Caveolin-1 and integrin β1 regulate embryonic stem cell proliferation via p38 MAPK and FAK in high glucose

The involvement of caveolin-1 (Cav-1) and integrin β1 (IN β1) in regulation of embryonic stem (ES) cell growth by high glucose is by no means clear cut. Therefore, the aim of this study was to examine the influence of high glucose on Cav-1 and IN β1 expression in mouse ES cells and their signaling pathways to modulate proliferation. High glucose significantly increased Cav-1 and IN β1 expression. In addition, increased IN β1 expression was inhibited by Cav-1 small interfering RNA (siRNA). High glucose caused reactive oxygen species generation and p38 mitogen-activated protein kinase (MAPK) phosphorylation. Inhibition of p38 MAPK blocked high glucose-induced Cav-1 and fibronectin (FN) expression. Moreover, phosphorylation of both Src and focal adhesion kinase (FAK) were increased by high glucose, which were inhibited by IN β1 antibody. In addition, high glucose increased the expression levels of PINCH1/2, integrin-linked kinase (ILK), and α-parvin [PIP] complex proteins, which were all inhibited by the FAK siRNA and Src specific inhibitor (PP2, 10(-7) M). High glucose also increased F-actin expression, which was inhibited by ILK, PINCH1/2, and α-parvin siRNAs. Finally, high glucose-induced increase of ES cell proliferation was inhibited by TRIO and F-actin binding protein (TRIOBP) siRNA. The results demonstrate that high glucose-induced Cav-1 and IN β1 activation can stimulate ES cell proliferation through the modification of focal adhesion signaling pathways.     

Gbetagamma activation of Src induces caveolae-mediated endocytosis in endothelial cells

Caveolae-mediated endocytosis in endothelial cells is stimulated by the binding of albumin to gp60, a specific albumin-binding protein localized in caveolae. The activation of gp60 induces its cell surface clustering and association with caveolin-1, the caveolar-scaffolding protein. This interaction leads to G(i)-induced Src kinase activation, which in turn signals dynamin-2-mediated fission and directed migration of caveolae-derived vesicles from apical to basal membrane. In this study, we investigated the possible role of the Gbetagamma heterodimer in signaling G(i)-induced Src activation and subsequent caveolae-mediated endocytosis. We observed using rat lung microvascular endothelial cells that expression of the C terminus of beta-adrenergic receptor kinase (ct-betaARK), an inhibitor Gbetagamma signaling, prevented gp60-dependent Src activation as well as caveolae-mediated endocytosis and transcellular transport of albumin and uptake of cholera toxin subunit B, a specific marker of caveolae internalization. Expression of ct-betaARK also prevented Src-mediated tyrosine phosphorylation of caveolin-1 and dynamin-2 and the resultant phosphorylation-dependent association of dynamin-2 and caveolin-1. Also, the direct activation of Gbetagamma using a specific cell-permeant activating peptide (myristoylated-SIRKALNILGYPDYD) simulated the effects of gp60 in inducing Src activation, caveolin-1, and dynamin-2 phosphorylation as well as caveolae-mediated endocytosis of cholera toxin subunit B. The myristoylated-SIRKALNILGYPDYD peptide-induced responses were inhibited by the expression of ct-betaARK. Taken together, our results demonstrate that Gbetagamma activation of Src signals caveolae-mediated endocytosis and transendothelial albumin transport via transcytosis.     

Caveolin-1-deficient mice show accelerated mammary gland development during pregnancy,premature lactation,and hyperactivation of the Jak-2/STAT5a signaling cascade

