Cancer cells, including melanoma, often metastasize regionally through lymphatics before metastasizing systemically through the blood 1 – 4 ; however, the reason for this is unclear. Here we show that melanoma cells in lymph experience less oxidative stress and form more metastases than melanoma cells in blood. Immunocompromised mice with patient-derived melanomas and immunocompetent mice with mouse melanomas had more melanoma cells per microliter of tumor-draining lymph than tumor-draining blood. Cells metastasizing through blood, but not lymph, became dependent on the ferroptosis inhibitor GPX4. Cells pre-treated with chemical ferroptosis inhibitors formed more metastases than untreated cells after intravenous, but not intralymphatic, injection. We observed multiple differences between lymph fluid and blood plasma that may contribute to decreased oxidative stress and ferroptosis in lymph, including higher levels of glutathione and oleic acid, and less free iron, in lymph. Oleic acid protected melanoma cells from ferroptosis in an Acsl3 -dependent manner and increased their capacity to form metastatic tumors. Melanoma cells from lymph nodes were more resistant to ferroptosis and formed more metastases after intravenous injection than melanoma cells from subcutaneous tumors. Exposure to the lymphatic environment thus protects melanoma cells from ferroptosis and increases their ability to survive during subsequent metastasis through the blood.

Metastasis requires cancer cells to undergo poorly-understood metabolic changes [1][2][3] . We found that metabolic differences among melanoma cells confer differences in metastatic potential as a result of differences in Monocarboxylate Transporter 1 (MCT1) function. In vivo isotope tracing in patient-derived xenografts revealed differences in nutrient handling between efficiently and inefficiently metastasizing melanomas, with circulating lactate being a more prominent source of tumor lactate in efficient metastasizers. Efficient metastasizers had higher MCT1 levels and MCT1 inhibition reduced lactate uptake. MCT1 inhibition had little effect on primary subcutaneous tumor growth but depleted circulating melanoma cells and reduced metastatic disease burden in patientderived xenografts and in mouse melanomas. MCT1 inhibition suppressed the oxidative pentose phosphate pathway and increased ROS levels. Anti-oxidants blocked the effect of MCT1 inhibition on metastasis. MCT1 high and MCT1 −/low cells from the same melanomas had similar Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Integrins mediate cell adhesion to the extracellular matrix and transmit signals within the cell that stimulate cell spreading, retraction, migration, and proliferation. The mechanism of integrin outside-in signaling has been unclear. We found that the heterotrimeric guanine nucleotide-binding protein (G protein), Gα13, directly bound to the integrin β3 cytoplasmic domain, and that Gα13-integrin interaction was promoted by ligand binding to the integrin αIIbβ3 and by guanosine triphosphate (GTP)-loading of Gα13. Interference of Gα13 expression or a myristoylated fragment of Gα13 that inhibited interaction of αIIbβ3 with Gα13 diminished activation of protein kinase c-Src and stimulated the small GTPase RhoA, consequently inhibiting cell spreading and accelerating cell retraction. We conclude that integrins are non-canonical Gα13-coupled receptors that provide a mechanism for dynamic regulation of RhoA.

Integrins are critical in thrombosis and hemostasis1. Antagonists of the platelet integrin αIIbβ3 are potent anti-thrombotic drugs, but also have the life-threatening adverse effect of bleeding2,3. It is thus desirable to develop new antagonists that do not cause bleeding. Integrins transmit signals bidirectionally4,5. Inside-out signaling activates integrins via a talin-dependent mechanism6,7. Integrin ligation mediates thrombus formation and outside-in signaling8,9, which requires Gα13 and greatly expands thrombi. Here we show that Gα13 and talin bind to mutually exclusive, but distinct sites within the integrin β3 cytoplasmic domain in opposing waves. The first talin binding wave mediates inside-out signaling and also “ligand-induced integrin activation”, but is not required for outside-in signaling. Integrin ligation induces transient talin dissociation and Gα13 binding to an ExE motif, which selectively mediates outside-in signaling and platelet spreading. The second talin binding wave is associated with clot retraction. An ExE motif-based inhibitor of Gα13-integrin interaction selectively abolishes outside-in signaling without affecting integrin ligation, and suppresses occlusive arterial thrombosis without affecting bleeding time. Thus, we have discovered a novel mechanism for the directional switch of integrin signaling and, based on this mechanism, we designed a potent new anti-thrombotic that does not cause bleeding.

