Immunohistochemical demonstration of metallothionein in normal human breast tissue and benign and malignant breast lesions

Meta-analysis of gene expression profiling reveals novel basal gene signatures in MCF-10A cells transformed with cadmium

Cadmium (Cd2+) is an environmental toxicant and a human carcinogen. Several studies show an association of Cd2+ exposure to the development of breast cancer. Previously, we have transformed the immortalized non-tumorigenic cell line MCF-10A with Cd2+ and have demonstrated that the transformed cells have anchorage independent growth. In a separate study, we showed that transformation of the immortalized urothelial cells with the environmental carcinogen arsenite (As3+) results in an increase in expression of genes associated with the basal subtype of bladder cancer. In this study, we determined if transformation of the MCF-10A cells with Cd2+ would have a similar effect on the expression of basal genes. The results of our study indicate that there is a decrease in expression of genes associated with keratinization and cornification and this gene signature includes the genes associated with the basal subtype of breast cancer. An analysis of human breast cancer databases indicates an increased expression of this gene signature is associated with a positive correlation to patient survival whereas a reduced expression/absence of this gene signature is associated with poor patient survival. Thus, our study suggests that transformation of the MCF-10A cells with Cd2+ produces a decreased basal gene expression profile that correlates to patient outcome.

The unique C- and N-terminal sequences of Metallothionein isoform 3 mediate growth inhibition and Vectorial active transport in MCF-7 cells

Background

The 3rd isoform of the metallothionein (MT3) gene family has been shown to be overexpressed in most ductal breast cancers. A previous study has shown that the stable transfection of MCF-7 cells with the MT3 gene inhibits cell growth. The goal of the present study was to determine the role of the unique C-terminal and N-terminal sequences of MT3 on phenotypic properties and gene expression profiles of MCF-7 cells.

Methods

MCF-7 cells were transfected with various metallothionein gene constructs which contain the insertion or the removal of the unique MT3 C- and N-terminal domains. Global gene expression analysis was performed on the MCF-7 cells containing the various constructs and the expression of the unique C- and N- terminal domains of MT3 was correlated to phenotypic properties of the cells.

Results

The results of the present study demonstrate that the C-terminal sequence of MT3, in the absence of the N-terminal sequence, induces dome formation in MCF-7 cells, which in cell cultures is the phenotypic manifestation of a cell’s ability to perform vectorial active transport. Global gene expression analysis demonstrated that the increased expression of the GAGE gene family correlated with dome formation. Expression of the C-terminal domain induced GAGE gene expression, whereas the N-terminal domain inhibited GAGE gene expression and that the effect of the N-terminal domain inhibition was dominant over the C-terminal domain of MT3. Transfection with the metallothionein 1E gene increased the expression of GAGE genes. In addition, both the C- and the N-terminal sequences of the MT3 gene had growth inhibitory properties, which correlated to an increased expression of the interferon alpha-inducible protein 6.

Conclusions

Our study shows that the C-terminal domain of MT3 confers dome formation in MCF-7 cells and the presence of this domain induces expression of the GAGE family of genes. The differential effects of MT3 and metallothionein 1E on the expression of GAGE genes suggests unique roles of these genes in the development and progression of breast cancer. The finding that interferon alpha-inducible protein 6 expression is associated with the ability of MT3 to inhibit growth needs further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-017-3355-9) contains supplementary material, which is available to authorized users.

Metallothionein - immunohistochemical cancer biomarker: a meta-analysis

Metallothionein (MT) has been extensively investigated as a molecular marker of various types of cancer. In spite of the fact that numerous reviews have been published in this field, no meta-analytical approach has been performed. Therefore, results of to-date immunohistochemistry-based studies were summarized using meta-analysis in this review. Web of science, PubMed, Embase and CENTRAL databases were searched (up to April 30, 2013) and the eligibility of individual studies and heterogeneity among the studies was assessed. Random and fixed effects model meta-analysis was employed depending on the heterogeneity, and publication bias was evaluated using funnel plots and Egger's tests. A total of 77 studies were included with 8,015 tissue samples (4,631 cases and 3,384 controls). A significantly positive association between MT staining and tumors (vs. healthy tissues) was observed in head and neck (odds ratio, OR 9.95; 95% CI 5.82-17.03) and ovarian tumors (OR 7.83; 1.09-56.29), and a negative association was ascertained in liver tumors (OR 0.10; 0.03-0.30). No significant associations were identified in breast, colorectal, prostate, thyroid, stomach, bladder, kidney, gallbladder, and uterine cancers and in melanoma. While no associations were identified between MT and tumor staging, a positive association was identified with the tumor grade (OR 1.58; 1.08-2.30). In particular, strong associations were observed in breast, ovarian, uterine and prostate cancers. Borderline significant association of metastatic status and MT staining were determined (OR 1.59; 1.03-2.46), particularly in esophageal cancer. Additionally, a significant association between the patient prognosis and MT staining was also demonstrated (hazard ratio 2.04; 1.47-2.81). However, a high degree of inconsistence was observed in several tumor types, including colorectal, kidney and prostate cancer. Despite the ambiguity in some tumor types, conclusive results are provided in the tumors of head and neck, ovary and liver and in relation to the tumor grade and patient survival.