It is well established that mammary gland development and lactation are tightly controlled by prolactin signaling. Binding of prolactin to its cognate receptor (Prl-R) leads to activation of the Jak-2 tyrosine kinase and the recruitment/tyrosine phosphorylation of STAT5a. However, the mechanisms for attenuating the Prl-R/Jak-2/STAT5a signaling cascade are just now being elucidated. Here, we present evidence that caveolin-1 functions as a novel suppressor of cytokine signaling in the mammary gland, akin to the SOCS family of proteins. Specifically, we show that caveolin-1 expression blocks prolactin-induced activation of a STAT5a-responsive luciferase reporter in mammary epithelial cells. Furthermore, caveolin-1 expression inhibited prolactin-induced STAT5a tyrosine phosphorylation and DNA binding activity, suggesting that caveolin-1 may negatively regulate the Jak-2 tyrosine kinase. Because the caveolin-scaffolding domain bears a striking resemblance to the SOCS pseudosubstrate domain, we examined whether Jak-2 associates with caveolin-1. In accordance with this homology, we demonstrate that Jak-2 cofractionates and coimmunoprecipitates with caveolin-1. We next tested the in vivo relevance of these findings using female Cav-1 (-/-) null mice. If caveolin-1 normally functions as a suppressor of cytokine signaling in the mammary gland, then Cav-1 null mice should show premature development of the lobuloalveolar compartment because of hyperactivation of the prolactin signaling cascade via disinhibition of Jak-2. In accordance with this prediction, Cav-1 null mice show accelerated development of the lobuloalveolar compartment, premature milk production, and hyperphosphorylation of STAT5a (pY694) at its Jak-2 phosphorylation site. In addition, the Ras-p42/44 MAPK cascade is hyper-activated. Because a similar premature lactation phenotype is observed in SOCS1 (-/-) null mice, we conclude that caveolin-1 is a novel suppressor of cytokine signaling.     

Involvement of cell-cell interactions in the rapid stimulation of Cas tyrosine phosphorylation and Src kinase activity by transforming growth factor-beta 1

Transforming growth factor-beta (TGF-beta) regulates a wide range of physiological and pathological cellular processes, including cell migration, mesenchymal transition, extracellular matrix synthesis, and cell death. Cas (Crk-associated substrate, 130 kDa), an adaptor protein localized at focal adhesions and stress fibers, is also known to have important functions in cell migration and the induction of immediate-early gene expression. Here, we report that a rapid and transient tyrosine phosphorylation of Cas is induced by TGF-beta 1 and that E-cadherin-mediated cell-cell interaction and the Src kinase pathway are involved in this early TGF-beta signaling. The addition of TGF-beta 1 to epithelial cells rapidly induced tyrosine phosphorylation of Cas and promoted the formation of complexes between focal adhesion molecules. Cas phosphorylation required the integrity of the actin cytoskeleton but was not dependent on cell adhesion, implying that Cas-dependent signaling may be distinct from integrin signaling. TGF-beta 1 also stimulated Src kinase activity, and specific inhibitors of Src completely blocked the induction of Cas phosphorylation by TGF-beta 1. The Cas phosphorylation and Src kinase activation seen in our results were induced in an epithelial phenotype-specific manner. Stable transfection of E-cadherin to L929 cells and L cells as well as E-cadherin blocking assay revealed that E-cadherin-mediated cell-cell interactions were essential for both Cas phosphorylation and Src kinase activation. Taken together, our data suggest that rapid Cas phosphorylation and Src kinase activation may play a novel role in TGF-beta signal transduction.     

RAGE recycles at the plasma membrane in S100B secretory vesicles and promotes Schwann cells morphological changes

RAGE is a multiligand receptor of the immunoglobulin superfamily involved in regeneration of injured peripheral nerve and cell motility. RAGE is implicated in the development of various chronic diseases, such as neurodegenerative disorders, inflammatory responses, and diabetic complications. The correlation between RAGE endocytic trafficking and RAGE function is still uninvestigated. S100B is one of the ligands of RAGE. The molecular mechanisms responsible of S100B translocation in exocytic vesicles are still poorly investigated. In the present study we elucidate the role of RAGE endocytic trafficking in promoting S100B secretion in Schwann cells. Here we show that RAGE-induced secretion of S100B requires phosphorylated caveolin1-dependent endocytosis of RAGE. Endocytosis of RAGE in response to ligand binding promotes the fusion of endosomes with S100B-positive secretory vesicles. Src promotes the fusion of endosomes with S100B-secretory vesicles. Inhibition of src induces RAGE degradation. RAGE-mediated src activation induces cav1 phosphorylation and relocalization in the perinuclear compartment. RAGE signaling and recycling are required for S100-induced Schwann cells morphological changes and are inhibited by high-glucose, suggesting a possible link between diabetes and peripheral nerve injury. Indeed, high glucose inhibits RAGE-mediated src activation. Src inhibition blocks RAGE recycling, S100B secretion, and morphological changes. In summary, we identified a novel pathway of vesicular trafficking required for the amplification of RAGE signaling and cytoskeleton dynamics that is potentially involved in the regeneration of injured peripheral nerve.     

