∆Np63/p40 correlates with the location and phenotype of basal/mesenchymal cancer stem-like cells in human ER+ and HER2+ breast cancers.

Yajing Liu,M Virginia Appleyard,Philip J Coates,Marta Nekulova,Michaela Galoczova,Lee B Jordan,Colin A Purdie,Borivoj Vojtesek,Alastair M Thompson,Iva Horakova,Rudolf Nenutil,Jitka Holcakova,Karen Murray,Philip Quinlan

doi:10.1002/cjp2.149

Abstract

ΔNp63, also known as p40, regulates stemness of normal mammary gland epithelium and provides stem cell characteristics in basal and HER2‐driven murine breast cancer models. Whilst ΔNp63/p40 is a characteristic feature of normal basal cells and basal‐type triple‐negative breast cancer, some receptor‐positive breast cancers express ΔNp63/p40 and its overexpression imparts cancer stem cell‐like properties in ER+ cell lines. However, the incidence of ER+ and HER2+ tumours that express ΔNp63/p40 is unclear and the phenotype of ΔNp63/p40+ cells in these tumours remains uncertain. Using immunohistochemistry with p63 isoform‐specific antibodies, we identified a ΔNp63/p40+ tumour cell subpopulation in 100 of 173 (58%) non‐triple negative breast cancers and the presence of this population associated with improved survival in patients with ER−/HER2+ tumours (p = 0.006). Furthermore, 41% of ER+/PR+ and/or HER2+ locally metastatic breast cancers expressed ΔNp63/p40, and these cells commonly accounted for <1% of the metastatic tumour cell population that localised to the tumour/stroma interface, exhibited an undifferentiated phenotype and were CD44+/ALDH−. In vitro studies revealed that MCF7 and T47D (ER+) and BT‐474 (HER2+) breast cancer cell lines similarly contained a small subpopulation of ΔNp63/p40+ cells that increased in mammospheres. In vivo, MCF7 xenografts contained ΔNp63/p40+ cells with a similar phenotype to primary ER+ cancers. Consistent with tumour samples, these cells also showed a distinct location at the tumour/stroma interface, suggesting a role for paracrine factors in the induction or maintenance of ΔNp63/p40. Thus, ΔNp63/p40 is commonly present in a small population of tumour cells with a distinct phenotype and location in ER+ and/or HER2+ human breast cancers.

Highlights

The human TP63 gene encodes two major variants that differ in their N-terminal sequences, with TAp63 containing a p53-like transactivation domain and ΔNp63 lacking this domain
In vitro studies revealed that MCF7 and T47D (ER+) and BT-474 (HER2+) breast cancer cell lines contained a small subpopulation of ΔNp63/p40+ cells that increased in mammospheres
ΔNp63/p40+ cells are commonly present in luminal-type human breast carcinomas p63, ΔNp63/p40, is present in the nuclei of normal basal/myoepithelial cells and pan-p63 or ΔNp63/p40 antibodies are used as a clinical marker to distinguish invasive from in situ lesions [4,5,6,7,25,26]

Summary

Introduction

The human TP63 gene encodes two major variants that differ in their N-terminal sequences, with TAp63 containing a p53-like transactivation domain and ΔNp63 ( known as p40) lacking this domain. With regard to p63 in breast cancer, ΔNp63/p40 promotes or maintains stem cell activities in murine models of triple negative breast cancer (TNBC) and human epidermal growth factor receptor 2 (HER2)-driven basal cancer [14,15,16]. P63 is present in some ER+ and/or HER2+ cancers, at lower levels than in TNBCs [4,5,6] and ΔNp63/p40+ cells have been reported to be unrelated to or to associate with a basal-like phenotype [9,20]. The incidence of ER+/HER2+ cancers that contain a ΔNp63/ p40+ tumour cell subpopulation is uncertain, partly due to the presence of ΔNp63/p40 in normal myoepithelium, which is a common component of surgically removed human breast cancers [4,25,26]. We investigated the phenotype of these cells and their relationship with CSC subtypes

Methods

Results

Conclusion