip-484 responsible for binding Lck was defined as a 10-residue C-terminal Src-related kinase homology domain, an 18-amino-acid spacer, and a 10-residue potential SH3 bi nding domain. This region is termed the LED (for Lck binding domain). The p resent data show that only the LED of Tip-484 is needed to activate Lck in vitro and in vivo. Finally, the LED was shown to form a complex with STAT3 in vitro, and expression of the LED in T cells led to STAT3 activation equa l to that of full-length Tip-484. These studies demonstrate that the 48-ami no-acid LED of Tip-484 can perform as effectively as the full-length protei n in vitro and in vivo.