Caveolin-1 phosphorylation in human squamous and epidermoid carcinoma cells: dependence on ErbB1 expression and Src activation

Previous studies have shown that EGF can induce the tyrosine phosphorylation of caveolin-1 in murine fibroblasts following ErbB1 (EGF receptor) mutation or overexpression, but the cell signaling events linking EGF action with caveolin phosphorylation are not fully established. In this regard, we examined multiple human carcinoma cell lines that express various ErbB family members, including A431 epidermoid carcinoma cells and several squamous carcinoma cell lines. In all cases, EGF treatment induced the tyrosine phosphorylation of caveolin-1 in a time- and EGF dose-dependent manner, and immunoblotting analysis revealed that this phosphorylation occurred at tyrosine-14. The EGF-dependent phosphorylation of caveolin-1 was observed at low temperatures (4 degrees C) and was enhanced by caveolae-disrupting agents (cyclodextrin), suggesting that this EGF-dependent system is in a low temperature-stable arrangement that allows for their interaction under conditions where mobility in the membrane is altered. To further assess the events linking EGF action with caveolin phosphorylation, we evaluated the ligand specificity of these responses and their dependence on known effectors of EGF receptor function. We observed that EGF and HB-EGF, but not heregulin, promoted caveolin-1 phosphorylation in A431 cells, suggesting that these responses are linked to EGF receptor activation and not solely occurring via the activation of other endogenous ErbB family members. In addition, the EGF-induced phosphorylation of caveolin-1 in A431 cells was blocked by the Src kinase antagonists PP1 and PP2, but not by the MEK inhibitor PD98059, the phosphoinositide 3-kinase inhibitors LY294002 and wortmannin, or cytoskeleton-disrupting agents, such as cytochalasin D, colchicine, and nocadazole. Altogether, these data indicate that multiple human carcinoma cells exhibit an EGF receptor-dependent tyrosine phosphorylation of caveolin-1 and that this process is sensitive to Src family kinase inhibitors. These observations support a role for caveolin tyrosine phosphorylation in the profile of cellular responses by which Src potentiates cancer progression following EGF receptor overexpression.     

Sphingosine 1-phosphate induces membrane ruffling and increases motility of human umbilical vein endothelial cells via vascular endothelial growth factor receptor and CrkII

Sphingosine 1-phosphate (S1P), a ligand for endothelial differentiation gene family proteins, is one of the most potent signal mediators released from activated platelets. Here, we report that S1P induces membrane ruffling of human umbilical vein endothelial cells (HUVECs) via the vascular endothelial growth factor receptor (VEGFR), Src family tyrosine kinase(s), and the CrkII adaptor protein. S1P induced prominent phosphorylation of CrkII in HUVECs, indicating that CrkII was involved in the S1P-induced signaling pathway. S1P-induced CrkII phosphorylation was blocked by pertussis toxin and overexpression of the carboxyl terminus of beta-adrenergic receptor kinase, indicating that the betagamma subunit of G(i) was required for the phosphorylation. Notably, the S1P-induced CrkII phosphorylation was also abolished by inhibitors of VEGFR or Src family tyrosine kinases. By using Picchu, a real time monitoring protein for CrkII phosphorylation, we found that S1P induced rapid CrkII phosphorylation at membrane ruffles. Finally, we observed that expression of a dominant negative mutant of CrkII inhibited the S1P-induced membrane ruffling and cell migration. These results delineated a novel S1P signaling pathway that involves sequential activation of G(i)-coupled receptor(s), VEGFR, Src family tyrosine kinase(s), and the CrkII adaptor protein, and which is responsible for both the induction of membrane ruffling and the increase in cell motility.     

Src-mediated tyrosine phosphorylation of caveolin-1 induces its association with membrane type 1 matrix metalloproteinase

