AG957, a
tyrphostin tyrosine kinase inhibitor, has been shown previously to inhibit p210(bcr-abl) phosphorylation with concurrent inhibition of p210(bcr-abl)-expressing K562 cell growth (Kaur G and Sausville EA, Anticancer Drugs 7: 815-824, 1996). To assess the specificity of the action of
AG957, we have examined its effect in another
tyrosine kinase-mediated system, anti CD-3-stimulated Jurkat T
Acute Lymphoblastic Leukemia cells. We also compared the effects of
AG957 with those of
geldanamycin, which can disrupt
tyrosine kinase signaling through binding to
heat shock protein (hsp90), and two
geldanamycin analogs, 17-amino-17-demethoxygeldanamycin (17AG) and
17-allylamino-17-demethoxygeldanamycin (
17AAG). At concentrations found to produce 90% inhibition of Jurkat T-cell growth,
AG957 within 4 hr of addition inhibited
mitogen-activated
protein (MAP)
kinase activation and activity, as shown by a decreased anti CD-3-stimulated erk-2 mobility shift in lysates of treated cells and a decrease in the stimulated
myelin basic protein peptide kinase activity in erk-2 immunoprecipitates, respectively.
AG957 did not inhibit this activity when added directly to immunoprecipitates. Effects in cells were found to be accompanied by a decrease in the anti CD-3-stimulated phosphorylation of p120cbl. Under conditions of a similar degree of growth inhibition,
geldanamycin initially did not inhibit MAP
kinase activation.
Geldanamycin analogs did not decrease anti CD-3-induced cbl phosphorylation, but did reduce basal p120cbl
tyrosine phosphorylation. The action of
AG957 occurred with an apparent shift of several
tyrosine-phosphorylated
proteins to apparent higher molecular weights, which also did not occur with the geldanamycins. These results suggest that growth inhibition by
AG957 can alter
tyrosine kinase signaling systems unrelated to p210(bcr-abl) with a prominent early effect on MAP
kinase activation in T-lymphoblasts.
AG957 and
geldanamycin affect
tyrosine kinase signaling by distinct mechanisms.