Differences in 2,3,7,8-tetrachlorodibenzo-p-dioxin-inducible CYP1A1 expression in human breast carcinoma cell lines involve altered trans-acting factors

Differences in expression of the CYP1A1 gene have previously been observed in human breast carcinoma cell lines exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Using an expression vector containing the functional 5'-regulatory region of human CYP1A1 (up to -1140) fused to the reporter gene CAT (for chloramphenicol acetyltransferase), the breast carcinoma cell lines, MCF-7, T47-D and ZR-75-1, classified as highly responsive to TCDD, were highly responsive to TCDD in the chloramphenicol acetyltransferase assay as well. Gel mobility shift assays have shown that these cell lines express a nuclear protein that binds the aryl hydrocarbon (Ah) receptor responsive element. The low or non-responsive cell lines, AL-1, BT-20 and CAMA-1, were low or non-responsive to TCDD in the chloramphenicol acetyltransferase assay, suggesting that the low-responsive phenotype is caused by altered trans-acting factors. However, the mechanism appears to differ among the cell lines. Whereas no induction was observed in AL-1, a fivefold induction in activity was observed in BT-20 and CAMA-1. The TCDD concentration giving half-maximum induction differed greatly between CAMA-1 and BT-20. The gel mobility shift assay showed the presence of a protein that bound specifically to the Ah responsive element in the non-responsive cell line AL-1, as well as the low-responsive cell lines, BT-20 and CAMA-1. The high basal activity but low induction observed in CAMA-1 may be due to an Ah receptor constitutively bound to the Ah responsive element.     

DNA repair in cells sensitive and resistant to cis-diamminedichloroplatinum(II): host cell reactivation of damaged plasmid DNA

cis-Diamminedichloroplatinum(II) (cis-DDP) has a broad clinical application as an effective anticancer drug. However, development of resistance to the cytotoxic effects is a limiting factor. In an attempt to understand the mechanism of resistance, we have employed a host cell reactivation assay of DNA repair using a cis-DDP-damaged plasmid vector. The efficiency of DNA repair was assayed by measuring the activity of an enzyme coded for by the plasmid vector. The plasmid expression vector pRSVcat contains the bacterial gene coding for chloramphenicol acetyltransferase (CAT) in a configuration which permits expression in mammalian cells. The plasmid was transfected into repair-proficient and -deficient Chinese hamster ovary cells, and CAT activity was subsequently measured in cell lysates. In the repair-deficient cells, one cis-DDP adduct per cat gene was sufficient to eliminate expression. An equivalent inhibition of CAT expression in the repair-proficient cells did not occur until about 8 times the amount of damage was introduced into the plasmid. These results implicate DNA intrastrand cross-links as the lesions responsible for the inhibition of CAT expression. This assay was used to investigate the potential role of DNA repair in mediating cis-DDP resistance in murine leukemia L1210 cells. The parent cell line L1210/0 resembled repair-deficient cells in that about one adduct per cat gene eliminated expression. In three resistant L1210 cell lines, 3-6-fold higher levels of damage were required to produce an equivalent inhibition. This did not correlate with the degree of resistance as these cells varied from 10- to 100-fold resistant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of protein-binding sites in the hepatitis B virus enhancer and core promoter domains.

We have investigated the role of liver-specific trans-acting factor(s) in the regulation of hepatitis B virus (HBV) gene expression. A recorder plasmid (pEcoAluCAT; HBV nucleotides 1 through 1878) was constructed containing the HBV enhancer and the promoter region of the pregenomic RNA, which was ligated to the bacterial chloramphenicol acetyltransferase (CAT) gene. Upon transfecting this plasmid into various cell lines, the CAT gene was expressed only in cells of liver origin. Moreover, competition cotransfections with pEcoAluCAT and plasmids containing HBV enhancer sequences in human hepatoblastoma-derived HepG2 cells indicated the presence of titratable trans-acting factor(s) in these cells. Gel mobility shift assays using HBV enhancer and core promoter domains confirmed the existence of sequence-specific DNA-binding proteins in liver cell nuclear extract which bound to these regions. These binding sites encompass 17- and 12-nucleotide palindromes in the HBV enhancer and core promoter domains, respectively, when mapped by the methylation interference assay.     

