Interaction of metallothionein with tumor suppressor p53 protein

Metallothionein-I+II in neuroprotection

Metallothionein (MT)-I+II synthesis is induced in the central nervous system (CNS) in response to practically any pathogen or disorder, where it is increased mainly in reactive glia. MT-I+II are involved in host defence reactions and neuroprotection during neuropathological conditions, in which MT-I+II decrease inflammation and secondary tissue damage (oxidative stress, neurodegeneration, and apoptosis) and promote post-injury repair and regeneration (angiogenesis, neurogenesis, neuronal sprouting and tissue remodelling). Intracellularly the molecular MT-I+II actions involve metal ion control and scavenging of reactive oxygen species (ROS) leading to cellular redox control. By regulating metal ions, MT-I+II can control metal-containing transcription factors, zinc-finger proteins and p53. However, the neuroprotective functions of MT-I+II also involve an extracellular component. MT-I+II protects the neurons by signal transduction through the low-density lipoprotein family of receptors on the cell surface involving lipoprotein receptor-1 (LRP1) and megalin (LRP2). In this review we discuss the newest data on cerebral MT-I+II functions following brain injury and experimental autoimmune encephalomyelitis.

Circulating monocytes in HIV-1-infected viremic subjects exhibit an antiapoptosis gene signature and virus- and host-mediated apoptosis resistance

Mechanisms that may allow circulating monocytes to persist as CD4 T cells diminish in HIV-1 infection have not been investigated. We have characterized steady-state gene expression signatures in circulating monocytes from HIV-infected subjects and have identified a stable antiapoptosis gene signature comprised of 38 genes associated with p53, CD40L, TNF, and MAPK signaling networks. The significance of this gene signature is indicated by our demonstration of cadmium chloride- or Fas ligand-induced apoptosis resistance in circulating monocytes in contrast to increasing apoptosis in CD4 T cells from the same infected subjects. As potential mechanisms in vivo, we show that monocyte CCR5 binding by HIV-1 virus or agonist chemokines serves as independent viral and host modulators resulting in increased monocyte apoptosis resistance in vitro. We also show evidence for concordance between circulating monocyte apoptosis-related gene expression in HIV-1 infection in vivo and available datasets following viral infection or envelope exposure in monocyte-derived macrophages in vitro. The identification of in vivo gene expression associated with monocyte resistance to apoptosis is of relevance to AIDS pathogenesis since it would contribute to: 1) maintaining viability of infection targets and long-term reservoirs of HIV-1 infection in the monocyte/macrophage populations, and 2) protecting a cell subset critical to host survival despite sustained high viral replication.

Cell death in the injured brain: roles of metallothioneins

In traumatic brain injury (TBI), the primary, irreversible damage associated with the moment of impact consists of cells dying from necrosis. This contributes to fuelling a chronic central nervous system (CNS) inflammation with increased formation of proinflammatory cytokines, enzymes and reactive oxygen species (ROS). ROS promote oxidative stress, which leads to neurodegeneration and ultimately results in programmed cell death (secondary injury). Since this delayed, secondary tissue loss occurs days to months following the primary injury it provides a therapeutic window where potential neuroprotective treatment could alleviate ongoing neurodegeneration, cell death and neurological impairment following TBI. Various neuroprotective drug candidates have been described, tested and proven effective in pre-clinical studies, including glutamate receptor antagonists, calcium-channel blockers, and caspase inhibitors. However, most of the scientific efforts have failed in translating the experimental results into clinical trials. Despite intensive research, effective neuroprotective therapies are lacking in the clinic, and TBI continues to be a major cause of morbidity and mortality. This paper provides an overview of the TBI pathophysiology leading to cell death and neurological impairment. We also discuss endogenously expressed neuroprotectants and drug candidates, which at this stage may still hold the potential for treating brain injured patients.

