Regulation of androgen receptor gene expression by steroids and retinoic acid in human breast-cancer cells.

Although the androgen receptor (AR) has been detected by ligand-binding assays, there is little known about the expression and regulation of the AR gene in human breast-cancer cells. AR mRNA, measured by Northern analysis in 18 cell lines, was found to be expressed predominantly in oestrogen- and progesterone-receptor-positive (ER+, PR+) lines as a single species of approximately 10.5 kb but was also comparatively abundant in I ER- and PR-negative cell line, MDA-MB-453. Dexamethasone (Dex), Organon 2058 (Org 2058), dihydrotestosterone (DHT), and all-trans-retinoic acid (RA) down-regulated AR mRNA levels in T-47D (ER+, PR+) cells 6 hr after treatment, whereas oestradiol (E2) had no effect. In MDA-MB-453 (ER-, PR-) cells, regulation of AR mRNA by RA differed from the other cell lines: RA increased the level of AR mRNA. DHT-binding assays indicated a corresponding increase in AR protein. Transfection of the androgen-responsive mouse mammary tumour virus long-terminal repeat (MMTV LTR) linked to a chloramphenicol acetyltransferase (CAT) reporter gene was used to examine the effect of altered AR levels on androgen action. The increased level of AR following RA pre-treatment in MDA-MB-453 cells resulted in enhanced induction of CAT activity by DHT and, conversely, a decrease in the level of AR following RA pretreatment in T-47D cells resulted in reduced induction of CAT activity by DHT. These data demonstrate that AR is expressed predominantly in ER+ and PR+ cell lines and its expression is regulated by ligands also known to regulate ER or PR, including progestins and retinoids. Androgen responsiveness measured by a transfected reporter gene was altered according to the extent of up- or down-regulation of AR expression, demonstrating that responsiveness is dependent on receptor concentration.     

Expression of the c-Ha-ras oncogene in mouse NIH 3T3 cells induces resistance to cisplatin.

The effect of expression of the c-Ha-ras oncogene on cisplatin (DDP) sensitivity was examined in murine NIH 3T3 cells transfected with the dexamethasone (DEX)-inducible mouse mammary tumor virus promoter linked to an activated c-Ha-ras gene [LTR H-ras(A) cells]. Treatment of these cells with 5 microM DEX for 24 h induced c-Ha-ras expression and produced an 8.2 +/- 1.3-fold (SD) increase in DDP resistance as quantitated by clonogenic assay. Induction of the c-Ha-ras oncogene reduced DDP accumulation by 40% and intrastrand adduct formation by 17%. In nontransfected wild-type NIH 3T3 cells, DEX did not induce DDP resistance nor did it decrease DDP accumulation. Induction of c-Ha-ras expression did not alter cellular glutathione content or the activity of glutathione-S-transferase in the LTR H-ras(A) cells. DEX increased cellular metallothionein content by 1.6-fold in NIH 3T3 cells and 3.3-fold in LTR H-ras(A) cells. We conclude that DEX-induced overexpression of a mutant c-Ha-ras gene confers DDP resistance and that this resistance is associated with an impairment of cellular drug accumulation and an increase in metallothionein content.     

Transactivation of human immunodeficiency virus by herpesviruses

We examined the interaction of human immunodeficiency virus (HIV) and herpes group viruses. For this purpose, a chimeric plasmid (pLTR-CAT) was constructed in which the long terminal repeat (LTR) sequences derived from a molecular clone of HIV were fused to a bacterial chloramphenicol acetyltransferase gene (CAT). Transient expression assays in transfected tissue culture cells were used to monitor the activity of the LTR. Basal levels of CAT activity were measured in HeLa and human lung fibroblast (HLF) cells transfected with pLTR-CAT. When HeLa or HLF cells transfected with pLTR-CAT were infected with herpesviruses, HIV LTR-directed expression of the CAT gene was detected. An enhancement of the HIV LTR-directed expression of CAT was observed for herpes simplex virus (HSV)-1 and HSV-2, cytomegalovirus and varicella zoster virus. Enhanced CAT expression directed by the LTR was also shown by cotransfection of recombinant plasmids containing two non-overlapping regions of HSV-1, a fragment from HSV-2 which is non-colinear with the regions used from HSV-1, the immediate early gene of pseudorabies virus and the adenovirus early gene EIA. HIV LTR-directed expression may be a useful model for studying the effects on HIV of various infectious agents known to be present in individuals with AIDS or HIV infection.     

Effect of transfection of a Drosophila topoisomerase II gene into a human brain tumour cell line intrinsically resistant to etoposide.

