Stromal contact selectively blocks late-phase and not early-phase ERK/MAPK activation.

K562 cells were treated with TPA with or without HESS-5 stromal cell contact for the indicated durations. The adjacent graph shows the relative phospho-ERK signal intensities, as determined by scanning densitometry, normalized according to tubulin signal. -str indicates no stromal cells present; +str, coculture with stromal cells. Whole cell lysates of indicated samples were subjected to immunoblotting with antibodies specific for phospho-ERK.