Dynamic regulation of tissue fluidity controls skin repair during wound healing.

During wound healing, different pools of stem cells (SCs) contribute to skin repair. However, how SCs become activated and drive the tissue remodeling essential for skin repair is still poorly understood. Here, by developing a mouse model allowing lineage tracing and basal cell lineage ablation, we monitor SC fate and tissue dynamics during regeneration using confocal and intravital imaging. Analysis of basal cell rearrangements shows dynamic transitions from a solid-like homeostatic state to a fluid-like state allowing tissue remodeling during repair, as predicted by a minimal mathematical modeling of the spatiotemporal dynamics and fate behavior of basal cells. The basal cell layer progressively returns to a solid-like state with re-epithelialization. Bulk, single-cell RNA, and epigenetic profiling of SCs, together with functional experiments, uncover a common regenerative state regulated by the EGFR/AP1 axis activated during tissue fluidization that is essential for skin SC activation and tissue repair.

The extracellular matrix dictates regional competence for tumour initiation.

The skin epidermis is constantly renewed throughout life1,2. Disruption of the balance between renewal and differentiation can lead to uncontrolled growth and tumour initiation3. However, the ways in which oncogenic mutations affect the balance between renewal and differentiation and lead to clonal expansion, cell competition, tissue colonization and tumour development are unknown. Here, through multidisciplinary approaches that combine in vivo clonal analysis using intravital microscopy, single-cell analysis and functional analysis, we show how SmoM2-a constitutively active oncogenic mutant version of Smoothened (SMO) that induces the development of basal cell carcinoma-affects clonal competition and tumour initiation in real time. We found that expressing SmoM2 in the ear epidermis of mice induced clonal expansion together with tumour initiation and invasion. By contrast, expressing SmoM2 in the back-skin epidermis led to a clonal expansion that induced lateral cell competition without dermal invasion and tumour formation. Single-cell analysis showed that oncogene expression was associated with a cellular reprogramming of adult interfollicular cells into an embryonic hair follicle progenitor (EHFP) state in the ear but not in the back skin. Comparisons between the ear and the back skin revealed that the dermis has a very different composition in these two skin types, with increased stiffness and a denser collagen I network in the back skin. Decreasing the expression of collagen I in the back skin through treatment with collagenase, chronic UV exposure or natural ageing overcame the natural resistance of back-skin basal cells to undergoing EHFP reprogramming and tumour initiation after SmoM2 expression. Altogether, our study shows that the composition of the extracellular matrix regulates how susceptible different regions of the body are to tumour initiation and invasion.

Pharmacological targeting of netrin-1 inhibits EMT in cancer.

Epithelial-to-mesenchymal transition (EMT) regulates tumour initiation, progression, metastasis and resistance to anti-cancer therapy1-7. Although great progress has been made in understanding the role of EMT and its regulatory mechanisms in cancer, no therapeutic strategy to pharmacologically target EMT has been identified. Here we found that netrin-1 is upregulated in a primary mouse model of skin squamous cell carcinoma (SCC) exhibiting spontaneous EMT. Pharmacological inhibition of netrin-1 by administration of NP137, a netrin-1-blocking monoclonal antibody currently used in clinical trials in human cancer (ClinicalTrials.gov identifier NCT02977195 ), decreased the proportion of EMT tumour cells in skin SCC, decreased the number of metastases and increased the sensitivity of tumour cells to chemotherapy. Single-cell RNA sequencing revealed the presence of different EMT states, including epithelial, early and late hybrid EMT, and full EMT states, in control SCC. By contrast, administration of NP137 prevented the progression of cancer cells towards a late EMT state and sustained tumour epithelial states. Short hairpin RNA knockdown of netrin-1 and its receptor UNC5B in EPCAM+ tumour cells inhibited EMT in vitro in the absence of stromal cells and regulated a common gene signature that promotes tumour epithelial state and restricts EMT. To assess the relevance of these findings to human cancers, we treated mice transplanted with the A549 human cancer cell line-which undergoes EMT following TGFß1 administration8,9-with NP137. Netrin-1 inhibition decreased EMT in these transplanted A549 cells. Together, our results identify a pharmacological strategy for targeting EMT in cancer, opening up novel therapeutic interventions for anti-cancer therapy.

Cell type and stage specific transcriptional, chromatin and cell-cell communication landscapes in the mammary gland.