The human brain tumour cell line HBT20 is intrinsically resistant to etoposide and does not express mdr-1 mRNA. These studies were conducted to determine whether transfecting a Drosophila (D) topoisomerase II (topo II) gene into HBT20 cells could increase their sensitivity to etoposide. A D-topo II construct in a pMAMneo vector under the control of a mouse mammary tumour virus (MMTV) promoter was transfected into HBT20 cells. The gene is inducible by dexamethasone (Dex). The growth rate of the transfected cells and percentage of the cells in G1, S and G2M was no different than the parental cells. Survival after etoposide exposure (10 microM x 2 h) was measured by colony formation. Parental cells and cells transfected by pMAMneo vector alone showed no enhanced etoposide sensitivity after 24 h of Dex stimulation. By contrast, D-topo II transfected cells were sensitised 3-fold when etoposide treatment was preceded by 24 h Dex stimulation. Northern blotting and Western blotting confirmed that Dex had induced D-topo II expression in the sensitised cells. However, in D-topo II-transfected cells increasing the duration of Dex stimulation to 48 h eliminated the sensitisation to etoposide although increased MMTV promoter activity and expression of the D-topo II gene persisted. Measurement of endogenous human topo-II mRNA and protein revealed a decrease after Dex exposure of greater than 24 h. At these distal times, the total cellular topo II levels (endogenous + exogenous) may be decreased, which may explain why increased sensitivity to etoposide could no longer be demonstrated. This model suggests that D-topo II gene transfection can sensitise de novo resistant HBT20 cells to etoposide but that the time frame of that sensitisation is limited.     

Doxorubicin stimulates transcription from the human immunodeficiency virus long terminal repeat sequences.

A recombinant plasmid carrying the long terminal repeat (LTR) of the human immunodeficiency virus 1 (HIV-1) linked to the reporter chloramphenicol acetyl transferase (CAT) gene was stably introduced into rat liver cells. The transfectant cells expressed CAT activity from the HIV LTR. The response to doxorubicin was studied and it was found that at the optimum concentration of 20 micrograms/ml doxorubicin, the expression of CAT from the HIV LTR was stimulated by 65-fold. Our results suggest caution against therapy including doxorubicin in the treatment of AIDS patients.     

A mouse mammary tumor virus-like long terminal repeat superantigen in human breast cancer

We previously reported a 660-bp mouse mammary tumor virus (MMTV)-like env gene sequence in approximately 38% of human breast cancer DNA, but not in normal breasts or other tumors. This MMTV-like env gene sequence was expressed in 66% of the env gene-positive human breast cancers. An entire proviral structure was identified in human breast cancer DNA with high homology to MMTV and low homology to known human endogenous retrovirus. MMTV-like long terminal repeat (LTR) sequences were also detected in 41.5% of human breast cancers. They contain hormone-responsive elements, TEF-1 family elements, and the open reading frame for the superantigen (SAg). We have now amplified and sequenced MMTV-like sag sequences from 10 human breast cancers, and we found that they are highly homologous to those of MMTV. However, deletions and insertions at the COOH-terminal of sag were observed. The immune function of the human MMTV-like LTR SAg was also investigated. The sag gene was cloned and expressed in a human B-cell line (Ramos). T-cell proliferation and cytokine releasing assays were performed after cocultivation of T cells with irradiated Ramos SAg-expressing cells. The results indicate that expression of the human SAg stimulates T-cell activation in vitro, as the mouse SAg does. Because the T-cell responses in vitro are considered similar to those in vivo, these results suggest that the human LTR SAg might also play a role in human breast carcinogenesis.     

Altered dexamethasone responsiveness and loss of growth control in tumorigenic mouse lung cell lines

Glucocorticoid hormones induce differentiation, inhibit proliferation, and, in mice, reduce carcinogen-induced tumorigenesis of lung epithelial cells. Therefore we examined dexamethasone effects on tumorigenic and non-tumorigenic mouse lung epithelial-derived cell lines. Non-tumorigenic cells were growth inhibited and exhibited CAT activity in pMMTV-CAT transfectants in response to dexamethasone. Tumorigenic cell lines exhibited a range of responses to dexamethasone. While one tumorigenic line was growth-inhibited and responsive in CAT assays, 2 other tumorigenic cell lines were unresponsive both in CAT and in growth assays. A fourth tumorigenic cell line exhibited intermediate sensitivity in CAT assays and was actually growth-enhanced by dexamethasone. Although no difference between cell lines was observed in the abundance of glucocorticoid receptor protein on Western blots, the least dexamethasone-responsive tumorigenic lines exhibited very little binding of ³H-dexamethasone. Clones of turnorigenic lines stably transfected with the rat glucocorticoid receptor gene were more dexarnethasone-sensitive in CAT assays and were growthinhibited by dexamethasone. These data suggest that the neoplastic progression of cell lines derived from mouse lung frequently involves the acquisition of diminished glucocorticoid responsiveness.     

