P21-activated kinase 5 is overexpressed during colorectal cancer progression and regulates colorectal carcinoma cell adhesion and migration.

P21-activated kinase 5 (PAK5) is the recently identified member of the group B p21-activated kinase (PAK) family which are effectors of the small GTPase Cdc42 and Rac1, known to regulate cell motility and activate cell-survival signaling pathways. However, overexpression of PAK5 has not been associated with any cancers so far. Interestingly, we found that PAK5 was overexpressed in a variety of colorectal carcinoma (CRC) cell lines in a Western-blotting examination. Therefore, in this study, we aim to examine the PAK5 expression during CRC progression and to answer if PAK5 is involved in malignant progression of CRC. By immunohistochemistry, our results showed that PAK5 expression was increased with CRC progression through the adenoma to carcinoma sequence, with the most significant increases in invasive and metastatic CRCs (p < 0.0001). Furthermore, increased PAK5 expression was also found with the development of CRC from lower Duke's grades to higher ones (p < 0.01). Moreover, PAK5 was also increased from well to poorly differentiated CRCs (p < 0.01). Using gain and loss of function experiments, we found that PAK5 reduced CRC cell adhesion but promoted their migration on collagen type I. Taken together, our study demonstrated that PAK5 expression increased significantly with malignant progression of CRC and that PAK5 might promote CRC metastasis by regulating CRC cell adhesion and migration.