Simian immunodeficiency virus and human immunodeficiency virus type 1 Nef proteins show distinct patterns and mechanisms of Src kinase activation

The nef gene from human and simian immunodeficiency viruses (HIV and SN) re gulates cell function and viral replication, possibly through binding of th e nef product to cellular proteins, including Src family tyrosine kinases, We shaw here that the Nef protein encoded by SIVmac239 interacts with and a lso activates the human Src kinases Lck and Hck This is in direct contrast to the inhibitory effect of HIV type 1 (HIV-1) Nef on Lck catalytic activit y. Unexpectedly, however, the interaction of SIV Nef with human Lck or Hck is not mediated via its consensus proline motif, which is known to mediate HIV-1 Nef binding to Src homology 3 (SH3) domains, and various experimental analyses failed to show significant interaction of SN Nef with the SH3 dom ain of either kinase. Instead, SIV Nef can bind Lck and Hck SH2 domains, an d its N-terminal 50 amino acid residues are sufficient for Src kinase bindi ng and activation. Our results provide evidence for multiple mechanisms by which Nef binds to and regulates Src kinases.