FIG. 3.

Activation of the PI-3′ kinase by PyV MT is involved in mammary tumor progression. (A) A panel of slide-mounted Mayer’s hematoxylin-stained mammary tissue sections from age-matched mice from nontransgenic FVB/N or transgenic MMTV-Y250F, MMTV/MT-Y315/322F, and wild-type MT strains. Cells were analyzed for apoptotic cell death as described previously (46). Digoxigenin-labeled DNA ends were detected with horseradish peroxidase-conjugated antidigoxigenin antibodies. Note the multiple apoptotic cells in the epithelial hyperplasias derived from the MT-Y315/322F strain and lack of comparable staining in mammary tissues from FVB/N, MT-Y250F, and wild-type MT mice. (B) Structure of Cre-inducible expression cassette carrying the dominant negative p85 inhibitor. The dark shaded box indicates the Mo-MuLV LTR; the arrows flanking the PGK-Neo cassette represent the LOX recombination sites. The unshaded box indicates the cDNA encoding the mutant p85 subunit of the PI-3′ kinase. (C) In situ apoptosis analyses (TUNEL) conducted with PyV MT mammary tumor cells infected with either a control adenovirus expressing a beta-galactosidase reporter (MT-LacZ) or an adenovirus vector expressing the Cre recombinase (MT-Cre). TUNEL analyses with PyV MT tumor cells possessing the inducible dominant negative p85 inhibitor infected with either the LacZ (MTΔ85nl-LacZ) or Cre adenovirus (MTΔ85nl-Cre) are also shown. Both sets of cells were infected at an MOI of 100. Note the presence of numerous cells undergoing apoptotic cell death in the Cre infection panel.