Extracellular galectin-3 induces MMP9 expression by activating p38 MAPK pathway via lysosome-associated membrane protein-1 (LAMP1).

Matrix metalloproteinases (MMPs) play a key role in matrix remodelling and thus invasion and metastasis. Extracellular galectin-3 has been shown to induce MMP9 secretion. Here, we demonstrate that galectin-3 induces MMP9 at transcript level and it is dependent on the surface levels of poly-N-acetyllactosamine (polyLacNAc). By employing signalling pathway inhibitors, MMP9 expression was shown to be induced via p38 MAP-kinase pathway. Using clones of melanoma cells expressing shRNAs to lysosome-associated membrane protein-1 (LAMP1), a major carrier of polyLacNAc, surface LAMP1 was demonstrated to serve as one of the key mediators of galectin-3-induced MMP9 expression via p38 MAPK pathway.

Role of tumor cell surface lysosome-associated membrane protein-1 (LAMP1) and its associated carbohydrates in lung metastasis.

PURPOSE: Expression of lysosome-associated membrane protein-1 (LAMP1) on the surface correlates with metastatic potential of B16 melanoma cells. Downregulation of their expression in high metastatic (B16F10) cells reduced their surface expression and metastatic potential. Present investigations explore if overexpression of LAMP1 on the surface of low metastatic (B16F1) cells augment their metastatic ability, and if so, how? METHODS: B16F1 cells were transduced with lentiviral vector carrying mutant-LAMP1 (Y386A) (mutLAMP1). Surface expression of LAMP1 and carbohydrates was analyzed by flow cytometry, immunofluorescence and/or immunoprecipitation and Western blotting. Cell spreading and motility were assessed on components of extracellular matrix (ECM) (fibronectin) and basement membrane (BM) (matrigel), and galectin-3-coated coverslips/plates. Metastatic potential was assessed using experimental metastasis assay. RESULTS: Pre-incubation with anti-LAMP1 antibodies significantly reduced lung metastasis of B16F10 cells. Overexpression of mutLAMP1 significantly increased its surface expression on B16F1 cells, resulting in increased cellular spreading and motility on fibronectin and matrigel. LAMP1 is the major carrier of poly-N-acetyllactosamine (polyLacNAc) on B16F10 cells. However, significantly higher expression of mutLAMP1 had no effect on galectin-3 binding on cell surface or on spreading or motility of cells on galectin-3-coated coverslips/plates. These cells also failed to show any gain in metastatic ability. This could be because LAMP1 from these cells carried significantly lower levels of polyLacNAc in comparison with B16F10 cells. CONCLUSIONS: PolyLacNAc on B16F10 cells and galectin-3 on lungs are the major participants in melanoma metastasis. Although surface LAMP1 promotes interactions with organ ECM and BM, carbohydrates on LAMP1 play a decisive role in dictating lung metastasis.

Regulation of melanoma metastasis to lungs by cell surface Lysosome Associated Membrane Protein-1 (LAMP1) via galectin-3.

Lysosome Associated Membrane Protein-1 (LAMP1), which lines the lysosomes, is often found to be expressed on surface of metastatic cells. We previously demonstrated that its surface expression on B16 melanoma variants correlates with metastatic potential. To establish the role of cell surface LAMP1 in metastasis and to understand the possible mechanism by which it facilitates lung colonization, LAMP1 was downregulated in high metastatic B16F10 cells using shRNAs cloned in a doxycycline inducible vector. This also resulted in significantly decreased LAMP1 on the cell surface. Being a major carrier of poly-N-acetyllactosamine (polyLacNAc) substituted ß1,6 branched N-oligosaccharides, the high affinity ligands for galectin-3, LAMP1 down regulation also resulted in appreciably decreased binding of galectin-3 to the cell surface. LAMP1 has been shown to bind to Extracellular Matrix (ECM), Basement Membrane (BM) components and also to galectin-3 (via carbohydrates) which is known to get incorporated into the ECM and BM. Although, LAMP1 downregulation had a marginal effect on cellular spreading and motility on fibronectin and matrigel, it significantly altered the same on galectin-3, and ultimately leading to notably reduced lung metastasis. The results thus for the first time provide direct evidence that cell surface LAMP1 facilitates lung metastasis by providing ligands for galectin-3 which has been shown to be expressed in highest amounts on lungs and constitutively on its vascular endothelium.