Identification of uPAR-positive Chemoresistant Cells in Small Cell Lung Cancer

BACKGROUND: The urokinase plasminogen activator (uPA) and its receptor (uPAR/CD87) are major regulators of extracellular matrix degradation and are involved in cell migration and invasion under physiological and pathological conditions. The uPA/uPAR system has been of great interest in cancer research because it is involved in the development of most invasive cancer phenotypes and is a strong predictor of poor patient survival. However, little is known about the role of uPA/uPAR in small cell lung cancer (SCLC), the most aggressive type of lung cancer. We therefore determined whether uPA and uPAR are involved in generation of drug resistant SCLC cell phenotype. METHODS AND FINDINGS: We screened six human SCLC cell lines for surface markers for putative stem and cancer cells. We used fluorescence-activated cell sorting (FACS), fluorescence microscopy and clonogenic assays to demonstrate uPAR expression in a subpopulation of cells derived from primary and metastatic SCLC cell lines. Cytotoxic assays were used to determine the sensitivity of uPAR-positive and uPAR-negative cells to chemotherapeutic agents. The uPAR-positive cells in all SCLC lines demonstrated multi-drug resistance, high clonogenic activity and co-expression of CD44 and MDR1, putative cancer stem cell markers. CONCLUSIONS: These data suggest that uPAR-positive cells may define a functionally important population of cancer cells in SCLC, which are resistant to traditional chemotherapies, and could serve as critical targets for more effective therapeutic interventions in SCLC

The DISABLED protein functions in CLATHRIN-mediated synaptic vesicle endocytosis and exoendocytic coupling at the active zone

Members of the DISABLED (DAB) family of proteins are known to play a conserved role in endocytic trafficking of cell surface receptors by functioning as monomeric CLATHRIN-associated sorting proteins that recruit cargo proteins into endocytic vesicles. Here, we report a Drosophila disabled mutant revealing a novel role for DAB proteins in chemical synaptic transmission. This mutant exhibits impaired synaptic function, including a rapid activity-dependent reduction in neurotransmitter release and disruption of synaptic vesicle endocytosis. In presynaptic boutons, Drosophila DAB and CLATHRIN were highly colocalized within two distinct classes of puncta, including relatively dim puncta that were located at active zones and may reflect endocytic mechanisms operating at neurotransmitter release sites. Finally, broader analysis of endocytic proteins, including DYNAMIN, supported a general role for CLATHRIN-mediated endocytic mechanisms in rapid clearance of neurotransmitter release sites for subsequent vesicle priming and refilling of the release-ready vesicle pool