Integrating social determinants of health principles into the preclinical medical curriculum via student-led pedagogical modalities

BACKGROUND

Dismantling structural inequities in health care requires that physicians understand the impacts of social determinants of health (SDH). Although many medical schools incorporate SDH education, integration of these principles into the preclinical curriculum remains challenging.

METHODS

Students and faculty at the University of Vermont, Larner College of Medicine developed the Social Medicine Theme of the Week (SMTW), a peer-teaching approach to integrating SDH topics across the preclinical curriculum as part of a broader social medicine curriculum. Students created objectives to link SDH-related topics to the weekly curriculum and presented them to the class. Student innovation led to the incorporation of creative online infographics that were published in the curriculum calendar. First year medical students and faculty members were surveyed to assess preferences and educational impact of the SMTW announcements with accompanying infographics.

RESULTS

Of the 40 student respondents, 77.5% reported that their knowledge of SDH had improved due to the SMTW. Most students (82.5%) preferred the infographic modality over traditional teaching modalities. Faculty respondents reported limited engagement with the SMTW and, although they supported the need for these objectives, many (61%) found it difficult to integrate SDH content into their class materials.

CONCLUSION

Student-led infographics are a popular method of integrating SDH content in the preclinical curriculum that can be optimized through faculty orientation and support. Success for this type of instruction requires opportunities for student developers, integration and formal assessment of objectives, faculty engagement and training, and institutional support for creating and delivering a robust social medicine curriculum.

A new roadmap for social medicine curriculum design based on mixed methods student and faculty evaluations of the preclinical curriculum

BACKGROUND

To support the development of social medicine curricula that empower medical school graduates to redress health inequities, we conducted a mixed methods student and faculty evaluation of an expanded and innovative preclinical social medicine curriculum.

METHODS

We implemented a longitudinal, interactive preclinical social medicine curriculum that was closely integrated with foundational science teaching then conducted a survey-based mixed methods student and faculty curriculum evaluation. Based on these results, we propose a novel conceptual roadmap for social medicine curriculum design.

RESULTS

Student and faculty evaluations of an expanded and innovative longitudinal preclinical social medicine curriculum were strongly favorable. Both student and faculty respondents indicated a particular desire for deeper coverage of race and poverty among other social medicine domains. Qualitative student evaluations highlighted the importance of faculty champions to social medicine teaching as well as the educational impact of stories that exemplify the practical impact of the social determinants of health on specific patient experiences. Qualitative faculty evaluations pointed to the challenges of curriculum integration and the need for faculty career development in social medicine teaching.

CONCLUSIONS

Based on mixed methods student and faculty curriculum evaluation data, we propose a novel conceptual roadmap for the design of social medicine curricula at other institutions.

Correction to: The design and implementation of a longitudinal social medicine curriculum at the University of Vermont's Larner College of Medicine

An amendment to this paper has been published and can be accessed via the original article.

The design and implementation of a longitudinal social medicine curriculum at the University of Vermont's Larner College of Medicine

BACKGROUND

Despite an abundant literature advocating that social determinants of health (SDH) be taught during undergraduate medical education, there are few detailed descriptions of how to design and implement longitudinal core curricula that is delivered to all students and accomplishes this goal.

METHODS

In this paper, we describe the design and implementation of a social medicine curriculum at the University of Vermont's Larner College of Medicine (UVM Larner). Using Kern's principles, we designed a longitudinal curriculum that extends through both preclinical and clinical training for all students and focused on integrating SDH material directly into basic science and clinical training.

RESULTS

We successfully developed and implemented two primary tools, a "Social Medicine Theme of the Week" (SMTW) in preclinical training, and SDH rounds in the clinical setting to deliver SDH content to all learners at UVM Larner.

CONCLUSIONS

Extensive student-faculty partnerships, robust needs assessment, and focusing on longitudinal and integrated SDH content delivery to all students were key features that contributed to successful design and implementation.

Induction of microvascular network growth in the mouse mesentery

OBJECTIVE

Motivated by observations of mesenteries harvested from mice treated with tamoxifen dissolved in oil for inducible gene mutation studies, the objective of this study was to demonstrate that microvascular growth can be induced in the avascular mouse mesentery tissue.

METHODS

C57BL/6 mice were administered an IP injection for five consecutive days of: saline, sunflower oil, tamoxifen dissolved in sunflower oil, corn oil, or peanut oil.

RESULTS

Twenty-one days post-injection, zero tissues from saline group contained branching microvascular networks. In contrast, all tissues from the three oils and tamoxifen groups contained vascular networks with arterioles, venules, and capillaries. Smooth muscle cells and pericytes were present in their expected locations and wrapping morphologies. Significant increases in vascularized tissue area and vascular density were observed when compared to saline group, but sunflower oil and tamoxifen group were not significantly different. Vascularized tissues also contained LYVE-1-positive and Prox1-positive lymphatic networks, indicating that lymphangiogenesis was stimulated. When comparing the different oils, vascularized tissue area and vascular density of sunflower oil were significantly higher than corn and peanut oils.

CONCLUSIONS

These results provide novel evidence supporting that induction of microvascular network growth into the normally avascular mouse mesentery is possible.

Assessing the effects of threonyl-tRNA synthetase on angiogenesis-related responses

Several recent reports have found a connection between specific aminoacyl-tRNA synthetases and the regulation of angiogenesis. As this new area of research is explored, it is important to have reliable assays to assess the specific angiogenesis functions of these enzymes. This review provides information about specific in vitro and in vivo methods that were used to assess the angiogenic functions of threonyl-tRNA synthetase including endothelial cell migration and tube assays as well as chorioallantoic membrane and tumor vascularization assays. The theory and discussion include best methods of analysis and quantification along with the advantages and limitations of each type of assay.

Abstract POSTER-BIOL-1335: Threonyl-tRNA synthetase overexpression correlates with angiogenesis and progression of human ovarian cancer

Ovarian tumors create a dynamic microenvironment that promotes angiogenesis and reduces immune responses. There is growing evidence that tRNA synthetases have a role in cell signaling separate from their function in protein synthesis. Our research has revealed that threonyl-tRNA synthetase (TARS) has an extracellular angiogenic activity. Exploration of protein and mRNA databases further showed a connection between TARS expression and ovarian cancer. The objective of this study was to test the hypothesis that TARS is secreted by ovarian cancer cells and that its expression in clinical samples correlates with angiogenic markers and ovarian cancer progression. TARS secretion by SKOV3 human ovarian cancer cells was induced by hypoxia or tumor necrosis factor-α (TNF-α) as detected by ELISA and Western blot of culture media (p<0.001). For the clinical study, TARS, vascular endothelial growth factor (VEGF) and PECAM were assessed by immunohistochemistry in serial sections of paraffin embedded ovarian tissues from 70 patients diagnosed with epithelial ovarian cancer and 12 control patients. Serum samples from 31 tissue-matched patients were analyzed by ELISA for TARS, CA125, and tumor necrosis factor-α (TNF-α). There was a strong association between the tumor expression of TARS and advancing stage of epithelial ovarian cancer (p<0.001). TARS expression and localization were also correlated with VEGF (p<0.001). A significant proportion of samples included heavy TARS staining of infiltrating leukocytes which also correlated with stage (p=0.017). Patient serum TARS was related to tumor TARS and angiogenic markers, but did not achieve significance with respect to stage. Multivariate Cox proportional hazard models revealed a surprising inverse relationship between TARS expression and mortality risk in late stage disease (p=0.062). Together these results show that TARS is secreted in response to cell stress and that its expression is increased in epithelial ovarian cancer according to stage and angiogenic progression. These findings and the association of TARS with disease survival provide clinical validation that TARS is associated with angiogenesis in ovarian cancer. These results encourage further study of TARS as a regulator of the tumor microenvironment and possible target for diagnosis and/or treatment in ovarian cancer.

Citation Format: Theresa L. Wellman, Midori Eckenstein, Cheung Wong, Mercedes Rincon, Takamaru Ashikaga, Sharon L. Mount, Christopher S. Francklyn, Karen M. Lounsbury. Threonyl-tRNA synthetase overexpression correlates with angiogenesis and progression of human ovarian cancer [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-BIOL-1335.

