Restoration of MAGI-1 expression in human papillomavirus-positive tumor cells induces cell growth arrest and apoptosis.
The cancer-causing high-risk human papillomavirus (HPV) E6 oncoproteins target a number of cellular proteins that contain PDZ domains. However, the role of many of these interactions in either the HPV life cycle or in HPV-induced malignancy remains to be defined. Previous studies had shown that MAGI-1 was one of the ... most strongly bound PDZ domain-containing substrates of E6, and one consequence of this interaction appeared to facilitate the perturbation of tight junctions (TJs) by E6. In this study, we describe the generation of a mutation, K499E, within the MAGI-1 PDZ1 domain, which is resistant to E6 targeting. This mutant allows restoration of MAGI-1 expression in HPV-positive cells and defines additional activities of MAGI-1 that are overcome as a consequence of the association with E6. The reexpression of MAGI-1 in HPV-positive cells results in an increased recruitment of ZO-1 and PAR3 to sites of cell-cell contact, repression of cell proliferation, and induction of apoptosis. While the K499E mutation does not significantly affect these intrinsic activities of MAGI-1 in HPV-negative cells, its resistance to E6 targeting in an HPV-positive setting results in more cells expressing the mutant MAGI-1 than the wild-type MAGI-1, with a corresponding increase in TJ assembly, induction of apoptosis, and reduction in cell proliferation. These studies provide compelling evidence of a direct role for the perturbation of MAGI-1 function by E6 in the HPV life cycle and in HPV-induced malignancy.It is clear that the targeting of PDZ-containing substrates by E6 is important for the normal viral life cycle and for the progression to malignancy. Nevertheless, which of these PDZ domain-containing proteins is relevant for HPV pathology is still elusive. In a previous study, we provided evidence that MAGI-1 is a sensitive proteolytic substrate for both the HPV-16 and HPV-18 E6 oncoproteins; however, the biological consequences associated with loss of MAGI-1 expression in HPV-positive cervical cancer cells are still poorly understood. Using a mutant MAGI-1, resistant to E6-mediated degradation, we show that its expression in cervical cancer cells promotes membrane recruitment of the tight junction-associated proteins ZO-1 and PAR3, represses cell proliferation, and promotes apoptosis. These findings suggest that E6-mediated inhibition of MAGI-1 function contributes to HPV pathology by perturbing tight junction assembly with concomitant stimulation of proliferation and inhibition of apoptosis.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Amino Acid Sequence, Apoptosis, Blotting, Western, Cell Adhesion Molecules, Cell Adhesion Molecules, Neuronal, Cell Proliferation, DNA-Binding Proteins, Fluorescent Antibody Technique, Guanylate Kinases, HEK293 Cells, HeLa Cells, Humans, Immunoprecipitation, Molecular Sequence Data, Mutation, Oncogene Proteins, Viral, PDZ Domains, Papillomaviridae, Protein Binding, Proteolysis, Repressor Proteins
Adaptor Proteins, Signal Transducing, Amino Acid Sequence, Apoptosis, Blotting, Western, Cell Adhesion Molecules, Cell Adhesion Molecules, Neuronal, Cell Proliferation, DNA-Binding Proteins, Fluorescent Antibody Technique, Guanylate Kinases, HEK293 Cells, HeLa Cells, Humans, Immunoprecipitation, Molecular Sequence Data, Mutation, Oncogene Proteins, Viral, PDZ Domains, Papillomaviridae, Protein Binding, Proteolysis, Repressor Proteins
J Virol
Date: Jul. 01, 2014
PubMed ID: 24696483
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