Transcriptional regulation of the mts1 gene in human lymphoma cells: the role of DNA-methylation

Expression profile and functional role of S100A14 in human cancer

S100A14 is one of the new members of the multi-functional S100 protein family. Expression of S100A14 is highly heterogeneous among normal human tissues, suggesting that the regulation of S100A14 expression and its function may be tissue- and context-specific. Compared to the normal counterparts, S100A14 mRNA and protein levels have been found to be deregulated in several cancer types, indicating a functional link between S100A14 and malignancies. Accordingly, S100A14 is functionally linked with a number of key signaling molecules such as p53, p21, MMP1, MMP9, MMP13, RAGE, NF-kB, JunB, actin and HER2. Of interest, S100A14 seems to have seemingly opposite functions in malignancies arising from the gastrointestional tract (tissues rich in epithelial components) compared to cancers in the other parts of the body (tissues rich in mesenchymal components). The underlying mechanism for these observations are currently unclear and may be related to the relative abundance and differences in the type of interaction partners (effector protein) in different cancer types and tissues. In addition, several studies indicate that the expression pattern of S100A14 has a potential to be clinically useful as prognostic biomarker in several cancer types. This review attempts to provide a comprehensive summary on the expression pattern and functional roles/related molecular pathways in different cancer types. Additionally, the prognostic potential of S100A14 in the management of human malignancies will be discussed.

Ca(2+)-binding protein expression in primary human thyrocytes

We recently identified several Ca(2+)-binding proteins (CaBP) from the S100 and annexin family to be regulated by TSH in FRTL-5 cells. Here, we study the regulation of S100A4, S100A6 and ANXA2 in primary human thyrocytes (PHT) derived from surrounding tissues (ST), cold benign thyroid nodules (CTN) and autonomously functioning thyroid nodules (AFTN). We investigated the expression and regulation of CaBP and the effect of their expression on Ca(2+) and TSHR signaling. We used an approach that accounts for the potential of an individual PHT culture to proliferate or to express thyroid differentiation features by assessing the expression of FOS and TPO. We found a strong correlation between the regulation of CaBP and the proliferation-associated transcription factor gene FOS. PKA and MEK1/2 were regulators of ANXA2 expression, while PI3-K and triiodothyronine were additionally involved in S100 regulation. The modulated expression of CaBP was reflected by changes in ATP-elicited Ca(2+) signaling in PHT. S100A4 increased the ratio of subsequent Ca(2+) responses and showed a Ca(2+) buffering effect, while ANXA2 affected the first Ca(2+) response to ATP. Overexpression of S100A4 led to a reduced activation of NFAT by TSH. Using S100A4 E33Q, D63N, F72Q and Y75K mutants we found that the effects of S100A4 expression on Ca(2+) signaling are mediated by protein interaction. We present evidence that TSH has the ability to fine-tune Ca(2+) signals through the regulation of CaBP expression. This represents a novel putative cross-regulating mechanism in thyrocytes that could affect thyrocyte signaling and physiology.

Hypoxia upregulates ovarian cancer invasiveness via the binding of HIF-1α to a hypoxia-induced, methylation-free hypoxia response element of S100A4 gene

Hypoxia is known to play important roles in the development and progression of tumors. We previously demonstrated that S100A4, a critical molecule for metastasis, was upregulated in ovarian cancer cells. Therefore, we examined the mechanisms of the upregulation of S100A4 expression in ovarian carcinoma cells, with particular attention paid to the effects of hypoxia. The expression levels of S100A4 were found to be correlated with the invasiveness of ovarian carcinoma cells in vitro and in vivo, and the upregulation of S100A4 expression was associated with hypomethylation of CpG sites in the first intron of S100A4 in ovarian carcinoma cell lines and tissues. The expression of S100A4 was increased under hypoxia and was associated with elevated invasiveness, which was inhibited by S100A4 small interfering RNA (siRNA). In addition, exposure to hypoxia reduced the methylation of hypoxia-response elements (HRE) of the S100A4 gene in a time-dependent fashion, in association with the increased binding of HIF-1α to a methylation-free HRE in ovarian carcinoma cells. These results indicate that hypoxia-induced hypomethylation plays an essential role in S100A4 overexpression and the epigenetic transformation of ovarian carcinoma cells into the "metastatic phenotype."

S100A4 expression in xenograft tumors of human carcinoma cell lines is induced by the tumor microenvironment

Increased expression of the invasion- and metastasis-associated protein S100A4 is found in many types of cancer, but the regulation of S100A4 expression is poorly understood. The microenvironment surrounding tumors has a significant effect on tumor progression, and in the present study, we investigated the role of the microenvironment in the expression of S100A4. Tumors of three different human carcinoma cell lines were established in the tongue or skin of mice, and S100A4 expression was assessed by quantitative RT-PCR, Western blotting, and immunohistochemical analysis in tumors and stromal tissue and in cancer cells grown in vitro. Tongue tumors of the oral squamous cell carcinoma cell line HSC-4 showed a pronounced increase in S100A4 expression during tumor growth, whereas only a minor increase was detected in skin tumors of the same cell line. The S100A4 expression correlated with the methylation status of cytosine-guanine sites in the first intron of the gene. For all cell lines, S100A4 expression in the tumor stroma was related to the presence of inflammatory cells rather than to the level of S100A4 in the tumor cells.

