Reduced expression of early growth response-1 gene in leiomyoma as identified by mRNA differential display

The role of angiogenic factors in fibroid pathogenesis: potential implications for future therapy

BACKGROUND

It is well established that tumors are dependent on angiogenesis for their growth and survival. Although uterine fibroids are known to be benign tumors with reduced vascularization, recent work demonstrates that the vasculature of fibroids is grossly and microscopically abnormal. Accumulating evidence suggests that angiogenic growth factor dysregulation may be implicated in these vascular and other features of fibroid pathophysiology.

METHODS

Literature searches were performed in PubMed and Google Scholar for articles with content related to angiogenic growth factors and myometrium/leiomyoma. The findings are hereby reviewed and discussed.

RESULTS

Multiple growth factors involved in angiogenesis are differentially expressed in leiomyoma compared with myometrium. These include epidermal growth factor (EGF), heparin-binding-EGF, vascular endothelial growth factor, basic fibroblast growth factor, platelet-derived growth factor, transforming growth factor-β and adrenomedullin. An important paradox is that although leiomyoma tissues are hypoxic, leiomyoma feature down-regulation of key molecular regulators of the hypoxia response. Furthermore, the hypoxic milieu of leiomyoma may contribute to fibroid development and growth. Notably, common treatments for fibroids such as GnRH agonists and uterine artery embolization (UAE) are shown to work at least partly via anti-angiogenic mechanisms.

CONCLUSIONS

Angiogenic growth factors play an important role in mechanisms of fibroid pathophysiology, including abnormal vasculature and fibroid growth and survival. Moreover, the fibroid's abnormal vasculature together with its aberrant hypoxic and angiogenic response may make it especially vulnerable to disruption of its vascular supply, a feature which could be exploited for treatment. Further experimental studies are required in order to gain a better understanding of the growth factors that are involved in normal and pathological myometrial angiogenesis, and to assess the potential of anti-angiogenic treatment strategies for uterine fibroids.

Profiling of differentially expressed genes in human uterine leiomyomas

Uterine leiomyomas are very common benign tumors resulting in clinically serious gynecological problems in women of reproductive age. Approximately, 1% of leiomyosarcoma was reported to arise in a preexisting leiomyoma. However, the molecular basis of these tumors is poorly understood. To understand the molecular changes during leiomyoma development, we profiled differentially expressed genes in ten paired leiomyoma and normal myometrial tissues using cDNA microarray chip analysis. We identified 67 genes (27 overexpressed and 40 underexpressed) which were scored as differentially expressed at least twofold in at least eight of ten patients. Eighteen of 67 genes have been already reported to be differentially expressed without their established functions in uterine leiomyoma and others have never been reported. Subsequently, the relative expression levels of representative genes from identified 67 genes were confirmed by reverse-transcriptase polymerase chain reaction and immunohistochemistry and were found to be consistent with the microarray data. This study could provide a new insight into the understanding of leiomyoma and leiomyosarcoma.

Estrogen-induced changes in IGF-I, Myb family and MAP kinase pathway genes in human uterine leiomyoma and normal uterine smooth muscle cell lines

Many studies have implicated numerous hormones, growth factors, cytokines and other signal transduction molecules in the pathogenesis of uterine leiomyoma. Estrogen and estrogen-related genes are thought to play a key role in the growth of uterine leiomyomas, but the molecular mechanisms are unclear. In an attempt to investigate various pathways that might be involved in estrogen-regulated uterine leiomyoma growth as well as to identify any novel effector genes, microarray studies comparing estrogen-treated uterine leiomyoma cells (UtLM) and normal myometrial cells to untreated cells were performed. Several genes were differentially expressed in estrogen treated UtLM cells, including insulin-like growth factor-I (IGF-I) and others potentially involved in the IGF-I signalling pathway, specifically genes for A-myb, a transcription factor which promotes cell cycle progression and for MKP-1, a dual specificity phosphatase that dephosphorylates mitogen-activated protein kinase. IGF-I and A-myb were up-regulated in estrogen-treated cells while MKP-1 was down-regulated. Two other cell cycle promoting genes, c-fos and myc, were also down-regulated in estrogen treated UtLM cells. These genes are typically up-regulated in response to estrogen in some cells, notably breast epithelial cells, yet consistently have lower expression levels in uterine leiomyoma tissue when compared to autologous myometrium. Our results demonstrate some novel genes that may play a role in the growth of uterine leiomyoma, strengthen the case for involvement of the IGF-I pathway in the response of UtLM to estrogen and corroborate evidence that uterine smooth muscle cells respond to estrogen with a different gene expression pattern than that seen in epithelial cells.

Antisense to the early growth response-1 gene (Egr-1) inhibits prostate tumor development in TRAMP mice

Egr-1 is a transcription factor induced by stress or injury, mitogens, and differentiation factors. Egr-1 regulates the expression of genes involved in growth control or survival. Expression of Egr-1 results in either promotion or regression of cell proliferation, depending on cell type and environment. Egr-1 acts as a tumor suppressor in many cell types and loss of Egr-1 has been proposed to contribute to cancer progression. There is strong new evidence however suggesting that Egr-1 overexpression is involved in prostate cancer progression. For example, Egr-1 expression levels are elevated in human prostate carcinomas in proportion to grade and stage. Furthermore, prostate cancer progression was significantly delayed in two models of prostate cancer mice lacking Egr-1. Our objective in the present study is to test whether inhibition of Egr-1 function would block cell proliferation and inhibit the transformed phenotype of prostate cancer cells in vitro and in vivo. We describe the development of high affinity and high specificity antisense oligonucleotides that efficiently inhibit Egr-1 expression. We show that inhibition of Egr-1 expression in mouse or human prostate cancer cells decreased proliferation and reduced the capacity of these cells to form colonies and to grow in soft agar. Conversely, stable expression of Egr-1 in normal human prostate epithelial 267B1 cells promoted transformation. In TRAMP mice, treatment with Egr-1 antisense oligonucleotides delayed the occurrence of prostate tumors. Importantly, Egr-1 antisense showed little or no toxicity when injected into animals. Finally, we identified a few genes such as cyclin D2, p19ink4d, and Fas that are directly regulated by Egr-1 in prostate cancer cells and that control cell cycle and survival.

Differential gene expression in uterine leiomyoma

Uterine leiomyomas are the most common tumor of the genitourinary system in women and are a major cause of morbidity. The molecular causes of the disease remain unclear. In this study, we examined gene expression in leiomyomas and normal myometrium. RNA was prepared and gene expression determined with the use of Affymetrix GeneChip U_95 arrays containing approximately 12,000 known genes and 48,000 expression sequence tags. Several genes were found to be differentially expressed in these two sample sets, and these genes were analyzed for their expression in a variety of other normal and diseased tissues. Four genes--doublecortin, calpain 6, interleukin-17B, and proteolipid protein 1--were found to be overexpressed in leiomyomas compared with normal myometrium and eighteen other tissues. Sets of genes were identified whose expression could be used to cluster samples with leiomyomas or normal myometrium with the use of Eisen Cluster software. We conclude that differences in gene expression can be detected between leiomyomas and normal myometrium and that these changes in gene expression may yield clues to the pathophysiology of this common tumor.