MAPK3 and neoplasm: In the HT29 treated tumor line, phospho-ERK 1/2 protein levels (relative to total ERK1/2 protein levels) were decreased in 5 min (67±0.06% of control value), reached a trough at 1 hr (46±0.06% of control), and remained decreased during the remainder of the time course (4 hrs, 68±0.10% of control value).