The initiation of a primary immune response requires contact between dendritic cells (DCs) and resting T cells. However, little is known about the proteins that mediate this initial contact. We show here that neuropilin-1, a receptor involved in axon guidance, was expressed by human DCs and resting T cells both in vitro and in vivo. The initial contact between DCs and resting T cells led to neuropilin-1 polarization on T cells. DCs and resting T cells specifically bound soluble neuropilin-1, and resting T cells formed clusters with neuropilin-1-transfected COS-7 cells in a neuropilin-1-dependent manner. Functionally, preincubation of DCs or resting T cells with blocking neuropilin-1 antibodies inhibited DC-induced proliferation of resting T cells. These data suggest that neuropilin-1 mediates interactions between DCs and T cells that are essential for initiation of the primary immune response and show parallels between the nervous and immune systems.

Activation of de novo fatty acid synthesis is a characteristic feature of cancer cells. We have recently described an interaction between acetyl-CoA carboxylase A (ACCA), a key enzyme in fatty acid synthesis, and BRCA1, which indicates a possible connection between lipid synthesis and genetic factors involved in susceptibility to breast and ovarian cancers. For this reason, we explored the role of ACCA in breast cancer cell survival using an RNA interference (RNAi) approach. We show that specific silencing of either the ACCA or the fatty acid synthase (FAS) genes in cancer cells results in a major decrease in palmitic acid synthesis. Depletion of the cellular pool of palmitic acid is associated with induction of apoptosis concomitant with the formation of reactive oxygen species (ROS) and mitochondrial impairment. Expression of a small interfering RNA (siRNA)-resistant form of ACCA mRNA prevented the effect of ACCA-RNAi but failed to prevent the effect of FAS gene silencing. Furthermore, supplementation of the culture medium with palmitate or with the antioxidant vitamin E resulted in the complete rescue of cells from both ACCA and FAS siRNA-induced apoptosis. Finally, human mammary epithelial cells are resistant to RNAi against either ACCA or FAS. These data confirm the importance of lipogenesis in cancer cell survival and indicate that this pathway represents a key target for antineoplastic therapy that, however, might require specific dietary recommendation for full efficacy. (Cancer Res 2006; 66(10): 5287-94)

Key Points• In polycythemia vera RBCs, JAK2V617F is able to activate an adhesion molecule through a Rap1/Akt pathway, despite the absence of EpoR.• In polycythemia vera, the abnormal adhesion of RBCs to laminin is due to the phosphorylation of Lu/BCAM by a JAK2V617F/Rap1/Akt pathway.Polycythemia vera (PV) is characterized by an increased RBC mass, spontaneous erythroid colony formation, and the JAK2V617F mutation. PV is associated with a high risk of mesenteric and cerebral thrombosis. PV RBC adhesion to endothelial laminin is increased and mediated by phosphorylated erythroid Lu/BCAM. In the present work, we investigated the mechanism responsible for Lu/BCAM phosphorylation in the presence of JAK2V617F using HEL and BaF3 cell lines as well as RBCs from patients with PV. High levels of Rap1-GTP were found in HEL and BaF3 cells expressing JAK2V617F compared with BaF3 cells with wild-type JAK2. This finding was associated with increased Akt activity, Lu/BCAM phosphorylation, and cell adhesion to laminin that were inhibited by the dominant-negative Rap1S17N or by the specific Rap1 inhibitor GGTI-298. Surprisingly, knocking-down EpoR in HEL cells did not alter Akt activity or cell adhesion to laminin. Our findings reveal a novel EpoR-independent IntroductionPolycythemia vera (PV) is the most common myeloproliferative neoplasm. 1 It is characterized by erythropoietin-independent erythroid colony formation in vitro, which is associated with somatic gain-of-function mutations in the gene encoding the tyrosine kinase JAK2. [2][3][4][5] The most frequent mutation is a substitution from valine to phenylalanine at position 617, which renders JAK2 constitutively active, leading to uncontrolled cell proliferation in the erythroid lineage and resulting in increased red cell mass. Patients with PV exhibit increased platelet and leukocyte counts and have a high risk of thrombosis, which is considered a major cause of mortality and morbidity in this disease. 6 In a previous work, we showed that PV RBCs were abnormally adherent to endothelial cells because of the interaction between erythroid Lutheran/basal cell-adhesion molecule (Lu/BCAM) and endothelial laminin. 7 Lu/BCAM is an adhesion protein of the immunoglobulin superfamily with a large tissue distribution. 8,9 It is the unique erythroid receptor of laminin ␣5 chain, constituent of laminin 511/521 isoforms, and a major component of the extracellular matrix. 10,11 Lu/BCAM is expressed as 2 isoforms of 85 and 78 kDa, named Lu and Lu(v13), respectively. 9,10 The 2 isoforms differ only by the length of their cytoplasmic domain, which is composed of 19 a.a. for Lu(v13) and 59 a.a. for Lu. The extra 40 a.a. of Lu comprise phosphorylated serines, 12 which have been shown to play a critical role in Lu/BCAM-mediated RBC adhesion to laminin in sickle cell disease. 13,14 We showed in our previous work that PV RBC adhesion to laminin was associated with Lu/BCAM hyperphosphorylation. Lu/BCAM phosphorylation also was strongly increased in a K562 cell line coexpressing Lu and JAK2V617F, ...