Lamellipodin promotes invasive 3D cancer cell migration via regulated interactions with Ena/VASP and SCAR/WAVE

Cancer invasion is a hallmark of metastasis. The mesenchymal mode of cancer cell invasion is mediated by elongated membrane protrusions driven by the assembly of branched F-actin networks. How deregulation of actin regulators promotes cancer cell invasion is still enigmatic. We report that increased expression and membrane localization of the actin regulator Lamellipodin correlate with reduced metastasis-free survival and poor prognosis in breast cancer patients. In agreement, we find that Lamellipodin depletion reduced lung metastasis in an orthotopic mouse breast cancer model. Invasive 3D cancer cell migration as well as invadopodia formation and matrix degradation was impaired upon Lamellipodin depletion. Mechanistically, we show that Lamellipodin promotes invasive 3D cancer cell migration via both actin-elongating Ena/VASP proteins and the Scar/WAVE complex, which stimulates actin branching. In contrast, Lamellipodin interaction with Scar/WAVE but not with Ena/VASP is required for random 2D cell migration. We identified a phosphorylation-dependent mechanism that regulates selective recruitment of these effectors to Lamellipodin: Abl-mediated Lamellipodin phosphorylation promotes its association with both Scar/WAVE and Ena/VASP, whereas Src-dependent phosphorylation enhances binding to Scar/WAVE but not to Ena/VASP. Through these selective, regulated interactions Lamellipodin mediates directional sensing of epidermal growth factor (EGF) gradients and invasive 3D migration of breast cancer cells. Our findings imply that increased Lamellipodin levels enhance Ena/VASP and Scar/WAVE activities at the plasma membrane to promote 3D invasion and metastasis.

Cellular localization of activated N-WASP using a conformation-sensitive antibody

The main regulators of Arp2/3 activity appear to be N-WASP and the other members of the Scar/WAVE family of proteins. We show here that after EGF stimulation, N-WASP is recruited to the nucleation zone of the dynamic leading edge compartment of carcinoma cells, with maximal recruitment of N-WASP within 1 min after EGF stimulation. The timing of N-WASP recruitment mirrors the timing of barbed-end formation at the leading edge. To determine the cellular activation of N-WASP after EGF stimulation, we made a conformation-sensitive antibody (CSA) against the CRIB domain of N-WASP that is predicted to recognize N-WASP in its open, active conformation, but not in its closed, inactive conformation. The ability of CSA to detect only active N-WASP was demonstrated by in vitro experiments using immunoprecipitation of active N-WASP from EGF-stimulated cells and Cdc42 activation of N-WASP activity. In cell staining experiments, N-WASP is maximally accessible to CSA 40 sec after EGF stimulation and this activated N-WASP is in the nucleation zone. These results indicate that active N-WASP is present at the leading edge of lamellipods, an unexpected finding given its reported involvement in filopod formation. This work establishes the feasibility of using antibodies directed against specific conformations or epitopes with changing accessibilities as a window on the status and localization of activity.

Functional interplay between gelatinases and hyperalgesia in endotoxin-induced localized inflammatory pain

The role of ECM-degrading proteinases in normal developmental processes and in pathological conditions is extensively studied. However, few reports describe the role ECM-degrading proteinases play in modulating hyperalgesia. The goal of this study is to describe the regulation of gelatinases during endotoxin mediated local inflammation, induced by intra plantar endotoxin (ET; 1.25 microg/50 microl) injection in Balb/c mice, and to correlate that with hyperalgesia. ET injections induced hyperalgesia, as determined by hot plate and paw pressure tests, which peaked by 24 h and recovered by 48 h post-injection. Contralateral paw of ET injected mice and saline injected paws in control mice elicited no hyperalgesia. Zymography showed that ET and saline injected paws elicited increased gelatinase activity by 9 h after injection. However, only the former maintained high levels of expression of a 90 kD gelatinase up to at least 96 h post ET injection, while in the latter gelatinase expression was down regulated by 24 h. Interestingly, the 90-kD gelatinase was upregulated in the contralateral paw of the ET-injected mice beyond 48 h post injection. Saline injection in that paw, during a time when gelatinases are upregulated, induced hyperalgesia. Intraperitoneal injection of either ZnCl(2) (100 microM), thymulin (5 microg/100 microl), or morphine (2 mg/kg/100 microl) reversed the ET-induced hyperalgesia and suppressed gelatinase activity. Furthermore, intraperitoneal injection of MPI, an ECM-degrading proteinase inhibitor, reversed ET induced hyperalgesia. Taken together, the above suggests that a functional interplay exists between gelatinase upregulation triggered by ET injections and hyperalgesia. The exact mechanism underlying such correlation remains to be determined.