Hypoxia-inducible factor-1 (HIF-1) promotes its degradation by induction of HIF-alpha-prolyl-4-hydroxylases

An important regulator involved in oxygen-dependent gene expression is the transcription factor HIF (hypoxia-inducible factor), which is composed of an oxygen-sensitive alpha-subunit (HIF-1alpha or HIF-2alpha) and a constitutively expressed beta-subunit. In normoxia, HIF-1alpha is destabilized by post-translational hydroxylation of Pro-564 and Pro-402 by a family of oxygen-sensitive dioxygenases. The three HIF-modifying human enzymes have been termed prolyl hydroxylase domain containing proteins (PHD1, PHD2 and PHD3). Prolyl hydroxylation leads to pVHL (von-Hippel-Lindau protein)-dependent ubiquitination and rapid proteasomal degradation of HIF-1alpha. In the present study, we report that human PHD2 and PHD3 are induced by hypoxia in primary and transformed cell lines. In the human osteosarcoma cell line, U2OS, selective suppression of HIF-1alpha expression by RNA interference resulted in a complete loss of hypoxic induction of PHD2 and PHD3. Induction of PHD2 by hypoxia was lost in pVHL-deficient RCC4 cells. These results suggest that hypoxic induction of PHD2 and PHD3 is critically dependent on HIF-alpha. Using a VHL capture assay, we demonstrate that HIF-alpha prolyl-4-hydroxylase capacity of cytoplasmic and nuclear protein extracts was enhanced by prolonged exposure to hypoxia. Degradation of HIF-1alpha after reoxygenation was accelerated, which demonstrates functional relevance of the present results. We propose a direct, negative regulatory mechanism, which limits accumulation of HIF-1alpha in hypoxia and leads to accelerated degradation on reoxygenation after long-term hypoxia.

Different mechanisms of syndecan-1 activation through a fibroblast-growth-factor-inducible response element (FiRE) in mucosal and cutaneous wounds

Syndecan-1 expression is enhanced in cutaneous and mucosal wounds. We have previously demonstrated that wounding-induced syndecan-1 expression in the skin occurs transcriptionally, through a fibroblast-growth-factor-inducible element (FiRE). Here, we show that FiRE is also activated in mucosal wounds. However, both the expression patterns and the activation mechanisms of FiRE are different from those in the skin. In the mucosa in vivo, the activation starts and ends earlier than in cutaneous wounds. FiRE is first detected at around 12 hours in keratinocytes, and the activation declines by the third day after wounding occurs. The activation is seen on the migrating sheet of epithelial mucosa, as in the case of cutaneous wounding. In contrast to the situation in vivo, organ-cultured mucosal wounds exhibit no FiRE activity, while organ-cultured cutaneous wounds show robust activity. Activation in mucosal wounds is enhanced, however, by the application of epidermal growth factor. This suggests that exogenous growth factor activity is required for activation of syndecan-1 in mucosal wounds but not in cutaneous wounds.

Endovascular treatment of aortic aneurysms in Finland: the first four years' experience

BACKGROUND AND AIMS

In this study the results of endovascular treatment of aortic aneurysms in Finland are presented and compared to the results of the Eurostar registry.

MATERIAL AND METHODS

A total of 229 patients with aortic aneurysm were treated in five different Finnish centres during 1996-2000. The data of these patients were collected prospectively by surgeon or interventional radiologist involved. During the same period of time 2464 patients were registered in the Eurostar registry.

RESULTS

The procedure was performed successfully in 97% of patients in Finland, and the 30-day mortality was 0,9%. A graft limb thrombosis was detected in 9% of the patients in Finland. A permanent primary endoleak at the first 30-day control was seen in 23 patients (10%). During the follow-up 17 secondary endoleaks (7%) were detected. A secondary intervention was necessary in 26% of the patients. Three patients (1.3%) had late rupture of the abdominal aortic aneurysm.

CONCLUSIONS

According to the Finnish short-time results, endovascular treatment of aortic aneurysms is safe and associated with relatively low morbidity and mortality. The mid-term results are more disappointing with relatively many graft thromboses and endoleaks, and a frequent need of secondary interventions.

