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Breast cancer is the most frequent cancer among women, and metastases in distant organs are the leading cause of the cancer‐related deaths. While survival of early‐stage breast cancer patients has increased dramatically, the 5‐year survival rate of metastatic patients has barely improved in the last 20 years. Metastases can arise up to decades after primary tumor resection, hinting at microenvironmental factors influencing the sudden outgrowth of disseminated tumor cells (DTCs). This review summarizes how the environment of the most common metastatic sites (lung, liver, bone, brain) is influenced by the primary tumor and by the varying dormancy of DTCs, with a special focus on how established metastases persist and grow in distant organs due to feed‐forward loops (FFLs). We discuss in detail the importance of FFL of cancer cells with their microenvironment including the secretome, interaction with specialized tissue‐specific cells, nutrients/metabolites, and that novel therapies should target not only the cancer cells but also the tumor microenvironment, which are thick as thieves. Graphical Abstract Metastases can arise decades after primary breast tumor resection. This review by M. Bentires‐Alj and colleagues describes how the environment of the most common metastatic sites is influenced by the primary tumor and the varying dormancy of disseminated tumor cells, with a focus on feed‐forward loops.

Although group 3 innate lymphoid cells (ILC3s) are efficient inducers of T cell responses in the spleen, they fail to induce CD4 + T cell proliferation in the gut. The signals regulating ILC3-T cell responses remain unknown. Here, we show that transcripts associated with MHC II antigen presentation are down-modulated in intestinal natural cytotoxicity receptor (NCR) − ILC3s. Further data implicate microbiota-induced IL-23 as a crucial signal for reversible silencing of MHC II in ILC3s, thereby reducing the capacity of ILC3s to present antigen to T cells in the intestinal mucosa. Moreover, IL-23-mediated MHC II suppression is dependent on mTORC1 and STAT3 phosphorylation in NCR − ILC3s. By contrast, splenic interferon-γ induces MHC II expression and CD4 + T cell stimulation by NCR − ILC3s. Our results thus identify biological circuits for tissue-specific regulation of ILC3-dependent T cell responses. These pathways may have implications for inducing or silencing T cell responses in human diseases. Group 3 innate lymphoid cells (ILC3s) promote T cell activation in the spleen but suppress it in the gut. Here, the authors show that this distinct regulation is mediated by gut microbiota-induced IL-23 and IFN-γ, respectively, and, along with the article by Rao et al, this work elucidates how cytokines set context specificity of ILC-T cell crosstalk by regulating ILC antigen presentation.

The actin cytoskeleton is tightly controlled by RhoGTPases, actin binding-proteins and nucleation-promoting factors to perform fundamental cellular functions. We have previously shown that ERK3, an atypical MAPK, controls IL-8 production and chemotaxis (Bogueka et al., 2020). Here, we show in human cells that ERK3 directly acts as a guanine nucleotide exchange factor for CDC42 and phosphorylates the ARP3 subunit of the ARP2/3 complex at S418 to promote filopodia formation and actin polymerization, respectively. Consistently, depletion of ERK3 prevented both basal and EGF-dependent RAC1 and CDC42 activation, maintenance of F-actin content, filopodia formation, and epithelial cell migration. Further, ERK3 protein bound directly to the purified ARP2/3 complex and augmented polymerization of actin in vitro. ERK3 kinase activity was required for the formation of actin-rich protrusions in mammalian cells. These findings unveil a fundamentally unique pathway employed by cells to control actin-dependent cellular functions.

Metastasis is the main cause of deaths related to solid cancers. Active transcriptional programmes are known to regulate the metastatic cascade but the molecular determinants of metastatic colonization remain elusive. Using an inducible piggyBac (PB) transposon mutagenesis screen, we have shown that overexpression of the transcription factor nuclear factor IB (NFIB) alone is sufficient to enhance primary mammary tumour growth and lung metastatic colonization. Mechanistically and functionally, NFIB directly increases expression of the oxidoreductase ERO1A , which enhances HIF1α‐VEGFA‐mediated angiogenesis and colonization, the last and fatal step of the metastatic cascade. NFIB is thus clinically relevant: it is preferentially expressed in the poor‐prognostic group of basal‐like breast cancers, and high expression of the NFIB/ERO1A/VEGFA pathway correlates with reduced breast cancer patient survival. Synopsis Transcriptional factor nuclear factor IB (NFIB) is sufficient to enhance lung metastatic colonization via enhanced angiogenesis, thus revealing a targetable network that promotes breast cancer colonization. NFIB was identified via an unbiased ex vivo piggyBac (PB) transposon insertional mutagenesis screen, and validated as an inducer of metastatic colonization in breast cancer. NFIB directly enhances ERO1A oxidoreductase expression, which in turn increases intracellular ROS levels, stabilizes HIF1alpha protein in the nucleus and upregulates VEGFA expression. Functionally, the NFIB‐ERO1A‐VEGFA axis enhances angiogenesis, promotes metastatic colonization and shortens overall survival of the animals. A correlation was found between NFIB, ERO1A, and VEGFA co‐expression and the metastatic potential in PDX models. Graphical Abstract Transcriptional factor nuclear factor IB (NFIB) is sufficient to enhance lung metastatic colonization via enhanced angiogenesis, thus revealing a targetable network that promotes breast cancer colonization.