The mammary gland (MG) is composed of three main epithelial lineages, the basal cells (BC), the estrogen receptor (ER) positive luminal cells (ER+ LC), and the ER negative LC (ER- LC). Defining the cell identity of each lineage and how it is modulated throughout the different stages of life is important to understand how these cells function and communicate throughout life. Here, we used transgenic mice specifically labelling ER+ LC combined to cell surface markers to isolate with high purity the 3 distinct cell lineages of the mammary gland and defined their expression profiles and chromatin landscapes by performing bulk RNAseq and ATACseq of these isolated populations in puberty, adulthood and mid-pregnancy. Our analysis identified conserved genes, ligands and transcription factor (TF) associated with a specific lineage throughout life as well as genes, ligands and TFs specific for a particular stage of the MG. In summary, our study identified genes and TF network associated with the identity, function and cell-cell communication of the different epithelial lineages of the MG at different stages of life.

RHOJ controls EMT-associated resistance to chemotherapy.

The resistance of cancer cells to therapy is responsible for the death of most patients with cancer1. Epithelial-to-mesenchymal transition (EMT) has been associated with resistance to therapy in different cancer cells2,3. However, the mechanisms by which EMT mediates resistance to therapy remain poorly understood. Here, using a mouse model of skin squamous cell carcinoma undergoing spontaneous EMT during tumorigenesis, we found that EMT tumour cells are highly resistant to a wide range of anti-cancer therapies both in vivo and in vitro. Using gain and loss of function studies in vitro and in vivo, we found that RHOJ-a small GTPase that is preferentially expressed in EMT cancer cells-controls resistance to therapy. Using genome-wide transcriptomic and proteomic profiling, we found that RHOJ regulates EMT-associated resistance to chemotherapy by enhancing the response to replicative stress and activating the DNA-damage response, enabling tumour cells to rapidly repair DNA lesions induced by chemotherapy. RHOJ interacts with proteins that regulate nuclear actin, and inhibition of actin polymerization sensitizes EMT tumour cells to chemotherapy-induced cell death in a RHOJ-dependent manner. Together, our study uncovers the role and the mechanisms through which RHOJ acts as a key regulator of EMT-associated resistance to chemotherapy.

NR2F2 controls malignant squamous cell carcinoma state by promoting stemness and invasion and repressing differentiation.

The nongenetic mechanisms required to sustain malignant tumor state are poorly understood. During the transition from benign tumors to malignant carcinoma, tumor cells need to repress differentiation and acquire invasive features. Using transcriptional profiling of cancer stem cells from benign tumors and malignant skin squamous cell carcinoma (SCC), we identified the nuclear receptor NR2F2 as uniquely expressed in malignant SCC. Using genetic gain of function and loss of function in vivo, we show that NR2F2 is essential for promoting the malignant tumor state by controlling tumor stemness and maintenance in mouse and human SCC. We demonstrate that NR2F2 promotes tumor cell proliferation, epithelial-mesenchymal transition and invasive features, while repressing tumor differentiation and immune cell infiltration by regulating a common transcriptional program in mouse and human SCCs. Altogether, we identify NR2F2 as a key regulator of malignant cancer stem cell functions that promotes tumor renewal and restricts differentiation to sustain a malignant tumor state.

Fat1 deletion promotes hybrid EMT state, tumour stemness and metastasis.

FAT1, which encodes a protocadherin, is one of the most frequently mutated genes in human cancers1-5. However, the role and the molecular mechanisms by which FAT1 mutations control tumour initiation and progression are poorly understood. Here, using mouse models of skin squamous cell carcinoma and lung tumours, we found that deletion of Fat1 accelerates tumour initiation and malignant progression and promotes a hybrid epithelial-to-mesenchymal transition (EMT) phenotype. We also found this hybrid EMT state in FAT1-mutated human squamous cell carcinomas. Skin squamous cell carcinomas in which Fat1 was deleted presented increased tumour stemness and spontaneous metastasis. We performed transcriptional and chromatin profiling combined with proteomic analyses and mechanistic studies, which revealed that loss of function of FAT1 activates a CAMK2-CD44-SRC axis that promotes YAP1 nuclear translocation and ZEB1 expression that stimulates the mesenchymal state. This loss of function also inactivates EZH2, promoting SOX2 expression, which sustains the epithelial state. Our comprehensive analysis identified drug resistance and vulnerabilities in FAT1-deficient tumours, which have important implications for cancer therapy. Our studies reveal that, in mouse and human squamous cell carcinoma, loss of function of FAT1 promotes tumour initiation, progression, invasiveness, stemness and metastasis through the induction of a hybrid EMT state.

