Talin2-mediated Traction Force Drives MMP Secretion and Cell Invasion

The protein talin is a key component in the intracellular complex of proteins linking the extracellular martrix to the actin cytoskeleton via integrins in the plasma membrane. Talin interacts with beta-integrin tails and actin to control integrin activation and force generation. It also binds to phosphatidylinositol 4 phosphate 5-kinase type I y 90 (PIPKIy90), an enzyme that catalyzes the production of phosphatidylinositol 4,5-bisphosphate (PIP2), and regulates vesicle trafficking. In this capacity, talin regulates focal adhesion dynamics, force generation and invadopodium stability, thus governing cell migration and invasion. There are two talin genes, Tln1 and Tln2, which encode talin1 and talin2; talin1 has been well studied and it is generally believed that talin2 functions redundantly with talin1. However, our preliminary data reveal some important differences between talin 1 and 2 that lead to different functionality. Thus, talin2 has stronger binding to â integrin tails than talin1 and that talin2 Ser339 is largely responsible for this affinity difference. Intriguingly, a new study shows that Fifth Finger Camptodactyly, a human genetic disease, is caused by a Leu mutation at talin2 Ser339. Talin2 is localized at invadopodia and is indispensable for traction force generation and invadopodium maturation. And, ablation of talin2 but not talin1 abolished the secretion of matrix metalloproteinase (MMP) 1 and 9. In this regard, talin2 promotes PIPKIy90 binding to Exo84 (a component of the exocyst involved in vesicle secretion) and interacts with non-muscle myosin IIA (NMMIIA), a major myosin involved in traction force generation. Based on these data, our central hypothesis is that talin2 interacts with NMMIIA to mediate traction force generation and promotes PIPKIy90-Exo84 complex formation, thus driving MMP1 and MMP9 secretion, invadopodium maturation and cell invasion. We will test this hypothesis by addressing the following SPECIFIC AIMS: 1) define how talin2-mediated traction force regulates MMP secretion and invadopodium maturation; 2) dissect how talin2 modulates PIPKIy90-Exo84 interaction to regulate MMP secretion and invadopodium maturation; 3) determine how NMMIIA interacts with talin2 to regulate traction force generation, MMP secretion, invadopodium maturation and cell invasion. Our proposed studies are designed to uncover a novel, fundamental role for talin2-mediated traction force in regulating MMP secretion, invadopodium maturation and cell invasion. Support for this connection is provided by the fact that talin2 was found to be down-regulated by Trastuzumab, a HER2-targeting antibody drug for breast cancers and our findings indicate that talin2 is essential to the traction force development required for invadopodium maturation and cell invasion. Thus, talin2 could be a target for therapies designed to inhibit the first steps of metastasis.