We have recently shown that stimulation of endothelial cells with vascular endothelial growth factor (VEGF) induces dissociation of caveolin-1 from the VEGFR-2 receptor, followed by Src family kinase-dependent tyrosine phosphorylation of the protein (Labrecque, L., Royal, I., Surprenant, D. S., Patterson, C., Gingras, D., and Beliveau, R. (2003) Mol. Biol. Cell 14, 334-347). In this study, we provide evidence that the VEGF-dependent tyrosine phosphorylation of caveolin-1 induces interaction of the protein with the membrane-type 1 matrix metalloproteinase (MT1-MMP). This interaction requires the phosphorylation of caveolin-1 on tyrosine 14 by members of the Src family of protein kinases, such as Src and Fyn, because it is completely abolished by expression of a catalytically inactive Src mutant or by site-directed mutagenesis of tyrosine 14 of caveolin-1. Most interestingly, the association of MT1-MMP with phosphorylated caveolin-1 induced the recruitment of Src and a concomitant inhibition of the kinase activity of the enzyme, suggesting that this complex may be involved in the negative regulation of Src activity. The association of MT1-MMP with phosphorylated caveolin-1 occurs in caveolae membranes and involves the cytoplasmic domain of MT1-MMP because it was markedly reduced by mutation of Cys574 and Val582 residues of the cytoplasmic tail of the enzyme. Most interestingly, the reduction of the interaction between MT1-MMP and caveolin-1 by using these mutants also decreases MT1-MMP-dependent cell locomotion. Overall these results indicate that MT1-MMP associates with tyrosine-phosphorylated caveolin-1 and that this complex may play an important role in MT1-MMP regulation and function.     

Caveolin-1-enhanced motility and focal adhesion turnover require tyrosine-14 but not accumulation to the rear in metastatic cancer cells

Caveolin-1 is known to promote cell migration, and increased caveolin-1 expression is associated with tumor progression and metastasis. In fibroblasts, caveolin-1 polarization and phosphorylation of tyrosine-14 are essential to promote migration. However, the role of caveolin-1 in migration of metastatic cells remains poorly defined. Here, caveolin-1 participation in metastatic cell migration was evaluated by shRNA targeting of endogenous caveolin-1 in MDA-MB-231 human breast cancer cells and ectopic expression in B16-F10 mouse melanoma cells. Depletion of caveolin-1 in MDA-MB-231 cells reduced, while expression in B16-F10 cells promoted migration, polarization and focal adhesion turnover in a sequence of events that involved phosphorylation of tyrosine-14 and Rac-1 activation. In B16-F10 cells, expression of a non-phosphorylatable tyrosine-14 to phenylalanine mutant failed to recapitulate the effects observed with wild-type caveolin-1. Alternatively, treatment of MDA-MB-231 cells with the Src family kinase inhibitor PP2 reduced caveolin-1 phosphorylation on tyrosine-14 and cell migration. Surprisingly, unlike for fibroblasts, caveolin-1 polarization and re-localization to the trailing edge were not observed in migrating metastatic cells. Thus, expression and phosphorylation, but not polarization of caveolin-1 favor the highly mobile phenotype of metastatic cells.     

Activation of Akt by Advanced Glycation End Products (AGEs): Involvement of IGF-1 Receptor and Caveolin-1

Diabetes is characterized by chronic hyperglycemia, which in turn facilitates the formation of advanced glycation end products (AGEs). AGEs activate signaling proteins such as Src, Akt and ERK1/2. However, the mechanisms by which AGEs activate these kinases remain unclear. We examined the effect of AGEs on Akt activation in 3T3-L1 preadipocytes. Addition of AGEs to 3T3-L1 cells activated Akt in a dose- and time-dependent manner. The AGEs-stimulated Akt activation was blocked by a PI3-kinase inhibitor LY 294002, Src inhibitor PP2, an antioxidant NAC, superoxide scavenger Tiron, or nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase inhibitor DPI, suggesting the involvement of Src and NAD(P)H oxidase in the activation of PI3-kinase-Akt pathway by AGEs. AGEs-stimulated Src tyrosine phosphorylation was inhibited by NAC, suggesting that Src is downstream of NAD(P)H oxidase. The AGEs-stimulated Akt activity was sensitive to Insulin-like growth factor 1 receptor (IGF-1R) kinase inhibitor AG1024. Furthermore, AGEs induced phosphorylation of IGF-1 receptorβsubunit (IGF-1Rβ) on Tyr1135/1136, which was sensitive to PP2, indicating that AGEs stimulate Akt activity by transactivating IGF-1 receptor. In addition, the AGEs-stimulated Akt activation was attenuated by β-methylcyclodextrin that abolishes the structure of caveolae, and by lowering caveolin-1 (Cav-1) levels with siRNAs. Furthermore, addition of AGEs enhanced the interaction of phospho-Cav-1 with IGF-1Rβ and transfection of 3T3-L1 cells with Cav-1 Y14F mutants inhibited the activation of Akt by AGEs. These results suggest that AGEs activate NAD(P)H oxidase and Src which in turn phosphorylates IGF-1 receptor and Cav-1 leading to activation of IGF-1 receptor and the downstream Akt in 3T3-L1 cells. AGEs treatment promoted the differentiation of 3T3-L1 preadipocytes and addition of AG1024, LY 294002 or Akt inhibitor attenuated the promoting effect of AGEs on adipogenesis, suggesting that IGF-1 receptor, PI3-Kinase and Akt are involved in the facilitation of adipogenesis by AGEs.     

