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Christian Schmidt

Publications and source records attributed to Christian Schmidt.

32 records · Page 2Linked to original sources
PubMed2003

At the crossroads of SUMO and NF-kappaB.

BACKGROUND: Recognition of pathogens by immune receptors leads to activation of macrophages, dendritic cells, and lymphocytes. Signals are communicated to enhance expression of target molecules such as cytokines and adhesion molecules, depending on activation of various inducible transcription factors, among which the family NF-kappaB transcription factors plays an evolutionarily conserved and critical role. Classical activation of NF-kappaB involves phosphorylation, polyubiquitination and subsequent degradation of the inhibitor molecules of NF-kappaB, referred to as IkappaB. Modification of IkappaBalpha, one of the mammalian IkappaB isoforms, with the small ubiquitin-like modifier (SUMO) results its protection from degradation. PRESENTATION OF THE HYPOTHESIS: SUMO-IkappaBalpha localizes in the nucleus. The nuclear SUMO-IkappaBalpha pool may be dynamic. SUMO-IkappaBalpha functions as synergy control factor. TESTING THE HYPOTHESIS: Immunoprecipitation from cellular fractions, 35S methionine pulse-chase, and FRET assays should reveal the localization of SUMO-IkappaBalpha and the dynamics of the pool. Expression of SUMOylation defective IkappaBalpha in an IkappaBalpha -/- background should yield insights into the function of SUMO-IkappaBalpha. IMPLICATION OF THE HYPOTHESIS: IkappaBalpha contains the required SUMOylation motif but IkappaBbeta does not. The suggested study would provide evidence whether or not IkappaBalpha and IkappaBbeta can substitute each other. In addition, the suggested assays would reveal a possible redundancy in controlling transcriptional activity of NF-kappaB.

Animals↗
PubMed2003

TGFbeta1 activates c-Jun and Erk1 via alphaVbeta6 integrin.

Transforming growth factor beta (TGFbeta) plays an important role in animal development and many cellular processes. A variety of cellular functions that are required for tumor metastasis are controlled by integrins, a family of cell adhesion receptors. Overexpression of alphaVbeta6 integrin is associated with lymph node metastasis of gastric carcinomas. It has been demonstrated that a full TGFbeta1 signal requires both alphaVbeta6 integrin and SMAD pathway. TGFbeta1 binds to alphaVbeta6 via the DLXXL motif, a freely accessible amino acid sequence in the mature form of TGFbeta1. Binding of mature TGFbeta1 to alphaVbeta6 leads to immobilization and tyrosine phosphorylation of proteins, which are associated with focal adhesions, a hallmark of integrin-mediated signal transduction. Here, we show that binding of mature TGFbeta1 recruits the mitogen-activated protein kinase kinase kinase 1 (MEKK1), a mediator of c-Jun activation, and the extracellular signaling-regulated kinase-1 (Erk1) to focal adhesions. In addition, the p21-activated kinase 1 (PAK1) is associated with focal adhesions and differentially phosphorylated upon TGFbeta1 stimulation. We conclude that TGFbeta1 activates c-Jun via the MEKK1/p38 MAP kinase pathway and influences cytoskeletal organization. These finding may provide a link between TGFbeta1 and the metastatic behavior of cancers.

Animals↗
PubMed2003

TGFbeta1 signaling via alphaVbeta6 integrin.

