Figure 2.

Calpain-dependent protein tyrosine phosphatase degradation. (A) Active fragments of PTP1B were detected by in-gel assay (Burridge & Nelson, 1995; Markova et al, 2003). (B,C) The calpain inhibitor calpeptin prevents UV-induced degradation of PTPs. PTP1B was immunoprecipitated before western blotting, and LAR-PTP was blotted directly from the lysate. Before UV irradiation, A431 cells were mock-treated or were treated with calpeptin (1 μM) at 37°C for 4 h. Cell lysates of all samples were generated in the presence of calpeptin (5 μM).