S100A4 mediated cell invasion and metastasis of esophageal squamous cell carcinoma via the regulation of MMP-2 and E-cadherin activity

It is well documented that S100A4 is upregulated in a large amount of invasive tumors and plays a pivotal role in tumor invasion and metastasis. However, the precise role and mechanism S100A4 exerts in the invasion and metastasis of esophageal squamous cell carcinoma (ESCC) have not been fully elucidated to date. Our data demonstrated that S100A4 was overexpressed in human ESCC tissues, especially in ESCC with poor differentiation, deep invasion and lymph node metastasis. Subsequently, the knockdown of S100A4 by RNAi in ESCC cell line (EC-1) could reduce cell invasion, metastasis and proliferation ability in vitro. Most importantly, S100A4 regulated MMP-2 positively and E-cadherin negatively in vivo and in vitro to some extent. Our results suggest that S100A4 is an important factor in the invasion, metastasis and proliferation of ESCC and may control invasion and metastasis at least in part through the regulation of MMP-2 and E-cadherin activity. S100A4 may serve as a biomarker for progression of ESCC and a potential molecular target for biotherapy of ESCC.

Epigenetic regulation of S100 protein expression

S100 proteins are small, calcium-binding proteins whose genes are localized in a cluster on human chromosome 1. Through their ability to interact with various protein partners in a calcium-dependent manner, the S100 proteins exert their influence on many vital cellular processes such as cell cycle, cytoskeleton activity and cell motility, differentiation, etc. The characteristic feature of S100 proteins is their cell-specific expression, which is frequently up- or downregulated in various pathological states, including cancer. Changes in S100 protein expression are usually characteristic for a given type of cancer and are therefore often considered as markers of a malignant state. Recent results indicate that changes in S100 protein expression may depend on the extent of DNA methylation in the S100 gene regulatory regions. The range of epigenetic changes occurring within the S100 gene cluster has not been defined. This article reviews published data on the involvement of epigenetic factors in the control of S100 protein expression in development and cancer.

Relationship of SNCG, S100A4, S100A9 and LCN2 gene expression and DNA methylation in bladder cancer

Microarray analysis of paired cultures of normal and cancerous urothelial cells revealed differences in cytokeratin and adhesion gene expression. Normal cells expressed autocrine growth factor genes more strongly whereas carcinoma cells were distinguished by concomitant expression of urothelial and epidermal differentiation markers. Expression of SNCG, S100A9 and LCN2 was also enhanced. In other cancers, overexpression of SNCG, LCN2 and S100A4 has been ascribed to DNA hypomethylation. We therefore investigated expression and methylation of SNCG, S100A4, S100A9 and LCN2 in urothelial cancer cell lines and tissues. SNCG and S100A4 were overexpressed in some cancer tissues and cell lines, but downregulated in others, whereas LCN2 and S100A9 were upregulated in few cancer cell lines, but regularly in tissues. Normal and cancerous urothelial cells expressing SNCG lacked promoter methylation. SNCG downregulation was associated with hypermethylation and could be reversed by the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine. S100A4 methylation at regulatory intronic sites and in the promoter region was lowest in leukocytes and fibroblasts, and denser in urothelial cells. Gene expression responded to 5-aza-2'-deoxycytidine. LCN2 promoter methylation was variable and even less consistently related to expression. The S100A9 promoter was partially methylated in nonexpressing cells, but 5-aza-2'-deoxycytidine had no effect. Our data indicate that SNCG methylation is cell type-specific and the gene is hypermethylated in some urothelial cancers. S100A4, S100A9 and LCN2 are genes with moderate CpG-density that show a less stringent relationship between DNA methylation and gene expression. Therefore, changes in methylation of these genes in cancer should be interpreted cautiously.

Expression profile of the S100 gene family members in oral squamous cell carcinomas

BACKGROUND

Several of the S100 gene members have been reported to be differentially expressed in many human pathological conditions, in particular, the malignancies. Identification and quantification of the differentially expressed S100 gene members in oral squamous cell carcinoma (OSCC) might facilitate their use as potential diagnostic and/or prognostic markers or targets for therapy.

METHODS

we examined the expression profile of 16 members of the S100 gene family at the mRNA level by semiquantitative reverse transcription-polymerase chain reaction (sRT-PCR) in 27 cases of OSCCs/their pair-wised normal controls obtained from Sudanese patients, and confirmed the sRT-PCR results by performing quantitative real time-polymerase chain reaction (qRT-PCR) for 6 of the 16 genes examined.

RESULTS

With sRT-PCR, 4 (25%; S100A4, S100A6, S100A8, S100A14) out of the 16 S100 gene members examined were found to be significantly down-regulated (P < 0.05) in the tumors compared to the normal controls. None of the S100 gene members examined were found to be significantly up-regulated in the tumors. qRT-PCR results confirmed the significant down-regulation of the S100A4, S100A6, and S100A14 genes in the tumors examined.

