The trefoil factor 1 participates in gastrointestinal cell differentiation by delaying G1-S phase transition and reducing apoptosis

Trefoil factor (TFF)1 is synthesized and secreted by the normal stomach mucosa and by the gastrointestinal cells of injured tissues. The link between mouse TFF1 inactivation and the fully penetrant antropyloric tumor phenotype prompted the classification of TFF1 as a gastric tumor suppressor gene. Accordingly, altered expression, deletion, and/or mutations of the TFF1 gene are frequently observed in human gastric carcinomas. The present study was undertaken to address the nature of the cellular and molecular mechanisms targeted by TFF1 signalling. TFF1 effects were investigated in IEC18, HCT116, and AGS gastrointestinal cells treated with recombinant human TFF1, and in stably transfected HCT116 cells synthesizing constitutive or doxycycline-induced human TFF1. We observed that TFF1 triggers two types of cellular responses. On one hand, TFF1 lowers cell proliferation by delaying G1-S cell phase transition. This results from a TFF1-mediated increase in the levels of cyclin-dependent kinase inhibitors of both the INK4 and CIP subfamilies, leading to lower E2F transcriptional activity. On the other hand, TFF1 protects cells from chemical-, anchorage-free-, or Bad-induced apoptosis. In this process, TFF1 signalling targets the active form of caspase-9. Together, these results provide the first evidence of a dual antiproliferative and antiapoptotic role for TFF1. Similar paradoxical functions have been reported for tumor suppressor genes involved in cell differentiation, a function consistent with TFF1.

Mouse Trefoil factor genes: genomic organization, sequences and methylation analyses

The mammalian Trefoil Factors (TFFs), TFF1/pS2, TFF2/SP and TFF3/ITF, are expressed and secreted throughout the gastrointestinal tract with a specific and complementary pattern. These proteins exhibit common functions in the protection and repair process of the gastrointestinal epithelial barrier. Here, we report the clustered organization of the three mouse TFF genes in a 40 kb DNA segment, in a head to tail orientation in the following order: TFF1, TFF2, and TFF3. Computer comparison of the mouse TFF promoter sequences to their human counterparts revealed conserved boxes in both mouse and human genes. Promoter methylation analyses showed that, in tissues where these genes are normally expressed, the proximal promoters of TFF1 and TFF2 are specifically not methylated and that of TFF3 is partially demethylated. In contrast, in organs that do not express TFFs, the promoters of the three genes are methylated. These findings strongly argue for the involvement of epigenetic mechanisms in the regulation of TFF expression in normal and pathological conditions.

Identification and characterization of a novel gastric peptide hormone: the motilin-related peptide

BACKGROUND & AIMS

This study looked for new proteins with expression restricted to the gastric epithelium that may provide insight to the differentiation and function of the gastric unit.

METHODS

A novel complementary DNA was isolated and sequenced, and its expression was examined in mouse tissues at both messenger RNA and protein levels. Subcellular localization was studied using immunoelectron microscopy. The posttraductional processing of the protein was analyzed in vitro by protein microsequencing and in vivo by Western blotting.

RESULTS

We identified a novel protein that is mainly expressed by the secretory granules of the stomach enteroendocrine cells. This protein has sequence similarity with prepromotilin, the precursor of the motilin hormone and the motilin-associated peptide. As for the prepromotilin, a posttraductional maturation leads to a secreted peptide that is further cleaved at a dibasic site and gives rise to the motilin-related peptide (MTLRP) and MTLRP-associated peptide.

CONCLUSIONS

We have identified and characterized a novel gene encoding the preproMTLRP protein. MTLRP presents similarity to motilin and is specifically expressed by enteroendocrine cells of the stomach and therefore represents a novel hormone.

Differential RNA expression of the pS2 gene in the human benign and malignant prostatic tissue

PURPOSE

The pS2 trefoil protein has been detected in close association with neuro-endocrine differentiation in prostate cancer and prostatic intraepithelial neoplasia. These preliminary results have suggested that pS2 is a candidate as a specific marker for prostate cancer tissue. To ascertain the specificity of pS2 in prostate cancer tissue, we have used an RT-PCR method from prostate biopsies provided from human malignant and benign prostatic hyperplasia (BPH) tissue.

MATERIALS AND METHODS

Prostate biopsies were obtained from transrectal biopsies from 153 patients with an abnormal DRE or a PSA more than 4 ng./ml. or symptoms of BPH and a PSA more than 4 ng./ml. Total RNA was extracted from fresh frozen specimens of tissue samples. Detection of pS2 transcript compared with GADPH transcripts was done using RT-PCR.

