© 2005 Foundation for Promotion of Cancer Research
Hypoxia-inducible Factor-1
is Associated with Risk of Aggressive Behavior and Tumor Angiogenesis in Gastrointestinal Stromal Tumor
1 Department of Pathology and 2 Department of Radiation Therapy, Kaohsiung Medical University Chung-Ho Memorial Hospital and 3 Graduate Institute of Occupational Safety and Health, Kaohsiung Medical University, Kaohsiung, Taiwan
For reprints and all correspondence: Chee-Yin Chai, Department of Pathology, Kaohsiung Medical University Chung-Ho Memorial Hospital, No. 100, Tzyou 1st Road, Kaohsiung City 807, Taiwan. E-mail: cychai{at}kmu.edu.tw
Received December 20, 2004; accepted March 9, 2005
 |
Abstract |
|---|
 TOP Abstract INTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Background: The objective of this study was to evaluate the relationship of HIF-1
expression and tumor angiogenesis, recurrence/distant metastasis, and its value in the prediction of aggressive behavior of gastrointestinal stromal tumor (GIST).
Methods: Paraffin-embedded specimens from 62 patients with GIST were divided into two groups, low risk (n = 31) and high risk (n = 31) according to the tumor size, mitotic count and proliferating cell nuclear antigen (PCNA) index. We investigated the expression of the HIF-1 and analyzed correlation with tumor angiogenesis monitored by expression of vascular endothelial growth factor (VEGF) and tumor microvessel density using immunohistochemical staining. The data were analyzed with 
2 test or Fisher's exact test and multivariate test.
Results: There were statistically significant differences between high risk (29/31; 93.5%) and low risk (8/31; 25.8%) of GIST in high expression of HIF-1 (P<0.0001). In addition, the incidence of recurrence/distant metastasis was significantly higher in cases of high HIF-1 expression (12/35; 34.3%) than in cases of low HIF-1 expression (1/24; 4.2%)(P = 0.009). Moreover, high VEGF expression (37/43; 86.0%) and microvessel density (30/32; 93.8%) were significantly higher in high HIF-1 expression tumors than in low-expression tumors (P < 0.0001).
Conclusions: Our findings suggest that HIF-1 may play an important role in aggressive behavior and tumor angiogenesis in GIST. In addition, high expression of HIF-1 was significantly correlated with tumor recurrence/distant metastasis, so it may provide an ancillary prognostic factor for GIST.
Key Words: gastrointestinal stromal tumor • hypoxia inducible factor-1 alpha (HIF-1) • immunohistochemistry, microvessel density (MVD) • vascular endothelial growth factor (VEGF)
|
INTRODUCTION |
|---|
|
TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract (1,2). Recent studies have shown that the tumor cells express a growth factor receptor with tyrosine kinase activity termed c-kit which can be detected by immunohistochemical staining for CD117, a specific marker for GIST (3,4). Until now, no single and absolute independent parameter has been proposed as a prognostic factor for GIST. Generally, prognostic features indicative of malignancy or high risk for aggressive clinical behavior include tumor size of 5 cm or larger, and mitotic rate of 2/10 high power field (HPF) or greater (5,6). In addition, nuclear atypia, marked cellularity, vessel invasion and necrosis are also reported to be associated with malignancy (7).
Angiogenesis is essential for the growth, invasion, and metastasis of tumor (8). The mechanism of angiogenesis has been shown to involve release of some substances from growing tumors that stimulate outgrowth of blood vessels from the host vasculature. Vascular endothelial growth factor (VEGF) plays an important role in tumor angiogenesis and in tumor metastasis (9,10). It induces endothelial cell migration and proliferation (11). VEGF is mainly produced by macrophages, vascular smooth muscle cells and tumor cells (12). Recently, studies have focused on the outcome of angiogenesis, the vascularity in the tumor. Tumor vascularity can be assessed by staining the blood vessel endothelia in the tissue and expressed in microvessel density (MVD) (13).