A microtransfection method using the luciferase-encoding reporter gene for the assay of human immunodeficiency virus LTR promoter activity

A microtransfection method, using either the DEAE-dextran or the Ca.phosphate procedure has been developed. A plasmid expressing the luciferase-encoding gene under the control of the human immunodeficiency virus (HIV) LTR promoter was constructed. Transfections were performed in 96-well plates, allowing statistical evaluation of the results. This microtransfection method requires the use of 100- to 1000-fold less plasmid and cells than in a conventional chloramphenicol acetyl transferase (CAT) assay. A Luciferase index which takes into account cell viability after transfection has been defined using a semi-automated absorbance assay. A 20-h incubation period post-transfection is sufficient for optimal results. Basal long terminal repeat activity and autologous Tat transactivation were studied in various lymphoid, monocytic and adherent human cell lines. Infection of microtransfected cells by HIV activated luc expression. This assay can thus also be used for rapid detection and quantitation of HIV. Antiviral activities of drugs can be assessed in a two-day test.     

Construction of trypanosome artificial mini-chromosomes.

We report the preparation of two linear constructs which, when transformed into the procyclic form of Trypanosoma brucei, become stably inherited artificial mini-chromosomes. Both of the two constructs, one of 10 kb and the other of 13 kb, contain a T.brucei PARP promoter driving a chloramphenicol acetyltransferase (CAT) gene. In the 10 kb construct the CAT gene is followed by one hygromycin phosphotransferase (Hph) gene, and in the 13 kb construct the CAT gene is followed by three tandemly linked Hph genes. At each end of these linear molecules are telomere repeats and subtelomeric sequences. Electroporation of these linear DNA constructs into the procyclic form of T.brucei generated hygromycin-B resistant cell lines. In these cell lines, the input DNA remained linear and bounded by the telomere ends, but it increased in size. In the cell lines generated by the 10 kb construct, the input DNA increased in size to 20-50 kb. In the cell lines generated by the 13 kb constructs, two sizes of linear DNAs containing the input plasmid were detected: one of 40-50 kb and the other of 150 kb. The increase in size was not the result of in vivo tandem repetitions of the input plasmid, but represented the addition of new sequences. These Hph containing linear DNA molecules were maintained stably in cell lines for at least 20 generations in the absence of drug selection and were subsequently referred to as trypanosome artificial mini-chromosomes, or TACs.     

Expression of prokaryotic genes after transfection of X-irradiated plasmids into primate cells

Expression of the prokaryotic gene for chloramphenicol acetyltransferase (EC 2.3.1.28) (CAT) in primate cells transfected with X-irradiated plasmid pSV2CAT was determined in transient expression assays. CAT expression did not depend upon the presence of supercoiled plasmids, but relaxed circular forms were essential. X-ray conversion of relaxed circles to linear forms paralleled the loss of CAT expression, with identical D0's in the first part of dose-response curves. X-ray-induced loss of supercoiled forms was complete at much lower doses. The D0 for inactivation of CAT expression by X irradiation of the plasmids in 1 mM Tris buffer was 270 Gy; it was 13 Gy for plasmids irradiated in water. The D0's for conversion of pSV2CAT to relaxed circle forms were only one-seventh as large as the D0's for CAT inactivation after X-ray in water or in 1 mM Tris buffer. Expression of the CAT gene in some representative repair-deficient human fibroblasts transfected with X-irradiated pSV2CAT was less than in monkey CV-1 cells or cell lines from normal human subjects. These results demonstrate a novel means to study low levels of X-ray damage in DNA correlating specific X-ray damage in the DNA with expression of the gene in unirradiated primate cells.     

Activation of an enhancerless gene by chromosomal integration.

Expression of enhancerless (E-) and enhancer-containing (E+) genes that are chromosomally integrated was examined. An E- plasmid (pE-cat) containing a chloramphenicol acetyltransferase (cat) gene linked to the simian virus 40 (SV40) early promoter or its E+ counterpart plasmid (pE+-cat) containing the SV40 enhancer was cotransfected into thymidine kinase (TK)-deficient L cells with a cloned tk gene. A number of TK+ transformants were isolated, and expression of the cointegrated cat gene in these cell lines was quantitatively determined by the assay of CAT activity. The results indicated unexpectedly that the E- cat gene was as actively expressed as the E+ cat gene. Analysis of CAT mRNA by primer extension indicated that the E- cat gene, as well as the E+ cat gene, was transcribed from the "native" initiation site contained in the SV40 early promoter region. The active expression of the E- cat gene was maintained in secondary TK+ transformants that arose by transfection with genomic DNA from the primary transformant. These results suggest that expression of the integrated E- cat gene is activated by endogenous enhancer elements.     