Cellular mechanisms of zinc dysregulation: a perspective on zinc homeostasis as an etiological factor in the development and progression of breast cancer

Worldwide, breast cancer is the most commonly diagnosed cancer among women and is the leading cause of female cancer deaths. Zinc (Zn) functions as an antioxidant and plays a role in maintaining genomic stability. Zn deficiency results in oxidative DNA damage and increased cancer risk. Studies suggest an inverse association between dietary and plasma Zn levels and the risk for developing breast cancer. In contrast, breast tumor biopsies display significantly higher Zn levels compared with normal tissue. Zn accumulation in tumor tissue also correlates with increased levels of Zn importing proteins. Further, aberrant expression of Zn transporters in tumors correlates with malignancy, suggesting that altered metal homeostasis in the breast could contribute to malignant transformation and the severity of cancer. However, studies have yet to link dysregulated Zn transport and abnormal Zn-dependent functions in breast cancer development. Herein, we summarize studies that address the multi-modal role of Zn dyshomeostasis in breast cancer with respect to the role of Zn in modulating oxidative stress, DNA damage response/repair pathways and cell proliferation/apoptosis, and the relationship to aberrant regulation of Zn transporters. We also compare Zn dysregulation in breast tissue to that of prostate, pancreatic and ovarian cancer where possible.

Over-expression of metallothionein predicts chemoresistance in breast cancer

Metallothionein (MT) plays a role in fundamental cellular processes such as proliferation, apoptosis and differentiation. We examined MT expression in women with invasive breast ductal carcinoma who underwent mastectomy/lumpectomy without neo-adjuvant treatment. We showed that MT was over-expressed in 87.9% of breast cancer tissues examined, with the mean percentage of positive cells at 30%. There were two patterns of MT expression: predominantly cytoplasmic in 75.9% and nuclear in 24.1% of MT-positive cases. Higher MT scores were associated with poorer histological grade (p = 0.009) but were independent of age, tumour size and oestrogen receptor status. For patients who were treated with adjuvant chemotherapy (cyclophosphamide/methotrexate/5 fluorouracil- or doxorubicin-based regimes), those with high MT expression had a significantly lower recurrence-free survival (p = 0.048), suggesting a role of MT in predicting disease recurrence. Down-regulation of MT in MCF-7 cells by silencing the MT-2A gene (the most abundantly expressed of the 10 known functional MT isoforms) increased chemosensitivity of the cells to doxorubicin. To examine the mechanisms underlying these clinical data, we used siRNAs to decrease MT-2A mRNA expression and protein expression. In MT down-regulated cells challenged with the IC(50) concentration of doxorubicin, we observed a significant reduction in cell viability. Cell cycle analysis also revealed a corresponding increase in apoptosis in the MT down-regulated cells following doxorubicin exposure, showing that down-regulation of MT increased susceptibility to doxorubicin cytotoxicity. The data suggest that MT could be a potential marker of chemoresistance and a molecular therapeutic target.

Metallothionein as a prognostic biomarker in breast cancer

Breast cancer is the most common cancer in women, with a general upward trend in incidence. Basic and clinical breast cancer research has continued at a rapid pace, in the endeavor to understand the biology of the disease so as to improve management of patients. Besides traditional pathological indicators, expression of molecular markers in breast cancer has also been comprehensively investigated. This paper will focus on the prognostic utility of metallothioneins (MTs), a family of low molecular weight metal binding proteins encoded by at least 10 functional MT genes that are associated with cell proliferation in breast cancer. Evidence that MT is a potential prognostic biomarker for breast cancer is supported by many reports in the literature. Expression of the MT protein has been detected by immunohistochemistry in a significant portion of invasive ductal breast cancers. MT expression has also been well studied in association with traditional clinico-pathological parameters of breast cancers. Generally, higher MT expression in breast cancers is predictive of worse patient outcomes. The relationship of MT isoforms to histological grade, estrogen receptor (ER) status, and prognosis will also be discussed.

Metallothionein immunostaining in adenoid cystic carcinomas of the salivary glands

Metallothionein (MT) is a protein that has been studied in several tumors as a prognostic factor and as a potential myoepithelial cell marker in breast cancer. The aims of this study were to assess the immunohistochemical staining of MT in adenoid cystic carcinomas of the salivary glands (ACC), and to analyze possible morphological and quantitative variations among the solid, cribriform, and tubular histological subtypes. MT was investigated in 15 cases of ACC using the immunohistochemical technique. All of the cases expressed the MT antigen. This expression was noteworthy in cells depicting myoepithelial differentiation. ACC with predominant tubular pattern presented a significantly lower mean index of MT immunopositivity than did solid or cribriform subtypes, while these two latter groups did not differ in terms of MT expression. Our results suggest that MT may be an important tool for immunolocalization of myoepithelial tumor cells in salivary gland neoplasms.

Metallothionein isoform II expression in hyperplastic, dysplastic and neoplastic prostatic lesions

BACKGROUND

Metallothionein is a low-molecular-weight cysteine-rich protein that has the ability to bind and sequestrate heavy metal ions. It is associated with metalloregulatory functions such as cell proliferation, growth and differentiation.

AIMS

To investigate the expression of metallothionein in hyperplastic, dysplastic and neoplastic prostatic lesions and to correlate its expression with histological grade of prostatic carcinoma.

METHOD

The study was carried out on formalin-fixed and paraffin-wax-embedded tissue blocks from 8 patients with benign prostatic hyperplasia, 6 patients with prostatic intraepithelial neoplasia (PIN) and 30 patients with prostatic carcinoma, using the streptavidin-biotin technique. The histological grade was defined and the carcinomas were divided into low-grade (Gleason Score 2-4), 12 moderate grade (Gleason Score 5-6) and 10 high-grade (Gleason Score 7-10) carcinomas.

