MMP13 and breast cancer: In support of the notion that MMP13 plays a causal role in RKIP-mediated suppression of breast cancer metastasis, expression of MMP13 is sufficient to rescue the invasion inhibited RKIP-expressing 4T1 cells Fig 3B, while the expression of MMP13 alone had no effect on the invasive capacity of the 4T1 cells Fig 3C.