Effects of Met‐enkephalin (MENK) on cell growth and phosphorylation of mitogen‐activated protein kinase (MAPK) family members in MOLT‐4 cells. (a) δ‐Opioid receptor (DOR) and CD10 expression and MENK secretion were detected by immunoblotting in MOLT‐4 cells. (b) Effect of MENK and MAPK inhibitors on cell growth in MOLT‐4 cells. (c) Effect of MENK on the phosphorylation of MAPK in MOLT‐4 T lymphocytes. (d) Apoptotic cells were counted in MENK (20 µM)‐treated MOLT‐4 cells by Hoechst staining. Tubulin and Coomassie blue served as loading controls. ERK‐I, ERK1/2 inhibitor; JNK‐I, c‐jun N‐terminal kinase inhibitor; p38‐I, p38 inhibitor; pp38, phosphorylated p38; siRNA, short interfering RNA. Error bars, SD from three independent assays.