SDF-1 stimulation results in increased tyrosine phosphorylation and activation of PI-3 kinase in CTS cells. (A) Total cell lysates, prepared from SDF-1α–stimulated CTS cells for the indicated times, were immunoprecipitated with anti-PY antibody (PY20). The immune complexes were subjected to immunoblot analysis with anti-p85 antibody. The changes in the immunoblotted bands of p85 are indicated (by fold increase) based on the densitometry values. (B) Total cell lysates were immunoprecipitated with anti-PY antibody (PY20). PI-3 kinase activity was measured by a PI-3 kinase assay as described in “Materials and methods.”