SUMMARY ID genes are required for breast cancer colonization of the lungs, but the mechanism remains poorly understood. Here, we show that Id1 expression induces a stem-like phenotype in breast cancer cells, while retaining epithelial properties, contrary to the notion that cancer stem-like properties are inextricably linked to the mesenchymal state. During metastatic colonization, Id1 induces a mesenchymal-to-epithelial transition (MET), specifically in cells whose mesenchymal state is dependent on the Id1 target protein Twist1 but not at the primary site, where this state is controlled by the zinc-finger protein Snail1. Knockdown of Id expression in metastasizing cells prevents MET and dramatically reduces lung colonization. Furthermore, Id1 is induced by TGFβ only in cells that have first undergone EMT, demonstrating that EMT is a pre-requisite for subsequent Id1-induced MET during lung colonization. Collectively, these studies underscore the importance of Id-mediated phenotypic switching during distinct stages of breast cancer metastasis.

COX-2-dependent prostaglandin (PG) E 2 synthesis regulates macrophage MMP expression, which is thought to destabilize atherosclerotic plaques. However, the administration of selective COX-2 inhibitors paradoxically increases the frequency of adverse cardiovascular events potentially through the loss of anti-inflammatory prostanoids and/or disturbance in the balance of pro-and anti-thrombotic prostanoids. To avoid these collateral effects of COX-2 inhibition, a strategy to identify and block specific prostanoid-receptor interactions may be required. We previously reported that macrophage engagement of vascular extracellular matrix (ECM) triggers proteinase expression through a MAPK erk1/2 -dependent increase in COX-2 expression and PGE 2 synthesis. Here we demonstrate that elicited macrophages express the PGE 2 receptors EP1-4. When plated on ECM, their expression of EP2 and EP4, receptors linked to PGE 2 -induced activation of adenylyl cyclase, is strongly stimulated. Forskolin and dibutryl cyclic-AMP stimulate macrophage matrix metalloproteinase (MMP)-9 expression in a dose-dependent manner. However, an EP2 agonist (butaprost) has no effect on MMP-9 expression, and macrophages from EP2 null mice exhibited enhanced COX-2 and MMP-9 expression when plated on ECM. In contrast, the EP4 agonist (PGE 1 -OH) stimulated macrophage MMP-9 expression, which was inhibited by the EP4 antagonist ONO-AE3-208. When compared with COX-2 silencing by small interfering RNA or inhibition by celecoxib, the EP4 antagonist was as effective in inhibiting ECM-induced proteinase expression. In addition, ECM-induced MMP-9 expression was blocked in macrophages in which EP4 was silenced by small interfering RNA. Thus, COX-2-dependent ECM-induced proteinase expression is effectively blocked by selective inhibition of EP4, a member of the PGE 2 family of receptors.Atherosclerosis is a chronic inflammatory disease characterized by lipid accumulation, macrophage recruitment, smooth muscle proliferation, and fibrosis (1, 2). Macrophage proteinase expression compromises the structural integrity of atherosclerotic lesions by degrading components of the extracellular matrix (ECM), 2 which contributes to lesion ulceration or rupture and subsequent sequelae of thrombosis, myocardial infarction, and stroke (3-6). A substantial body of evidence has identified cyclooxygenase (COX)-2 as a targetable component of the signaling pathway responsible for increased proteinase expression by macrophages in atherosclerotic lesions. COX metabolizes arachidonic acid to an unstable endoperoxide, which is then converted to the principal prostaglandins (PG) by specific synthases (7,8). COX-2 expression is elevated in atherosclerotic lesions (9 -14). PGE 2 , an important mediator of the inflammatory response, stimulates proteinase expression by a variety of cells including macrophages (15-18). Both PGE synthase and matrix metalloproteinase (MMP) activities are elevated in regions of symptomatic plaques rich in macrophages and susceptible to rupture (13,19). Moreover, tr...

Understanding the mechanism by which embryonic stem (ES) cells self-renew is crucial for the realization of their therapeutic potential. Earlier, overexpression of Id proteins was shown to be sufficient to maintain mouse ES cells in a self-renewing state even in the absence of serum. Here, we use ES cells derived from Id deficient mice to investigate the requirement for Id proteins in maintaining ES cell self-renewal. We find that Id1(-/-) ES cells have a defect in self-renewal and a propensity to differentiate. We observe that chronic or acute loss of Id1 leads to a down-regulation of Nanog, a critical regulator of self-renewal. In addition, in the absence of Id1, ES cells express elevated levels of Brachyury, a marker of mesendoderm differentiation. We find that loss of both Nanog and Id1 is required for the up-regulation of Brachyury, and ectopic Nanog expression in Id1(-/-) ES cells rescues the self-renewal defect, indicating that Nanog is the major downstream target of Id1. These results identify Id1 as a critical factor in the maintenance of ES cell self-renewal and suggest a plausible mechanism for its control of lineage commitment.