FIG. 6.

An inhibitor of Src family tyrosine kinases does not block Nef-induced MHC-I down-regulation. (A) CEM-GFP cells were infected by a 24-h coculture with virus-producing 293T cells. Several days later, both infected and uninfected cells were treated for 24 h with herbimycin A (Herb. A) at increasing concentrations and then analyzed for MHC-I levels (horizontal axis) by monitoring infection through GFP production. A minor downward shift in MHC-I levels was noted for both infected and uninfected cells following herbimycin A treatment. (B) Phosphotyrosine Western blot of infected cells before (lanes 1 to 3) and after (lanes 4 to 6) a 15-min treatment with 5 mM hydrogen peroxide (a tyrosine phosphatase inhibitor), which reveals that herbimycin A efficiently inhibits tyrosine kinase activity at both 2 and 4 μM.