Attachment of leukemia cells to the stroma-derived cell lines HS-5 (human) or MS-5 (murine) conferred a significant protection against ATO-induced cell death in three out of the six tested cell lines (LAMA84-R, AR230-R and SUP-B15), but this protective effect was abrogated by the pharmacological inhibition of MEK1/2 (Fig. 1B). This evidence concerns the gene MAP2K1 and leukemia.