Results of infrainguinal bypass surgery: an analysis of 263 consecutive operations

BACKGROUND AND AIMS

The purpose of this clinical study was to assess the success of infrainguinal revascularization in the treatment of lower limb ischaemia.

MATERIAL AND METHODS

226 consecutive patients underwent 263 femoropopliteal (n = 194) or femorodistal (n = 69) bypass operations during 1988-1996 at a university hospital. Records of all patients were reviewed. Late control visits including clinical and colour doppler ultrasound examinations were programmed for 109 patients. Initial success, primary and secondary patencies, limb salvage and survival rates were determined and factors affecting outcome were analysed in various patient categories.

RESULTS

Initial success rate was 92% (243/263). The primary and secondary patencies were 70/83% and 52/63% at one and five years, respectively. The corresponding limb salvage rates for patients with chronic critical ischaemia were 82% and 77%. The number of diseased vessels in the treated limb correlated negatively with the primary patency. Advanced age did not affect primary patency or limb salvage rates. Diabetes and the use of distal revascularizations were independent predictors of poorer limb salvage. Diabetes and renal insufficiency proved to shorten life expectancy.

CONCLUSIONS

Infrainguinal revascularizations are effective regardless of patient's age. The extent of atherosclerotic changes in the operated limb, diabetes and renal insufficiency are factors affecting outcome.

C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation

HIF is a transcriptional complex that plays a central role in mammalian oxygen homeostasis. Recent studies have defined posttranslational modification by prolyl hydroxylation as a key regulatory event that targets HIF-alpha subunits for proteasomal destruction via the von Hippel-Lindau ubiquitylation complex. Here, we define a conserved HIF-VHL-prolyl hydroxylase pathway in C. elegans, and use a genetic approach to identify EGL-9 as a dioxygenase that regulates HIF by prolyl hydroxylation. In mammalian cells, we show that the HIF-prolyl hydroxylases are represented by a series of isoforms bearing a conserved 2-histidine-1-carboxylate iron coordination motif at the catalytic site. Direct modulation of recombinant enzyme activity by graded hypoxia, iron chelation, and cobaltous ions mirrors the characteristics of HIF induction in vivo, fulfilling requirements for these enzymes being oxygen sensors that regulate HIF.

Proximal promoter of the murine syndecan-1 gene is not sufficient for the developmental pattern of syndecan expression in B lineage cells

Syndecan-1 (CD138) is a cell membrane proteoglycan that binds extracellular matrix components and various growth factors. The role of syndecan-1 in the control of cell growth and morphology has been illustrated by its altered expression in hematological malignancies such as multiple myeloma as well as some solid tumors. It has been reported that the expression of syndecan-1 in cells of the B lineage is developmentally regulated such that pre-B cells and plasma cells express syndecan-1 while mature B cells do not. Thus, we investigated whether the proximal promoter region of the murine syndecan-1 promoter was able to confer the observed on-off-on expression of syndecan-1 in cells of the B lineage as they develop from pre-B cells to plasma cells. Experiments carried out using deletion mutants of the proximal promoter cloned upstream of the CAT reporter gene transfected into murine cell lines, representing the above stages of B-cell development, such as BA/F3 (pro-B cell), 70Z/3 (pre-B cell), 2PK3 (late mature B cell), and MPC-11 (plasma cell), showed detectable levels of CAT expression. The WEHI-231 (mature B cell) cell lines did not show detectable levels of CAT reporter activity. The strong levels of expression were observed with a fragment of the proximal promoter spanning the region from -365 to -95 (from the translation start point). However, Northern analysis of RNA obtained from the five murine B-cell lines, representing various stages of B-cell development, showed that the 70Z/3, MPC-11 but not BA/F3, and 2PK3 cells expressed detectable levels of syndecan-1 mRNA. By FACS analysis, using a rat anti mouse syndecan-1 antibody, syndecan-1 expression on the cell surface was found to correlate with the observed mRNA expression patterns in these cell lines. Our results indicate that the proximal promoter of the murine syndecan-1 promoter is not sufficient for the observed developmental pattern of syndecan expression in B cells.