S100B protein stimulates microglia migration via RAGE-dependent up-regulation of chemokine expression and release

The Ca(2+)-binding protein of the EF-hand type, S100B, is abundantly expressed in and secreted by astrocytes, and release of S100B from damaged astrocytes occurs during the course of acute and chronic brain disorders. Thus, the concept has emerged that S100B might act an unconventional cytokine or a damage-associated molecular pattern protein playing a role in the pathophysiology of neurodegenerative disorders and inflammatory brain diseases. S100B proinflammatory effects require relatively high concentrations of the protein, whereas at physiological concentrations S100B exerts trophic effects on neurons. Most if not all of the extracellular (trophic and toxic) effects of S100B in the brain are mediated by the engagement of RAGE (receptor for advanced glycation end products). We show here that high S100B stimulates murine microglia migration in Boyden chambers via RAGE-dependent activation of Src kinase, Ras, PI3K, MEK/ERK1/2, RhoA/ROCK, Rac1/JNK/AP-1, Rac1/NF-κB, and, to a lesser extent, p38 MAPK. Recruitment of the adaptor protein, diaphanous-1, a member of the formin protein family, is also required for S100B/RAGE-induced migration of microglia. The S100B/RAGE-dependent activation of diaphanous-1/Rac1/JNK/AP-1, Ras/Rac1/NF-κB and Src/Ras/PI3K/RhoA/diaphanous-1 results in the up-regulation of expression of the chemokines, CCL3, CCL5, and CXCL12, whose release and activity are required for S100B to stimulate microglia migration. Lastly, RAGE engagement by S100B in microglia results in up-regulation of the chemokine receptors, CCR1 and CCR5. These results suggests that S100B might participate in the pathophysiology of brain inflammatory disorders via RAGE-dependent regulation of several inflammation-related events including activation and migration of microglia.     

Caveolin-2-deficient mice show increased sensitivity to endotoxemia

Caveolin proteins are structural components of caveolae and are involved in the regulation of many biological processes. Recent studies have shown that caveolin-1 modulates inflammatory responses and is important for sepsis development. In the present study, we show that caveolin-1 and caveolin-2 have opposite roles in lipopolysaccharide (LPS)-induced sepsis using caveolin-deficient (Cav-1^-/- and Cav-2^-/-) mice for each of these proteins. While Cav-1^-/- mice displayed delayed mortality following challenge with LPS, Cav-2^-/- mice were more sensitive to LPS compared to wild-type (WT). With Cav-2^-/- mice, this effect was associated with increased intestinal injury and increased intestinal permeability. This negative outcome was also correlated with enhanced expression of iNOS in epithelial intestinal cells, and enhanced production of nitric oxide (NO). By contrast, Cav-1^-/- mice demonstrated a decrease in iNOS expression with decreased NO production, but no alteration in intestinal permeability. The differential expression of iNOS was associated with a significant increase of STAT-1 activation in these mice. Intestinal cells of Cav-2^-/- mice showed increased phosphorylation of STAT-1 at tyrosine 701 compared to wild-type. However, Cav-1^-/- mice-derived intestinal cells showed decreased levels of phosphorylation of STAT-1 at tyrosine 701. Since caveolin-2 is almost completely absent in Cav-1^-/- mice, we conclude that it is not just the absence of caveolin-2 that is responsible for the observed effects, but that the balance between caveolin-1 and caveolin-2 is important for iNOS expression and ultimately for sepsis outcome.     