RESULTS

Biopsy results showed that 108 patients had prostate cancer (average Gleason score 6.39+/-0.74) and 45 patients had BPH. PS2 RT-PCR results showed that PS2 RNA expression was negative in 83% of the BPH cases. Conversely, 92% of prostate cancer specimens were positive (Chi-square: 86.09, p<0.001). There was no correlation with tumor stage or the Gleason score. Comparing the expression of pS2 in BPH and localized prostate cancer, we found a sensitivity of 92% and a specificity of 82%.

CONCLUSIONS

On this large sample of prostate biopsies from patients at risk of having prostate cancer, pS2 was demonstrated as an interesting marker significantly associated with prostate cancer. Further work on the expression of pS2 according to differentiation and hormonal status is in progress.

Down-regulation of BRCA1 in human sporadic breast cancer; analysis of DNA methylation patterns of the putative promoter region

Germ-line alterations of BRCA1 are responsible for about 50% of familial breast cancers. Although its biological function(s) has not yet been fully determined, it has been suggested that it may act as a tumor suppressor gene in breast and ovarian cancers. In sporadic breast cancers alterations of BRCA1 have not been detected and in vitro experiments have indicated that BRCA1 negatively regulates cellular proliferation. The present study was designed to identify and quantify, the BRCA1 mRNA levels, in normal and neoplasic human breast tissue. BRCA1 mRNA molecules were quantified using competitive reverse transcriptase PCR assays. DNA methylation patterns of this gene have been analysed by Southern blot experiments using methylation sensitive restriction enzymes. We found that BRCA1 mRNA levels were significantly lower in sporadic breast cancers (37 cases analysed, 24 cases of invasive ductal carcinomas not otherwise specified (NOS), two lobular carcinomas in situ two medullary carcinomas, four invasive lobular carcinomas, two invasive mucinous carcinomas and three invasive ductal carcinomas with predominantly in situ component) compared with normal breast tissues (P=0.0003). This down-regulation of BRCA1 is observed in all histologic types analysed. In invasive ductal carcinomas NOS, this down-regulation does not correlate with any of the prognostic factors studied (tumor size, node status, histologic grade, hormone receptor status). In the samples analysed, alterations of DNA methylation patterns were not dectected in the vicinity of the major transcription start site. These data suggest the involvement of BRCA1 in the carcinogenesis of these histologic types.

The pS2/TFF1 trefoil factor, from basic research to clinical applications

pS2/TFF1 trefoil factor is normally expressed in the stomach, and is found ectopically in gastrointestinal inflammatory disorders and in various carcinomas. It is involved in stomach ontogenesis and in the maintenance of the integrity of the mucosa, and may represent a pharmacological tool for prevention and healing of gastrointestinal ulcerations. In breast cancer, it can be used to select patients suitable for hormone therapy. pS2/TFF1 is a pleiotropic factor involved in mucin polymerization, cell motility, cell proliferation and/or differentiation, and possibly in the nervous system.

The estrogen responsive element of the pS2 gene is recognized by a methylation sensitive DNA binding protein

The human pS2 gene is specifically expressed is a subclass of estrogen receptor containing human breast cancer cells. In the MCF7 cell line, its induction by estradiol is a primary transcriptional event. The exact location of its estrogen responsive element has been determined using a chimeric recombinant transfected into HeLa cells and a transient expression assay. In this study we found, using electrophoretic mobility shift experiments, that in HeLa cells the estrogen responsive element (ERE) of the pS2 gene is recognized by a methylation sensitive DNA binding protein (MSDBP) different from the estrogen receptor. Competition experiments have shown that the binding of this protein requires at least one CpG in the center of the palindromic sequence and that imperfect palindromic sequences are also recognized. Although the presence of CpG is necessary, CpG-rich oligonucleotides, containing consensus sequences for Sp1 or AP2, do not interfere with its binding to the pS2 oligonucleotide, indicating that the ERE sequence itself participates in the specificity of its binding. This protein binds the pS2 sequence with a relatively high affinity (apparent Kd = 10(-10) M) and its binding is strongly reduced by the methylation of the cytosines at CpG sites. UV cross-linking experiments and peptide mapping indicate that this protein has an apparent molecular weight of 46 kDa and is present in several cell lines, including non-human cell lines. Taken together, these data suggest that this protein might have a potential role in regulating gene activity or in chromatin structure of some genes possessing an ERE.

Abundance of BRCA1 transcripts in human cancer and lymphoblastoid cell lines carrying BRCA1 germ-line alterations

A competitive polymerase chain reaction has been developed for quantitation of BRCA1 mRNA. In human cancer cell lines, the amount of BRCA1 mRNA is relatively low, ranging from 6 to 38 copies per cell. The decay rate of these transcripts in actinomycin-treated cells indicates that the half-life of these molecules is about 4 hr, suggesting that the low concentration of BRCA1 messages is not due to molecular unstability. In human lymphoblastoid cell lines derived from patients carrying germ-line alterations of BRCA1, the amount of BRCA1 mRNA per cell is lowered only in cell lines exhibiting alterations leading to specific loss of transcripts from the mutated allele. These data indicate that the amount of BRCA1 available in these cells can be related directly to the number of "active" allele.

