MenaINV dysregulates cortactin phosphorylation to promote invadopodium maturation

Abstract

Invadopodia, actin-based protrusions of invasive carcinoma cells that focally activate extracellular matrix-degrading proteases, are essential for the migration and intravasation of tumor cells during dissemination from the primary tumor. We have previously shown that cortactin phosphorylation at tyrosine residues, in particular tyrosine 421, promotes actin polymerization at newly-forming invadopodia, promoting their maturation to matrix-degrading structures. However, the mechanism by which cells regulate the cortactin tyrosine phosphorylation-dephosphorylation cycle at invadopodia is unknown. Mena, an actin barbed-end capping protein antagonist, is expressed as various splice-isoforms. The MenaINV isoform is upregulated in migratory and invasive sub-populations of breast carcinoma cells, and is involved in tumor cell intravasation. Here we show that forced MenaINV expression increases invadopodium maturation to a far greater extent than equivalent expression of other Mena isoforms. MenaINV is recruited to invadopodium precursors just after their initial assembly at the plasma membrane, and promotes the phosphorylation of cortactin tyrosine 421 at invadopodia. In addition, we show that cortactin phosphorylation at tyrosine 421 is suppressed by the phosphatase PTP1B, and that PTP1B localization to the invadopodium is reduced by MenaINV expression. We conclude that MenaINV promotes invadopodium maturation by inhibiting normal dephosphorylation of cortactin at tyrosine 421 by the phosphatase PTP1B.

Tumor Cell Invadopodia: Invasive Protrusions that Orchestrate Metastasis

“…Mena INV expression potentiates invadopodium activity by sensitizing growth factor receptor and ECM signals by its ability to inhibit PTP1B, a tyrosine phosphatase of c-Met, EGFR and cortactin [8, 22]. Of particular significance are two recent findings; 1) that macrophage contact with tumor cells, as occurs in and around TMEM (Box 2), initiates Mena INV expression through NOTCH-signaling dependent transcription [16] and 2) that expression of Mena INV greatly stimulates invadopodium assembly and function in tumor cells by enhancing the phosphorylation of cortactin Y421, a well-known regulatory step in initiating invadopodium formation in invasive tumor cells [22](Figures 1 and 2). Mena INV promotes phosphorylation of cortactin at tyrosine 421 by displacing PTP1B from the invadopodium core [22].…”

“…Of particular significance are two recent findings; 1) that macrophage contact with tumor cells, as occurs in and around TMEM (Box 2), initiates Mena INV expression through NOTCH-signaling dependent transcription [16] and 2) that expression of Mena INV greatly stimulates invadopodium assembly and function in tumor cells by enhancing the phosphorylation of cortactin Y421, a well-known regulatory step in initiating invadopodium formation in invasive tumor cells [22](Figures 1 and 2). Mena INV promotes phosphorylation of cortactin at tyrosine 421 by displacing PTP1B from the invadopodium core [22]. In preventing the localization of PTP1B to invadopodia, Mena INV can sensitize cells to a wide range of extracellular stimuli and driver mutations in the tumor cell that promote invadopodium maturation by a common mechanism of cortactin phosphorylation [6, 22](Figures 1 and 2)(Text Box 3).…”

“…Mena INV promotes phosphorylation of cortactin at tyrosine 421 by displacing PTP1B from the invadopodium core [22]. In preventing the localization of PTP1B to invadopodia, Mena INV can sensitize cells to a wide range of extracellular stimuli and driver mutations in the tumor cell that promote invadopodium maturation by a common mechanism of cortactin phosphorylation [6, 22](Figures 1 and 2)(Text Box 3). …”

“…Mena INV-Hi expressing tumor cells have greatly enhanced invadopodium assembly, streaming, TMEM association and intravasation activities, while Mena11a-expressing cells have these phenotypes suppressed [2, 22, 73, 74, 87]. Consistent with these findings in mice, in human breast tumors, TMEM and Mena Calc scores are prognostic for metastasis in breast cancer patients [70, 86] and add complimentary information to other currently used prognostics that are based on proliferation alone [72].…”

“…Mena INV expression increases tumor cell motility, invadopodium assembly and invasion, and potentiates chemotactic responses to EGF and HGF [8, 22, 88] and haptotactic responses to fibronectin [89]. Mena INV and its associated invadopodium, are required for TMEM-dependent transendothelial migration of tumor cells from patient biopsies and are necessary for intravasation of all subtypes of breast cancer cells [16, 73].…”