Figure 3.

UV induces calcium-dependent calpain activation and protein tyrosine phosphatase degradation. (A) Relative calpain activity after various types of treatment. A431 cells were pretreated with calpeptin as in Fig 2B,C. AG1478 (100 nM), genistein (100 μM) or H₂O₂ (5 mM) was present for 15 min, ionomycin (2 μM) for 2 min or BAPTA (2 μM) for 30 min before UV irradiation. Calpain activity of lysates was determined using a commercially available kit (Calbiochem). The activity of untreated cells, set at 1, represents cleavage of 53 pmol/min of substrate at 37°C. (B,C) Modulation of intracellular calcium levels affects UV-induced PTP degradation. (B) Cell-permeable calcium chelator blocks UV-induced PTP degradation. A431 cells were cultivated in calcium-free medium for 30 min, and then treated with BAPTA (2 μM) for 30 min before irradiation. Immunoblots of lysates are shown. (C) Ionomycin enhances UV-induced PTP degradation. Ionomycin treatment is as in (A); immunoblots of lysates are shown.