p38MAPK builds a hyaluronan cancer niche to drive lung tumorigenesis.

Expansion of neoplastic lesions generates the initial signal that instigates the creation of a tumor niche. Nontransformed cell types within the microenvironment continuously coevolve with tumor cells to promote tumorigenesis. Here, we identify p38MAPK as a key component of human lung cancer, and specifically stromal interactomes, which provides an early, protumorigenic signal in the tissue microenvironment. We found that lung cancer growth depends on short-distance cues produced by the cancer niche in a p38-dependent manner. We identified fibroblast-specific hyaluronan synthesis at the center of p38-driven tumorigenesis, which regulates early stromal fibroblast activation, the conversion to carcinoma-associated fibroblasts (CAFs), and cancer cell proliferation. Systemic down-regulation of p38MAPK signaling in a knock-in model with substitution of activating Tyr182 to phenylalanine or conditional ablation of p38 in fibroblasts has a significant tumor-suppressive effect on K-ras lung tumorigenesis. Furthermore, both Kras-driven mouse lung tumors and orthotopically grown primary human lung cancers show a significant sensitivity to both a chemical p38 inhibitor and an over-the-counter inhibitor of hyaluronan synthesis. We propose that p38MAPK-hyaluronan-dependent reprogramming of the tumor microenvironment plays a critical role in driving lung tumorigenesis, while blocking this process could have far-reaching therapeutic implications.

Interactions of Melanoma Cells with Distal Keratinocytes Trigger Metastasis via Notch Signaling Inhibition of MITF.

The most critical stage in initiation of melanoma metastasis is the radial to vertical growth transition, yet the triggers of this transition remain elusive. We suggest that the microenvironment drives melanoma metastasis independently of mutation acquisition. Here we examined the changes in microenvironment that occur during melanoma radial growth. We show that direct contact of melanoma cells with the remote epidermal layer triggers vertical invasion via Notch signaling activation, the latter serving to inhibit MITF function. Briefly, within the native Notch ligand-free microenvironment, MITF, the melanocyte lineage master regulator, binds and represses miR-222/221 promoter in an RBPJK-dependent manner. However, when radial growth brings melanoma cells into contact with distal differentiated keratinocytes that express Notch ligands, the activated Notch intracellular domain impairs MITF binding to miR-222/221 promoter. This de-repression of miR-222/221 expression triggers initiation of invasion. Our findings may direct melanoma prevention opportunities via targeting specific microenvironments.

UBTD1 is a mechano-regulator controlling cancer aggressiveness.

Ubiquitin domain-containing protein 1 (UBTD1) is highly evolutionary conserved and has been described to interact with E2 enzymes of the ubiquitin-proteasome system. However, its biological role and the functional significance of this interaction remain largely unknown. Here, we demonstrate that depletion of UBTD1 drastically affects the mechanical properties of epithelial cancer cells via RhoA activation and strongly promotes their aggressiveness. On a stiff matrix, UBTD1 expression is regulated by cell-cell contacts, and the protein is associated with ß-catenin at cell junctions. Yes-associated protein (YAP) is a major cell mechano-transducer, and we show that UBTD1 is associated with components of the YAP degradation complex. Interestingly, UBTD1 promotes the interaction of YAP with its E3 ubiquitin ligase ß-TrCP Consequently, in cancer cells, UBTD1 depletion decreases YAP ubiquitylation and triggers robust ROCK2-dependent YAP activation and downstream signaling. Data from lung and prostate cancer patients further corroborate the in cellulo results, confirming that low levels of UBTD1 are associated with poor patient survival, suggesting that biological functions of UBTD1 could be beneficial in limiting cancer progression.

Three-Dimensional Cell Culture Conditions Affect the Proteome of Cancer-Associated Fibroblasts.