CONCLUSION

S100 gene family members might play an important role in the pathogenesis of the OSCCs examined. Findings of the present work warrant in-depth studies of the S100 gene family members, in particular, the S100A4, S100A6, S100A8, and S100A14 to further understand their possible role(s) in OSCC tumorigenesis.

Hypomethylation-induced expression of S100A4 in endometrial carcinoma

Expression of various S100 genes has been associated with clinically aggressive subtypes in a variety of different cancers. We hypothesized that S100A4 would be overexpressed in endometrial carcinoma compared to benign endometrium. Quantitative real-time RT-PCR (qRT-PCR) was used to quantify the mRNA level of S100A4 in benign endometrium (n=19), endometrioid adenocarcinoma (n=87), and non-endometrioid tumors (n=21). Immunohistochemistry was used to verify the results of qRT-PCR and to assess protein localization. Possible mechanisms of S100A4 gene regulation were also examined. S100A4 was overexpressed in the grade 3 endometrioid tumors, uterine papillary serous carcinoma, and uterine malignant mixed müllerian tumor. Expression in grade 1 and grade 2 endometrioid tumors was comparable to that of normal endometrium, which was quite low. Expression was significantly higher in stage III and IV tumors compared with stage I. By immunohistochemistry, S100A4 was expressed in the tumor cell cytoplasm of poorly differentiated tumors, but was not detected in normal endometrial glandular epithelium. In benign endometrium, S100A4 expression was confined to stromal cells. S100A4 was not regulated by estrogen or progesterone, and its expression in tumors was not significantly correlated to estrogen receptor or progesterone receptor content. However, methylation of the S100A4 gene was detected in benign endometrium and grade 1 tumors with low S100A4 expression. In contrast, grade 3 endometrioid tumors with high S100A4 mRNA and protein expression showed no methylation of the gene. These methylation results were verified in endometrial cancer cell lines with differential baseline levels of S100A4 protein. These results suggest that hypomethylation is an important mechanism of regulating the expression of the S100A4 gene. These results support the emerging concept that hypomethylation may play a role in the upregulation of genes during later stages of tumorigenesis.

DNA methylation and immunohistochemical analysis of the S100A4 calcium binding protein in human prostate cancer

BACKGROUND

The role of DNA methylation in the transcriptional regulation of S100A4 is unknown in human prostate cancer.

METHODS

Critical CpG sites within intron 1 of S100A4 were sequenced in DNA obtained from prostatic adenocarcinoma, non-malignant epithelium, and prostate cancer cell lines. S100A4 protein expression was assessed by immunohistochemistry and Western blotting.

RESULTS

Methylation was seen in all cases of cancer, non-malignant epithelium, and in prostate cancer cell lines, but was absent in all cases of blood DNA. S100A4 immunoexpression was absent in all cases of malignant and non-malignant epithelium, while strong-moderate expression was seen in the stroma and lymphocytes. Western blotting showed absent S100A4 expression in LNCaP and Du145 cells and low levels in PC-3 cells.

CONCLUSIONS

S100A4 protein is not expressed in benign or malignant prostatic epithelium nor in LNCaP and Du145 cells. The mechanism underlying absent S100A4 expression in prostatic epithelium and cell lines may involve methylation.

Focal S100A4 Protein Expression Is an Independent Predictor of Development of Metastatic Disease in Cystectomized Bladder Cancer Patients

OBJECTIVE

The prognosis of patients with apparently localized, operable, muscle-invasive bladder cancer depends to a large extent on the presence or absence of subclinical, microscopic distant metastases at the time of surgery. Expression of the S100A4 protein has been shown to correlate with the risk of metastasis in both animal tumour-model systems and clinical investigations in other tumour types. The purpose of the present study was to investigate the prognostic potential of S100A4 protein expression for predicting distant metastatic relapse in muscle-invasive bladder cancer.

METHODS

We analyzed 108 consecutive patients, treated for transitional cell bladder cancer with preoperative radiotherapy and cystectomy. Pretherapeutic biopsies of the bladder tumours were investigated for immunohistochemical expression of S100A4 protein and results, along with clinical and histopathological data, compared with the pattern of relapses over a 10+ yr follow-up period.

RESULTS

Focal S100A4 protein expression emerged as the only significant independent predictor of distant metastatic relapse and distant metastasis-free survival in multivariate analysis.

CONCLUSION

There is a potential role for this marker in denoting patients with high or low risk of distant relapse independent of clinical stage and grade.

