LAUSR

&NA; The matrix metalloproteinases (MMPs) are implicated in tumor invasion and metastasis. Given their multiple tumor promoting roles, MMPs are promising targets for the treatment of metastatic cancer. Using a siRNA library screen of 140 membrane trafficking genes, we identified 41 genes in HEC‐1B and 36 in Ishikawa cancer cells that decreased metalloproteinases activity. The 16 genes common in both cancer cell lines that decreased MMPs activity are involved in cargo sorting, vesicle formation and vesicle recycling. The top two genes clathrin‐B and cofilin‐1 were chosen for post hoc functional studies. Higher expression of both genes was confirmed in cancer cells and knockdown with respective siRNAs inhibited their invasive potential and matrix metalloproteinases activity. Membrane Type 1‐ Matrix Metalloproteinase (MT1‐MMP) is a master switch proteinase and regulator of invasion and metastasis. A marked decrease in MT1‐MMP expression and activity was seen in clathrin‐B and cofilin‐1 knockdown cancer cells which was associated with a marked decreased expression of invadopodia formation proteins. Our results suggest that the decreased expression of clathrin‐B and cofilin‐1 decreases the expression of MT1‐MMP and results in attenuation of MT1‐MMP at the cell surface, thus inhibiting tumor cell invasion and metastasis.