In vitro cell culture systems are an invaluable tool for cell biological research to study molecular pathways and to characterize processes critical in human pathophysiology. However, the experimental conditions in two-dimensional (2D) cell cultures often differ substantially from the in vivo situation, which continuously raises concerns about the reliability and conferrability of the obtained results. Three-dimensional (3D) cell cultures have been shown to closer mimic in vivo conditions and are commonly employed, for example, in pharmacological screens. Here, we introduce a 3D cell culture system based on a mixture of collagen I and matrigel amenable to stable isotope labeling by amino acids in cell culture (SILAC) and quantitative mass spectrometry-based proteomics analyses. We study the extra- and intracellular proteomic response of skin fibroblast isolated from healthy volunteers in comparison to cancer-associated fibroblasts (CAF) on 3D culture conditions. Both, control cells and CAF, change their proteomic composition based on the culture conditions. Critically, cell type differences observed in 2D are often not preserved in 3D, which commonly closer resemble phenotypes observed in vivo. Especially, extracellular matrix and plasma membrane proteins are differentially regulated in 2D versus 3D.

Fibroblast activation in cancer: when seed fertilizes soil.

In solid cancers, activated fibroblasts acquire the capacity to provide fertile soil for tumor progression. Specifically, cancer-associated fibroblasts (CAFs) establish a strong relationship with cancer cells. This provides advantages to both cell types: whereas cancer cells initiate and sustain CAF activation, CAFs support cancer cell growth, motility and invasion. This results in tumor progression, metastasis and chemoresistance. Numerous studies have detailed the mechanisms involved in fibroblast activation and cancer progression, some of which are reviewed in this article. Cancer cells and CAFs are "partners in crime", and their interaction is supported by inflammation. An understanding of the enemy, the cancer cell population and its "allies" should provide novel opportunities for targeted-drug development. Graphical Abstract Molecular mechanism of fibroblast activation. a Normal fibroblasts are the most common cell type in the extracellular matrix and are responsible for the synthesis of collagens and fibrilar proteins. Under normal conditions, fibroblasts maintain tissue homeostasis and contribute to proper cell communication and function. Fibroblasts can be activated by a diverse set of factors secreted from cancer or immune cells. Not only growth factors such as TGF-ß, PDGF, HGF and FGF but also interleukins, metalloproteinases and reactive oxygen species can promote activation. Likewise, transcriptional factors such as NF-κB and HSF-1 play an important role, as do the gene family of metalloproteinase inhibitors, Timp and the NF-κB subunit, p62. Interestingly, fibroblasts themselves can stimulate cancer cells to support activation further. b Once activated, fibroblasts undergo a phenotype switch and become cancer-associated fibroblasts (CAFs) expressing various markers such as α-SMA, FSP1, vimentin and periostatin. c Recently, the LIF/GP130/IL6-R pathway has been identified as a signaling cascade involved in fibroblast activation. Upon LIF stimulation, JAK is phosphorylated and further activates STAT3, a transcriptional factor that is then translocated into the nucleus where it promotes the transcription of genes responsible for cell growth, differentiation, proliferation and apoptosis. Ruxolitinib can inhibit JAK and prevent STAT3 activation. Further on, the maintenance of JAK activation is supported by epigenetical changes and post-translational modifications. Once pSTAT3 is acetylated by histon acetyltransferase, p300, it leads to the loss of expression of SHP-1, which is a negative regulator of the JAK/STAT pathway. Silencing of SHP-1 steers the constitutive activation of JAK and STAT3.

Fibroblast-led collective invasion of carcinoma cells with differing roles for RhoGTPases in leading and following cells.

Imaging of collectively invading cocultures of carcinoma cells and stromal fibroblasts reveals that the leading cell is always a fibroblast and that carcinoma cells move within tracks in the extracellular matrix behind the fibroblast. The generation of these tracks by fibroblasts is sufficient to enable the collective invasion of the squamous cell carcinoma (SCC) cells and requires both protease- and force-mediated matrix remodelling. Force-mediated matrix remodelling depends on integrins alpha3 and alpha5, and Rho-mediated regulation of myosin light chain (MLC) activity in fibroblasts, but these factors are not required in carcinoma cells. Instead, carcinoma cells use Cdc42 and MRCK (myotonic dystrophy kinase-related CDC42-binding protein kinases) mediated regulation of MLC to follow the tracks generated by fibroblasts.

