Hormone-replacement therapy influences gene expression profiles and is associated with breast-cancer prognosis: a cohort study

BACKGROUND: Postmenopausal hormone-replacement therapy (HRT) increases breast-cancer risk. The influence of HRT on the biology of the primary tumor, however, is not well understood. METHODS: We obtained breast-cancer gene expression profiles using Affymetrix human genome U133A arrays. We examined the relationship between HRT-regulated gene profiles, tumor characteristics, and recurrence-free survival in 72 postmenopausal women. RESULTS: HRT use in patients with estrogen receptor (ER) protein positive tumors (n = 72) was associated with an altered regulation of 276 genes. Expression profiles based on these genes clustered ER-positive tumors into two molecular subclasses, one of which was associated with HRT use and had significantly better recurrence free survival despite lower ER levels. A comparison with external data suggested that gene regulation in tumors associated with HRT was negatively correlated with gene regulation induced by short-term estrogen exposure, but positively correlated with the effect of tamoxifen. CONCLUSION: Our findings suggest that post-menopausal HRT use is associated with a distinct gene expression profile related to better recurrence-free survival and lower ER protein levels. Tentatively, HRT-associated gene expression in tumors resembles the effect of tamoxifen exposure on MCF-7 cells

Involvement of Eicosanoid Signaling in Intestinal Epithelial Cell Survival

Eicosanoids are known to be involved in many different aspects of eukaryotic physiology and pathology. Notably, over the past 10 years much attention has been given to cyclooxygenase-2 (COX-2) due to its involvement in colorectal cancer. Less is known about the other major branch of arachidonic acid metabolism, namely the lipoxygenases (LO). The cysteinyl leukotrienes (CysLTs) are a family of metabolites derived from 5-LO, and they are fairly well known because they play a pathogenic role in asthmatic disease. One member of this family, LTD4 , aggravates asthma by exerting a powerful mitogenic effect on bronchiolar smooth muscle. In light of this observation and the fact that tissue levels of leukotrienes are high in the precancerous inflammatory bowel disease known as ulcerative colitis, the present studies focused mainly on the influence of leukotrienes in general, and LTD4 in particular, on the survival of intestinal epithelial cells. Stimulation of intestinal epithelial cells with leukotrienes heightened the expression of colorectal oncogenic factors, such as COX-2, b-catenin, and Bcl-2, and simultaneously boosted the resistance of the cells to death induced by non-steroidal anti-inflammatory drugs. In analogy with this, levels of the LTD4 receptor CysLT1 R were significantly increased in roughly 50% of 84 colorectal cancer specimens, and this was accompanied by a markedly poorer disease outcome. Interestingly, in addition to the plasma membrane, the CysLT1 R receptor was specifically found in cell nuclei, possibly because this protein contains a putative nuclear-localizing sequence. This finding indicates that leukotrienes may even act as intracellular messengers

Leukotrienes induce cell-survival signaling in intestinal epithelial cells

BACKGROUND & AIMS: Inflammatory bowel conditions, particularly ulcerative colitis, are associated with an increased incidence of neoplastic transformation. High levels of proinflammatory leukotrienes (LTs) and up-regulated expression of cyclooxygenase (COX)-2 are characteristic of inflammation. Moreover, COX-2 has been implicated in cell survival and early colon carcinogenesis. Other aspects of interest for intestinal cell viability are the levels of beta-catenin and the antiapoptotic protein Bcl-2. We investigated the possibility that LTs participate in the regulation of these survival factors. METHODS: We used the human intestinal epithelial cell line Int 407 and the rat intestinal epithelial cell line IEC-6. Immunoblotting was applied to ascertain protein expression and distribution, and enzyme immunoassay methodology was used to measure prostaglandin E(2) (PGE(2)) production. Apoptotic ability was assessed by trypan blue exclusion, Hoechst staining, DNA fragmentation, and a caspase-3 activity assay. RESULTS: LTD(4) and LTB(4), but not LTC(4), caused a time- and dose-dependent increase in expression and/or membrane accumulation of COX-2, beta-catenin, and Bcl-2, as well as PGE(2) production. Apoptosis assays showed that the effects of LTs on these transformation-associated proteins correlated well with the ability of these LTs to reduce programmed cell death. CONCLUSIONS: The results suggest that inflammatory conditions are associated with the expression and distribution of proteins that are characteristic of transformed cells; such conditions may involve a signaling mechanism comprising an altered rate of apoptosis

Do leukotrienes increase cell viability in human intestinal epithelial cells?

In this preliminary report we present data showing that leukotrienes increase the baseline cell viability in human intestinal epithelial cells and that LTB4 partially reverses the morphological hallmarks of non-necrotic cell death induced by the COX-2 specific inhibitor NS-398. The proposed signaling mechanisms regulating these events are summarized in fig. 3. Please view the work on LT signal transduction in these cells by Thodeti et al. in this volume

The leukotriene receptor CysLT1 and 5-lipoxygenase are upregulated in colon cancer.

The metabolites of arachidonic acid are well connected to pathological situations such as inflammation, cancer and asthmA. Sheng et al. [7] found that COX-2 is upregulated in colon cancer tissue and tumor cell lines indicating that COX-2 is involved in colon cancer. This is supported by studies showing that patients treated with nonsteroidal anti-inflammatory drugs, inhibitors of COX-2, exhibit a lower frequency of colon cancer [8]. When the non-transformed intestinal epithelial cell line, Int 407 was stimulated with LTD4 or LTB4 we observed an accumulation of COX-2 in membrane fractions as well as an increased production of prostaglandin E2 [5]. Treatment of these cells with the COX-2 inhibitor NS-398 caused apoptosis and this effect could be prevented by LTD4 [5] or LTB4 [4]. Similar results were obtained when cell viability with LTD4 or LTB4 in the presence or absence of NS-398 was assayed [4,5]. The results demonstrate that these leukotrienes can suppress the NS-398 induced apoptosis in intestinal cells