Clonal isolation of different strains of mouse mammary tumor virus-like DNA sequences from both the breast tumors and non-Hodgkin's lymphomas of individual patients diagnosed with both malignancies.

PURPOSE: In a previous study, we had detected the presence of mouse mammary tumor virus (MMTV)-like envelope (ENV) gene sequences in both the breast tumors and non-Hodgkin's lymphoma tissue of two of our breast tumor patients who had been diagnosed simultaneously with both malignancies. The aim of this study was to determine if MMTV-like DNA sequences are present in the breast tumors and non-Hodgkin's lymphomas of additional patients suffering from both malignancies and if so to characterize these sequences in detail. EXPERIMENTAL DESIGN: DNA was extracted from formalin-fixed, paraffin-embedded tissue sample blocks of breast tumors and non-Hodgkin's lymphomas from patients suffering from both malignancies. A 250-bp region of the MMTV ENV gene and a 630-bp region of the MMTV long terminal repeat (LTR) open reading frame (ORF) that encodes the MMTV superantigen (sag) gene were amplified by PCR from the isolated DNA. Amplified products were analyzed by Southern blotting, cloned, and sequenced. RESULTS: MMTV-like ENV and LTR sequences were detected in both the breast tumors and non-Hodgkin's lymphomas of 6 of 12 patients suffering from both malignancies. A novel mutant of the MMTV ENV gene was identified in these patients. Characterization of the MMTV-like LTR highly variable sag sequences revealed total or nearly total identity to three distinct MMTV proviruses from two different branches of the MMTV phylogenetic tree. CONCLUSIONS: The presence of MMTV-like ENV and LTR sequences in both the breast tumors and non-Hodgkin's lymphomas of 6 additional patients suggests a possible involvement of these sequences in these two malignancies. MMTV-like LTR sequence homology to different MMTV proviruses revealed the presence of more than one strain of MMTV-like sequences in each individual suggesting the possibility of multiple infections in these patients.     

Strength and specificity of different gene promoters in oral cancer cells

Gene therapy of oral cancer will require expression of genes by promoters that are both powerful and relatively tumor specific. We compared the level of expression of a reporter gene from promoters of human cytomegalovirus (CMV), SV40 virus, mouse mammary tumor virus (MMTV), human papillomaviruses (HPV) types 16 and 18, and the human multi-drug-resistance gene (mdr1), in several lines of oral cancer cells. In the oral cancer cell line 686LN the rank order of expression levels was: CMV > SV40 > HPV > mdr1 > MMTV. Unlike in previous reports the mdr1 promoter was no more active in two cancer cell lines with mutations in the p53 gene than in two other lines with wild-type p53, and its expression level could not be increased by either doxorubicin or taxol. On the other hand, expression from the MMTV promoter was increased over 10-fold by the presence of 1 microM dexamethasone. Thus, by an appropriate choice of promoter and inducer a wide variety of expression levels, over a 3-log range, could be attained in 686LN cells. The oral cancer-specificity of each promoter was judged by comparing expression in the neuroblastoma line IMR32. The most specific promoters were those from papillomaviruses, which were up to 45 times more active in the oral cancer cells, and the least specific was the CMV promoter. In order to find if an HPV-derived promoter was sufficient to produce expression of a suicide phenotype the 686 promoter was cloned adjacent to the thymidine kinase gene of herpes simplex and the construct was expressed from an adenovirus vector. The vector reduced the growth of 686LN cells over a 5-day period by up to 32% when optimal concentrations of virus and ganciclovir were used. These data will be valuable in the design of new constructs for gene therapy of oral cancer.     

Detection and identification of mouse mammary tumor virus-like DNA sequences in blood and breast tissues of breast cancer patients

Mouse mammary tumor virus (MMTV) is a well-known cause of mammary tumors in mice transmitted as endogenous proviruses or exogenously as infectious virions. The hypothesis that a retrovirus homologous to MMTV is involved in human breast cancers has resulted in renewed interest in the etiology of human breast cancer. Therefore, the detection of MMTV-like exogenous sequences in 30–40 % of invasive breast cancer has increased attention towards this hypothesis. To detect the prevalence of MMTV in Pakistani population, 666-bp-long MMTV envelop and 630-bp LTR sequences were amplified from breast cancer patient samples (tissue biopsies and peripheral blood) using mouse with mammary tumor as control. MMTV-like virus env and LTR DNA sequences were detected in 20 and 26 % of breast tumor samples, respectively, from the total of 80 breast cancer patients’ blood and tissue samples. No significant association was observed between age, grade of disease, and lymph node involvement with the prevalence of MMTV-like sequences. Our data add to the growing number of studies implicating MMTV-like virus in human breast cancer, but still clear causal association of MMTV to breast cancer remains to be reputable.