BACKGROUND: Transforming growth factor beta1 (TGFbeta1) is a potent inhibitor of epithelial cell growth, thus playing an important role in tissue homeostasis. Most carcinoma cells exhibit a reduced sensitivity for TGFbeta1 mediated growth inhibition, suggesting TGFbeta1 participation in the development of these cancers. The tumor suppressor gene DPC4/SMAD4, which is frequently inactivated in carcinoma cells, has been described as a key player in TGFbeta1 mediated growth inhibition. However, some carcinoma cells lacking functional SMAD4 are sensitive to TGFbeta1 induced growth inhibition, thus requiring a SMAD4 independent TGFbeta1 pathway. RESULTS: Here we report that mature TGFbeta1 is a ligand for the integrin alphaVbeta6, independent of the common integrin binding sequence motif RGD. After TGFbeta1 binds to alphaVbeta6 integrin, different signaling proteins are activated in TGFbeta1-sensitive carcinoma cells, but not in cells that are insensitive to TGFbeta1. Among others, interaction of TGFbeta1 with the alphaVbeta6 integrin resulted in an upregulation of the cell cycle inhibitors p21/WAF1 and p27 leading to growth inhibition in SMAD4 deleted as well as in SMAD4 wildtype carcinoma cells. CONCLUSIONS: Our data provide support for the existence of an alternate TGFbeta1 signaling pathway that is independent of the known SMAD pathway. This alternate pathway involves alphaVbeta6 integrin and the Ras/MAP kinase pathway and does not employ an RGD motif in TGFbeta1-sensitive tumor cells. The combined action of these two pathways seems to be necessary to elicit a complete TGFbeta1 signal.

Antigens, Neoplasm↗
PubMed2003

Inhibition of constitutive NF-kappa B activity by I kappa B alpha M suppresses tumorigenesis.

We have demonstrated that nuclear factor-kappa B (NF-kappa B) is constitutively activated in human pancreatic adenocarcinoma and human pancreatic cancer cell lines but not in normal pancreatic tissues or in immortalized, nontumorigenic pancreatic epithelial cells, suggesting that NF-kappa B plays a critical role in the development of pancreatic adenocarcinoma. To elucidate the role of constitutive NF-kappa B activity in human pancreatic cancer cells, we generated pancreatic tumor cell lines that express a phosphorylation defective I kappa B alpha (S32, 36A) (I kappa B alpha M) that blocks NF-kappa B activity. In this study, we showed that inhibiting constitutive NF-kappa B activity by expressing I kappa B alpha M suppressed the tumorigenicity of a nonmetastatic human pancreatic cancer cell line, PANC-1, in an orthotopic nude mouse model. Immunohistochemical analysis showed that PANC-1-derived tumors expressed vascular endothelial growth factor (VEGF) and induced angiogenesis. Inhibiting NF-kappa B signaling by expressing I kappa B alpha M significantly reduced expression of Bcl-x(L) and Bcl-2. The cytokine-induced expression of VEGF and Interleukin-8 in PANC-1 cells is also decreased. Taken together, these results suggest that the inhibition of NF-kappa B signaling can suppress tumorigenesis of pancreatic cancer cells and that the NF-kappa B signaling pathway is a potential target for anticancer agents.

Adenocarcinoma↗
PubMed2003

Restoring apoptosis in pancreatic cancer cells by targeting the nuclear factor-kappaB signaling pathway with the anti-epidermal growth factor antibody IMC-C225.

We have previously demonstrated that RelA is constitutively activated in the majority of human pancreatic cancers and plays an important role in tumorigenesis and metastasis. The antiapoptotic gene bcl-xl is a downstream target of RelA, and regulation of bcl-xl transcription is mediated directly by the nuclear factor kappaB (NF-kappaB) binding sites present in the upstream promoter element of the bcl-xl gene. In this study we investigated the effects of inhibition of epidermal growth factor receptor (EGFR) signaling pathway with the anti-EGFR monoclonal antibody IMC-C225 on constitutive NF-kappaB activation and regulation of apoptosis-related genes in human pancreatic cancer cells. We found that activation of EGFR can be blocked with the anti-EGFR antibody IMC-C225 in the human pancreatic cancer cell line MDA Panc-28, leading to a marked decrease in constitutive NF-kappaB DNA binding activity. Our data also suggest that downregulation of NF-kappaB DNA binding activity by IMC-C225 leads to a decrease in bcl-xl and bfl-1 expression. Therefore, targeting the NF-kappaB signaling pathway with an anti-EGFR antibody may be one strategy to restore apoptosis in human pancreatic cancer cells, thereby enhancing the effect of chemotherapy and radiation therapy.

Antibodies, Monoclonal↗
PubMed2003

Mechanisms of proinflammatory cytokine-induced biphasic NF-kappaB activation.

