MAPK1 and infection: Treatment with shRNAs silencing ERK1 and/or ERK2 did not trigger detectable killing of A375 cells 2 days after infection (although G1 growth arrest was noted, data not shown), but progressively increased killing was observed 4 days (p < 0.0001 for ERK1 and ERK1 plus ERK2 shRNAs; and p < 0.002 for ERK2 shRNA) and 6 days (p < 0.002 for ERK1 shRNA and p < 0.001 for ERK2 and ERK1 plus ERK2 shRNAs) after infection (Figure 1B).