Laminin-binding integrins are essential for the maintenance of functional mammary secretory epithelium in lactation

Integrin dimers α3/β1, α6/β1 and α6/β4 are the mammary epithelial cell receptors for laminins, which are major components of the mammary basement membrane. The roles of specific basement membrane components and their integrin receptors in the regulation of functional gland development have not been analyzed in detail. To investigate the functions of laminin-binding integrins, we obtained mutant mice with mammary luminal cell-specific deficiencies of the α3 and α6 integrin chains generated by the Cre-Lox approach. During pregnancy, mutant mice displayed decreased luminal progenitor activity and retarded lobulo-alveolar development. Mammary glands appeared functional at the onset of lactation in mutant mice, however myoepithelial cell morphology was markedly altered, suggesting cellular compensation mechanisms involving cytoskeleton reorganization. Notably, lactation was not sustained in mutant females, and the glands underwent precocious involution. Inactivation of the p53 gene rescued the growth defects but did not restore lactogenesis in mutant mice. These results suggest that the p53 pathway is involved in the control of mammary cell proliferation and survival downstream of laminin-binding integrins and underline an essential role of cell interactions with laminin for lactogenic differentiation.

Deciphering the Mammary Stem Cell Niche: A Role for Laminin-Binding Integrins

Integrins, which bind laminin, a major component of the mammary basement membrane, are strongly expressed in basal stem cell-enriched populations, but their role in controlling mammary stem cell function remains unclear. We found that stem cell activity, as evaluated in transplantation and mammosphere assays, was reduced in mammary basal cells depleted of laminin receptors containing α3- and α6-integrin subunits. This was accompanied by low MDM2 levels, p53 stabilization, and diminished proliferative capacity. Importantly, disruption of p53 function restored the clonogenicity of α3/α6-integrin-depleted mammary basal stem cells, while inhibition of RHO or myosin II, leading to decreased p53 activity, rescued the mammosphere formation. These data suggest that α3/α6-integrin-mediated adhesion plays an essential role in controlling the proliferative potential of mammary basal stem/progenitor cells through myosin II-mediated regulation of p53 and indicate that laminins might be important components of the mammary stem cell niche.

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α3- and α6-integrins are required for mammary basal stem cell function

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p53 is activated in mammary basal cells depleted of α3- and α6-integrins

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RHO and myosin II mediate p53 activation in α3- and α6-integrin-depleted cells

p53 controls the plasticity of mammary luminal progenitor cells downstream of Met signaling

Background

The adult mammary epithelium is composed of basal and luminal cells. The luminal lineage comprises two major cell populations, positive and negative for estrogen and progesterone receptors (ER and PR, respectively), both containing clonogenic progenitor cells. Deregulated ER/PR⁻ luminal progenitor cells are suspected to be at the origin of basal-type triple-negative (TNBC) breast cancers, a subtype frequently associated with loss of P53 function and MET signaling hyperactivation. Using mouse models, we recently reported that p53 restricts luminal progenitor cell amplification whereas paracrine Met activation stimulates their growth and favors a luminal-to-basal switch. Here, we analyzed how these two critical pathways interact to control luminal progenitor function.

Methods

We have (i) established and analyzed the gene expression profile of luminal progenitors isolated by ICAM-1, a robust surface marker we previously identified; (ii) purified luminal progenitors from p53-deficient and p53-proficient mouse mammary epithelium to compare their functional and molecular characteristics; and (iii) analyzed their response to HGF, the major Met ligand, in three-dimensional cultures.

Results

We found that luminal progenitors, compared to non-clonogenic luminal cells, overexpress Trp53 and numerous p53 target genes. In vivo, loss of Trp53 induced the expansion of luminal progenitors, affecting expression of several important p53 target genes including those encoding negative regulators of cell cycle progression. Consistently, p53-deficient luminal progenitors displayed increased proliferative and self-renewal activities in culture. However, they did not exhibit perturbed expression of luminal-specific markers and major regulators, such as Hey1, Elf5, and Gata3. Moreover, although expressing Met at higher level than p53-proficient luminal progenitors, p53-deficient luminal progenitors failed to acquire basal-specific features when stimulated by HGF, showing that p53 promotes the plastic behavior of luminal progenitors downstream of Met activation.

