Mitochondrial Calcium Uniporter Drives Metastasis and Confers a Targetable Cystine Dependency in Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic disease with few effective treatments. Here we show that the mitochondrial calcium uniporter (MCU) promotes PDAC cell migration, invasion, metastasis, and metabolic stress resistance by activating the Keap1-Nrf2 antioxidant program. The cystine transporter SLC7A11 was identified as a druggable target downstream of the MCU-Nrf2 axis. Paradoxically, despite the increased ability to uptake cystine, MCU-overexpressing PDAC demonstrated characteristics typical of cystine-deprived cells and were hypersensitive to cystine deprivation-induced ferroptosis. Pharmacologic inhibitors of SLC7A11 effectively induced tumor regression and abrogated MCU-driven metastasis in PDAC. In patient-derived organoid models in vitro and patient-derived xenograft models in vivo, MCU-high PDAC demonstrated increased sensitivity to SLC7A11 inhibition compared with MCU-low tumors. These data suggest that MCU is able to promote resistance to metabolic stress and to drive PDAC metastasis in a cystine-dependent manner. MCU-mediated cystine addiction could be exploited as a therapeutic vulnerability to inhibit PDAC tumor growth and to prevent metastasis. SIGNIFICANCE: Elevated mitochondrial calcium uptake in PDAC promotes metastasis but exposes cystine addiction and ferroptosis sensitivity that could be targeted to improve pancreatic cancer treatment.

Spatiotemporal regulation of store-operated calcium entry in cancer metastasis.

The store-operated calcium (Ca2+) entry (SOCE) is the Ca2+ entry mechanism used by cells to replenish depleted Ca2+ store. The dysregulation of SOCE has been reported in metastatic cancer. It is believed that SOCE promotes migration and invasion by remodeling the actin cytoskeleton and cell adhesion dynamics. There is recent evidence supporting that SOCE is critical for the spatial and the temporal coding of Ca2+ signals in the cell. In this review, we critically examined the spatiotemporal control of SOCE signaling and its implication in the specificity and robustness of signaling events downstream of SOCE, with a focus on the spatiotemporal SOCE signaling during cancer cell migration, invasion and metastasis. We further discuss the limitation of our current understanding of SOCE in cancer metastasis and potential approaches to overcome such limitation.

Fascin promotes lung cancer growth and metastasis by enhancing glycolysis and PFKFB3 expression.

Fascin is a pro-metastatic actin-bundling protein that is upregulated in all metastatic carcinomas. Fascin promotes cancer cell migration and invasion by facilitating membrane protrusions, such as filopodia and invadopodia. Aerobic glycolysis is a key feature of cancer metabolism and provides critical intermediate metabolites for tumor growth. Here, we report that fascin increases glycolysis in lung cancer to promote tumor growth and metastasis. Fascin promotes glycolytic flux by increasing the expression and activities of phosphofructose-kinases 1 and 2 (PFK1 and 2). Fascin mediates glycolytic functions via activation of yes-associated protein 1 (YAP1) through its canonical actin-bundling activity by promoting the binding of YAP1 to a TEAD1/4 binding motif located 30 bp upstream of the PFKFB3 transcription start site to activate its transcription. Examination of the TCGA database suggests that the fascin-YAP1-PFKFB3 axis is likely conserved across different types of cancers. Importantly, pharmacological inhibitors of fascin suppressed YAP1-PFKFB3 signaling and glycolysis in cancer cell lines, organoid cultures, and xenograft metastasis models. Taken together, our data reveal that the glycolytic function of fascin is essential for the promotion of lung cancer growth and metabolism, and suggest that pharmacological inhibitors of fascin may be used to reprogram cancer metabolism in lung and potentially other cancers with fascin upregulation.

How does fascin promote cancer metastasis?

Fascin is an F-actin-bundling protein that cross-links individual actin filaments into straight and stiff bundles. Fascin overexpression in cancer is strongly associated with poor prognosis and metastatic progression across different cancer types. It is well established that fascin plays a causative role in promoting metastatic progression. We will review the recent progress in our understanding of mechanisms underlying fascin-mediated cancer metastasis. This review will cover the biochemical basis for fascin-bundling activity, the mechanisms by which cancer cells upregulate fascin expression and the mechanism underlying fascin-mediated cancer cell migration, invasion, and metastatic colonization. We propose that fascin has broad roles in both metastatic dissemination and metastatic colonization. Understanding these mechanisms will be crucial to the development of anti-metastasis therapeutics targeting fascin.

