What signals operate in the mammary niche?

Adult stem cells reside in a specialized microenvironment, the niche, which controls their behavior. As mammary stem cells, and consequently their niches, are still poorly defined, we look at better-characterized adult mammalian stem cell niches in the hematopoietic system and the skin. We attempt to define the mammary stem cell niche functionally, based on the widely used mammary fat pad reconstitution assay. We note that the concept of the niche needs to be extended from the specialized microenvironment described in the hematopoietic system, to a model that takes into account the macroenviroment, as recently shown in the skin, and systemic clues as we will illustrate for the mammary gland where the reproductive hormones are major determinants of stem cell activation. In fact, in the mammary gland a special type of stem cells is determined only during pregnancy. Reproductive hormones act on hormone receptor positive cells, sensor cells, in the mammary epithelium to induce paracrine signaling that leads to activation of stem cells. Some of the downstream mediators are in common with other niches such as Wnt and possibly Notch signaling. Other signals are specific to the mammary gland such as amphiregulin and RANKL.

The secreted protease Adamts18 links hormone action to activation of the mammary stem cell niche

Giovanna Ambrosini, Patrik Aouad, Dalya Ataca, Cathrin Brisken, Philipp Bucher, Marian Caikovski, Céline Berthe Constantin, Csaba Ferenc László, Renuga Devi Rajaram, Marie Shamseddin

Estrogens and progesterone control breast development and carcinogenesis via their cognate receptors expressed in a subset of luminal cells in the mammary epithelium. How they control the extracellular matrix, important to breast physiology and tumorigenesis, remains unclear. Here we report that both hormones induce the secreted protease Adamts18 in myoepithelial cells by controlling Wnt4 expression with consequent paracrine canonical Wnt signaling activation. Adamts18 is required for stem cell activation, has multiple binding partners in the basement membrane and interacts genetically with the basal membrane-specific proteoglycan, Col18a1, pointing to the basement membrane as part of the stem cell niche. In vitro, ADAMTS18 cleaves fibronectin; in vivo, Adamts18 deletion causes increased collagen deposition during puberty, which results in impaired Hippo signaling and reduced Fgfr2 expression both of which control stem cell function. Thus, Adamts18 links luminal hormone receptor signaling to basement membrane remodeling and stem cell activation. How hormonal signaling in the mammary epithelium controls the surrounding extracellular matrix is unclear. Here, the authors show that a secreted protease, Adamts18, induced by upstream estrogen-progesterone activated Wnt4 in myoepithelial cells, remodels the basement membrane and contributes to mammary epithelial stemness.

2020

Role of RIP4 in lung adenocarcinoma differentiation

Jawahar Kopparam

Various studies have attributed NF-kB activation to promote KRAS mediated non-small cell lung cancer progression. In order to identify key genes regulating NF-kB activation and cell survival in lung adenocarcinoma, a synthetic lethal partner screen for KRAS was conducted in cell lines expressing mutant or wildtype KRAS. This screen identified an important role of Receptor-interacting serine/threonine protein kinase 4 (RIP4) in KRAS mediated oncogenesis. But altering RIP4 expression did not affect the viability of KRAS mutant cells, however a novel role of RIP4 in maintaining tumor differentiation was observed. Loss of epithelial differentiation and extracellular matrix remodeling are known to facilitate cancer progression and are associated with poor prognosis in patients with lung cancer. Bioinformatics analyses of human lung adenocarcinoma samples showed that poorly differentiated tumors express low levels of RIP4, whereas high levels are associated with better overall survival. Interleukin 6 (IL6) signaling is activated in lung adenocarcinoma expressing oncogenic KRAS and contributes to cancer invasiveness. Knockdown of RIP4 using shRNA in vitro enhanced activation of IL-6 signaling and also the ability of the cells to invade through collagen. In contrast, overexpression of RIP4 inhibited IL6-mediated Signal Transducer and activator of Transcription 3 (STAT3) activation, which abrogated IL6-dependent induction of lysyl oxidase, a collagen cross-linking enzyme. Tumor-specific Rip4 knockdown in an autochthonous mouse model of lung adenocarcinoma initiated by Kras(G12D) expression with loss of p53, progressed to a poorly differentiated state marked by an increase in Hmga2, reduced Ttf1 and enrichment of genes regulating extracellular matrix (ECM) remodeling and JAK-STAT signaling. Activated STAT3 can enhance NF-kB activation by interacting with NF-kB and promoting its nuclear retention. Tumors with RIP4 knockdown also exhibited enhanced STAT3- NF-kB interaction suggesting a cross talk between the two pathways. Tail vein injections of cells overexpressing RIP4 showed a reduced potential to invade and form tumors. Analysis of factors regulating RIP4 expression revealed that RIP4 is induced in a p53 dependent manner in response to chemotherapy. Altering the induced RIP4 levels in vitro had a modest effect on chemotherapy induced cell death. Our work has identified that loss of RIP4 enhances IL6 signaling in lung cancer cells, promoting the expression of ECM remodeling genes and cancer dedifferentiation.

EPFL2016

Amphiregulin is an essential mediator of estrogen receptor alpha function in mammary gland development

Cathrin Brisken

Most mammary gland development occurs after birth under the control of systemic hormones. Estrogens induce mammary epithelial cell proliferation during puberty via epithelial estrogen receptor alpha (ERalpha) by a paracrine mechanism. Epidermal growth factor receptor (EGFR) signaling has long been implicated downstream of ERalpha signaling, and several EGFR ligands have been described as estrogen-target genes in tumor cell lines. Here, we show that amphiregulin is the unique EGF family member to be transcriptionally induced by estrogen in the mammary glands of puberal mice at a time of exponential expansion of the ductal system. In fact, we find that estrogens induce amphiregulin through the ERalpha and require amphiregulin to induce proliferation of the mammary epithelium. Like ERalpha, amphiregulin is required in the epithelium of puberal mice for epithelial proliferation, terminal end buds formation, and ductal elongation. Subsequent stages, such as side-branching and alveologenesis, are not affected. When amphiregulin(-/-) mammary epithelial cells are in close vicinity to wild-type cells, they proliferate and contribute to all cell compartments of the ductal outgrowth. Thus, amphiregulin is an important paracrine mediator of estrogen function specifically required for puberty-induced ductal elongation, but not for any earlier or later developmental stages.

2007

Role of RIP4 in lung adenocarcinoma differentiation

Jawahar Kopparam

EPFL2016