Heterotypic cell-cell communication regulates glandular stem cell multipotency.

Glandular epithelia, including the mammary and prostate glands, are composed of basal cells (BCs) and luminal cells (LCs)1,2. Many glandular epithelia develop from multipotent basal stem cells (BSCs) that are replaced in adult life by distinct pools of unipotent stem cells1,3-8. However, adult unipotent BSCs can reactivate multipotency under regenerative conditions and upon oncogene expression3,9-13. This suggests that an active mechanism restricts BSC multipotency under normal physiological conditions, although the nature of this mechanism is unknown. Here we show that the ablation of LCs reactivates the multipotency of BSCs from multiple epithelia both in vivo in mice and in vitro in organoids. Bulk and single-cell RNA sequencing revealed that, after LC ablation, BSCs activate a hybrid basal and luminal cell differentiation program before giving rise to LCs-reminiscent of the genetic program that regulates multipotency during embryonic development7. By predicting ligand-receptor pairs from single-cell data14, we find that TNF-which is secreted by LCs-restricts BC multipotency under normal physiological conditions. By contrast, the Notch, Wnt and EGFR pathways were activated in BSCs and their progeny after LC ablation; blocking these pathways, or stimulating the TNF pathway, inhibited regeneration-induced BC multipotency. Our study demonstrates that heterotypic communication between LCs and BCs is essential to maintain lineage fidelity in glandular epithelial stem cells.

Mechanisms of stretch-mediated skin expansion at single-cell resolution.

The ability of the skin to grow in response to stretching has been exploited in reconstructive surgery1. Although the response of epidermal cells to stretching has been studied in vitro2,3, it remains unclear how mechanical forces affect their behaviour in vivo. Here we develop a mouse model in which the consequences of stretching on skin epidermis can be studied at single-cell resolution. Using a multidisciplinary approach that combines clonal analysis with quantitative modelling and single-cell RNA sequencing, we show that stretching induces skin expansion by creating a transient bias in the renewal activity of epidermal stem cells, while a second subpopulation of basal progenitors remains committed to differentiation. Transcriptional and chromatin profiling identifies how cell states and gene-regulatory networks are modulated by stretching. Using pharmacological inhibitors and mouse mutants, we define the step-by-step mechanisms that control stretch-mediated tissue expansion at single-cell resolution in vivo.

Cancer cells undergoing epigenetic transition show short-term resistance and are transformed into cells with medium-term resistance by drug treatment.

To elucidate the epigenetic mechanisms of drug resistance, epigenetically reprogrammed H460 cancer cells (R-H460) were established by the transient introduction of reprogramming factors. Then, the R-H460 cells were induced to differentiate by the withdrawal of stem cell media for various durations, which resulted in differentiated R-H460 cells (dR-H460). Notably, dR-H460 cells differentiated for 13 days (13dR-H460 cells) formed a significantly greater number of colonies showing drug resistance to both cisplatin and paclitaxel, whereas the dR-H460 cells differentiated for 40 days (40dR-H460 cells) lost drug resistance; this suggests that 13dR-cancer cells present short-term resistance (less than a month). Similarly, increased drug resistance to both cisplatin and paclitaxel was observed in another R-cancer cell model prepared from N87 cells. The resistant phenotype of the cisplatin-resistant (CR) colonies obtained through cisplatin treatment was maintained for 2-3 months after drug treatment, suggesting that drug treatment transforms cells with short-term resistance into cells with medium-term resistance. In single-cell analyses, heterogeneity was not found to increase in 13dR-H460 cells, suggesting that cancer cells with short-term resistance, rather than heterogeneous cells, may confer epigenetically driven drug resistance in our reprogrammed cancer model. The epigenetically driven short-term and medium-term drug resistance mechanisms could provide new cancer-fighting strategies involving the control of cancer cells during epigenetic transition.

Epidermal autonomous VEGFA/Flt1/Nrp1 functions mediate psoriasis-like disease.

Psoriasis is a common chronic skin disorder characterized by keratinocyte hyperproliferation with altered differentiation accompanied by inflammation and increased angiogenesis. It remains unclear whether the first events that initiate psoriasis development occur in keratinocytes or inflammatory cells. Here, using different psoriasis mouse models, we showed that conditional deletion of Flt1 or Nrp1 in epidermal cells inhibited psoriasis mediated by Vegfa overexpression or c-Jun/JunB deletion. Administration of anti-Nrp1 antibody reverted the psoriasis phenotype. Using transcriptional and chromatin profiling of epidermal cells following Vegfa overexpression together with Flt1 or Nrp1 deletion, we identified the gene regulatory network regulated by Vegfa/Nrp1/Flt1 during psoriasis development and uncovered a key role of Fosl1 in regulating the chromatin remodeling mediated by Vegfa overexpression in keratinocytes. In conclusion, our study identifies an epidermal autonomous function of Vegfa/Nrp1/Flt1 that mediates psoriatic-like disease and demonstrates the clinical relevance of blocking Vegfa/Nrp1/Flt1 axis in psoriasis.

