To partially test the generality of the results reported here, we evaluated the effects of MG132 treatment on PDGF-stimulated MEK and ERK phosphorylation in NIH 3T3 fibroblasts as before, alongside parallel measurements for primary mouse embryonic fibroblasts (MEFs) and HT-1080 human fibrosarcoma cells (Fig. 5). The gene discussed is MAPK1; the disease is fibrosarcoma.