KRAS and gastric cancer: Under normal culture conditions (Figure 4d, lanes indicated as "N"), basal phosphorylation of p44/42 was increased in KRAS-amplified cells (HSC45, MKN1, and SH101P4) as compared to NUGC4 gastric cancer cells, in which there is neither amplification nor mutation of KRAS. While the phosphorylation of p44/42 was modestly increased in MKN1 cells after serum stimulation, the effect of serum stimulation on HSC45 and SH101P4 cells was minimal, which indicated that p44/42 is constitutively active in the latter two cell lines.