Aberrant expression of zinc transporter ZIP4 (SLC39A4) significantly contributes to human pancreatic cancer pathogenesis and progression

Mammary gland zinc metabolism: regulation and dysregulation

Zinc (Zn) is required for numerous metabolic processes serving both a structural and catalytic role. The mammary gland has a unique Zn requirement resulting from the need to also transfer an extraordinary amount of Zn into milk (~0.5-1 mg Zn/day) during lactation. Impairments in this process can result in severe Zn deficiency in the nursing offspring which has adverse consequences with respect to growth and development. Moreover, dysregulated mammary gland Zn metabolism has recently been implicated in breast cancer transition, progression and metastasis, thus there is a critical need to understand the molecular mechanisms which underlie these observations. Tight regulation of Zn transporting mechanisms is critical to providing an extraordinary amount of Zn for secretion into milk as well as maintaining optimal cellular function. Expression of numerous Zn transporters has been detected in mammary gland or cultured breast cells; however, understanding the molecular mechanisms which regulate mammary Zn metabolism as well as the etiology and downstream consequences resulting from their dysregulation is largely not understood. In this review, we will summarize the current understanding of the regulation of mammary gland Zn metabolism and its regulation by reproductive hormones, with a discussion of the dysregulation of this process in breast cancer.

The important role of the apoptotic effects of zinc in the development of cancers

Zinc is a trace element that is essential for the normal function of cells. It is a cofactor for the structure and function of a wide range of cellular proteins including enzymes, transcription factors, and structural proteins. Recent studies have shown that zinc plays a role in the development of various cancers. Unfortunately no established common relationships of zinc with cancer development and progression have been identified. Zinc is known to have systemic effects such as regulation of the immune system as well as direct cellular effects resulting in regulation of gene expression, bioenergetics, metabolic pathways, signal transduction and cell invasion. Zinc is also reported to regulate cell proliferation and growth. In this review presentation we focus on the effects of zinc that are involved in the regulation of apoptosis in malignant cells. We selected the apoptotic effects of zinc because zinc is reported to both induce apoptosis in some cancers and to protect other cancer cells against apoptosis induced by other factors. The effects of zinc in the regulation of apoptosis appear to be cell type specific. More importantly the reported effects of zinc on cancer cells must be viewed from the perspective of the physiological regulation of zinc homeostasis. Thus one must be mindful of the experimental conditions under which zinc effects are investigated relative to the physiological and pathological conditions of cellular zinc distribution and concentrations that can exist in situ.

Profiling of 95 microRNAs in pancreatic cancer cell lines and surgical specimens by real-time PCR analysis

BACKGROUND

MicroRNAs (miRNAs) are involved in cancer pathogenesis, apoptosis, and cell growth, thereby functioning as tumor suppressors or oncogenes. However, expression alterations and roles of these miRNAs in pancreatic cancer are largely unknown. We hypothesized that pancreatic cancer may have a unique miRNA profile, which may play a critical role in pancreatic cancer development, progression, diagnosis, and prognosis.

METHODS

Differential expression of 95 miRNAs was analyzed by real time RT-PCR using the QuantiMir System. All 95 miRNAs chosen for the array are based on their potential functions related to cancer biology, cell development, and apoptosis. The expression of miRNAs for pancreatic cancer tissue samples or cancer cell lines was normalized to U6 RNA and compared with those in relatively normal pancreatic tissues or normal human pancreatic ductal epithelial (HPDE) cells. Human pancreatic tissue with chronic pancreatitis also was included for analysis.

RESULTS

In the initial analysis, the expression of most 95 miRNAs was substantially changed in pancreatic cancer tissues (n=5) and cell lines (n=3) compared with relatively normal pancreatic tissues and HPDE cells. However, each pancreatic cancer tissue or cell type had a substantially different profiling pattern with other cases or cell types as well as chronic pancreatitis tissue, indicating the individual diversity of pancreatic cancer. Further analysis was performed on 10 pancreatic cancer cell lines and 17 pairs of pancreatic cancer/normal tissues. Eight miRNAs were significantly upregulated in most pancreatic cancer tissues and cell lines, including miR-196a, miR-190, miR-186, miR-221, miR-222, miR-200b, miR-15b, and miR-95. The incidence of upregulation of these eight genes between normal control subjects and tumor cells or tissues ranged from 70-100%. The magnitude of increase of these miRNAs in pancreatic cancer samples ranged from 3- to 2018-fold of normal control subjects.