Frequent inactivation of CDKN2A and rare mutation of TP53 in PCNSL

Twenty primary central nervous system lymphomas (PCNSL) from immunocompetent patients (nineteen B-cell lymphomas and one T-cell lymphoma) were investigated for genetic alterations and/or expression of the genes BCL2, CCND1, CDK4, CDKN1A, CDKN2A, MDM2, MYC, RB1, REL, and TP53. The gene found to be altered most frequently was CDKN2A. Eight tumors (40%) showed homozygous and two tumors (10%) hemizygous CDKN2A deletions. Furthermore, methylation analysis of six PCNSL without homozygous CDKN2A loss revealed methylation of the CpG island within exon 1 of CDKN2A in three instances. Reverse transcription PCR analysis of CDKN2A mRNA expression was performed for 11 tumors and showed either no or weak signals. Similarly, immunocytochemistry for the CDKN2A gene product (p16) remained either completely negative or showed expression restricted to single tumor cells. None of the PCNSL showed amplification of CDK4. Similarly, investigation of CCND1 revealed no amplification, rearrangement or overexpression. The retinoblastoma protein was strongly expressed in all tumors. Only one PCNSL showed a mutation of the TP53 gene, i.e., a missense mutation at codon 248 (CGG to TGG:Arg to Trp). No evidence of BCL2 gene rearrangement was found in 11 tumors investigated. The bcl-2 protein, however, was strongly expressed in most tumors. None of the 20 PCNSL demonstrated gene amplification of MDM2, MYC or REL. In summary, inactivation of CDKN2A by either homozygous deletion or DNA methylation represents an important molecular mechanism in PCNSL. Mutation of the TP53 gene and alterations of the other genes investigated appear to be of minor significance in these tumors.

DNA demethylation and carcinogenesis

DNA methylation plays an important role in the establishment and maintenance of the program of gene expression. Tumor cells are characterized by a paradoxical alteration of DNA methylation pattern: global DNA demethylation and local hypermethylation of certain genes. Hypermethylation and inactivation of tumor suppressor genes are well documented in tumors. The role of global genome demethylation in carcinogenesis is less studied. New data provide evidence for independence of DNA hypo- and hypermethylation processes in tumor cells. These processes alter expression of genes that have different functions in malignant transformation. Recent studies have demonstrated that global decrease in the level of DNA methylation is related to hypomethylation of repeated sequences, increase in genetic instability, hypomethylation and activation of certain genes that favor tumor growth, and increase in their metastatic and invasive potential. The recent data on the role of DNA demethylation in carcinogenesis are discussed in this review. The understanding of relationships between hypo- and hypermethylation in tumor cells is extremely important due to reversibility of DNA methylation and attempts to utilize for anti-tumor therapy the drugs that modify DNA methylation pattern.

S100A4 (p9Ka) protein in colon carcinoma and liver metastases: association with carcinoma cells and T-lymphocytes

The presence of the EF-hand-calcium-binding protein S100A4 in the carcinoma cells of the primary tumour is associated with a shorter survival time of a group of breast cancer patients. In colon cancer, primary tumours as well as metastases to the liver can be studied. Here we show, using quantitative PCR applied to RNA from 24 normal colon, four liver tissues, 24 colon carcinoma specimens, and 24 livers containing colonic carcinoma metastases, that the level of S100A4 mRNA was significantly higher in the carcinomas compared to normal specimens (Mann-Whitney U-test, P=0.05), and in liver metastases compared to carcinoma specimens (P=0.039). The latter comparison included seven liver metastases and their matched primary carcinomas (P<0.001) from the same patient. In situ hybridization and immunocytochemistry techniques have localized S100A4 to both carcinoma cells and lymphocytes in the malignant specimens. The percentage of specimens stained for S100A4 in the epithelial cells is significantly higher for those isolated from carcinomas and metastases than from the corresponding normal tissue, and from metastases than from corresponding carcinoma (Fisher Exact text, P<0.0016, P=0.04, respectively). In most specimens, S100A4 is present in clusters of T lymphocytes and this distribution is also found in the lymphoid, uninflamed appendix.

Overexpression of S100A4 in pancreatic ductal adenocarcinomas is associated with poor differentiation and DNA hypomethylation

Using the National Center for Biotechnology Information Serial Analysis of Gene Expression database, we found that S100A4, a calcium-binding protein previously implicated in metastasis, was expressed in five of seven pancreatic carcinoma libraries but not in the two normal pancreatic duct libraries. We confirmed the overexpression of S100A4 using reverse transcriptase-polymerase chain reaction, which demonstrated that 18 of 19 (95%) pancreatic carcinoma cell lines expressed S100A4. Using immunohistochemistry, we found that 57 of 61 invasive pancreatic carcinomas (93%), 3 of 18 high-grade pancreatic intraepithelial neoplasia lesions (17%), and 0 of the 69 low-grade pancreatic intraepithelial neoplasia lesions expressed S100A4 protein, whereas normal pancreatic tissue and tissue affected by chronic pancreatitis did not label. Expression of S100A4 was associated with poor differentiation of the pancreatic adenocarcinomas (P = 0.001). We found that three CpG sites in the first intron of the S100A4 gene were approximately 90% methylated in microdissected normal pancreatic duct cells using bisulfite-modified sequencing and in two cell lines and three primary pancreatic carcinomas with a reduced or absent expression of S100A4. In contrast, these CpGs were 100% hypomethylated in 11 of 12 pancreatic cancer cell lines by methylation-specific polymerase chain reaction. The association between the expression of S100A4 and hypomethylation of the first intron of S100A4 was statistically significant (P = 0.002). These data suggest that the majority of pancreatic carcinomas undergo selection for hypomethylation and overexpression of S100A4. Because most pancreatic carcinomas express S100A4, it may be a useful target for early detection strategies.