In mouse models of breast cancer, anti-CCL2 therapy—thought to be potentially useful in treating cancer—is shown to accelerate the growth of lung metastases on discontinuation due to a surge of recruitment of bone marrow monocytes and increased interleukin-6-dependent vascularization of the lung metastatic environment. Anti-cancer action of CCL2/interleukin-6 inhibitors Inflammatory monocytes have previously been shown to infiltrate and promote the growth of metastases, by secreting cytokines such as CCL2. This has led to the demonstration that neutralizing CCL2 or blocking its receptor CCR2 may have therapeutic benefit. However, in a mouse model of breast cancer, Laura Bonapace et al . now show that disruption of anti-CCL2 therapy not only halts the therapeutic effects, but accelerates the growth of lung metastases and the death of animals, compared with untreated lesions. This is due to a surge of recruitment of bone marrow monocytes and increased interleukin-6-dependent vascularization of the lung metastatic environment. While these findings highlight the need for caution over the use of anti-CCL2 agents alone, the authors show that combined anti-CCL2 and anti-interleukin-6 therapies can reduce metastases and increase survival in a mouse model. Secretion of C–C chemokine ligand 2 (CCL2) by mammary tumours recruits CCR2-expressing inflammatory monocytes to primary tumours and metastatic sites, and CCL2 neutralization in mice inhibits metastasis 1 by retaining monocytes in the bone marrow. Here we report a paradoxical effect of CCL2 in four syngeneic mouse models of metastatic breast cancer. Surprisingly, interruption of CCL2 inhibition leads to an overshoot of metastases and accelerates death. This is the result of monocyte release from the bone marrow and enhancement of cancer cell mobilization from the primary tumour, as well as blood vessel formation and increased proliferation of metastatic cells in the lungs in an interleukin (IL)-6- and vascular endothelial growth factor (VEGF)-A-dependent manner. Notably, inhibition of CCL2 and IL-6 markedly reduced metastases and increased survival of the animals. CCL2 has been implicated in various neoplasias and adopted as a therapeutic target 1 , 2 , 3 . However, our results call for caution when considering anti-CCL2 agents as monotherapy in metastatic disease and highlight the tumour microenvironment as a critical determinant of successful anti-metastatic therapy.

Cancer initiation and progression follow complex molecular and structural changes in the extracellular matrix and cellular architecture of living tissue. However, it remains poorly understood how the transformation from health to malignancy alters the mechanical properties of cells within the tumour microenvironment. Here, we show using an indentation-type atomic force microscope (IT-AFM) that unadulterated human breast biopsies display distinct stiffness profiles. Correlative stiffness maps obtained on normal and benign tissues show uniform stiffness profiles that are characterized by a single distinct peak. In contrast, malignant tissues have a broad distribution resulting from tissue heterogeneity, with a prominent low-stiffness peak representative of cancer cells. Similar findings are seen in specific stages of breast cancer in MMTV-PyMT transgenic mice. Further evidence obtained from the lungs of mice with late-stage tumours shows that migration and metastatic spreading is correlated to the low stiffness of hypoxia-associated cancer cells. Overall, nanomechanical profiling by IT-AFM provides quantitative indicators in the clinical diagnostics of breast cancer with translational significance. Nanomechanical signatures of human breast biopsies obtained using an atomic force microscope show close correlation between softening of cancer cells and progression of cancer.

Tumor-specific T cells are frequently exhausted by chronic antigenic stimulation. We here report on a human antigen-specific ex vivo model to explore new therapeutic options for T cell immunotherapies. T cells generated with this model resemble tumor-infiltrating exhausted T cells on a phenotypic and transcriptional level. Using a targeted pooled CRISPR-Cas9 screen and individual gene knockout validation experiments, we uncover sorting nexin-9 (SNX9) as a mediator of T cell exhaustion. Upon TCR/CD28 stimulation, deletion of SNX9 in CD8 T cells decreases PLCγ1, Ca 2+ , and NFATc2-mediated T cell signaling and reduces expression of NR4A1/3 and TOX. SNX9 knockout enhances memory differentiation and IFNγ secretion of adoptively transferred T cells and results in improved anti-tumor efficacy of human chimeric antigen receptor T cells in vivo. Our findings highlight that targeting SNX9 is a strategy to prevent T cell exhaustion and enhance anti-tumor immunity. The efficacy of T-cell-based cancer immunotherapies can be compromised by T cell exhaustion. Here the authors develop a human ex vivo exhaustion model and, based on a CRISPR-Cas9 screen, identify SNX9 as a regulator of T cell exhaustion, showing that SNX9 knockout is associated with improved T cell function and anti-tumor activity in preclinical cancer models.