The transcription factor NF-kappaB regulates genes involved in innate and adaptive immune response, inflammation, apoptosis, and oncogenesis. Proinflammatory cytokines induce the activation of NF-kappaB in both transient and persistent phases. We investigated the mechanism for this biphasic NF-kappaB activation. Our results show that MEKK3 is essential in the regulation of rapid activation of NF-kappaB, whereas MEKK2 is important in controlling the delayed activation of NF-kappaB in response to stimulation with the cytokines TNF-alpha and IL-1alpha. MEKK3 is involved in the formation of the IkappaBalpha:NF-kappaB/IKK complex, whereas MEKK2 participates in assembling the IkappaBbeta:NF-kappaB/IKK complex; these two distinct complexes regulate the proinflammatory cytokine-induced biphasic NF-kappaB activation. Thus, our study reveals a novel mechanism in which different MAP3K and IkappaB isoforms are involved in specific complex formation with IKK and NF-kappaB for regulating the biphasic NF-kappaB activation. These findings provide further insight into the regulation of cytokine-induced specific and temporal gene expression.

Animals↗
PubMed2003

Cardiovascular risk factors and estimated risk for CAD in a randomized trial comparing calcineurin inhibitors in renal transplantation.

Cardiovascular morbidity and mortality is high in patients following renal transplantation. The present analysis assessed major cardiovascular risk factors and estimated the risk of coronary artery disease in the largest present-day comparative trial of tacrolimus vs. microemulsified cyclosporine A. In this 6-month study, 557 patients were randomly allocated to therapy with tacrolimus (n = 286) or cyclosporine A (n = 271) concomitantly with azathioprine and corticosteroids. The primary endpoint was the incidence of and time to acute rejection. Blood pressure, serum cholesterol, HDL cholesterol, triglycerides, and blood glucose were measured at baseline, and at months 1, 3, and 6. Ten-year risk of coronary heart disease was estimated according to the Framingham risk algorithm. Tacrolimus resulted in significantly lower summary measures (time-weighted average) of serum cholesterol (p = 0.0004) and mean arterial blood pressure (p = 0.0156), but in a higher summary measure of blood glucose (p = 0.0028) than cyclosporine. The summary measure of serum triglycerides was not different between treatment groups (p = 0.368). The mean 10-year coronary artery disease risk estimate was significantly lowered in men (p = 0.0032) treated with tacrolimus, but was unchanged in women. Tacrolimus and cyclosporine A microemulsion exert a compound-specific impact on cardiovascular risk factors and appear to affect the predicted rate of cardiovascular morbidity in different manners.

Calcineurin Inhibitors↗
PubMed2003

NF-kappaB in pancreatic cancer.

Although the genetic profile of pancreatic cancer is emerging as a result of much research, the role of specific genetic alterations that initiate tumorigenesis and produce its cardinal clinical features of locally aggressive growth, metastasis, and chemotherapy resistance remains unresolved. Recently, a number of studies have shown that the inhibition of constitutive NF-kappaB activation, one of the frequent molecular alterations in pancreatic cancer, inhibits tumorigenesis and metastasis. It also sensitizes pancreatic cancer cell lines to anticancer agent-induced apoptosis. Therefore because of the crucial role of NF-kappaB in pancreatic cancer, it is a potential target for developing novel therapeutic strategies for the disease. In vivo and in vitro models that mimic the tumorigenic phenotypes in the appropriate histological and molecular concert would be very useful for confirming the suspected role of the pancreatic cancer signature genetic lesions and better understanding the molecular basis of this disease.

Animals↗
PubMed2003

Function of nuclear factor kappaB in pancreatic cancer metastasis.

