Figure 3.

Protein tyrosine phosphatase 1B (PTP1B) is required for α₁-antitrypsin (A1AT) to activate protein phosphatase 2A (PP2A). Neutrophils isolated from PiZZ A1AT homozygote individuals have (A) less PTP1B activity and (B) greater PP2A_C phosphorylation than PiMM individuals (n = 10 per group). Loss of PTP1B expression in A549 cells prevents A1AT-induced (C) activation of PP2A and (D) dephosphorylation of p-PP2A_C(Tyr307). Densitometry analysis was performed on immunoblots from 3 separate days. Graphs represent mean ± SEM of three measurements from each subject (n = 10 per group). P values shown, comparing both treatments connected by a line. Representative immunoblots are shown demonstrating equal cellular protein content. DU = densitometry units.