Search

AbstractIt is well accepted that atherosclerosis occurs in a site-specific manner especially at branch points where disturbed blood flow (d-flow) predisposes to the development of plaques. Investigations both in vivoand in vitrohave shown that d-flow is pro-atherogenic by promoting oxidative and inflammatory states in the artery wall. In contrast, steady laminar blood flow (s-flow) is atheroprotective by inhibition of oxidative stress and inflammation in the vessel wall. The mechanism for inflammation in endothelial cells (ECs) exposed to d-flow has been well studied and includes redox-dependent activation of apoptosis signal-regulating kinase 1 (ASK1) and Jun NH2-terminal kinase (JNK) that ultimately lead to the expression of adhesive molecules. In contrast, s-flow leads to the activation of the mitogen extracellular-signal-regulated kinase kinase 5/extracellular signal-regulated kinase-5 (MEK5/ERK5) pathway that prevents pro-inflammatory signaling. Important transcriptional events that reflect the pro-oxidant and pro-inflammatory condition of ECs in d-flow include the activation of activator protein 1 (AP-1) and nuclear factor kappaB (NFκB), whereas in s-flow, activation of Krüppel-like factor 2 (KLF2) and nuclear factor erythroid 2-like 2 (Nrf2) are dominant. Recent studies have shown that protein kinase c zeta (PKCζ) is highly activated under d-flow conditions and may represent a molecular switch for EC signaling and gene expression. The targeted modulation of proteins activated in a site-specific manner holds the promise for a new approach to limit atherosclerosis. Antioxid. Redox Signal. 15, 1405–1414. [ABSTRACT FROM AUTHOR]

Inflammation is a hallmark of many diseases, such as atherosclerosis, chronic obstructive pulmonary disease, arthritis, infectious diseases, and cancer. Although steroids and cyclooxygenase inhibitors are effective antiinflammatory therapeutical agents, they may cause serious side effects. Therefore, developing unique antiinflammatory agents without significant adverse effects is urgently needed. Vinpocetine, a derivative of the alkaloid vincamine, has long been used for cerebrovascular disorders and cognitive impairment Its role in inhibiting inflammation, however, remains unexplored. Here, we show that vinpocetine acts as an antiinflammatory agent in vitro and in vivo. In particular, vinpocetine inhibits TNF-α-induced NF-κB activation and the subsequent induction of proinflammatory mediators in multiple cell types, including vascular smooth muscle cells, endothelial cells, macrophages, and epithelial cells. We also show that vinpocetine inhibits monocyte adhesion and chemotaxis, which are critical processes during inflammation. Moreover, vinpocetine potently inhibits TNF-α- or LPS-induced up-regulation of proinflammatory mediators, including TNF-α, lL-1β, and macrophage inflammatory protein-2, and decreases interstitial infiltration of polymorphonuclear leukocytes in a mouse model of TNF-α- or LPSinduced lung inflammation. Interestingly, vinpocetine inhibits NF-κB-dependent inflammatory responses by directly targeting IKK, independent of its well-known inhibitory effects on phosphodiesterase and Ca2+ regulation. These studies thus identify vinpocetine as a unique antiinflammatory agent that may be repositioned for the treatment of many inflammatory diseases. [ABSTRACT FROM AUTHOR]

The article examines the in vivo role and signaling mechanism of extracellular signal-regulated protein kinase (ERK)5 in regulating hypertrophy-induced apoptosis and cardiac hypertrophy in mice. Study demonstrates the increased apoptosis and upregulated p53 expression levels. It shows the significant function of ERK5 in cardiomyocyte survival and cardiac hypertrophic remodeling. Its role in hypertrophic remodeling can be mediated through myocyte enhancer factor (MEF)2 activity.

The article discusses the study which aims to examine the role of cyclic nucleotide phosphodiesterases (PDE1) in balancing intracellular cardiomyocyte hypertrophy and cyclic guanosine monophosphate (cGMP). In the process, PDE1A used small interfering RNA to neonatal and adult rat ventricular myocytes in determining the chronic isoproterenol infusion in vivo in human hearts. Thus, PDE1A reduced the intracellular cGMP and cGMP-dependent protein kinase towards cardiomyocyte hypertrophy.

