Interdigitating dendritic cell sarcoma: a rare malignancy responsive to ABVD chemotherapy.

Interdigitating dendritic cell sarcoma (IDCS) is an aggressive neoplasm of which fewer than 25 cases have been reported in the world literature. This malignancy is difficult to diagnose because of its rarity, and because of the subtle histopathologic features that distinguish IDCS from similar tumors arising from reticular cells. To date, there exists no consensus on a standard chemotherapeutic regimen for IDCS. Patients with this malignancy have been treated with chemotherapy regimens used against non-Hodgkin's lymphomas. Responses to these regimens have been variable, but mostly unsuccessful. In this article we describe a case of IDCS occurring in a 44 year old female who presented with abdominal pain and inguinal adenopathy. Staging of the tumor with CT scan, PET scan, and bone marrow biopsy demonstrated inguinal and abdominal lymphadenopathies, a large mass encasing the small bowel, and extensive liver infiltration. Morphologic and cytochemical analysis of biopsies from the abdominal mass and inguinal node were consistent with a diagnosis of IDCS, and immunohistochemical stains of the lymph node were positive for CLA, Kp-1, S-100, while negative for CD1a, CD3, CD20, CKER, and HMB45. Treatment of this patient with ABVD chemotherapy resulted in rapid clinical improvement with a marked decrease in tumor burden after two cycles of ABVD, and a complete response after six cycles of therapy.

2,3,7,8-tetrachlorodibenzo-p-dioxin modulates expression of the prostaglandin G/H synthase-2 gene in rat thymocytes.

As an approach to understanding the molecular mechanism(s) of thymic gene expression mediated by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we investigated the effect of TCDD on expression of prostaglandin G/H synthase-2 (PGHS-2) in rat thymocytes by reverse transcription-polymerase chain reaction. Incubation of thymocytes with increasing doses of TCDD resulted in inhibition of PGHS-2 gene expression in a concentration-dependent manner, with an IC50 of 10 nM. In contrast, TCDD had no appreciable effect on expression of glyceraldehyde phosphate dehydrogenase. Because the xenobiotic-responsive element is conserved in the PGHS-2 promoter from several animal species, it seems likely that inhibition of PGHS-2 expression by TCDD may occur at the level of transcription. To test this hypothesis in cultured thymocytes, we characterized the Ah receptor in the thymoma cell line WEHI 7.1. Reverse transcription-polymerase chain reaction experiments indicated that TCDD inhibited PGHS-2 expression in this cell line. Sucrose density gradient centrifugation experiments indicated that WEHI 7.1 cytosol exhibited 9 to 10S ligand-binding activity characteristic of the Ah receptor. The viability of WEHI 7.1 cells incubated with TCDD was comparable to that of control cells, whereas dexamethasone induced toxicity in a concentration-dependent manner. Transient transfection experiments using PGHS-2 promoter fragments ligated into a chloramphenicol acetyltransferase reporter plasmid suggested that TCDD inhibits PGHS-2 transcription, and deletion of the xenobiotic-responsive element failed to exhibit this repression. These results demonstrate that TCDD is a potent inhibitor of PGHS-2 gene expression, and they represent the first mechanistic evidence for TCDD-dependent inhibition of transcription in thymocytes.

Promoter of the canine tracheobronchial mucin gene.

The mucin gene is up-regulated in diseases such as cystic fibrosis (CF) and asthma. To understand the mechanisms involved in transcriptional regulation of mucin gene expression we have characterized the region of the mucin gene up-stream of the transcriptional start site and analysed the cis-acting elements required for mucin promoter activity. We isolated clones from a dog genomic library containing the promoter region for the tracheobronchial mucin gene (TBM). The authenticity of the promoter was tested by nucleotide sequencing, primer extension analysis, electrophoretic mobility shift assay (EMSA) and reporter gene expression analysis. The canine TBM promoter is different from housekeeping gene promoters (as it is not rich in GC content and contains TATA- and CAAT-like sequences) and different from that of regulatory genes (because it contains many TATA- and CAAT-like sequences and multiple transcriptional initiation sites). Reporter gene analysis using canine TBM promoter-chloramphenicol acetyltransferase (CAT) fusion plasmids established the regions responsible for promoter activity and verified the positions of the major mucin transcriptional initiation sites. Reporter gene analysis also established that a region of the canine TBM promoter and first exon containing all of the transcriptional initiation sites is more active in mucin expressing cells (e.g. CT1 cells-immortalized canine tracheal epithelial cells, human CFT1 cells-immortalized tracheal epithelial cells from a CF subject, or HBE1 cells-immortalized tracheal epithelial cells from non-CF subject) than in mucin non-expressing cells (COS7, 3T3), suggesting cell specificity. The promoter region contained cAMP response element (CRE) sequences, and the TBM gene transcription was enhanced when cAMP analogs were added to transfected cells. EMSA indicated the presence of at least two DNA binding proteins in CT1 cells. This is the first report describing the characterization of a TBM gene promoter. The information obtained in the present studies will be valuable in understanding mucin gene regulation in normal and pathological conditions.

