Expression of catalytically active CD148 confers Ab1-sensitive growth inhibition on CHO cells and the Ab1 activity is abrogated by coexpression of inactive CD148 mutants. (A) CHO cells were transiently transfected with CD148 expression plasmids (mock, WT, and C-S and ΔCyto forms) as indicated. The cells were replated at 16 hours and incubated from 30 hours after transfection in growth medium supplemented with either Ab1, Ab1.Fab, or control IgG₁ (67 nM). Bars represent mean A₅₇₀ determination values (± SEM) of 12 independent samplings for each group at 3 days (72 hours) after transfection, expressed as percent of control (the cells grown without agents). The protein levels of transfected genes were evaluated by Ab1 immunoblot on 5.0 μg lysate protein (insert). (B) CHO cells were cotransfected with 2.5 μg WT plasmid in combination with 2.5 μg plasmid expressing C-S (WT + C-S) or ΔCy (WT +ΔCy) form of CD148. The cells were treated with Ab1, Ab1.Fab, or control IgG₁ (67 nM), and cell proliferation and CD148 protein levels were examined as described in panel A. The arrowhead (in insert) indicates the ΔCy mutant.