Inflammation and oxidative stress are pathogenic mediators of many diseases, but molecules that could be therapeutic targets remain elusive. Inflammation and matrix degradation in the vasculature are crucial for abdominal aortic aneurysm (AAA) formation. Cyclophilin A (CypA, encoded by Ppia) is highly expressed in vascular smooth muscle cells (VSMCs), is secreted in response to reactive oxygen species (ROS) and promotes inflammation. Using the angiotensin II (AngII)-induced AAA model in Apoe−/− mice, we show that Apoe−/−Ppia−/− mice are completely protected from AngII–induced AAA formation, in contrast to Apoe−/−Ppia+/+ mice. Apoe−/−Ppia−/− mice show decreased inflammatory cytokine expression, elastic lamina degradation and aortic expansion. These features were not altered by reconstitution of bone marrow cells from Ppia+/+ mice. Mechanistic studies showed that VSMC-derived intracellular and extracellular CypA are required for ROS generation and matrix metalloproteinase-2 activation. These data define a previously undescribed role for CypA in AAA formation and suggest CypA as a new target for treating cardiovascular disease. [ABSTRACT FROM AUTHOR]

The article presents a study on the activation of B cell receptor (Bcr) kinase through angiotensin (Ang) II which inhibits the peroxisome proliferators-activated receptor (PPAR) γ transcriptional activity in vascular smooth muscle cells (VSMCs). Ang II and platelet derived growth factor-mediated inflammatory response in VSMCs is being mediated by Bcr. PPAR γ activity was reduced by Ang II and that Bcr has a critical role in the Ang II-mediated inhibition of PPAR γ activity.

The article discusses a study which examines the effects of MEK5/ERK5 association on small ubiquitin-related modification of ERK5, an atypical mitogen activated protein kinase with transcriptional activity. The study demonstrates that ERK5 transcriptional activity is subject to downregulation by diabetes-dependent SUMOylation, which resulted in a proapoptotic condition contributing to poor post-myocardial infarction left ventricular function.

The article discusses a study which showed reactive oxygen species (ROS) and advanced glycation end products (AGE) lead to shear-stress-induced extracellular signal-regulated kinase (ERK5) SUMOylation an inhibition of shear stress-mediated ERK5 transcriptional activity. The manner in which the possible pathological role of ERK5 SUMOylation in diabetes mellitus in vivo was examine is described.

The article presents a study on the influence of implant mesial inclination on dental implant stress distribution. It mentions the construction of a two-dimensional finite element models including a bridge-shaped superstructure, implants, cortical bone, and cancellous bone. Implant mesial inclination on three points of the occlusal plane were determined and stress distributions were calculated. Study results and recommendations are also presented.

Osteoprotegerin (OPG), also known as osteoclastogenesis inhibitory factor or tumor necrosis factor receptor superfamily member 11B, is well known as a modulator of bone remodeling. The contribution of OPG to cardiovascular disease (CVD) has been suggested, but its molecular mechanism is complex and remains unclear. In the present study, Alves-Lopes et al. (Clin. Sci. (Lond.) (2021) 135(20): https://doi.org/10.1042/CS20210643) reported the critical role of syndecan-1 (SDC-1, also known as CD138), a surface protein part of the endothelial glycocalyx, in OPG-induced vascular dysfunction. The authors found that in endothelial cells (ECs), through SDC-1, OPG increased eNOS Thr495 phosphorylation, thereby inhibiting eNOS activity. Furthermore, the OPG--SDC-1 interaction increased reactive oxygen species (ROS) production through NOX1/4 activation. Both the reduced eNOS activity and induced ROS production inhibited NO production and impaired EC function. In vascular smooth muscle cells (VSMCs), the OPG--SDC-1 interaction increased ROS production through NOX1/4 activation, subsequently increased MLC phosphorylation-mediated Rho kinase-MYPT1 regulation, leading to increased vascular contraction. Ultilizing wire myography and mechanistic studies, the authors nicely provide the evidence that SDC-1 plays a crucial role in OPG-induced vascular dysfunction. As we mentioned above, the molecular mechanism and roles of OPG in cardiovascular system are complex and somewhat confusing. In this commentary, we briefly summarize the OPG-mediated signaling pathways in cardiovascular system. [ABSTRACT FROM AUTHOR]

