Integrin α6 cleavage:: A novel modification to modulate cell migration

Integrins play a major role in cell adhesion and migration. Previous work reported that a cleaved form of integrin alpha 6 (alpha 6p) was detected in invasive human prostate cancer tissue, absent in normal prostate tissue and was produced by urokinase-type Plasminogen Activator (uPA) in a plasmin-independent manner. Using site-directed mutagenesis we identified amino acid residues R594 and RS95, located in the stalk region of integrin alpha 6, as essential for cleavage. The cleavage site is located on the extracellular region of the protein between the beta-barrel domain and the thigh domain. Prostate cancer cells (PC3N) were stably transfected to overexpress the cleavable, wild-type (PC3N-alpha 6-WT) or the non-cleavable form of integrin alpha 6 (PC3N-alpha 6-RR). The number of cells invading laminin 111- and laminin 332-coated filters by PC3N-alpha 6-WT cells increased by threefold as compared to PC3N-a6-RR cells. Plasminogen activator inhibitor-1 (PAI-1) reduced the invasion of PC3N-alpha 6-WT cells by approximately 42% through laminin 332-coated filters and plasmin inhibitor aprotinin had no significant effect. Linear cell migration increased production of integrin alpha 6p in the PC3N-alpha 6-WT cells and not in the PC3N-alpha 6-RR cells and 32% of the PC3N-alpha 6-WT cells migrated on laminin 111 in the linear migration assay as compared to the 5% PC3N-alpha 6-RR cells. These data taken together suggest that the uPA-mediated cell surface cleavage of the alpha 6 integrin extracellular domain is involved in tumor cell invasion and migration on laminin. (c) 2007 Elsevier Inc. All rights reserved.