Conclusions

Our study reveals a crosstalk between Met- and p53-mediated signaling pathways in the regulation of luminal progenitor function. In particular, it shows that neither p53 loss alone nor p53 loss combined with Met signaling activation caused an early detectable cell fate alteration in luminal progenitors. Conceivably, additional events are required to confer basal-specific characteristics to luminal-derived TNBCs.

Electronic supplementary material

The online version of this article (10.1186/s13058-019-1101-8) contains supplementary material, which is available to authorized users.

Podoplanin regulates mammary stem cell function and tumorigenesis by potentiating Wnt/β-catenin signaling

Stem cells (SCs) drive mammary development, giving rise postnatally to an epithelial bilayer composed of luminal and basal myoepithelial cells. Dysregulation of SCs is thought to be at the origin of certain breast cancers; however, the molecular identity of SCs and the factors regulating their function remain poorly defined. We identified the transmembrane protein podoplanin (Pdpn) as a specific marker of the basal compartment, including multipotent SCs, and found Pdpn localized at the basal-luminal interface. Embryonic deletion of Pdpn targeted to basal cells diminished basal and luminal SC activity and affected the expression of several Wnt/β-catenin signaling components in basal cells. Moreover, Pdpn loss attenuated mammary tumor formation in a mouse model of β-catenin-induced breast cancer, limiting tumor-initiating cell expansion and promoting molecular features associated with mesenchymal-to-epithelial cell transition. In line with the loss-of-function data, we demonstrated that mechanistically Pdpn enhances Wnt/β-catenin signaling in mammary basal cells. Overall, this study uncovers a role for Pdpn in mammary SC function and, importantly, identifies Pdpn as a new regulator of Wnt/β-catenin signaling, a key pathway in mammary development and tumorigenesis.

Complication-related removal of totally implantable venous access port systems: Does the interval between placement and first use and the neutropenia-inducing potential of chemotherapy regimens influence their incidence? A four-year prospective study of 4045 patients

BACKGROUND

Totally implantable venous access port systems are widely used in oncology, with frequent complications that sometimes necessitate device removal. The aim of this study is to investigate the impact of the time interval between port placement and initiation of chemotherapy and the neutropenia-inducing potential of the chemotherapy administered upon complication-related port removal.

PATIENTS AND METHODS

Between January 2010 and December 2013, 4045 consecutive patients were included in this observational, single-center prospective study. The chemotherapy regimens were classified as having a low (<10%), intermediate (10-20%), or high (>20%) risk for inducing neutropenia.

RESULTS

The overall removal rate due to complications was 7.2%. Among them, port-related infection (2.5%) and port expulsion (1%) were the most frequent. The interval between port insertion and its first use was shown to be a predictive factor for complication-related removal rates. A cut-off of 6 days was statistically significant (p = 0.008), as the removal rate for complications was 9.4% when this interval was 0-5 days and 5.7% when it was ≥6 days. Another factor associated with port complication rate was the neutropenia-inducing potential of the chemotherapy regimens used, with removal for complications involved in 5.5% of low-risk regimens versus 9.4% for the intermediate- and high-risk regimens (p = 0.003).

CONCLUSION

An interval of 6 days between placement and first use of the port reduces the removal rate from complications. The intermediate- and high-risk for neutropenia chemotherapy regimens are related to higher port removal rates from complications than low-risk regimens.

Surgery for early stage endometrial carcinoma in the obese patient

Obese patients have increased risk of developing endometrial cancer proportional to the excess in body mass index. In this review, we explored the latest information on surgical management and its adaptation to the obese condition. Mini-invasive treatments (laparoscopic, robotic, vaginal, or combinations) should be systematically considered. Prevention and active treatment of obesity seem an interesting approach to reduce incidence and severity of the disease.

Paracrine Met signaling triggers epithelial-mesenchymal transition in mammary luminal progenitors, affecting their fate

HGF/Met signaling has recently been associated with basal-type breast cancers, which are thought to originate from progenitor cells residing in the luminal compartment of the mammary epithelium. We found that ICAM-1 efficiently marks mammary luminal progenitors comprising hormone receptor-positive and receptor-negative cells, presumably ductal and alveolar progenitors. Both cell populations strongly express Met, while HGF is produced by stromal and basal myoepithelial cells. We show that persistent HGF treatment stimulates the clonogenic activity of ICAM1-positive luminal progenitors, controlling their survival and proliferation, and leads to the expression of basal cell characteristics, including stem cell potential. This is accompanied by the induction of Snai1 and Snai2, two major transcription factors triggering epithelial–mesenchymal transition, the repression of the luminal-regulatory genes Elf5 and Hey1, and claudin down-regulation. Our data strongly indicate that paracrine Met signaling can control the function of luminal progenitors and modulate their fate during mammary development and tumorigenesis.