On the other hand, most solid tumors develop regions of low oxygen tension because of an imbalance in oxygen supply and consumption. Hypoxia in the tumor microenvironment is sufficient to activate hypoxia-inducible factor (HIF)-dependent gene expression (14). Hypoxia-inducible factor-1 alpha (HIF-1) is overexpressed in most human malignancies (15). A major role for HIF modulates gene expression, tumor angiogenesis (16), tumor progression and aggressive behavior in solid tumors (17). VEGF expression can be induced by exposure of tumor cells to hypoxia or growth factors and this expression is due in part to increased VEGF gene transcription, which is mediated by HIF-1 (18,19). HIF-1 stimulates processes like angiogenesis, glycolysis, erythropoiesis and apoptosis (20). HIF-1 plays a critical role in angiogenesis during vascular development, and it is a heterodimer composed of two subunits: HIF-1 and HIF-1ß. HIF-1 is the oxygen-regulated subunit that determines HIF-1 activity (21). Under non-hypoxic conditions, HIF-1 is subject to ubiquitination and proteasomal degradation. Thus, under hypoxic conditions, HIF-1 transcriptional activity increases rapidly due to HIF-1 protein overexpression (22).
HIF-1 is a primary determinant of HIF activity. HIF-1 expression has been studied in many cancers, including lung, prostate and breast carcinomas. The results reveal that HIF-1 expression is related to the patient's prognosis in these tumors (17). Therefore, it is worth finding out whether HIF-1 is an accurate and reliable prognostic factor for GIST. However, to the best of our knowledge, there is only one report to date concerned with the association of HIF-1 expression and angiogenesis in GIST (23). In our study, we not only evaluated the relationship between HIF-1 expression and tumor angiogenesis, but also looked at the correlation between HIF-1 expression and the proposed aggressive behavior of GIST in order to evaluate the applicability of immunohistochemical staining of HIF-1 expression in surgical specimens for the assessment of the biological behavior of GIST.
|
SUBJECTS AND METHODS |
|---|
|
TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
|---|
PATIENTS
Sixty-two cases of GIST were obtained from the archives of the Department of Pathology, Kaohsiung Medical University Chung-Ho Memorial Hospital between 1991 and 2000. All 62 patients had undergone subtotal gastrectomy, performed complete tumor resection or received segmental enterectomy with anastomosis. The diagnoses of GIST are based on the positive for CD117 (c-kit) by immunohistochemical stain. They were classified as low- or high-risk tumors as suggested by Gunawan et al. (5): high risk indicated either (i) a size
5 cm and mitotic count 2/10 HPF or (ii) a size 5 cm or mitotic count 2/10 HPF, and a proliferating cell nuclear antigen (PCNA) index >10%, whereas low risk indicated either (iii) a size <5 cm and mitotic count <2/10 HPF or (iv) a size 5 cm or mitotic count 2/10 HPF, and a PCNA index 
10% (5,6). Of the 62 cases, 31 were classified as low risk, and 31 as high risk. Cellularity, the presence or absence of vessel invasion, tumor necrosis and hemorrhage were also recorded. Vessel invasion is defined by the presence of intravascular tumor cells, either covered by endothelium or associated with thrombus. All patients had regular follow up with abdominal computed tomography (CT) scans and magnetic resonance imaging (MRI). Follow up was available for 59 cases after surgical resection (ranging from 22.5 months to 12.3 years; mean, 50.5 months). Some of our patients received adjuvant radiation or chemotherapy. They were beneficial to the patients with GISTs. Four of our patients had undergone STI 571 treatment. STI 571 is a small molecule kinase inhibitor, which displays potency as a competitive inhibitor of the ATP binding site and shows a high degree of specificity for c-kit. Tumor recurrence/distant metastasis was found in 13 of 62 cases. Twelve of 13 (92.3%) recurrence/distant metastasis cases were in the high-risk category for GIST.
IMMUNOHISTOCHEMICAL STAINING
Immunohistochemical staining (IHC) using the streptavidin-biotin method was performed to detect HIF-1, VEGF protein and CD31. In brief, sections were de-paraffinized and autoclave-treated at 121°C for 10 min in 0.1 M citrate buffer (pH 6.0). Endogeneous peroxidase in the section was blocked by incubation in 3% hydrogen peroxide for 5 min at room temperature. After washing with Tris buffer solution (TBS) and incubation with 5% BSA, the sections were incubated with primary antibodies HIF-1 (H-206, 1:50; Santa Cruz Biotechnology, Santa Cruz, CA) and VEGF (A-20, 1:200; Santa Cruz Biotechnology) overnight at 4°C. The primary antibodies CD31 (JC70A, 1:30; DAKO, Denmark) were applied at room temperature for 30 min. Biotinylated second antibody and peroxidase-conjugated streptavidin from the DAKO Universal LSAB kit (DAKO, Denmark) were applied for 20 min each. Finally, sections were incubated in 3'3-diaminobenzidine (DAB) for 5 min, followed by hematoxylin counterstaining and mounting. Negative controls were obtained by replacing the primary antibody with non-immune serum.
