Kinase Activity is Required for Growth Regulation but not Invasion Suppression by Syk Kinase in Pancreatic Adenocarcinoma Cells

Syk (spleen tyrosine kinase) is a nonreceptor tyrosine kinase containing two tandem amino-terminal SH2 domains, followed by an extended linker region and a carboxyterminal kinase domain (Sada et al., 2001). Tyrosine-352 (Y352) in the linker region is trans-phosphorylated by src family members, promoting the activation of syk (Kimura et al., 1996; Sada et al., 2001). Activation further involves the autophosphorylation of syk on tyrosines 525 and 526 (YY525/6) in the activation loop of the kinase domain, which promotes substrate-specific catalytic activity and is required for signaling by syk (Sada et al., 2001; Zhang et al., 1998); this modification is thus indicative of the functional enzyme. The active form of syk then localizes to appropriate substrates or bridging molecules primarily through interactions with its SH2 domains and linker tyrosines (Kimura et al., 1996; Sada et al., 2001).