Primary structure of the canine U1 snRNA.

The nucleotide (nt) sequence of the canine U1 snRNA was determined. It exhibited significant homology (90-98%) with known U1 sequences. The RNA can be folded according to the secondary structure previously proposed for the U1 snRNA. It contained the conserved sequence UUACCUG in loop A (nt 6-12), required for the recognition of the 5' splice site, and the sequence UGCACU in loop B (nt 68-73), required for recognition of the U1-70K protein. The U1 snRNA was localized in the nucleus and its transcription was sensitive to alpha-amanitin, suggesting that it is transcribed by RNA polymerase II. Southern analysis revealed that the canine genome possesses 5-10 copies of U1 snRNA-encoding genes.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated gene expression in the immature rat thymus.

To examine the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on thymic gene expression in vitro, freshly isolated rat thymocytes were incubated with 10 nM TCDD, and reverse transcriptase polymerase chain reaction experiments were performed using primers specific for prostaglandin G/H synthase (PGHS) and glyceraldehyde 3-phosphate dehydrogenase. TCDD selectively repressed PGHS gene expression, with maximal inhibition occurring within 60 min. Gel retardation assays demonstrated that dioxin transiently induced binding of the ubiquitous transcription factor NF kappa B to its cognate response element at early time points. However, TCDD had little ability to induce transformation of the Ah receptor to the xenobiotic responsive element in thymic cytosol. These results indicate that TCDD exerts changes in thymocyte gene expression prior to inducing toxicity.

Inhibition of Ah (dioxin) receptor transformation by 9-hydroxy ellipticine. Involvement of protein kinase C?

9-Hydroxy ellipticine (9-OHE), a metabolite of the anti-neoplastic agent ellipticine, is known to bind the aryl hydrocarbon (Ah) receptor in rat lung cytosol and to inhibit aryl hydrocarbon hydroxylase activity (AHH) in rat hepatic microsomes. In this study, the effects of 9-OHE on the transformation of the rat hepatic cytosolic Ah receptor to a form that binds the xenobiotic responsive enhancer element-3 (XRE-3) of the cytochrome P4501A1 gene was investigated. Sucrose density gradient analysis of [3H]-2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) binding in rat hepatic cytosol indicated that 9-OHE inhibited binding of the radiolabeled ligand to the Ah receptor with an IC50 of 90 microM. Gel retardation assays revealed that at low concentrations of 9-OHE the Ah receptor bound to XRE-3, as was the case with the TCDD-liganded receptor. However, in the presence of high concentrations of 9-OHE, the Ah receptor failed to transform to a form that could bind to XRE-3. In vitro studies indicated that incubation of rat hepatic cytosol with TCDD resulted in concentration-dependent increases in levels of protein kinase C (PKC) mediated phosphorylation as compared to vehicle-treated extracts. Furthermore, 9-OHE concentrations that exhibited agonist activity with respect to Ah receptor transformation did not alter PKC phosphorylation in hepatic cytosol, whereas higher concentrations exhibited significant concentration-dependent decrease in PKC-mediated phosphorylation. These results demonstrate that the antagonistic effect of 9-OHE observed at high concentrations is due to inhibition of Ah receptor-XRE complex formation, a phenomenon that correlates with alterations in PKC activity.

Early effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on rat thymocytes in vitro.

TCDD is known to induce thymic atrophy in several mammalian species through activation of programmed cell death, or apoptosis. To investigate the time course of events which precede TCDD-induced thymic apoptosis in vitro, experiments were performed with thymocytes isolated from immature rats. Peak accumulation of both total and specifically bound [3H]TCDD was observed at 60 min post incubation. Incubation of cells with 10 nM TCDD resulted in significant increases in RNA polymerase activity and incorporation of [3H]uridine at 30 min, indicating increased RNA synthesis in response to TCDD. TCDD-induced stimulation of [3H]uridine incorporation was not significantly altered in the presence of cycloheximide, while this effect was abrogated in the presence of actinomycin D. Incubation of thymocytes with 10 nM TCDD also stimulated the activity of poly(A)polymerase, the enzyme catalyzing mRNA polyadenylation, at time points beyond 30 min. No significant increases in [35S] incorporation were observed in cells treated with 10 nM TCDD, although analysis of detergent and high salt extracted nuclear proteins by SDS-PAGE and coomassie blue staining revealed the increased abundance of at least two proteins with molecular masses of 52,000 and 42,000 Da, respectively. These studies reveal that thymocyte nuclei rapidly accumulated TCDD in vitro, leading to increased RNA synthesis, poly(A)polymerase activity and protein synthesis. These events correlate closely with the process of programmed cell death.