IMMUNOSTAINING EVALUATION
HIF-1 protein immunoreactivity was present in the nuclei with or without cytoplasms of neoplastic cells. Using the semiquantitative scale described previously (17), the HIF-1 protein expressions were classified as follows: –, no staining; 1+, nuclear staining in <1% of cells; 2+, nuclear staining in 1–10% of cells with or without weak cytoplasmic staining; 3+, nuclear staining in 10–50% of cells with or without distinct cytoplasmic staining; and 4+, nuclear staining in >50% of cells with or without strong cytoplasmic staining. For further analysis, using a cut-off point to define two groups of low and high HIF-1 expression, –, 1+ or 2+ staining patterns were regarded as low expression, and 3+ or 4+ staining patterns were regarded as high expression (Fig. 1A and B).
|
VEGF expression was observed in at least 10% of tumor cells to the intensity of cytoplasmic staining. VEGF staining was classified into the following four grades: no staining, weak, distinct and strong cytoplasmic staining. Distinct and strong cytoplasmic staining was defined as high VEGF expression (Fig. 1C); negative or weak cytoplasmic staining was defined as low VEGF expression.
MICROVESSEL DETECTION AND COUNTING
For CD31 staining, microvessel density (MVD) was assessed by light microscopy at the site of the highest number of capillaries and venules. In each tumor, ‘hot-spot’ areas displaying the highest vessel density were identified by scanning tumor sections at low-power magnification (x100). The maximum vessel density was determined from these ‘hot-spot’ areas at fields under high-power magnification (x20 objective and x10 ocular, 0.94 mm2 per field) (Fig. 1D), and the mean of counts for three fields was calculated. Large vessels with thick muscular walls were excluded from the counts, and vessel lumens were not necessary for a structure to be defined as a vessel (24). MVD was classified as either<15.0 or 15.0/HPF; 15.0 was the median value.
STATISTICAL ANALYSIS
Correlations between clinicopathological characteristics, risk of aggressive behavior, follow up and angiogenesis-associated factors with HIF-1 protein expression were assessed by using the 2 test or Fisher's exact test. Logistic regression was used to analyze the correlation of HIF-1 expression with tumor size, mitotic count, PCNA index, necrosis and hemorrhage. All statistical analyses were performed with the SPSS 8.0 statistical software program. P values <0.05 were considered to be statistically significant.
|
RESULTS |
|---|
|
TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
|---|
CORRELATION BETWEEN HIF-1
EXPRESSION AND CLINICOPATHOLOGIC CHARACTERISTICSThe 62 cases were classified into two tumor risk categories according to tumor size and mitotic count (5,6). The correlations between expression of HIF-1
and the clinicopathologic characteristics described are shown in Table 1. High HIF-1 expression was observed in tumor size 5 cm (27/30; 90.0%), mitotic count 2/10 HPF (26/26; 100%), PCNA index >10% (26/30; 86.7%), high-risk category (29/31; 93.5%) and presence of necrosis (21/23; 91.3%) and hemorrhage (32/45; 71.1%). The high expression of HIF-1 was significantly correlated with tumor size, mitotic count, PCNA index, risk categories, necrosis and hemorrhage (P < 0.0001, P < 0.0001, P < 0.0001, P < 0.0001, P < 0.0001 and P = 0.004, respectively). In contrast, no statistically significant correlation was found with sex, age, location, vessel invasion or cellularity. For HIF-1 expression, we found that high-risk category was an independent predictor of HIF-1 expression by multivariate analysis (P < 0.0001) (data not shown). Therefore, we further performed a multivariate analysis regarding the tumor size, mitotic count, PCNA index, necrosis and hemorrhage, which proved to be independently predictive using logistic regression analysis, as summarized in Table 2. A high mitotic count was associated significantly with high expression of HIF-1 (P < 0.0001).
