title: Requirement for both Shc and phosphatidylinositol 3' kinase signaling pathways in polyomavirus middle T-mediated mammary tumorigenesis.
abstract: Transgenic mice expressing the polyomavirus (PyV) middle T antigen (MT) develop multifocal mammary tumors which frequently metastasize to the lung. The potent transforming activity of PyV MT is correlated with its capacity to activate and associate with a number of signaling molecules, including the Src family tyrosine kinases, the 85-kDa Src homology 2 subunit of the phosphatidylinositol 3' (PI-3') kinase, and the Shc adapter protein. To uncover the role of these signaling proteins in MT-mediated mammary tumorigenesis, we have generated transgenic mice that express mutant PyV MT antigens decoupled from either the Shc or the PI-3' kinase signaling pathway. In contrast to the rapid induction of metastatic mammary tumors observed in the strains expressing wild-type PyV MT, mammary epithelial cell-specific expression of either mutant PyV MT resulted in the induction of extensive mammary epithelial hyperplasias. The mammary epithelial hyperplasias expressing the mutant PyV MT defective in recruiting the PI-3' kinase were highly apoptotic, suggesting that recruitment of PI-3' kinase by MT affects cell survival. Whereas the initial phenotypes observed in both strains were global mammary epithelial hyperplasias, focal mammary tumors eventually arose in all female transgenic mice. Genetic and biochemical analyses of tumorigenesis in the transgenic strains expressing the PyV MT mutant lacking the Shc binding site revealed that a proportion of the metastatic tumors arising in these mice displayed evidence of reversion of the mutant Shc binding site. In contrast, no evidence of reversion of the PI-3' kinase binding site was noted in tumors derived from the strains expressing the PI-3' kinase binding site MT mutant. Tumor progression in both mutant strains was further correlated with upregulation of the epidermal growth factor receptor family members which are known to couple to the PI-3' kinase and Shc signaling pathways. Taken together, these observations suggest that PyV MT-mediated tumorigenesis requires activation of both Shc and PI-3' kinase, which appear to be required for stimulation of cell proliferation and survival signaling pathways, respectively.
authors.affiliation: Institute for Molecular Biology and Biotechnology, and Department of Biology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: M A
authors.initials: MA
authors.lastname: Webster
authors.forename: J N
authors.initials: JN
authors.lastname: Hutchinson
authors.forename: M J
authors.initials: MJ
authors.lastname: Rauh
authors.forename: S K
authors.initials: SK
authors.lastname: Muthuswamy
authors.forename: M
authors.initials: M
authors.lastname: Anton
authors.forename: C G
authors.initials: CG
authors.lastname: Tortorice
authors.forename: R D
authors.initials: RD
authors.lastname: Cardiff
authors.forename: F L
authors.initials: FL
authors.lastname: Graham
authors.forename: J A
authors.initials: JA
authors.lastname: Hassell
authors.forename: W J
authors.initials: WJ
authors.lastname: Muller
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000595:Amino Acid Sequence; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000502:physiology*; D017209:Apoptosis; D001483:Base Sequence; D001665:Binding Sites; D001940:Breast / Q000473:pathology; D002471:Cell Transformation, Neoplastic; D002472:Cell Transformation, Viral; D004247:DNA; D018450:Disease Progression; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D006965:Hyperplasia; D008297:Male; D008325:Mammary Neoplasms, Experimental / Q000737:chemistry / Q000209:etiology / Q000821:virology*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011120:Polyomavirus / Q000502:physiology; D011506:Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics; D020893:Receptor, ErbB-3; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D014018:Tissue Distribution; D015854:Up-Regulation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000952:Antigens, Polyomavirus Transforming; D004247:DNA; D066246:ErbB Receptors; D019869:Phosphatidylinositol 3-Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3; D055765:Shc Signaling Adaptor Proteins; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; C528034:Shc1 protein, mouse