Production of virus by embryonic cultures co-cultivated with breast tumour cells or infected with milk from breast cancer patients

Evidence for Copurification of HERV-K–Related Transcripts and a Reverse Transcriptase Activity in Human Platelets From Patients With Essential Thrombocythemia

We have previously reported that particles resembling retroviral particles and possessing an RNA-directed DNA polymerase activity can be prepared from platelets. Furthermore, we and others have shown that these particles are present at higher levels in patients with essential thrombocythemia and polycythemia vera. We show here that these particles package RNA molecules that encode HERV-K–related pol genes. A subset of the RNA molecules that are packaged are likely to encode the RNA directed DNA polymerase activity and, because these RNAs possess long/full-length open reading frames for the reverse transcriptase and RNaseH (also for part of the integrase domains in genomic clones) of HERV-K, we propose that these transcripts are indeed strong candidates for encoding the enzyme activity found in these particles. Moreover, by using a modification of the polymerase chain reaction-based reverse transcriptase assay in which activated DNA is added during cDNA synthesis to suppress DNA polymerase-mediated RNA-directed DNA synthesis, we have found that the particle-associated enzyme behaves like a retroviral reverse transcriptase, further supporting the conclusion that retrovirus-like, perhaps HERV-K sequences, encode this enzyme activity.

Human endogenous retrovirus expression and reverse transcriptase activity in the T47D mammary carcinoma cell line

We have examined the human mammary tumor cell line T47D and have found that these cells produce virus-like particles which band at the typical density for retroviral particles on a sucrose gradient, possess reverse transcriptase activity, and package HERV-K10-like sequences. Using this information and a bacterial expression system to identify long open reading frames, we have identified individual clones which have full-length open reading frames for reverse transcriptase and RNase H and which could encode the reverse transcriptase activity detected in these cells.

Demonstration of mouse mammary tumour virus (MuMTV) antigenicity in human milk by means of immunodiffusion technique

Using the micro-Ouchterlony immunodiffusion technique, we were able to demonstrate mouse mammary tumour virus (MuMTV) antigenicity in the 1.26-1.28 g/ml density fraction prepared from pooled human milk samples after treatment with detergents and ether. The cross-reacting antigen(s) was precipitated by rabbit antisera to MuMTV-B particles prepared from murine milk and intracytoplasmic A particles (iAp) isolated from mouse mammary tumour tissue. By confluence of precipitin lines, the human milk "core" antigen(s) was shown to be identical with the main antigen(s) of iAp which are known to share antigenicity with the MuMTV-B particle cores. Electron microscopy of the human "core" fraction revealed abundant particulate structures of 40-70 nm in diameter. However, the structural entities bearing the cross-reactive antigen(s) remain to be identified.

An ultrastructural study of normal human mammary epithelial cells in culture

The ultrastructure of normal human mammary cells cultured from post-weaning breast fluids is described. Cells from confluent monolayers in two week old cultures were studied. The epithelial nature of these cells was established by the demonstration of a well developed system of cell-to-cell interdigitation and numerous desmosomes. These cells also share with breast epithelial cells in vivo, polarity, with blunt short microvilli on the apical surface and an oriented arrangement of organelles in the basal and apical portions of the cells. The Golgi apparatus, which is the most highly developed organelle, is localized in the apical pole and contains substantial quantities of secretory material in the cisternae and vesicles. A variegated palisade of finely granular material mixed with tonofilaments is seen in the basal portion of the cells; many of these tonofilaments end in the terminal web of the desmosomes. The regular occurrence of these cells in breast fluids during the terminal phases of lactation suggests that their separation is a part of normal breast involution.

In vitro production of mouse mammary tumor virus in a mouse mammary tumor ascites line

An ascites line derived from a spontaneous mouse mammary carcinoma produces, on explantation and cultivation in vitro, large amounts of oncornavirus particles. The biochemical, biophysical, and electron microscopic characteristics of the virions are described. Molecular hybridization and immunological methods identify these virions as mouse mammary tumor virus.

Detection and isolation of a new DNA polymerase from human breast tumor cell line HBT-3 by (dT)12-18-cellulose chromatography

Column chromatography on (dT)(12-18)-cellulose was used to detect and isolate a novel DNA polymerase activity from human breast tumor cell line HBT-3. The new enzyme is similar to those of mammalian RNA tumor viruses in its molecular size, preference for poly(A).(dT)(12-18) as compared to either poly(dA).(dT)(12-18) or poly(A).poly(dT), and ability to copy poly(C).(dG)(12-18). A similar DNA polymerase activity, defined by its binding to (dT)(12-18)-cellulose, is not detectable in several other cell lines of human tumors.

Further evidence for oncornaviruses in human milk: the production of cores

Cores, or nucleoids, have been isolated from particles in human milk. The cores have a density of 1.26-1.27 g/ml and contain a 60-70S RNA in association with an RNA-instructed DNA polymerase. The data offer further evidence of similarity between human milk particles and animal RNA tumor viruses. In addition, core isolation provides a new method for detection of these particles by minimizing the difficulties generated by the presence of cell-associated debris often found in the density region (1.16-1.19 g/ml) characteristic of the intact virion. The procedures described now make available preparations of purified subviral components of a putative human RNA tumor virus.