Targeting of HIF-alpha to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation

Hypoxia-inducible factor (HIF) is a transcriptional complex that plays a central role in the regulation of gene expression by oxygen. In oxygenated and iron replete cells, HIF-alpha subunits are rapidly destroyed by a mechanism that involves ubiquitylation by the von Hippel-Lindau tumor suppressor (pVHL) E3 ligase complex. This process is suppressed by hypoxia and iron chelation, allowing transcriptional activation. Here we show that the interaction between human pVHL and a specific domain of the HIF-1alpha subunit is regulated through hydroxylation of a proline residue (HIF-1alpha P564) by an enzyme we have termed HIF-alpha prolyl-hydroxylase (HIF-PH). An absolute requirement for dioxygen as a cosubstrate and iron as cofactor suggests that HIF-PH functions directly as a cellular oxygen sensor.

FT-IR breath test in the diagnosis and control of treatment of methanol intoxications

A portable Fourier transform infrared (FT-IR) multicomponent point-of-care analyzer was tested for the diagnosis of methanol intoxications. Breath analysis with FT-IR was fast and easy, and no sample preparation was needed. The analyzer was adequately sensitive and accurate in detecting and quantitating clinically relevant amounts of ethanol and methanol in the breath of seriously ill patients. FT-IR spectrometry was also suitable for nearly on-line monitoring of the exhaled ethanol and methanol during hemodialysis. The breath analysis results correlated well with blood samples. The FT-IR method used also has a traceable calibration to physical properties of the analyte, and the measured spectra can be saved for later analysis.

Activation of fibroblast collagenase-1 expression by tumor cells of squamous cell carcinomas is mediated by p38 mitogen-activated protein kinase and c-Jun NH2-terminal kinase-2

Collagenase-1 [matrix metalloproteinase (MMP)-1] is expressed by stromal fibroblasts of various invasive malignant tumors. Here, we have examined the molecular mechanisms of tumor-induced expression of MMP-1 by stromal fibroblasts. Treatment of fibroblasts with conditioned media of tumor cells derived from squamous cell carcinomas (SCCs) of the oral cavity and larynx resulted in activation of fibroblast MMP-1 expression at the transcriptional level. The induction of MMP-1 expression correlates with activation of c-Jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase and phosphorylation of c-Jun and activating transcription factor-2 (ATF-2) and is dependent on the activity of p38 mitogen-activated protein kinase. Furthermore, using fibroblasts derived from JNK2-/- mice, we show that JNK2 is required for induction of fibroblast collagenase-3 expression in response to conditioned SCC tumor cell medium. Together, these results provide evidence that stress-activated p38 and JNK pathways play a crucial role in paracrine regulation of collagenolytic capacity of stromal fibroblasts in SCCs and suggest JNK2 as a novel target for inhibition of MMP-1 expression and tumor invasion.

Proximal promoter-independent activation of the far-upstream FGF-inducible response element of syndecan-1 gene

Far upstream enhancers are predicted to act by looping and activating general transcription factors on core promoters and to require proximal promoter sequences for appropriate gene activation in time and space. We have previously described an FGF-inducible response element (FiRE) located far upstream on the syndecan-1 gene. The FiRE is activated specifically by members of the fibroblast growth factor (FGF) family in NIH3T3 cells. Here we describe the requirements of syndecan-1 proximal promoter for the activation of FiRE by FGF-2. Transient and stable transfections revealed that neither proximal promoter SP1 sites nor TATA-box are required for the FGF-2 induced activation of FiRE. Notably, the enhancer is activated in both orientations by FGF-2 even in the absence of proximal promoter. Importantly, removal of the promoter did not affect the growth factor specificity of FiRE. Proximal promoter independent activation of syndecan-1 gene by FGF-2 might be required during development when syndecan-1 proximal promoter needs to be largely attenuated but simultaneous transient and rapid FGF-2 induced transcription is required.

