Modulation of epithelial neoplasia and lymphoid hyperplasia in PTEN+/- mice by the p85 regulatory subunits of phosphoinositide 3-kinase

Abstract

Mice with heterozygous deletion of the PTEN tumor suppressor gene develop a range of epithelial neoplasia as well as lymphoid hyperplasia. Previous studies suggest that PTEN suppresses tumor formation by acting as a phosphoinositide phosphatase to limit signaling by phosphoinositide 3-kinase (PI3K). Here, we examined the effect of deleting various regulatory subunits of PI3K (p85alpha and p85beta) on epithelial neoplasia and lymphoid hyperplasia in PTEN+/- mice. Interestingly, we found the loss of one p85alpha allele with or without the loss of p85beta led to increased incidence of intestinal polyps. Signaling downstream of PI3K was enhanced in the PTEN+/-p85alpha+/-p85beta-/- polyps, as judged by an increased fraction of both cells with cytoplasmic staining of the transcription factor FKHR and cells with positive staining for the proliferation marker Ki-67. In contrast, the incidence of prostate intraepithelial neoplasia was not significantly altered in PTEN+/- mice heterozygous for p85alpha or null for p85beta, whereas the fraction of proliferating cells in prostate intraepithelial neoplasia was reduced in mice lacking p85beta. Finally, there was no significant change in T lymphocyte hyperplasia in the PTEN+/- mice with various p85 deletions, although anti-CD3-stimulated AKT activation was somewhat reduced in the p85alpha+/- background. These results indicate that decreasing the levels of different p85 regulatory subunits can result in enhanced PI3K signaling in some tissues and decreased PI3K signaling in others, supporting the model that, although p85 proteins are essential for class I(A) PI3K signaling, they can function as inhibitors of PI3K signaling in some tissues and thus suppress tumor formation.

Fig. 1.

Loss of one p85α allele increased intestinal polyps incidence in PTEN^+/- mice. (A) The distribution of the number of macroscopic intestinal polyps per animal in 5- to 10-month-old mice. The total numbers of mice analyzed for each genotype were the same as those in Table 1. (B) Immunohistochemistry of prostate PIN from 5- to 10-month-old animals revealed cytoplasmic localization of FKHR and elevated S6 phosphorylation. For each genotype, representative staining of adjacent sections from the same lesion are shown. (C) The relative distribution of FKHR staining in cells from intestinal epithelial neoplasia. Few cells with exclusive nuclear staining of FKHR were found in all lesions analyzed. Results shown are mean ± SEM (n = 4 mice per genotype). (D) The percentage of Ki-67-positive cells in intestinal epithelial neoplasia. Results shown are mean ± SEM (n = 4 mice per genotype; ^*, P < 0.05 compared to PTEN^+/- mice, two-tailed t test).

Fig. 2.

Loss of p85β reduces cell proliferation in PIN of PTEN^+/- mice. (A) Immunohistochemistry of prostate PIN from 5- to 10-month-old males revealed elevated Akt phosphorylation, cytoplasmic localization of FKHR, and elevated S6 phosphorylation. For each genotype, representative staining of adjacent sections from the same lesion are shown. (B) The relative distribution of FKHR staining of cells in PIN. Results shown are mean ± SEM (n = 9 independent lesions from three mice per genotype). (C) The percentage of Ki-67-positive cells in PIN. Results shown are mean ± SEM (n = 9 independent lesions from three mice per genotype; ^*, P < 0.05 compared to PTEN^+/- mice, two-tailed t test).

Fig. 3.

Loss of one p85α allele reduces Akt activation in T cells from PTEN^+/- mice. (A) The levels of CD44 in splenic CD4⁺ T cells were profiled in 8- to 10-week-old mice, and the percentage of CD44^high cells was calculated for each profile by using the same gate. Representative profiles of four experiments are shown. (B) Heterozygosity of the p85α allele led to reduced Akt activation in T cells in vitro. T cells from 6- to 8-week-old animals were stimulated with anti-CD3ε antibody and the phosphorylation of Akt and p44/42 Erk were assessed by Western blot. Representative blots of four independent experiments from four groups of mice are shown. (C) Heterozygosity of the p85α allele did not significantly attenuate the onset of lymphoid hyperplasia in PTEN^+/- mice. Kaplan-Meier curve of s.c. lymphoid hyperplasia-free mice over time is shown. The total number of mice analyzed are shown in parentheses.