Characterization of Sp1, AP-1, CBF and KRC binding sites and minisatellite DNA as functional elements of the metastasis-associated mts1/S100A4 gene intronic enhancer

The mts1/S100A4 gene encodes a small acidic calcium-binding protein that is expressed in a cell-specific manner in development, tumorigenesis and certain tissues of adult mice. A composite enhancer that is active in murine mammary adenocarcinoma cells was previously identified in the first intron of the mts1/S100A4 gene. Here we present a detailed analysis of the structure and function of this enhancer in the Mts1/S100A4-expressing CSML100 and non-expressing CSML0 mouse adenocarcinoma cell lines. In CSML100 cells the enhancer activity is composed of at least six cis-elements interacting with Sp1 and AP-1 family members and CBF/AML/PEBP2 and KRC transcription factors. In addition, a minisatellite-like DNA sequence significantly contributes to the enhancer activity via interaction with abundant proteins, which likely have been described previously under the name minisatellite-binding proteins. Extensive mutational analysis of the mts1/S100A4 enhancer revealed a cooperative function of KRC and the factors binding minisatellite DNA. This is the first example of an enhancer where two nuclear factors earlier implicated in different recombination processes cooperate to activate transcription. In Mts1/S100A4-negative CSML0 cells the strength of the enhancer was 7- to 12.5-fold lower compared to that in CSML100 cells, when referred to the activities of three viral promoters. In CSML0 cells the enhancer could be activated by exogenous AP-1 and CBF transcription factors.

Increased expression of deoxyribonucleic acid methyltransferase gene in human astrocytic tumors

The relationship between the grade of astrocytic tumor and the expression of deoxyribonucleic acid methyltransferase (DNA-MTase) gene was examined. The levels of DNA-MTase messenger ribonucleic acid (mRNA) were measured by semiquantitative reverse transcriptase-polymerase chain reaction in surgical specimens from 12 astrocytic tumors (4 astrocytomas, 6 anaplastic astrocytomas, and 2 glioblastomas) and two normal brain tissues, and in four glioma cell lines. Compared to normal brain tissues, the levels of DNA-MTase mRNA were increased by 16- to 55-fold in low grade astrocytomas, and significantly increased by 200- to 4500-fold in high grade astrocytomas (anaplastic astrocytomas and glioblastomas) and more than 4500-fold in glioma cell lines. In situ hybridization with paraffin-embedded surgical specimens of human astrocytic tumors showed DNA-MTase mRNA was abundantly expressed in high grade astrocytomas. The detection of increased DNA-MTase expression in astrocytic tumor indicates involvement in the tumorigenesis and suggests that blocking of this change with specific inhibitors may offer new therapeutic strategies for malignant astrocytic tumors.

DNA methylation and cancer

The methylation of DNA is an epigenetic modification that can play an important role in the control of gene expression in mammalian cells. The enzyme involved in this process is DNA methyltransferase, which catalyzes the transfer of a methyl group from S-adenosyl-methionine to cytosine residues to form 5-methylcytosine, a modified base that is found mostly at CpG sites in the genome. The presence of methylated CpG islands in the promoter region of genes can suppress their expression. This process may be due to the presence of 5-methylcytosine that apparently interferes with the binding of transcription factors or other DNA-binding proteins to block transcription. In different types of tumors, aberrant or accidental methylation of CpG islands in the promoter region has been observed for many cancer-related genes resulting in the silencing of their expression. How this aberrant hypermethylation takes place is not known. The genes involved include tumor suppressor genes, genes that suppress metastasis and angiogenesis, and genes that repair DNA suggesting that epigenetics plays an important role in tumorigenesis. The potent and specific inhibitor of DNA methylation, 5-aza-2'-deoxycytidine (5-AZA-CdR) has been demonstrated to reactivate the expression most of these "malignancy" suppressor genes in human tumor cell lines. These genes may be interesting targets for chemotherapy with inhibitors of DNA methylation in patients with cancer and this may help clarify the importance of this epigenetic mechanism in tumorigenesis.

Interaction in vivo and in vitro of the metastasis-inducing S100 protein, S100A4 (p9Ka) with S100A1

The calcium-binding protein S100A4 (p9Ka) has been shown to cause a metastatic phenotype in rodent mammary tumor cells and in transgenic mouse model systems. mRNA for S100A4 (p9Ka) is present at a generally higher level in breast carcinoma than in benign breast tumor specimens, and the presence of immunocytochemically detected S100A4 correlates strongly with a poor prognosis for breast cancer patients. Recombinant S100A4 (p9Ka) has been reported to interact in vitro with cytoskeletal components and to form oligomers, particularly homodimers in vitro. Using the yeast two-hybrid system, a strong interaction between S100A4 (p9Ka) and another S100 protein, S100A1, was detected. Site-directed mutagenesis of conserved amino acid residues involved in the dimerization of S100 proteins abolished the interactions. The interaction between S100A4 and S100A1 was also observed in vitro using affinity column chromatography and gel overlay techniques. Both S100A1 and S100A4 can occur in the same cultured mammary cells, suggesting that in cells containing both proteins, S100A1 might modulate the metastasis-inducing capability of S100A4.