Transcriptional targeting of adenoviral gene delivery into migrating wound keratinocytes using FiRE, a growth factor-inducible regulatory element

Impaired cutaneous wound healing is a common complication in diabetes, ischemia and venous insufficiency of lower extremities, and in long-term treatment with corticosteroids or other immunosuppressive agents. In development of gene therapy for wound repair, expression of therapeutic transgenes should be precisely targeted and controlled. Here, we describe a recombinant adenovirus RAdFiRE-EGFP, in which a growth factor inducible element (FiRE) of the murine syndecan-1 gene controls the expression of enhanced green fluorescent protein (EGFP) reporter gene. Treatment of RAdFiRE-EGFP-transduced murine epidermal keratinocytes in culture with FiRE-activating growth factor markedly enhanced the expression of EGFP. In ex vivo organ culture of wounded murine skin transduced with RAdFiRE-EGFP, the EGFP expression was specifically detected in wound margin keratinocytes, but not in intact skin. Activity of EGFP was first detected 2 days after a single application of RAdFiRE-EGFP and persisted up to 10 days. Similarly, FiRE-driven EGFP expression was detected specifically in epidermal keratinocytes in the edge of incisional wounds in murine skin transduced with RAdFiRE-EGFP. In contrast, adenovirus-mediated lacZ expression driven by CMV promoter was detected scattered in epidermal, dermal and subcutaneous layers in ex vivo and in vivo wounds, as well as in intact skin. These data demonstrate the feasibility of FiRE as a tool for transcriptional targeting of adenovirus-mediated transgene expression to cutaneous wound edge keratinocytes.

Prospective trial of infrapopliteal artery balloon angioplasty for critical limb ischemia: angiographic and clinical results

PURPOSE

To evaluate the safety and efficacy of infrapopliteal percutaneous transluminal angioplasty (PTA) as a primary treatment of chronic critical limb ischemia in a prospective trial.

MATERIALS AND METHODS

Infrapopliteal PTA was performed on 72 limbs of 60 patients (mean age, 72 y; range, 38-92 y) and patients were followed for 12-24 months.

RESULTS

The primary angiographic success rate for the stenoses was 84% (102 of 121) and that for the occlusions was 61% (41 of 67) with corresponding restenosis rates of 32% and 52% at follow-up angiography performed a mean of 10 months after primary PTA. The rate of major complications was 2.8% (access site pseudoaneurysms in two patients). The primary clinical success was 63% (45 of 72). A 48% cumulative primary patency rate, a 56% secondary patency rate, and a 80% cumulative limb salvage rate were registered at 18 months, as determined with use of Kaplan-Meier analysis. Lack of angiographic improvement at the site of the most severe ischemia and renal insufficiency (serum creatinine level > 130 micromol/L) were independent predictors of poorer long-term clinical results, as determined with use of Cox multiple regression analysis.

CONCLUSIONS

Infrapopliteal PTA is a feasible primary treatment of chronic critical limb ischemia with moderate primary angiographic and clinical success, a low complication rate, and a cumulative limb salvage rate comparable with surgical techniques.

Hypoxia inducible factor-alpha binding and ubiquitylation by the von Hippel-Lindau tumor suppressor protein

The von Hippel-Lindau tumor suppressor protein (pVHL) has emerged as a key factor in cellular responses to oxygen availability, being required for the oxygen-dependent proteolysis of alpha subunits of hypoxia inducible factor-1 (HIF). Mutations in VHL cause a hereditary cancer syndrome associated with dysregulated angiogenesis, and up-regulation of hypoxia inducible genes. Here we investigate the mechanisms underlying these processes and show that extracts from VHL-deficient renal carcinoma cells have a defect in HIF-alpha ubiquitylation activity which is complemented by exogenous pVHL. This defect was specific for HIF-alpha among a range of substrates tested. Furthermore, HIF-alpha subunits were the only pVHL-associated proteasomal substrates identified by comparison of metabolically labeled anti-pVHL immunoprecipitates from proteosomally inhibited cells and normal cells. Analysis of pVHL/HIF-alpha interactions defined short sequences of conserved residues within the internal transactivation domains of HIF-alpha molecules sufficient for recognition by pVHL. In contrast, while full-length pVHL and the p19 variant interact with HIF-alpha, the association was abrogated by further N-terminal and C-terminal truncations. The interaction was also disrupted by tumor-associated mutations in the beta-domain of pVHL and loss of interaction was associated with defective HIF-alpha ubiquitylation and regulation, defining a mechanism by which these mutations generate a constitutively hypoxic pattern of gene expression promoting angiogenesis. The findings indicate that pVHL regulates HIF-alpha proteolysis by acting as the recognition component of a ubiquitin ligase complex, and support a model in which its beta domain interacts with short recognition sequences in HIF-alpha subunits.