Aminoacyl-tRNA synthetase dependent angiogenesis revealed by a bioengineered macrolide inhibitor

Aminoacyl-tRNA synthetases (AARSs) catalyze an early step in protein synthesis, but also regulate diverse physiological processes in animal cells. These include angiogenesis, and human threonyl-tRNA synthetase (TARS) represents a potent pro-angiogenic AARS. Angiogenesis stimulation can be blocked by the macrolide antibiotic borrelidin (BN), which exhibits a broad spectrum toxicity that has discouraged deeper investigation. Recently, a less toxic variant (BC194) was identified that potently inhibits angiogenesis. Employing biochemical, cell biological, and biophysical approaches, we demonstrate that the toxicity of BN and its derivatives is linked to its competition with the threonine substrate at the molecular level, which stimulates amino acid starvation and apoptosis. By separating toxicity from the inhibition of angiogenesis, a direct role for TARS in vascular development in the zebrafish could be demonstrated. Bioengineered natural products are thus useful tools in unmasking the cryptic functions of conventional enzymes in the regulation of complex processes in higher metazoans.

Abstract 5224: Non-canonical activity of threonyl-tRNA synthetase promotes angiogenesis and invasion in a mouse model of ovarian cancer

Despite clear connections between the tumor microenvironment and ovarian cancer invasion, the underlying molecular mechanisms remain elusive. We have recently shown that the protein synthesis regulator threonyl-tRNA synthetase (TARS) has a unique extracellular angiogenic activity separate from its canonical function. Secreted TARS promotes endothelial cell migration and tube formation, and a selective TARS inhibitor, BC194, disrupts normal vessel development in zebra fish and chick embryo models. TARS expression also correlates with tumor stage and angiogenesis in human ovarian cancer. The objective of this study was to validate the biological and clinical relationship between TARS and ovarian tumor progression using a syngenic mouse model of epithelial ovarian cancer. Tumors were initiated by intraperitoneal injection of ID8 mouse ovarian cancer cells, and tumors formed at 4-6 weeks were scored for invasiveness and analyzed by immunostaining for TARS expression and microvascular density. To test the hypothesis that overexpression of TARS promotes invasion, cells were stably transfected with a TARS expression plasmid prior to injection. To test the hypothesis that TARS inhibition reduces tumor invasion, animals harboring ID8 tumors were treated with the high-affinity TARS inhibitor BC194. We found that TARS levels were elevated in ovarian tumors as compared with normal ovarian tissue. Overexpression of TARS in ID8 cells also resulted in enhanced invasiveness and microvascular density of the resulting tumors (p = 0.026). Preliminary results also indicated that inhibition of TARS by BC194 treatment reduced tumor angiogenesis and growth (p = 0.005) without observed toxicities in the animals. Overall, these results show that modifying TARS expression or activity can affect in vivo ovarian tumor angiogenesis and progression. These results encourage further study of TARS as a regulator of the tumor microenvironment and as a possible target for diagnosis and treatment of ovarian cancer.

Citation Format: Peibin Wo, Theresa Wellman, Alan Howe, Christopher Francklyn, Karen M. Lounsbury. Non-canonical activity of threonyl-tRNA synthetase promotes angiogenesis and invasion in a mouse model of ovarian cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5224. doi:10.1158/1538-7445.AM2015-5224

Threonyl-tRNA synthetase overexpression correlates with angiogenic markers and progression of human ovarian cancer

Background

Ovarian tumors create a dynamic microenvironment that promotes angiogenesis and reduces immune responses. Our research has revealed that threonyl-tRNA synthetase (TARS) has an extracellular angiogenic activity separate from its function in protein synthesis. The objective of this study was to test the hypothesis that TARS expression in clinical samples correlates with angiogenic markers and ovarian cancer progression.

Methods

Protein and mRNA databases were explored to correlate TARS expression with ovarian cancer. Serial sections of paraffin embedded ovarian tissues from 70 patients diagnosed with epithelial ovarian cancer and 12 control patients were assessed for expression of TARS, vascular endothelial growth factor (VEGF) and PECAM using immunohistochemistry. TARS secretion from SK-OV-3 human ovarian cancer cells was measured. Serum samples from 31 tissue-matched patients were analyzed by ELISA for TARS, CA-125, and tumor necrosis factor-α (TNF-α).

Results

There was a strong association between the tumor expression of TARS and advancing stage of epithelial ovarian cancer (p < 0.001). TARS expression and localization were also correlated with VEGF (p < 0.001). A significant proportion of samples included heavy TARS staining of infiltrating leukocytes which also correlated with stage (p = 0.017). TARS was secreted by ovarian cancer cells, and patient serum TARS was related to tumor TARS and angiogenic markers, but did not achieve significance with respect to stage. Multivariate Cox proportional hazard models revealed a surprising inverse relationship between TARS expression and mortality risk in late stage disease (p = 0.062).

Conclusions

TARS expression is increased in epithelial ovarian cancer and correlates with markers of angiogenic progression. These findings and the association of TARS with disease survival provide clinical validation that TARS is associated with angiogenesis in ovarian cancer. These results encourage further study of TARS as a regulator of the tumor microenvironment and possible target for diagnosis and/or treatment in ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-620) contains supplementary material, which is available to authorized users.

Differential regulation of GLUT1 and GLUT8 expression by hypoxia in mammary epithelial cells

Glucose is a major substrate for milk synthesis and is taken up from the blood by mammary epithelial cells (MECs) through facilitative glucose transporters (GLUTs). The expression levels of GLUT1 and GLUT8 are upregulated dramatically in the mammary gland from late pregnancy through early lactation stages. This study aimed to test the hypothesis that this increase in GLUT1 and GLUT8 expression involves hypoxia signaling through hypoxia inducible factor-1α (HIF-1α) in MECs. Mouse mammary glands showed significantly more hypoxia in midpregnancy through early lactation stages compared with in the virgin stage, as stained by the hypoxia marker pimonidazole HCl. Treatment with hypoxia (2% O2) significantly stimulated glucose uptake and GLUT1 mRNA and protein expression, but decreased GLUT8 mRNA expression in bovine MECs. In MECs, hypoxia also increased the levels of HIF-1α protein in the nuclei, and siRNA against HIF-1α completely abolished the hypoxia-induced upregulation of GLUT1, while having no effect on GLUT8 expression. A 5'-RCGTG-3' core HIF-1α binding sequence was identified 3.7 kb upstream of the bovine GLUT1 gene, and HIF-1α binding to this site was increased during hypoxia. In conclusion, the mammary glands in pregnant and lactating animals are hypoxic, and MECs respond to this hypoxia by increasing GLUT1 expression and glucose uptake through a HIF-1α-dependent mechanism. GLUT8 expression, however, is negatively regulated by hypoxia through a HIF-1α-independent pathway. The regulation of glucose transporters through hypoxia-mediated gene transcription in the mammary gland may provide an important physiological mechanism for MECs to meet the metabolic demands of mammary development and lactation.

Negative regulation of HIF-1α by an FBW7-mediated degradation pathway during hypoxia

Hypoxia inducible factor-1α (HIF-1α) stimulates expression of genes associated with angiogenesis and is associated with poor outcomes in ovarian and other cancers. In normoxia, HIF-1α is ubiquitinated and degraded through the E3 ubiquitin ligase, von Hippel-Lindau; however, little is known about the regulation of HIF-1α in hypoxic conditions. FBW7 is an E3 ubiquitin ligase that recognizes proteins phosphorylated by glycogen synthase kinase 3β (GSK3β) and targets them for destruction. This study used an ovarian cancer cell model to test the hypothesis that HIF-1α phosphorylation by GSK3β in hypoxia leads to interaction with FBW7 and ubiquitin-dependent degradation. Expression of constitutively active GSK3β reduced HIF-1α protein and transcriptional activity and increased ubiquitination of HIF-1α in hypoxia, whereas pharmacologic inhibition of GSK3 or expression of siGSK3β promoted HIF-1α stabilization and activity. A mechanism through FBW7 was supported by the observed decrease in HIF-1α stabilization when FBW7 was overexpressed and both the elevation of HIF-1α levels and decrease in ubiquitinated HIF-1α when FBW7 was suppressed. Furthermore, HIF-1α associated with FBW7γ by co-immunoprecipitation, and the interaction was weakened by inhibition of GSK3 or mutation of GSK3β phosphorylation sites. The relevance of this pathway to angiogenic signaling was supported by the finding that endothelial cell tube maturation was increased by conditioned media from hypoxic SK-OV-3 cell lines expressing suppressed GSK3β or FBW7. These data introduce a new mechanism for regulation of HIF-1α during hypoxia that utilizes phosphorylation to target HIF-1α for ubiquitin-dependent degradation through FBW7 and may identify new targets in the regulation of angiogenesis.