RESULTS

Patchy metallothionein staining of epithelial cells was observed in normal and benign prostatic tissues. All cases of PIN and 20 of 30 patients with prostatic carcinoma showed positive staining for metallothionein. Metallothionein expression considerably increased from low-grade to high-grade tumours. The proportion of cells staining positively for metallothionein was directly correlated with histological grade of prostatic carcinoma. The epithelial cells lack uniformity in staining intensity, but the percentage of strongly positive cells increased with the histological grade of prostatic carcinoma.

CONCLUSIONS

The high incidence of metallothionein expression in PIN in our study suggests that it is associated with early prostate tumorigenesis. Also, metallothionein expression was directly correlated with the histological grade of prostatic carcinoma, suggesting that metallothionein may be a useful marker for predicting the prognosis of prostate cancer.

Expression of metallothoinein isoform 3 is restricted at the post-transcriptional level in human bladder epithelial cells

This study was designed to define the effect that overexpression of MT-3 would have on a cell culture model of bladder urothelium. Stable and inducible transfection was used to achieve overexpression of the MT-3 gene in the UROtsa cell line. When the UROtsa cells were stably transfected with the MT-3 coding sequence, there was highly elevated expression of MT-3 mRNA, but no MT-3 protein. An inducible vector showed that low basal levels of MT-3 mRNA and protein could be produced, but that induction only increased MT-3 mRNA and not protein. The clones expressing low basal levels of MT-3 protein also had reduced growth rates compared to control cells. Site directed mutagenesis was used to produce an MT-3 coding sequence where the prolines in positions 7 and 9 were converted to threonines. When this altered MT-3 was stably transfected into the UROtsa cells, the cells were able to accumulate the mutated form of the MT-3 protein. These studies show that MT-3 protein expression is inhibited by post-transcriptional control in the urothelial cell. Modifying the MT-3 protein to resemble the MT-1 isoform removes this component of post-transcriptional control and allows accumulation of the mutated MT-3 protein. The altered sequence involved in post-transcriptional control of MT-3 protein expression is the same sequence implicated in the neuronal growth inhibitory activity associated specifically with the MT-3 isoform of the MT gene family.

Post-Transcriptional Regulation of Metallothionein Isoform 1 and 2 Expression in the Human Breast and the MCF-10A Cell Line

Studies have shown, using immunohistochemical staining, that the MT-1 and MT-2 proteins (MT-1/2) are overexpressed in a substantial subset of ductal breast cancers, that overexpression occurs early in the disease process, and that this overexpression is indicative of a poor prognosis. Normal ductal breast epithelium fails to immunostain for the MT-1/2 protein, whereas the myoepithelial cells of the ducts stain intensely. There is no information regarding the expression of the mRNAs for the eight active MT-1 and MT-2 genes in normal breast duct epithelium. Microdissection of normal breast samples was used to obtain total RNA from enriched populations of ductal epithelium and myoepithelium. Analysis by reverse-transcription polymerase chain reaction (RT-PCR) demonstrated that the identity of the MT isoform-specific genes expressed (MT-2A and MT-1X) and their relative levels of expression were similar between the myoepithelial and ductal components. These findings indicate that the ductal and myoepithelial components express similar amounts of MT-2A and MT-1X mRNAs, but that they have distinctly different expression of the MT-1/2 protein. Confluent cultures of MCF-10A breast epithelial cells were exposed to Cd(+2) to test for evidence of post-transcriptional regulation of MT-1/2 protein accumulation in ductal epithelium. It was demonstrated that Cd(+2) elicited only a marginal induction of MT-1E, MT-1X, or MT-2A mRNAs, whereas, there was a marked increase in MT-1/2 protein, reaching levels of 6% of total cell protein under conditions of extended exposure. This study suggests that the mechanism underlying the finding of increased MT-1/2 protein expression in ductal breast cancer may involve, to some degree, the post-transcriptional regulation of MT-1/2 protein expression.

Metallothionein expression in human neoplasia

The metallothionein family is a class of low-molecular-weight, cysteine-rich proteins with high affinity for metal ions. Four major isoforms (metallothionein-1, -2, -3, and -4) have been identified in mammals, involved in many pathophysiological processes, including metal ion homeostasis and detoxification, protection against oxidative damage, cell proliferation and apoptosis, drug and radiotherapy resistance and several aspects of the carcinogenic process. In the present review we examine the expression of metallothionein in different human tumours and its correlation with histopathological variables, tumour cell proliferation or apoptosis, resistance to radiation or chemotherapy, patient survival and prognosis. A variable profile of metallothionein and its isoforms' expression has been observed in different cancer types. Although metallothionein expression has been implicated in carcinogenic evolution, its use as a marker of tumour differentiation, cell proliferation and prognosis predictor remains unclear. Detailed studies focused on the expression of metallothionein isoforms and isotypes in different tumour types could elucidate the role of this group of proteins in the carcinogenic process, delineating its possible clinical significance for the management of patients.

Clinicopathological significance of metallothioneins in breast cancer

Metallothioneins (MTs) are a family of metal binding proteins that play an important role in maintaining transition metal ion homoeostasis, redox balance in the cell and fundamental cellular processes such as proliferation and apoptosis. In humans, there are 4 groups of MT proteins which are encoded by 10 functional MT isoforms. In breast tissues, MT is primarily expressed in myoepithelial and malignant epithelial cells. Immunohistochemical studies have revealed that 26% to 100% of invasive ductal breast cancers express the MT protein. The MT-1F and MT-2A isoforms have been reported to be associated with higher histological grade in breast cancer, whereas higher MT-1E mRNA expression was found in estrogen receptor-negative tumors compared to their estrogen receptor-positive counterparts. A number of studies have shown that MT expression in breast cancer is associated with poorer prognosis. In addition, metallothionein expression may have a potential role in protecting the breast cancer cell from chemotherapeutic threats to survival.

