title: Augmentation of Fas ligand-induced apoptosis by MUC1 mucin.
abstract: Apoptosis is a physiological mechanism responsible for a wide range of cellular processes during growth, development, carcinogenesis, and inflammation. In this study, we determined whether MUC1 affects Fas ligand (FasL)-induced apoptosis using MUC1 expressing (MUC1(+)) and MUC1(-) cells. Following treatment with 50 nM FasL, apoptosis, caspase-8 activity, and cell surface Fas receptor were measured by cytosolic nucleosome ELISA, colorimetric enzyme assay, and immunofluorescence analysis, respectively. Our results showed that (i) treatment with FasL increased caspase-8 activity (maximum at 4 h) and apoptosis (maximum at 8 h) in both MUC1(+) and MUC1(-) cells, (ii) FasL-induced caspase-8 activity and apoptosis were significantly greater in MUC1(+) cells compared with MUC1(-) cells, (iii) FasL treatment increased cell surface expression of Fas receptor in MUC1(+) cells to a greater extent compared with MUC1(-) cells, (iv) increased cell surface expression of Fas in MUC1(+) cells was not blocked by an inhibitor of protein synthesis (cycloheximide), but was completely abrogated by brefeldin A, an inhibitor of post-translational protein trafficking to the cell surface, and (v) brefeldin A inhibited the increased sensitivity of MUC1(+) cells to FasL-induced apoptosis. We conclude that MUC1(+) cells were more sensitive to FasL-induced apoptosis compared with MUC1(-) cells due to up-regulation of Fas receptor on the cell surface by a mechanism involving increased intracellular trafficking.
authors.affiliation: Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, MD 21201, USA.
authors.forename: Rupesh
authors.initials: R
authors.lastname: Chaturvedi
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Srivastava
authors.forename: Akinori
authors.initials: A
authors.lastname: Hisatsune
authors.forename: Sharmila
authors.initials: S
authors.lastname: Shankar
authors.forename: Erik P
authors.initials: EP
authors.lastname: Lillehoj
authors.forename: K Chul
authors.initials: KC
authors.lastname: Kim
mesh_terms: D000818:Animals; D000954:Antigens, Surface; D017209:Apoptosis; D016466:CHO Cells; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D018929:Cell Culture Techniques; D002462:Cell Membrane / Q000502:physiology; D006224:Cricetinae; D003412:Cricetulus; D004797:Enzyme-Linked Immunosorbent Assay; D053222:Fas Ligand Protein; D005455:Fluorescent Antibody Technique; D008024:Ligands; D008562:Membrane Glycoproteins / Q000378:metabolism*; D018396:Mucin-1 / Q000378:metabolism*; D015854:Up-Regulation; D019014:fas Receptor / Q000096:biosynthesis
chemical_list: D000954:Antigens, Surface; D053222:Fas Ligand Protein; D008024:Ligands; D008562:Membrane Glycoproteins; D018396:Mucin-1; D019014:fas Receptor; D053181:Caspase 8; D020169:Caspases