Chlamydia trachomatis translocates the effector
protein Tarp (translocated actin-recruiting
phosphoprotein) into the host cell cytoplasm where it is quickly
tyrosine phosphorylated. Abl and
Src kinases have been implicated in
Tarp phosphorylation; however, we observed that the situation is more complex. Chemical inhibition of
Src family kinases confirmed a role for these
kinases in
Tarp phosphorylation.
Infection of Src, Yes, Fyn (SYF)-deficient cells showed a dampened, but incompletely blocked,
Tarp phosphorylation. Inhibition of Abl in an SYF background still did not completely block
Tarp phosphorylation. Consequently, we tested additional
kinases and found that Syk, but not Btk or Jak2, is a potent
kinase of
Tarp in vitro. Inhibition of Syk in an SYF background further blocked
Tarp phosphorylation. Under these conditions, inclusion formation still proceeded normally. These data reveal a highly promiscuous substrate property of
Tarp and set the stage for further functional characterization of
Tarp phosphorylation during host cell
infection.