The kappaB and V(D)J recombination signal sequence binding protein KRC regulates transcription of the mouse metastasis-associated gene S100A4/mts1

A kappaB-like sequence, Sb, is integral to the composite enhancer located in the first intron of the metastasis-associated gene, S100A4/mts1. Oligonucleotides containing this sequence form three specific complexes with nuclear proteins prepared from S100A4/mts1-expressing CSML100 adenocarcinoma cells. Protein studies show the Sb-interacting complexes include NF-kappaB/Rel proteins, p50.p50 and p50.p65 dimers. Additionally, the Sb sequence was bound by an unrelated approximately 200-kDa protein, p200. Site-directed mutagenesis in conjunction with transient transfections indicate that p200, but not the NF-kappaB/Rel proteins, transactivates S100A4/mts1. To identify candidate genes for p200, double-stranded DNA probes containing multiple copies of Sb were used to screen a randomly primed lambdagt11 cDNA expression library made from CSML100 poly(A)(+) RNA. Two clones corresponding to the DNA-binding proteins KRC and Alf1 were identified. KRC encodes a large zinc finger protein that binds to the kappaB motif and to the signal sequences of V(D)J recombination. In vitro DNA binding assays using bacterially expressed KRC fusion proteins, demonstrate specific binding of KRC to the Sb sequence. In addition, introduction of KRC expression vectors into mammalian cells induces expression of S100A4/mts1 and reporter genes driven by S100A4/mts1 gene regulatory sequences. These data indicate that KRC positively regulates transcription of S100A4/mts1.

P15INK4b gene methylation and myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are clonal disorders, which frequently undergo leukemic transformation. It was recently shown that the promoter of the p15INK4b but not the p16INK4a gene is frequently and selectively hypermethylated in MDS. The p15INK4b gene is a cyclin dependent kinase inhibitor gene, which is actively transcribed after TGFbeta exposure. Methylation of the p15INK4b gene is significantly correlated with blastic bone marrow involvement, and sequential analyses have shown that methylation increases with disease evolution toward AML. These data strongly suggest that p15INK4b gene methylation is a mechanism allowing leukemic cells to escape to inhibitory signals from the bone marrow environment, however the exact role of p15INK4b gene methylation in disruption of the signal mediated by TGFbeta remains to be investigated.

Differential reactivity of the rat S100A4(p9Ka) gene to sodium bisulfite is associated with differential levels of the S100A4 (p9Ka) mRNA in rat mammary epithelial cells

Elevated intracellular levels of S100A4, an S100-related calcium-binding protein, induce metastatic capability in benign mammary tumor-derived epithelial cells and in transgenic mice bearing oncogene-induced benign mammary tumors. The S100A4(p9Ka) gene in rat mammary epithelial cells expressing low levels of S100A4 yields a reduced number of fragments upon digestion with the methylation-sensitive restriction enzyme, HpaII, compared with the gene from high S100A4-expressing cells. Genomic sequencing of two potential regulatory elements in the S100A4 gene, an intronic enhancer and TATA box region, revealed that in low S100A4-expressing cells, most cytosine bases exhibited high levels of resistance to conversion to thymine by sodium bisulfite. In derivative cell lines, which express high levels of S100A4, only a small number of cytosine bases were resistant to treatment with sodium bisulfite. In contrast, cytosine bases in the DNA surrounding an upstream regulatory region, which binds inhibitory GC factor in the low-expressing cell lines, are sensitive to conversion to thymine by sodium bisulfite in both low- and high-expressing cell lines. The results suggest that the rat S100A4 gene is maintained in a different state in the low-expressing cell lines and that this state might be a consequence of the pattern of methylation in this regulated gene that does not contain a CpG island.

Identification of a novel cis-acting element for fibroblast-specific transcription of the FSP1 gene

The FSP1 gene encodes a filament-binding S100 protein with paired EF hands that is specifically expressed in fibroblasts. This led us to look for cis-acting elements in the FSP1 promoter that might engage nuclear transcription factors unique to fibroblasts. The first exon of FSP1 is noncoding, therefore, a series of luciferase reporter minigenes were created containing varying lengths of 5'-flanking sequence, the first intron, and the noncoding region of the second exon. A position and promoter-dependent proximal element between -187 and -88 bp was shown to be active in fibroblasts but not in epithelium. Sequence in the first intron from +777 to +964 had an enhancing effect that was not cell type specific. Hsv TK reporter constructs driven by this promoter/intron cassette in transgenic mice were coexpressed appropriately with FSP1 in tissue fibroblasts. Gel mobility shift competitor assays identified a novel domain, FTS-1 (fibroblast transcription site-1; TTGAT from -177 to -173 bp), that specifically interacts with nuclear extracts from fibroblasts. The necessity of this binding site was confirmed by site-specific mutagenesis. Database searches also turned up putative FTS-1 sites in the early promoter regions of other fibroblast expressed proteins, including the alpha1 and alpha2(I), and alpha1(III) collagens and the alphaSM-actin gene. We hypothesize that the selective engagement of FTS-1 elements may contribute to the mesenchymal phenotype of fibroblasts and perhaps other dedifferentiated cells.