TONAL SCHEMATA ARE SHAPED BY CULTURE-SPECIFIC music exposure. The acquisition process of tonal schemata has been delineated in Western mono-musical children, but cross-cultural variations have not been explored. We examined how Japanese children acquire tonal schemata in a bi-musical culture characterized by the simultaneous, and unbalanced, appearances of Western (dominant) music along with traditional Japanese (non-dominant) music. Progress of this acquisition was indexed by gauging children's sensitivities to musical scale membership (differentiating scale-tones from non-scale-tones) and differences in tonal stability among scale tones (differentiating the tonic from another scale tone). Children (7-, 9-, 11-, 13-, and 14-year-olds) and adults judged how well two types of target tones (scale tone vs. non-scale tone; tonic vs. non-tonic) fit a preceding Western or traditional Japanese tonal context. Results showed that even 7-year-olds showed sensitivity to Western scale membership while sensitivity to Japanese scale membership did not appear until age nine. Also, sensitivity to the tonic emerged at age 13 for both types of melodies. These results suggest that even though they are exposed to both types of music simultaneously from birth, Japanese children begin by acquiring the tonal schema of the dominantWestern music and this age of acquisition is not delayed relative to Western monomusical peers. [ABSTRACT FROM AUTHOR]

Healthy kidney structure and environment rely on epithelial integrity and interactions between epithelial cells and other kidney cells. The Ser/Thr kinase 90 kDa ribosomal protein S6 kinase 1 (p90RSK) belongs to a protein family that regulates many cellular processes, including cell motility and survival. p90RSK is predominantly expressed in the kidney, but its possible role in chronic kidney disease (CKD) remains largely unknown. Here, we found that p90RSK expression is dramatically activated in a classic mouse obstructive chronic kidney disease model, largely in the interstitial FSP-1-positive fibroblasts. We generated FSP-1-specific p90RSK transgenic mouse (RSK-Tg) and discovered that these mice, after obstructive injury, display significantly increased fibrosis and enhanced tubular epithelial damage compared with their wt littermates (RSK-wt), indicating a role of p90RSK in fibroblast-epithelial communication. We established an in vitro fibroblast-epithelial coculture system with primary kidney fibroblasts from RSK-Tg and RSK-wt mice and found that RSK-Tg fibroblasts consistently produce excessive H2O2 causing epithelial oxidative stress and inducing nuclear translocation of the signaling protein β-catenin. Epithelial accumulation of β-catenin, in turn, promoted epithelial apoptosis by activating the transcription factor forkhead box class O1 (FOXO1). Of note, blockade of reactive oxygen species (ROS) or β-catenin or FOXO1 activity abolished fibroblast p90RSK-mediated epithelial apoptosis. These results make it clear that p90RSK promotes kidney fibrosis by inducing fibroblast-mediated epithelial apoptosis through ROS-mediated activation of β-catenin/FOXO1 signaling pathway. [ABSTRACT FROM AUTHOR]

We investigated tonal perception of melodies from 2 cultures (Western and traditional Japanese) by 5 different cultural groups (44 Japanese, 25 Chinese, 16 Vietnamese, 18 Indonesians, and 25 U.S. citizens). Listeners rated the degree of "melodic completeness" of the final tone (a tonic vs. a nontonic) and "happiness-sadness" in the mode (major vs. minor, YOH vs. IN) of each melody. When Western melodies were presented, American and Japanese listeners responded similarly, such that they reflected implicit tonal knowledge of Western music. By contrast, the responses of Chinese, Vietnamese, and Indonesian listeners were different from those of American and Japanese listeners. When traditional Japanese melodies were presented, Japanese listeners exhibited responses that reflected implicit tonal knowledge of traditional Japanese music. American listeners also showed responses that were like the Japanese; however, the pattern of responses differed between the 2 groups. Alternatively, Chinese, Vietnamese, and Indonesian listeners exhibited different responses from the Japanese. These results show large differences between the Chinese/Vietnamese/Indonesian group and the American/Japanese group. Furthermore, the differences in responses to Western melodies between Americans and Japanese were less pronounced than that between Chinese, Vietnamese, and Indonesians. These findings imply that cultural differences in tonal perception are more diverse and distinctive than previously believed. [ABSTRACT FROM AUTHOR]

A major advantage of satellite communications is the ability to implement communication networks virtually anywhere in Japan very simply. The NTT Group has been utilizing satellite communications to provide services in situations where optical fiber, mobile telephony, and other terrestrial facilities are impractical: remote islands, offshore areas, and stricken regions where people have been forced to temporarily flee in the face of earthquakes and other natural disasters. The Group continues to pursue research and development on satellite systems to make them more efficient and advanced. Here we present an overview of NTT's new satellite communications modem unit called COM-U (satellite circuit-terminating common unit), that markedly improves the spectrum utilization efficiency of satellite transponders and the maintenance and operations of satellite communications used for remote island and disaster relief satellite communications. [ABSTRACT FROM AUTHOR]