The mitochondrial deoxyguanosine kinase is required for cancer cell stemness in lung adenocarcinoma.

The mitochondrial deoxynucleotide triphosphate (dNTP) is maintained by the mitochondrial deoxynucleoside salvage pathway and dedicated for the mtDNA homeostasis, and the mitochondrial deoxyguanosine kinase (DGUOK) is a rate-limiting enzyme in this pathway. Here, we investigated the role of the DGUOK in the self-renewal of lung cancer stem-like cells (CSC). Our data support that DGUOK overexpression strongly correlates with cancer progression and patient survival. The depletion of DGUOK robustly inhibited lung adenocarcinoma tumor growth, metastasis, and CSC self-renewal. Mechanistically, DGUOK is required for the biogenesis of respiratory complex I and mitochondrial OXPHOS, which in turn regulates CSC self-renewal through AMPK-YAP1 signaling. The restoration of mitochondrial OXPHOS in DGUOK KO lung cancer cells using NDI1 was able to prevent AMPK-mediated phosphorylation of YAP and to rescue CSC stemness. Genetic targeting of DGUOK using doxycycline-inducible CRISPR/Cas9 was able to markedly induce tumor regression. Our findings reveal a novel role for mitochondrial dNTP metabolism in lung cancer tumor growth and progression, and implicate that the mitochondrial deoxynucleotide salvage pathway could be potentially targeted to prevent CSC-mediated therapy resistance and metastatic recurrence.

Fascin Controls Metastatic Colonization and Mitochondrial Oxidative Phosphorylation by Remodeling Mitochondrial Actin Filaments.

The deregulation of the actin cytoskeleton has been extensively studied in metastatic dissemination. However, the post-dissemination role of the actin cytoskeleton dysregulation is poorly understood. Here, we report that fascin, an actin-bundling protein, promotes lung cancer metastatic colonization by augmenting metabolic stress resistance and mitochondrial oxidative phosphorylation (OXPHOS). Fascin is directly recruited to mitochondria under metabolic stress to stabilize mitochondrial actin filaments (mtF-actin). Using unbiased metabolomics and proteomics approaches, we discovered that fascin-mediated mtF-actin remodeling promotes mitochondrial OXPHOS by increasing the biogenesis of respiratory Complex I. Mechanistically, fascin and mtF-actin control the homeostasis of mtDNA to promote mitochondrial OXPHOS. The disruption of mtF-actin abrogates fascin-mediated lung cancer metastasis. Conversely, restoration of mitochondrial respiration by using yeast NDI1 in fascin-depleted cancer cells is able to rescue lung metastasis. Our findings indicate that the dysregulated actin cytoskeleton in metastatic lung cancer could be targeted to rewire mitochondrial metabolism and to prevent metastatic recurrence.

The fucose salvage pathway inhibits invadopodia formation and extracellular matrix degradation in melanoma cells.

The fucose salvage pathway is a two-step process in which mammalian cells transform L-fucose into GDP-L-fucose, a universal fucose donor used by fucosyltransferases to modify glycans. Emerging evidence indicates the fucose salvage pathway and the fucosylation of proteins are altered during melanoma progression and metastasis. However the underlying mechanisms are not completely understood. Here, we report that the fucose salvage pathway inhibits invadopodia formation and extracellular matrix degradation by promoting α-1,2 fucosylation. Chemically or genetically increasing the fucose salvage pathway decreases invadopodium numbers and inhibits the proteolytic activity of invadopodia in WM793 melanoma cells. Inhibiting fucosylation by depleting fucokinase abrogates L-fucose-mediated inhibition of invadopodia, suggesting dependence on the fucose salvage pathway. The inhibition of invadopodium formation by L-fucose or ectopically expressed FUK could be rescued by treatment with α-1,2, but not α-1,3/α-1,4 fucosidase, implicating an α-1,2 fucose linkage-dependent anti-metastatic effect. The expression of FUT1, an α-1,2 fucosyltransferase, is remarkably down-regulated during melanoma progression, and the ectopic expression of FUT1 is sufficient to inhibit invadopodium formation and ECM degradation. Our findings indicate that the fucose salvage pathway can inhibit invadopodium formation, and consequently, invasiveness in melanoma via α-1,2 fucosylation. Re-activation of this pathway in melanoma could be useful for preventing melanoma invasion and metastasis.