CONCLUSIONS

Pancreatic cancer tissues or cell lines have a unique miRNA profiling pattern at the individual basis compared with relatively normal pancreatic tissues or cells as well as pancreatitis tissue. Upregulation of eight miRNAs occurs in most pancreatic cancer tissues and cell types. These miRNAs may share common pathways in pancreatic cancer pathogenesis. This study may provide useful information for further investigations of functional roles of miRNAs in pancreatic cancer development, progression, diagnosis, and prognosis.

Metal ions modulate the folding and stability of the tumor suppressor protein S100A2

The EF-hand protein S100A2 is a cell cycle regulator involved in tumorigenesis, acting through regulation of the p53 activation state. Metal ion-free S100A2 is homodimeric and contains two Ca(2+)-binding sites and two Zn(2+)-binding sites per subunit, whereby the Zn(2+) ion binding to one of the sites is coordinated by residues from two homodimers. The effect of selective binding of these metal ions was investigated using site-specific mutants which lacked one or both zinc sites. CD analysis of secondary structure changes on metallation showed that Zn(2+) binding was associated with a decrease in the secondary structure content, whereas Ca(2+) had the opposite effect in two of the three S100A2 mutants studied. The energy of unfolding (DeltaG(U)) of the apo wild-type S100A2 was determined to be 89.9 kJ mol(-1), and the apparent midpoint transition temperature (T(m)(app))) was 58.4 degrees C. In addition, a detailed study of the urea and thermal unfolding of the S100A2 mutants in different metallation states (apo, Zn(2+) and Ca(2+)) was performed. Thermal denaturation experiments showed that Zn(2+) acts as a destabilizer and Ca(2+) as a stabilizer of the protein conformation. This suggests a synergistic effect between metal binding, protein stability and S100A2 biological activity, according to which Ca(2+) activates and stabilizes the protein, the opposite being observed on Zn(2+) binding.

Krüppel-like factor 4 regulates adaptive expression of the zinc transporter Zip4 in mouse small intestine

Epithelial cells of the small intestine are the site of zinc absorption. Intestinal uptake of zinc is inversely proportional to the dietary supply of this essential micronutrient. The mechanism responsible for this adaptive differential in apical zinc transport is not known. The zinc transporter Zip4 (Slc39a4) is essential for adequate enteric zinc uptake. In mice, Zip4 expression is upregulated at low zinc intakes with a concomitant ZIP4 localization to the apical enterocyte plasma membrane. With the present experiments, we show that the zinc finger transcription factor Krüppel-like factor 4 (KLF4), produced in high abundance in the intestine, is expressed at elevated levels in mice fed a low-zinc diet. In the murine intestinal epithelial cell (IEC) line MODE-K, zinc depletion of culture medium with cell-permeant and cell-impermeant chelators increased Zip4 and Klf4 mRNA and Zip4 heterogeneous nuclear RNA expression. Zinc depletion led to increased KLF4 in nuclear extracts. Knockdown of KLF4 using small interfering RNA transfection drastically limited ZIP4 induction upon zinc depletion and reduced 65Zn uptake by depleted IECs. EMSAs with nuclear extracts of IECs showed KLF4 binding to cis elements of the mouse Zip4 promoter, with increased binding under zinc-limited conditions. Reporter constructs with the Zip4 promoter and mutation studies further demonstrated that Zip4 is regulated through a KLF4 response element. These data from experiments with mice and murine IECs demonstrate that KLF4 is induced during zinc restriction and is a transcription factor involved in adaptive regulation of the zinc transporter ZIP4.

Thymosin beta-10 is aberrantly expressed in pancreatic cancer and induces JNK activation

Thymosin beta-10 (T beta 10) has been shown to be associated with several cancers; however, its role in pancreatic cancer is not understood. The expression of T beta 10 was determined by immunohistochemistry and real-time polymerase chain reaction. The phosphorylation of JNK and the cytokine secretion was determined by using the Bio-Plex phosphoprotein and cytokines assays. Pancreatic cancer tissues and cells expressed higher amounts of T beta 10 than normal surrounding tissues and human pancreatic duct epithelial cells. Exogenous T beta 10 caused the phosphorylation of JNK and increased the secretion of cytokines interleukin (IL)-7 and IL-8 in BxPC-3 cells. T beta 10 might be a promising marker and a novel therapeutic target for pancreatic cancer.

