Estrogens, androgens, and EGF receptor expression in gastric carcinoma induced by N-methyl-N'-nitro-N-nitrosoguanidine

Transcript level of AKR1C3 is down-regulated in gastric cancer

Steroid hormones have been shown to play a role in gastric carcinogenesis. Large amounts of steroid hormones are locally produced in the peripheral tissues of both genders. Type 5 of 17β-hydroxysteroid dehydrogenase, encoded by the AKR1C3 gene, plays a pivotal role in both androgen and estrogen metabolism, and its expression was found to be deregulated in different cancers. In this study we measured AKR1C3 transcript and protein levels in nontumoral and primary tumoral gastric tissues, and evaluated their association with some clinicopathological features of gastric cancer (GC). We found decreased levels of AKR1C3 transcript (p < 0.0001) and protein (p = 0.0021) in GC tissues compared with the adjacent, apparently histopathologically normal, mucosa. Lower levels of AKR1C3 transcript were observed in diffuse and intestinal types of GC, whereas AKR1C3 protein levels were decreased in tumors with multisite localization, in diffuse histological type, T3, T4, and G3 grades. We also determined the effect of the histone deacetylase inhibitor sodium butyrate (NaBu) on AKR1C3 expression in EPG 85-257 and HGC-27 GC cell lines. We found that NaBu elevates the levels of both AKR1C3 transcript and protein in the cell lines we investigated. Together, our results suggest that decreased expression of AKR1C3 may be involved in development of GC and can be restored by NaBu.

Androgen receptor promotes gastric cancer cell migration and invasion via AKT-phosphorylation dependent upregulation of matrix metalloproteinase 9

Androgen receptor (AR) plays an important role in many kinds of cancers. However, the molecular mechanisms of AR in gastric cancer (GC) are poorly characterized. Here, we investigated the role of AR in GC cell migration, invasion and metastatic potential. Our data showed that AR expression was positively correlated with lymph node metastasis and late TNM stages. These findings were accompanied by activation of AKT and upregulation of matrix metalloproteinase 9 (MMP9). AR overexpression induced increases in GC cell migration, invasion and proliferation in vitro and in vivo. These effects were attenuated by inhibition of AKT, AR and MMP9. AR overexpression upregulated MMP9 protein levels, whereas this effect was counteracted by AR siRNA. Inhibition of AKT by siRNA or an inhibitor (MK-2206 2HC) decreased AR protein expression in both stably transfected and parental SGC-7901 cells. Luciferase reporter and chromatin immunoprecipitation assays demonstrated that AR bound to the AR-binding sites of the MMP9 promoter. In summary, AR overexpression induced by AKT phosphorylation upregulated MMP9 by binding to its promoter region to promote gastric carcinogenesis. The AKT/AR/MMP9 pathway plays an important role in GC metastasis and may be a novel therapeutic target for GC treatment.

Association between polymorphisms in long non-coding RNA PRNCR1 in 8q24 and risk of gastric cancer

A long ncRNA (lncRNA) prostate cancer non-coding RNA 1 (PRNCR1) in the 8q24 has been reported to be upregulated in prostate cancer with a function of activating androgen receptor (AR). AR plays a key role in the gender disparity, cell migration, and invasion of gastric cancer (GC). We hypothesized that single nucleotide polymorphisms (SNPs) in the lncRNA PRNCR1 may be related to the risk of GC. We conducted a case-control study to investigate the association between SNPs in the lncRNA PRNCR1 and the risk of GC. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was used to determine the genotypes of 613 subjects including 219 cases with GC and 394 controls. We found that patients with the rs13252298AG genotype displayed a 1.50-fold increased risk of GC (AG vs. AA, 95 % confidence interval (CI) = 1.05-2.12, p = 0.02). Interestingly, the rs7007694CT and CC and the rs1456315GG genotypes displayed a decreased risk of GC (rs7007694CT vs. TT, odds ratio (OR) = 0.68, 95 % CI = 0.48-0.97, p = 0.03; rs7007694CC vs. TT, OR = 0.36, 95 % CI = 0.13-0.97, p = 0.04; rs1456315GG vs. AA, OR = 0.30, 95 % CI = 0.13-0.70, p = 0.004, respectively). Our results suggest that SNPs in the lncRNA PRNCR1 may be a biomarker for the etiology of GC.