Disturbed blood flow (d-flow) causes endothelial cell (EC) dysfunction, leading to atherosclerotic plaque formation. We have previously shown that d-flow increases SUMOylation of p53 and ERK5 through down regulation of sentrin/SUMO-specific protease 2 (SENP2) function; however, it is not known how SENP2 itself is regulated by d-flow. Here, we determined that d-flow activated the serine/threonine kinase p90RSK, which subsequently phosphorylated threonine 368 (T368) of SENP2. T368 phosphorylation promoted nuclear export of SENP2, leading to down regulation ofeNOS expression and upregulation of proinflammatory adhesion molecule expression and apoptosis. In an LDLR-deficient murine model of atherosclerosis, EC-specific overexpression of p90RSK increased EC dysfunction and lipid accumulation in the aorta compared with control animals; however, these pathologic changes were not observed in atherosclerotic mice overexpressing dominant negative p90RSK (DN-p90RSK). Moreover, depletion of SENP2 in these mice abolished the protective effect of DN-p90RSK overexpression. We propose that p90RSK-mediated SENP2-T368 phosphorylation is a master switch in d-flow-induced signaling, leadingto EC dysfunction and atherosclerosis. [ABSTRACT FROM AUTHOR]

Because ERK5 inhibits endothelial inflammation and dysfunction, activating ERK5 might be a novel approach to protecting vascular endothelial cells (ECs) against various pathological conditions of the blood vessel. We have identified small molecules that protect ECs via ERK5 activation and determined their contribution to preventing cardiac allograft rejection. Using high-throughput screening, we identified certain statins and antimalarial agents including chloroquine, hydroxychloroquine, and quinacrine as strong ERK5 activators. Pitavastatin enhanced ERK5 transcriptional activity and Kruppel-like factor-2 expression in cultured human and bovine ECs, but these effects were abolished by the depletion of ERK5. Chloroquine and hydroxychloroquine upregulated ERK5 kinase activity and inhibited VCAM-1 expression in an ERK5-dependent but MAPK/ERK kinase 5– and Kruppel-like factor 2/4–independent manner. Leukocyte rolling and vascular reactivity were used to evaluate endothelial function in vivo, and we found that EC-specific ERK5 knockout (ERK5-EKO) mice exhibited increased leukocyte rolling and impaired vascular reactivity, which could not be corrected by pitavastatin. The role of endothelial ERK5 in acute cardiac allograft rejection was also examined by heterotopic grafting of the heart obtained from either wild-type or ERK5-EKO mice into allomismatched recipient mice. A robust increase in both inflammatory gene expression and CD45-positive cell infiltration into the graft was observed. These tissue rejection responses were inhibited by pitavastatin in wild-type but not ERK5-EKO hearts. Our study has identified statins and antimalarial drugs as strong ERK5 activators and shown that ERK5 activation is preventive of endothelial inflammation and dysfunction and acute allograft rejection. [ABSTRACT FROM AUTHOR]

Atherosclerosis is readily observed in regions of blood vessels where disturbed blood flow (d-flow) is known to occur. A positive correlation between protein kinase C ζ (PKCζ) activation and d-flow has been reported, but the exact role of d-flow--mediated PKCζ activation in atherosclerosis remains unclear. We tested the hypothesis that PKCζ activation by d-flow induces endothelial cell (EC) apoptosis by regulating p53. We found that d-flow--mediated peroxynitrite (ONOO-) increased PKCζ activation, which subsequently induced p53 SUMOylation, p53--CBcl-2 binding, and EC apoptosis. Both d-flow and ONOO- increased the association of PKCζ with protein inhibitor of activated STATy (PIASy) via the Siz/PIAS-RING domain (amino acids 301--410) of PIASy, and overexpression of this domain of PIASy disrupted the PKCζ--PIASy interaction and PKCζ-mediated p53 SUMOylation. En face confocal microscopy revealed increases in nonnuclear p53 expression, nitrotyrosine staining, and apoptosis in aortic EC located in d-flow areas in wild-type mice, but these effects were significantly decreased in p53-/- mice. We propose a novel mechanism for p53 SUMOylation mediated by the PKCζ--PIASy interaction during d-flow--mediated EC apoptosis, which has potential relevance to early events of atherosclerosis. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptors (PPAR) decrease the production of cytokine and inducible nitric-oxide synthase (iNOS) expression, which are associated with aging-related inflammation and insulin resistance. Recently, the involvement of the induction of hemeoxygenase-1 (HO-1) in regulating inflammation has been suggested, but the exact mechanisms for reducing inflammation by HO-1 remains unclear, We found that overexpression of HO-1 and [Ru(CO)3Cl2]2, a carbon monoxide (CO)-releasing compound, increased not only ERK5 kinase activity, but also its transcriptional activity measured by luciferase assay with the transfection of the Gal4-ERK5 reporter gene. This transcriptional activity is required for coactivation of PPARδ by ERK5 in C2C12 cells. [Ru(CO)3Cl2]2 activated PPARδ transcriptional activity via the MEK5/ERK5 signaling pathway. The inhibition of NF-κB activity by ERK5 activation was reversed by a dominant negative form of PPARδ suggesting that ERK5/PPAR6 activation is required for the anti-inflammatory effects of CO and HO-1. Based on these data, we propose a new mechanism by which CO and HO-1 mediate anti-inflammatory effects via activating ERK5/PPARδ, and ERK5 mediates CO and HO-1-induced PPARδ activation via its interaction with PPARδ. [ABSTRACT FROM AUTHOR]

