Alexandra Paye

MT-MMPS as Regulators of Vessel Stability Associated with Angiogenesis

The development of vascular system depends on the coordinated activity of a number of distinct families of molecules including growth factors and their receptors, cell adhesion molecules, extracellular matrix (ECM) molecules, and proteolytic enzymes. Matrix metalloproteases (MMPs) are a family of ECM degrading enzymes required for both physiological and pathological angiogenesis. Increasing evidence, point to a direct role of membrane type-MMPs (MT-MMPs) in vascular system stabilization, maturation, and leakage. Our understanding of the nature of MT-MMP interaction with extracellular and cell surface molecules and their multiple roles in vessel walls and perivascular stroma may provide new insights into mechanisms underlying vascular cell–ECM interactions and cell fate decisions in pathological conditions. Regulation of vascular leakage by MT-MMP interactions with the ECM could also lead to novel targeting opportunities for drug delivery in tumor. This review will shed lights on the emerging roles of MT1-MMP and MT4-MMP in vascular system alterations associated with cancer progression.

Membrane‐type 4 matrix metalloproteinase (MT4‐MMP) induces lung metastasis by alteration of primary breast tumour vascular architecture

The present study aims at investigating the mechanism by which membrane‐type 4 matrix metalloproteinase (MT4‐MMP), a membrane‐anchored MMP expressed by human breast tumour cells promotes the metastatic dissemination into lung. We applied experimental (intravenous) and spontaneous (subcutaneous) models of lung metastasis using human breast adenocarcinoma MDA‐MB‐231 cells overexpressing or not MT4‐MMP. We found that MT4‐MMP does not affect lymph node colonization nor extravasation of cells from the bloodstream, but increases the intravasation step leading to metastasis. Ultrastructural and fluorescent microscopic observations coupled with automatic computer‐assisted quantifications revealed that MT4‐MMP expression induces blood vessel enlargement and promotes the detachment of mural cells from the vascular tree, thus causing an increased tumour vascular leak. On this basis, we propose that MT4‐MMP promotes lung metastasis by disturbing the tumour vessel integrity and thereby facilitating tumour cell intravasation.

EGFR Activation and Signaling in Cancer Cells Are Enhanced by the Membrane-Bound Metalloprotease MT4-MMP

MT4-MMP (MMP-17) is a glycosylphosphatidyl inositol-anchored matrix metalloprotease expressed on the surface of cancer cells that promotes tumor growth and metastasis. In this report, we identify MT4-MMP as an important driver of cancer cell proliferation through CDK4 activation and retinoblastoma protein inactivation. We also determine a functional link between MT4-MMP and the growth factor receptor EGFR. Mechanistic experiments revealed direct association of MT4-MMP and its positive effects on EGFR phosphorylation in response to TGFα and EGF in cancer cells. Notably, the effects of MT4-MMP on proliferation and EGFR activation did not rely on metalloprotease activity. Clinically, MT4-MMP and EGFR expressions were correlated in human triple-negative breast cancer specimens. Altogether, our results identify MT4-MMP as a positive modifier of EGFR outside-in signaling that acts to cooperatively drive cancer cell proliferation.

The proteolytic activity of MT4‐MMP is required for its pro‐angiogenic and pro‐metastatic promoting effects

Membrane‐type 4 matrix metalloprotease (MT4‐MMP) expression in breast adenocarcinoma stimulates tumor growth and metastatic spreading to the lung. However, whether these pro‐tumorigenic and pro‐metastatic effects of MT4‐MMP are related to a proteolytic action is not yet known. Through site directed mutagenesis MT4‐MMP has been inactivated in cancer cells through Glutamic acid 249 substitution by Alanine in the active site. Active MT4‐MMP triggered an angiogenic switch at day 7 after tumor implantation and drastically accelerated subcutaneous tumor growth as well as lung colonization in recombination activating gene‐1‐deficient mice. All these effects were abrogated upon MT4‐MMP inactivation. In sharp contrast to most MMPs being primarily of stromal origin, we provide evidence that tumor‐derived MT4‐MMP, but not host‐derived MT4‐MMP contributes to angiogenesis. A genetic approach using MT4‐MMP‐deficient mice revealed that the status of MT4‐MMP produced by host cells did not affect the angiogenic response. Despite of this tumor intrinsic feature, to exert its tumor promoting effect, MT4‐MMP requires a permissive microenvironment. Indeed, tumor‐derived MT4‐MMP failed to circumvent the lack of an host angio‐promoting factor such as plasminogen activator inhibitor‐1. Overall, our study demonstrates the key contribution of MT4‐MMP catalytic activity in the tumor compartment, at the interface with host cells. It identifies MT4‐MMP as a key intrinsic tumor cell determinant that contributes to the elaboration of a permissive microenvironment for metastatic dissemination.

Dynamics of internalization and recycling of the prometastatic membrane type 4 matrix metalloproteinase (MT4‐MMP) in breast cancer cells

Membrane type 4 matrix metalloproteinase (MT4‐MMP) [matrix metalloproteinase (MMP) 17] is a GPI‐anchored membrane‐type MMP expressed on the cell surface of human breast cancer cells. In triple‐negative breast cancer cells, MT4‐MMP promotes primary tumour growth and lung metastases. Although the trafficking and internalization of the transmembrane membrane type 1 MMP have been extensively investigated, little is known about the regulatory mechanisms of the GPI‐anchored MT4‐MMP. Here, we investigated the fate and cellular trafficking of MT4‐MMP by analysing its homophilic complex interactions, internalization and recycling dynamics as compared with an inert form, MT4‐MMP‐E249A. Oligomeric and dimeric complexes were analysed by cotransfection of cells with FLAG‐tagged or Myc‐tagged MT4‐MMP in reducing and nonreducing immunoblotting and coimmunoprecipitation experiments. The trafficking of MT4‐MMP was studied with an antibody feeding assay and confocal microscopy analysis or cell surface protein biotinylation and western blot analysis. We demonstrate that MT4‐MMP forms homophilic complexes at the cell surface, and internalizes in early endosomes, and that some of the enzyme is either autodegraded or recycled to the cell surface. Our data indicate that MT4‐MMP is internalized by the clathrin‐independent carriers/GPI‐enriched early endosomal compartments pathway, a mechanism that differs from that responsible for the internalization of other membrane‐type MMP members. Although MT4‐MMP localizes with caveolin‐1, MT4‐MMP internalization was not affected by inhibitors of caveolin‐1 or clathrin endocytosis pathways, but was reduced by CDC42 or RhoA silencing with small interfering RNA. We provide a new mechanistic insight into the regulatory mechanisms of MT4‐MMP, which may have implications for the design of novel therapeutic strategies for metastatic breast cancer.