|
|
CORRELATION BETWEEN AGGRESSIVE BEHAVIOR RISK CATEGORY, HIF-1
, VEGF EXPRESSION, MVD VALUE AND FOLLOW-UP DATATo clarify the actual prognostic values of HIF-1
, VEGF expression and tumor MVD for GIST, we selected 59 patients with regular follow-up. Recurrence/distant metastasis was found in 13 (22.03%) of these 59 patients. The incidence of patients with recurrence/distant metastasis was significantly higher in the high-risk category (12/29; 41.4%) than in the low-risk category (1/30; 3.3%) (P < 0.0001). The incidence was also significantly higher in high HIF-1 expression (12/35; 34.3%) than in low HIF-1 expression (1/24; 4.2%) patients. In addition, the angiogenesis-associated factors, VEGF high expression (13/40; 32.5%) and MVD value 15/HPF (12/30; 40.0%) were markedly increased in recurrence/distant metastasis. The results showed that HIF-1 expression, VEGF expression and MVD value in GIST were significantly correlated with recurrence/distant metastasis (P = 0.009, P = 0.005 and P = 0.001, respectively) (Table 3).
|
CORRELATION BETWEEN HIF-1
EXPRESSION AND ANGIOGENESIS-ASSOCIATED FACTORSHIF-1
expression was examined by both VEGF expression and tumor vascularity (Table 4). VEGF expression was observed in significantly higher levels in tumors with high HIF-1 expression (37/37; 100%) than in tumors with low HIF-1 expression (6/25; 24.0%). MVD was increased by HIF-1 and high VEGF expression. MVD was higher in tumors with high HIF-1 expression (30/37; 81.1%) than in tumors with low HIF-1 expression (2/25; 8.0%). Both MVD and VEGF expression were significantly correlated with HIF-1 expression (P < 0.0001).
|
|
DISCUSSION |
|---|
|
TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
|---|
GISTs are the most common mesenchymal tumor arising within the gastrointestinal tract. There are frequent gain-of-function mutations in GISTs that result in activation of KIT signaling, which leads to uncontrolled cell proliferation and resistance to apoptosis. GISTs are generally thought to be malignant, but they have different degrees of aggressiveness, resulting in varying incidences of recurrence and metastases. Predicting the potential biological behavior of these tumors remains difficult and an analysis of the literature to resolve this issue provides many conflicting reports (25). Age, the mitotic count (fewer or greater than 2/10 HPF) and size of the tumor (<5 cm versus
5 cm) are generally accepted as independent prognostic factors (5,6). Preliminary data suggest that tumors with an intermediate risk on the basis of size and mitotic count may be more accurately classified as high- or low-risk using PCNA index (5,6).
Tumorigenesis is a multistep process that requires the acquisition of certain properties common to all tumors. These properties include uncontrolled cell division, suppression of senescence, inhibition of apoptosis and induction of angiogenesis (26). The role of angiogenesis in the development and progression of human cancers has been widely studied (27). New blood vessels can be stimulated to grow when factors that promote angiogenesis are up-regulated or those that inhibit angiogenesis are down-regulated (8,28). Hypoxia in the tumor microenvironment is sufficient to activate HIF-dependent gene expression (14). However, tumor growth rate may not always be associated with hypoxic conditions, whereas HIF-1 expression may be influenced by factors other than hypoxia. A major role for HIF-1 in determining gene expression, tumor angiogenesis and growth has been demonstrated (29). Our data revealed that the expression of HIF-1 is correlated with the mitotic count, indicating that the larger the proliferative rate, the higher the risk of tumor hypoxia. HIF-1 overexpression is associated with increasing VEGF expression, one of its main downstream effectors, confirming angiogenesis as one of the proposed mechanisms by which HIF-1 activation stimulates tumor growth and leads to increasing VEGF-mediated tumor angiogenesis.
In the present study, expression of HIF-1 and VEGF have been found to be associated with an aggressive behavior risk category and we have shown that HIF-1 expression is associated with VEGF expression and angiogenesis in GIST. It is now widely accepted that VEGF expression is mediated by HIF-1 during hypoxia. It has been previously reported that expression of HIF-1 is correlated with VEGF expression and tumor vascularity in several cancers, including breast, colon and prostate cancer (17,30,31). We found that high levels of HIF-1 were correlated with VEGF and MVD, highlighting the important role of HIF-1 in the control of angiogenesis in GIST. These findings suggest that HIF-1 may play an important role in tumor growth and progression of GIST through regulation of VEGF, and that it should be associated with increased tumor angiogenesis.