[Carcinoma-associated fibroblasts in cancer: the great escape]. / L'invasion des cellules tumorales - quand les fibroblastes s'en mêlent.

Cellular and molecular crosstalks between cancer and non-cancer tumor-associated cells result in tumor growth and metastatic spreading. During carcinoma development, tumor cells secrete signaling molecules that influence the surrounding non-cancer cells, which, in return, favor tumor cell growth, survival, migration and metastasis. Carcinoma-associated fibroblasts (CAF) are the most abundant population of non-cancer cells found in tumors, and their presence is often associated with poor clinical prognosis. Here, we summarize the pro-carcinogenic roles of CAF cells during carcinogenesis, with a specific focus on their abilities to drive cancer cell-dependent pro-invasive extracellular matrix remodeling.

NETscape or NEThance: tailoring anti-cancer therapy.

Neutrophils, major regulators of innate immunity, have recently emerged as key components of the tumor microenvironment. The role of neutrophils in cancer has been linked to their ability to form neutrophil extracellular traps (NETs), structures composed of decondensed DNA decorated with enzymes that are released into the extracellular space. Here, we discuss the pivotal roles of NETs in influencing responses to anticancer therapies such as chemotherapy, radiotherapy, immunotherapy, and targeted therapy. Highlighting recent insights, we delve into the dual nature of NETs in the context of anticancer treatments, examining their potential to either counteract or enhance treatment outcomes. Strategic targeting of NETs may be a promising avenue for crafting combination therapies to counteract resistance or enhance anticancer treatments' efficacy.

Pluripotent stem cell model reveals essential roles for miR-450b-5p and miR-184 in embryonic corneal lineage specification.

Approximately 6 million people worldwide are suffering from severe visual impairments or blindness due to corneal diseases. Corneal allogeneic transplantation is often required to restore vision; however, shortage in corneal grafts and immunorejections remain major challenges. The molecular basis of corneal diseases is poorly understood largely due to lack of appropriate cellular models. Here, we described a robust differentiation of human-induced pluripotent stem cells (hiPSCs) derived from hair follicles or skin fibroblasts into corneal epithelial-like cells. We found that BMP4, coupled with corneal fibroblast-derived conditioned medium and collagen IV allowed efficient corneal epithelial commitment of hiPSCs in a manner that recapitulated corneal epithelial lineage development with high purity. Organotypic reconstitution assays suggested the ability of these cells to stratify into a corneal-like epithelium. This model allowed us identifying miR-450b-5p as a molecular switch of Pax6, a major regulator of eye development. miR-450b-5p and Pax6 were reciprocally distributed at the presumptive epidermis and ocular surface, respectively. miR-450b-5p inhibited Pax6 expression and corneal epithelial fate in vitro, altogether, suggesting that by repressing Pax6, miR-450b-5p triggers epidermal specification of the ectoderm, while its absence allows ocular epithelial development. Additionally, miR-184 was detectable in early eye development and corneal epithelial differentiation of hiPSCs. The knockdown of miR-184 resulted in a decrease in Pax6 and K3, in line with recent findings showing that a point mutation in miR-184 leads to corneal dystrophy. Altogether, these data indicate that hiPSCs are valuable for modeling corneal development and may pave the way for future cell-based therapy.

Neutrophil extracellular traps formed during chemotherapy confer treatment resistance via TGF-ß activation.