Stable transfection and overexpression of metallothionein isoform 3 inhibits the growth of MCF-7 and Hs578T cells but not that of T-47D or MDA-MB-231 cells

The third isoform of metallothionein (MT-3) is overexpressed in some breast cancers and its expression is associated with a poor disease outcome. In the PC-3 prostate cancer cell line, MT-3 expression has been shown to inhibit cell growth and increase drug resistance. The goal of the present study was to determine if MT-3 overexpression would influence the growth of human breast cancer cell lines. To determine this, the coding sequence of the MT-3 gene was stably transfected into two estrogen receptor positive (MCF-7 and T-47D) and two estrogen receptor negative cell lines (Hs578T and MDA-MB-231) having no basal expression of MT-3. Cell growth was determined by counting DAPI-stained nuclei, cadmium resistance by the colony formation assay, MT mRNA expression by RT-PCR, and MT protein by immuno-blot. It was demonstrated that MCF-7 and Hs578T cells that overexpress the MT-3 gene were growth inhibited compared to untransfected cells. In contrast, T-47D and MDA-MB-231 cells that overexpress MT-3 were not growth inhibited. Stable transfection of the MT-1E gene had no effect on the growth of any of the four cell lines. It was also demonstrated that the overexpression of both MT-3 and MT-1E only increased the resistance of MCF-7 cells to Cd(+2). In all instances, stable transfection of the MT-3 or MT-1E gene had no effect on the expression of the other MT isoforms. The study shows that MT-3 can influence the growth of some breast cancer cell lines.

Metallothionein: early marker in the carcinogenesis of ulcerative colitis-associated colorectal carcinoma

Metallothioneins (MTs) are zinc-binding proteins whose overexpression may lead to sequestration of zinc ions and consequently to functional inactivation of the p53 tumor suppressor gene. The aim of the study was to investigate the potential role of MTs in the carcinogenesis of ulcerative colitis (UC) as well as possible effects on p53 function. The monoclonal antibodies E9 (anti-MT), DO-7, and 1801 (anti-p53) and the polyclonal antibody CM-1 (anti-p53) were used to stain formalin-fixed, paraffin-embedded colon specimens obtained from 14 patients with UC-associated colorectal carcinoma (CAC), 13 with high-grade dysplasia (HGD), 10 with low-grade dysplasia (LGD), and 30 with UC without dysplasia or carcinoma. Statistical significance (p <0.05) was assessed using Fisher's exact test. Positive MT staining (> 20% of tumor, dysplastic, or epithelial cells) was found in most UC and LGD but in only a small percentage of HGD and CAC (p <0.01 for CAC vs. UC and LGD vs. HGD). Positive p53 immunoreactivity was observed predominantly in HGD and CAC but not in LGD and UC (p <0.01 for CAC vs. UC and HGD vs. LGD). In histologically normal tissue neighboring CAC, significant MT expression was found in six of seven specimens with simultaneous lack of p53 expression. MT overexpression may represent an important early step in the development of CAC independent of p53 expression and should be investigated in the long term as an independent cancer risk factor in UC.

Expression of metallothionein in lung carcinoma: correlation with histological type and grade

AIMS

Over-expression of cellular metallothionein occurs frequently in human tumours but the underlying mechanism remains unknown. The aim of this study was to assess metallothionein expression in cases of lung carcinoma and to correlate it with histopathological parameters.

METHODS AND RESULTS

Tumour tissue samples from 89 patients with lung carcinoma were immunostained by the streptavidin-biotin-peroxidase technique, using a monoclonal antibody against both metallothionein-1 and -2 isoforms. Positive matallothionein immunostaining was prominent in 44 out of 89 (49%) and negative in 45 out of 89 (51%) cases of lung carcinoma examined. Metallothionein positivity was prominent in 32 out of 43 (74%) cases of squamous cell lung carcinoma, and in 12 out of 35 (34%) cases of adenocarcinoma, while it was negative in all 11 cases of small-cell lung carcinoma examined, presenting a statistically significant difference between the different histological types. The intensity of metallothionein staining revealed a statistically significant difference between the squamous cell and adenocarcinoma cases examined. The pattern and extent of metallothionein staining in tumour cells and the expression of metallothionein in stromal cells were not correlated with histopathological parameters (type and grade) in metallothionein-positive cases of lung carcinoma examined. No association was found between metallothionein expression and lymph node status in the examined cases of lung carcinoma.

CONCLUSIONS

Our findings indicate that expression of metallothionein was evident in squamous cell lung carcinoma and adenocarcinoma, but absent in small-cell lung carcinoma, supporting evidence for participation of this protein in the biological mechanisms underlying the carcinogenic evolution in the lung.