The angiogenic process is so complex that additional studies concerning other regulators of angiogenic factors are needed. Tumor progression is closely dependent on an imbalance between cellular proliferation and death. Recent experimental results have shown that some tumor suppressor genes are involved in the regulation of angiogenesis (32). By reviewing papers, oncogenes and tumor suppressor genes such as VHL, p53, V-SRC and bcl-2 have been shown in vitro to influence angiogenesis by regulating the balance between stimulators and inhibitors of angiogenesis and have also been reported to be associated with HIF-1 and VEGF expression (32–38). Some recent studies have demonstrated that hypoxia and loss of p53 or VHL activity affect HIF-1 protein stability via altered ubiquitination (39). Therefore, further study is necessary. According to our study, HIF-1 may also be a potential target for antiangiogenic therapeutic strategies for GIST.
The criteria for benign and malignant tumors differ greatly among the various published studies. In the past, prognosis was traditionally determined using the aggressiveness risk category, tumor size and the mitotic activity. According to our study, HIF-1 expression is statistically significantly correlated with risk of aggressive behavior. In addition, in our study, primary GISTs were classified as low- or high-risk tumors for aggressive clinical behavior as suggested by tumor size and mitotic count. However, our results revealed that high expression of HIF-1 was a significant influence by showing a high mitotic count more than tumor size. Therefore, we inferred that mitotic activity is an important indicator of tumor aggressiveness; furthermore, this may be through promoted expression of HIF-1 in GISTs. We also tried to correlate the expression of HIF-1 with the incidence of recurrence/distant metastasis. Our result revealed that the HIF-1 expression was statistically significantly correlated with tumor recurrence/distant metastasis. This reason for this phenomenon may be due to many other factors; incomplete resection of the tumor, for example, may also increase the risk of recurrence/distant metastasis. Other factors such as expression adhesion molecules, and continuing mutation of oncogenes can also affect the risk of a distant tumor metastasis. Therefore, HIF-1 and VEGF expression may provide an ancillary prognostic factor for GIST.
In conclusion, this study demonstrates that the expression of HIF-1 is associated with risk of aggressive behavior and VEGF expression, which leads to increasing VEGF-mediated tumor angiogenesis. There is a statistically significant correlation between the expression of HIF-1 and the aggressive behavior risk category, and there is also a statistically significant association with recurrence/distant metastasis of GIST. Therefore, HIF-1 could serve as an ancillary parameter for the prediction of aggressive behavior, and it may be an independent prognostic factor for GIST.
|
Acknowledgments |
|---|
The excellent technical assistance of Mr Kwo-Tung Huang is gratefully acknowledged.
|
References |
|---|
|
TOPAbstractINTRODUCTIONSUBJECTS AND METHODSRESULTSDISCUSSIONReferences |
|---|
1 Miettinen M, Sarlomo-Rikala M, Lasota J. Gastrointestinal stromal tumors: recent advances in understanding of their biology. Hum Pathol 1999;30:1213–20.[CrossRef][Web of Science][Medline]
2 Miettinen M, Monihan JM, Sarlomo-Rikala M, Kovatich AJ, Carr NJ, Emory TS, et al. Gastrointestinal stromal tumors/smooth muscle tumors (GISTs) primary in the omentum and mesentery: clinicopathologic and immunohistochemical study of 26 cases. Am J Surg Pathol 1999;23:1109–18.[CrossRef][Web of Science][Medline]
3 Fletcher CDM, Berman JJ, Corless C, Gorstein F, Lasota J, Longley BJ, et al. Diagnosis of gastrointestinal stromal tumors: A consensus approach. Hum Pathol 2002;33:459–65.[CrossRef][Web of Science][Medline]
4 Graadt van Roggen JF, van Velthuysen MLF, Hogendoorn PCW. The histopathological differential diagnosis of gastrointestinal stromal tumours. J Clin Pathol 2001;54:96–102.
