Cloning and functional study of a novel human metallothionein-I isoform induced by paraquat

Paraquat reduces natural killer cell activity via metallothionein induction

Paraquat (PQ), one of the most widely used herbicides, has been used for several decades in agriculture. Some studies suggest that PQ has effects on the immune system. Moreover, previous studies have shown that PQ imparted some immunosuppressive effects. In the present study, cytotoxicity assays using splenic NK cells from mice treated for 28 days with PQ (at 0.2, 1, and 5 mg/kg) were performed to determine whether PQ altered the function of NK cells. Given that PQ was expected to induce an immunosuppressive effect, it was hypothesized that a gene involved in cellular metal ion homeostasis, metallothionein-1 (MT-1), could play an important role in this outcome. This belief was based on the fact that MT1 encodes a protein responsible for zinc ion homeostasis, and that a reduction in free zinc ion levels impairs NK cell function. The results showed that PQ treatments led to increased MT expression in several organs (liver, kidneys, testes) and in splenocytes, caused a reduction of both free zinc ions in sera and in free intracellular zinc, and reduced the expression of GATA-3, a zinc-finger transcription factor important for maturation and activity of T-cells and NK cells. These results provide a basis for a new molecular mechanism to describe potential immunosuppressive effects of PQ in vivo.

Biology of SNU cell lines

SNU (Seoul National University) cell lines have been established from Korean cancer patients since 1982. Of these 109 cell lines have been characterized and reported, i.e., 17 colorectal carcinoma, 12 hepatocellular carcinoma, 11 gastric carcinoma, 12 uterine cervical carcinoma, 17 B-lymphoblastoid cell lines derived from cancer patients, 5 ovarian carcinoma, 3 malignant mixed Mllerian tumor, 6 laryngeal squamous cell carcinoma, 7 renal cell carcinoma, 9 brain tumor, 6 biliary tract, and 4 pancreatic carcinoma cell lines. These SNU cell lines have been distributed to biomedical researchers domestic and worldwide through the KCLB (Korean Cell Line Bank), and have proven to be of value in various scientific research fields. The characteristics of these cell lines have been reported in over 180 international journals by our laboratory and by many other researchers from 1987. In this paper, the cellular and molecular characteristics of SNU human cancer cell lines are summarized according to their genetic and epigenetic alterations and functional analysis.

Stable expression of C/EBPalpha in prostate cancer cells down-regulates metallothionein and increases zinc-induced toxicity

BACKGROUND

The transcription factor C/EBPalpha regulates terminal differentiation of various cell types. C/EBPalpha is expressed in prostate epithelium but its role in prostate development and malignant transformation is unknown. In examining the effect of forced expression of C/EBPalpha on the global gene expression profile in prostate cancer cells, we found that C/EBPalpha significantly decreased the RNA level of metallothioneins (MTs).

METHODS

The prostate cancer cell lines DU145, LNCaP, and PC3 with stable overexpression of C/EBPalpha were established with a retroviral expression system. MT expression was assayed by Western blot analysis and with the MT promoter in a plasmid using luciferase as a reporter.

RESULTS

Under basal conditions and in response to zinc, forced overexpression of C/EBPalpha decreased expression of MT isoforms 1A, B, F, and H, IIA and III. Following zinc exposure C/EBPalpha inhibited MT promoter activity by 1.5-2.5-fold. Overexpression of C/EBPalpha led to increased cytotoxicity of zinc at concentration of 150 microM in DU145 and LNCaP cells.

CONCLUSIONS

Our data demonstrated that expression of MTs in prostate cancer cells is inhibited by C/EBPalpha and the effect may have functional significance in regulating the growth of prostate cancer cells and the response of these cells to environment stresses.

Molecular mechanisms of heptaplatin effective against cisplatin-resistant cancer cell lines: less involvement of metallothionein

Background

Heptaplatin is a new platinum derivative with anticancer activity against various cancer cell lines, including cisplatin-resistant cancer cell lines (Cancer Chemother Pharmacol 1995; 35: 441).

Methods

Molecular mechanisms of heptaplatin effective against cisplatin-resistant cancer cell lines has been investigated in connection with metallothionein (MT). Cytotoxicity was determined by an MTT assay. MT mRNA, was determined by RT-PCR assay. Transfection study was carried out to examine the function of MT.

Results

Of various gastric cancer cell lines, SNU-638 and SNU-601 showed the highest and lowest levels of MT mRNA, respectively, showing 80-fold difference. The IC₅₀ values of SNU-638 to cisplatin, carboplatin and heptaplatin were 11.2-fold, 5.1-fold and 2.0-fold greater than those of SNU-601, respectively. Heptaplatin was more effective against cisplatin-resistant and MT-transfected gastric cancer sublines than cisplatin or carboplatin was. In addition, heptaplatin attenuated cadmium, but not zinc, induction of MT.

Conclusion

These results indicate that molecular mechanisms of heptaplatin effective against cisplatin-resistant gastric cancer sublines is at least in part due to the less involvement of MT in heptaplatin resistance as well as its attenuation of MT induction.