Deficiency of Pten accelerates mammary oncogenesis in MMTV-Wnt-1 transgenic mice

Abstract

mutations in mice lead to the development of a variety of tumors, but mammary carcinomas are infrequently found, especially in mice under the age of six months. function have a growth advantage over cells retaining a wild type allele. Tumors with LOH contained high levels of activated AKT/PKB, a downstream target of the PTEN/PI3K pathway. to induce ductal carcinoma in the mammary gland. This animal model may be useful for testing therapies specific for tumors deregulated in the PTEN/PI3K/AKT pathway.

Background

mutations in mice lead to the development of a variety of tumors, but mammary carcinomas are infrequently found, especially in mice under the age of six months.

Results

function have a growth advantage over cells retaining a wild type allele. Tumors with LOH contained high levels of activated AKT/PKB, a downstream target of the PTEN/PI3K pathway.

Conclusions

to induce ductal carcinoma in the mammary gland. This animal model may be useful for testing therapies specific for tumors deregulated in the PTEN/PI3K/AKT pathway.

Introduction

].

].

].

].

]. The relationship between components of this pathway is also conserved in flies and worms.

].

], which account for over 85% of human breast cancers.

functions.

Results

]. The lack of a mammary phenotype in our studies could be due to differences in the targeting constructs, the genetic backgrounds, or even environmental agents.

mutations, the majority of tumors (14/22) arose in the salivary tissue; only a small number of tumors (2/22) were mammary in origin, and, interestingly, some (6/22) were bilateral or unilateral muzzle tumors of epithelial origin, similar histopathologically to lesions found in mammary and salivary tissues.

.

), suggesting a more aggressive phenotype.

).

).

when measured by the TUNEL (terminal deoxynucleotidyltransferase-mediated UTP end labeling) assay, which labels the ends of fragmented DNA present in apoptotic cells, and immunohistochemical staining for Ki67, a cell proliferation marker (data not shown).

). These squamous lesions were usually multi-focal and located both at the periphery of the adenocarcinomas and in other mammary glands free of adenocarcinomas.

+/- mice harbored metastatic foci at similar frequencies (5/10). (Statistical evaluation was not performed because the sample sizes were too small.)

Discussion

].

heterozygous mice (KP, RP, submitted). The presence of areas unstained with antibody specific for phosphorylated AKT suggests that additional factors other than Pten may influence the activation of AKT.

background already have highly suppressed apoptosis and accelerated proliferation rates, and any incremental changes, if present, may be difficult to detect with our current assays. Nonetheless, a seemingly minor difference in either apoptosis or proliferation could have a dramatic impact on tumor growth over time.

].

is inactivated, and with predictable kinetics, this model may be useful for testing the efficacy of these therapies.

mice. This would allow the testing of therapeutic interventions directed to specific steps of the signaling pathway regulated by Pten.

Mice

knockout allele. Mice were monitored weekly for tumor formation by visual inspection and/or palpation; most tumors were found when they were approximately 0.5 cm. Most of tumors were harvested for further analysis when they were 1.5 cm in diameter. Tissues were fixed in 10% buffered formalin and paraffin-embedded. For histological survey, one H-E section per block was analyzed.

Immunohistochemical staining and TUNEL assay

].

Southern hybridization

] using the RTS RadPrime DNA labeling system (Life Technologies). The probe was incubated with Cot-1 DNA (Life Technologies) at 70°C for 10 minutes before addition to the hybridization solution.

Acknowledgements

We thank Jennifer Doherty and Wendy Hively for technical assistance; Maria Merino and Carlos Cordon-Cardo for consultation on pathology samples; Osseh Saine, Marlon Scopio, and Jose Vargas for excellent animal care. YL is a recipient of the US Army Breast Cancer Research Program Fellowship Award.

Figures and Tables

+/- cohort (22) had 2 mammary, 6 muzzle, and 14 salivary tumors.

probe. Two bands could be observed, representing wild type and mutant alleles, as indicated at the left. Genotypes of mice are shown at the top.

+/- with LOH (C and D). A 40x objective was used. Blue arrows indicate the smooth boundaries of tumors, red arrow marks the infiltrating front of the tumor, and white arrows label the highly cellular stroma. (D) shows a part of an intraductal squamous lesion.

+/- (C-F). (E) and (C, F) were from tumors with or without LOH, respectively. A 40x objective was used.

+/+ (C, D). (A) and (B) were from tumors with or without LOH, respectively. A 40x objective was used.