Determining Biological Effectors of alpha6 Integrin Cleavage

Abstract

Cancer metastasis is a multi–step process that initiates with a tumor cell obtaining the ability to migrate. A multitude of changes occur in such a cell including changes to cell adhesion molecules such as integrins. In cancer cells, integrins are known to be involved in migration, invasion and metastasis. Investigation by our group of the α6 integrin led to the discovery of a cleaved form of the integrin lacking the ligand binding domain, called α6p. While it is known that the integrin is cleaved by urokinase plasminogen activator (uPA) little is known about how this process is regulated. There is a need to better understand the players involved in regulation of α6 cleavage as inhibiting this event from occurring may contribute to prolonged or increased patient survival or ultimately a cure.The existence of the integrin–actin complex has been known for many years. In this study actin was identified as a potential regulator of α6 cleavage. Using a diverse set of tumor cell lines (DU145, PC3 and MDA–MB–231) and a number of actin modifing compounds (latrunculin A, jasplakinolide and siRNA) it is reported here that disassembling actin filaments leads to an increase in α6p production. Although the increase in cleavage product did not always correlate with an increase in uPA receptor, an increase in uPAR was observed when actin was complexed by small molecule inhibitors. Taken together the results demonstrate a potential role for actin filaments to protect α6 integrin from uPA–uPAR induced cleavage via a multi–protein complex.