Metastasis is the major cause of cancer death, and the development of therapy resistance is common. The tumor microenvironment can confer chemotherapy resistance (chemoresistance), but little is known about how specific host cells influence therapy outcome. We show that chemotherapy induces neutrophil recruitment and neutrophil extracellular trap (NET) formation, which reduces therapy response in mouse models of breast cancer lung metastasis. We reveal that chemotherapy-treated cancer cells secrete IL-1ß, which in turn triggers NET formation. Two NET-associated proteins are required to induce chemoresistance: integrin-αvß1, which traps latent TGF-ß, and matrix metalloproteinase 9, which cleaves and activates the trapped latent TGF-ß. TGF-ß activation causes cancer cells to undergo epithelial-to-mesenchymal transition and correlates with chemoresistance. Our work demonstrates that NETs regulate the activities of neighboring cells by trapping and activating cytokines and suggests that chemoresistance in the metastatic setting can be reduced or prevented by targeting the IL-1ß-NET-TGF-ß axis.

Secretion of IL1 by Dedifferentiated Melanoma Cells Inhibits JAK1-STAT3-Driven Actomyosin Contractility of Lymph Node Fibroblastic Reticular Cells.

Fibroblastic reticular cells (FRC) are immunologically specialized myofibroblasts that control the elasticity of the lymph node, in part through their contractile properties. Swelling of tumor-draining lymph nodes is a hallmark of lymphophilic cancers such as cutaneous melanoma. Melanoma displays high intratumoral heterogeneity with the coexistence of melanoma cells with variable differentiation phenotypes from melanocytic to dedifferentiated states. Factors secreted by melanoma cells promote premetastatic lymph node reprograming and tumor spreading. Elucidating the impact of the melanoma secretome on FRC could help identify approaches to prevent metastasis. Here we show that melanocytic and dedifferentiated melanoma cells differentially impact the FRC contractile phenotype. Factors secreted by dedifferentiated cells, but not by melanocytic cells, strongly inhibited actomyosin-dependent contractile forces of FRC by decreasing the activity of the RHOA-RHO-kinase (ROCK) pathway and the mechano-responsive transcriptional coactivator Yes1 associated transcriptional regulator (YAP). Transcriptional profiling and biochemical analyses indicated that actomyosin cytoskeleton relaxation in FRC is driven by inhibition of the JAK1-STAT3 pathway. This FRC relaxation was associated with increased FRC proliferation and activation and with elevated tumor invasion in vitro. The secretome of dedifferentiated melanoma cells also modulated the biomechanical properties of distant lymph node in premetastatic mouse models. Finally, IL1 produced by dedifferentiated cells was involved in the inhibition of FRC contractility. These data highlight the role of the JAK1-STAT3 and YAP pathways in spontaneous contractility of resting FRC. They also suggest that dedifferentiated melanoma cells specifically target FRC biomechanical properties to favor tumor spreading in the premetastatic lymph node niche. Targeting this remote communication could be an effective strategy to prevent metastatic spread of the disease. SIGNIFICANCE: Communication between dedifferentiated melanoma cells and lymph node fibroblasts reprograms the biomechanical properties of the premetastatic lymph node niche to promote tumor invasion. See related commentary by Lund, p. 1692.

Mesenchymal Stem Cells and PRP Therapy Favorize Leak Closure After Sleeve Gastrectomy in Zucker Rats.

INTRODUCTION: Sleeve gastrectomy (SG) is the most performed bariatric surgery but gastric leaks following SG occur in up to 2% of cases. Regenerative medicine is emerging as a promising field offering multiple possibilities in wound healing. We studied the efficiency of locally administered mesenchymal stem cells (MSCs) and platelet-rich plasma (PRP) on leak closure following SG in rats. METHODS: The amount of PRP and MSCs extracted from one rat was analyzed and a model of gastric leak was developed in 10-week-old male Zucker rats. Twenty-four rats underwent SG fashioned with a leak. After 24 h, a second surgery was performed. The control group was treated by peritoneal lavage and drainage only while the experimental group received an additional treatment of locally administered MSCs and PRP at the leak orifice. Analysis of the leak healing process was done by an anatomopathological examination of the stomach 1, 2, 3, and 4 weeks after SG. RESULTS: The extraction of MSCs and PRP from one rat was necessary for three recipients. Anatomopathological examination suggests that the closure of the leak orifice was faster in the experimental group. Statistical analysis revealed a significantly increased mucosae renewal and fibrosis score at the leak orifice after treatment with MSCs and PRP (p < 0.001). CONCLUSION: These results suggest that PRP and MSCs may accelerate the closure of leaks following SG in rats and may become a new tool in the treatment of human gastric leaks but more research on this topic is needed to confirm these findings.