A Novel Class of Natural FXR Modulators with a Unique Mode of Selective Co-regulator Assembly.

The farnesoid X receptor (FXR) is an important target for drug discovery. Small molecules induce a conformational change in FXR that modulates its binding to co-regulators, thus resulting in distinct FXR functional profiles. However, the mechanisms for selectively recruiting co-regulators by FXR remain elusive, partly because of the lack of FXR-selective modulators. We report the identification of two natural terpenoids, tschimgine and feroline, as novel FXR modulators. Remarkably, their crystal structures uncovered a secondary binding pocket important for ligand binding. Further, tschimgine or feroline induced dynamic conformational changes in the activation function 2 (AF-2) surface, thus leading to differential co-regulator recruiting profiles, modulated by both hydrophobic and selective hydrogen-bond interactions unique to specific co-regulators. Our findings thus provide a novel structure template for optimization for FXR-selective modulators of clinical value.

Monoubiquitination Inhibits the Actin Bundling Activity of Fascin.

Fascin is an actin bundling protein that cross-links individual actin filaments into straight, compact, and stiff bundles, which are crucial for the formation of filopodia, stereocillia, and other finger-like membrane protrusions. The dysregulation of fascin has been implicated in cancer metastasis, hearing loss, and blindness. Here we identified monoubiquitination as a novel mechanism that regulates fascin bundling activity and dynamics. The monoubiquitination sites were identified to be Lys247 and Lys250, two residues located in a positive charge patch at the actin binding site 2 of fascin. Using a chemical ubiquitination method, we synthesized chemically monoubiquitinated fascin and determined the effects of monoubiquitination on fascin bundling activity and dynamics. Our data demonstrated that monoubiquitination decreased the fascin bundling EC50, delayed the initiation of bundle assembly, and accelerated the disassembly of existing bundles. By analyzing the electrostatic properties on the solvent-accessible surface of fascin, we proposed that monoubiquitination introduced steric hindrance to interfere with the interaction between actin filaments and the positively charged patch at actin binding site 2. We also identified Smurf1 as a E3 ligase regulating the monoubiquitination of fascin. Our findings revealed a previously unidentified regulatory mechanism for fascin, which will have important implications for the understanding of actin bundle regulation under physiological and pathological conditions.

Disseminating Melanoma Cells Surf on Calcium Waves.

Dysregulated calcium signaling has been increasingly implicated in tumor dissemination and progression. In a recent study we investigated the mechanism underlying calcium-mediated melanoma invasion and metastasis, and discovered that hyperactive Ca2+ oscillation in melanoma cells promoted invasion and metastasis through promoting invadopodium formation and extracellular matrix remodeling.

Revealing a natural marine product as a novel agonist for retinoic acid receptors with a unique binding mode and inhibitory effects on cancer cells.

Retinoids display anti-tumour activity on various cancer cells and therefore have been used as important therapeutic agents. However, adverse side effects and RA (retinoic acid) resistance limit further development and clinical application of retinoid-based therapeutic agents. We report in the present paper the identification of a natural marine product that activates RARs (RA receptors) with a chemical structure distinct from retinoids by high-throughput compound library screening. Luffariellolide was uncovered as a novel RAR agonist by inducing co-activator binding to these receptors in vitro, further inhibiting cell growth and regulating RAR target genes in various cancer cells. Structural and molecular studies unravelled a unique binding mode of this natural ligand to RARs with an unexpected covalent modification on the RAR. Functional characterization further revealed that luffariellolide displays chemotherapeutic potentials for overcoming RA resistance in colon cancer cells, suggesting that luffariellolide may represent a unique template for designing novel non-retinoid compounds with advantages over current RA drugs.