In vitro and in vivo growth and invasion of HT1080 transfectants. (A) Stably transfected polyclonal HT1080/mock (♦), HT1080/CD9 (◇), and HT1080/CD44 cells (○) were plated onto each well of 24-well plates. After incubation for 24, 48, or 72 hours, MTT assay was performed. Data are means plus or minus SD of triplicate determinations. (B) HT1080/mock (♦), HT1080/CD9 (◇), and HT1080/CD44 (○) cells were subcutaneously injected into the backs of C.B-17/Icr-scid mice (n = 5). Tumors were measured with calipers at 3, 6, 9, 12, and 15 days after injection. Tumor volume was calculated using the following formula: volume = W² × L / 2, where W is the short diameter and L is the long diameter. Data are means plus or minus SD. (C) HT1080/mock, HT1080/CD9, and HT1080/CD44 cells in serum-free RPMI medium were added to the upper compartment of Matrigel-coated invasion chambers. Data are means plus SD of triplicate determinations. *P < .05; **P < .005 using the Student t test. (D) HT1080/mock, HT1080/CD9, and HT1080/CD44 cells were cultured in serum-free RPMI medium for 20 hours. In an experiment, HT1080/mock cells were stimulated with 50 ng/mL TPA (HT1080/mock+TPA). The culture supernatant was concentrated and electorophoresed. The gels were incubated for 40 hours in reaction buffer and stained with Coomassie Brilliant Blue.