Cooperation between Pik3ca and p53 Mutations in Mouse Mammary Tumor Formation

Jessica R Adams,Jeff C Liu,Timothy F Lane,Wei Wang,Sean E Egan,Keli Xu,Katherine L Wright,Amanda J Loch,Natalia M Ruiz Agamez,Eldad Zacksenhaus,Ruth G Wong

doi:10.1158/0008-5472.can-10-0738

Abstract

PIK3CA, which codes for the p110α catalytic subunit of phosphatidylinositol 3-kinase, is one of the most frequently mutated genes in human breast cancer. Here, we describe a mouse model for PIK3CA-induced breast cancer by using the ROSA26 (R26) knock-in system, in which targeted Pik3ca alleles can be activated through transgenic expression of Cre recombinase. We mated Pik3ca(H1047R) and Pik3ca(wt) knock-in lines with MMTV-Cre transgenics, which express Cre in mammary epithelium. Starting at approximately 5 months of age, female R26-Pik3ca(H1047R);MMTV-Cre mice, but not control R26-Pik3ca(wt);MMTV-Cre mice, developed mammary tumors, as well as lymphoid and skin malignancies. R26-Pik3ca(H1047R);MMTV-Cre mammary tumors were typically either adenosquamous carcinoma or adenomyoepithelioma. As p53 is the most commonly mutated gene in breast cancer, we tested for genetic interaction between Pik3ca(H1047R) and p53 loss-of-function mutations in R26-Pik3ca(H1047R);p53(loxP/+);MMTV-Cre mice. This led to decreased survival of double-mutant animals, which developed lymphoma and mammary tumors with rapid kinetics. Mammary tumors that formed in p53(loxP/+);MMTV-Cre conditional mutants were either poorly differentiated adenocarcinoma or spindle cell/EMT, whereas R26-Pik3ca(H1047R);p53(loxP/+);MMTV-Cre mammary tumors were mostly adenosquamous carcinoma or spindle cell/EMT indicating that double-mutant mice develop a distinct spectrum of mammary tumors. Thus, an oncogenic variant of PIK3CA implicated in multiple human breast cancer subtypes can induce a very diverse spectrum of mammary tumors in mice. Furthermore, Pik3ca(H1047R) shows cooperation with p53, which altered the specific tumors that formed. Thus, the two most frequently mutated genes in human breast cancer show cooperation in mammary tumor formation.

Highlights

The phosphoinositide 3-kinase (PI3K) signaling pathway is one of the most frequently mutated pathways in cancer
To test for the ability of Pik3caH1047R or wild-type Pik3ca (Pik3cawt) to induce mammary tumors, we used the Creconditional ROSA26 (R26) knock-in system, whereby Cremediated deletion of loxP-flanked transcriptional stop sequences allows for tissue-specific expression of either allele (Fig. 1A; refs. 21, 22). mESC were targeted and screened to identify clones with Cre-inducible transgene expression (Supplementary Fig. 1)
R26-Pik3caH1047R and R26Pik3cawt mice were mated with MMTV-Cre mice, which express Cre-recombinase in mammary epithelium

Summary

Introduction

The phosphoinositide 3-kinase (PI3K) signaling pathway is one of the most frequently mutated pathways in cancer. One common and direct mechanism by which the PI3K pathway is activated in breast, endometrial, colorectal, urinary tract, thyroid, and ovarian cancer is through gain-of-function mutations in PIK3CA [1,2,3]. PIK3CA mutations are important in human breast cancer, with activated alleles detected in 25% to 30% of tumors [4,5,6,7]. Have been found in ductal carcinoma in situ, suggesting that they play a role in breast tumor initiation [8,9,10]. PIK3CA mutations can induce p53dependent growth inhibition [12] and mutations in both genes occur together in some human breast tumors [13, 14]

Methods

Results

Conclusion