Activation of hypoxia-inducible factor-1 protects airway epithelium against oxidant-induced barrier dysfunction

The respiratory epithelium forms an important barrier against inhaled pollutants and microorganisms, and its barrier function is often compromised during inflammatory airway diseases. Epithelial activation of hypoxia-inducible factor-1 (HIF-1) represents one feature of airway inflammation, but the functional importance of HIF-1 within the respiratory epithelium is largely unknown. Using primary mouse tracheal epithelial (MTE) cells or immortalized human bronchial epithelial cells (16HBE14o-), we evaluated the impact of HIF-1 activation on loss of epithelial barrier function during oxidative stress. Exposure of either 16HBE14o- or MTE cells to H(2)O(2) resulted in significant loss of transepithelial electrical resistance and increased permeability to fluorescein isothiocyanate-dextran (4 kDa), and this was attenuated significantly after prior activation of HIF-1 by preexposure to hypoxia (2% O(2); 6 h) or the hypoxia mimics CoCl(2) or dimethyloxalylglycine (DMOG). Oxidative barrier loss was associated with reduced levels of the tight junction protein occludin and with hyperoxidation of the antioxidant enzyme peroxiredoxin (Prx-SO(2)H), events that were also attenuated by prior activation of HIF-1. Involvement of HIF-1 in these protective effects was confirmed using the pharmacological inhibitor YC-1 and by short-hairpin RNA knockdown of HIF-1α. The protective effects of HIF-1 were associated with induction of sestrin-2, a hypoxia-inducible enzyme known to reduce oxidative stress and minimize Prx hyperoxidation. Together, our results suggest that loss of epithelial barrier integrity by oxidative stress is minimized by activation of HIF-1, in part by induction of sestrin-2.

Abstract 3092: FBW7 targets hypoxia inducible factor-1α (HIF-1α) for proteasomal degradation during hypoxia

Hypoxia Inducible Factor-1α (HIF-1α) mediates expression of genes associated with endothelial cell-mediated angiogenesis and is associated with poor outcomes in a variety of cancers. In normoxia, HIF-1α is ubiquitinated and degraded through interactions with the E3 ubiqutin ligase, von Hippel-Lindau (vHL); however, little is known about the negative regulation of HIF-1α in hypoxia. FBW7, an E3 ubiquitin ligase, has been shown to interact with several transcription factors including those phosphorylated by glycogen synthase kinase 3β (GSK3β). The current study tested the hypothesis that phosphorylation of HIF-1α by GSK3β increases the FBW7-mediated ubiquitination and degradation of HIF-1α, thereby resulting in suppression of the hypoxia-mediated angiogenic response in SKOV-3 ovarian cancer cells. HIF-1α protein and VEGF transcript levels in hypoxia were increased when GSK3β activity was inhibited and were reduced by expression of constitutively active GSK3β (GSK3S9A). Additionally, expression of GSK3S9A increased HIF-1α ubiquitination. Conditioned media from SKOV-3 cells expressing shRNA against GSK3β (shGSK3) had an enhanced effect on endothelial tube formation in a Matrigel matrix, suggesting that GSK3β exerts an inhibitory effect on hypoxia-mediated angiogenesis. Overexpression of the β and γ isoforms of FBW7 decreased HIF-1α stabilization, and HIF-1α interacts with FBW7 by co-immunoprecipitation. Furthermore, knockdown of FBW7 using siRNA resulted in increased HIF-1α levels in hypoxia. These data suggest a new mechanism for negative regulation of HIF-1α during hypoxia that utilizes phosphorylation by GSK3β and interaction with FBW7 leading to ubiquitination and proteasomal degradation. Results of this study better define the signaling pathways necessary for HIF-1α-mediated signaling and may identify new targets that mediate angiogenesis in disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3092. doi:10.1158/1538-7445.AM2011-3092

A protein kinase Cdelta-dependent protein kinase D pathway modulates ERK1/2 and JNK1/2 phosphorylation and Bim-associated apoptosis by asbestos

Inhalation of asbestos and oxidant-generating pollutants causes injury and compensatory proliferation of lung epithelium, but the signaling mechanisms that lead to these responses are unclear. We hypothesized that a protein kinase (PK)Cdelta-dependent PKD pathway was able to regulate downstream mitogen-activated protein kinases, affecting pro- and anti-apoptotic responses to asbestos. Elevated levels of phosphorylated PKD (p-PKD) were observed in distal bronchiolar epithelial cells of mice inhaling asbestos. In contrast, PKCdelta-/- mice showed significantly lower levels of p-PKD in lung homogenates and in situ after asbestos inhalation. In a murine lung epithelial cell line, asbestos caused significant increases in the phosphorylation of PKCdelta-dependent PKD, ERK1/2, and JNK1/2/c-Jun that occurred with decreases in the BH3-only pro-apoptotic protein, Bim. Silencing of PKCdelta, PKD, and use of small molecule inhibitors linked the ERK1/2 pathway to the prevention of Bim-associated apoptosis as well as the JNK1/2/c-Jun pathway to the induction of apoptosis. Our studies are the first to show that asbestos induces PKD phosphorylation in lung epithelial cells both in vivo and in vitro. PKCdelta-dependent PKD phosphorylation by asbestos is causally linked to a cellular pathway that involves the phosphorylation of both ERK1/2 and JNK1/2, which play opposing roles in the apoptotic response induced by asbestos.

Protein kinase A-mediated CREB phosphorylation is an oxidant-induced survival pathway in alveolar type II cells

Oxidant stress plays a role in the pathogenesis of pulmonary diseases, including fibrotic lung disease and cancer. We previously found that hydrogen peroxide (H₂O₂) initiates an increase in Ca²⁺/cAMP-response element binding protein (CREB) phosphorylation in C10 alveolar type II cells that requires activation of extracellular regulated kinases 1/2 (ERK1/2). Here, we investigated the role of crosstalk between protein kinase A (PKA) and epidermal growth factor receptor (EGFR) in oxidant-induced signaling to ERK1/2 and CREB in C10 cells. Application of H₂O₂ increased nuclear accumulation of PKA, and inhibition of PKA with H89 reduced oxidant-mediated phosphorylation of both CREB and ERK1/2. Single cell measurements of cAMP and redox status, using a FRET-based biosensor and a redox-sensitive GFP, respectively, indicated that H₂O₂ increases production of cAMP that correlates with redox state. Inhibition of EGFR activity decreased both H₂O₂-induced CREB phosphorylation and translocation of PKA to the nucleus, suggesting that crosstalk between PKA and EGFR underlies the oxidant-induced CREB response. Furthermore, knockdown of CREB expression using siRNA led to a decrease in bcl-2 and an increase in oxidant-induced apoptosis. Together these data reveal a novel role for crosstalk between PKA, ERK1/2 and CREB that mediates cell survival during oxidant stress.

Inflammatory levels of nitric oxide inhibit airway epithelial cell migration by inhibition of the kinase ERK1/2 and activation of hypoxia-inducible factor-1 alpha

Increased synthesis of NO during airway inflammation, caused by induction of nitric-oxide synthase 2 in several lung cell types, may contribute to epithelial injury and permeability. To investigate the consequence of elevated NO production on epithelial function, we exposed cultured monolayers of human bronchial epithelial cells to the NO donor diethylenetriaamine NONOate. At concentrations generating high nanomolar levels of NO, representative of inflammatory conditions, diethylenetriaamine NONOate markedly reduced wound closure in an in vitro scratch injury model, primarily by inhibiting epithelial cell migration. Analysis of signaling pathways and gene expression profiles indicated a rapid induction of the mitogen-activated protein kinase phosphatase (MPK)-1 and decrease in extracellular signal-regulated kinase (ERK)1/2 activation, as well as marked stabilization of hypoxia-inducible factor (HIF)-1alpha and activation of hypoxia-responsive genes, under these conditions. Inhibition of ERK1/2 signaling using U0126 enhanced HIF-1alpha stabilization, implicating ERK1/2 dephosphorylation as a contributing mechanism in NO-mediated HIF-1alpha activation. Activation of HIF-1alpha by the hypoxia mimic cobalt chloride, or cell transfection with a degradation-resistant HIF-1alpha mutant construct inhibited epithelial wound repair, implicating HIF-1alpha in NO-mediated inhibition of cell migration. Conversely, NO-mediated inhibition of epithelial wound closure was largely prevented after small interfering RNA suppression of HIF-1alpha. Finally, NO-mediated inhibition of cell migration was associated with HIF-1alpha-dependent induction of PAI-1 and activation of p53, both negative regulators of epithelial cell migration. Collectively, our results demonstrate that inflammatory levels of NO inhibit epithelial cell migration, because of suppression of ERK1/2 signaling, and activation of HIF-1alpha and p53, with potential consequences for epithelial repair and remodeling during airway inflammation.

