MMP9 and esophageal squamous cell carcinoma: Interestingly, Western blotting analysis also displayed that overexpression of PAK1 remarkably promoted the expression of MMP-2 and MMP-9 (Fig. 3g, Left), which were well known to play a crucial role in tumor invasion and metastatic processes by degrading the extracellular matrix in various types of cancer including ESCC [31].