Immunohistochemical localization of metallothionein in benign and malignant epithelial ovarian tumors

Metallothioneins (MTs) are a group of low-molecular-weight proteins that are overexpressed in a variety of human neoplasms and are related to differentiation and prognosis in some tumor types. This study investigated immunohistochemically detectable metallothionein expression in benign and malignant ovarian surface epithelial tumors of serous, mucinous, and endometrioid types. MT expression was observed in 56% of carcinomas (n = 139) and in 2% of benign neoplasms (n = 81). Of the malignant tumors, MT expression was found in 68% of endometrioid, 56% of mucinous, and 52% of serous neoplasms. There was increased MT expression in grade 3 carcinomas (64%) as compared with grade 2 (60%) and grade 1 (23%). The overexpression of MT in malignant as opposed to benign ovarian surface epithelial tumors may suggest a role in tumorigenesis. Analogous to the situation in endometrial carcinomas, there is a tendency toward higher expression in poorly differentiated tumors. Whether high MT expression is an independent prognostic factor and increased expression indicates chemotherapy resistance in ovarian cancer, as has been previously suggested, should be determined by further studies.

Metallothionein expression in canine and feline mammary and melanotic tumours

Moderate to strong immunohistochemical metallothionein (MT) positivity (MT expression) is associated with a poor prognosis in some human tumours. The aim of this study was to determine MT expression in mammary tumours and cutaneous melanomas in dogs and cats. Canine (67) and feline (47) mammary tumours, and cutaneous melanomas (canine 40, feline 26) were immunolabelled with MT monoclonal antibody E9. The overall incidence of MT expression of these tumours was similar to that observed in various human neoplasms. However, a striking interspecies difference was detected. In dogs, MT expression occurred in 100% of benign and 57% of malignant mammary tumours. In cats, however, 30% of malignant mammary tumours expressed MT but benign mammary tumours and cases of fibroadenomatous hyperplasia did not. Moderate to strong MT immunoreactivity was detected in 30% of benign and 25% of malignant cutaneous melanomas in dogs, and in 6% of malignant melanomas in cats. The findings in feline mammary tumours resembled findings reported in human breast cancer, but the cause of tumour-associated MT expression is unknown. Studies are in progress to determine whether the MT state (apo [metal-free] or holo [metal-bound]) accounts for the paradoxical association of MT expression with individual types of tumours and the animal species in which they arise.

P-glycoprotein, metallothionein and NM23 protein expressions in breast carcinoma

Cellular drug resistance and increased metastatic potential are the major obstacles in the successful treatment of cancer with chemotherapy. The aim of this study was to investigate whether the immunohistochemical expression of two proteins implicated in drug resistance (P-glycoprotein and metallothionein) and the product of the suppressor gene nm23 could be related to prognosis in breast cancer. Seventy-two patients with palpable or occult breast carcinoma, not treated with chemotherapy or endocrine therapy, were examined. Immunohistochemical methods were used to determine the expression of P-glycoprotein (PG), metallothionein (MT), nm23, as well as the estrogen receptor (ER), the p53 status, and the Ki67 index. The results were correlated with clinical and morphological features. Cytoplasmic and membrane-specific immunostainings of PG were seen exclusively in tumor cells and identified in 14 of 72 cases (19.4%). Only a statistically significant association with metastases, (p = 0.06) and recurrences (p = 0.1) was observed. MT-positive reaction was identified in the cytoplasm of the tumor cells in 47 (65.3%) cases. Statistical significance was associated with metastases (p = 0.07), but not with death or recurrences. Specific immunostaining of nm23 protein was seen only in the cytoplasm of tumor cells. A positive reaction was observed in 55 of 72 (89.3%) cases. Although a significant association between nm23 protein expression and other morphologic and immunohistochemical variables did not exist, we observed a higher morbidity in patients with the MT-positive/nm23-negative tumor phenotype. Univariate analysis for survival selected the following variables: histologic grade (p = 0.001), ER (p = 0.002), mitotic index (p = 0.005), Ki 67 index (p = 0.068), MT (p = 0.046) and PG (p = 0.085). The Cox model provided the following independent variables: histologic grade (p = 0.021) and metallothionein (p = 0.03). These data confirm the prognosis observed in patients with PG or metallothionein expression as well as the independence of these two variables. It also suggests that nm23 is not necessarily involved in the development of an invasive phenotype.

In vivo gene expression profile analysis of metallothionein in renal cell carcinoma

The antiapoptotic and mitogenic responses of metallothionein (MT) have been well documented in vitro. While MT protein overexpression, frequently encountered in a number of human primary tumors, has been shown to be correlated with disease progression, little information is available on the in vivo isoform expression of MT. In this study we have demonstrated the occurrence of MT proteins and further defined their differential expression profile in human primary renal cell carcinoma (RCC). Pooled normal human kidney RNA and paired biopsy specimens (tumor and control) obtained from 11 patients diagnosed with RCC with tumor grade ranging from 1-3 and a pathological staging of T2-T3 (N0M0) were used for the study. Samples were analyzed for the presence of MT protein using immunohistochemical (IHC) analysis and for MT isoform-specific mRNA expression by reverse transcriptase polymerase chain reaction. Metallothionein protein assumed both cytoplasmic and nuclear staining in cancer cells and was detected in eight of 11 samples (72%) with polyclonal antibodies. The immunoreactivity of MT protein, but not its cellular localization, in RCC specimens suggests a relationship between and advanced disease. While alterations in the basal level of expression of MT-1E, MT-1F and MT-1X genes remained unchanged, significant up-regulation of MT-2A and down-regulation of MT-1A and MT-1G transcripts was observed in RCC tissue specimens when compared with controls. Intriguingly, the paired RCC biopsy specimens had lower MT-1H transcripts than pooled normal human controls. We here provide the first report of the differential expression of MT isoforms in human RCC and that this data further support the role of MT-2A in tumorigenesis.