Conduction defects after coronary artery bypass grafting--a disappearing problem?

BACKGROUND AND AIMS

To evaluate the incidence of conduction defects (CDs) following coronary artery bypass grafting (CABG) in three different patient populations, to assess the etiologic factors associated with CDs, and to find out their effect on immediate postoperative outcome of the patient.

MATERIAL AND METHODS

Three patient populations were prospectively studied: cohort A consisted of 180 CABG-patients operated between 1990-91, cohort B of 100 patients operated during the year 1993 and cohort C of 118 patients operated from April 1997 to June 1997. Cold crystalloid cardioplegia was used throughout the study years. In the first cohort A, two separate cavae were cannulated and clamped, venting through the right upper pulmonary vein was used, iced cold saline was used in pericardium, and cardioplegia was given until a myocardial temperature of 10-15 degrees of Celcius was attained. In the two later cohorts, two-stage venous cannula and aortic root venting were used and cardioplegia was given only until the activity of the myocardium stopped. Proximal anastomoses were performed after aortic declamping in cohort A, and during aortic occlusion in the two later cohorts.

RESULTS

The incidence of permanent CDs in cohort A was 36%, in cohort B 5% and in cohort C 1%. Permanent atrioventricular (AV-) and left-sided blocks disappeared first. Left main coronary artery stenosis and low myocardial temperatures were associated with CDs. Patients with permanent CDs had more often low cardiac output after the operation, their values of cardiac enzymes were higher, and they had more often postoperative infarction than patients without CDs.

CONCLUSIONS

The disappearance of all long lasting AV- and left-sided blocks simultaneously with decreasing plasma levels of cardiac enzymes is evidence that protection of both conduction tissue and myocardium had considerably improved in the two later cohorts. Giving cardioplegia in smaller amounts and more often at the same time when raising the general temperature during perfusion were the main reasons for the disappearance of postoperative CDs.

The use of low-resolution FT-IR spectrometry for the analysis of alcohols in breath

Fast and reliable diagnostic methods are needed for detection or exclusion of industrial solvents as a cause of intoxication. Analyzing human breath reveals the presence of any volatile substance. A portable Fourier transform infrared (FT-IR) multicomponent point-of-care analyzer was developed for exhaled breath. The analyzer proved to be accurate and precise in laboratory tests for simultaneous measurement of methanol and ethanol in water. Ethanol, in addition to normal contents of breath, was simultaneously analyzed in human experiments, and the results correlated well with blood samples. FT-IR method has a traceable calibration to physical properties of the analyte. The measured spectra can also be saved and analyzed later. Breath analysis with FT-IR is fast and easy, and no preparation of the sample is needed.

Involvement of protein kinase A in fibroblast growth factor-2-activated transcription