Androgen receptor may be responsible for gender disparity in gastric cancer

Men are at a higher risk of developing gastric cancer than women. However, the exact mechanisms responsible for the gender differences remain unclear. Recently, a number of epidemiological and genotyping studies have attributed the gender disparity in male-predominant cancers to the disruption of androgen receptor (AR) homeostasis. Moreover, previous data indicated that AR expression is an independent unfavorable prognostic factor in gastric cancer, suggesting that AR may play an important role in gastric carcinogenesis. In addition, mounting evidence suggests that AR is involved in many signaling pathways associated with gastric carcinogenesis. On the basis of the aforementioned evidence, we postulate that AR exhibits oncogenic properties in gastric cancer via several possible mechanisms, which may partly explain the higher prevalence of gastric cancer among males.

Inhibition by rat C-erbB-2/neu antisense oligonucleotide of gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine in Wistar rats

The effect of prolonged administration of a rat C-erbB-2/neu (C-erbB-2) antisense oligonucleotide on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and on the labeling and apoptotic indices of gastric cancer was examined in Wistar rats After oral treatment with MNNG for 25 weeks, the rats received intraperitoneal injections of a C-erbB-2 antisense-liposome complex or a sense-liposome complex at a dose of 50 microgram oligonucleotide/kg body weight every other day until the end of the experiment in week 52. In week 52, the incidence of gastric cancers was significantly lover in rats treated with the C-erbB-2 antisense oligonucleotide than in rats treated with the sense oligonucleotide. Administration of the C-erbB-2 antisense oligonucleotide also significantly decreased the bromodeoxyuridine-labeling index and significantly increased the apoptotic index of gastric cancers. The mean cellular fluorescence of gastric antral cells in MNNG-treated rats was positively correlated with the dose of FITC-labeled C-erbB-2 antisense oligonucleotide. Our findings indicate that the antisense oligonucleotide inhibits gastric carcinogenesis through decreased cell proliferation and increased apoptosis induction and suggest that antisense strategies may provide new treatment for gastric cancer.

17Beta-estradiol modulates gastroduodenal preneoplastic alterations in rats exposed to the carcinogen N-methyl-N'-nitro-nitrosoguanidine

Gastric cancers are a significant cause of morbidity worldwide. Epidemiological studies and animal models show that males have higher incidences of gastric cancers compared with females, suggesting that sex hormones may modulate gastric cancer risk. An animal model of the initiation phase of gastric cancer was used to determine the effects of systemic estrogen administration on morphological progression of preneoplastic lesions and to define cell populations at which estrogens may act. Preneoplastic progression in antral and duodenal mucosa was examined in male rats that received the chemical carcinogen, N-methyl-N'-nitro-nitrosoguanidine (MNNG), during treatment with implants containing 17beta-estradiol or oil vehicle. Histopathological changes in antral and duodenal gland morphology, numbers of proliferating cells and apoptotic bodies, and antral gastrin cell numbers and protein storage levels were determined 4 weeks later. With MNNG treatment, duodenal villous heights were significantly decreased, and epithelial cells displayed histological features of hyperplasia and dysplasia. Antral glands showed epithelial hyperplasia and dysplasia, increased mucosal height, and decreased mucin levels. Antral gastrin storage protein levels were decreased by MNNG. Systemic treatment with 17beta-estradiol significantly reversed MNNG-induced alterations in duodenal gland heights while increasing mucin and gastrin levels in antral glands. Cell proliferation and apoptosis rates were not significantly different between groups. The present results indicate that systemic 17beta-estradiol treatment influences antral and duodenal gland differentiation during the initiation phase of chemical gastroduodenal carcinogenesis in male rats. These results explain, in part, a potential pathway through which protective effects of estrogens on chemical carcinogenesis are mediated in the upper gastrointestinal tract.

MUC6 expression in breast tissues and cultured cells: abnormal expression in tumors and regulation by steroid hormones

Neoplastic transformation of epithelial cells is commonly associated with alterations in the expression of mucin genes. The mechanisms involved in this process are largely unknown. MUC6, isolated from a stomach cDNA library, is mainly expressed in stomach antral glands, as detected by using in situ hybridization and immunohistochemistry. We examined MUC6 expression in normal and pathological breast tissues using immunohistochemistry with MUC6-specific antibodies and in cultured breast cancer cells using immunocytochemistry and Northern blotting. MUC6 was generally not detected in normal breast (1/11) but was detected in fibrocystic disease without atypia (7/17, 41%), in atypical fibrocystic disease (11/11, 100%) and in carcinoma (57/60, 95%). To study the mechanisms involved in mucin gene up-regulation in breast cancer, we examined baseline, growth-related and steroid-induced levels of MUC1, MUC3 and MUC6 in 4 breast cancer cell lines, 2 of which express estrogen receptors. MUC6 levels were up-regulated at post-confluence in 2/4 cell lines, whereas no changes were detected for the other mucin genes examined. MUC6 and MUC3 were constitutively expressed, and steroid-induced, in BT-474 and MCF-7 cells, respectively. As a control, pS2 was induced in both cell lines. Our results indicate that (1) MUC6 is overexpressed in breast cancer and in benign breast disease, (2) in vitro, MUC6 and MUC3 are up-regulated by steroids and (3) abnormal expression of MUC6 in breast cancers may, in part, be explained by hormonal changes associated with tumor development.

