p63 suppresses the ability of pregnancy-identified mammary epithelial cells (PIMECs) to drive HER2-positive breast cancer

• Published in: Cell death & disease 2021-05, Vol.12 (6), Article 525
• Main Authors: Eyermann, Christopher E., Li, Jinyu, Alexandrova, Evguenia M.
• Format: Article
• Language: English
• Subjects: 13/31; 13/51; 45/62; 45/77; 45/91; 631/67/1347; 631/80/304; 64/60; 96/100; 96/35; 96/63; Animal models; Antibodies; Biochemistry; Biomedical and Life Sciences; Breast cancer; Cell Biology; Cell Culture; Epithelial cells; ErbB-2 protein; Flow cytometry; HSF1 protein; Immunodeficiency; Immunology; Interleukin 13; Interleukin 4; Life Sciences; Mammary gland; MAP kinase; Nerve growth factor; p53 Protein; Phenotypes; Pregnancy; Tumor suppressor genes; Wnt protein
• ISSN: 2041-4889; 2041-4889
• DOI: 10.1038/s41419-021-03795-5

While pregnancy is known to reduce a woman’s life-long risk of breast cancer, clinical data suggest that it can specifically promote HER2 (human EGF receptor 2)-positive breast cancer subtype (HER2+ BC). HER2+ BC, characterized by amplification of HER2, comprises about 20% of all sporadic breast cancers and is more aggressive than hormone receptor-positive breast cancer (the majority of cases). Consistently with human data, pregnancy strongly promotes HER2+ BC in genetic mouse models. One proposed mechanism of this is post-pregnancy accumulation of PIMECs (pregnancy-identified mammary epithelial cells), tumor-initiating cells for HER2+ BC in mice. We previously showed that p63, a homologue of the tumor suppressor p53, is required to maintain the post-pregnancy number of PIMECs and thereby promotes HER2+ BC. Here we set to test whether p63 also affects the intrinsic tumorigenic properties of PIMECs. To this end, we FACS-sorted YFP-labeled PIMECs from p63+/−;ErbB2 and control p63+/+;ErbB2 females and injected their equal amounts into immunodeficient recipients. To our surprise, p63+/− PIMECs showed increased, rather than decreased, tumorigenic capacity in vivo, i.e., significantly accelerated tumor onset and tumor growth, as well as increased self-renewal in mammosphere assays and proliferation in vitro and in vivo. The underlying mechanism of these phenotypes seems to be a specific reduction of the tumor suppressor TAp63 isoform in p63+/− luminal cells, including PIMECs, with concomitant aberrant upregulation of the oncogenic ΔNp63 isoform, as determined by qRT-PCR and scRNA-seq analyses. In addition, scRNA-seq revealed upregulation of several cancer-associated (Il-4/Il-13, Hsf1/HSP), oncogenic (TGFβ, NGF, FGF, MAPK) and self-renewal (Wnt, Notch) pathways in p63+/−;ErbB2 luminal cells and PIMECs per se. Altogether, these data reveal a complex role of p63 in PIMECs and pregnancy-associated HER2+ BC: maintaining the amount of PIMECs while suppressing their intrinsic tumorigenic capacity.