Cancer stem cells (CSCs) are critical for cancer progression and chemoresistance. How lipid metabolism regulates CSCs and chemoresistance remains elusive. Here, we demonstrate that JAK/STAT3 regulates lipid metabolism, which promotes breast CSCs (BCSCs) and cancer chemoresistance. Inhibiting JAK/STAT3 blocks BCSC self-renewal and expression of diverse lipid metabolic genes, including carnitine palmitoyltransferase 1B (CPT1B), which encodes the critical enzyme for fatty acid β-oxidation (FAO). Moreover, mammary-adipocyte-derived leptin upregulates STAT3-induced CPT1B expression and FAO activity in BCSCs. Human breast-cancer-derived data suggest that the STAT3-CPT1B-FAO pathway promotes cancer cell stemness and chemoresistance. Blocking FAO and/or leptin re-sensitizes them to chemotherapy and inhibits BCSCs in mouse breast tumors in vivo. We identify a critical pathway for BCSC maintenance and breast cancer chemoresistance.

Highlights d STAT3 in CD8 + T effector cells upregulates FAO while inhibiting glycolysis and IFNg d PD-1 increases FAO and inhibits IFNg through activating STAT3 in tumor CD8+ T cells d Leptin associated with increased fat tissues activates STAT3 in CD8 + T effector cells d Blocking leptin-STAT3-FAO pathway reactivates breast tumor CD8 + T cells

Chronic graft-versus-host disease (cGVHD) is an autoimmune-like syndrome mediated by pathogenic CD4+ T and B cells, but the function of extrafollicular and germinal center CD4+ T and B interactions in cGVHD pathogenesis remains largely unknown. Here we show that extrafollicular CD4+ T and B interactions are sufficient for inducing cGVHD, while germinal center formation is dispensable. The pathogenesis of cGVHD is associated with the expansion of extrafollicular CD44hiCD62loPSGL-1loCD4+ (PSGL-1loCD4+) T cells. These cells express high levels of ICOS, and the blockade of ICOS/ICOSL interaction prevents their expansion and ameliorates cGVHD. Expansion of PSGL-1loCD4+ T cells is also prevented by BCL6 or Stat3 deficiency in donor CD4+ T cells, with the induction of cGVHD ameliorated by BCL6 deficiency and completely suppressed by Stat3 deficiency in donor CD4+ T cells. These results support that Stat3- and BCL6-dependent extrafollicular CD4+ T and B interactions play critical functions in the pathogenesis of cGVHD.

STIM1 and STIM2 are dynamic transmembrane endoplasmic reticulum Ca 2؉ sensors, coupling directly to activate plasma membrane Orai Ca 2؉ entry channels. Despite extensive sequence homology, the STIM proteins are functionally distinct. We reveal that the short variable N-terminal random coil sequences of STIM1 and STIM2 confer profoundly different activation properties. Using Orai1-expressing HEK293 cells, chimeric replacement of the 43-amino-acid STIM1 N terminus with that of STIM2 attenuates Orai1-mediated Ca 2؉ entry and drastically slows store-induced Orai1 channel activation. Conversely, the 55-amino-acid STIM2 terminus substituted within STIM1 strikingly enhances both Orai1-mediated Ca 2؉ entry and constitutive coupling to activate Orai1 channels. Hence, STIM N termini are powerful coupling modifiers, functioning in STIM2 to "brake" the otherwise constitutive activation of Orai1 channels afforded by its high sensitivity to luminal Ca 2؉ .The transmembrane ER 4 proteins STIM1 and STIM2 function as sensors of Ca 2ϩ within ER stores (1, 2). Depletion of luminal Ca 2ϩ within the ER triggers aggregation and translocation of STIMs into junctions closely associated with the plasma membrane, where they activate the highly Ca 2ϩ -selective Orai family of store-operated channels (SOCs) via conformational coupling (3-8). Recent investigations of the cytoplasmic portion of STIM1 revealed that it alone is sufficient to activate Orai (9 -12) via a short (ϳ100 amino acids) region centered around the second coiled-coil domain (see Fig. 1) (13-15). However, although activation of Orai1 is mediated entirely within the C-terminal portion of STIM, physiological control of STIM1 and STIM2 is exerted via their N-terminal ER-luminal Ca 2ϩ -sensing domains. The extent to which structural differences between these domains in STIM1 and STIM2 contribute to their distinct properties (16 -19) remains poorly understood. Although STIM2 has the capacity to sense ER Ca 2ϩ and activate SOCs (16,17,19), overexpressed STIM2 inhibits endogenous SOCs (18). Moreover, the kinetics of SOC activation by STIM2 are much slower than STIM1 (17). STIM2 was recently revealed to have a decreased Ca 2ϩ -sensing affinity when compared with STIM1 by virtue of three amino acid substitutions in the Ca 2ϩ -binding EF-hand domain (16). Although the lower affinity of the STIM2 EF-hand accounts for differences in the activation thresholds of STIM1 and STIM2 (16,20,21), it does not explain the slow kinetics of STIM2 nor its dominance over endogenous SOC activation. However, recent investigations reveal similar abilities of the cytosolic portions of STIM1 and STIM2 to activate Orai1 (12). Hence, although activation of Orai1 is mediated entirely within the C-terminal portion of STIM, physiological control of STIM1 and STIM2 is exerted via their N-terminal ER-luminal Ca 2ϩ -sensing domains.The initial triggering events for STIM1 and STIM2 proteins involve the unfolding and aggregation of the N-terminal domains resulting from dissociation of Ca 2ϩ from the luminal EF-h...