Estrogen receptor alpha and beta expression in upper gastrointestinal tract with regulation of trefoil factor family 2 mRNA levels in ovariectomized rats

This study compared expression of two estrogen receptor (ER alpha and ER beta) genes in the rat upper gastrointestinal tract and the effects of 17 beta-estradiol administration on gastric trefoil factor family (TFF) mRNA steady-state levels in ovariectomized rats. Estrogen receptor alpha and beta cDNA fragments from fundic mucosa were cloned by reverse transcriptase polymerase chain reaction (RT-PCR) and sequenced. Both ER subtypes were detected in fundus, antrum and duodenum by RT-PCR. Northern analysis of poly(A)+ mRNA from fundic mucosa showed that ER alpha mRNA is expressed as a single transcript at 6.5 kb and ER beta is expressed as multiple transcripts with major transcripts ranging from 1.1-4.7 kb. ER beta mRNA was expressed in greater abundance than ER alpha mRNA. Fundic TFF2 mRNA steady-state levels were increased by 17 beta-estradiol administration in ovariectomized rats with no significant change in TFF1 mRNA levels. These studies show expression of both ER subtypes in the rat upper gastrointestinal tract with regulation of TFF2 mRNA by 17 beta-estradiol. These results suggest that estrogens, probably acting via ER beta, have a direct role in regulating gastric physiology.

Hormonal regulation of the human pepsinogen C gene in breast cancer cells. Identification of a cis-acting element mediating its induction by androgens, glucocorticoids, and progesterone

Pepsinogen C is an aspartic proteinase mainly involved in the digestion of proteins in the stomach, which is also synthesized by certain human breast tumors. To examine the possibility that extragastric production of this proteolytic enzyme could be mediated by hormonal factors, we have analyzed pepsinogen C gene expression in human breast cancer cells subjected to different hormonal treatments. Northern blot analyses revealed the expression of pepsinogen C gene by T-47D breast cancer cells after induction with dihydrotestosterone, dexamethasone, and progesterone but not with estradiol, retinoic acid, or ethanol. Reverse transcription-polymerase chain reaction analysis in a series of breast cancer cell lines confirmed the amplification of pepsinogen C mRNA after induction with dihydrotestosterone, in those cells expressing the androgen receptor mRNA. The promoter region of the pepsinogen C gene was functionally characterized by transient expression of a vector containing the promoter region cloned in front of the chloramphenicol acetyltransferase (CAT) reporter gene. CAT activity in T-47D cells was stimulated in the presence of dihydrotestosterone, dexamethasone, and progesterone but not by estradiol. By further deletion mapping of the pepsinogen C promoter, a minimal region (AGAACTattTGTTCC) was identified as being responsible for glucocorticoid-, androgen-, and progesterone-regulated gene expression.

Steroid hormone receptors in three human gastric cancer cell lines

Steroid hormone receptors in three human gastric adenocarcinoma cell lines and their transplanted tumors (except nontumorigenic KATO-III) in nude mice were determined by dextran-coated charcoal assay. Progesterone receptors (PgR) were found in all cell lines, transplanted NUGC-3, and AZ 521 tumors. Estrogen receptors (ER) were found in KATO-III cells, transplanted NUGC-3, and AZ 521 tumors, whereas glucocorticoid receptors (GR) were found only in NUGC-3 tumor and no androgen receptor was found in any cell lines or transplanted tumors. Since NUGC-3 cells had ER, PgR, and GR, it was used for the study of the effects of steroid hormones on growth. The results showed the cell cycle phase distributions and growth rate of transplanted tumors were similar in hormone-treated and nontreated groups. The persistent expression of PgR in gastric cancer cell lines and tumors, and the slight increase of tumor volumes in the progesterone-treated group suggests that progesterone and its receptors may be important in the pathogenesis of gastric cancer, but their biological function remains to be elucidated.