Genes overexpressed in cerebral arteries following salt-induced hypertensive disease are regulated by angiotensin II, JunB, and CREB

Although changes in gene expression are necessary for arterial remodeling during hypertension, the genes altered and their mechanisms of regulation remain uncertain. The goal of this study was to identify cerebral artery genes altered by hypertension and define signaling pathways important in their regulation. Intact cerebral arteries from Dahl salt-sensitive normotensive and hypertensive high-salt (HS) rats were examined by immunostaining, revealing an increased phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and expression of the proliferative marker Ki-67 in arteries from hypertensive animals. Arterial RNA analyzed by microarray and validated with RT-quantitative PCR revealed that jun family member junB and matricellular genes plasminogen activator inhibitor-1 (PAI-1) and osteopontin (OPN) were significantly overexpressed in HS arteries. Fisher exact test and annotation-based gene subsets showed that genes upregulated by Jun and Ca2+/cAMP-response element-binding protein (CREB) were overrepresented. A model of cultured rat cerebrovascular smooth muscle cells was used to test the hypothesis that angiotensin II (ANG II), JunB, and CREB are important in the regulation of genes identified in the rat hypertension model. ANG II induced a transient induction of junB and a delayed induction of PAI-1 and OPN mRNA levels, which were reduced by ERK inhibition with U-0126. Silencing junB using small-interfering RNA reduced mRNA levels of OPN but not PAI-1. The silencing of CREB reduced PAI-1 induction by ANG II but enhanced the transcription of OPN. Together, these results suggest that salt-induced hypertensive disease promotes changes in matricellular genes that are stimulated by ANG II, regulated by ERK, and selectively regulated by JunB and CREB.

Asbestos-mediated CREB phosphorylation is regulated by protein kinase A and extracellular signal-regulated kinases 1/2

Asbestos is a ubiquitous, naturally occurring fiber that has been linked to the development of malignant and fibrotic lung diseases. Asbestos exposure leads to apoptosis, followed by compensatory proliferation, yet many of the signaling cascades coupled to these outcomes are unclear. Because CREs (Ca(2+)/cAMP-response elements) are found in the promoters of many genes important for regulation of proliferation and apoptosis, CREB (CRE binding protein) is likely to play an important role in the development of asbestos-mediated lung injury. To explore this possibility, we tested the hypotheses that asbestos exposure leads to CREB phosphorylation in lung epithelial cells and that protein kinase A (PKA) and extracellular signal-regulated kinases 1/2 (ERK1/2) are central regulators of the CREB pathway. Persistent CREB phosphorylation was observed in lung sections from mice following inhalation of crocidolite asbestos. Exposure of C10 lung epithelial cells to crocidolite asbestos led to rapid CREB phosphorylation and apoptosis that was decreased by the inhibition of PKA or ERK1/2 using the specific inhibitors H89 and U0126, respectively. Furthermore, crocidolite asbestos selectively induced a sustained increase in MAP kinase phosphatase-1 mRNA and protein. Silencing CREB protein dramatically reduced asbestos-mediated ERK1/2 phosphorylation, yet significantly increased the number of cells undergoing asbestos-induced apoptosis. These data reveal a novel and selective role for CREB in asbestos-mediated signaling through pathways regulated by PKA and ERK1/2, further providing evidence that CREB is an important regulator of apoptosis in asbestos-induced responses of lung epithelial cells.

Asbestos-induced peribronchiolar cell proliferation and cytokine production are attenuated in lungs of protein kinase C-delta knockout mice

The signaling pathways leading to the development of asbestos-associated diseases are poorly understood. Here we used normal and protein kinase C (PKC)-delta knockout (PKCdelta-/-) mice to demonstrate multiple roles of PKC-delta in the development of cell proliferation and inflammation after inhalation of chrysotile asbestos. At 3 days, asbestos-induced peribronchiolar cell proliferation in wild-type mice was attenuated in PKCdelta-/- mice. Cytokine profiles in bronchoalveolar lavage fluids showed increases in interleukin (IL)-1beta, IL-4, IL-6, and IL-13 that were decreased in PKCdelta-/- mice. At 9 days, microarray and quantitative reverse transcriptase-polymerase chain reaction analysis of lung tissues revealed increased mRNA levels of the profibrotic cytokine, IL-4, in asbestos-exposed wild-type mice but not PKCdelta-/- mice. PKCdelta-/- mice also exhibited decreased lung infiltration of polymorphonuclear cells, natural killer cells, and macrophages in bronchoalveolar lavage fluid and lung, as well as increased numbers of B lymphocytes and plasma cells. These changes were accompanied by elevated mRNA levels of immunoglobulin chains. These data show that modulation of PKC-delta has multiple effects on peribronchiolar cell proliferation, proinflammatory and profibrotic cytokine expression, and immune cell profiles in lung. These results also implicate targeted interruption of PKC-delta as a potential therapeutic option in asbestos-induced lung diseases.

Methylation-controlled J protein promotes c-Jun degradation to prevent ABCB1 transporter expression

Methylation-controlled J protein (MCJ) is a newly identified member of the DnaJ family of cochaperones. Hypermethylation-mediated transcriptional silencing of the MCJ gene has been associated with increased chemotherapeutic resistance in ovarian cancer. However, the biology and function of MCJ remain unknown. Here we show that MCJ is a type II transmembrane cochaperone localized in the Golgi network and present only in vertebrates. MCJ is expressed in drug-sensitive breast cancer cells but not in multidrug-resistant cells. The inhibition of MCJ expression increases resistance to specific drugs by inducing expression of the ABCB1 drug transporter that prevents intracellular drug accumulation. The induction of ABCB1 gene expression is mediated by increased levels of c-Jun due to an impaired degradation of this transcription factor in the absence of MCJ. Thus, MCJ is required in these cells to prevent c-Jun-mediated expression of ABCB1 and maintain drug response.

Oxidants and signaling by mitogen-activated protein kinases in lung epithelium

Oxidants in cigarette smoke and generated from asbestos fibers activate mitogen-activated protein kinase (MAPK) signaling cascades in lung epithelial cells in vitro and in vivo. These signaling pathways lead to the enhanced ability of Jun and Fos family members (i.e., components of the activator protein [AP]-1 transcription factor) to activate transcription of a number of AP-1-dependent target genes involved in cell proliferation or death, differentiation, and inflammation. Research by the Basbaum laboratory has been critical in showing that mucin transcription in response to cigarette smoke and gram-positive bacteria is mediated through activation of the epidermal growth factor receptor and MAPK cascades. Work from our laboratories supports the concept that MAPK signaling and AP-1 transactivation by cigarette smoke and asbestos may synergize in lung epithelial cell injury, compensatory proliferation of lung epithelial cells, and carcinogenesis, supporting a mechanistic framework for the striking increases in lung cancer incidence in asbestos workers who smoke. Targeting of MAPKs and inter-related signaling cascades may be critical to the prevention of lung cancers and control of mucin overproduction in a number of lung diseases including asthma, cystic fibrosis, chronic bronchitis, and chronic obstructive pulmonary disease.