Polypeptide growth factors activate common signal transduction pathways, yet they can induce transcription of different target genes. The mechanisms that control this specificity are not completely understood. Recently, we have described a fibroblast growth factor (FGF)-inducible response element, FiRE, on the syndecan-1 gene. In NIH 3T3 cells, the FiRE is activated by FGF-2 but not by several other growth factors, such as platelet-derived growth factor or epidermal growth factor, suggesting that FGF-2 activates signaling pathways that diverge from pathways activated by other growth factors. In this paper, we report that the activation of FiRE by FGF-2 requires protein kinase A (PKA) in NIH 3T3 cells. The PKA-specific inhibitor H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide) blocked the FGF-2-induced activation of FiRE, the transcription of the syndecan-1 gene, and cell proliferation. Also, expression of a dominant-negative form of PKA inhibited the FGF-2-induced FiRE activation and the transcription of the syndecan-1 gene. The binding of activator protein-1 transcription-factor complexes, required for the activation of FiRE, was blocked by inhibition of PKA activity before FGF-2 treatment. In accordance with the growth factor specificity of FiRE, the activity of PKA was stimulated by FGF-2 but not by platelet-derived growth factor or epidermal growth factor. Furthermore, a portion of the PKA catalytic subunit pool was translocated to the nucleus by FGF-2. Noticeably, the total cellular cAMP concentration was not affected by FGF-2 stimulus. We propose that the FGF-2-selective transcriptional activation through FiRE is caused by the ability of FGF-2 to control PKA activity.

Transcriptional regulation of Syndecan-1 expression by growth factors

Syndecan-1 is a prototype member of a family of transmembrane heparan sulfate proteoglycans. Syndecan-1 binds extracellular matrix components and fibroblast growth factors (FGFs) and modifies the function of FGFs. Syndecan-1 is constitutively expressed by several epithelial cells, but expression is also induced during many biological phenomena, such as tissue regeneration and the epithelial-mesenchymal interactions during organ development. Growth factors have been the prime candidates to induce syndecan-1 expression in these situations. In fibroblasts syndecan-1 is induced by FGF-2 and in keratinocytes by epidermal growth factor (EGF) and keratinocyte growth factor (KGF). The search for cis-acting elements regulating the growth factor-induced syndecan-1 expression has led to identification of a novel FGF-inducible response element (FiRE). FiRE is activated in fibroblasts and keratinocytes by the same growth factors that induce syndecan-1 expression in these cells. In adult tissues the activation of FiRE is restricted to migrating keratinocytes of healing wounds. The composition of the transcription factor binding to FiRE differs depending on the cell type and the activating growth factor. The FiRE provides a powerful tool for studies on growth factor specificity and regeneration of tissues. Moreover, it implies a novel transcriptional link that creates an FGF action-controlling autoregulatory loop between the heparan sulfate proteoglycans and the heparin-binding FGFs.

Extracellular matrix-dependent activation of syndecan-1 expression in keratinocyte growth factor-treated keratinocytes

Syndecan-1 is a major heparan sulfate proteoglycan of the epidermis. Its expression is strongly induced in migrating and proliferating keratinocytes during wound healing and, on the other hand, diminished or lost in invasive squamous cell carcinoma. We have recently found in the syndecan-1 gene an enhancer (fibroblast growth factor-inducible response element (FiRE)) that activates gene expression in wound edge keratinocytes (Jaakkola, P., Kontusaari, S., Kauppi, T., Määttä, A., and Jalkanen, M. (1998) FASEB J. 12, 959-969). Now, we demonstrate that the activation of this enhancer by keratinocyte growth factor (KGF) is modulated by the components of the extracellular matrix (ECM). MCA-3D mouse immortal keratinocytes growing on fibrillar collagen failed to activate FiRE and subsequently to induce syndecan-1 in response to KGF. The same cells growing on fibronectin or laminin, however, increased FiRE-dependent reporter gene expression upon KGF treatment. The inhibition of the KGF induction by collagen appears to be specific for signaling to FiRE, as the increase in cell proliferation by KGF was not affected. The effect was selective to KGF, as EGF-induction was independent on ECM composition. Changes in the transcription factor binding were not involved in the differential activation of FiRE, as the levels and composition of the AP-1 complexes were unchanged. However, application of anisomycin, an activator of Jun amino-terminal kinase, resulted in a lower response in cells growing on collagen compared with fibronectin. These results indicate that the composition of ECM and availability of growth factors can play a role in the epidermal regulation of syndecan-1 expression and that FiRE is a novel target for gene regulation by the extracellular matrix.

Angiographic predictors of graft patency and disease progression after coronary artery bypass grafting with arterial and venous grafts

BACKGROUND

There are few data about angiographic determinants of functional graft patency and native artery disease progression after coronary artery bypass grafting operation with arterial grafts compared with venous grafts.