Immunohistochemical localization of metallothionein in endometrial lesions

Metallothioneins (MTs) are a group of ubiquitous low-molecular-weight proteins essential for the protection of cells against heavy metal ion toxicity. The immunohistochemical expression of MT was studied by immunohistochemistry using a monoclonal antibody (E9) against a conserved epitope of I and II isoforms in a series of 89 endometrial carcinomas, 34 cases of hyperplasia, and 32 samples of normal endometrium. In secretory phase endometrium, extensive MT expression was detected in most cases (92.4%). In contrast, MT immunoreactivity was confined to small foci in 22.2% of proliferative phase cases. The MT values in normal endometrium were inversely correlated with oestrogen receptor (ER) content (p<0.0001), progesterone receptor (PgR) content and with PCNA (p<0.0001) and MIB1 (p=0.001) scores. In hyperplastic lesions, MT expression was detected only in 3.3% of cases, while in the group of carcinomas it was observed in 23.1%. A statistically significant difference of MT expression was observed between carcinomas and simple hyperplasias (p=0.03). In carcinomas, MT expression was positively correlated with grade (p=0.0065), MIB1 (p=0.022), and p53 (p=0.006) expression, and inversely with PgR (p=0.03). A trend of inverse correlation between MT and ER receptor was also detected (p=0.07). These data suggest that MT expression seems to be under hormonal control in normal endometrium; that it may modify p53 expression; and that it could be used as an additional biological marker indicating aggressive behaviour in endometrial lesions.

Immunohistochemical detection of maspin is a useful adjunct in distinguishing radial sclerosing lesion from tubular carcinoma of the breast

Maspin is a recently described member of the serpin family of protease inhibitors that is consistently expressed at high levels in mammary myoepithelial cells. This feature was used in the immunohistochemical evaluation of tubular carcinoma (TC) and radial sclerosing lesion (RSL) of the breast, and compared with other markers of myoepithelial cells. Ten cases of TC and 11 cases of RSL were studied for the expression of maspin, alpha-smooth muscle actin (alpha-SMA), metallothionein (MT), and S-100 protein by immunohistochemistry. Myoepithelial cells stained strongly and diffusely for maspin creating a pattern of an outer continuous ring surrounding the epithelium of tubules of all RSLs. This pattern was absent in all TCs; however, the single-layered epithelium comprising the tubules of two TCs was positive for maspin with a moderate to strong intensity. Myoepithelial cells were not positive for MT in a consistent manner. Benign nonproliferative epithelium stained focally and weakly for maspin in four of 11 cases of RSL and was negative for MT in all 11 cases. Foci of mild to moderate epithelial hyperplasia noted in five of 11 cases of RSL stained diffusely with a weak to moderate intensity for maspin and focally with a strong intensity for MT. alpha-SMA was consistently expressed in myoepithelial cells but also in stromal myofibroblasts and blood vessels, creating a pattern that was less satisfactory than maspin in distinguishing RSL from TC. Immunohistochemical staining for S-100 protein was of no differential diagnostic value. In conclusion, immunohistochemical staining for maspin is diagnostically useful and superior to MT, S-100, and alpha-SMA, in distinguishing RSL from TC. The epithelial immunoreactivity for maspin in two of 10 TCs merits further investigation from a prognostic viewpoint.

Prognostic evaluation of metallothionein expression in human colorectal neoplasms

AIM

To investigate the role of metallothionein in colorectal tumours and the possible relation with other factors associated with tumour progression: expression of cathepsin D (CD), CD44, p53, Rb, bcl-2, c-erbB-2, epidermal growth factor receptor (EGFR), proliferation indices (Ki-67, proliferating cell nuclear antigen (PCNA)), and conventional clinicopathological variables.

METHODS

The immunohistochemical expression of metallothionein was investigated in 23 cases of colorectal adenoma and 94 adenocarcinomas. Metallothionein expression was examined by the avidinbiotin peroxidase immunoperoxidase (ABC) using the monoclonal mouse antibody E9, on formalin fixed, paraffin embedded tissue.

RESULTS

Positive metallothionein expression (> 5% of neoplastic cells) was observed in 30.4% of adenomas and 25.5% of adenocarcinomas, while 8.7% of adenomas and 14.9% carcinomas showed focal metallothionein positivity. In contrast, 60.9% of adenomas and 59.6% of carcinomas almost completely lacked metallothionein expression. In the series of adenocarcinomas, metallothionein expression was inversely correlated with CD44 in neoplastic cells (p = 0.01). There was no statistically significant difference of metallothionein expression, or the other variables examined, between adenocarcinomas and adenomas.

CONCLUSIONS

Metallothionein expression does not seem to indicate aggressive biological behaviour in colorectal adenocarcinomas, in comparison with the other types of carcinoma. The inverse correlation with CD44 could suggest that the decreased metallothionein expression may contribute to the metastatic spread of the lymph node involvement in colorectal cancer. Metallothionein expression does not seem to represent an independent prognostic marker in colorectal cancer.