The role of metallothionein in oncogenesis and cancer prognosis

The antiapoptotic, antioxidant, proliferative, and angiogenic effects of metallothionein (MT)-I+II has resulted in increased focus on their role in oncogenesis, tumor progression, therapy response, and patient prognosis. Studies have reported increased expression of MT-I+II mRNA and protein in various human cancers; such as breast, kidney, lung, nasopharynx, ovary, prostate, salivary gland, testes, urinary bladder, cervical, endometrial, skin carcinoma, melanoma, acute lymphoblastic leukemia (ALL), and pancreatic cancers, where MT-I+II expression is sometimes correlated to higher tumor grade/stage, chemotherapy/radiation resistance, and poor prognosis. However, MT-I+II are downregulated in other types of tumors (e.g. hepatocellular, gastric, colorectal, central nervous system (CNS), and thyroid cancers) where MT-I+II is either inversely correlated or unrelated to mortality. Large discrepancies exist between different tumor types, and no distinct and reliable association exists between MT-I+II expression in tumor tissues and prognosis and therapy resistance. Furthermore, a parallel has been drawn between MT-I+II expression as a potential marker for prognosis, and MT-I+II's role as oncogenic factors, without any direct evidence supporting such a parallel. This review aims at discussing the role of MT-I+II both as a prognostic marker for survival and therapy response, as well as for the hypothesized role of MT-I+II as causal oncogenes.

Analyzing M-CSF dependent monocyte/macrophage differentiation: expression modes and meta-modes derived from an independent component analysis

Background

The analysis of high-throughput gene expression data sets derived from microarray experiments still is a field of extensive investigation. Although new approaches and algorithms are published continuously, mostly conventional methods like hierarchical clustering algorithms or variance analysis tools are used. Here we take a closer look at independent component analysis (ICA) which is already discussed widely as a new analysis approach. However, deep exploration of its applicability and relevance to concrete biological problems is still missing. In this study, we investigate the relevance of ICA in gaining new insights into well characterized regulatory mechanisms of M-CSF dependent macrophage differentiation.

Results

Statistically independent gene expression modes (GEM) were extracted from observed gene expression signatures (GES) through ICA of different microarray experiments. From each GEM we deduced a group of genes, henceforth called sub-mode. These sub-modes were further analyzed with different database query and literature mining tools and then combined to form so called meta-modes. With them we performed a knowledge-based pathway analysis and reconstructed a well known signal cascade.

Conclusion

We show that ICA is an appropriate tool to uncover underlying biological mechanisms from microarray data. Most of the well known pathways of M-CSF dependent monocyte to macrophage differentiation can be identified by this unsupervised microarray data analysis. Moreover, recent research results like the involvement of proliferation associated cellular mechanisms during macrophage differentiation can be corroborated.

Identification of bladder cancer patients at risk for recurrence or progression: an immunohistochemical study based on the expression of metallothionein

Despite similarities in tumor stage and grade the individual outcome of bladder cancer patients is not predictable. The ideal tool for treatment stratification has not yet been found. Metallothionein (MT) overexpression is correlated with poor tumor differentiation, resistance to chemotherapy, and impaired survival in different malignancies. The clinical relevance of MT expression for defining patients at high risk for recurrence or progression was assessed. MT was detected immunohistochemically and evaluated semiquantitively in tumor specimens of 103 male and 19 female patients (transsurethral resection: n = 94, cystectomy: n = 28). Mean age of the patients was 68 (38-87) yr. According to histopathological features, three groups were distinguished for further analysis (pTa-1G1-2, pTis/pT1G3, and muscle invasive tumors). A cutoff value of 50% immunoreactive cells was used for further analysis. The 5-yr tumor specific survival rate was significantly lower in patients with high MT expression (32 vs. 72%). Accordingly, impaired 5-yr recurrence (90 vs. 58%), and progression rates (78 vs. 54%) were associated with high MT expression. All patients suffering from pTis and pT1G3 tumors with MT expression above the cutoff value showed recurrence within less than 40 mo, whereas 26% of those patients with MT expression below the cutoff value remained long-term recurrence free. Long term progression free survival was detected in 75% of pT1G3 patients with MT expression below the cutoff value. In contrast, 68% of pT1G3 tumor patients with MT expression above the cutoff value progressed, all within the first 12 mo after initial tumor resection. A correlation between high MT expression and prognosis was demonstrated especially in pT1G3 and pTis tumors, where >50% MT expression was linked to shorter tumor-specific survival and increased recurrence/progression rates. Thus, MT expression seems to be a promising marker for further risk stratification in the clinical treatment of bladder cancer patients.