PURPOSE: We seek to elucidate the role of constitutive nuclear factor kappaB (NFkappaB) activity in human pancreatic cancer cells. We have demonstrated that the transcription factor NFkappaB is activated constitutively in human pancreatic adenocarcinoma and human pancreatic cancer cell lines but not in normal pancreatic tissues or in immortalized/nontumorigenic pancreatic epithelial cells, suggesting that NFkappaB plays a critical role in development of pancreatic adenocarcinoma. EXPERIMENTAL DESIGN: By pooling all of the puromycin resistant clones after inhibitor of nuclear factor-kappaB phosphorylation mutant (IkappaBalphaM) retroviral infection, we generated pancreatic tumor cell lines that express a IkappaBalphaM (S32, 36A) that blocks NFkappaB activity. Inhibition of metastatic phenotype was assayed in an orthotopic nude mouse model. NFkappaB activity was determined by electrophoretic mobility shift assay, and the expression of NFkappaB downstream target genes was analyzed by Northern, Western, and immunohistochemical analyses. RESULTS: We showed that inhibiting constitutive NFkappaB activity by expressing IkappaBalphaM suppresses liver metastasis, but not tumorigenesis, from the metastatic human pancreatic tumor cell line AsPc-1 in an orthotopic nude mouse model. Furthermore, inhibiting NFkappaB activation by expressing IkappaBalphaM significantly reduced in vivo expression of a major proangiogenic molecule, vascular endothelial growth factor, and, hence, decreased neoplastic angiogenesis. Inhibiting NFkappaB activation by expressing IkappaBalphaM and using pharmacologic NFkappaB inhibitor PS-341 also significantly reduced cytokine-induced vascular endothelial growth factor and interleukin-8 expression in AsPc-1 pancreatic cancer cells. CONCLUSION: These results demonstrated that the inhibition of NFkappaB signaling can suppress the angiogenic potential and metastasis of pancreatic cancer, and suggest that the NFkappaB signaling pathway is a potential target for anticancer agents.

Animals↗
PubMed2002

The function of multiple IkappaB : NF-kappaB complexes in the resistance of cancer cells to Taxol-induced apoptosis.

The Rel/NF-kappaB transcription factors play a key role in the regulation of apoptosis and in tumorigenesis by controlling the expressions of specific genes. To determine the role of the constitutive activity of RelA in tumorigenesis, we generated pancreatic tumor cell lines that express a dominant negative mutant of IkappaBalpha (IkappaBalphaM). In this report, we show that the inhibition of constitutive NF-kappaB activity, either by ectopic expression of IkappaBalphaM or by treating the cells with a proteasome inhibitor PS-341 which blocks intracellular degradation of IkappaBalpha proteins, downregulates the expression of bcl-xl. We identified two putative NF-kappaB binding sites (kappaB/A and B) in the bcl-xl promoter and found that these two sites interact with different NF-kappaB proteins. p65/p50 heterodimer interacts with kappaB/A site whereas p50/p50 homodimer interacts with kappaB/B. The bcl-xl promoter reporter gene assays reveal that NF-kappaB dependent transcriptional activation is mainly mediated by kappaB/A site, indicating that bcl-xl is one of the downstream target genes regulated by RelA/p50. Both IkappaBalphaM and PS-341 completely abolish NF-kappaB DNA binding activity; however, PS-341, but not ectopic expression of IkappaBalphaM, sensitized cells to apoptosis induced by Taxol. This is due to the Taxol-mediated reactivation of RelA through phosphorylation and degradation of IkappaBbeta and the re-expression of NF-kappaB regulated bcl-xl gene in these cancer cells as ectopic expression of the bcl-xl gene confers resistance to Taxol-induced apoptosis in PS-341 sensitized cells. These results demonstrate the important function of various NF-kappaB/IkappaB complexes in regulating anti-apoptotic genes in response to apoptotic stimuli, and they raise the possibility that NF-kappaB : IkappaBalpha and NF-kappaB : IkappaBbeta complexes are regulated by different upstream activators, and that NF-kappaB plays a key role in pancreatic tumorigenesis.

Antineoplastic Agents↗
PubMed2002

Stroke volume variations for assessment of cardiac responsiveness to volume loading in mechanically ventilated patients after cardiac surgery.

