Multimerization of polyomavirus middle-T antigen.
The oncogenic protein of polyomavirus, middle-T antigen, associated with cell membranes and interacts with a variety of cellular proteins involved in mitogenic signalling. Middle-T antigen may therefore mimic the function of cellular tyrosine kinase growth factor receptors, like the platelet-derived growth factor or epidermal growth factor receptor. Growth factor receptor signalling is initiated upon the binding of a ligand to the extracellular domain of the receptor. This results in activation of the intracellular tyrosine kinase domain of the receptor, followed by receptor phosphorylation, presumably as a consequence of dimerization of two receptor molecules. Similar to middle-T antigen, phosphorylation of growth factor receptors leads to recruitment of cellular signalling molecules downstream in the signalling cascade. In this study, we investigated whether middle-T antigen, similar to tyrosine kinase growth factor receptors, is able to form dimeric signalling complexes. We found that association with cellular membranes was a prerequisite for multimerization, most likely dimer formation. A chimeric middle-T antigen carrying the membrane-targeting sequence of the vesicular stomatitis virus G protein instead of the authentic polyomavirus sequence still dimerized. However, mutants of middle-T antigen unable to associate with 14-3-3 proteins, like d18 and S257A, did not form dimers but were still oncogenic. This indicates that both membrane association and binding of 14-3-3 are necessary for dimer formation of middle-T antigen but that only the former is essential for cell transformation.
Senften
M
M
Friedrich Miescher Institute, Basel, Switzerland.
Dilworth
S
S
Ballmer-Hofer
K
K
D048948:14-3-3 Proteins; D016475:3T3 Cells; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000378:metabolism*; D001704:Biopolymers; D051379:Mice; D010766:Phosphorylation; D011120:Polyomavirus / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D017384:Sequence Deletion; D014446:Tyrosine 3-Monooxygenase
D048948:14-3-3 Proteins; D000952:Antigens, Polyomavirus Transforming; D001704:Biopolymers; D011506:Proteins; D014446:Tyrosine 3-Monooxygenase; D016392:Proto-Oncogene Proteins pp60(c-src)