Dysregulation of apoptosis in endothelial cells (EC) and fibroblasts contributes to fibrosis. We have shown previously that apoptosis of EC triggers the proteolysis of extracellular matrix components and the release of a C-terminal fragment of perlecan, which in turn inhibits apoptosis of fibroblasts. Here we have defined the receptors and pathways implicated in this anti-apoptotic response in fibroblasts. Neutralizing α2β1 integrin activity in fibroblasts exposed to either medium conditioned by apoptotic EC (SSC) or a recombinant perlecan C-terminal fragment (LG3) prevented resistance to apoptosis and is associated with decreased levels of Akt phosphorylation. Co-incubation of fibroblasts for 24 h with SSC or LG3 in the presence of PP2 (AG1879), a biochemical inhibitor of Src family kinases (SFKs) and focal adhesion kinase, showed a significantly decreased anti-apoptotic response. However, focal adhesion kinase gene silencing with RNA interference did not inhibit the anti-apoptotic response in fibroblasts. Src phosphorylation was increased in fibroblasts exposed to SSC, and transfection of fibroblasts with constitutively active Src mutants induced an anti-apoptotic response that was not further increased by SSC. Also, Src-/- Fyn-/- fibroblasts failed to mount an anti-apoptotic response in presence of SSC for 24 h but developed a complete anti-apoptotic response when exposed to SSC for 7 days. These results suggest that extracellular matrix fragments produced by apoptotic EC initiate a state of resistance to apoptosis in fibroblasts via an α2α1 integrin/SFK (Src and Fyn)/phosphatidylinositol 3-kinase (PI3K)-dependent pathway. In the long term, additional SFK members are recruited for sustaining the anti-apoptotic response, which could play crucial roles in abnormal fibrogenic healing. [ABSTRACT FROM AUTHOR]

The downstream of kinase (Dok) family of adapter proteins consists of at least five members structurally characterized by an NH2-terminal tandem of conserved pleckstrin homology and phosphotyrosine binding domains linked to a unique COOH-terminal region. To determine the role of the novel adapter protein Dok-4 in endothelial cells, we first investigated the cell localization of Dok-4. Most surprisingly, immunofluorescence microscopy, cell fractionation studies, and studies with enhanced green fluorescent protein chimeras showed that wild type Dok-4 (Dok-4-WT) specifically localized in mitochondria. An NH2-terminal deletion mutant of Dok-4 (Dok-4-(ΔN11–29)), which lacks the mitechondrial targeting sequence, could not accumulate in mitochondria. Co-immunoprecipitation revealed an interaction of c-Src with Dok-4-WT in endothelial cells. Most interestingly, overexpression of Dok-4-WT, but not Dok-4-(ΔN1–99), increased mitochondrial c-Src expression, whereas knock-down of endogenous Dok-4 with a small interfering RNA vector greatly inhibited mitochondrial localization of c-Src, suggesting a unique function for Dok-4 as an anchoring protein for c-Src in mitochondria. Dok-4-WT significantly decreased 39-kDa subunit complex I expression. PP2, a specific Src kinase inhibitor, prevented the Dok-4-mediated complex I decrease, suggesting the involvement of Src kinase in regulation of complex I expression. Dok-4-WT enhanced tumor necrosis factor-α (TNT-α)-mediated reactive oxygen species (ROS) production, supporting the functional relevance of a Dok-4-Src-complex I/ROS signaling pathway in mitochondria. Finally, Dok-4 enhanced TNF-α-mediated NF-κB activation, whereas this was inhibited by transfection with Dok-4 small interfering RNA. In addition, Dok-4-induced NF-KB activation was also inhibited by transfection of a dominant negative form of c-Src. These data suggest a role for mitochondrial Dok-4 as an anchoring molecule for the tyrosine kinase c-Src, and in turn as a regulator of TNF-α-mediated ROS production and NF-κB activation. [ABSTRACT FROM AUTHOR]