DOI:http://dx.doi.org/10.7554/eLife.06104.001

Throughout the life of a female mammal, the mammary glands undergo different phases of development to prepare for, and adapt to, feeding offspring. Luminal cells line the inside of branch-like structures throughout the mammary gland and are responsible for producing milk. When the mammary gland grows, new luminal cells develop from a kind of cell called luminal progenitor cells. However, these progenitor cells are also thought to be the source of certain types of breast cancer.

Recently, it has been suggested that luminal progenitor cells display a receptor protein called Met on their surface. When Met and ‘co-receptor’ proteins bind to a molecule called HGF, this triggers a cascade of signals that can cause certain cells to change their properties. This is known as the epithelial–mesenchymal transition. Although this transition is important for new tissues to develop, it can also result in cancerous tumors forming if it is not correctly controlled. Luminal cells do not produce HGF themselves, which suggests that Met signaling in these cells is triggered by the HGF released from neighboring cells. However, neither the mechanisms behind this signaling nor the effects of signaling on the luminal progenitor cells are well understood.

Di-Cicco et al. set out to identify where Met, its co-receptors and HGF are located in the mouse mammary gland during different phases of development. This revealed that one of the co-receptors—called ICAM-1—can be used as a marker to identify certain types of luminal progenitor cell. Di-Cicco et al. found that these progenitor cells display Met on their surface, and other types of mammary cell—called stromal cells and myoepithelial cells—produce HGF.

When exposed to HGF, luminal progenitor cells grown in culture in the laboratory proliferated and went through the epithelial–mesenchymal transition. These findings suggest that myoepithelial and stromal cells regulate luminal progenitor cells by producing HGF to activate Met signaling in these cells. Such interactions could be of great importance during mammary development and tumorigenesis. The next big challenge will be to determine the circumstances under which luminal progenitor cells stimulated by HGF can give rise to breast cancers. This work will allow us to better define the cell population that should be targeted by anti-cancer drugs.

DOI:http://dx.doi.org/10.7554/eLife.06104.002

A new laparoscopic method of bowel radio-protection before pelvic chemoradiation of locally advanced cervix cancers

BACKGROUND

Chemoradiation therapy (CRT) has become the mainstay of locally advanced cervical carcinomas (LACC). However, the price to pay is a significant rate of both early and late colo-rectal toxicities, which may impact on survivors' quality of life. To reduce the incidence of such complications, we suggest a simple technique of pelvic radioprotection.

MATERIALS AND METHODS

An omental flap is created which is placed to fill the Douglas pouch to both increase the space between rectum and uterine cervix and prevent small bowel to fall in and to be exposed to radiation. In addition, a long sigmoid loop is retracted and fixed in the left paracolic gutter to prevent its irradiation as well.

RESULTS

From May 2011 to May 2012, 51 successive LACC patients were offered this procedure in addition of a laparoscopic staging. All but 2 with too small an omentum benefitted from omentoplasty, while sigmoidopexy was performed in all but one patient with a long and free sigmoid loop. No immediate adverse effect was observed. The volume of retro-uterine omental flap averaged 7.17 ± 3.79 cm(3). Sequential measurements of the utero-rectal space throughout CRT duration showed a real and durable increase in the distance between these organs, resulting in a drop in the dose of irradiation to recto-sigmoid. With 10 ± 4.5-month median follow-up, we did not observe any rectal or small bowel early or late adverse effects of CRT.

CONCLUSIONS

Although this series is preliminary, this simple procedure, feasible by laparoscopy (or laparotomy), seems effective to prevent recto-sigmoid as well as small bowel from radio-induced complications due to pelvic CRT.