Metallothionein expression and nuclear size in benign, borderline, and malignant serous ovarian tumours

Metallothioneins (MTs) are low-molecular-weight proteins involved in metalloregulatory functions such as cell proliferation, growth, and differentiation. In recent years, MT expression has been linked with carcinogenesis, resistance to cancer therapy, and tumour progression. However, the significance of MT expression in ovarian cancers is at present inadequately documented. In this study, MT immunohistochemistry was performed in 12 benign, 14 borderline, and eight malignant serous tumours of the ovary. The intensity of the immunostaining was evaluated by image analysis. There was a significantly higher number of MT-immunopositive cells in the multilayered epithelial cells of borderline serous tumours (atypical proliferative serous tumours) than in the single layered epithelial cells within the same tumour, and in the single cell layer of benign serous tumours. There was no difference in the expression of MTs in the single layered tumour cells of benign and borderline serous tumours. Significantly higher numbers of MT-immunopositive cells were observed in both the single and the multilayered epithelial cells of serous carcinomas, the highest number being observed in the multiple layers of serous carcinomas. The positively stained malignant tumour cells in both single and multiple layers were larger than the negatively stained cells in benign, borderline, and malignant serous ovarian tumours. There was moderate to intense staining. These findings indicate that there is increased expression of MTs in the progression of malignancy, which could be used as a marker in grading the three groups of ovarian serous tumours and for determining prognosis.

Differences in metallothionein expression in transplantable mouse mammary tumor lines

In order to elucidate a possible role of metallothionein (MT) in mammary carcinogenesis, MT and sex hormone receptor (estrogen receptor, ER; progesterone receptor, PR) expressions were investigated immunohistochemically in a transplantable pregnancy-dependent mouse mammary tumor (TPDMT-4) and related autonomous tumor sublines (T4-OI96, T4-OI165 and T4-OI320CY) recovered from pregnant and virgin DDD mice. TPDMT-4 showed MT expression in tumor cells, while the expression was less evident in T4-OI165 and T4-OI96 among the autonomous tumor lines; in T4-OI320CY, the MT expression was similar to that in TPDMT-4. Chromatographic study of MT contents in the tumor lines confirmed the results of the immunohistochemical examination. PR and ER were localized in the tumor cells of TPDMT-4, but not in those of autonomous tumor sublines. In TPDMT-4, a significant correlation was observed between MT and ER expressions (r = 0.83, P < 0.01), but not between MT and PR expressions (r = 0.26, P > 0.4), also between MT expression and mitotic activity (r = -0.34, P > 0.3). Since T4-OI96 and T4-OI165 are known to be more malignant than T4-OI320CY, the present study indicates a negative correlation between the MT positivity and progression of the transplantable mammary tumor in mice.

High metallothionein expression is associated with features predictive of aggressive behaviour in endometrial carcinoma

AIMS

Metallothioneins (MTs) are a group of ubiquitous low molecular weight proteins with a high affinity for heavy metal ions. The aim of the present study was to investigate MT expression in a series of endometrial carcinomas. We wished to determine whether MT expression in endometrial carcinoma was related to established prognostic factors such as tumour grade, stage and histological type. We also wanted to establish if high MT expression in curettings of endometrial carcinoma was predictive of high expression in the subsequent hysterectomy specimen.

METHODS AND RESULTS

Sixty-three cases of endometrial carcinoma were included in the study. These comprised 57 endometrioid adenocarcinomas (15 grade 1, 25 grade 2, 17 grade 3), three papillary serous adenocarcinomas, two mucinous adenocarcinomas and one clear cell adenocarcinoma. Forty-five tumours were stage I, 10 were stage II and eight were stage III. In 28 cases, diagnostic endometrial curettings, performed prior to hysterectomy, were available for study. Immunohistochemical staining was performed using the anti-MT monoclonal antibody E9. The intensity and distribution of MT staining were assessed using a semiquantitative method. This resulted in an intensity distribution (ID) score out of a maximum of 300. The mean ID score of grade 1 and 2 endometrioid adenocarcinomas was 67 and 63, respectively, while for grade 3 tumours the mean ID score was 114. This was statistically significant (P = 0.05). The three papillary serous adenocarcinomas had high ID scores with a mean of 208. The mean ID score of stage I tumours was 69. This was lower than those of stage II and III tumours which had mean ID scores of 116 and 128, respectively. However, these differences were not statistically significant (P = 0.288). A significant correlation was observed between MT ID scores in endometrial curettings and in the subsequent hysterectomy (P = 0.013).

CONCLUSIONS

MT isoforms can be demonstrated in most endometrial adenocarcinomas. High MT ID scores are associated with high grade and high stage endometrial adenocarcinomas and with the aggressive papillary serous adenocarcinoma. Whether this is of value as an independent prognostic factor has yet to be established.

Metallothionein and apoptosis in primary human hepatocellular carcinoma and metastatic adenocarcinoma

AIMS

Differences in expression of metallothionein (MT) have been reported in various human tumours. MT is mainly expressed in proliferating epithelial tumour cells but in human hepatocellular carcinoma (HCC) there is only a minimal expression of MT. Since MT is a zinc binding protein and certain inducers of MT including zinc play a role in apoptosis, studies were undertaken to compare the expression of MT and the presence of apoptotic cells (APPC) in both primary HCC and metastatic adenocarcinoma.

METHODS AND RESULTS

Histological sections of 13 cases of primary HCC and eight cases of metastatic adenocarcinoma were obtained from archival samples. They were stained for MT using a polyclonal antibody which crossreacts readily with human MT and for APPC by the TUNEL technique. Normal human liver had consistent MT staining with no detectable APPC. The primary HCC showed moderate MT staining with a small number of APPC while metastatic adenocarcinoma showed no MT staining with a large number of APPC.

CONCLUSIONS

These results suggest a relationship between absence of MT and appearance of APPC in human liver tumours, especially in metastatic adenocarcinomas.