Transcriptional up‐regulation of MMPs 12 and 13 by asbestos occurs via a PKCδ‐dependent pathway in murine lung

Asbestos is a known inflammatory, carcinogenic, and fibrotic agent, but the mechanisms leading to asbestos-induced lung diseases are unclear. Using a murine inhalation model of fibrogenesis, we show that asbestos causes significant increases in mRNA levels of lung matrix metalloproteinases (MMPs 12 and 13) and tissue inhibitor of metalloproteinases (TIMP1), as well as increased activities of MMP 2, 9, and 12 in bronchoalveolar lavage fluids (BALF). Asbestos-exposed PKCdelta knockout (PKCdelta-/-) mice exhibited decreased expression of lung MMP12 and MMP13 compared with asbestos-exposed wild-type mice. Studies using small molecule inhibitors in murine alveolar epithelial type II cells (C10) and primary lung fibroblasts confirmed that asbestos transcriptionally up-regulates MMPs via an EGFR (or other growth factor receptors)/PI3K/PKCdelta/ERK1/2 pathway. Moreover, use of a broad-spectrum MMP inhibitor showed that MMPs play an important role in further enhancing asbestos-induced signaling events by activating EGFR. These data reveal a potentially important link between asbestos signaling and integrity of the extracellular matrix (ECM) that likely contributes to asbestos-induced lung remodeling and diseases.

Ca2+ source-dependent transcription of CRE-containing genes in vascular smooth muscle

Altered Ca2+ handling has immediate physiological and long-term genomic effects on vascular smooth muscle function. Previously we showed that Ca2+ entry through voltage-dependent Ca2+ channels (VDCCs) or store-operated Ca2+ channels (SOCCs) results in phosphorylation of the Ca2+/cAMP response element (CRE)-binding protein in cerebral arteries. Here, oligonucleotide array analysis was used to determine gene transcription profiles resulting from these two Ca2+ entry pathways in human cerebrovascular smooth muscle cell cultures. Results were confirmed and expanded using quantitative RT-PCR, Western blot, and immunofluorescence. A distinct, yet overlapping, set of CRE-regulated genes was induced by VDCC activation using K+ membrane depolarization vs. SOCC activation by thapsigargin (TG). Membrane depolarization selectively induced a sustained increase in early growth response-1 (Egr-1) mRNA and protein, which were inhibited by the VDCC blocker nimodipine and the SOCC inhibitor 2-aminoethoxydiphenylborate (2-APB). TG selectively induced a sustained increase in MAPK phosphatase-1 (MKP-1) mRNA and protein, and these effects were decreased by 2-APB, but not by nimodipine. The physiological agonist ANG II also stimulated expression of Egr-1 and MKP-1. Coadministration of 2-APB prevented expression of Egr-1 and MKP-1, whereas nimodipine blocked only Egr-1 expression. TG and ANG II induced phosphorylation of ERK, which was sensitive to 2-APB and was selectively required for CRE-binding protein phosphorylation. Our findings thus indicate that Ca2+ entry through VDCCs and store-operated Ca2+ entry can differentially regulate CRE-containing genes in vascular smooth muscle and also imply that agonist-induced signals involved in modulation of gene transcription can be controlled by multiple sources of Ca2+.

Pressure elevation slows the fibroblast response to wound healing

OBJECTIVE

Chronic venous insufficiency and venous ulceration are consequences of elevated pressure within affected limbs. We hypothesized that wounded cells maintained at different atmospheric pressures heal at different rates and that pressure would adversely affect the processes necessary for wound healing.

METHODS

We have developed an in vitro model that replicates venous hypertension in a unique pressurized incubator using neonatal fibroblasts. Neonatal fibroblasts grown to confluence were wounded with a standardized linear incision and then placed in a unique pressure incubator at atmospheric pressure, atmospheric pressure plus 30 mm Hg, atmospheric pressure plus 60 mm Hg, and atmospheric pressure plus 120 mm Hg. Cells were observed daily until complete healing of the wound occurred. Twelve to 18 hours after wounding, proliferating cell nuclear antigen analysis was done by immunocytochemistry.

RESULTS

Wounds at atmospheric pressure plus 30 mm Hg were healed by day 3, those at atmospheric pressure plus 60 mm Hg by day 4, and those grown at atmospheric pressure plus 120 mm Hg took > or =4 days for complete healing. Significantly less proliferating cell nuclear antigen activity was present in cells grown at atmospheric pressure plus 60 mm Hg (P < .0001) and atmospheric pressure plus 120 mm Hg (P < .02). Wound edge fluorescence analysis demonstrated less fluorescence in each group compared with atmospheric pressure.

CONCLUSIONS

In this model of wound healing under pressure, neonatal fibroblasts grown to confluence and given a standardized wound displayed characteristics consistent with delayed healing. Elevated pressure has a role in the delayed migration and proliferation seen in this model.

CLINICAL RELEVANCE

The elevated pressure in patients with venous insufficiency causes their wounds to heal less quickly. Understanding and quantifying the physiology and role of elevated tissue pressure due to venous hypertension will lead to a better understanding of wound healing in these patients.

Excitation-transcription coupling in smooth muscle

Calcium (Ca2+) signals affect virtually every biological process, including both contraction and gene transcription in smooth muscle. Ca2+-regulated gene transcription is known to be important for both physiological and pathological responses in smooth muscle. The aim of this review is to discuss the current understanding of gene transcription regulated by excitation through Ca2+ signalling using a comparison of the two most characterized Ca2+-regulated transcription factors in smooth muscle, Ca2+-cyclic AMP response element binding protein (CREB) and nuclear factor of activated T-cells (NFAT). Recent studies have shown commonalities and differences in the regulation of CREB and NFAT through both voltage- and non-voltage-gated Ca2+ channels that lead to expression of smooth muscle cell specific differentiation markers as well as markers of proliferation. New insights into the regulation of specific genes through companion elements on the promoters of Ca2+-regulated genes have led to new models for transcriptional regulation by Ca2+ that are defined both by the source and duration of the Ca2+ signal and the composition of enhancer elements found within the regulatory regions of specific genes. Thus the combination of signalling pathways elicited by particular Ca2+ signals affect selective promoter elements that are key to the ultimate pattern of gene transcription.

Erythropoietin disrupts hypoxia-inducible factor signaling in ovarian cancer cells

OBJECTIVE

The objective of this study was to evaluate the effects of recombinant erythropoietin (EPO) on HIF-1alpha induced angiogenic pathways in ovarian cancer cells.

METHODS

Using Western blots and both quantitative and non-quantitative RT-PCR, HIF-1alpha protein and VEGF transcription levels were assessed. Cell growth was measured using flow cytometry.

RESULTS

EPO treatment decreased hypoxia-induced HIF-1alpha protein levels and VEGF transcription, with no effect on cell growth. Inhibition of HIF-1alpha signaling by EPO was also observed in MCF-7 breast cancer cells.

CONCLUSION

These novel findings suggest that EPO may exhibit anti-angiogenic properties, thus encouraging further exploration of signaling pathways between EPO and HIF-1alpha.

Oxidant-mediated cAMP response element binding protein activation: calcium regulation and role in apoptosis of lung epithelial cells

Oxidant stress-mediated regulation of extracellular signal-regulated kinases (ERK1/2) is linked to pathologic outcomes in lung epithelium, yet a role for Ca2+ and Ca2+/cAMP-response element binding protein (CREB) in ERK1/2 signaling has not been defined. In this study, we tested the hypotheses that oxidants induce Ca2+-mediated phosphorylation of ERK and CREB, and that CREB is required for oxidant-induced proliferation and apoptosis. H2O2 initiated an influx of extracellular Ca2+ that was required for phosphorylation of both ERK and CREB in C10 lung epithelial cells. H2O2-mediated CREB phosphorylation was sensitive to MEK inhibition, suggesting that crosstalk between Ca2+, ERK, and CREB signaling pathways contributes to the oxidant-induced response. Reduction of CREB activity, using a dominant-negative CREB construct, inhibited c-fos steady-state mRNA levels, but unexpectedly enhanced bcl-2 steady-state mRNA levels after H2O2 exposure. Whereas inhibition of CREB activity had no detectable effect on H2O2 stimulation of cell cycle, loss of CREB activity significantly reduced the number of cells undergoing apoptosis. These data support a novel communication between Ca2+-ERK1/2 and CREB elicited by H2O2, and further provide evidence that CREB is an important regulator of apoptosis in oxidant-mediated responses of lung epithelial cells.