Laser-based diagnostics applied to the study of BN nanotubes synthesis

The boron nitride nanotubes (BNNTs) synthesis, using CO2-laser vaporization of a BN target under nitrogen gas, is investigated by UV-laser induced fluorescence (LIF) of the vapor phase and UV-Rayleigh scattering (RS) of the gas-suspended nanoparticles. The LIF signal from B atoms is mainly detected in the 1.5 mm-thick region above the BN target. It originates from a boron-rich vapor region confined near the hot boron droplet formed at the target surface. Then, recombination between hot boron and N2 gas occurs through a fast condensation process as revealed by both the depletion of B atoms from the vapor phase and the RS signal arising from the grown BN nanoparticles. Fluorescence spectra exhibit a strong peak at 250 nm due to boron fluorescence and mainly to nanoparticles Rayleigh scattering. A narrow peak is observed at 210 nm and a broader peak at 189 nm. These bands are tentatively assigned to fluorescence or photoluminescence (PL) from gaseous or solid BN species respectively since both gas and solid phases coexist in the plume due to the rapid cooling process. Two very weak bands occur at 308 nm and 350 nm. They are related to PL of defects bands from BN nanostructures on the basis of ex situ PL spectra of h-BN crystallites and multi-wall BNNTs. Detection of oxygen impurities is shown feasible through LIF from BO radical which is detected just above the BN target evaporated under vacuum pressure (approximately 1 mbar). An optical diagnostic strategy is demonstrated from these first in situ observations during BNNTs synthesis.

Purification of single-walled boron nitride nanotubes and boron nitride cages

Continuous laser vaporization of a BN target under N2 atmosphere is up to now the unique route to single-walled boron nitride nanotubes (BN-SWNTs). Although grams of product can be obtained by this technique, the raw material contains in addition to the BN-SWNTs, different by-products made of boron and nitrogen. Since these materials are undesirable for the studying of the intrinsic properties of the nanotubes, we have undertaken a purification process using chemical and physical methods to separate the different components. We show here that most impurities can be removed by successive cycles of washing, sonication, and centrifugation. Furthermore, the two different types of boron nitride nanostructures i.e., BN-SWNTs and BN-cages can be isolated. Efficiency of the separation was monitored by transmission electron microscopy (TEM) at the different steps of the process. Finally, we envisage the further purification of the nanotubes-enriched fraction by functionalizing the nanotubes in a non covalent manner by specific polymers as for carbon nanotubes and BN multi-walled nanotubes.

Autoprélèvement vaginal à la recherche d'une vaginose bactérienne pendant la grossesse : étude pilote

OBJECTIVE

To study the feasibility of a screening for bacterial vaginosis by a self-collected vaginal swab during pregnancy. To measure bacterial vaginosis prevalence in a non-representative sample of women.

PATIENTS AND METHODS

A self-collected swab was suggested to 398 women who consulted between 15 and 33 weeks of gestation in three different centres. Gram stain evaluation using Nugent criteria was used for the diagnosis of bacterial vaginosis.

RESULTS

Three hundred and forty-one women agreed to take part in the study (86%). The quality of the swabs was satisfactory in 93% of the cases. Concerning the 15 non-interpretable slides, the cellular and bacterial density was too poor, owing to a poor quality or a low vaginal flora. Thirty-one women (9%) had a bacterial vaginosis--Nugent score included between 7 and 10--and this frequency did not vary according to the centre. Thirty-five women (10%) had an intermediate flora--score between 4 and 6--and this result varied from 2 to 12% depending on the centre, but the difference was not significant.

DISCUSSION AND CONCLUSION

Self-collected swabs to detect bacterial vaginosis are well accepted by most of pregnant women, and the quality of the swabs seems to be satisfactory. In case vaginal flora is intermediate--between 4 and 6--the interpretation of the slides could be difficult.

Thyrotropin-releasing hormone and gonadotropin-releasing hormone-associated peptide modulation of [Ca2+]i in human lactotrophs

The effect of thyrotropin-releasing hormone (TRH) and gonadotropin-releasing hormone-associated peptide (GAP) was studied on both secretion and intracellular free Ca2+ concentrations ([Ca2+]i) in human pituitary cells cultured from prolactin (PRL)-secreting tumors. Secretion was measured during a 30-min incubation period and we used a microspectrofluorimetric method in individual cells and indo-1 as the fluorescent probe. TRH (10(-8) M) significantly increased PRL release in five out of the six cell populations. In these five cases, more than 68% of individual cells responded to TRH by an increase in [Ca2+]i. No significant increase in PRL secretion was found in another culture in which TRH increased [Ca2+]i in only 37% of the cells. The effect of GAP (10(-7) M) was studied in five cell populations. In three of them, a decrease of 20% to 51% of the PRL basal secretory rate was observed under GAP. GAP inhibited [Ca2+]i in respectively 59%, 46% and 94% of the cells from these cultures. The inhibitory effect of GAP was blocked by a pertussis toxin (PT) pretreatment which demonstrates the involvement of a PT-sensitive G-protein in GAP action. In two other cultures, GAP did not significantly alter PRL secretion or individual cell [Ca2+]i. These observations suggest that GAP might play a role in the control of PRL secretion in the human.