A minisatellite "core" element constitutes a novel, chromatin-specific activator of mts1 gene transcription

Expression of the mts1 gene is often associated with malignant transformation of tumor cells. Transcription of the gene is controlled by a number of positive and negative regulatory elements, all of them being localized in the first intron (+38 to +1215) of the mts1 gene. Through analysis of the distribution of DNase I hypersensitive sites in the first intron of the gene we revealed a structurally conserved region that consisted of a non-canonical NFkB binding site and a minisatellite "core" element. Deletion of the minisatellite core DNA in the context of the first intron had no effect on its regulatory capacity when assayed in transient transfections, while a fivefold decrease was observed in a pool of stably transfected cells. The minisatellite core sequence CTGGGCAGGCAG is involved in DNA-protein interactions in vivo, and is similar to a binding site for the previously identified minisatellite DNA sequence binding protein (Msbp-1). The core DNA interacted in vitro with a protein that had an apparent molecular mass of 40 kDa. These data indicate that the minisatellite DNA represents the novel, chromatin-specific element in the mts1 complex enhancer.

Hypomethylation of the metastasis-associated S100A4 gene correlates with gene activation in human colon adenocarcinoma cell lines

The DNA methylation status of the metastasis-associated S100A4 gene in S100A4-positive and -negative human colon adenocarcinoma cell lines was examined. Northern and Western blot analyses revealed that HT-29, SW480, SW620, WiDr and Colo201 cells expressed S100A4, whereas SW837, LoVo and DLD-1 cells expressed little S100A4. Using CpG methylation-sensitive and -insensitive restriction enzymes and PCR-based methylation assay, it was found that the S100A4 gene in HT-29, SW480, SW620, WiDr and Colo201 cells, but not in SW837, LoVo and DLD-1 cells, was hypomethylated and that the hypomethylation of the second intron was correlated well with the expression of S100A4. 5-Aza-2'-deoxycytidine, an inhibitor of the eukaryotic DNA methyltransferase, induced the expression of the S100A4 gene in SW837, LoVo and DLD-1 cells, while it showed no effect on the expression of the gene in WiDr cells. These results indicate that hypomethylation of the S100A4 gene results in the expression of the gene in colon adenocarcinoma cells.

Repression of the candidate tumor suppressor gene S100A2 in breast cancer is mediated by site-specific hypermethylation

The calcium-binding protein S100A2 is expressed in normal breast tissue but downregulated during breast cancer progression. Hence it was previously identified as a candidate tumor suppressor gene. In this report, we investigated the molecular basis of S100A2 gene expression in normal and tumorigenic human breast epithelial cells. We cloned the gene coding for S100A2 including its 5' flanking region. To locate positively or negatively acting elements responsible for transcriptional regulation, promoter deletion studies were performed. Results from these experiments demonstrate that an enhancer element is located 1.2 kb upstream of the transcription start site. This element contains two AP1-like binding sites suggesting that transcriptional activation of S100A2 might be mediated by immediate early genes. Interestingly, the enhancer stimulates transcription in both normal and tumorigenic cells, indicating that repression of endogenous S100A2 transcription in tumorigenic cells might lie at an epigenetic level. Indeed, the proximal promoter region was found, by genomic sequencing, to be unmethylated in normal but hypermethylated in tumorigenic cells. Hypermethylation of the promoter at the same CpG sites was also found in a breast cancer biopsy. In addition, site specific in vitro methylation led to reduced expression of the S100A2 gene in normal cells. These experiments provide strong evidence that S100A2 repression in tumor cells is mediated by site-specific methylation. Since transcription of a number of known tumor suppressor genes is also repressed by methylation, our observation is consistent with the suggestion that S100A2 might have a tumor suppressor function.

CpG methylation inactivates the transcriptional activity of the promoter of the human p53 tumor suppressor gene

Alterations of the methylation patterns of DNA are common in cancer cells and could conceivably comprise a subset of causal events in the carcinogenesis process. Although it has previously been shown that methylation of CpG islands in the 5'-control regions of tumor suppressor genes such as p16, Von Hippel-Lindau (VHL) syndrome gene, and the retinoblastoma (RB) gene can suppress expression and function of these gene products, the elements that control the expression of the p53 gene have not been examined in detail. In this study we examined the effect of CpG methylation in a region of the p53 promoter containing major transcription start sites. A region of the p53 promoter (from -199 to +142) containing 15 CpG dinucleotides was placed in a pCAT reporter plasmid and reporter activity was assessed in host CV-1 cells. We show for the first time that transcriptional activation of the p53 tumor suppressor gene, as assessed by a reporter plasmid construct, can be down-regulated by cytosine methylation in the basal promoter region. We believe these data suggest a role for methylation of CpG sequences in the regulation of transcription of p53. This implies that the tumor suppressor gene p53 could, therefore, contribute to carcinogenesis by inactivation via methylation of a key element in cell cycle control.

