MAP2K7 and cancer: Conversely, pretreatment of the cancer cell lines with a PI3K inhibitor (GDC0941) or a MEK inhibitor (PD98059) respectively, decreased the phosphorylation to levels observed in the control (Supplementary Figure S2A), indicating the influence of the GTPCH/BH4 metabolism in stromal fibroblasts on the adjacent breast cancer cell PI3K and MAPK pathways.