Pressure-induced cellular senescence: A mechanism linking venous hypertension to venous ulcers1

INTRODUCTION

Slow healing of ulcers in chronic venous insufficiency (CVI) has long been thought secondary to venous hypertension. Dermal fibroblasts isolated from venous ulcers have morphologies and protein production suggestive of premature aging. In this study, we hypothesized that neonatal fibroblasts (NNF) cultured under elevated pressure will demonstrate premature aging and that this effect will be augmented by an inflammatory mediator, transforming growth factor beta (TGF-beta).

MATERIALS AND METHODS

A unique pressure incubator was used to culture NNF at atmospheric pressure (ATM), ATM + 30 mmHg, ATM + 60 mmHg, and ATM +120 mmHg. Some pressure-exposed NNF were also cultured with TGF- beta (1 ng/ml). Growth rates were determined by flow cytometry. Senescent cells were identified by staining with a marker for cellular senescence, beta-galactosidase (SA-beta-Gal). Light microscopy and digital imaging were used to evaluate cell morphology. Paired linear models and comparison of the slopes were used for statistical analysis of growth. chi2 analysis was used to compare senescence rates.

RESULTS

NNF cultured at ATM + 60 mmHg and ATM + 120 mmHg showed increased SA-beta-Gal activity (P <0.05), and reduced growth rates (P <0.05) at 11 days. These effects were not seen at ATM + 30 mmHg. NNF grown with TGF-beta did not show augmented SA-beta-Gal staining.

CONCLUSIONS

Pressure-exposed NNF demonstrated an accelerated aging phenomenon similar to fibroblasts isolated from venous ulcers. This aging effect was directly related to the level of pressure. TGF-beta did not augment the aging effect. This study suggests that pressure elevations result in altered cell function and accelerated aging that may contribute to the slowed healing seen in patients with venous insufficiency.

The γ-Glutamylcysteine Synthetase and Glutathione Regulate Asbestos-induced Expression of Activator Protein-1 Family Members and Activity

Asbestos fibers cause persistent increases in activator protein-1 (AP-1) family member proto-oncogenes in lung epithelial and mesothelial cells that are linked to proliferation and cell transformation. Using lung epithelial cells, the progenitor cells of lung cancers, we report that crocidolite asbestos initially depletes intracellular glutathione followed by up-regulation of both catalytic and modifier subunits of gamma-glutamylcysteine synthetase. In vivo asbestos inhalation experiments confirm increased protein levels of gamma-glutamylcysteine synthetase in mouse lungs. We also show that asbestos-induced mRNA levels of fos/jun proto-oncogenes, fra-1 transactivation, and AP-1 to DNA binding activity are glutathione-dependent. Epidermal growth factor receptor activity by asbestos is blocked by N-acetyl-l-cysteine, suggesting that it is an initial redox-activated event leading to downstream AP-1 proto-oncogene up-regulation. The overexpression of subunits of gamma-glutamylcysteine synthetase in combination completely blocked asbestos-induced up-regulation of AP-1 proto-oncogene expression. However, when overexpressed individually, the modifier subunit had more dramatic effects than the catalytic subunit. Our work shows that the glutathione-controlled redox status of the epithelial cell plays a pivotal role in asbestos-induced epidermal growth factor receptor and proto-oncogene activation as well as AP-1 activity.

In situ detection and visualization of S-nitrosylated proteins following chemical derivatization: identification of Ran GTPase as a target for S-nitrosylation

The formation of S-nitrosylated proteins is a nitric oxide-dependent post-translational modification important in signal transduction, yet the in situ detection of S-nitrosylated proteins remains problematic. In this study, we adapted a recently developed biotin derivatization approach to visualize S-nitrosylated proteins in intact cells. This strategy circumvents the use of antibodies directed against S-nitrosocysteine, which may have problematic specificity, due to epitope instability. Endogenous protein S-nitrosylation could be observed in intact cells and in mouse lung sections using fluorophore-conjugated streptavidin and confocal microscopy, and was enhanced by S-nitrosothiols and reduced following treatment with the nitric oxide synthase inhibitor, L-N-monomethyl arginine. Intriguingly, protein S-nitrosylation was detected mainly in the nuclear compartment of cells under baseline conditions and was enhanced when nuclear export was blocked with leptomycin B. We also determined that the small GTPase Ran, a key regulator of nucleocytoplasmic transport, is a target for S-nitrosylation. These findings demonstrate that biotin derivatization is a useful approach to detect S-nitrosylated proteins in situ in cellular compartments or tissues, and will be useful in the assessment of altered S-nitrosylation in pathological conditions.

Store-operated Ca2+ entry activates the CREB transcription factor in vascular smooth muscle

Ca2+-regulated gene transcription is a critical component of arterial responses to injury, hypertension, and tumor-stimulated angiogenesis. The Ca2+/cAMP response element binding protein (CREB), a transcription factor that regulates expression of many genes, is activated by Ca2+-induced phosphorylation. Multiple Ca2+ entry pathways may contribute to CREB activation in vascular smooth muscle including voltage-dependent Ca2+ channels and store-operated Ca2+ entry (SOCE). To investigate a role for SOCE in CREB activation, we measured CREB phosphorylation using immunofluorescence, intracellular Ca2+ levels using a fluorescence resonance energy transfer (FRET)-based Cameleon indicator, and c-fos transcription using RT-PCR. In this study, we report that SOCE activates CREB in both cultured smooth muscle cells and intact arteries. Depletion of intracellular Ca2+ stores with thapsigargin increased nuclear phospho-CREB levels, intracellular Ca2+ concentration, and transcription of c-fos. These effects were abolished by inhibiting SOCE through lowering extracellular Ca2+ concentration or by application of 2-aminoethoxydiphenylborate and Ni2+. Inhibition of Ca2+ influx through voltage-dependent Ca2+ channels using nimodipine partially blocked intact artery responses, but was without effect in cultured smooth muscle cells. Our findings indicate that Ca2+ entry through store-operated Ca2+ channels leads to CREB activation, suggesting that SOCE contributes to the regulation of gene expression in vascular smooth muscle.

VEGF and HIF-1alpha expression are increased in advanced stages of epithelial ovarian cancer

OBJECTIVE

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor that is elevated in epithelial ovarian cancer. Hypoxia inducible factor-1alpha (HIF-1alpha) is a transcription factor that plays a regulatory role in the expression of VEGF. Currently, there is limited information regarding VEGF and HIF-1alpha expression in epithelial ovarian cancer specimens. The objective of this study was to measure VEGF and HIF-1alpha expression in epithelial ovarian cancer samples and to compare VEGF and HIF-1alpha expression between ovarian cancer and normal ovarian tissue

METHODS

. Serial sections of paraffin-embedded ovarian tissues from a study group of 16 control patients and 37 patients diagnosed with epithelial ovarian cancer were analyzed for expression of VEGF and HIF-1alpha using immunohistochemistry.

RESULTS

There was a strong correlation between the average expression scores of VEGF and HIF-1alpha expression (r(2) = 0.991). There was a significant increase in expression of VEGF in stage III and IV tumors over that in controls (P < 0.005). There was also a significant increase in HIF-1alpha expression in stage III and IV tumors over that in controls (P < 0.005 and P < 0.05, respectively).

CONCLUSION

VEGF and HIF-1alpha are both expressed in epithelial ovarian cancer. VEGF expression correlated with HIF-1alpha expression, suggesting that HIF-1alpha may contribute to the overexpression of VEGF observed in epithelial ovarian cancer.

Nitric oxide and reactive oxygen species exert opposing effects on the stability of hypoxia-inducible factor-1alpha (HIF-1alpha) in explants of human pial arteries

Hypoxia induces angiogenesis, partly through stabilization of hypoxia-inducible factor-1alpha (HIF-1alpha), leading to transcription of pro-angiogenic factors. Here we examined the regulation of HIF-1alpha by hypoxia and nitric oxide (NO) in explants of human cerebrovascular smooth muscle cells. Cells were treated with NO donors under normoxic or hypoxic (2% O2) conditions, followed by analysis of HIF-1alpha protein levels. Treatment with the NO donor sodium nitroprusside reduced levels of HIF-1alpha, whereas NO donors, NOC-18 and S-nitrosoglutathione, increased HIF-1alpha levels. SIN-1, which releases both NO and superoxide (O2*-), reduced HIF-1alpha levels, suggesting that inhibitory NO donors may elicit effects through peroxynitrite (ONOO*-). O2*- generation by xanthine/xanthine oxidase also reduced HIF-1alpha levels, confirming an inhibitory role for reactive oxygen species (ROS). Furthermore, superoxide dismutase increased HIF-1alpha levels, and the NO scavenger carboxy-PTIO reversed HIF-1alpha stabilization by NO donors. Effects on HIF-1alpha levels correlated with vascular endothelial growth factor transcription but did not affect HIF-1alpha transcription, as measured by RT-PCR and luciferase-reporter assays. The results indicate that HIF-1alpha is stabilized by agents that produce NO and reduce ROS but destabilized by agents that increase ROS, including O2*- and ONOO*-. Thus we propose that the effect of NO on HIF-1alpha signaling is critically dependent on the form of NO and the physiological environment of the responding cell.

