U2OS Control siRNA ERK5 siRNA1 ERK5 siRNA2 No. of mice with PN/ No. of mice injected 8/10 7/9 (one mouse died) 0/10* 0/9* (one mouse died)  Average No. of PN per mouse±s.d 7.1±3.2 7.8±3.4 0** 0**

Table 2: ERK5 knockdown decreases the metastatic potential of U2OS cells. PN: pulmonary nodules. Asterisks indicate statistically significant difference between the Control siRNA and ERK5 siRNA1/2 groups (*P<0.05, one-way ANOVA; **P<0.01, Student's t-test).