IGF-1 induces migration and invasion by MM cells. MM cells H929 (A, D), MM144 (B), and OPM-2 (C) starved in serum-free medium for 3 hours were plated on polycarbonate pore membranes (5-μM pore size) on which HUVECs (A-C) or bone marrow stromal cell lines (D-E) were previously grown for 24 hours to form a continuous monolayer. MM cells were exposed to IGF-I (12.5 ng/mL to 200 ng/mL) or IL-6 (12.5 ng/mL to 50 ng/mL; E) added to the lower chamber. After 4 hours of incubation, cells in the lower chamber were harvested and counted microscopically following trypan blue staining. Results are representative of 3 independent experiments. H929 cells (F) starved in serum-free medium for 3 hours were incubated in the presence or absence of IGF-I as indicated. After 48 hours, cells were subjected to MTT assay. Results are shown as means ± SE (n = 4) and are representative of 3 separate experiments.