"The extracellular loop 2 of TM4SF5 inhibits integrin a2 on hepatocytes under collagen

Abstract

Four-transmembrane L6 family member 5 (TM4SF5) and its homolog L6, a tumor antigen, form a four-transmembrane L6 family. TM4SF5 expression causes uncontrolled cell proliferation and angiogenesis. Although other genuine transmembrane 4 superfamily (TM4SF) members co-operate with integrins for cell migration, roles of TM4SF5 in the cellular spreading and migration are unknown. Using hepatocarcinoma cell clones that ectopically express TM4SF5, we found that cross talks via an extracellular interaction between TM4SF5 and integrin 2 in collagen type I environment inhibited integrin 2 functions such as spreading on and migration toward collagen I, which were recovered by suppression of TM4SF5 or structural disturbance of its second extracellular loop using a peptide or mutagenesis. Altogether, the observations suggest that TM4SF5 in hepatocytes negatively regulates integrin 2 function via an interaction between the extracellular loop 2 of TM4SF5 and integrin 2 during cell spreading on and migration through collagen I environment.