Influence of oxygen radical injury on DNA methylation

One of the most prevalent products of oxygen radical injury in DNA is 8-hydroxyguanosine. Cells must be able to withstand damage by oxygen radicals and possess specific repair mechanisms that correct this oxidative lesion. However, when these defenses are oversaturated, such as under conditions of high oxidative stress, or when repair is inefficient, the miscoding potential of this lesion can result in mutations in the mammalian genome. In addition to causing genetic changes, active oxygen species can lead to epigenetic alterations in DNA methylation, without changing the DNA base sequence. Such changes in DNA methylation patterns can strongly affect the regulation of expression of many genes. Although DNA methylation patterns have been found to be altered during carcinogenesis, little is known about the mechanism(s) that produce this loss of epigenetic controls of gene expression in tumors. Replacement of guanine with the oxygen radical adduct 8-hydroxyguanine profoundly alters methylation of adjacent cytosines, suggesting a role for oxidative injury in the formation of aberrant DNA methylation patterns during carcinogenesis. In this paper, we review both the genetic and epigenetic mechanisms of oxidative DNA damage and its association with the carcinogenic process, with special emphasis on the influence of free radical injury on DNA methylation.

A kappaB-related binding site is an integral part of the mts1 gene composite enhancer element located in the first intron of the gene

The transcription of the mts1 gene correlates with the metastatic potential of mouse adenocarcinomas. Here we describe strong enhancer whose location coincides with the DNase I hypersensitivity area in the first intron of the mts1 gene. The investigation of the transcriptional activity of a series of plasmids bearing deletions in the first intron sequences revealed that the observed enhancer has a composite structure. The enhancer activity is partially formed by the kappaB-related element: GGGGTTTTTCCAC. This sequence element was able to form several sequence-specific complexes with nuclear proteins extracted from both Mts1-expressing CSML100 and Mts1-non-expressing CSML0 adenocarcinoma cells. Two of these complexes were identified as NF-kappaB/Rel-specific p50.p50 homo- and p50.p65 heterodimers. The third complex was formed by the 200-kDa protein. Even though the synthetic kappaB-responsible promoter was active in mouse adenocarcinoma cells, a mutation preventing NF-kappaB binding had no effect on the mts1 natural enhancer activity. On the contrary, the mutation in the kappaB-related element, which abolished the binding of the 200-kDa protein, led to the functional inactivation of this site in the mts1 first intron. The mts1 kappaB-like element activated transcription from its own mts1 gene promoter, as well as from the heterologous promoter in both CSML0 and CSML100 cells. However, in vivo occupancy of this site was observed only in Mts1-expressing CSML100 cells, suggesting the involvement of the described element in positive control of mts1 transcription.

The role of DNA methylation in cancer genetic and epigenetics

The past few years have seen a wider acceptance of a role for DNA methylation in cancer. This can be attributed to three developments. First, the documentation of the over-representation of mutations at CpG dinucleotides has convincingly implicated DNA methylation in the generation of oncogenic point mutations. The second important advance has been the demonstration of epigenetic silencing of tumor suppressor genes by DNA methylation. The third development has been the utilization of experimental methods to manipulate DNA methylation levels. These studies demonstrate that DNA methylation changes in cancer cells are not mere by-products of malignant transformation, but can play an instrumental role in the cancer process. It seems clear that DNA methylation plays a variety of roles in different cancer types and probably at different stages of oncogenesis. DNA methylation is intricately involved in a wide diversity of cellular processes. Likewise, it appears to exert its influence on the cancer process through a diverse array of mechanisms. It is our task not only to identify these mechanisms, but to determine their relative importance for each stage and type of cancer. Our hope then will be to translate that knowledge into clinical applications.

Activation of mts1 transcription by insertion of a retrovirus-like IAP element

The mechanism of activation of mestatasis-associated mts1 gene transcription in the mouse myelomonocytic leukaemia WEHI-3 cell line is described. Northern blot analysis showed that WEHi-3 cells expressed two types of mts1-specific mRNA: standard (550 nt) and additional (about 800 nt). The steady-state expression level of the 800-nt RNA was isolated and sequence analysis showed that it contained a 357-bp fragment represented by long terminal repeat (LTR) sequences and a 5' untranslated region of the gag gene of the intracisternal A-particle (IAP) element. The chimeric IAP::mts1 800-nt mRNA is initiated from the 5' LTR promoter. The rearranged and normal loci of mts1 were cloned and partially sequenced. The results suggested that the insertion of the IAP sequences into the first intron of mts1 brings the gene under control of the strong IAP promoter. The additional chimeric 800-nt IAP::mts1 RNA transcript was the result of a splicing event linking IAP sequences with the coding part of mts1. We suggest that the chimeric IAP::mts1 RNA is capable of producing a functional Mts1 protein.