Targeting Discoidin Domain Receptors DDR1 and DDR2 overcomes matrix-mediated tumor cell adaptation and tolerance to BRAF-targeted therapy in melanoma.

Resistance to BRAF/MEK inhibitor therapy in BRAFV600 -mutated advanced melanoma remains a major obstacle that limits patient benefit. Microenvironment components including the extracellular matrix (ECM) can support tumor cell adaptation and tolerance to targeted therapy; however, the underlying mechanisms remain poorly understood. Here, we investigated the process of matrix-mediated drug resistance (MMDR) in response to BRAFV600 pathway inhibition in melanoma. We demonstrate that physical and structural cues from fibroblast-derived ECM abrogate anti-proliferative responses to BRAF/MEK inhibition. MMDR is mediated by drug-induced linear clustering of phosphorylated DDR1 and DDR2, two tyrosine kinase collagen receptors. Depletion and pharmacological targeting of DDR1 and DDR2 overcome ECM-mediated resistance to BRAF-targeted therapy. In xenografts, targeting DDR with imatinib enhances BRAF inhibitor efficacy, counteracts drug-induced collagen remodeling, and delays tumor relapse. Mechanistically, DDR-dependent MMDR fosters a targetable pro-survival NIK/IKKα/NF-κB2 pathway. These findings reveal a novel role for a collagen-rich matrix and DDR in tumor cell adaptation and resistance. They also provide important insights into environment-mediated drug resistance and a preclinical rationale for targeting DDR signaling in combination with targeted therapy in melanoma.

A Novel Screen for Expression Regulators of the Telomeric Protein TRF2 Identified Small Molecules That Impair TRF2 Dependent Immunosuppression and Tumor Growth.

Telomeric repeat-binding factor 2 (TRF2) is a subunit of the shelterin protein complex, which binds to and protects telomeres from unwanted DNA damage response (DDR) activation. TRF2 expression plays a pivotal role in aging and cancer, being downregulated during cellular senescence and overexpressed during oncogenesis. Cancers overexpressing TRF2 often exhibit a poor prognosis. In cancer cells, TRF2 plays multiple functions, including telomere protection and non-cell autonomous roles, promoting neo-angiogenesis and immunosuppression. We present here an original screening strategy, which enables identification of small molecules that decrease or increase TRF2 expression. By screening a small library of Food and Drug Agency (FDA)-approved drugs, we identified two molecules (AR-A014418 and alexidine·2HCl) that impaired tumor growth, neo-angiogenesis and immunosuppression by downregulating TRF2 expression in a mouse xenograft model. These results support the chemotherapeutic strategy of downregulating TRF2 expression to treat aggressive human tumors and validate this cell-based assay capable of screening for potential anti-cancer and anti-aging molecules by modulating TRF2 expression levels.

Pathogenic NR2F1 variants cause a developmental ocular phenotype recapitulated in a mutant mouse model.