METHODS

Baseline and follow-up coronary angiograms at a mean of 2 years after operation in 91 patients with 194 arterial and 204 venous graft anastomoses were analyzed.

RESULTS

Ninety-two percent of the arterial and 87% of the venous graft anastomoses were patent at follow-up angiography (p = 0.05, odds ratio = 2.63). Unlike that of arterial grafts, the patency rate of venous graft anastomoses correlated negatively with decreasing severity of the bypassed lesion. In contrast to venous grafts, in which angiographic graft function was basically dichotomous (fully patent or occluded), compromised flow of the arterial graft anastomoses was registered in 12%. Progression of the disease was more common in segments bypassed with venous grafts than with arterial grafts (p = 0.001, odds ratio = 2.03).

CONCLUSIONS

Angiographic determinants of functional graft patency and progression of occlusive changes in the bypassed artery segments are different for arterial and venous grafts.

The activation and composition of FiRE (an FGF-inducible response element) differ in a cell type- and growth factor-specific manner

The expression of the heparan sulfate proteoglycan, syndecan-1, is induced both in keratinocytes and in fibroblasts during development and tissue regeneration. Here we report that in keratinocytes the syndecan-1 gene was stimulated by EGF but not by FGF-2. In fibroblasts it was stimulated by FGF-2 but not by EGF. Likewise, the recently discovered FGF-inducible response element (FiRE) on the gene of syndecan-1 was stimulated by FGF-2 in fibroblasts and by EGF in keratinocytes, but not vice versa. The FiRE has two binding sites for an activator protein-1 (AP-1), one for an FGF-inducible nuclear factor (FIN-1) and one for an upstream stimulatory factor-1 (USF-1). The growth factor-stimulated binding of these transcription factors, as well as their requirement for FiRE activation, varied between the two cell types. First, although AP-1s were required for activation of FiRE in both cell types, the binding of AP-1 to FiRE was increased by growth factor-stimulation only in fibroblasts and not in keratinocytes. Secondly, FiRE did not bind FIN-1 nor needed the FIN-1 binding site for EGF-stimulated activation in keratinocytes, in contrast to the FGF-stimulated activation of FiRE in fibroblasts. Thirdly, EGF, which did not activate FiRE in fibroblasts, failed to activate FIN-1 in these cells. Finally, an USF-1 binding site that was necessary for activation of FiRE in keratinocytes was not needed in fibroblasts. These data suggest mechanisms by which members of the EGF- and FGF-families can differentially stimulate transcription through AP-1 regulated elements in a cell type-specific manner.

Wound reepithelialization activates a growth factor-responsive enhancer in migrating keratinocytes

Wound reepithelialization and keratinocyte migration require strictly ordered gene expression, which is assumed to be initiated by locally released mitogens and exposure of the cells to different matrix components. The mechanisms triggering gene expression specifically during reepithelialization are poorly understood. The far upstream AP-1-driven, FGF-inducible response element (FiRE) of the syndecan-1 gene was activated during cutaneous wound healing in transgenic mice. FiRE was induced selectively in migrating but not in proliferating keratinocytes at the wound edge. The activation was initiated at the start of the cell migration, was persistent throughout the merging and stratification phases, and was terminated after completion of reepithelialization. Although FiRE has been found within the gene of syndecan-1, the proximal promoter of syndecan-1 was not required for activation of FiRE in the migrating keratinocytes. The wounding induced activation was inhibited by blocking cell surface growth factor receptors with suramin. However, the activation of FiRE in resting skin required simultaneous growth factor- and stress-induced signals, but could also be elicited by the phosphatase inhibitor, okadaic acid. The activation by both wounding and chemical stimuli was blocked by inhibiting extracellular regulated kinase and p38 MAP kinases, suggesting the involvement of at least two parallel signal transduction pathways in wounding induced gene activation. As FiRE shows specificity for migrating keratinocytes only, it can be a useful tool for future wound healing studies and for targeting genes to injured tissues.

