Figure 2.

Conditional expression of MKP-1 inhibits UV-induced apoptosis. (A) U937 cells expressing hMTIIa-MKP-1 were pretreated for 4 h with 1 μM CdSO₄ (Cd++) as indicated before exposure to UV radiation (200 J/m²). At the indicated times, chromosomal DNA was isolated, resolved on a 2% agarose gel and visualized by ethidium bromide staining. (B) DNA fragmentation was quantified by cell cycle FACS analysis on aliquots of cells treated as above and stained with PI. Cells appearing as a sub-G1 peak were scored as apoptotic. (C) Cells were treated as above and caspase-3 activity was measured by cleavage of the Ac-DEVD-AMC fluorogenic substrate as described in Materials and Methods. Data are presented as fold activation over untreated cells and are means +/− SEM of three experiments performed in triplicate and assayed in duplicate. (D) Cells were treated as above and PARP expression and cleavage was determined by Western blot analysis.