Pathogenic NR2F1 variants cause a rare autosomal dominant neurodevelopmental disorder referred to as the Bosch-Boonstra-Schaaf Optic Atrophy Syndrome. Although visual loss is a prominent feature seen in affected individuals, the molecular and cellular mechanisms contributing to visual impairment are still poorly characterized. We conducted a deep phenotyping study on a cohort of 22 individuals carrying pathogenic NR2F1 variants to document the neurodevelopmental and ophthalmological manifestations, in particular the structural and functional changes within the retina and the optic nerve, which have not been detailed previously. The visual impairment became apparent in early childhood with small and/or tilted hypoplastic optic nerves observed in 10 cases. High-resolution optical coherence tomography imaging confirmed significant loss of retinal ganglion cells with thinning of the ganglion cell layer, consistent with electrophysiological evidence of retinal ganglion cells dysfunction. Interestingly, for those individuals with available longitudinal ophthalmological data, there was no significant deterioration in visual function during the period of follow-up. Diffusion tensor imaging tractography studies showed defective connections and disorganization of the extracortical visual pathways. To further investigate how pathogenic NR2F1 variants impact on retinal and optic nerve development, we took advantage of an Nr2f1 mutant mouse disease model. Abnormal retinogenesis in early stages of development was observed in Nr2f1 mutant mice with decreased retinal ganglion cell density and disruption of retinal ganglion cell axonal guidance from the neural retina into the optic stalk, accounting for the development of optic nerve hypoplasia. The mutant mice showed significantly reduced visual acuity based on electrophysiological parameters with marked conduction delay and decreased amplitude of the recordings in the superficial layers of the visual cortex. The clinical observations in our study cohort, supported by the mouse data, suggest an early neurodevelopmental origin for the retinal and optic nerve head defects caused by NR2F1 pathogenic variants, resulting in congenital vision loss that seems to be non-progressive. We propose NR2F1 as a major gene that orchestrates early retinal and optic nerve head development, playing a key role in the maturation of the visual system.

Hypoxia-inducible factor 1{alpha} is a new target of microphthalmia-associated transcription factor (MITF) in melanoma cells.

In melanocytes and melanoma cells alpha-melanocyte stimulating hormone (alpha-MSH), via the cAMP pathway, elicits a large array of biological responses that control melanocyte differentiation and influence melanoma development or susceptibility. In this work, we show that cAMP transcriptionally activates Hif1a gene in a melanocyte cell-specific manner and increases the expression of a functional hypoxia-inducible factor 1alpha (HIF1alpha) protein resulting in a stimulation of Vegf expression. Interestingly, we report that the melanocyte-specific transcription factor, microphthalmia-associated transcription factor (MITF), binds to the Hif1a promoter and strongly stimulates its transcriptional activity. Further, MITF "silencing" abrogates the cAMP effect on Hif1a expression, and overexpression of MITF in human melanoma cells is sufficient to stimulate HIF1A mRNA. Our data demonstrate that Hif1a is a new MITF target gene and that MITF mediates the cAMP stimulation of Hif1a in melanocytes and melanoma cells. Importantly, we provide results demonstrating that HIF1 plays a pro-survival role in this cell system. We therefore conclude that the alpha-MSH/cAMP pathway, using MITF as a signal transducer and HIF1alpha as a target, might contribute to melanoma progression.

A Feed-Forward Mechanosignaling Loop Confers Resistance to Therapies Targeting the MAPK Pathway in BRAF-Mutant Melanoma.

Aberrant extracellular matrix (ECM) deposition and stiffening is a physical hallmark of several solid cancers and is associated with therapy failure. BRAF-mutant melanomas treated with BRAF and MEK inhibitors almost invariably develop resistance that is frequently associated with transcriptional reprogramming and a de-differentiated cell state. Melanoma cells secrete their own ECM proteins, an event that is promoted by oncogenic BRAF inhibition. Yet, the contribution of cancer cell-derived ECM and tumor mechanics to drug adaptation and therapy resistance remains poorly understood. Here, we show that melanoma cells can adapt to targeted therapies through a mechanosignaling loop involving the autocrine remodeling of a drug-protective ECM. Analyses revealed that therapy-resistant cells associated with a mesenchymal dedifferentiated state displayed elevated responsiveness to collagen stiffening and force-mediated ECM remodeling through activation of actin-dependent mechanosensors Yes-associated protein (YAP) and myocardin-related transcription factor (MRTF). Short-term inhibition of MAPK pathway also induced mechanosignaling associated with deposition and remodeling of an aligned fibrillar matrix. This provided a favored ECM reorganization that promoted tolerance to BRAF inhibition in a YAP- and MRTF-dependent manner. Matrix remodeling and tumor stiffening were also observed in vivo upon exposure of BRAF-mutant melanoma cell lines or patient-derived xenograft models to MAPK pathway inhibition. Importantly, pharmacologic targeting of YAP reversed treatment-induced excessive collagen deposition, leading to enhancement of BRAF inhibitor efficacy. We conclude that MAPK pathway targeting therapies mechanically reprogram melanoma cells to confer a drug-protective matrix environment. Preventing melanoma cell mechanical reprogramming might be a promising therapeutic strategy for patients on targeted therapies. SIGNIFICANCE: These findings reveal a biomechanical adaptation of melanoma cells to oncogenic BRAF pathway inhibition, which fuels a YAP/MRTF-dependent feed-forward loop associated with tumor stiffening, mechanosensing, and therapy resistance. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/10/1927/F1.large.jpg.