A new in vitro model of venous hypertension: the effect of pressure on dermal fibroblasts

PURPOSE

Venous hypertension leads to venous stasis ulcers. White cell activation, protein leakage from pressurized capillaries, and cytokine imbalances have all been implicated as indirect effects of venous hypertension that contribute to dermal changes seen in chronic venous insufficiency. The direct effect of increased tissue pressures on dermal elements has not been investigated. Prior studies have shown that fibroblasts isolated from venous ulcers have altered growth rates, morphologies, and protein production similar to senescent or aged fibroblasts. We hypothesize that neonatal fibroblasts (NNFs) cultured in conditions of increased atmospheric pressure will demonstrate altered cell function when compared with those grown at normal atmospheric pressure (ATM).

METHODS

A pressure incubator was used to culture populations of NNFs at ATM, 60 mm Hg over ATM (ATM + 60 mm Hg), and 120 mm Hg over ATM (ATM + 120 mm Hg). NNF population growth rates were determined by periodic flow cytometry analysis over a 2-week period. Light microscopy and digital imaging were used to evaluate cell morphology. Senescence-associated B-galactosidase (SA-beta-Gal) activity was determined using the X-Gal stain. Fibronectin production was assessed by exposing cells sequentially to anti-fibronectin antibodies and Oregon Green-conjugated goat anti-mouse secondary antibodies. Flow cytometry then was used to determine relative proportions of cells staining positively for fibronectin. Statistical analysis was accomplished with analysis of variance.

RESULTS

Populations of cells grown under increased pressures (both ATM + 60 and ATM + 120) showed reduced growth rates (P <.001). Similarly, morphologies of cells grown under pressure had increased cytoplasm to nuclear ratios with abnormal nuclear shapes. Populations of cells grown under pressure had higher percentages of cells staining positive for fibronectin (ATM = 45%, ATM + 60 = 59%, ATM + 120 = 79%). After 14 days of growth under pressure, fibroblast populations did not demonstrate augmented productions of the senescence marker SA-beta-Gal (ATM =.5%, ATM + 60 =.25%, ATM + 120 =.75%).

CONCLUSIONS

This study demonstrated that NNFs grown in culture under increased pressures undergo a transformation not seen in cells grown at atmospheric pressure. Cells grown under pressure demonstrated reduced growth rates, increased fibronectin production, and abnormal morphologies similar to fibroblasts isolated from venous ulcers. This study suggests that pressure elevations (like venous hypertension) can directly result in altered cell function and morphology that may contribute to the delayed wound healing seen in patients with venous ulcers. This model uses a pressurized incubator that may prove to be a valuable adjunct in studying the effects of venous hypertension.

Asbestos-induced apoptosis is protein kinase C delta-dependent

Alveolar epithelial and mesothelial cells undergo apoptosis in response to asbestos, a phenomenon that may be important in injury and/or initiation of compensatory proliferation. Here, we report a functional role of protein kinase (PKC)delta in apoptosis by crocidolite asbestos. We first show that asbestos increases the kinase activity of PKC delta in alveolar type II epithelial cells (C10 line) and causes its translocation to mitochondria, events associated with caspase-9 cleavage and apoptosis as detected by the Apostain technique. Pretreatment of C10 cells with rottlerin (Rot), a PKC delta-selective inhibitor, before addition of asbestos prevented cleavage of caspase-9 and blocked the appearance of apoptotic cells. Asbestos-induced apoptosis also was inhibited in cells stably expressing a dominant-negative kinase-deficient mutant of PKC delta (dnPKC delta), but not dnPKC alpha. Activities of PKC alpha and PKC zeta increased after exposure to asbestos, but neither isoform migrated to mitochondria. A general inhibitor of PKCs, bisindolylmaleimide I, had no effect on asbestos-induced apoptosis. Hydrogen peroxide (H2O2) induced activation of PKCs delta, alpha, zeta, and theta, translocation of PKC delta to mitochondria, and caspase-9 cleavage. However, H2O2-induced apoptosis was not inhibited by cell lines stably expressing either dnPKC delta or dnPKC alpha, suggesting that activation of PKC delta has a distinct role in the development of asbestos-induced apoptosis.

Increased localization and substrate activation of protein kinase C delta in lung epithelial cells following exposure to asbestos

The protein kinase C (PKC) family consists of several isozymes whose substrates may be necessary for the regulation of key cellular events important in the pathogenesis of proliferative diseases. Asbestos is a carcinogen and fibroproliferative agent in lung that may cause cell signaling events through activation of PKC. Here we used a murine inhalation model of asbestos-induced inflammation and fibrosis to examine immunoreactivity of PKC delta and its substrate, phosphorylated-adducin (p-adducin), in cells of the lung. Moreover, we characterized PKC delta and p-adducin expression in a pulmonary epithelial cell line (C10) in both log versus confluent cells and in cells after mechanical wounding or crocidolite asbestos exposure. Both PKC delta and p-adducin were almost exclusively expressed in bronchiolar and alveolar type II (ATII) epithelial cells in lung sections and increased in these cell types after inhalation of asbestos by mice. Increases in membrane and nuclear localization of PKC delta were seen in log phase as compared to confluent C10 cells. Moreover, enhanced immunoreactivity of PKC delta was observed in epithelial cells expressing proliferating cell nuclear antigen (PCNA) after mechanical wounding or exposure to asbestos fibers. These studies show that activated PKC delta in pulmonary epithelial cells is a consequence of inhalation of asbestos and may be linked to the activation of cell proliferation.

Membrane depolarization mediates phosphorylation and nuclear translocation of CREB in vascular smooth muscle cells

Diverse signals have the potential to modulate gene transcription through the Ca2+ and cAMP response element binding protein (CREB) in vascular smooth muscle cells (VSMCs). A key step in the transmission of these signals is import into the nucleus. Here, we provide evidence that the Ran GTPase, which regulates nuclear import, exerts different regulation over PDGF-BB, Ca2+, and cAMP signaling to CREB in VSMCs. PDGF-BB, membrane depolarization, and forskolin increased levels of activated CREB (P-CREB) and c-fos in VSMCs and intact aorta. The calcium channel antagonist nimodipine reduced the level of P-CREB stimulated by membrane depolarization, but not by PDGF-BB or forskolin. Block of Ran-mediated nuclear import, by wheat germ agglutinin or an inactivating Ran mutant (T24N Ran), significantly reduced nuclear P-CREB in response to PDGF-BB or membrane depolarization, but enhanced levels of P-CREB in response to forskolin. Contrary to expectation, block of nuclear import led to the appearance of P-CREB in the cytoplasm after depolarization. Furthermore, blocking nuclear export with leptomycin B reduced P-CREB stimulation by both depolarization and PDGF-BB. These results suggest that translocation of CREB between the nucleus and the cytoplasm provides an important role in CREB activating pathways in VSMCs.

Calcium signaling and oxidant stress in the vasculature

Recent evidence suggests that oxidant stress plays a major role in several aspects of vascular biology. Oxygen free radicals are implicated as important factors in signaling mechanisms leading to vascular pathologies such as postischemic reperfusion injury and atherosclerosis. The role of intracellular Ca(2+) in these signaling events is an emerging area of vascular research that is providing insights into the mechanisms mediating these complex physiological processes. This review explores sources of free radicals in the vasculature, as well as effects of free radicals on Ca(2+) signaling in vascular endothelial and smooth muscle cells. In the endothelium, superoxides enhance and peroxides attenuate agonist-stimulated Ca(2+) responses, suggesting differential signaling mechanisms depending on radical species. In smooth muscle cells, both superoxides and peroxides disrupt the sarcoplasmic reticulum Ca(2+)-ATPase, leading to both short- and long-term effects on smooth muscle Ca(2+) handling. Because vascular Ca(2+) signaling is altered by oxidant stress in ischemia-related disease states, understanding these pathways may lead to new strategies for preventing or treating arterial disease.

