Activation of MLCK by ERK2.

PMNLs were allowed to undergo phagocytosis of EIgG for 5 minutes or incubated without EIgG, then lysed with NP-40. ERK2 was immunoprecipitated from lysates to obtain activated and unactivated ERK2, respectively. Cytosol isolated from resting PMNLs or buffer was added to samples along with [γ-³²P]ATP and peptide substrate (plain bars), and kinase activity was quantitated as described for Figure 1, or PMNL myosin replaced peptide substrate (cross-hatched bars) and was immunoprecipitated. R, ERK2 immunoprecipitated from resting PMNLs incubated at 37°C; P, ERK2 immunoprecipitated from phagocytosing PMNLs. +, cytosol present; −, no cytosol; +ML-7, cytosol incubated before kinase assay with 10 μmol/L ML-7. Data represent the mean ± SEM of 3 experiments. MLCK activity in PMNLs at 22°C = 100%. *Significantly different from control (left bar); P < .005. Other data are not significantly different from each other.