OBJECTIVE: We hypothesized that measuring stroke volume variation (SVV) during mechanical ventilation by continuous arterial pulse contour analysis allows the accurate prediction and monitoring of changes in cardiac index (CI) in response to volume administration. DESIGN AND SETTING: Prospective study in an university hospital. PATIENTS: Twenty mechanically ventilated patients following cardiac surgery. INTERVENTIONS: Volume loading with oxypolygelatin (3.5%) 20 ml x body mass index over 10 min. MEASUREMENTS AND RESULTS: SVV, central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), left ventricular end-diastolic area index (LVEDAI) by transesophageal echocardiography, intrathoracic blood volume index (ITBVI) by transpulmonary thermodilution and CI were determined immediately before and after volume loading. SVV decreased, while CI, CVP, PAOP, ITBVI, and LVEDAI increased significantly. Percentage changes in CI were significantly correlated to percentage changes in SVV (r(2)=-0.59, p<0.001), ITBVI (r(2)=0.79, p<0.001), and PAOP (r(2)=0.33, p<0.05) and to baseline values of SVV (r(2)=0.55, p<0.05) and LVEDAI (r(2)=-0.68, p<0.001). CONCLUSIONS: SVV may help to determine the preload condition of ventilated patients following cardiac surgery and to predict and continuously monitor effects of volume administered as part of their hemodynamic management.

Aged↗
PubMed2002

Intrathoracic blood volume index measured by thermodilution for preload monitoring after cardiac surgery.

OBJECTIVE: To investigate the accuracy of measurement of intrathoracic blood volume index by single thermodilution (ITBVI*) and its sensitivity to detect changes in preload after cardiac surgery compared with conventional transpulmonary arterial dye dilution ITBVI and with conventional monitoring (central venous pressure [CVP] and left ventricular end-diastolic area index [EDAI] by transesophageal echocardiography). DESIGN: Prospective clinical study. SETTING: University hospital. PARTICIPANTS: Nineteen patients immediately after cardiac surgery. INTERVENTIONS: Volume loading was administered with 20 mL of oxypoligelatine (Haemaccel [Behringwerke Aktiengesellschaft Corp, Marburg, Germany]) 3.5% times body mass index over 10 minutes. MEASUREMENTS AND MAIN RESULTS: Intrathoracic blood volume index was measured by dye dilution (ITBVI) and thermodilution (ITBVI*) immediately before and after volume loading. Measurements of ITBVI and ITBVI* correlated closely (r = 0.94; p < 0.0001). With volume loading, ITBVI and ITBVI* increased significantly from 877 +/- 195 mL/m(2) to 967 +/- 180 mL/m(2) and from 889 +/- 195 mL/m(2) to 954 +/- 185 mL/m(2). Percent changes in ITBVI (deltaITBVI) and ITBVI* (deltaITBVI*) did not differ significantly and correlated closely (r = 0.90; p < 0.0001). Percent changes in cardiac index (CI) as a result of volume loading (deltaCI) revealed significant correlation to deltaITBVI (r = 0.85; p < 0.0001) and to deltaITBVI* (r = 0.76; p < 0.0005). No significant correlation could be found between deltaCI and deltaEDAI or deltaCVP. CONCLUSION: In patients undergoing cardiac surgery, determination of ITBVI* revealed close agreement with measurements derived by ITBVI. Enhancement in cardiac preload was adequately detected by ITBVI*.

Blood Volume↗
PubMed2002

The mode of mechanical integrin stressing controls intracellular signaling in osteoblasts.

Following the idea that integrin receptors function as mechanotransducers, we applied defined physical forces to integrins in osteoblastic cells using a magnetic drag force device to show how cells sense different modes of physical forces. Application of mechanical stress to the beta1-integrin subunit revealed that cyclic forces of 1 Hz were more effective to stimulate the cellular calcium response than continuous load. Cyclic forces also induced an enhanced cytoskeletal anchorage of tyrosine-phosphorylated proteins and increased activation of the focal adhesion kinase (FAK) and mitogen activated protein (MAP) kinase. These events were dependent on an intact cytoskeleton and the presence of intracellular calcium. Analyses of the intracellular spatial organization of the calcium responses revealed that calcium signals originate in a restricted region in the vicinity of the stressed receptors, which indicates that cells are able to sense locally applied stress on the cell surface via integrins. The calcium signals can spread throughout the cell including the nucleus, which shows that calcium also is a candidate to transmit mechanically induced information into different cellular compartments.

Calcium↗