Calcium homeostasis in growth hormone (GH)-secreting adenoma cells: effect of GH-releasing factor

Human GH-secreting tumors are heterogenous regarding their basal secretory activity and response to GH-releasing factor (GRF). We have investigated whether such different secretory properties could be accounted for by alterations of intracellular mechanisms occurring at the calcium level. Basal free intracellular calcium concentrations ([Ca2+]i) and Ca2+ responses to GRF were studied in single cells cultured from fragments of five GH-secreting pituitary adenomas. We used the microspectrofluorimetric method and indo-1 as the fluorescent probe. The cell populations cultured from the tumors of patients A and C showed increased hormone secretion in response to GRF in vitro, whereas cultures from patients B, D, and E were unresponsive to the peptide. Basal [Ca2+]i measured in the five cell populations ranged from 82 +/- 18 to 118 +/- 27 nM. A 10-sec application of 10 nM GRF induced an increase in [Ca2+]i in 60% and 54% of A and C cells, respectively. In the nonresponsive cell populations, the number of calcium responses to GRF was lower, 26% (B cells), 5% (D cells), and 10% (E cells). Two principal responses types were observed: 1) an initial increase in [Ca2+]i, followed by a sustained plateau phase lasting for more than 200 sec; and 2) a monophasic peak of increased [Ca2+]i lasting approximately 1 min before returning to baseline levels. GRF responses were totally suppressed in the absence of Ca2+ ions in the external medium. Sixteen to 30% of the cells cultured from four of the five tumors showed spontaneous fluctuations of [Ca2+]i. These spontaneous Ca2+ transients were suppressed in Ca(2+)-free medium. The number of cells exhibiting such Ca2+ transients decreased with time in culture. Basal hormone secretion was higher in cultures from patient D, in which no spontaneous Ca2+ transients were observed in any of the 72 studied cells, and in cultures from patients E, in which only 16% of cells were spontaneously active. We conclude that 1) in human responsive somatotrophs, the involvement of Ca2+ in GRF stimulus-secretion coupling mechanisms is apparently similar to that described in somatotrophs of other species; 2) the lack of a secretory response to GRF observed in some tumors may result from impairment of Ca2+ responsiveness in either cell recruitment or response amplitude and/or duration; and 3) spontaneous rhythmic Ca2+ activity is apparently dissociated from basal hormone secretion in some of these tumor cells.

Growth hormone-releasing factor stimulates calcium entry in the GH3 pituitary cell line

The GH3 pituitary cell line has been extensively used to study various aspects of the stimulus secretion coupling process. It is known that GH3 cells release PRL and GH in the basal state and in response to various secretagogues. However, this cell line was considered unsuitable as a model for studying the effects of GHRF since the neuropeptide did not affect GH secretion or gene expression. This suggested that the GH3 cells may lack GHRF receptors. The present study investigates the effect of GHRF on free intracellular Ca2+ concentrations in GH3 cells. Cytosolic free calcium concentrations ([Ca2+]i) were monitored in individual cells by microspectrofluorimetry using the fluorescent dye indo 1. When the cells were challenged with a brief application of GHRF (100 nM; 15 sec), 36 out of 59 of these cells responded within a few seconds by a marked increase in [Ca2+]i. GHRF enhanced the frequency of [Ca2+]i oscillations in spontaneously active cells or triggered [Ca2+]i oscillations in inactive cells. The response to GHRF was totally blocked by external Ca2+ free solutions and Ca2+ channel blockers. Combined electrophysiological and fluorescent experiments were carried out in 16 cells. Eleven responded to GHRF. In all cases, the Ca2+ transients triggered by GHRF were associated with action potentials. The Ca2+ responses observed in our experiments clearly show that GH3 cells possess membrane receptors to GHRF. Thus, it is likely that the lack of secretory response observed in GH3 cells does not result from the absence of binding sites to the peptide. It is more likely to be related to alterations of transduction mechanisms resulting in uncoupling between stimulation and secretion.