MMP9 and cancer: As MLK3 regulates both FRA-1 and cancer cell invasion, we hypothesized that it may control the expression of FRA-1-dependent MMPs, such as MMP-1,15, 17, 32 MMP-233, 34 and MMP-9.17 As shown in Figure 5a, induced expression of MLK3 upregulates MMP-1 and MMP-9 mRNA but reduces MMP-2 mRNA levels.