Suppression of human melanoma metastasis by the metastasis suppressor gene, BRMS1

We recently identified a novel metastasis suppressor gene, BRMS1, in breast cancer. Since the BRMS1 gene maps to chromosome 11q13.1-q13.2 and since chromosome 11q defects have been described in various stages of human melanoma progression, we hypothesized that BRMS1 may function as a tumor or metastasis suppressor in melanomas as well. Quantitative real-time RT-PCR revealed that BRMS1 mRNA expression was high in melanocytes, considerably reduced in early melanoma-derived cell lines, and barely detectable in advanced/metastatic cell lines. Stable transfectants of BRMS1 in the human melanoma cell lines MelJuSo and C8161.9 did not alter the tumorigenicity of either cell line, but significantly suppressed metastasis compared to vector-only transfectants. Orthotopic tumors continued to express BRMS1, but expression was lost in lung metastases. In vitro morphology, growth rate, and histology of BRMS1 transfectants were similar to controls. BRMS1 transfectants were less invasive in a collagen sandwich assay and had restored homotypic gap junctional intercellular communication (GJIC). Thus, BRMS1 functions as a metastasis suppressor in more than one tumor type (i.e., breast carcinoma and cutaneous melanoma) by modifying several metastasis-associated phenotypes.     

Quantification of expression of linked cloned genes in a simian virus 40-transformed xeroderma pigmentosum cell line.

We wished to determine whether simian virus 40 (SV40)-transformed xeroderma pigmentosum cells, despite their defective DNA repair, were suitable for DNA-mediated gene transfer experiments with linked genes. Expression of a nonselectable gene (cat, coding for chloramphenicol acetyltransferase [CAT]) linked to a selectable gene (gpt, coding for xanthine-guanine phosphoribosyltransferase [XPRT]) in the plasmid pSV2catSVgpt was quantified after transfection of SV40-transformed xeroderma pigmentosum [XP20s(SV40)] and normal human [GM0637(SV40)] fibroblast cell lines. A novel autoradiographic assay with [3H]xanthine incorporation showed 0.5 to 0.7% phenotypic expression of XPRT in both cell lines. Without selection, transient CAT activity was 20 times greater in the GM0637(SV40) than in the XP20s(SV40) cells, and transient XPRT activity was 5 times greater. Both of these transient activities were increased and equalized in both cell lines by transfection with pRSVcat or pRSVgpt. Genotypic transformation to gpt+ occurred at a frequency of 2 X 10(-4) to 4 X 10(-4) in both cell lines with pSV2catSVgpt. After 2 to 3 months in selective medium, stable expression of the (nonselected) cat gene was found in 11 (92%) of 12 gpt-containing clones derived from GM0637(SV40) cells and in 13 (81%) of 16 gpt-containing clones from XP20s(SV40) cells. However, the levels of CAT activity did not correlate with those of XPRT activity, and both of these activities varied more than 100-fold among different clones. Copies (1 to 4) of the gpt gene were integrated in four clones of the GM0637(SV40) cells having an XPRT activity of 1 to 5 nmol/min per mg, but 5 to 80 copies were integrated in four XP20s(SV40) clones with an XPRT activity of 0.8 to 1.8 nmol/min per mg. This study shows that XP20s(SV40) is as suitable for gene transfer experiments as the normal human line GM0637(SV40).     

Ectopic expression of the ErbB-3 binding protein ebp1 inhibits growth and induces differentiation of human breast cancer cell lines

Ebp1, an ErbB-3 binding protein, translocates from the cytoplasm to the nucleus of human breast cancer cells after treatment with the ErbB-3 ligand, heregulin. The purpose of these studies was to examine the effects of ectopic expression of ebp1 on the biological properties of human ErbB-3-expressing breast carcinoma cell lines. Ectopic expression of ebp1 in ErbB-2, ErbB-3-expressing breast carcinoma cell lines resulted in inhibition of colony formation, a decreased proliferation rate, an accumulation of cells in the G2/M phase of the cell cycle, and suppression of growth in soft agar. Ectopic expression of ebp1 led to a more differentiated phenotype in AU565 breast cancer cells, as evidenced by increased expression of lipid droplets and of the milk protein casein. Basal phosphorylation of extracellular regulated kinases (Erks) 1 and 2, kinases activated by heregulin treatment, was also observed in ebp1 transfectants. The promoter for the intercellular adhesion molecule-1 gene, a heregulin-inducible gene, was constitutively activated in ebp1 transfectants as determined by reporter construct analysis. These data demonstrate that ectopic expression of the ErbB-3 binding protein Ebp1 inhibits proliferation and induces differentiation of ErbB-2, ErbB-3-expressing human breast carcinoma cell lines.     