Caveolin-1 up-regulation during epithelial to mesenchymal transition is mediated by focal adhesion kinase

Emerging evidence has shown that caveolin-1 is up-regulated in a number of metastatic cancers and can influence various aspects of cell migration. However, in general, the role of caveolin-1 in cancer progression is poorly understood. In the present study, we examined alterations in caveolin-1 expression during epithelial-to-mesenchymal transition (EMT) and the ability of caveolin-1 to alter cancer cell adhesion, an aspect of cell motility. We employed two EMT cell models, the human embryonic carcinoma cell line NT2/D1, and TGF-beta1-treated NMuMG cells, which are derived from normal mouse mammary epithelia. Caveolin-1 expression was substantially up-regulated in both cell lines following the induction of EMT and was preceded by increased activation of focal adhesion kinase (FAK) and Src, two known tyrosine kinases involved in EMT. We hypothesized that caveolin-1 expression could be influenced by increased FAK phosphorylation, to which Src is a known contributor. Examination of FAK+/+ and FAK-/- mouse embryonic fibroblasts revealed that in cells devoid of FAK, caveolin-1 expression is strikingly diminished. Using FAK and superFAK constructs and the novel FAK inhibitor PF-228, we were able to demonstrate that indeed, FAK can regulate caveolin-1 expression. We also found that Src can contribute to increases in caveolin-1 expression, however, only in the presence of FAK. From the culmination of this data and our functional analyses, we conclude that caveolin-1 expression can be up-regulated during EMT, and further, once expressed, caveolin-1 can greatly influence cancer cell adhesion.     

Src介导骨桥蛋白诱导的血管平滑肌细胞黏附和迁移过程

为阐明酪氨酸激酶Src在整合素被骨桥蛋白(OPN)激活所触发的细胞黏附和迁移信号途径中所起的作用,应用Src特异性抑制剂PP2阻断Src,观察OPN诱导的血管平滑肌细胞(VSMC)黏附和迁移活性的改变,并利用免疫沉淀检查PP2对整合素下游信号分子黏着斑激酶(FAK)和整合素偶联激酶(ILK)磷酸化及其相互作用的影响。结果显示,PP2可明显抑制OPN诱导的VSMC黏附和伤口愈合(黏附和迁移活性分别为对照组的76.6%和33.8%);OPN可显著诱导FAK磷酸化(磷酸化水平达对照组的1.9倍),促进ILK去磷酸化,并使FAK与ILK的结合减少(降至对照组的46.4%)。10μmol/LPP2可明显抑制OPN诱导的FAK磷酸化、拮抗OPN诱导对ILK的去磷酸化作用、促进FAK与ILK之间的结合。研究结果表明,Src作为OPN-整合素-FAK信号途径中的信号分子,通过影响FAK和ILK的磷酸化以及两者之间的相互作用来调节VSMC的黏附和迁移活性。     

Caveolin-2-deficient mice show increased sensitivity to endotoxemia

Caveolin proteins are structural components of caveolae and are involved in the regulation of many biological processes. Recent studies have shown that caveolin-1 modulates inflammatory responses and is important for sepsis development. In the present study, we show that caveolin-1 and caveolin-2 have opposite roles in lipopolysaccharide (LPS)-induced sepsis using caveolin-deficient (Cav-1^-/- and Cav-2^-/-) mice for each of these proteins. While Cav-1^-/- mice displayed delayed mortality following challenge with LPS, Cav-2^-/- mice were more sensitive to LPS compared to wild-type (WT). With Cav-2^-/- mice, this effect was associated with increased intestinal injury and increased intestinal permeability. This negative outcome was also correlated with enhanced expression of iNOS in intestinal epithelial cells, and enhanced production of nitric oxide (NO). By contrast, Cav-1^-/- mice demonstrated a decrease in iNOS expression with decreased NO production, but no alteration in intestinal permeability. The differential expression of iNOS was associated with a significant increase in STAT-1 activation in these mice. Intestinal cells of Cav-2^-/- mice showed increased phosphorylation of STAT-1 at tyrosine 701 compared to wild-type. However, Cav-1^-/- mice-derived intestinal cells showed decreased levels of phosphorylation of STAT-1 at tyrosine 701. Since caveolin-2 is almost completely absent in Cav-1^-/- mice, we conclude that it is not just the absence of caveolin-2 that is responsible for the observed effects, but that the balance between caveolin-1 and caveolin-2 is important for iNOS expression and ultimately for sepsis outcome.Key words: caveolin, sepsis, nitric oxide, lipopolysaccharide, permeability, endotoxemia, inflammation