Mechanical forces rewire metabolism in the tumor niche.

Tumor niche extracellular matrix stiffening and tumor cell metabolic reprogramming are two fundamental mediators of tumor progression. We recently elucidated a mechanistic interconnection between mechanotransduction and tumor metabolic rewiring in cancer. We demonstrated a stiffness-dependent amino acid crosstalk between stromal and cancer cells that fuels tumor progression and metastatic spreading.

Tumor-Stroma Mechanics Coordinate Amino Acid Availability to Sustain Tumor Growth and Malignancy.

Dysregulation of extracellular matrix (ECM) deposition and cellular metabolism promotes tumor aggressiveness by sustaining the activity of key growth, invasion, and survival pathways. Yet mechanisms by which biophysical properties of ECM relate to metabolic processes and tumor progression remain undefined. In both cancer cells and carcinoma-associated fibroblasts (CAFs), we found that ECM stiffening mechanoactivates glycolysis and glutamine metabolism and thus coordinates non-essential amino acid flux within the tumor niche. Specifically, we demonstrate a metabolic crosstalk between CAF and cancer cells in which CAF-derived aspartate sustains cancer cell proliferation, while cancer cell-derived glutamate balances the redox state of CAFs to promote ECM remodeling. Collectively, our findings link mechanical stimuli to dysregulated tumor metabolism and thereby highlight a new metabolic network within tumors in which diverse fuel sources are used to promote growth and aggressiveness. Furthermore, this study identifies potential metabolic drug targets for therapeutic development in cancer.

SPARC represses E-cadherin and induces mesenchymal transition during melanoma development.

During progression of melanoma, loss of the cell-cell adhesion molecule E-cadherin contributes to uncontrolled growth and invasive behavior of transformed melanocytes. Secreted protein acidic and rich in cysteine (SPARC) is a nonstructural matricellular protein that regulates cell-matrix interactions leading to alterations in cell adhesion and proliferation. Overexpression of SPARC has been associated with progression of various cancers, including melanoma; however, its role in primary tumor development is not well defined. We show that normal human melanocytes overexpressing SPARC adopt a fibroblast-like morphology, concomitant with loss of E-cadherin and P-cadherin expression, and increased expression of mesenchymal markers. Concurrent with these changes, SPARC expression stimulates melanocyte motility and melanoma cell invasion. Expression of SPARC results in transcriptional down-regulation of E-cadherin that correlates with induction of Snail, a repressor of E-cadherin. Conversely, SPARC depletion leads to up-regulation of E-cadherin and reduces Snail levels, and SPARC-null cells exhibit a marked change in their mesenchymal phenotype. Finally, analysis of SPARC, Snail, and E-cadherin levels in melanocytes and malignant melanoma cell lines further supports the functional relationship among these proteins during melanoma progression. Our findings provide evidence for the role of SPARC in early transformation of melanocytes and identify a novel mechanism, whereby tumor-derived SPARC promotes tumorigenesis by mediating Snail induction and E-cadherin suppression.