The calcium-activated chloride channel anoctamin 1 (ANO1) is located within the 11q13 amplicon, one of the most frequently amplified chromosomal regions in human cancer, but its functional role in tumorigenesis has remained unclear. The 11q13 region is amplified in ∼15% of breast cancers. Whether ANO1 is amplified in breast tumors, the extent to which gene amplification contributes to ANO1 overexpression, and whether overexpression of ANO1 is important for tumor maintenance have remained unknown. We have found that ANO1 is amplified and highly expressed in breast cancer cell lines and primary tumors. Amplification of ANO1 correlated with disease grade and poor prognosis. Knockdown of ANO1 in ANO1-amplified breast cancer cell lines and other cancers bearing 11q13 amplification inhibited proliferation, induced apoptosis, and reduced tumor growth in established cancer xenografts. Moreover, ANO1 chloride channel activity was important for cell viability. Mechanistically, ANO1 knockdown or pharmacological inhibition of its chloride-channel activity reduced EGF receptor (EGFR) and calmodulin-dependent protein kinase II (CAMKII) signaling, which subsequently attenuated AKT, v-src sarcoma viral oncogene homolog (SRC), and extracellular signal-regulated kinase (ERK) activation in vitro and in vivo. Our results highlight the involvement of the ANO1 chloride channel in tumor progression and provide insights into oncogenic signaling in human cancers with 11q13 amplification, thereby establishing ANO1 as a promising target for therapy in these highly prevalent tumor types.

The authors uncover a role for the tyrosine phosphatase SHP2 in the propagation and maintenance of breast cancer tumor initiating cells. This role of SHP2 contributes to the growth and metastasis of tumors in vivo and is mediated by a newly uncovered downstream pathway that, through regulation of ERK, modulates the activity of transcription factors such as ZEB1 and Myc, also affecting microRNAs such as let-7. A genetic signature of SHP2 activation is indicative of increased aggressiveness in human breast cancers. New cancer therapies are likely to arise from an in-depth understanding of the signaling networks influencing tumor initiation, progression and metastasis. We show a fundamental role for Src-homology 2 domain-containing phosphatase 2 (SHP2) in these processes in human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancers. Knockdown of SHP2 eradicated breast tumor-initiating cells in xenograft models, and SHP2 depletion also prevented invasion in three-dimensional cultures and in a transductal invasion assay in vivo . Notably, SHP2 knockdown in established breast tumors blocked their growth and reduced metastasis. Mechanistically, SHP2 activated stemness-associated transcription factors, including v-myc myelocytomatosis viral oncogene homolog (c-Myc) and zinc finger E-box binding homeobox 1 (ZEB1), which resulted in the repression of let-7 microRNA and the expression of a set of 'SHP2 signature' genes. We found these genes to be simultaneously activated in a large subset of human primary breast tumors that are associated with invasive behavior and poor prognosis. These results provide new insights into the signaling cascades influencing tumor-initiating cells as well as a rationale for targeting SHP2 in breast cancer.

SHP2 is a cytoplasmic protein tyrosine phosphatase (PTPase) involved in multiple signaling pathways and was the first identified proto-oncogene PTPase. Previous work in glioblastoma (GBM) has demonstrated the role of SHP2 PTPase activity in modulating the oncogenic phenotype of adherent GBM cell lines. Mutations in PTPN11 , the gene encoding SHP2, have been identified with increasing frequency in GBM. Given the importance of SHP2 in developing neural stem cells, and the importance of glioma stem cells (GSCs) in GBM oncogenesis, we explored the functional role of SHP2 in GSCs. Using paired differentiated and stem cell primary cultures, we investigated the association of SHP2 expression with the tumor stem cell compartment. Proliferation and soft agar assays were used to demonstrate the functional contribution of SHP2 to cell growth and transformation. SHP2 expression correlated with SOX2 expression in GSC lines and was decreased in differentiated cells. Forced differentiation of GSCs by removal of growth factors, as confirmed by loss of SOX2 expression, also resulted in decreased SHP2 expression. Lentiviral-mediated knockdown of SHP2 inhibited proliferation. Finally, growth in soft-agar was similarly inhibited by loss of SHP2 expression. Our results show that SHP2 function is required for cell growth and transformation of the GSC compartment in GBM.