A549 cells normally have a human alveolar basal epithelial
appearance. However, they acquired a different phenotype following
U0126 treatment and appeared to be flat and spread (Fig. 1A).
Because actin microfilaments and associated proteins determine
the cell shape [11], the actin skeleton was stained in A549 cells.
Control cells showed a diffuse distribution of actin; however,
U0126 increased the sizes and promoted the formation of actin
stress fibers in A549 cells (Fig. 1A). Indeed, treatment of A549 cells
with U0126 resulted in cell flattening marked by the reestablishment
of actin stress fibers. We addressed whether the U0126-induced
morphology change was due to inhibition of MEK/ERK
signaling activation. Thus, A549 cells were serum starved in the presence or absence of U0126, stimulated with 10% FBS for 10 min,
and the cell lysates were probed for phospho-MEK or -ERK relative
to total MEK or ERK protein levels as an indicator of activated MEK/
ERK signaling. As shown in Fig 1B, MEK and ERK phosphorylation
was decreased after U0126 treatment after serum stimulation.