Coupling of Ca(2+) to CREB activation and gene expression in intact cerebral arteries from mouse : roles of ryanodine receptors and voltage-dependent Ca(2+) channels

Pathological changes of the vasculature are characterized by changes in Ca(2+) handling and alterations in gene expression. In neurons and other cell types, [Ca(2+)](i) often drives changes in gene expression. However, the relationship between Ca(2+) signaling and gene expression in vascular smooth muscle is not well understood. This study examines the ability of Ca(2+) influx through voltage-dependent, L-type Ca(2+) channels (VDCCs) and Ca(2+) release through ryanodine receptors (RyRs) to activate the transcription factor, cAMP-responsive element binding protein (CREB), and increase c-fos levels in intact cerebral arteries. Membrane depolarization increased the fraction of nuclei staining for phosphorylated CREB (P-CREB) and levels of c-fos mRNA in intact mouse cerebral arteries. Ryanodine, which inhibits RyRs, increased P-CREB staining and c-fos levels. Forskolin, an activator of adenylyl cyclase, and sodium nitroprusside, an NO donor, increased P-CREB and c-fos levels. Nisoldipine, an inhibitor of VDCCs, reversed the effects of depolarization and ryanodine on P-CREB and c-fos levels, but not the effects of forskolin or sodium nitroprusside. Inhibition of Ca(2+)/calmodulin-dependent protein kinase (CaM kinase) blocked increases in P-CREB and c-fos levels seen with membrane depolarization, suggesting that CaM kinase has an important role in the pathway leading from Ca(2+) influx to CREB-mediated changes in c-fos levels. Our data suggest that membrane depolarization increases [Ca(2+)](i) through activation of VDCCs, leading to increased P-CREB and c-fos, and that RyRs have a profound effect on this pathway by indirectly regulating Ca(2+) entry through VDCCs. These results provide the first evidence of Ca(2+) regulation of CREB and c-fos in arterial smooth muscle.

Gender differences in coronary artery diameter reflect changes in both endothelial Ca2+ and ecNOS activity

Elevation of nitric oxide (NO) release from the vascular endothelium may contribute to some of the gender-associated differences in coronary artery function. The mechanisms by which gender affects NO release from the endothelium of coronary arteries are not known. In this study, endothelial function was examined in pressurized coronary arteries from female and male rats. Diameter and endothelial cell intracellular Ca2+ concentration ([Ca2+]i) in intact arteries, as well as enzymatic activity of endothelial constitutive nitric oxide synthase (ecNOS) in arterial lysates, was measured. Elevation of intravascular pressure to 60 mmHg constricted coronary arteries from female animals less than coronary arteries from male animals (18% and 31% constriction, respectively). The increased arterial diameter of coronary arteries from females was associated with elevated endothelial [Ca2+]i (female 174 nM, male 90 nM; P < 0.001). Elevation of Ca2+ activated ecNOS with a similar slope and half-activation constant ( approximately 160 nM) for both female and male coronary arteries. However, at [Ca2+] > 100 nM, ecNOS activity was significantly higher in coronary arteries from female rats compared with their male equivalents (P < 0.01). Maximal activity for ecNOS at saturating Ca2+ (300 nM) was 37% higher in coronary arteries from female animals compared with male animals (P < 0.05). Thus elevated [Ca2+]i in the endothelium of female coronary arteries alone is predicted to increase the production of NO (by nearly 2-fold). This gender difference combined with increased ecNOS activity at a given [Ca2+] in females indicates that tonic NO production should be nearly threefold greater in female coronary arteries compared with male coronary arteries. We conclude that, in the regulation of endothelial Ca2+ and ecNOS, gender differences contribute significantly to the overall decrease in myogenic tone observed in coronary arteries of females.

Ran-binding protein 1 (RanBP1) forms a ternary complex with Ran and karyopherin beta and reduces Ran GTPase-activating protein (RanGAP) inhibition by karyopherin beta

The nuclear accumulation of proteins containing nuclear localization signals requires the Ran GTPase and a complex of proteins assembled at the nuclear pore. RanBP1 is a cytosolic Ran-binding protein that inhibits RCC1-stimulated release of GTP from Ran. RanBP1 also promotes the binding of Ran to karyopherin beta (also called importin beta and p97) and is a co-stimulator of RanGAP activity. Yeast karyopherin beta inhibits the GTP hydrolysis by Ran catalyzed by RanGAP. To further define the roles of RanBP1 and karyopherin beta in Ran function, we explored the effects of RanBP1 and karyopherin beta on mammalian proteins known to regulate Ran. Like RanBP1, karyopherin beta prevented the release of GTP from Ran stimulated by RCC1 or EDTA. As with the yeast protein, mammalian karyopherin beta completely blocked RanGAP activity. However, the addition of RanBP1 to this assay partially rescued the inhibited RanGAP activity. Kinetic analysis of the effects on RanGAP activity by karyopherin beta and RanBP1 revealed a combination of competitive and noncompetitive interactions. Solution binding assays confirmed the ability of RanBP1 to associate with Ran and karyopherin beta in a ternary complex, and RanBP1 binding was not competed out by the addition of karyopherin beta. These results demonstrate that RanBP1 and karyopherin beta interact with distinct sites of Ran and suggest that RanBP1 plays an essential role in nuclear transport by permitting RanGAP-mediated hydrolysis of GTP on Ran complexed to karyopherin beta.

Mutations within the Ran/TC4 GTPase. Effects on regulatory factor interactions and subcellular localization

Ran, a member of the Ras superfamily of GTPases, is predominantly localized in the nucleus and is a necessary component in the active transport of proteins through nuclear pores. Disruption of Ran function affects the regulation of mitosis, DNA synthesis, and RNA processing and export. To explore the mechanisms of Ran function, mutants of the Ran GTPase were characterized, several of which are capable of dominantly interfering with nuclear protein import. Unlike wild-type Ran, the putative gain-of-function mutant (G19V Ran) was not sensitive to the exchange factor, RCC1. In addition the G19V Ran and effector domain mutants (L43E and E46G Ran) were not sensitive to the GTPase-activating protein, Fug1. Epitope-tagged G19V Ran and L43E Ran isolated from transfected BHK21 cells were each about 50% GTP-bound, whereas the wild-type and a C-terminal deletion mutant (Delta-DE Ran) were primarily bound to GDP. While G19V Ran interacted with known Ran-binding proteins and with an isolated Ran-binding domain, the T24N Ran did not, and binding by L43E Ran was substantially reduced. Wild-type HA1-tagged Ran expressed in BHK21 cells was nuclear, whereas the G19V, T24N, L43E, and E46G forms of Ran were predominantly localized at the nuclear envelope, and Delta-DE Ran was primarily cytosolic. Similar results were observed when permeabilized BHK21 cells were incubated with extracts of COS cells expressing the mutants. Thus mutations that affect the interaction of Ran with regulatory proteins and effectors can disrupt the normal subcellular localization of Ran, lending support for the current model of Ran-mediated nuclear import.

A nuclear export signal is essential for the cytosolic localization of the Ran binding protein, RanBP1

RanBP1 is a Ran/TC4 binding protein that can promote the interaction between Ran and beta-importin /beta-karyopherin, a component of the docking complex for nuclear protein cargo. This interaction occurs through a Ran binding domain (RBD). Here we show that RanBP1 is primarily cytoplasmic, but the isolated RBD accumulates in the nucleus. A region COOH-terminal to the RBD is responsible for this cytoplasmic localization. This domain acts heterologously, localizing a nuclear cyclin B1 mutant to the cytoplasm. The domain contains a nuclear export signal that is necessary but not sufficient for the nuclear export of a functional RBD In transiently transfected cells, epitope-tagged RanBP1 promotes dexamethasone-dependent nuclear accumulation of a glucocorticoid receptor-green fluorescent protein fusion, but the isolated RBD potently inhibits this accumulation. The cytosolic location of RanBP1 may therefore be important for nuclear protein import. RanBP1 may provide a key link between the nuclear import and export pathways.