A Spontaneous Aggressive ERα+ Mammary Tumor Model Is Driven by Kras Activation

Katie M Campbell,Kathleen A O’Leary,Debra E Rugowski,William A Mulligan,Erica K Barnell,Zachary L Skidmore,Kilannin Krysiak,Malachi Griffith,Linda A Schuler,Obi L Griffith

doi:10.1016/j.celrep.2019.06.098

Abstract

The NRL-PRL murine model, defined by mammary-selective transgenic rat prolactin ligand rPrl expression, establishes spontaneous ER+ mammary tumors in nulliparous females, mimicking the association between elevated prolactin (PRL) and risk for development of ER+ breast cancer in postmenopausal women. Whole-genome and exome sequencing in a discovery cohort (n= 5) of end-stage tumors revealed canonical activating mutations and copy number amplifications of Kras. The frequent mutations in this pathway were validated in an extension cohort, identifying activating Ras alterations in 79% of tumors (23 of 29). Transcriptome analyses over the course of oncogenesis revealed marked alterations associated with Ras activity in established tumors compared with preneoplastic tissues; in cell-intrinsic processes associated with mitosis, cell adhesion, and invasion; as well as in the surrounding tumor environment. These genomic analyses suggest that PRL induces a selective bottleneck for spontaneous Ras-driven tumors that may model a subset of aggressive clinical ER+ breast cancers.

Highlights

Epidemiologic evidence has linked higher levels of circulating prolactin (PRL) with increased risk for estrogen receptor alpha (ER+) breast cancers, in postmenopausal women (Tikk et al, 2014; Tworoger and Hankinson, 2008; Tworoger et al, 2013)
To distinguish the contributions of PRL to breast cancer from its actions in pregnancy, we generated the NRL-PRL murine model, where transgenic rat PRL is secreted by mammary epithelia to mimic the local production of PRL reported in women (Marano and Ben-Jonathan, 2014; McHale et al, 2008; O’Leary et al, 2015; Rose-Hellekant et al, 2003)
In a discovery set of five independent, histologically diverse carcinomas and matched adjacent tumor-free mammary glands from aged NRL-PRL females, we found that all tumors contained somatic alterations in Kras, including canonical activating mutations (i.e., G12, G13, and Q61) or amplifications that resulted in elevated Ras pathway activation

Summary

Introduction

Epidemiologic evidence has linked higher levels of circulating prolactin (PRL) with increased risk for estrogen receptor alpha (ER+) breast cancers, in postmenopausal women (Tikk et al, 2014; Tworoger and Hankinson, 2008; Tworoger et al, 2013). In young adult nulliparous NRL-PRL females, prior to evidence of detectable mammary lesions, ductal epithelia proliferate more rapidly and exhibit increased progenitor activity and Wnt signaling, resulting in reduced maturation of luminal progenitors compared with wild-type (WT) littermates (O’Leary et al, 2017; Rose-Hellekant et al, 2003). NRL-PRL females develop hyperplastic lesions that strongly express ER and progesterone receptor (PR) and eventually develop histologically diverse and metastatic carcinomas (O’Leary et al, 2015; Rose-Hellekant et al, 2003). In contrast to the preneoplastic lesions, established tumors express variable ER and low PR, resembling the luminal B subtype of clinical breast cancer (Arendt et al, 2011; O’Leary et al, 2015)

Results

Discussion

Conclusion