5 Gunawan B, Bergmann F, Hoer J, Langer C, Schumpelick V, Becker H, et al. Biological and clinical significance of cytogenetic abnormalities in low-risk and high-risk gastrointestinal stromal tumors. Hum Pathol 2002;33:316–21.[CrossRef][Web of Science][Medline]
6 Franquemont DW. Differentiation and risk assessment of gastrointestinal stromal tumors. Am J Clin Pathol 1995;103:41–7.[Web of Science][Medline]
7 Yan H, Marchettini P, Acherman YI, Gething SA, Brun E, Sugarbaker PH. Prognostic assessment of gastrointestinal stromal tumor. Am J Clin Oncol 2003;26:221–8.[CrossRef][Web of Science][Medline]
8 Folkman J. What is the evidence that tumors are angiogenesis dependent? J Natl Cancer Inst 1990;82:4–6.
9 Dvorak HF, Brown LF, Detmar M, Dvorak AM. Vascular permeability factor/vascular endothelial growth factor, microvascular hypermeability, and angiogenesis. Am J Pathol 1995;146:1029–39.[Abstract]
10 Senger DR, Van de Water L, Brown LF, Nagy JA, Yeo KT, Yeo TK, et al. Vascular permeability factor (VPF, VEGF) in tumor biology. Cancer Metastasis Rev 1993;12:303–24.[CrossRef][Web of Science][Medline]
11 Folkman J, Merler E, Abernathy C, Williams G. Isolation of a tumor factor responsible for angiogenesis. J Exp Med 1971;133:275–88.[Abstract]
12 Guang-Wu H, Sunagawa M, Jie-En L, Shimada S, Gang Z, Tokeshi Y, et al. The relationship between microvessel density, the expression of vascular endothelial growth factor (VEGF), and the extension of nasopharyngeal carcinoma. Laryngoscope 2000;110:2066–69.[CrossRef][Web of Science][Medline]
13 Vermeulen PB, Gasparini G, Fox SB, Toi M, Martin L, McCulloch P, et al. Quantification of angiogenesis in solid human tumours: an international consensus on the methodology and criteria of evaluation. Eur J Cancer 1996;32A:2474–84.[CrossRef][Web of Science][Medline]
14 Dachs GU, Patterson AV, Firth JD, Ratcliffe PJ, Townsend KM, Stratford IJ, et al. Targeting gene expression to hypoxic tumor cells. Nat Med 1997;3:515–20.[CrossRef][Web of Science][Medline]
15 Sun X, Kanwar JR, Leung E, Lehnert K, Wang D, Krissansen GW. Gene transfer of antisense hypoxia inducible factor-1 alpha enhances the therapeutic efficacy of cancer immunotherapy. Gene Ther 2001;8:638–45.[CrossRef][Web of Science][Medline]
16 Maxwell PH, Dachs GU, Gleadle JM, Nicholls LG, Harris AL, Stratford IJ, et al. Hypoxia-inducible factor-1 modulates gene expression in solid tumors and influences both angiogenesis and tumor growth. Proc Natl Acad Sci USA 1997;94:8104–9.
17 Zhong H, De Marzo AM, Laughner E, Lim M, Hilton DA, Zagzag D, et al. Overexpression of hypoxia-inducible factor 1 alpha in common human cancers and their metastases. Cancer Res 1999;59:5830–5.
18 Forsythe JA, Jiang BH, Iyer NV, Agani F, Leung SW, Koos RD, et al. Activation of vascular endothelial growth factor gene transcription by hypoxia-inducible factor 1. Mol Cell Biol 1996;16:4604–13.
19 Carmeliet P, Dor Y, Herbert JM, Fukumura D, Brusselmans K, Dewerchin M, et al. Role of HIF-1alpha in hypoxia-mediated apoptosis, cell proliferation and tumour angiogenesis. Nature 1998;394:485–90.[CrossRef][Medline]
20 Semenza GL. HIF-1: mediator of physiological and pathophysiological responses to hypoxia. J Appl Physiol 2000;88:1474–80.
21 Wang GL, Jiang BH, Rue EA, Semenza GL. Hypoxia-inducible factor-1 is basic-helix-loop-helix-PAS heterodimer regulated by cellular O2 tension. Proc Natl Acad Sci USA 1995;92:5510–4.
22 Huang LE, Gu J, Schau M, Bunn HF. Regulation of hypoxia-inducible factor 1alpha is mediated by an O2-dependent degradation domain via the ubiquitin-proteasome pathway. Proc Natl Acad Sci USA 1998;95:7987–92.