Stent grafting for abdominal aortic aneurysms in Finland--a feasibility study

BACKGROUND AND AIMS

Endovascular repair of abdominal aortic aneurysms (AAA) is a feasible procedure in selected patients. In order to assess how many AAAs are suitable for such a procedure, a survey has been conducted in Helsinki, Kuopio, and Tampere University Hospitals.

MATERIAL AND METHODS

AAAs having a maximum diameter of 45 mm or more at ultrasonography were included for further evaluation and assessment by angiography and/or spiral CT angiography to determine the length and width of infrarenal aneurysmal neck as well as the dimensions of the distal abdominal aorta and iliac arteries.

RESULTS

Among a total of 75 patients with AAA examined in three centres, ultrasonography overestimated the size of the aneurysm in 12 cases that were demonstrated by angiography and CT to have a diameter of less than 45 mm. Among those patients with larger aneurysms, 17 (27%) were suitable for endovascular repair. Stent grafting has been performed in 10 patients until May, 1997. Perigraft leakage occurred in one patient who required the insertion of an additional collar stent graft.

CONCLUSIONS

Large numbers of suitable patients are not easy to find but, by performing joint screening in Finland, epidemiological data on suitable aneurysms and improving co-operation between centres can be achieved. Therefore, it would be wise to centralise endovascular repair of AAA.

Activation of an enhancer on the syndecan-1 gene is restricted to fibroblast growth factor family members in mesenchymal cells

Fibroblast growth factors (FGFs) induce a variety of biological effects on different cell types. They activate a number of genes, including immediate-early genes, such as the transcription factors Fos and Jun, which are also common targets for other tyrosine kinase receptor-activating growth factors. Here we describe a secondary far-upstream enhancer on the syndecan-1 gene that is activated only by members of the FGF family in NIH 3T3 cells, not by other receptor tyrosine kinase-activating growth factors (e.g., epidermal growth factor, platelet-derived growth factor, insulin-like growth factor, or serum). This FGF-inducible response element (FiRE) consists of a 170-bp array of five DNA motifs which bind two FGF-inducible Fos-Jun heterodimers, one inducible AP-2-related protein, a constitutively expressed upstream stimulatory factor, and one constitutive 46-kDa transcription factor. Mutational analysis showed that both AP-1 binding motifs are required, but not sufficient, for FiRE activation. Moreover, agents such as 12-O-tetradecanoylphorbol-13-acetate, okadaic acid, or forskolin, which are known to activate AP-1 complexes and AP-1-driven promoters, fail to activate FiRE. However, FiRE can be activated by the tyrosine kinase phosphatase inhibitor orthovanadate. Taken together, this data implies a differential activation of growth factor-initiated signaling on AP-1-driven regulatory elements.

Familial abdominal aortic aneurysms: screening of 71 families

OBJECTIVE

To find out the local prevalence of familial abdominal aortic aneurysms.

DESIGN

Retrospective open study.

SETTING

University hospital, Finland.

SUBJECTS

71 families of patients operated on for abdominal aortic aneurysm.

INTERVENTIONS

Ultrasound screening, personal interviews and study of population registers, death certificates and hospital records.

MAIN OUTCOME MEASURES

The diagnosis of asymptomatic abdominal aortic aneurysms.

RESULTS

148 of the 291 patients operated on replied to our letter (51%). The ultrasound examination was carried out on 123 siblings and detected abdominal aortic aneurysm in one sister (1/78 about 1%) and four brothers (4/45 about 9%). By the other methods data were obtained on 77 siblings (54 men and 23 women) of whom two sisters and six brothers were found to have abdominal aortic aneurysms. When the figures for the 71 families were combined, 10% of the brothers (10/99) and 3% of the sisters (3/101) had abdominal aortic aneurysms. These siblings were from 11 different families and so the prevalence of families with at least two affected persons was 16% (11/71). The index patient in 65 families was male and the prevalence of risk families (with two or more cases of aneurysm) in this group was 15% (10/65). The index case was a woman in six families giving a prevalence of 33% (2/6) (p = 0.2 between the groups).

CONCLUSION

The screening of families of patients with abdominal aortic aneurysms should be restricted to the brothers of these patients.