Involvement of DNA methylation in the control of the expression of an estrogen-induced breast-cancer-associated protein (pS2) in human breast cancers

pS2 gene has been used to investigate the relationship between alterations of DNA methylation patterns in human tumors and gene expression. The expression of pS2, which is transcriptionally controlled by estrogens in breast cancer cell lines, is restricted to estrogen-receptor-rich human breast tumors. We found that the CCGG site within the promoter/enhancer sequence of pS2 was hypomethylated in estrogen-receptor-rich breast tumors expressing this gene. The amount of DNA molecules unmethylated at this site was related to the amount of pS2 mRNA detected in the samples. The demethylation of this region, which contains the estrogen responsive element, was confirmed by genomic sequencing. Transient expression of functional human estrogen receptors stimulated the expression of the endogenous pS2 in HeLa cells, but failed, in BT-20 cells, to stimulate expression of this gene. Since the promoter/enhancer region of pS2 is unmethylated in HeLa cells and methylated in BT-20 cells, these data also support the hypothesis that DNA methylation might be involved in the control of pS2 expression.

Genomic sequencing indicates a correlation between DNA hypomethylation in the 5' region of the pS2 gene and its expression in human breast cancer cell lines

The methylation status of the cytosines located on the 5' region of the pS2 gene have been investigated in two human breast cancer cell lines. The genomic sequencing method used is based on an oxydative deamination by NaHSO3 of the unmethylated cytosines, but not 5-methylcytosine. Data obtained indicate that in the DNA extracted from the pS2-expressing cell line, MCF7, the CpG located at the 5' flanking sequence of pS2 are unmethylated. In contrast in the non-expressing cell line, BT20, these CpG are largely methylated. However, this correlation is not observed at all CpG sites, since a significant portion of the cloned PCR fragments obtained from BT20 cells are unmethylated at specific CpG sites. These results suggest that the methylation status of only some of the CpG located at the 5' flanking sequences of pS2 might differ between expressing and nonexpressing cell lines.

Human breast and colon cancers exhibit alterations of DNA methylation patterns at several DNA segments on chromosomes 11p and 17p

In breast and colon adenocarcinomas methylation patterns at CCGG sites of several loci located on the short arm of chromosome 11 were determined by Southern blot analysis. Results obtained indicate that all tumor samples (20/20) exhibit DNA methylation changes when compared to their normal counterparts. In colon tumors, gamma-globin gene is usually hypomethylated (9/10), whereas Ha-ras gene, which is located in the same region, retains an unmodified DNA methylation pattern. Hypomethylation of parathyroid hormone (5/10) and catalase genes (4/10) are also frequently detected in colon tumor specimens. For the catalase gene the region around exon 2 is the only one which is affected by these changes. In breast adenocarcinoma, modifications of the methylation patterns are less frequently observed. However, hypomethylation of the gamma-globin gene is a very common event in these tumors (8/10), and it is also detected (2/2) in lobular carcinoma in situ which is an early step in breast tumorigenesis. In addition, hypermethylation of a CpG island is also observed at the locus 17p13.3 in both colon (5/5) and breast (4/9) adenocarcinomas. In the tumoral tissues analyzed these hypermethylations are not associated with the hypermethylation of the 5' flanking sequences which contain a limited amount of CpG. Some of these alterations seem, therefore, to be tumor and sequence specific.

Expression of an estrogen-induced breast cancer-associated protein (pS2) in benign and malignant human ovarian cysts

BACKGROUND

In human mammary tumors, pS2 expression is directly controlled by estrogens and restricted to a subclass of breast carcinomas. In addition, recent studies have suggested that this gene is expressed in both the invasive and preinvasive forms of breast cancer.

EXPERIMENTAL DESIGN

pS2 gene expression was investigated in benign and malignant ovary tumors and whenever possible, pS2 expression was also studied in cells collected from cystadenoma fluids. In several cases, particularly with cells from cystadenoma fluids, the limited amount of material available prevented the used of the traditional RNA detection methods such slot/dot blots or Northern blots. Therefore, a rapid and sensitive polymerase chain reaction assay of pS2 expression has been developed and used in this study.

RESULTS

In human ovarian tumors, data obtained show that pS2 transcripts and proteins are present in all mucinous cystadenomas studied and at a lower frequency in endometrioid cystadenomas. Quantitation of the CA 19-9 mucin concentration in ovarian fluids indicate that pS2 expression is always associated with high mucin concentrations, but mucin-positive and pS2-negative samples are also frequently observed.

CONCLUSIONS

These data suggest that pS2 expression is restricted to subclasses of human ovarian cystadenomas.