23 Takahashi R, Tanaka S, Hiyama T, Ito M, Kitadai Y, Sumii M, et al. Hypoxia-inducible factor-1alpha expression and angiogenesis in gastrointestinal stromal tumor of the stomach. Oncol Rep 2003;10:797–802.[Web of Science][Medline]
24 Weidner N, Semple JP, Welch WR, Folkman J. Tumor angiogenesis and metastasis-correlation in invasive breast carcinoma. N Engl J Med 1991;324:1–8.[Abstract]
25 Connolly EM, Gaffney E, Reynolds JV. Gastrointestinal stromal tumours. Br J Surg 2003;90:1178–86.[CrossRef][Web of Science][Medline]
26 Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57–70.[CrossRef][Web of Science][Medline]
27 Weidner N, Folkman J. Tumoral vascularity as a prognostic factor in cancer. Important Adv Oncol 1996;167–90.
28 Folkman J. How is blood vessel growth regulated in normal and neoplastic tissue? G.H.A. Clowes Memorial Award Lecture. Cancer Res 1986;46:467–73.
29 Maxwell PH, Wiesener MS, Chang GW, Clifford SC, Vaux EC, Cockman ME. The tumour suppressor protein VHL targets hypoxia-inducible factors for oxygen-dependent proteolysis. Nature 1999;399:271–5.[CrossRef][Medline]
30 Quintero M, Mackenzie N, Brennan PA. Hypoxia-inducible factor 1 (HIF-1) in cancer. Eur J Surg Oncol 2004;30:465–8.[CrossRef][Medline]
31 Mizukami Y, Li J, Zhang X, Zimmer MA, Iliopoulos O, Chung DC. Hypoxia-inducible factor-1-independent regulation of vascular endothelial growth factor by hypoxia in colon cancer. Cancer Res 2004;64:1765–72.
32 Dameron KM, Volpert OV, Tainsky MA, Bouck N. Control of angiogenesis in fibroblasts by p53 regulation of thrombospondin-1. Science 1994;265:1582–4.
33 Ravi R, Mookerjee B, Bhujwalla ZM, Sutter CH, Artemov D, Zeng Q, et al. Regulation of tumor angiogenesis by p53-induced degradation of hypoxia-inducible factor 1alpha. Genes Dev 2000;14:34–44.
34 Biroccio A, Candiloro A, Mottolese M, Sapora O, Albini A, Zupi G, et al. Bcl-2 overexpression and hypoxia synergistically act to modulate vascular endothelial growth factor expression and in vivo angiogenesis in a breast carcinoma line. FASEB J 2000;14:652–60.
35 Iervolino A, Trisciuoglio D, Ribatti D, Candiloro A, Biroccio A, Zupi G, et al. Bcl-2 overexpression in human melanoma cells increases angiogenesis through VEGF mRNA stabilization and HIF-1-mediated transcriptional activity. FASEB J 2002;16:1453–5.
36 Pidgeon GP, Barr MP, Harmey JH, Foley DA, Bouchier-Hayes DJ. Vascular endothelial growth factor (VEGF) upregulates BCL-2 and inhibits apoptosis in human and murine mammary adenocarcinoma cells. Br J Cancer 2001;85:273–8.[CrossRef][Web of Science][Medline]
37 Fernandez A, Udagawa T, Schwesinger C, Beecken W, Achilles-Gerte E, McDonnell T, et al. Angiogenic potential of prostate carcinoma cells overexpressing bcl-2. J Natl Cancer Inst 2001;93:208–13.
38 Jiang BH, Agani F, Passaniti A, Semenza GL. V-SRC induces expression of hypoxia-inducible factor 1 (HIF-1) and transcription of genes encoding vascular endothelial growth factor and enolase 1: involvement of HIF-1 in tumor progression. Cancer Res 1997;57:5328–35.
39 Semenza GL. Hypoxia, clonal selection, and the role of HIF-1 in tumor progression. Crit Rev Biochem Mol Biol 2000;35:71–103.[CrossRef][Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  Y. Sumiyoshi, Y. Kakeji, A. Egashira, K. Mizokami, H. Orita, and Y. Maehara Overexpression of Hypoxia-Inducible Factor 1{alpha} and p53 Is a Marker for an Unfavorable Prognosis in Gastric Cancer Clin. Cancer Res., September 1, 2006; 12(17): 5112 - 5117. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||