Inhibition of the Raf/MEK/ERK pathway up-regulates expression of the coxsackievirus and adenovirus receptor in cancer cells.
Recombinant adenoviruses are presently being tested clinically as a new strategy for the treatment of cancer. An important determining factor for the successful entry of such adenoviruses into target cells is expression of the coxsackievirus and adenovirus receptor (CAR) at the cell surface. Recent observations suggest that expression of this receptor, which physiologically participates in formation of cell-cell adhesions, is frequently reduced in highly malignant cancer cells. This raises the possibility that those tumors representing the greatest therapeutic challenge might be the least susceptible to infection with therapeutic adenoviruses. We explored the role of the Raf-MEK-ERK pathway on CAR expression in a panel of cancer cells because this pathway is frequently up-regulated in cancer cells and is known to down-regulate cell-cell adhesion molecules. We found that disruption of signaling through the Raf-MEK-ERK pathway by inhibition of MEK up-regulated CAR expression, which was accompanied by increased representation of the protein at the cell surface. After Raf-MEK-ERK inhibition, adenovirus entry into cells was increased and cell killing by replication competent adenoviruses was enhanced in a CAR-dependent manner. Conversely, induction of Raf-1 resulted in reduction and disruption of CAR expression at the cell surface. We conclude that loss of CAR expression in cancer cells is, at least in part, mediated through the Raf-MEK-ERK signal transduction pathway and that pharmacological restoration of CAR at the cell surface could improve adenovirus-based treatments of cancer.
Cancer Research Institute, University of California, San Francisco 94143, USA.
Mario
M
Anders
Christine
C
Christian
Martin
M
McMahon
Frank
F
McCormick
W Michael
WM
Korn
D000260:Adenoviruses, Human / Q000378:metabolism / Q000502:physiology; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D015179:Colorectal Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D062727:Coxsackie and Adenovirus Receptor-Like Membrane Protein; D004285:Dogs; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics; D048728:MAP Kinase Kinase Kinase 1; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology; D010190:Pancreatic Neoplasms / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D011991:Receptors, Virus / Q000096:biosynthesis* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
C568771:CLMP protein, human; C568772:CLMP protein, mouse; D062727:Coxsackie and Adenovirus Receptor-Like Membrane Protein; D004791:Enzyme Inhibitors; D008164:Luminescent Proteins; D011991:Receptors, Virus; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human; C482578:Map3k1 protein, mouse