Somatostatin receptor-1 induces cell cycle arrest and inhibits tumor growth in pancreatic cancer

Functional somatostatin receptors (SSTR) are lost in human pancreatic cancer. Transfection of SSTR-1 inhibited pancreatic cancer cell proliferation in vitro. We hypothesize that stable transfection of SSTR-1 may inhibit pancreatic cancer growth in vivo possibly through cell cycle arrest. In this study, we examined the expression of SSTR-1 mRNA in human pancreatic cancer tissue specimens, and investigated the effect of SSTR-1 overexpression on cell proliferation, cell cycle, and tumor growth in a subcutaneous nude mouse model. We found that SSTR-1 mRNA was downregulated in the majority of pancreatic cancer tissue specimens. Transfection of SSTR-1 caused cell cycle arrest at the G(0)/G(1) growth phase, with a corresponding decline of cells in the S (mitotic) phase. The overexpression of SSTR-1 significantly inhibited subcutaneous tumor size by 71% and 43% (n = 5, P < 0.05, Student's t-test), and inhibited tumor weight by 69% and 47% (n = 5, P < 0.05, Student's t-test), in Panc-SSTR-1 and MIA-SSTR-1 groups, respectively, indicating the potent inhibitory effect of SSTR-1 on pancreatic cancer growth. Our data demonstrate that overexpression of SSTR-1 significantly inhibits pancreatic cancer growth possibly through cell cycle arrest. This study suggests that gene therapy with SSTR-1 may be a potential adjuvant treatment for pancreatic cancer.

Small interfering RNA therapy in cancer: mechanism, potential targets, and clinical applications

BACKGROUND

Small interfering RNA (siRNA) has become a powerful tool in knocking down or silencing gene expression in most cells. siRNA-based therapy has shown great promise for many diseases such as cancer. Major targets for siRNA therapy include oncogenes and genes that are involved in angiogenesis, metastasis, survival, antiapoptosis and resistance to chemotherapy.

OBJECTIVES

This review briefly summarizes current advances in siRNA therapy and clinical applications in cancers, especially in pancreatic cancer.

METHODS

This review article covers several aspects of siRNA therapy in cancer, which include the types of siRNA, the delivery systems for siRNA, and the major targets for siRNA therapy. Specific attention is given to siRNA in pancreatic cancer, which is our main research focus.

RESULTS/CONCLUSION

siRNA can be introduced into the cells by using either chemically synthesized siRNA oligonucleotides (oligos), or vector-based siRNA (shRNA), which allows long lasting and more stable gene silencing. Nanoparticles and liposomes are commonly used carriers, delivering the siRNA with better transfection efficiency and protecting it from degradation. In combination with standard chemotherapy, siRNA therapy can also reduce the chemoresistance of certain cancers, demonstrating the potential of siRNA therapy for treating many malignant diseases. This review will provide valuable information for clinicians and researchers who want to recognize the newest endeavors within this field and identify possible lines of investigation in cancer.

The genetics of essential metal homeostasis during development

The essential metals copper, zinc, and iron play key roles in embryonic, fetal, and postnatal development in higher eukaryotes. Recent advances in our understanding of the molecules involved in the intricate control of the homeostasis of these metals and the availability of natural mutations and targeted mutations in many of the genes involved have allowed for elucidation of the diverse roles of these metals during development. Evidence suggests that the ability of the embryo to control the homeostasis of these metals becomes essential at the blastocyst stage and during early morphogenesis. However, these metals play unique roles throughout development and exert pleiotropic, metal-specific, and often cell-specific effects on morphogenesis, growth, and differentiation. Herein, we briefly review the major players known to be involved in the homeostasis of each of these essential metals and their known roles in development.

Mesothelin is a malignant factor and therapeutic vaccine target for pancreatic cancer

Given the high fatality rate of pancreatic cancer, an effective treatment for this devastating disease is urgently needed. We have shown that mesothelin expression was higher in human pancreatic cancer cells than in human pancreatic duct epithelial cells, and mesothelin mRNA was substantially overexpressed in 18 of 21 (86%) clinical pancreatic adenocarcinoma specimens when compared with the surrounding normal tissues. However, the biological functions of mesothelin in tumor progression are not clearly understood. Here we studied the effects of mesothelin overexpression in pancreatic cancer cell proliferation and migration in vitro and pancreatic cancer progression in vivo. We found that forced expression of mesothelin significantly increased tumor cell proliferation and migration by 90% and 300%, respectively, and increased tumor volume by 4-fold in the nude mice xenograft model when compared with the vector control cell line. Silencing of mesothelin inhibited cell proliferation and migration in pancreatic cancer cells and ablated tumor progression in vivo. Vaccination with chimeric virus-like particles that contain human mesothelin substantially inhibited tumor progression in C57BL/6J mice. The increases in mesothelin-specific antibodies and CTL activity and the decrease in regulatory T cells correlated with reduced tumor progression and prolonged survival. This study revealed novel functions of mesothelin and suggested a new therapeutic vaccine strategy whereby mesothelin is targeted to control pancreatic cancer progression.