Leptin Receptor + (LepR + ) stromal cells in adult bone marrow are a critical source of growth factors, including Stem Cell Factor (SCF), for the maintenance of hematopoietic stem cells (HSCs) and early restricted progenitors 1 – 6 . LepR + cells are heterogeneous, including skeletal stem cells, osteogenic, and adipogenic progenitors 7 – 12 , though few markers have been available to distinguish these subsets or to compare their functions. Here we show expression of an osteogenic growth factor, Osteolectin 13 , 14 , distinguishes peri-arteriolar LepR + cells poised to undergo osteogenesis from peri-sinusoidal LepR + cells poised to undergo adipogenesis (but retaining osteogenic potential). Peri-arteriolar LepR + Osteolectin + cells are rapidly dividing, short-lived, osteogenic progenitors that increase in number after fracture and are depleted during aging. Deletion of Scf from adult Osteolectin + cells did not affect the maintenance of HSCs or most restricted progenitors but depleted common lymphoid progenitors (CLPs), impairing lymphopoiesis, bacterial clearance, and survival after acute bacterial infection. Peri-arteriolar Osteolectin + cell maintenance required mechanical stimulation. Voluntary running increased, while hindlimb unloading decreased, the frequencies of peri-arteriolar Osteolectin + cells and CLPs. Deletion of the mechanosensitive ion channel, Piezo1 , from Osteolectin + cells depleted Osteolectin + cells and CLPs. A peri-arteriolar niche for osteogenesis and lymphopoiesis in bone marrow is maintained by mechanical stimulation and depleted during aging.

The integrin family of cell adhesion receptors mediates bi-directional signaling: “inside-out” signaling activates the ligand binding function of integrins and “outside-in” signaling mediates cellular responses induced by ligand binding to integrins leading to cell spreading, retraction, migration, and proliferation. Integrin signaling requires both heterotrimeric G proteins and monomeric small G proteins. This review focuses on recent development in the roles of G proteins in integrin outside-in signaling. The finding of direct interaction between the heterotrimeric G protein subunit Gα13 and integrin β subunits reveals a new mechanism for integrin signaling, and also uncovers a crosstalk between the signaling pathways initiated by G protein-coupled receptors (GPCRs) and integrins. This crosstalk, which may be referred to as “inside-outside-in” signaling, dynamically regulates contractility and greatly promotes integrin outside-in signaling

Interleukin 4 (IL‐4) exerts a decisive role in the coordination of protective immune responses against parasites, particularly helminths. A disregulation of IL‐4 function is possibly involved in the genesis of allergic disease states. The search for important amino acid residues in human IL‐4 by mutational analysis of charged invariant amino acid positions identified two distinct functional sites in the 4‐helix‐bundle protein. Site 1 was marked by amino acid substitutions of the glutamic acid at position 9 in helix A and arginine at position 88 in helix C. Exchanges at both positions led to IL‐4 variants deficient in binding to the extracellular domain of the IL‐4 receptor (IL‐4R(ex)). In parallel, up to 1000‐fold increased concentrations of this type of variant were required to induce T‐cell proliferation and B‐cell CD23 expression. Site 2 was marked by amino acid exchanges in helix D at positions 121, 124 and 125 (arginine, tyrosine and serine respectively in the wild‐type). IL‐4 variants affected at site 2 exhibited partial agonist activity during T‐cell proliferation; however, they still bound with high affinity to IL‐4R(ex). [The generation of an IL‐4 antagonist by replacing tyrosine 124 with aspartic acid has been described before by Kruse et al. (1992) (EMBO J., 11, 3237‐3244)]. These findings indicate that IL‐4 functions by binding IL‐4R(ex) via site 1 which is constituted by residues on helices A and C.(ABSTRACT TRUNCATED AT 250 WORDS)

Objective Reactive oxygen species (ROS) are known to regulate platelet activation; however, the mechanisms of ROS production during platelet activation remain unclear. Platelets express different isoforms of nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidases (NOXs). Here we investigated the role of NOX1 and NOX2 in ROS generation and platelet activation using NOX1 and NOX2 knockout mice. Approach and Results NOX1−/Y platelets showed selective defects in G protein-coupled receptor (GPCR)-mediated platelet activation induced by thrombin and thromboxane A2 analog U46619, but were not affected in platelet activation induced by collagen-related peptide (CRP), a glycoprotein VI (GPVI) agonist. In contrast, NOX2−/− platelets showed potent inhibition of CRP-induced platelet activation, and also showed partial inhibition of thrombin-induced platelet activation. Consistently, production of ROS was inhibited in NOX1−/Y platelets stimulated with thrombin, but not CRP, whereas NOX2−/− platelets showed reduced ROS generation induced by CRP or thrombin. Reduced ROS generation in NOX1/2 deficient platelets is associated with impaired activation of Syk and phospholipase Cγ2 (PLCγ2), but minimally affected mitogen-activated protein kinase pathways. Interestingly, laser-induced arterial thrombosis was impaired but the bleeding time was not affected in NOX2−/− mice. WT thrombocytopenic mice injected with NOX2−/− platelets also showed defective arterial thrombosis, suggesting an important role for platelet NOX2 in thrombosis in vivo but not hemostasis. Conclusions NOX1 and NOX2 play differential roles in different platelet activation pathways and in thrombosis. ROS generated by these enzymes promotes platelet activation via the Syk/PLCγ/calcium signaling pathway.