False-negative errors in next-generation sequencing contribute substantially to inconsistency of mutation databases.

BACKGROUND: More than 11,000 laboratories and companies developed their own next-generation sequencing (NGS) for screening and diagnosis of various diseases including cancer. Although inconsistencies of mutation calls as high as 43% in databases such as GDSC (Genomics of Drug Sensitivity in Cancer) and CCLE (Cancer Cell Line Encyclopedia) have been reported, not many studies on the reasons for the inconsistencies have been published. Methods: Targeted-NGS analysis of 151 genes in 35 cell lines common to GDSC and CCLE was performed, and the results were compared with those from GDSC and CCLE wherein whole-exome- or highly-multiplex NGS were employed. RESULTS: In the comparison, GDSC and CCLE had a high rate (40-45%) of false-negative (FN) errors which would lead to high rate of inconsistent mutation calls, suggesting that highly-multiplex NGS may have high rate of FN errors. We also posited the possibility that targeted NGS, especially for the detection of low-level cancer cells in cancer tissues might suffer significant FN errors. CONCLUSION: FN errors may be the most important errors in NGS testing for cancer; their evaluation in laboratory-developed NGS tests is needed.

Monitoring circulating tumor DNA by analyzing personalized cancer-specific rearrangements to detect recurrence in gastric cancer.

Circulating tumor DNA (ctDNA) has emerged as a candidate biomarker for cancer screening. However, studies on the usefulness of ctDNA for postoperative recurrence monitoring are limited. The present study monitored ctDNA in postoperative blood by employing cancer-specific rearrangements. Personalized cancer-specific rearrangements in 25 gastric cancers were analyzed by whole-genome sequencing (WGS) and were employed for ctDNA monitoring with blood up to 12 months after surgery. Personalized cancer-specific rearrangements were identified in 19 samples. The median lead time, which is the median duration between a positive ctDNA detection and recurrence, was 4.05 months. The presence of postoperative ctDNA prior to clinical recurrence was significantly correlated with cancer recurrence within 12 months of surgery (P = 0.029); in contrast, no correlation was found between cancer recurrence and the presence of preoperative ctDNA, suggesting the clinical usefulness of postoperative ctDNA monitoring for cancer recurrence in gastric cancer patients. However, the clinical application of ctDNA can be limited by the presence of ctDNA non-shedders (42.1%, 8/19) and by inconsistent postoperative ctDNA positivity.

Clinical implications of proliferation activity in T1 or T2 male gastric cancer patients.

Proliferation activity has already been established as a prognostic marker or as a marker for anticancer drug sensitivity. In gastric cancer, however, the prognostic significance of proliferation activity is still being debated. Several studies evaluating proliferation activity using Ki-67 have shown controversial results in terms of the relationship between proliferation activity and overall survival (OS) or drug sensitivity in gastric cancer patients. Because cytoskeleton-associated protein 2 (CKAP2) staining has recently been introduced as a marker of proliferation activity, we analyzed 437 gastric cancer tissues through CKAP2 immunohistochemistry, and we evaluated the chromatin CKAP2-positive cell count (CPCC) for proliferation activity. Although the CPCC did not show any significant correlation with OS in the male, female or total number of cases, it did show a significant correlation in the T1 or T2 male patient subgroup, according to log-rank tests (P=0.001) and univariate analysis (P=0.045). Additionally, multivariate analysis with the Cox proportional hazard regression model showed a significant correlation between the CPCC and OS (P=0.039) for the co-variables of age, gender, T stage, N stage, histology, tumor location, tumor size and adjuvant chemotherapy. In male gastric cancer cell lines, faster-growing cancer cells showed higher sensitivity to cisplatin than slow-growing cells. Thus our study indicates that CPCC-measured proliferation activity demonstrates a significantly worse prognosis in T1 or T2 male gastric cancer patients. The CPCC will help to more precisely classify gastric cancer patients and to select excellent candidates for adjuvant chemotherapy, which in turn will facilitate further clinical chemotherapeutic trials.