Metallothionein and Fas (CD95) are expressed in squamous cell carcinoma of the tongue

Metallothionein (MT) is a chelator present in myoepithelial cells, whilst the Fas-receptor (APO-1, CD95) has been described primarily in human T Jurkat cells. 20 cases of carcinoma of the tongue were investigated immunocytochemically with regard to MT, Fas and Bcl-2. In normal oral squamous epithelium, MT is located in the basal/parabasal dividing cells only. In well-differentiated nests of carcinomas, MT is observed almost entirely in peripherally located cells. In situ end-labelling indicates apoptosis in the centre of these nests, but not in the peripheral areas. Less-differentiated areas show more general MT-positivity, but little apoptosis. All 24 tumours are Fas-positive, but normal epithelia are mainly negative (P < 0.0001). Bcl-2 protein was sparse in the tumours compared with MT and Fas (P < 0.0001). We thus suggest that MT, possibly due to its chelating properties, may contribute to delaying cells entering apoptosis, both in normal epithelium near the base and in less-differentiated regions of carcinoma. Moreover, Fas may be present in cells of human malignancies, as well as those of established malignant cell lines.

Overexpression of resistance-related proteins (metallothioneins, glutathione-S-transferase pi, heat shock protein 27, and lung resistance-related protein) in osteosarcoma. Relationship with poor prognosis

BACKGROUND

The prognosis for patients with osteosarcoma has improved over the past 20 years, mainly due to developments in chemotherapy. Some proteins have been reported to show drug resistance. Theoretically, overexpression of some of these proteins makes treatment difficult, leading to poorer outcome.

METHODS

Specimens taken from conventional osteosarcomas of the extremity bones from 60 patients younger than 30 years were used. In all cases, preoperative oncostatic chemotherapy was undertaken after biopsy. If available, biopsy specimens were also used for sequential comparison. Among resistance-related proteins, expression of metallothioneins (MTs), glutathione-S-transferase pi (GST pi), heat shock protein 27 (Hsp27), and lung resistance-related protein (LRP) was evaluated immunohistochemically in paraffin sections. The log rank test was used for univariate analysis and the Cox regression model for multivariate analysis.

RESULTS

At biopsy, only overexpression of Hsp27 was associated with poor prognosis. At surgery, a relationship was observed between poor prognosis and overexpression of GST pi, Hsp27, and LRP. Groups overexpressing one protein tended to overexpress another. Overexpression of these proteins in surgical specimens also correlated with histologic response to preoperative chemotherapy and clinical stage. In multivariate analysis, Hsp27 overexpression at biopsy was an independent prognostic factor.

CONCLUSIONS

Inherent overexpression of Hsp27 is independently related to poor outcome in osteosarcoma patients. Overexpression of GST pi, Hsp27, and LRP at surgery might be associated with failure of preoperative chemotherapy. Control of the expression of these proteins may improve the outcome for patients with osteosarcoma.

Immunohistochemical expression of metallothionein in normal human colorectal mucosa, in adenomas and in adenocarcinomas and their associated metastases

The immunohistochemical distribution pattern of metallothionein, a low molecular weight protein with strong affinity for divalent heavy metal ions, has been investigated in normal and neoplastic conditions of the large bowel. Utilizing a monoclonal mouse antibody the following formalin-fixed paraffin-embedded surgical or biopsy samples were studied: tubulo-villous adenomas (8 cases); adenocarcinomas with various degree of differentiation (85), nine of which were mucinous-type; synchronous tubular or tubulo-villous adenomas separate from carcinomas (30); transitional mucosa (45); metastases in lymph nodes (43); and distant metastases (45). Twenty biopsies from the right and left colon of 10 patients affected by irritable bowel syndrome were also analyzed. Normal colonic mucosa as well as transitional mucosa showed metallothionein immunopositivity in enterocytes at the luminal surface and crypts. Evident nuclear and cytoplasmic staining was encountered in tubulo-villous adenomas; the same reactivity was noted in the basal glandular component of colorectal carcinomas-synchronous adenomas, while less intense staining was noted in the apical villous portions. A variable metallothionein immunostaining was observed in adenocarcinomas (62.3%), in lymph node (55.8%) and distant hepatic (17.2%) and omental (43.8%) metastases, although it was not always concordant with that reported in the corresponding primary tumour. Whether the metallothionein positivity observed in normal and neoplastic cells is the result of expression of a stable form of the protein or an accumulation in the nucleus and cytoplasm remains to be clarified.

Metallothionein expression in human breast cancer

Metallothioneins are ubiquitous low molecular weight proteins characterised by high cysteine content and affinity for binding heavy metals. Abnormal metallothionein function and expression have been implicated in various disease states, including neoplasia. The aim of this study was to investigate metallothionein expression in human breast carcinoma. Sections of routinely fixed and processed blocks of tumour from 100 consecutive cases of primary operable breast carcinoma were stained for metallothionein using a recently developed monoclonal antibody and a standard immunohistochemical technique. Expression was scored on the basis of microscopical assessment of percentage of tumour cells staining. One patient was lost to follow-up and excluded from the study. A significant association (P < 0.0001) was observed between metallothionein expression and tumour type, with low levels being observed in tumours of good prognostic type. There was also a significant association with local recurrence (P < 0.02) and a significant difference (P < 0.02) in both survival and disease-free interval between tumours showing low and high levels of expression, the latter indicating a poor prognosis. No relationship was observed with patient age, tumour size, lymph node stage, histological grade, vascular invasion, menopausal status or oestrogen receptor status. The assessment of metallothionein expression in human breast cancer appears to provide prognostic information and may have important implications for understanding its development.