Store-operated calcium entry (SOCE) is a key evolutionarily conserved process whereby decreases in endoplasmic reticulum Ca 2؉ content lead to the influx of Ca 2؉ across the plasma membrane. How this process is regulated in specific tumor cell types is poorly understood. In an effort to address this concern, we obtained and tested primary Wilms tumor cells, finding no detectable SOCE in this cell type. Analysis of the expression levels of STIM1 and ORAI1 (the molecular mediators of SOC) revealed poor STIM1 expression. Analysis of the STIM1 promoter using the TESS search system (University of Pennsylvania) revealed four putative response elements to the zinc-finger proteins WT1 (Wilms tumor suppressor 1) and EGR1 (early growth response 1). Either overexpression of WT1 or knockdown of EGR1 resulted in loss of STIM1 expression and a resultant decrease in SOCE. Furthermore, examination of Egr1 knock-out animals revealed loss of STIM1 expression in multiple tissues. Finally, using chromatin immunoprecipitation, we reveal direct binding of both WT1 and EGR1 to putative response elements located within 500 bp of the transcriptional start site of STIM1. Considering that WT1 and EGR1 are well described oncogenes and tumor suppressors, these observations may reveal new mechanisms responsible for distinct Ca 2؉ signals in cancer cells. Changes in cytosolic Ca2ϩ levels are a common component of the signal transduction pathways for numerous growth factors and cytokines. Thus, activation of phospholipase C-coupled receptors (primarily via either G protein or tyrosine kinase receptors) results in the generation of the second messenger inositol 1,4,5-trisphosphate (1). Inositol 1,4,5-trisphosphate diffuses rapidly through the cytosol and interacts with its receptor on the endoplasmic reticulum (ER), 2 resulting in both transient ER Ca 2ϩ release and a lengthy increased influx of Ca 2ϩ across the plasma membrane, a process termed capacitative or store-operated Ca 2ϩ entry (SOCE) (2). SOCE has been shown to regulate numerous fundamental processes in cell biology, including migration (3, 4), proliferation (4 -6), and differentiation (7,8). Given the impact of these pathways on cancer cell biology, it is not surprising that altered Ca 2ϩ signaling can be observed in numerous classes of cancer cells. Indeed, inhibition of either the phosphatidylinositol pathway (9) or calcium influx (10, 11) can induce either growth arrest or cell death in a variety of tumor cells. Despite these observations, Ca 2ϩ signals remain poorly utilized therapeutic targets. This is in part because these studies were all performed prior to the discovery of the identities of the molecular mediators of SOCE. Without this insight, it was not possible to link changes in Ca 2ϩ signals with changes in the expression and function of oncogenes and tumor suppressors that cause tumor formation.After nearly 20 years of investigations into the mysteries of SOCE, the identities of the key molecular components of this process have finally been revealed (for recent reviews...