ABSTRACT
Tumor cell invasion involves targeted localization of proteins required for interactions with the extracellular matrix and for proteolysis. The localization of many proteins during these cell-extracellular matrix interactions relies on membrane trafficking mediated in part by SNAREs. The SNARE protein syntaxin4 (Stx4) is involved in the formation of invasive structures called invadopodia; however, it is unclear how Stx4 function is regulated during tumor cell invasion. Munc18c is known to regulate Stx4 activity, and here we show that Munc18c is required for Stx4-mediated invadopodium formation and cell invasion. Biochemical and microscopic analyses revealed a physical association between Munc18c and Stx4, which was enhanced during invadopodium formation, and that a reduction in Munc18c expression decreases invadopodium formation. We also found that an N-terminal Stx4-derived peptide associates with Munc18c and inhibits endogenous interactions of Stx4 with synaptosome-associated protein 23 (SNAP23) and vesicle-associated membrane protein 2 (VAMP2). Furthermore, expression of the Stx4 N-terminal peptide decreased invadopodium formation and cell invasion in vitro Of note, cells expressing the Stx4 N-terminal peptide exhibited impaired trafficking of membrane type 1 matrix metalloproteinase (MT1-MMP) and EGF receptor (EGFR) to the cell surface during invadopodium formation. Our findings implicate Munc18c as a regulator of Stx4-mediated trafficking of MT1-MMP and EGFR, advancing our understanding of the role of SNARE function in the localization of proteins that drive tumor cell invasion.
Subject(s)
Adenocarcinoma/metabolism , Extracellular Matrix/metabolism , Fibrosarcoma/metabolism , Munc18 Proteins/metabolism , Neoplasm Proteins/metabolism , Podosomes/metabolism , Qa-SNARE Proteins/metabolism , Adenocarcinoma/pathology , Binding, Competitive , Cell Line, Tumor , ErbB Receptors/metabolism , Extracellular Matrix/pathology , Fibrosarcoma/pathology , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Humans , Matrix Metalloproteinase 14/metabolism , Munc18 Proteins/antagonists & inhibitors , Munc18 Proteins/chemistry , Munc18 Proteins/genetics , Neoplasm Invasiveness , Neoplasm Proteins/antagonists & inhibitors , Neoplasm Proteins/chemistry , Neoplasm Proteins/genetics , Peptide Fragments/chemistry , Peptide Fragments/genetics , Peptide Fragments/metabolism , Podosomes/pathology , Protein Interaction Domains and Motifs , Protein Multimerization , Protein Transport , Qa-SNARE Proteins/chemistry , Qa-SNARE Proteins/genetics , Qb-SNARE Proteins/antagonists & inhibitors , Qb-SNARE Proteins/chemistry , Qb-SNARE Proteins/metabolism , Qc-SNARE Proteins/antagonists & inhibitors , Qc-SNARE Proteins/chemistry , Qc-SNARE Proteins/metabolism , RNA Interference , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/metabolism , Vesicle-Associated Membrane Protein 2/antagonists & inhibitors , Vesicle-Associated Membrane Protein 2/chemistry , Vesicle-Associated Membrane Protein 2/metabolismABSTRACT
BACKGROUND: In asthma and chronic obstructive pulmonary disease (COPD), airway mucus hypersecretion contributes to impaired mucociliary clearance, mucostasis and, potentially, the development of mucus plugging of the airways. SUMMARY: Excess mucus production can be targeted via therapies that focus on inhibition mucin synthesis, via reducing expression of mucin (MUC) genes, and/or inhibition of mucin secretion into the airways. KEY MESSAGES: This review discusses a number of therapeutic approaches to reduce airway mucus in asthma and COPD, including the use of synthetic and natural products. In particular, it highlights areas where clinical trials of inhibitors of particular target molecules are lacking. Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors are an example of a targeted therapy that has been researched to reduce mucus synthesis, as have inhibitors of EGFR's downstream signalling pathways, for example, mitogen-activated protein kinase-13 and hypoxia inducible factor-1. However, their efficacy and safety profiles are currently not up to the mark. There is clinical potential in Bio-11006, which reduces mucus secretion via the inhibition of myristoylated alanine-rich C-kinase substrate and is currently in Phase IIb trial.
