FIG. 4.

ATF3 and CHOP are induced by eIF2 kinase GCN2 in response to amino acid depletion. GCN2^+/+ and GCN2^−/− MEF cells were grown in leucine-depleted medium for the indicated number of hours, exposed to thapsigargin (Tg), or subjected to no stress. Whole-cell lysates were prepared from the cultured cells, and the levels of phosphorylated eIF2α (eIF2α-P), total eIF2α, ATF3, ATF4, and CHOP were measured by immunoblot analysis. The same amount of protein lysate was analyzed in each lane. Relative levels of phosphorylated eIF2α or ATF3 under the indicated stress condition were normalized to levels of total eIF2α in each lysate preparation.