Establishment of two basal-like breast cancer cell lines with extremely low tumorigenicity from Taiwanese premenopausal women

The research of carcinogenetic mechanisms of breast cancer in different ethnic backgrounds is an interesting field, as clinical features of breast cancers vary among races. High premenopausal incidence is distinctive in East-Asian breast cancer. However, human cell lines derived from Asian primary breast tumor are rare. To provide alternative cell line models with a relevant genetic background, we aimed to establish breast cancer cell lines from Taiwanese patients of Han-Chinese ethnicity. Fresh tissue from mammary tumors were digested into organoids, plated and grown in basal serum-free medium of human mammary epithelial cells (HuMEC) with supplements. Cells were further enriched by positive selection with CD326 (epithelial cell adhesion molecule; EpCAM)-coated micro-magnetic beads. Two breast cancer cell lines derived from premenopausal women were successfully established by this method, and named Chang-Gung Breast Cancer 01 (CGBC 01) and 02 (CGBC 02). These two cell lines had a similar phenotype with weak expression of estrogen receptor (ER), progesterone receptor (PR), and without amplification of receptor tyrosine protein kinase erbB-2 (HER2/neu). Genome-wide Single Nucleotide Polymorphism (SNP) array showed multiple copy number alterations in both cell lines. Based on gene expression profiles, CGBC 01 and 02 were clustered into basal-like subtype with reference to the breast cancer cell line gene expression database. The tumorigenicity of both cell lines was extremely low in both anchorage-independence assay and transplantation into the mammary fat pads of nude mice. CGBC 01 and CGBC 02 are low tumorigenic breast cancer cell lines, established from Han-Chinese premenopausal breast cancer patients, which serve as in vitro models in studying the biological features of Asian breast cancer.     

Biological Properties of Melanoma and Endothelial Cells after Plasmid AMEP Gene Electrotransfer Depend on Integrin Quantity on Cells

The data on the biological responsiveness of melanoma and endothelial cells that are targeted by Antiangiogenic MEtargidin Peptide (AMEP) are limited; therefore, the antiproliferative, antimetastatic and antiangiogenic effects of AMEP were investigated in murine melanoma and human endothelial cells after plasmid AMEP gene electrotransfer into the cells in vitro. Plasmid AMEP, a plasmid coding for the disintegrin domain of metargidin targeting specific integrins, had cytotoxic and antiproliferative effects on murine melanoma and human endothelial cells. Among the metastatic properties of cells, migration, invasion and adhesion were investigated. Plasmid AMEP strongly affected the migration of murine melanoma and human endothelial cell lines and also affected the invasion of highly metastatic murine melanoma B16F10 and human endothelial cell lines. There was no effect on cell adhesion on Matrigel^TM or fibronectin in all cell lines. The antiangiogenic effect was shown with tube formation assay, where human microvascular endothelial cell line (HMEC-1) proved to be more sensitive to plasmid AMEP gene electrotransfer than the human umbilical vein endothelial cell line (HUVEC). The study indicates that antiproliferative and antimetastatic biological responses to gene electrotransfer of plasmid AMEP in murine melanoma cells were dependent on the integrin quantity on melanoma cells and not on the expression level of AMEP. The strong antiangiogenic effect expressed in human endothelial cell lines was only partly dependent on the quantity of integrins and seemed to be plasmid AMEP dose dependent.     

Expression of the K-fgf proto-oncogene is controlled by 3'' regulatory elements which are specific for embryonal carcinoma cells.

Expression of the K-fgf/hst proto-oncogene appears to be restricted to cells in the early stages of development, such as embryonal carcinoma (EC) cells. When EC cells are induced to differentiate, K-fgf expression is drastically repressed. To identify cis-acting DNA elements responsible for this type of regulation, we constructed a plasmid in which cat gene expression was driven by about 1 kilobase of upstream K-fgf human DNA sequences, including the putative promoter, and transfected it into undifferentiated F9 EC cells or HeLa cells as prototypes of cells which express or do not express, respectively, the K-fgf proto-oncogene. This plasmid was essentially inactive in both cell types, and the addition of more than 8 kilobases of DNA sequences upstream of the K-fgf promoter did not lead to any increase in chloramphenicol acetyltransferase (CAT) expression. On the other hand, when we inserted in this plasmid DNA sequences which are 3' of the human K-fgf coding sequences, we could detect a significant stimulation of CAT activity. Analysis of these sequences led to the identification of enhancerlike DNA elements which are part of the 3' noncoding region of K-fgf exon 3 and promote CAT expression only in undifferentiated mouse F9 or human NT2/D1 EC cells, but not in HeLa, 3T3, or differentiated F9 cells, therefore mimicking the physiological expression of the K-fgf proto-oncogene. Similar elements are also present in the 3' region of the murine K-fgf proto-oncogene, in a region showing high homology to the human K-fgf sequences. These regulatory elements can promote CAT expression from heterologous promoters in an EC-specific manner, suggesting that they interact with a specific cellular transacting protein(s) whose expression is developmentally regulated.