p63 is a prosurvival factor in the adult mammary gland during post-lactational involution, affecting PI-MECs and ErbB2 tumorigenesis

Abstract

In embryogenesis, p63 is essential to develop mammary glands. In the adult mammary gland, p63 is highly expressed in the basal cell layer that comprises myoepithelial and interspersed stem/progenitor cells, and has limited expression in luminal epithelial cells. In adult skin, p63 has a crucial role in the maintenance of epithelial stem cells. However, it is unclear whether p63 also has an equivalent role as a stem/progenitor cell factor in adult mammary epithelium. We show that p63 is essential in vivo for the survival and maintenance of parity-identified mammary epithelial cells (PI-MECs), a pregnancy-induced heterogeneous population that survives post-lactational involution and contain multipotent progenitors that give rise to alveoli and ducts in subsequent pregnancies. p63 þ / À glands are normal in virgin, pregnant and lactating states. Importantly, however, during the apoptotic phase of post-lactational involution p63 þ / À glands show a threefold increase in epithelial cell death, concomitant with increased activation of the oncostatin M/Stat3 and p53 pro-apoptotic pathways, which are responsible for this phase. Thus, p63 is a physiologic antagonist of these pathways specifically in this regressive stage. After the restructuring phase when involution is complete, mammary glands of p63 þ / À mice again exhibit normal epithelial architecture by conventional histology. However, using Rosa LSL-LacZ ;WAP-Cre transgenics (LSL-LacZ, lox-stop-lox b-galactosidase), a genetic in vivo labeling system for PI-MECs, we find that p63 þ / À glands have a 30% reduction in the number of PI-MEC progenitors and their derivatives. Importantly, PI-MECs are also cellular targets of pregnancy-promoted ErbB2 tumorigenesis. Consistent with their PI-MEC pool reduction, one-time pregnant p63 þ / À ErbB2 mice are partially protected from breast tumorigenesis, exhibiting extended tumor-free and overall survival, and reduced tumor multiplicity compared with their p63 þ / þ ErbB2 littermates. Conversely, in virgin ErbB2 mice p63 heterozygosity provides no survival advantage. In sum, our data establish that p63 is an important survival factor for pregnancy-identified PI-MEC progenitors in breast tissue in vivo.

Bovine CD49 positive-cell subpopulation remarkably increases in mammary epithelial cells that retain a stem-like phenotype

“…Within this type of colonies the stem cells subpopulation is reported to be present (Martignani et al, 2010;Prater et al, 2014). In addition to this test, we reported that after 35 days of culture a cell population capable of forming alveolar like-structures in vivo with cellular doublelayer and luminal antigens, such as K18 and EpCAM (if expressed at high levels) (Stingl et al, 2005), or basal, such as P63 (Yallowitz et al, 2014), is present as confirmed by xenografts in NOD-SCID mice. We also observed the presence in the lumen of regenerate structure the signal for protein milk indicating a proper polarization and functional activity.…”

Maintaining epithelial stemness with p63

“…It has been proposed that DNp63 abundance must be decreased in stem cells to allow their activation and the subsequent maturation of mammary progenitors. In accordance with this model, DNp63 is enriched in normal human mammary stem cells, whereas DNp63 is low in abundance or absent in the progenitors (26,39,40). Chakrabarti and co-workers (26) showed that DNp63, but not TAp63, In epithelial selfrenewing tissues, stem cells divide infrequently to produce a stem cell daughter and a nonstem-committed progenitor cell (transit-amplifying cell).…”

“…In the normal mammary gland, p63 is confined to the basal/myoepithelial compartment (36). DNp63 preserves the self-renewing capacity of mammary stem cells, partially by promoting their quiescent state (26,(37)(38)(39). DNp63 and TAp63 isoforms are present in mouse mammary stem and progenitor cells, respectively.…”

p63 threonine phosphorylation signals the interaction with the WW domain of the E3 ligase Itch

“…3,6,14,38. We have previously investigated the molecular mechanism of Itch recognition for the p63 transcription factor 39 in particular, because this powerful transcription factor is crucial for the development of epithelia, 31,[40][41][42][43][44][45] it is involved in cancer, [46][47][48][49][50][51][52][53][54][55][56][57][58][59] and when it is mutated it causes severe genetic diseases.…”