Protein kinase C (PKC)-induced phosphorylation of cardiac troponin I (cTnI) depresses the acto-myosin interaction and may be important during the progression of heart failure. Although both PKCβII and PKC∊ can phosphorylate cTnI, only PKCβ expression and activity are elevated in failing human myocardium during end-stage heart failure. Furthermore, although increased cTnI phosphorylation was observed in mice with cardiac-specific PKCβ II overexpression, no differences were observed in cTnI phosphorylation status between wild type and cardiac-specific PKC∊ overexpression mice. A potentially important downstream effector of PKCs is p90 ribosomal S6 kinase (p90RSK), which plays an important role in cell growth by activating several transcription factors as well as Na+/H+ exchanger. Since both Ser23 and Ser24 of cTnI are contained in putative consensus sequences of p90RSK phosphorylation sites, we hypothesized that p90RSK is downstream from PKCβ II and can be a cTnI (Ser23/24) kinase, p90RSK, but not ERK½ activation, was increased in PKCβII overexpression mice but not in PKC∊ overexpression mice. p90RSK could phosphorylate cTnI in vitro with high substrate affinity but not cardiac troponin T (cTnT). To confirm the role of p90RSK in cTnI phosphorylation in vivo, we generated adenovirus containing a dominant negative form of p90RSK (Ad-DN-p90RSK). We found that the inhibition of p90RSK prevented H2O2-mediated cTnI (Ser23/24) phosphorylation but not ERK½ and PKCα/βII activation. Next, we generated cardiac-specific p90RSK transgenic mice and observed that cTnI (Ser23/24) phosphorylation was significantly increased. LY333,531, a specific PKCβ inhibitor, inhibited both p90RSK and cTnI (Ser23/24) phosphorylation by H2O2. Taken together, our data support a new redox-sensitive mechanism regulating cTnI phosphorylation in cardiomyocytes. [ABSTRACT FROM AUTHOR]

Endothelial cell (EC) migration contributes to reendothelialization after angioplasty or rupture of atherosclerotic plaques. Extracellular signal-regulated kinase (ERK)½ translocates to the nucleus and activates transcription factors such as Ets-like transcription factor-1 and early growth response factor-1 (Egr-1) during reendothelialization. Because ERK½ does not possess a nuclear localization signal (NLS), its mechanism of translocation and accumulation in the nucleus remains unclear. Because Gab1 has a putative NLS in its N-terminal region, and Gab1 associates with phosphorylated ERK½, we hypothesized that Gab1 participates in ERK½ and Egr-1 nuclear accumulation. Using regenerating EC as a model system, we found that endogenous growth factor receptor-bound protein 2-associated binder-1 (Gab1) translocates into the nucleus in migrating EC. Wild-type red fluorescent protein-tagged Gab1 could be observed in both nucleus and cytoplasm, whereas the putative NLS deletion mutant (ΔNLS-Gab1) specifically localized in the cytoplasm. In addition, reduction of Gab1 expression by antisense Gab1 oligos or overexpression of ΔNLS-Gab1 inhibited serum-induced ERK½ and Egr-1 nuclear accumulation, suggesting a functional role for the NLS of Gab1 and a role for Gab1ERK½ interactions in ERK½-Egr-1 nuclear accumulation. To investigate whether Gab1-ERK½ interaction is critical for ERK½ and Egr-1 nuclear accumulation, we created a dominant-negative Gab1 construct that consisted of the c-Met binding domain (amino acids 442536) of Gab1. We found that overexpression of the c-Met binding domain of Gab1 disrupted serum-induced Gab1ERK1 interaction and inhibited ERK1 and Egr-1 nuclear accumulation. These data suggest that Gab1-ERK½ binding and their nuclear translocation play a crucial role in Egr-1 nuclear accumulation. [ABSTRACT FROM AUTHOR]