P53 mediated regulation of metallothionein transcription in breast cancer cells

Recent studies have shown that only breast cancer epithelial cells with intact p53 can induce metallothionein (MT) synthesis after exposure to metals. In this study, the potential role of p53 on regulation of MT was investigated. Results demonstrate that zinc and copper increased metal response elements (MREs) activity and MTF-1 expression in p53 positive MN1 and parental MCF7 cells. However, inactivation of p53 by treatment with pifithrin-alpha or the presence of inactive p53 inhibited MRE-dependent reporter gene expression in response to metals. MTF-1 levels remained unchanged after treatment with zinc in cells with nonfunctional p53. The introduction of wild-type p53 in MDD2 cells, containing nonfunctional p53, enhanced the ability of zinc to increase MRE-dependent reporter gene expression. The cellular level of p21Cip1/WAF1 was increased in MDD2 cells after p53 transfection, confirming the presence of active p53. The treatment of MN1 and parental MCF7 with trichostatin A led to a sixfold increase in the MRE activity in response to zinc. On the contrary, MRE activity remained unaltered in MDD2 cells with inactive p53. The above results demonstrate that activation of p53 is an important factor in metal regulation of MT.

Downregulated expression of metallothionein and its clinicopathological significance in hepatocellular carcinoma

AIM

Metallothionein (MT) protein is related to different stages of development and progression of various tumors in humans. The aim of the present study was to investigate expression and localization of MT and their association with clinicopathological characteristics in hepatocellular carcinoma (HCC).

METHODS

Histological specimens of 400 HCC with corresponding non-cancerous liver tissues were stained for MT (E9), P53 and Ki-67 by immunohistochemical staining using tissue microarrays. RNA expression of MT-1X and MT-2A isoforms was determined by real-time reverse transcription-polymerase chain reaction in a set of independent samples of 161 HCC.

RESULTS

Downregulated expression of MT at both mRNA and protein levels was detected in HCC, compared with non-cancerous liver tissues. The frequencies of MT positivity were significantly lower in cases with positive hepatitis B surface antigen than in those with negative hepatitis B surfaceantigen (P = 0.042). The positive rate of MT expression was more frequent in tumors </=2 cm than in tumors >2 cm in diameter (P = 0.007). There was a tendency for MT expression to decrease with the progression of histological grade. Mainly nuclear expression of MT correlated with poorly differentiated HCC. No statistical correlation was found between P53, Ki-67 and MT expression.

CONCLUSIONS

Downregulated expression of MT in HCC may play a role in hepatocarcinogenesis and be a marker of hepatocellular differentiation. Hepatitis B virus infection may be correlated to downregulated expression of MT. The mainly nuclear MT immunostaining may reflect an aggressive behavior in poorly differentiated HCC.

The zinc/thiolate redox biochemistry of metallothionein and the control of zinc ion fluctuations in cell signaling

Free zinc ions are potent effectors of proteins. Their tightly controlled fluctuations ("zinc signals") in the picomolar range of concentrations modulate cellular signaling pathways. Sulfur (cysteine) donors generate redox-active coordination environments in proteins for the redox-inert zinc ion and make it possible for redox signals to induce zinc signals. Amplitudes of zinc signals are determined by the cellular zinc buffering capacity, which itself is redox-sensitive. In part by interfering with zinc and redox buffering, reactive species, drugs, toxins, and metal ions can elicit zinc signals that initiate physiological and pathobiochemical changes or lead to cellular injury when free zinc ions are sustained at higher concentrations. These interactions establish redox-inert zinc as an important factor in redox signaling. At the center of zinc/redox signaling are the zinc/thiolate clusters of metallothionein. They can transduce zinc and redox signals and thereby attenuate or amplify these signals.

Metallothionein functions and structural characteristics

Metallothioneins (MTs) are low molecular weight proteins characterized by a high cysteine content and give rise to metal-thiolate clusters. Most MTs have two metal clusters containing three and four bivalent metal ions, respectively. The MT gene family in mammals consists of four subfamilies designated MT-1 through MT-4. MT-3 is expressed predominantly in brain and MT-4 in differentiating stratified squamous epithelial cells. Many reports have addressed MT structure and function, but despite the increasing experimental data several topics remain to be clarified, and the true function of this elusive protein has yet to be disclosed. Owing to their induction by a variety of stimuli, MTs are considered valid biomarkers in medicine and environmental studies. Here, we will discuss only a few topics taken from the latest literature. Special emphasis will be placed on MT antioxidant functions, the related oxidation of cysteines, which can give rise to intra/intermolecular bridges, and the relations between MTs and diseases which could be originated by metal dysregulation.